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PUBLIC R

OADS
A JOURNAL OF HIGHWAY RESEARCH

py) UNITED STATES DEPARTMENT OF AGRICULTURE

fy BUREAU OF PUBLIC ROADS

VOM S. NO. 2 v APRIL, 1924

GENERAL VIEW OF SLABS FOR IMPACT TEST, ARLINGTON, VA.

WASHINGTON : GOVERNMENT PRINTING OFFICE ; 1924

PUBLIC ROA:

A JOURNAL OF HIGHWAY RESEARCH
U. S. DEPARTMENT OF AGRICULTURE

BUREAU OF PUBLIC ROADS

CERTIFICATE: By direetion of the Secretary of Agriculture, the matter contained herein is published as administrative information and is required
for the proper transaction of the public business.

VOLF DINO Fe 2 APRIL, 1924 H. S. FAIRBANK, Editor

ZABLE OF CONTENTS
Page
Impact Tests on Concrete Pavement Slabs .

Resistance of various designs determined by Bureau of Public Roads experiments.

Motor Vehicle’ Registrahon 15,092 157. 9, » oe 14

$225,/84,932 amount of annual license fees and gasoline taxes.

The Brick Roads of Florida . ; 18

Observations of the behavior of brick surfaces laid on confined sand subgrades.

Road Miatertal Tests ‘and Inspection’. News . 9 2) 2 Ss he ce

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IMPACT TESTS ON CONCRETE PAVEMENT SLABS.

RESISTANCE OF VARIOUS DESIGNS DETERMINED BY BUREAU OF PUBLIC ROADS EXPERIMENTS.

By LESLIE W. TELLER, Assistant Testing Engineer, U. S. Bureau of Public Roads.

ONTINUING the study of the magnitude and
€& effect of motor truck impact begun four years
ago, the Bureau of Public Roads has recently
completed a series of tests to determine the resistance
of pavement slabs of various designs to impact of
motor vehicles. Previous reports dealing with earlier
hases of the investigation have announced the find-
ings of the bureau with respect to the possible magni-
tude of the impact forces resulting from the operation
of trucks over road surfaces of different degrees of
roughness, the relative strength of such forces compared
with the static weight of the vehicle, the effect of dif-
ferences in tire and spring equipment and variations
in sprung and unsprung load upon the character and
intensity of the impact, and the effect of the impact
upon a limited number of specially constructed slabs
of various designs.'

This report deals with the results of the tests of a
second series of slabs more comprehensive in its range
of types. As in the case of the previous reports, this
one deals with only one phase of the investigation
which is being continued. The results reported are
not entirely conclusive. They are to be regarded as
sign boards which point the way rather than as a guar-
anty of safe arrival at the destination. If viewed thus
broadly, it is felt that their publication will accomplish
a useful purpose.

Some of the results are erratic and in the absence of
check tests can not be explained, but in the main they
are quite consistent. Some of the indications are
Bere rent throughout the tests, while others do not
show so clearly in the data, and in such cases careful
observations made in- the course of the tests and the
knowledge of the investigators as to conditions which
influenced the results of individual tests have been
drawn upon as well as the recorded test data in form-
ing the conclusions which are presented below.

CONCLUSIONS DRAWN FROM THE TESTS.

The exact nature of the tests must be borne in mind
in applying the conclusions drawn from them to other
conditions. The conclusions are stated in terms of
maximum impacts delivered by the different weights
of motor truck. Failure is assumed to have occurred
when cracking takes place. The maximum impact
values are such as ould be expected under conditions
of high speed and rough surface. Smoothness of the
surface and suitable tire equipment will reduce the
maximum impact pressures with a resulting higher
load carrying capacity than that indicated by the tests.

The essential features of the tests involve:

(1) Specimens 7 feet square laid on a moderately
plastic clay subgrade, the wet portion having water
standing almost level with the surface, the dry portion
being merely damp with capillary moisture.

(2) Repeated impacts increasing to the maximum
which caused cracking applied at the corner and at
the center of one edge by an impact machine dealing

1 Previous reports on these investigations will be found in several issues of Public
Roads, as follows: Vol. 3, No. 35, March, 1921; Vol. 4, No. 6, October, 1921; Vol. 4,
No. 7, November, 1921; and Vol. 4, No. 8, December, 1921.

93439—24——-1

Construction view—wet subgrade section showing tile cross drains and subgrade
cut for slabs of various thickness.

blows closely resembling impact of motor trucks.
Rolling loads were not applied. No impacts were
delivered at the centers of the slabs.

The conclusions drawn from the test are as follows:

The resistance of the road slab depends in part upon
the supporting value of the subgrade. <A subgrade of
high supporting value materially increases the resist-
ance to impact.

Impact resistance of rigid slabs varies neither
directly as the depth of the slab nor as the square of the
depth but as some power less than two.

ta general, plain concrete slabs show no more re-
sistance to impact delivered at the edge than to impact
delivered at-a corner.

Transverse cracks and longitudinal cracks near the
sides of a road slab may be caused by impact delivered
at the edge of the slab.

Plain concrete of 1:3:6 mix offers resistance to impact
ranging from about 60 per cent to 80 per cent of the
resistance of plain concrete of 1:114:3 mix. The lean
mix also shows more variation in strength. :

Reinforcing steel in concrete slabs, if present in
sufficient amount and so placed as to receive tensile
stress, adds to the resistance of the slab to impact.

Reinforcing steel placed longitudinally and _ trans-
versely in equal percentages is more effective in pre-
venting corner failures than the same amount placed
in one direction.

For a given percentage of steel, small deformed rods
closely spaced seem to be more effective than large
deformed rods widely spaced.

There is very little evidence of cushioning by bitu-
minous tops on concrete bases at temperatures of 90° F.
or less.

In these tests there was no evidence that bituminous
tops on concrete bases added to the slab strength of
the base, with the possible exception of the 4-inch and
6-inch bases on the dry subgrade.

Laid on the wet plastic subgrade none of the un-
reinforced slabs was capable of resisting impact at the
edge or corner equivalent to that of a 5-ton truck;
only the 8-inch, 1: 114: 3 slabs and the 2-inch Topeka

2

tops on 8-inch, 1:114:3 bases resisted edge or corner
impact equivalent to that of a 3-ton truck; all un-
reinforced slabs of lesser thickness failed under edge or
corner impact less than that of a 2-ton truck.

Laid on a dry subgrade the 8-inch plain concrete
slabs of 1: 114: 3 mix and the 8-inch edge thickness,
unreinforced, 1: 114: 3 bases with 2-inch Topeka tops
resisted edge and corner impact equivalent to that of a
5-ton truck with a safe margin; no other slabs were
capable of resisting the 5-ton truck impact even under
the favorable conditions of dry subgrade support. A
section of 6-inch plain concrete base, 1: 114: 3 mix, with
a 2-inch Topeka top resisted the edge impact of a 3-ton
truck; no other slabs of lesser edge thickness, laid on
the dry subgrade, were capable of resisting impact
greater than that of a 2-ton truck.

None of the systems of steel reinforcing tested
added sufficiently to the strength of a 6-inch 1:1144:3
concrete slab to enable it to resist the edge and corner
impact of a 3-ton truck when the slab was supported
by a very wet, plastic subgrade, nor to resist the edge
or corner impact of a 5-ton truck when the slab was
supported by a dry subgrade.

In some of the tests there was evidence that while the
presence of the steel did not assist greatly in preventing
the formation of the first crack it did prevent the de-
velopment of the crack and the further failure of the
slab.

OBJECT AND ORDER OF THE TESTS.

The object of this series of tests which, like the other
series, was conducted at the Arlington Experimental
Farm, Arlington, Va., was to secure data on the com-
parative resistance of sections of various types of
road slabs when subjected to impact forces of the same
magnitude as those applied to actual roads by modern
truck trafic of different weights.

To carry out this purpose three distinct steps were
required, as follows:

1. The determination of the magnitude of the
maximum impact to which a road slab is subjected by
motor trucks of different sizes.

2. The application of similar impact forces to the test
sections.

3. The measurement of the effect of these impacts
on the various test sections.

In order to carry out the first step in the program, a
series of about 100 road tests was run to determine
the maximum impact to which a road slab is subjected
when different sizes of motor trucks are driven over it,
fully loaded and at their maximum speed.

At the present time, the Bureau of Public Roads is
conducting a similar but much more elaborate series of
tests to determine this and other information regarding
actual motor truck impact. But for the purpose of the
impact tests on pavement slabs the tests were limited
to standard types of 2-ton, 3-ton, and 5-ton trucks.
Standard equipment in the way of solid tires, wheels,
springs, and spring suspension was used. These
trucks were driven over typical concrete roads, main-
tained in good condition, and the maximum rear wheel
impact was measured by means of an especially de-
signed accelerometer.

DESCRIPTION OF THE TEST SECTIONS.

As in the first series of impact tests, the attempt was
made to reproduce two subgrade conditions—a dry,
well-drained type and a thoroughly saturated one.
Extra precautions were taken to insure as much con-

trast as possible between the bearing values of the two
subgrades.

One hundred and twenty-four slabs were laid,
embracing in all about 40 different types. Each slab
was laid in duplicate, and the more important types
were placed on both the dry and the wet subgrades.
All slabs were 7 feet square.

The types of slabs may be roughly divided into five
groups:

1. Plain concrete.

2. Reinforced concrete.

3. Concrete bases and bitumimous tops.

4. Bituminous bases and bituminous tops.

5. Macadam bases and bituminous tops.

Tests of the slabs of all five groups have been com-
preted but this report does not deal with the tests of

ituminous tops on macadam and bituminous bases.
The behavior of these slabs is materially different from
that of the concrete slabs and the concrete bases with
bituminous tops, and it is felt that the results of the
tests of these groups should receive further study be-
fore they are announced.

A detailed description of each of the slabs in groups
1, 2, and 8 as to materials used, mixtures and thick-
ness, is given in Table I.

TABLE I.—Description of test slabs.

(Series 222-267 laid on wet subgrade; Series 314-337 laid on dry subgrade; Series
1R-18R laid on dry subgrade.)

PLAIN CONCRETE SLABS AND BASES.

Base course. Binder course. Surface course.
Slab
No. hick. Thick- Thick-
nda. | Material. nices Material. noes Material.
Inches. Inches. Inches.
222 | 6 | 1:3:6con- 14 | Bituminous con- 13 | Sheet asphalt.
crete. crete.
223 | AD a +f as ch % heeaee® ee eS Do.
224 | i) eS C0... 22h necklace tepenet Mamta 4 | Bituminous concrete.
» 225 sat Ce Aes 16. nat bchicsl aoaoee tees Do.
226 oh Ee eee! ee ee ee Bee Oe eee 2 Do.
227 i Ne 1 ean es OR eee a yale enn. Os 2 Do.
228 <p Sere Pee See eee RC.) SON 2 | Topeka
229 a (pe WPS eat See te ln eee 2 Do.
230 CD ty Gi ae ¢ Di Calon RE ae) bce a2 2 Do.
concrete.
204 ho OR es Osis had Seen era ee eae 2 Do.
232 29356 06ie ce sce ae ee ee 2. ees 2 Do.
| crete.
233 | Py NAD i Le OR 5 5 MO BE SES rah I se. SP 2 Do.
234 | O) SL 2 SR Leelee as eae eee 2 Do.
' concrete.
235 Bil trate G0 pag ese cd oaceea eee 2 Do.
236 | Bt aoa oe CUR et Ne oe ee 2 Do.
crete.
237 2 a ie dE Rolly Oca a, OM LA LN 2 Do.
238 | DB OR S06 Se eens ceed 2 eee 2 Do.
concrete.
250:) Bho ea a (yee KE pee, (es te RR i! ¥ Do.
ye errors) Bie errata, a Roem, ee Pe ee 4 | 1: 14:3 concrete.
72 ee ee pe 2 PEE OS 1 EY Tee 5 Sele ev 4 Do.
Bee Nb gece che KEES Pica ares bataboeaie a oan eae eee 6 Do.
2 eh See SS Oe PE Ee tm ee 6 Do.
7 | See Sees a Hiern eT ba 2S HR 6 {| 1:3:6 concrete.
oS ee OO mR! oe. Lacandotantss So case x sate Get nessa coe 6 Do.
SDD Macs a ere ance ashe Satin at ee ic ke eae ane bree eae 8 | 1: 14:3 concrete,
ET Ne xm oA c SUR CE ae eee Seco oe ee 8 Do.
7 he nen ON ee oR EE Sate, ars ST Se ee 8 | 1:3:6 concrete.
YES Vaasa ben deenateatiedens evens ter ethnernrce 8 Do.
314 | 6 A EE A Re ee | a SS a Se 2 | Topeka.
concrete. |
165 BLurs 2 ETS pry ers ee. ST ee 2 Do.
316 | GC) eG 5 OC Odite fe. eae cls canes enn PS 2 Do.
SAV al ee, noes Wasa ta wt atin a yma Son ope Foi Oc ol 2 Do.
318 | 4 et tT oe, ee Se See ee 2 Do.
4 concrete.
a + Ay ER SOR Pa eS 8 eae 2 Do.
320 oe Lj Peps ee epee en MEE AO SEE 2 Do.
321 BATS ete BG gee gute RO otter ta ee ae 2 Do.
5-7 2 a eee Sees Sep Coe ee eres we SP 4/1: a 3 concrete.
= 7 OE PIENE MerDy, OR as Sion ea Pt 4 0.
Sc AED, fe ren: SES 1 Nie PWS A eee eng) NS 6 Do.
22h Ee [SAS PE + Cie reek ays Se 6 Do.
326 nw ennn nla nnn nnn nn nn] ow een onan enna eens ee nnee 6 | 1:3:6 concrete.
S2t |amenmas fa ose esawes ine mien sd pan dene ces eeemnenne 6 0.
BO aac Sa cll eh toc Sons ng A a a ale ce ee 8 | 1: 14:3 concrete.
ver Ok Pre ek We, Fy | pes IS Ra 8 Do.

TasLEe I.—Description of test slabs—Continued.
CONCRETE SLABS WITH MESH REINFORCING—WET SUBGRADE.

Surface course.
j |
Ze | Reinforcement.
er Material. oe >
Description. Per cent.
|
| Inches. | |
250 4 | 1; 14:3 concrete. _......-... © IBV ER TON ees dels, 0, 21
251 DD Pee CUE aes Sar ee wre ie aie La go eC a Oe <2i
252 YS Sao 1 ee ey ee Pa | Le POP UN Gs Us cn dunccauannee . 42
253 Ss eae DO ene eee oP ota as Se 1) ey Se es ee ee . 42
254 a ee Pe Pe ae eg ee Vie LORS ING. Be ok aa ees 66
255 | iS SE Ge ee ee ee AN rs FON ee SS Cee ae . 66
256 A) ee CM a eR on cee Sie OU gt ht sae ee Sa . 41
257 | Rilenns Ge Soe ee ae a a ea ae 41
258 4 | wets 1 oe aw, Se | SINVOES. NOs DUS of was can . 82
259 i One Sy ee hs ar eee cel boauA! "2 1 on ae ae a ew . 82
260 | i eee ORR gone Se tans eg Cel BVOr IR: Mews be oS. onl .19
261 O i282... Ob aig Heda Sralsmates' banat ae a Si een 19
262 er ide ae alienioticd bon unk 2 AVON ING Dic cents Ben oe. . 38
263 | i Ree Sis A ee ee Sea eee ee Sa eS 38
264 | ip La Fie, Se Aes ee Pee cavers ING Bo Pe cae . 46
265 a Ot be ae a ee err | ae i ee, eee, ee . 46
266 | oy a oe le, , ee oe ) Sia vets NON 100-2 252+ Late . 58
267 | 6 | ps ae 57 Reh cic ee ogee 58

CONCRETE SLABS WITH MESH REINFORCING—DRY SUBGRADE.

|
| Inches. |
330 4} 15:14; 3 concrete. .....:<s--- PIRYOR INO 08 fc coccge kee 0. 21
331 . Sete he NE be a ea Notce ie Sons Oras Soc cicada 2 | eal
332 4 | Feat) ‘TMG Pie een ca aiMaver NG. 10.6, as ace nc 41
333 Loy tes Pt a ig, AA Selene, SE Pate cle ieee See eee . 41
334 gS eee ei ea | 2 lover ING. Cota ctdease ete. . 38
335 © Tee slow Ge eatin Se om tora ores LE ele tens PO Se SO 5.
336 fh hee ORs oe a ae shat aus oe fh Sievers iW. So. 2 cc. ecctces . 46
337 Oe.>. RN en oe otis oe tan i ween i eS a Ss . 46
CONCRETE SLABS WITH ROD REINFORCING—DRY SUBGRADE.
Surface course.
Reinforcement.
ro po ; Sn en
O. | |
Thick- : :
iad Material. <p m ; shape
ber of ni of rods Per cent.
l Javers rods. | center to
| y center. |
Inches. Inch. Inches. |
1-R 6 | 1:14:.3 concrete_.....-.._--.- 1 3 33 | 0.5
2-R A Se ee ee ee 1 2 32 a
3-R el of: ene eee Pare rene 2 ; ri 1.0
4-R i Out Se ase ee ee 2 2 33 | 1.0
5-R ne ee Ens ret Re ee a 2 3 5
6-R eh ee sy a RE aS EE ae 2 2 2 en
7-R ee 7 Ce Pe ay Saye wets eS ane: 1 $ 103 .6
&-R 1a | Cees 1 ae ae ee ae, a, ] 3 104 eee
9-R a ORE “ake Py ei ie ee 2 & 10% | 1.0
10-R ee Sees, ee es ok 2 3 | 104 1.0
11-R | i Ere a ae eer a pee 2 3 204 5
12-R Bae Gee coe a ok dew 2 3 203 | «d
13-R Bitieee: fe pn ae Se py 1 q 20 wD
14-R EAE Sen = Be oe ck eta 1 q 20 Pals)
15-R SS eee ARP oie Sy re ws cise 2 q 20 1.0
16-R Fh saree | a ee epee 2 ; 20 1.0
17-R a ae masn! (os 2 6h 6 coe. 2 3 40 | ae
18-R ch I (a eee ee Se 2 Z| 40 6

CONSTRUCTION OF THE TEST SECTIONS.

Every effort was made to have each slab built exactly
according to specifications. The subgrade on which
the slabs rest was brought to grade by cutting. No
fills were permitted. In the wet subgrade, a tile drain
was placed transversely, every eight feet, connecting
the longitudinal side ditches. These tile lines came
between slabs so as not to disturb the soil under the
slabs and their function was to lead water from the side
ditches back into the subgrade.

All concrete was mixed in a standard gasoline-driven
mixer, the materials being measured in a cubic-foot
measure. The coarse aggregate used was washed,

Construction view—wet subgrade section, bases laid and forms for bituminous
material in place.

Potomac River gravel and the fine aggregate a good
quality of concrete sand purchased locally. As soon
as the concrete was poured it was protected with canvas
until the following morning when it was covered with
earth and kept wet for two weeks. Curing was com-
pleted by exposure to the air.

Three 6 by 12 inch compression cylinders were made
of the concrete as it came from the mixer and these
were cured in the same manner as the slab.

All concrete was placed rather dry and was finished
by striking off flush with the forms with a screed. No
troweling was permitted.

The plans called for all steel in the reinforced slabs to
be placed 2 inches from the top surface of the slabs.
For the reinforcing itself, except in the rod-reinforced
sections, a fabric type was used—rods one way 6 inches
apart, held together with perpendicular wire cross
members every 12 inches. The cross members were
not welded to the rods, but were attached to them with
wire clips. Greater bond strength would probably
have been developed had these members been electri-
cally welded. When two layers of reinforcing were
used, the rods were placed at right angles to each other
with one sheet laid directly on the other. Test on this
steel showed it to be an intermediate grade steel with an
ultimate strength of 70,000 pounds. In sections 1—-R
to 18—R, square, deformed bars were used, the sizes and
spacing being given in Table I.

After the concrete had cured for one year, the bitu-
minous slabs were laid. This was done by contract,
the material being mixed and placed under the super-
vision of the Bureau of Public Roads.

Four and six inch concrete bases on the wet-subgrade
sections were cracked in rolling the bituminous tops,
the lean mixes being badly broken up. This unfortu-
nate occurrence eliminated several very interesting sec-
tions from the tests, but it is worth noting that 6-inch
1 : 14:38 concrete bases were cracked in construction
where a fairly bad subgrade condition obtained, while
4 inch bases of the same mix withstood the same roller
loads undamaged on a good subgrade. While the
ditches surrounding the wet-subgrade sections had not
been filled with water up to the time the rolling took
pie the position of these sections at the foot of the
nll and the presence of capillary water created a
naturally poorer subgrade condition than that which
existed in the dry-subgrade sections.

TESTING THE SLABS.

The second step in the program called for the
application of impact to the test sections. The
testing was begun in May, 1923. Prior to this time
the ditches surrounding the wet subgrades had for
several months been kept filled with water to the level
of the under side of the 6 inch slabs. The magnitude
of the impact forces to be applied had previously been
determined by the preliminary road tests using actual
motor trucks. As it was obviously impracticable to
use a motor truck for testing the slabs, a special
portable impact machine was designed and two of
them were built.

THE IMPACT MACHINE.

This machine, which is shown in the accompanying
illustration, consists essentially of a rear wheel of a
motor truck fastened solidly to the middle of a truck
spring and so arranged that it can be raised to any
desired height from the surface under test and dropped
suddenly. Power is furnished by an electric motor
which operates through a train of gears, raising the
wheel by means of a pair of cams. The whole
mechanism is suitably mounted on a framework of
structural steel.

Adjustments permit changing tire, wheel, spring,
sprung weight, unsprung weight, or height of drop at
will. The impact machine proved to be very satis-
factory and reliable and no trouble was experienced
from this source throughout the tests.

Load conditions corresponding to those of 2-ton,
3-ton, and 5-ton trucks were used.

THE METHOD OF TEST.

In testing a slab the machine was set up so that the
wheel was over the point where the load was to be
applied. The unsprung weight was made to corre-
spond to that of a 2-ton truck. By means of the
corner screws the machine was next set for a very low
drop, usually one-quarter inch or less. The truck
spring was then loaded to equal the sprung. load of the
same truck. ‘This was done by pulling down the ends of
the spring with screws until its deflection indicated the
required sprung load. From three to five blows were
delivered, after which the machine was raised slightly
and three to five blows were again delivered at the
new height. Each time the machine was raised it was
necessary to pull the ends of the spring down an equal
amount so that the spring deflection would remain
constant. This procedure was continued until the
data indicated that the maximum impact of which
this weight of truck was capable had been delivered.
If the slab had not failed, the loadings were increased
to those of a 3-ton truck and corresponding impacts
delivered. If a 5-ton truck impact failed to break the
slab, the impacts were increased until failure occurred.

POINTS OF LOADING USED.

As the data desired were only comparative, it was
originally intended to test one of each pair of slabs
at the center point and the other one at the corner.
But road tests indicated that the edge of a slab was
one of its weakest points. Also, the testing of the
first series of slabs had shown that for small slabs
center resistances are dependent upon the area of the

Rolling asphalt tops.

Roller weight, 250 pounds per inch of width.

slab.! With these points in mind, it seemed that more
and better information could be obtained by testing
not at the center of the slab but at the center of the
edge. The results show this to be true. These are
called edge tests in the data.

In the corner tests the load was applied as near to
the corner as it was possible to get the wheel and still
have the area of contact entirely on the slab. This
means the center of the wheel was over a point which
was about 7 inches back from the corner, measuring
along the diagonal of the slab.

DATA OBTAINED.

To compare the various slabs it was necessary to
know the maximum impact applied to the slab by the
wheel as it comes down and strikes the surface. There
are several ways of doing this, all of which have been
used at different times in connection with these tests.
Among these methods may be mentioned: (1) A space-
time curve; (2) copper-cylinder method; (3) deforma-
tion of spherical steel surface (Kreuger apparatus) ;
and (4) mass xX acceleration method, measuring the
acceleration with an accelerometer.’

The first method is probably the most precise and
the most difficult to use successfully. Because of the
time required, it is 1mpracticable for such tests as
these. ‘The second method is an approximation, as it
introduces a new factor for which correction can not
readily be made; 1. e., the cushioning effect of the cylin-
der itself. The third method offers practical difficulties
which render it unsuitable for this work.

By far the most satisfactory method is the mass X
acceleration method, using an accelerometer to measure
the acceleration. For this purpose a special accelero-
meter was used, which was devised and developed in
the Bureau of Public Roads. This instrument ‘is
described in Proceedings of the American Society for
Testing Materials, 1923, ‘‘An accelerometer for measur-
ing impact,” by E. B. Smith. In use it gives a reading
which indicates the maximum negative acceleration
which occurs when the falling truck wheel is brought
to rest by the resistance of the slab. Knowing the
unsprung weight of the impact machine, it is a simple
matter to calculate the maximum impact by means of
the formula

1 Public Roads, Vol. 4, No. 7, November, 1921. ‘Tests of impact on pavements
by the Bureau of Public Roads.”’

* For descriptions of these methods see Public Roads, Vol. 4, No. 6, October,
1921. ‘Tests of impact on pavements by the Bureau of Public Roads.”

f= Ma+P
in which /’= Maximum force (impact).

M ae -=weight of unsprung portion divided
by 32.2.

P=spring pressure existing when wheel is in
contact with slab.

In practice this method has proved to be easy to
use and sufficiently accurate for all practical purposes.
Inasmuch as the accelerometer was actually mounted
on a motor truck in the preliminary road tests, previ-
ously described, and certain readings obtained and
then later it was mounted on the impact machine where

TOP.—THE IMPACT MACHINE.

BOTTOM.—CLOSE-UP OF IMPACT MACHINE AND
SET-UP OF APPARATUS FOR THE EDGE TEST,
SHOWING GRAPHIC STRAIN GAUGES IN TOP AND
BOTTOM OF THE CONCRETE BASE, DEFLECTION
DIAL, THERMOMETER IN BITUMINOUS MATERIAL,
AND ACCELEROMETER MOUNTED ON SHELF BE-
LOW AXLE.

the sprung and unsprung weight conditions
of the truck were duplicated, 1t seems rea-
sonable to assume that impacts which, un-
der these two conditions, give equal accel-
erometer readings are equal in magnitude. |

The effect of the impact is to deflect the == A=
slab. It is necessary, therefore, to measure &)
the amount of this deflection. An Ames
dial reading to one-thousandth of an inch
and ‘‘choked”’ to hold its maximum reading, was used
for this purpose.

This deiuetion of one part of the slab caused cer-
tain stresses of compression and tension to be set up
in the material itself. Concrete being weak in ten-
sion, the tensile stress is obviously the governing one.
Hence it was necessary to measure the maximum ten-
sile stress created by the impact. An instrument known
as a graphic strain gage was used very successfully
to measure these deformations. This instrument also
was devised in the Bureau of Public Roads, and its
construction and operation is described in “‘ Engineer-
ing News-Record,” March 22, 1923, in an article en-
titled “A new impact strain gage,” by A. T. Goldbeck.

ea pe
Re GT eR |
<—? ,
a ee i

aie. ip PRS AT et

cn

In addition to the data thus obtained, it was neces-
sary to know exactly the height of drop used each time.
For this purpose a stylus connected directly to the
truck wheel was used to trace a record on a paper
which was carried on a drum. By determining the
point at which the wheel comes in contact with the slab
this total height of drop can be divided into the com-
ponent parts of free fall, rubber deformation and slab
deflection.

AUXILIARY TESTS.

In addition to the actual impact test on each slab, an
auxiliary test was always made to determine the load
supporting value of the subgrade. Also in the case of
the concrete slabs, compression tests were run on the 6

by 12 inch test cylinders, previ-

*. ously mentioned, to determine

‘iy the modulus of elasticity and the

crushing strength of the concrete
at the time of test.

The subgrade bearing value
determination was made with a
portable apparatus shown in the
accompanying illustration. The
method of test is to apply a con-
stantly increasing unit load to a
small circular bearing blockscraped
to intimate contact with the sub-
grade, and to measure the pene-
tration of this foot into the soil
under the load. This test is de-

scribed in Public Roads, volume 4, No. 5,September, 1921.
‘Preliminary report on the Bates experimental road.”

The determination of the modulus of elasticity by
means of a compressometer is familiar to all and will
not be described except to say that the instrument
devised and built by the Bureau of Public Roads and
described in American Society for Testing Materials
Proceedings, 1923, “‘Slag as a concrete aggregate,”’
by Raymond Harsch, gives excellent results and
apparently is free from the lag so common in instru-
ments of this type.

Typical modulus of elasticity curves for concrete of
the two mixes used are shown in the accompanying
diagram.

TaBLe I].—Average compressive strength of all test cylinders.

Compressive strength in
pounds per square inch.

Class af sections.

1:3:6 mix. | 1:13:3 mix.

Dry subgrade... cca ne hat ecb nent ssa eeeeaataneeeoee 1, 420 4, 180
Dry subgrade, rod-reinforced slabs... ico ec eens cece oes onan sean 5, 948
WY GT, BUSES oo rin leh odin ees eek bere ee eee 1, 477 4, 459

a
THE SUBGRADE AND ITS EFFECT ON SLAB RESISTANCE.

These slab tests have especially emphasized the im-
portant part the subgrade. plays in the resistance of a
road slab of any type. The rigid slabs on the wet
subgrade showed roughly two-thirds of the resistance
of duplicate slabs on the good subgrade.

The results of the subgrade determination varied
somewhat, but it was nearly always possible to get
two curves to check closely out of three or four tests,
which is the number of tests usually made at each
slab. The load-penetration curve was plotted for each
test and these curves averaged for each subgrade.
The three average curves grouped in the figure repro-
duced on page 10 show clearly the difference in bearing
value of the three subgrades. There was consider-
able variation in moisture content of the samples taken
and no relation could be found between moisture con-
tent and bearing value. The reason for this is thought
to be primarily in the varying soil characteristics of
the sit acsit samples due to the topographic location
of the different slabs. No laboratory analysis was
attempted on the many samples taken. Except to
say that the moisture for the samples taken ran on
the average from 5 to 10 per cent higher on the wet
subgrade than on the dry, it is not thought worth
while to present the data on these moisture tests.

BEHAVIOR OF THE CONCRETE SLABS,

It was considered that a rigid slab had failed when
the strain gage record indicated the formation of the
first crack. This was selected as a definite point of
comparison for slabs of this type, but the behavior of
the section beyond this point was also considered in
comparing reinforced types.

It is not possible to derive an exact mathematical
relation from the results of such tests as these, but it
would seem from the examination of the most nearly
comparable sections that the resistance of the slabs
varies neither directly with the depth nor with the
ee of the depth, but as some power less than two.
There are other factors present on which there are no
data, such as the relation between bending and shear-
ing stresses in different depths of slabs, which may
be, and probably are, very important. |

Impacts were applied at the corner and at the center
of one side of each type of slab. There seems to be
practically the same resistance at both points of load-
ing in the plain concrete slabs. When there was steel
present in sufficient amount and in the proper place
to resist tension, the tests showed a corresponding in-
crease 1n resistance.

The edge test invariably resulted in a transverse
crack beginning with an incipient crack on the bot-
tom of the slab directly under the wheel. ‘This crack
developed rapidly across the slab. Thin slabs punched
out immediately following the formation of the crack.
One 8-inch, 1:3:6 slab developed a longitudinal crack
which divided the slab into quarters. It is probable in
this case that the inertia of the heavy slab caused
tension which exceeded the strength of the concrete.

The corner test caused a curved crack across the
corner due to tension in the top fibers of the slab.
The unit fiber deformation at failure was the same

TaBLE JII.—Test data on rigid slabs.
LAID ON WET SUBGRADE.

Construction
; 3 |
: — 8 ———= | Maximum unit fiber | Average
: Average | :
No. p Point ot FPELbaion | impact elasticity strength
| = oe = ——e Reg resisted <a - ae ea ___| at failure :
, , cylinders
Thick-| nix | Thick-| Material
} ness | : ness ‘ Elastic At failure
aes Pounds
| ounds per er
Inches Inches | Pounds | sq. ine - in.
222 6 1:3:6 $4.) Baleet aapialt to ee eee 1 ee ee ee ee 10, 800 0.000230 | 0.000300 | 2,027, 500 989
223 6 | 1:3:6 19 oe Oo ee ts Seay See ee CODNGE Ss dee bap Josneeees 8, 000 (2) ee em ace 1,118
224 6) 1:3:6 4 | Bitumilsods contrete. oi. eee eck ee ge ole ee eee ee re 8, 000 (3) i ge) ee ey 2; 086
225 6 | 1:3:6 4 | ca geie dy cent ec de Seen ae geome Cornerer sa nen. tits, eto 8, 000 el) Bee ed S See 1, 738
226 6} 1:38:36. a NS en 2 |: eee ON eee ke a ee EN ee” OR en Se ee 8, 000 3) CGP Waco d eee 1, 141
227 6} 1:3:6 a toate QO thst nacbescess ahemeree eee eee Wonner.: 35-5 215 eae 8, 000 (2) fe) Pe ne, ene ee. a 901
228 4] 1:3:6 7 fae 85) 0.) :9: Ce ee bee TR OE eave SM ee ie ie 2, 000 (4) ‘td eee Da mene, 1, 384
229 a} 42536 2 | Sis fae AG. acc eek oe ee ee OVDIOR nee cue ee ane 2, 000 (5) BS) era 2. ae 798
230 4 | 1:14:38 a WD. sc Sn io ee anho one ee ee EPG auls coceccee cts eee 4 ree, ee ae a Pe a S 3, 365
231 4 | 1:14:3 BR REE, | OIG 5 PE EL PER eg ah OOTIGE SS sc egos oe Me Gee RN Rtn eC a, 7 Wg 9 > 3, 817
232 6| 1:3:6 ah eee Tr ees Se EOE eta eC age 2 soe ee | O10. 15. scree C2) a aoe 2, 001
233 6 | 1:3:6 S4i.- 2. DO. ihnta oe eA ee Larner ht ras 8, 000 (2) Se! he eee 1, 708
234 6 | 1:14:3 eS tt i ce ea je ee DEO spiny Ure otueie tana 11, 850 . 000306 . 000324 | 4, 330, 000 | 4, 268
235 6 | A: 1}: 3 re ee ft i ee a ey) Se CS Le & LOPUOT 22 fase cune ha Gee 9, 500 . 000284 . 000305 | 4, 390, 000 | 4, 418
236 8| 1:3:6 3 ees G0) kde che, neok ed eee ee ee Pdvecs 2 ede ae 16,100} 5000225 | 000257 | 3,270, 000 1, 673
237 8 | 73:6 1. pee do Pp ae ae Thre ee ae, ie Tel gh, TE ee OTTO S« 35 dod ase et 11, 600 | . 000330 . 000379 ; 2,815, 000 | 1, 849
238 8 1: 19:3 | eS | oe id Ls ps eye ee ee Ree ese ee LES om! OMe cts set Jae | 25, 250 , 000242 . 000267 4, 685, 000 | 5, 100
239 OBS C8 OSI fi ae, keri Cae cme aN Rs he Aer, Corners Sb hace 2h cos 25,700 .000290/ | 000204 4'040,000 4, 458
240 4 1: 13:3 faite gr ear aiien Kylie ot 5 Aa tn Sst ox tn RD atthe os ee eee Ee ee ROG6.02.. ee ae (8) . 000155 . 000208 | 4, 450, 000 | 4, 350
241 4 | 1: 13:3 Re ae Re ee OS RE TE 2 ee ee ClOrTROr . eo FO ee ee (8) eOOOTSS Lae. 2s ES 4, 590, 000 5, 076
242 6 | l: 13:3 Ea ee a i ee ee ee, eS Sew Lo [5 REE cn ~ no OD ee 11, 650 | . 000272 . 000291 4, 200, 000 | 4, 480
243 6 | 1: 13:3 StepRabs i) eoiediny Be sates te oo hee ee ee RSOTOT Af ot ee, ae 14, 000 - 000258 | . 000370 | 4,410,000 | 5, 213
= 6 1 3: if Eee ty eee. Me i were ane tele ee EES Ts ene een Se eee eet 9, 200 . 000218 . 000283 2, 805, 000 1, 803
np 6 *, 3: D famed keel eves 28 nae nea dnodignaayp wakes aeons eee Corner erase. Sey yt ee See 9, 960 my is 3s) Mn, ee 3, 290, 000 | 1, 832
are : + 3 Se eee, tr ee a le ee. saree a sae 27, 100 . 000292 . 000302 | 4,778, 000 | 4, 857
“ie : : 3: 2 SE GRRE Cen Be ee ee EE ets 2 ae re LOTS Coe nce see 24, 700 . 000267 | . 000495 | 4, 190, 000 3, 701
on : 13: DO Pea hil ddl ctr c moe ina cease a ee ee eee TUCO a ete otc ose 14, 275 . 000242 | . 000284 2, 235, 000 1, 160
Dee RB cess Cl ele ects St RAK ws day ts ch cain ten Sn Gormek . Fe eas ee keee 15, 075 - 000269 | . 000360 | 2, 455, 000 1, 385

1 Laid on 14-inch binder course.
2 Static load broke corner off.

* Static load cracked base.

‘ Static load caused new cracks; badly cracked in rolling.

6 Static load caused 0.65 inch deflection; badly cracked in rolling.
6 Too badly broken to test.

7 Not obtained.

8 Static load, 8,000.

fi

TaBLE III.—Test data on rigid slabs—Continued.
LAID ON WET SUBGRADE—Continued.

F Maximum unit fiber
Construction of concrete slab. Gates. | Average | Av¥erage
; Point of Maximum = f , crushing
eR — = LSS application impact |-———————" ‘modulus o strength
. of load resisted | elasticity | oF 3 ey}.
- Thick- . : : : ; . . at failure. ; °° CY
| “nese 1 =: Reinforcing. : Elastic. | At failure. | | inders.
| | ! |
- + -- —--- ; = — Sa = | -—- = | —— —
Pounds Pounds
: Inches. Pounds. ' per sq. in. (per sq. in.
£7) 1:94:3 § I layer No.S (0:21 permemt) _.................-.-.........-.-..--- | Wie. ____.-.2.---- SD 0.000310 | 4, 270, 000 4, 400
4 | 1314%:3)1..-.- = a ee oe 10, 730 0. 000265 . 000307 4, 125, 000 | 4, 330
4 | 1:18:53 § BiayersrNolG (0:42 per@ent) _ _.c. - ee sen see - se eee - es ee [as 7, 550 . 000203 | . 000365 | 4, 250, 000 » 4, 243
4 | 1:98:3.7..... 7 | Ao eee ee ee ee eee Confer... ... 2... 8, 500 .000260 | .000275 | 4, 270, 000 | 4, 740
. 4 | l:ig:8 «2 layers No. 8 (0:66 per cent) __2..........................-....--.- ( agen. ........2ec 7, 790 . 000293 . 000360 | 3, 970, 000 4, 326
| 4| 1:1$:3 [_---- inline 9 il AE AAR Corner.....-.----- 10, 260 000286 | — .000309 | 4) 125, 000 4) 163
4) eae 2 @ Pee NO. 1010.41 BMieodt)_..... ence cee. TOR. ae eee 7, 025 000278 | . 000801 4, 422,000 | 4, 643
| 4} i:i#:3 £.... i On et —— 7, 790 . 000253 | . 000315 ' 4, 610, 000 4, 961
4 ane 2 ee est | ee eget... --.---a%- 8, 300 000283 | . 000343 | 4, 120, 000 3, 976
i Ap Ad Pe le | ee yo aes 10, 950 000281 . .000317 | 4, 650, 000 | 4,184
6 | 1:14:3 } 1 _ DUO. UO POMOUn OOH Ue... osc ccc cen cncncdue-ncdencccensce EGie:.......----- 16, 600 . 000267 . .000298 4, 255, 000 4, 733
eo Cee! «= I ee ene nc Leesan eee et eoMeer......-..--- 16, 200 O00864 |... ..--2.-2 4, 400, 000 | 4, 583
6 | 1:14:3 | 2 lations io. & (0083 perteent)_.............--.--------~ ~~~ seme ee oe | B@ge._............. 19, 150 . 000293 000327 | 3, 930, 000 | 4, 223
Pe i iin ne Riis a one Upc do cenanne cee eus OOPMOP............ 21, 500 - 000298 000314 4, 390, 000 | 4, 200
6 | 1:13:3 | 2 layers ee (Grae Beem). eee een ne nc-eee eee. 17, 700 . 000309 | 000315 3, 940, 000 4, 410
BP it al ee Sh 17, 000 . 000247 - . 000281 | 4, 495, 000 5, 530
6 | 1:13:38 | 2 lwyers No. 10 (0:58 per cent)....._._......._-.-_....--.-. --- 68. EG@ge....-.-....-.. 16, 350 . 000278 | . 000297 | 4, 030, 000 4, 446
6 } boty s |.--20 eee eee. ea eee 2 Copper. _.........- 14, 560 . 000308 000414 4, 595, 000 4, 572
LAID ON DRY SUBGRADE.
Construction. an i
| Maximum unit fiber
= | ieee =a = : . " Average
Point . deformation. Average |
Concrete. Top course. of appli- ee : modulus of | oe
LE SEE ae cation resisted. | _.. ... _| elasticity ‘of 3 cylin-
of load. : at failure. me
Thick- : : . Thick- , ; . ‘
“aa Mix. Reinforcing aoe Material. Elastic. | At failure.
Pounds : Pounds
Inches. Inches. Pounds. per sq. in. | per sq. in.
ee ees eee 2 Oo. aeceanceu xe 2 Magpie To- | Edge_._... 5 0. 000235 0. 000282 (1) =a
peka
Se ee oe eee cee eke enceee-skae| 7) 2e}.---. Gee). 2.5228 Corner.... 19, 950 . 000298 . 000371 OP
Si EUSSs SS gS ee Sk i. | ae WOU own a oe Edge.....- 19, 800 . 000296 . 000319 | 3,340, 000 2/325
ne en ks te hace ca cteccasuenss | Cr Corner..-. 17, 060 . 000296 | 000371 | 3, 200, 000 1, 794
SU Re en ee ee eee eee eeeue| 2D eee ee BO. meek eee C2522. 13, 650 . 000272 000340 | 3,300, 000 Orele
de) Le) a er al ae | rr Edge___._- 19, 400 . 000314 000372 | 3,300, 000 3, 660
aoe ec oka sass acccwccsacens 7 ae | i. ae: |: 37, 800 . 000295 000315 | 3, 660, 000 3, 940
Le RR IE Oe eg ine. ae Ggmiee a. soe Corner-.--- 39, 800 . 000292 000312 | 4, 640, 000 3, 340
4 | UL pe SRR epee | | aE _, e Edge:__.... 13, 300 (?) 000353 | 4, 750, 000 4, 488
fo A | eee eke 2nd aS ee ee ee, 2 Corner _..' 14, 000 © . 000308 000319 | 4, 000, 000 3, 938
Ch) LR ASSES ee Seo oe a ee ee) ee. on ee Edge....-- 20, 000 . 000271 000297 | 4, 330, 000 4, 698
a 00 N aa lS i O — = | = el 5, 446
es i at OPIN ere ee ee ee ee Sue enh on ee ao oeheea cee Rdge...... 18, 300 000237 | 000292 2, 620, 000 1, 632
a re |r eo oe cee ese en|ooeuen ce i ee. | i ee ee oe 1, 331
te ae eh in we Smee edna ne eee een den cceuwacene | Edge._._-, 41, 500 . 000337 . 000395 3, 620, 000 3, 334
a a a Es ee oe eon ' Corner...-! 42, 580 - 000264 | . 000451 | 4, 450, 000 | 4, 993
Apaletess. | 1 ees ror OnO el memmentys........-.---.---<|o-------.----- ae - ee -- Edge:.._.. 13, 410 . 000278 | . 000295 | 4, 170, 000 | 3, 493
Ue = 8 on ce ete a nn nnn e------ Corner... 11, 600 . 000280 | .000312 | 4, 500, 000 | 4,709
4 11eia3 | 1 layer io: 10 (04 percent) _...............-.|.----.-. ae 2 | Edge.._.-- 11, 250 © - 000243 - 000332 | 4, 850, 000 | 4, 183
Coo TE a SS Se a | ae || Si: ee , Corner..-_- 11, 150 . 000215 | 000301 4, 420, 000 3, 782
6 | likes | 2 leamaii No. 6 (0.38 per cent) .__.--.-...._._.-- ee, Wedge... .- 20, 000 . 000262 000279 | 4, 700, 000 | 4, 769
GPiaryrs |... Vee on: ee eS! a “Gomer... 23,700 , — . 000256 (4) 4, 710, 000 | F ~
tyme? (coe e ee. on a I - a ee a ee , 626
6 ! 1:1}:3 | 2 layers No. 8 (0.46 per cent) _.....--..--..-.-- | ee | aS e, .: e | | Corner... --| 21, 800 | 000244 . 000277 | 4, 330, 000 | 3, 861
| ; ——
Maximum unit fiber | Average
; ,; Maximum deformation. Average | crushing
Point of applica- : | ‘modulus of.
Reinforcing of 6-inch 1: 14:3 concrete slabs val offlomd: —_ — clesticity | eimangeb
Elastic. | At failure. 2 failure. [iladows.
Pounds Pounds
Pounds. per aq. in. | per sq. in.
1 layer ?-inch rods 3 inches center to center...._......_.-....-.--...------------- Ha@@ew. .....0252:- 23, 050 0.000271 0.000308 : 4, 550, 000 6, 068
ae oo . SNe eee eee 24, 100 . 000281 | . 000302 4, 960, 000 6, 193
2dayers4-inen rods\a7 inches center to center .-.......-..........---.--.--.------- ges... Sess. 21, 450 . 000296 | .000355 . 4,395, 000 5, 920
ae OI ne MS lala a a wae aes ons e| OE- ----caeeens 29, 200 - 000281 , .000301 4,625, 000 — 6, 508
2 layers ¢-inch rods 7? inckes center to conter_......_.................-..----.--.- Eee .=-~--225--- 22, 000 - 000286 | =. 000348 4, 765, 000 5, 548
i rr er eee eee eseneducecbesesesucs Caepmer..........-- 24, 700 . 000247 [roo aaezie _ 4, 950, 000 5 aoe
1 layer $-inch rods 10} inches center to center ..............--.-----.---..--------- os 22, 930 . 000228 | . 000308 , 4,510, 000 - 6, 427
a ee a ener "ae 24, 900 . 000273 |....-.....-. 5, 000, 080 6, 635
2 iavers inch rods 10; memes cenver to cetiter...._._.....-.-.---...---.---------- M@gom_..........- 23, 600 . 000267 : .000304 . 4, 630, 000 5, 701
see ES D.Sc eee | ae 28, 650 - 000277 | . 000308 4, 835, 000 5, 833
2 layers }-inch rods 204 inches center to center.._._.....__---.--.------------------ Fieese..o..< Sens | 19, 350 . 000243 | . 000300 4, 540, 000 6, 161
ee ee ee ee i ed deccteec ayes eee at Copmer....._...... 24, 650 » OUGRS7 |..........-- 4, ba 000 6, te
“1 layer 3-inch rods 20 inches center to center._..._....._--------------------e----- Hig@e@....-...-.=--- : 20, 900 . 000281 . 000367 4, 940, 000 5,
|e ip ue ee eaten danke Copmer_.........-- : 24, 150 . 000297 . 000399 4, 155, eo 5, aa
Clave oe cil oaeeo inicres Center to ceuter .............-----.---....---- swe .we a 23, 850 . 000247 | . 000348 5, 125, 5, 866
cal i oe ee Co | 26, 550 . 000243 . 000345 . 4, 805, 000 Hie
2 layers $-inch rods 40 inches center to center_._.._._..-.--------.-------.--_-_----- HeBeee ._.--..-- a0 23, 050 . 000301 . 000348 . 4, 515, 000 6,
ee cee A ‘sal 8, ene ee 2 Curner......---se | 27, 100 . 000292 . 000304 4, 420, 000 4, 880

1 No test cylinders. 2 Not obtained. 3 Broken during preliminary test last year. 4‘ Beyond gauge length.

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10

the same impact which caused failure fail to open up
a crack into which water and mud could work and
attack the steel.

Results of the tests on slabs reinforced with deformed

| bars show a definite increase in strength, particularly
4 in the corner tests where the steel was in a

etter posi-

tion to take tensile stress. The compression cylinders

| indicate a somewhat stronger concrete in this group of

Swtmee,| slabs for no known reason, the same care having been

e3| taken in placing all of the slabs.
“| ever, the subgrade shows a lower bearing value than

To offset this, how-

"I ws| the other sections on the dry subgrade.

In the corner test the slabs having 1 per cent of steel
show about 13 per cent more strength than the slabs
having 0.5 per cent. A study of the behavior of the
breaks after failure leads to the conclusion that, for a

‘gume_oc.| given percentage of steel, small rods closely spaced are

Subgrade bearing value determination. Shot from an overhead container falls at
a constant rate into a drum supported by a small bearing block. The penetration
of this block into the subgrade is measured by an Ames dial,

as that on the bottom of the slab in the edge test. The
area broken off in the corner tests seems to depend on
the condition of the subgrade, as it is noticeable that
smaller areas are broken off where the subgrade is
frm. It was found possible to break off a corner
by an impact delivered at the quarter point of one
edge; i. e., at a point 21 inches from the corner along
one edge. This would seem to indicate that some
corner breaks may start from impacts delivered along
the edge which produce tension in the bottom of slab.

THE/EFFECT OF REINFORCING.

A study of the data must inevitably lead to the
conclusion that fabric reinforcing of the type used in
these tests at or near the center of a road slab does not
appreciably increase its resistance to impact. Obser-
vation at the time of test bears this out. In the per-
centages used in these test sections, no great additional
strength was noticed after the formation of the first
crack, and in no case did repeated applications of

LOAD IN
S
ole) area
15 |
J LT ae eee

WET SUBGRADE

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Load-penetration curves. Soil bearing value tests.

more effective than large rods widely spaced.

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23 4 0 1 2°3,4°0 | 2”) 3a
DEFORMATION IN THOUSANDTHS-OF AN INCH

Typical modulus of elasticity curves obtained from 6 by 12 inch compression
cylinders.

In the edge test there was little additional resistance
to the formation of the first crack. This was to be
expected in view of the fact that the steel was placed
in the upper part of the slab. But a very marked re-
sistance to further failure was apparent in all the slabs.
In no case was it possible to develop the crack through
to the top of the slab, although a complete transverse
crack showed at the bottom. Additional very high
impacts failed to break down this resistance. This
was not true of the mesh-reinforced slabs.

LITTLE EVIDENCE OF CUSHIONING BY BITUMINOUS TOPS.

In examining the data with the idea of finding out to
what extent bituminous tops on concrete cushion the
impact of traffic, there are a number of facts to be
borne in mind. Lveryone is familiar with the springi-

Transverse crack, the result of impact 0a a 6-inch 1:13:3 Transverse crack with corners broken off in a 4-inch, Transverse and longitudinal crack resulting from im-
plain concrete slab. mesh-reinforced concrete slab. pact on an 8-inch, 1:3:6 plain concrete slab.

Typical failures in edge tests of concrete slabs laid on wet subgrade.

6-inch mesh-reinforced concrete slab. 6-inch plain concrete slab.

Typical failures in corner tests of concrete slabs laid on wet subgrade.

Low percentage of steel and one-way placing result in wide crack under additional Effect of a larger percentage of steel—a small crack which does not open up under
impact. additional impact,

Typical failures of rod-reinforced sections in corner test.

td

ey ee ee |

Effect of large rods apparent in this crack. High percentage of steel and two-way placing result in second crack about 7 inches

a the corner than the first. First crack refused to open under additional
ows.

Typical failures of rod-reinforeed sections in corner test.

Topeka top beginning

Set-up of strain gauges and deflection dial for the edge test.
to crack,

ness of an asphalt city pavement on a hot day, and it
is easy to jump to the conclusion that such a surface
acts as a cushion to the blows of traffic.

But even in this springy state, while undoubtedly
the bituminous mixture yields readily to a steady
pressure, it is doubtful if it moves appreciably under
an impact whose duration is but a small fraction of a
second. ‘To cushion a wheel impact, something must
act to bring the wheel slowly to rest; in this case the
asphalt top must move and move _ considerably.
Observations during the impact tests show that it
does move, but under a single blow its movement is
very slight indeed. The results of all comparable
slabs with and without asphalt tops (2-inch modified
Topeka) show little evidence of cushioning due to
these tops.

TOP OF SLAB
TOP GAGE?

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BOTTOM GAGE, |

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Determination of neutral axis from strain gauge measurement on concrete slabs with
bituminous tops. The neutral axis remains fixed until the lower fibers begin to fail.

BOTTOM OF SLAB

The temperature is an extremely important factor
in the behavior of bituminous mixtures. The tests
herein described were made during the summer months
and the temperatures of the asphalt varied from 25°
to 32° C. (77° to 90° F.) Undoubtedly at higher
temperatures more movement would take place in
the material under a wheel impact.

Table IV shows the results from which these con-
clusions were drawn.

TaBLeE IV.—Data on cushioning of bituminous tops.

: With 2-inch
Concrete. Plain. Topeka top.

Impact | Impact

Mix Thick- | Height | of 2-ton | Height | of 2-ton

mia ness. of drop. : truck of drop. truck

| wheel. wheel.

Drv subgrade: Inches. | Inches. | Pounds. | Inches. | Pounds.
1 a. in 4 0.97; 11,440 | 0.95 12, 060
re WM eee Ss ee 6 Ras | 18, 300 . 62 19, 800
el: a i 6 | -68 | 20, 000 . 60 24, 500
i <_.) e | 8 1.15! 41,500 | 1,28 37, 800

Wet subgrade: | | |
i... Ce... 4 (1) - ) \eo eee ee
eo) 2 (3) rene Se es 6 48 9, 200 .47 9, 460
Leer Oe s. > toe eee eee res 6 1, 06 | 11, 600 | 1. 18 11, 330
ke a re 8 40, 8,660 46 8,975
LEO onc. Saeesces ene 8 1.53, 27, 100 | 1.92 2he200
1 Failed under static load.
- , : ;

To draw an absolute conclusion regarding cushion-

ing, every condition of subgrade, sprung weight,
unsprung weight, height of drop, etc., should be iden-
tical. With these conditions constant, a top which
acts as a cushion should show a lower impact force for
a given height of drop. The slabs lsted in the table
are compared in this manner, and with one exception
they show no evidence of this effect. The 8-inch
slabs of the 1 : 14 : 3 mix show indications of such an
action toward the end of the test where very heavy
impacts were being applied. At the impact which
broke the 4-inch and 6-inch slabs no cushioning is
apparent.

It is realized that perfect conditions for comparison
did not obtain in the case of these tests, especially
in the matter of subgrade support. They more nearly
duplicate road conditions, however, and for this reason
should be more valuable than some laboratory tests
which do not in any way compare with truck-wheel
impact.

Strain gauges on top of slab are for determination of
Those in edge of slab locate the neutral plane.

Set-up for the corner test.
maximum tensile stress.

14

EFFECT OF BITUMINOUS TOPS ON SLAB STRENGTH.

The resistance of the concrete slabs of the different
mixes and thickness is not, in general, increased by the
addition of a bituminous top of the thickness used in
these tests, except possibly in the case of the 4-inch
and 6-inch bases on the dry subgrade. Several showed
distinctly less resistance, but it should be noted that
these were slabs laid on the wet subgrade and in several
cases there was evidence of deterioration in the concrete
under the bituminous layer. Evaporation of moisture
from the concrete was prevented and this may have
caused the weakened condition of these bases. The
1 : 3:6 mix seemed to be affected to a greater degree
than the 1 : Ide 3 mie

There was very little bond between the concrete
bases and the bituminous surfaces of any of the types
used. Certainly there was not enough to resist appre-
ciable horizontal shearing stresses. These observations
were borne out by the strain gage readings in the edge
test, which showed no raising of the neutral plane of

the slab when a bituminous top was added. The
average of all of the edge tests on these slabs on the
dry subgrade showed the neutral plane to be 0.37 inch
above the horizontal center plane of the slab. The
same data for the concrete slabs without bituminous
tops showed an average measurement of 0.39 inch above
the horizontal center plane. The fact that all the
slabs showed this plane to be above center may be
due to a lesser density of the concrete next to the
subgrade.

Topeka tops proved to be extremely tough and
resistant to cracking, more so than the sheet asphalt
with binder course. Even after the failure of the
concrete bases, the bituminous layer bridged the
crack and withstood the impact, materially reducing
the destructive effect of the succeeding blows. On the
dry subgrade, where the foundation support was good,
these Topeka tops withstood very severe punishment
with little deformation or cracking.

MOTOR VEHICLE REGISTRATION 15,092,177.

$225,784,932 AMOUNT OF ANNUAL LICENSE FEES AND GASOLINE TAXES.

By ANDREW P. ANDERSON, Highway Engineer, U. S. Bureau of Public Roads.

crease in the number of motor vehicles. A total

of 15,092,177 passenger cars, motor trucks, and
commercial vehicles were registered in the 48 States and
District of Columbia during the registration year 1923.
This is an actual increase over 1922 of 2,853,802 regis-
trations, 408,136 more cars than the total number
registered in 1915, or 1,078,722 more than the greatest
previous increase recorded during one year.

There are now approximately 2 motor vehicles for
every 15 persons of our total population, and if the
increase during the present year should be as great as
during the past, we shall have at the end of the year 1
motor vehicle for every 6 persons of our total estimated
population—enough to transport our entire population
at one time should the necessity arise.

The statistics of motor-vehicle registrations read more
like a tale from Baron Munchausen or the Arabian
Nights than prosaic records of actual facts. In 19138,
the earliest year for which fairly reliable data are avail-
able, the total number of vehicles registered was only
1,258,062, or approximately one-twelfth of the present
number. In 1919 the registrations had increased to
7,065,446, or almost exactly one-half of the total for
1923. This rate of increase obviously can not continue
indefinitely, but the records of the past give no clue as
to when or how it will cease.

Owners of these motor vehicles are insistent in their
demand for improved roads, and they are apparently
contributing substantially to the funds available for
road work, especially for the maintenance of State high-
ways. ‘Total gross receipts from registration fees,
together with the licenses of drivers, acstiait etc.,
which in 1913 amounted to only $8,192,253, in 1923.
amounted to $188,970,992.24. Thus, while the number
of motor vehicle registrations increased only 12 times
during the 10-year period, the funds so collected in-
creased 23 times.

[= YEAR 1923 has shown a truly remarkable in-

Practically the whole amount of the license fees col-
lected, after deducting the sums required to pay the cost -
of registration, is now devoted to road work or to the
financing of debts incurred for road construction, and
by far the greater part of these funds is expended by
or under the supervision of the State highway depart-
ments. Of the total of $188,970,992.24 collected dur-
ing 1923, $153,226,636.16 has been or will be applied
to road work conducted by or under the supervision of
the State highway departments, although in a few
States this supervision or control is not as complete as
it should be.

AVERAGE MOTOR TRUCK FEE MORE THAN TWICE THAT OF AVER-
AGE PASSENGER CAR.

Returns from 29 States in which the records permit
the segregation of fees paid for motor trucks from those
paid for passenger cars show that the fee paid for the
average truck is more than twice as great as the average
fee paid per passenger car. In these 29 States a total
of $24,020,784.89 was paid in fees for 1,103,076 motor
trucks and only $91,031,927.06 for 8,671,635 passenger
cars.

In addition to the direct fees paid by the motor-
vehicle owner or operator, he also pays a large amount
in indirect fees or taxes. In most States motor
vehicles are taxed as personal property. Many cities
levy wheel taxes or additional registration fees. The
Federal Government collects an excise tax of 5 per
cent of the manufacturer’s sale price on all passenger
cars, parts, tires, and accessories and 3 per cent on
the sale price of motor trucks. And over and above
all these taxes the majority of the States now tax
gasoline or motor fuel. This form of tax has proved
to be most popular with the State legislatures. First
adopted by the States of Oregon, New Mexico, and
Colorado in 1919, this form of taxation is now in
force in 35 States, the tax ranging from 1 to 4 cents

1d

TaBLe I.—Motor vehicle registration, licenses, and revenues, registration year 1923.

! |
| | Registration fees, licenses, Amount of registration |
| and permits. fees paid.
Grand | Private Taxis, : Amount | . Total | Per cent
State. total motor! passenger Sad Leet Pate | applicable to | registration, | 'Bctease
cars. | cars, a aiiieial Total gross bighway work Private i922, ° during
; | receipts by or under | passenger Motor trucks. 1923.
| : | Supervision of cars, |
| State highway |
| | department.
Alabema............:-- 126, 642 109, 535 13, 845 D, 202 5OO | $1, M017. 56 | Sl, 206 440 Ge |... 2c). | eee ene elk. 90, 052 | 40. 4
Apemee__._....------ 49,175 42,176 6, 565 434 392 281, 670. 75 O01, G0, Me |-5...._-___ ___. __ i. 38, 034 oy 3
Armomees........-.....- 113, 300 102, 000 LL. __—_——s 300 | 1, 435, 090. 00 | 430, 527.12 , $1, 224,000.00 $192, 100. 00 84, 596 33 9
Caimemaia.............- 1, 100, 283 | 1, 056, 756 a ee 14,694 | 10, 608, 544. 00 4,906, 015.00 ; $, 081, 836. 00 814, 138. 00 861, 807 7
Colepradoz:............- 188, 956 | 175, 669 13, 287 (?) 2, 473 1, 126; 218. 55 1 534, 953. 81 898, 666. 40 153, 741. 57 162, 328 16.4
Connectient........._.. 181, 748 | 148, 791 29, 140 3, 817 4, 450 4, 329,432.16 | 4,329,432.16 | 2, 302, 154.23 . 956, 368. 93 152, 977 18.8
Delorrare. _............ 29, 977 ! 24, 709 i ae 467 516, 209. 00 516, 209. 00 287, 950. 00 108, 379. 00 24, 560 29 4
District of Columbia?_.- 74, 811 3 65, 681 37,187 31, 943 1, va eee | ee Se ee 52 Tez | 4a 7
Poridaga...........--.--- 151, 990 | 125, 140 2a, Sau 3, 320 975 LE gs ag eg el gl 116, 170 30.8
eee la 222... 3. 1738, 889 | 151, 325 22, 469 95 | 1,011 2, 156, 406. 08 2, 095, 762.60 | 1, 756, 219. 20 | 344, 831. 04 143, 423 © 21,9
.
W@emos...........--._-. 62, 379 57, 200 | Sl) ee 655 914, 014. 58 | 229, 840. 14 807, 678. 15° 87, 309. 43 53, 874 » 15.8
Pee eee... 2-2 -- 969, 331 | 847, 005 Le, a |--2------- 7,611 9, 653,796.04 | 9,653, 796.04 | 7, 132,472.16 1, 820, 379. 48 781, 974 : 23.9
itig@aeas ._-_-_--__._.-- 583, 342 510, 114 (ce. <a 6, 042 3, 693, 715. 00 3, 492, 498. 00 2, 651, 084. UO © 794, 003. 00 469, 939 24. 1
SMS 571, 061 534, 796 LS 3, 044 8, 827, 062. 99 | 48.000, 00; 08 |..._._.__..___- ». ee 500, 158 | 14. 2
Kegens..-.............- 375, 594 | 349, 038 26, 556 . 1, 950 3;400,0068,00', © 1, 790,000.00 |.--..-........- PE aos 327, 194 | 14.8
|
MWemmicky.............. 198, 377 | 177, 834 | —_—— ae 844 2rOtemesas | «=§62) Ore) Wee, OO |... -- 2 154, 021 28.8
Lowmiama..........._.- 136, 622 116, 003 Abad) re «See 400 2,191, 240.81: 2,191, 240. 81 1, 800, 186. 81 336, 000. 00 102, 284 . 33.6
aime. ....-.------.._- 108, 609 | 90, 177 15, 614 | 2, 818 1, 400 1, 660, 268. 17 re, i ne 92, 539 | i. 4
Mamyland.........-...- 169, 351 | 153, 661 11, 609 4, 081 4, 846 3, 536, 955. 20 3, 183, 259.68 | 2, 230, 333. 05 | 461, 539. 95 165, 624 18 24,0
Massachusetts. .-_._..- 481,150 407, 645 (o:. - —_——e 11,033 | 6,989,633.25 6,639, 155.42} 4,314,529.50 1,117,834. 00 385, 231 | 24.8
Wiican. ......-.-...- 730, 658 | 657, 148 72, 000 1, 510 4,165 10, 500, 786. 05 | 4, 741,624.91 | 8,135, 757. 89 | 7 1, 225, 958. 00 578, 210 : 26. 4
Meineseta.........-..- 448, 187 399, 404 he ee 3, 220 7, 316, 772. 03 7, 316, 772.03 | 6, 212, 601. 93 959, 495. 66 - 380, 557 | 17.8
IMiesissippl.__...-.....- 104, 286 93, 846 10, 440 (2) 114 1, 077, 616. 22 em, Gee ky ee = a on wns oe eee. ee 7 io | 34.4
Wieeorn.-........-.-.- 476, 598 | 430, 340 1,25), 0 eal 2, 570 4,016) 285.00 | ° 4,085, 383-60 |...29......22.. ie See 392, 523 21.5
Mroutema...-......-.-- 73, 828 65, 449 Stele 374 729, 621. 50 9 73, 325. 64 604, 663. 75 93, 162. 75 62, 650 | 17.8
Iiebrasled .....-_.....- 286, 053 259, 382 2eNGel | -.-=...... 1, 608 3, 353, 175.32 | 2,932, 242.63 | 2,754, 430. 61 498, 750. 99 256, 654 11.4
Peevods.....-......---. 15, 699 13, 699 a (ieee seca o 112 153, 888. 10 10 144, 992, 15 119, 798. 10 | 30, 000. 00 . 12,116 © 29. 6
New Hampshire-_--...-_- 59, 604 52, 608 6, 99 (5) 1, 987 1, 571, 326. 96 digetiar: Gay. Ga | seen. i some cen wn oc) 48, 406 a2
New Jersey...---...--- 430, 958 330, 552 89, 105 11,301 8, 811 7, 653, 780. 37 7,515, 116.03 | 3,069, 466.75 » 2,407, 423. 50 342, 286 | 25.9
New Mexico....-.-.--- 32, 032 29, 032 et. || ae 215 295, 000. 00 | 280, 250. 00 251, 995. 00 | 36, 000. 00 . 25, 473 | 25.7
\ - t
New'Vork.........____ 1, 204,213 | 962, 681 203,846 | 37,686) 22,153 | 19, 862,441.52 | 14,896, 831.14 | 11, 689,802.97 , 5,391,418.25 —-1, 002, 293 , 20.1
North Carolina !!__.__- 246, 812 225, 488 21, 324 (2) 1, 300 3, dae, Ome (2 | * 3, 700: OOO. OW |-..-...--2...-- a 182, 550 35. 2
North Dakota_._._...- 109, 266 105, 958 3; 2a0 21 645 760, 852. 45 Fee OCs | ie a 99, 052 10.3
a 1, 069, 100 927, 200 141, Gea). cae ae 15, 000 9, 662, 370. 29 Se, OM CO Nee ones ccces a - MEH on cn oe wcuces. 858, 716 24.5
Olgapoma____-....._.. 307, 000 288, 424 18, 576 (2) 823 Oo, 2c, viet | 122 SUmMOd | -..-..-.2...-. ------..-...... 249, 659 23. 0
@aeeane. .-..-._.-...-.. 165,962 | 13 152, 135 12, 987 840 3,140 | 4, 069, 609. 40 | 142, 924, 707.05 j.-..-..-.------ eae 134, 125 oe
Pennsylvania_.....___. 1,043,770 | 15 969, 361 oo 19,220 | 15, 844,303.80 | 15, 844,303.80 | 9, 944,691.80 3, 410, 031. 50 829, 737 | 25.8
Rhode Island__-...__.- 76, 312 60, 620 13, 930 1, 762 1, 575 1, 286, 659. 47 1, 196, 909. 47 727, 704. 72 275, 240. 27 © 66, 083 ies
South Carolina__..__.. 127, 467 115, 892 Le 547 902, 608. 69 722, 086. 95 728, 644. 01 | 153, 593. 69 95, 239 33.8
South Dakota...._.___- 131, 700 121, 164 TGrgao |s--- 225. 471 1, 130, 959, 27 Dh Oeee GU: SUL coc eee. -o- as I eee ee a 125, 241 | §. 2
Tennessee___...----_-- | 173, 365 154, 181 ee 751 Ztdeeee | 2, 0me 806. 14))--.._...-22-.._B.----.---5.-.- 135, 716 27.8
or 688, 233 | 16 688, 233 2) MR es ee | 3, 346 Opeetpome.od | 2pate a Ase. -..---.----e--- + -2-- nee 526, 238 30. 8
ee ene ~ a 59, 525 | §1, 625 7/810 Veh ea | 766 430, 104, 72 Gao ea ~ oe oie ye -- - +e Se Se 49, 164 val, A
Vemnont.............-- 52, 776 49, 420 5 i 839 938, 860. 30 860, 803. 03 674, 868. 63 | 83, 394. 50 43, 881 | 20. 2
Were lh. -«<.s.-.---.-- 218, 896 187, 977 UaOL |. . ceeeeeed I, 813 3, 200,161.66 | 3, 200, 161.66 | 2, 422, 993, 72 | 482, 670. 25 168, 000 | 30. 3
Washington_._..__.._- 258, 264 | 218, 580 37, 100 2, 584 3, 560 3, 898,597.77 3, 741,167.81 | 2, 726,121.45 | 843, 041. 92 210, 716 | 22, 6
West Virginia_....._-- 157, 924 ! 143, 548 17 7, 456 6, 920 1, 353 2, 608, 508. 37 | 8 2, 608, 508. 37 1, 940, 093. 23 | 229, 157. 66 112, 763 | 40. 0
Wisegmsin._.-......._- 457, 271 : 422, 718 34, 553 (?) 5, 645 4, 958,933.55 , 4,693,887.30 | 4, 227, 180. 00 625, 619. 55 382, 542 ; 19. 5
yous ._.......-- 39, 831 35, 294 4, 537 (2) 291 414,096.39 , 14 414, 096. 39 314, 003. 00 ) 89, 202. 00 30, 637 ! 30. 1
ta ee ae enn Coe te Mi ee
a ! 15, 092,177 | 13, 457,214 | 1, 552, 569 82,394 | 171,372 1188, 970,992.24 153, 226, 636. 16 | 91, 031,927.06 | 24, 020, 784. 89 12, 238, 375 | 23. 6

! Where no data are given these vehicles are not registered as a separate class but included with passenger cars or trucks.

2 Included with passenger cars.

3 Includes re-registrations, but does not include nonresident registrations.

4 Approximate.
§ Included with trucks.

6 Approximate amount available for State-aid road work. ;

7 Includes receipts from taxicabs, motor busses, and cars for hire.
§ For State highway work and financing State highway bonds. ;
9 State’s share for period Jan. 1 to Apr. 1 when new law becomes effective.

10 Includes $48,115 used to finance State highway bonds.

11 All data for the State of North Carolina are for the first 6 months of the registration year, which begins on July 1.
12 To be expended by counties under general regulation made by State highway department.
13 Includes ambulances and commercial cars under 1-ton capacity.

M4 To finance State highway bonds.

15 Includes 88,650 commercial vehicles having a chassis weight of less than 2,000 pounds.

16 Includes motor trucks.
17 Solid-tire vehicles only.

18 Nonresident registrations included in both years for this computation.

16

er gallon. In Massachusetts legislation providing
for a tax of 2 cents per gallon has been passed, but is
inoperative pending a referendum at the general
election next November. In Minnesota provision has
been made to submit to the voters at the next general
election a constitutional amendment permitting such
a tax to be levied.

The total gross receipts from gasoline taxes amounted
to $36,813,939.61 during the calendar year 1923. Of
this total, $21,528,559.18 is applicable to highway
work conducted by or under the direct supervision of
the State highway departments. Only one State, North
Dakota, devotes no part of the revenue from this tax
to highway work, and only two States, Alabama and
Pennsylvania, place no part of these revenues under the
direct control of the State highway department.

In compiling the statistics the registration year has
been used as the basis rather than the calendar year.
In most States the registration year coincides with the
calendar year and in only one State, North Carolina,
does the registration year differ very widely from the cal-
endar year. In all cases where theregistration year ends
later than January 31 the registration data given are for
the period from the beginning of the registration year to
the close of the calendar year 1923. It is believed that
this method serves to give the most reliable information
as to the actual number of cars in use.

Tables I to IV, inclusive, show in more detail the
statistics of motor-vehicle registration, revenues, and
gasoline taxes for the year 1923 and also comparative
data as to registrations and gross receipts for each of
the years 19138 to 1923, inclusive.

TasBLe II].—Summary of combined passenger car and motor truck registrations for years 19138 to 1923, inclusive.

|
State. 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923
AAO Seeeees oe 5, 300 8, 672 11, 634 21, 636 32, 873 46, 171 58, 898 74, 637 82, 366 90, 052 126, 642
lon 7 6 ee 3, 613 5, 040 7, 753 12, 300 19, 890 23, 905 28, 979 34, 601 35, 611 38, 034 49, 175
0 rae 3, 583 5, 642 8, 021 15, 000 28, 693 41, 458 49, 450 59, 082 67, 408 84, 596 113, 300
Goloria.............--e toe 1 100, 000 123, 504 163, 797 232, 440 306, 916 407, 761 477, 450 583, 623 680, 614 861, 807 | 1, 100, 283
ce a ine 13, 000 17, 756 28, 894 43, 296 87, 460 83, 244 104, 865 129, 255 145, 739 162, 328 188, 956
Connecticut...........-.-.------- 23, 200 27, 786 41, 121 56, 048 74, 645 86, 067 102, 410 119, 134 134, 141 152, 977 181, 748
Delaware..................------ 2, 440 3, 050 5, 052 7, 102 10, 700 12, 955 16, 152 18, 300 21, 413 24, 560 29, 977
District of Columbia.._._..-.---- 4, 000 4, 833 8, 009 13, 118 15, 493 30, 490 35, 400 34, 161 40, 625 52, 792 274,811
Be oe 3 3, 000 3 3, 368 3 10, 850 20, 718 3 27, 000 54, 186 55, 400 73,914 | . 97,957 116, 170 151, 990
ee ae ee 3 20, 000 20, 915 25, 000 46, 025 70, 324 104, 676 137, 000 146, 000 131, 976 143, 423 173, 889
Ce 2, 113 3, 346 7,071 | 12, 999 24,731 32, 289 42, 220 50, 861 51, 294 53, 874 62, 379
Vic ..---.--.-2--------an ee 94, 656 131, 140 180,832 248, 429 340, 292 389, 620 478, 438 568, 924 663,348 —«-781, 974 969, 331
Indvana.........---.------------- 45, 000 66, 500 96,915 139, 065 192, 194 227, 160 297, 255 333, 067 400,342 469, 939 583, 342
De oe ee ee eee be eee 70, 299 106, 087 145, 109 198, 587 254, 462 278, 313 364, 043 437, 378 461, 084 500, 158 571, 061
ic 11 34, 550 49, 374 72, 520 112, 122 159, 343 189, 163 228, 600 294, 159 289, 539 327, 194 375, 594
Mabmai@lcy . ........-.--.-0---+-2-- 7, 210 11, 766 19, 500 | 31, 500 47, 420 | 65, 884 90, 008 112, 683 126, 802 154, 021 198, 377
Louisiana.____......--.---------- 110,000! 112,000 11, 380 17, 000 28, 394 | 40, 000 51, 000 73, 000 77, 885 102, 284 136, 622
Witte). . aes eee ee ae 11, 022 15, 700 21, 545 30, 972 41, 499 | 44, 572 53, 425 | 62, 907 77, 527 92, 539 108, 609
Maryland..........-.__.- ieee 14, 217 20, 213 31, 047 44, 245 60, 943 | 74, 666 95,634 | 102, 841 136, 249 165, 624 169, 351
Massachusetts....__.------------ 62, 660 77, 246 102,633: 136, 809 174,274} 193, 497 247, 182 274, 498 360, 732 385, 231 481, 150
Michigan...-_.-- Tr 54, 366 76, 389 114,845 160, 052 247, 006 262, 125 325, 813 412,717 476, 452 578, 210 730, 658
Minnesota.....------------------ 46, 000 67, 862 93,269 446,000] 54,000 204, 458 259,741 | 324, 166 323, 475 380, 557 448, 187
Mississippi-......--.-----_- co 3, 850 5, 694 9, 669 | 25, 000 36, 600 48, 400 59, 000 | 68, 486 65, 039 77, 571 | 104, 286
Missouri...-......--------------- 38, 140 54, 468 76, 462 103, 587 147, 528 188, 040 244,363 —-297, 008 346, 437 392,523. 476, 598
Wimia....-.--.---...-------.. 5, 916 10, 200 14, 540 | 25, 105 42, 749 51, 053 59, 324 60, 650 58, 785 62, 650 73, 828
Nebraska. ...-.------------------ 13, 411 16, 385 59,000 101, 200 148,101 «173, 374 200, 000 219, 000 238, 704 256, 654 286, 053
Newer. 98 1, 091 1, 487 2,009 4, 919 7, 160 | 8, 159 9, 305 10, 464 10, 821 12, 116 15, 699
New Hampshire. ...._-- co oe 8, 237 9, 571 13, 449 | 17, 508 22, 267 24, 817 31, 625 34, 680 42, 039 48, 406 59, 604
New Jersey...-.----------------- 51, 360 62, 961 81,848 | 109,414 141, 918 155, 519 190, 873 297, 737 272, 994 342, 286 430, 958
New Mexico.._.--..------------- 1, 898 3, 090 5, 100 | 8, 228 14, 086 17, 647 18, 082 22, 100 22, 559 25, 473 32, 032
New Var... ee 134, 495 168, 223 255,242 314, 222 406,016 459, 288 566,511 | 676, 205 812,031 1,002,293 | 1, 204, 213
North Carolina__...-..---------- 10, 000 14, 677 21, 000 | 33, 904 55, 950 72, 310 109,017. 140, 860 148, 627 182, 550 46, 812
North Dakota.....-.-...--------- 15, 187 17,347! 24, 908 40, 446 62, 993 71, 678 82,885 90, 840 92, 644 99, 052 109, 266
Oboes he, eee ce 86, 156 122, 504 181,332 252, 431 346, 772 412, 775 511,031; 621, 390 720, 634 858,716 | 1,069, 100
Olea... 14... eee 3 3, 000 13,500: 25,032! 52,718 100,199 . 121, 500 144,500. 212, 880 221, 300 249,659! 307, 000
Oregon_....---------------------- 13, 975 16,447 | 23, 585 33, 917 48, 632 63, 324 83,332 ' 108, 790 118, 198 134, 125 165, 962
Pennsylvania....--.-..--__--_-_- 80, 178 112, 854 160,137 230, 578 325, 153 394, 186 482,117! 570, 164 689, 589 829, 737 | 1, 043, 770
Rhode Island. ..-..-.--.--------- 10, 295 12, 331 16, 362 | 21, 406 37, 046 36, 218 44, 833 | 50, 477 54,608 | 66, 083 312
South Carolina_.....-...-.-----_- 10, 000 14, 000 15,000; 125, 000 38, 332 55, 492 70,143 | 93, 843 89, 836 95, 239 127, 467
South Dakota...........--------- 14, 457 20, 929 28, 724 44, 27% | 67, 158 90, 521 104,628 | 120, 395 119, 274 125, 241 131, 700
Venmestes......2--22--..-_.-- 0 110,000! 8 19, 769 77,618} 130,000 1 48, 000 1 63, 000 80,422, 101,852 117, 025 135, 716 173, 365
ot 132,000 | 1 40, 000 140,000 1125,000' 192,961! 251, 118 331,310; 427, 698 467, 616 526, 238 688, 233
i. i 4, 000 2, 253 eae 13,507, 24,076 32,273 35,236; 42, 616 47,485 49, 164 59, 525
Venmont._.___.._...----.-.------ 5, 913 8, 475 11, 499 15, 671 21, 633 22, 553 26, 807 31, 625 37, 265 43, 881 52, 776
Virginia........-.---------..----- 9, 022 13, 984 21,357 | 35, 426 | 55, 661 72, 228 94,100 | 115, 470 139, 200 168, 000 218, 896
Weasigeton...-.-. 22... ks. 24, 178 30, 253 38, 823 | 60,734: 91,337} 117,278 148,775 | 173,920 185, 359 210, 716 258, 264
Wier Vitet@ia.. 8.322 ctcu- 22202. 5, 144 6, 159 13, 270". 20, 571 | 31,300 —-38, 750 50,203 «80, 664 93, 940 112, 763 157, 924
Vi haa. 34, 346 53, 161 79,741, 115,645 | 158,637 196, 253 936, 290 293, 298 341, 841 382,542 | 457, 271
Wyoming......-.-..--..------_-- 1, 584 2, 428 3,976 7, 125 | 12, 523 16, 200 21, 371 23, 926 26, 866 30, 637 39, 831
nt lee. ... aac... ee 1, 258,062 | 1,711,339 | 2,445,666 3,512,996 | 4,983,340 | 6, 146,617 | 7,565,446 9, 231, 941 | 10, 463, 295 | 12, 238,375 | 15, 092, 177
|

! Estimated.

2 Includes reregistrations, but does not include nonresident registrations.
3 State registrations only.

‘ Cars registered during 1916 only; total in State, approximately 138,000.

© Cars registered during 1917 only; total, approximately 160,000.
6 Total cumulative registrations; annual registration not required.
7 Cars registered during 1915 only; total, approximately 26,000

Le

TaBsLe II].—Summary of total gross receipts from motor vehicle registration fees, licenses, and permits, etc., for years 1913 to 1928.

7 | 1918 |

1913 | i |

States. 1915 | 1916 | 1919 1920 1921 1922 1923
— ee on ie ‘ —— a 5 ba e = — =| “ a = nee Rca caer va ee. || oe ae
Alabama.........-.. $83,000 | $113,202 | $180,744} $203,655 | $217,700 | $470,274 | $541,348.70 | $835, 178.00 | $1, 147, 265.00 1 $1, 262, 800. 00 | $1, 541, 017. 56
Amigenawe. _.._...--.- 2/7, S46 34, O77 | 45, 579 73, 000 117, 643 142, 288 164, 755. 68 192, 368. 92 | 195, 969. 75 216, 598. 26 281, 670. 75
Arkansas... -__- 17,411 56, 420 80, 551 150,000 | 205,176 | 410,649 | 500,970.00, 591,464.50 —-856, 543.60 ‘1, 030, 196.60 | 1, 435, 090. 00
Calsforné@........-.. 75, 000 1,338,785 | 2,027,432 | 2,192,699 | 2,846,030 | 3,524,036 | 4,468,721.67 | 5,714,717.40' 6,834, 089.52 | 8, 384, 606. 40 | 10, 608, 544. 00
Colorado. 1. «.-_--- 60, 833 | 80, 047 120, 801 197, 795 296, 808 379, 559 490, 432. 31 819, 872. 74 | 906, 059. 27 | 991, 677. 22 1, 126, 278. 55
5 | |
Connecticut. __-__--- 316, 667 406, 623 536, 970 768, 728 1, 080, 757 1, 285, 164 1, 516, 136. 91 1, 852, 591.00 ; 2, 129, 861. 12 3, 567, 744. 84 4, 329, 432. 16.
Delaware ee = 24, 735 | 35, 672 55, 596 85, 249 133, 883 232, 449 286, 333. 00 329, 980. 00 | 375, 469. 00 ; 426, 377. 00 516, 209. 00
District of Columbia 13, 228 20, 147 29, 396 47, 624 55, 928 | 220, 753 274, 184. 00 266, 285. 00 209, 583. 00 | 3a0, 720; 50 357, 918. 00
ey ------- 6, 000 2 6, 736 60, 000 Tea, 170 3 170, 000 ; 345, 775 401, 317. 40 554, 690, 14 | 734, 845.50 | 1, 538, 342,26 | 1, 963, 065. 99
Georgia. _......._..- 12, 000 |; 104, 575 125, 000 154, 735 229, 653 | 331, 816 429, 848. 00 1,919, 338.92 ' 1, 705,941.24 | 1, 830, 047. 61 2, 156, 406. 08
VWdelao__...__.______- 35, 160 58, 580 121; 259 | 213, 758 412, 641 576, 555 729, 702. 94 882, 034. 51 841, 212. 93 812, 943. 72 | 914, O14. 58
Dilyeeige. .....-...-.- 507, 629 699, 725 924, 906 1, 236, 566 1, 588, 835 2, (64,330 | 3, 262, 714. 00 5, 915, 700.17: 6, 803, 556.21 . 7, 882,482.02 | 9, 653, 796. 04
igpcieme@. .....-..--.- 150, 345 432, 309 587, 318 817, 285 1, 096, 159 1, 293,128 1,558, 740.50 | 2,029, 694.00 | 2,422, 227.00 ' 2,999, 588.50 | 3, 693, 715. 00
ee 787, 411 1, 040, 136 1, 533, 054 I, 77G7ia0 2, 249,655 ; 2,547,596 : 3,077, 445. 81 7, 507, 202.08 | 7, 719,127.47 | 7, 928, 388. O6 8, 827, 062. 99
Tepmees._........-..- 186, 066 268, 471 387, 588 585, 762 830, 878 | 978, 837 1, 150, 000.00 | 1,419, 345.50 ° 1,400, 000.00 /} 3, 100,000.00 | 3, 435, 606. 00
! H i
Kentucky.....-.--.- 52, 000 85, 883 117,117 | 184,741 | 287,314 | 402,250 565,520.21 | 815, 549.31! 1,771, 887.02 | 2, 140,444.31 | 2, 678, 732. 89
Ibeulsiana._......... 3 10, 000 3 12, 000 75, 600 112, 000 166, 835 240, 000 | 306, 000. 00 390, 000. 00 453, 276.00 | 1, 756, 226. 42 2, 191, 240. 81
WWitame. ._._....._... 138, 509 192, 542 268, 412 363, 562 491, 696 570, 171 | 685, 570. 25 818, 755.50 . 1, 004, 750. 25 1, 41 gar. Sif 1, 660, 268. 17
Maryland..........- 150, 000 268, 231 386, 565 565, 302 807,395 | 1, 189, 984 1, 776, 410. 22 | 2, 124,924.84 : 2, 460, 162. 04 | 2, 824, 843. 91 3, 536, 955. 20
Massachusetts. .-..- 764, 154 923, 961 1, 235, 724 1, 602, 958 1, 969, 994 2, 184, 821 2, 667, 853. 85 3, 860, 231.70: 4,717,389. 30 | 5, 685, 527. 05 6, 989, 633. 25
Michigan__........- 190, 329 (4) 373, 833 1, 739, 344 | 2,47], 271 | 2, 875, 266 | 3, 719,433.39 | 5, 754,900.96 ' 6, 751, 924. 5! | &, 385, 022.17 | 10, 500, 786. 05
Minnesota_..-..--.. 40, 000 132, 298 3 160, 540 82, 469 100, 000 1, 076, 811 | 218, 469. 50 143,794.50 5, 672,424.61: 6, 543, 685. 7 i, o10, i200
Mississippi_-..-___--- 24, 735 ol, 146 | 76, 700 175, 000 250, 000 335, 000 | 400, 000. 00 800, 000. OO ° 751, 946. 63 1, 179, 803. 00 1,077, 616, 22
Misgewrl_.......---- 173, 510 235, 873 | 323, 289 439, 315 617, 942 1, 394, 762 1, 725, 076. 70 | 2,111, 696. 85 2, 505, 393.90 | 3, 512, 182. 97 4, 016, 383. 60
Meontama..._._.--.-- 12, 000 aig 33, 120 52, 768 290, 936 350, 914 407, 848. 00 416, 245. 00 © 594, 520. 50 | 619, 899. 50 729, 621. 50
Nebraska. ....-..... 26, 000 34, 325 3 183, 000 311, 334 | 451, 303 536, 897 : 304, 450.55 | 2,800,000.00 2,824,811.25 | 3,031, 699.93 | 3, 353, 175. 32
Newadax....____..._ 3, 323 4, 331 7, 875 20, 116 31, 166 31, 083 3%, O00. 75 103, 318. 33 | 102, 800. 00 | 120, 937. 73 153, 888. 10:
New Hampshire.-_-__- 152, 834 185, 288 257, 776 344, 434 425, 305 509, 335 599, 621. 25 654, 702. 04 . 876, 322. 14 1, 246, 098. 46 1, 571, 326. 96
New Jersey___..---.- 661, 446 814, 536 1, 062, 923 1, 406, 806 1, 923, 164 2,431,757 | 2,931, 902. 15 3, 503, 936.76 | 3,974,063. 75 | 6, 251, 418. 50 7, 653, 780. 37
New Mexico..._.--- 15, 084 19, 663 29, 625 47, 865 80, 843 105, 631 + 111, 150. 00 200, 000. 00 - 198, 632. 77 | 243, 813. 61 295, 000. 00
Loe 1, 275, 727 I, 529, 852 I, 991, 181 2, 658, 042 | 4, 284, 144 4,945, 298 | 5,984,659. 50 | 8, 863, 250. 59 | 10, 288, 858. 25 | 12, 736, 364. 37 | 19, 862, 441. 52
North Carolina_---_- 60, 000 89, 580 123, 000 206, 101 321, 923 394, 739 1, 313, 950. 73 1, 785, 000. 00 2, 259, 240. 43 2, 715, 331. 58 | 3, 728, 044. 72
North Dakota.___-_- 41, 961 55, 964 79, 245 125, 283 211, 586 471, 429 636, 842. 40 691, 500. 00 | 683, 052. 45 698, 931. 70 760, 852. 45
0 457, 538 685, 457 984, 622 1, 286, 405 1, 766, 427 2,125,426 ' 2, 593,000.00 | 6, 400,000.00 . 6, 894, 159. 73 7, 888, 992, 38 9, 662, 370. 29
Okiamoma_._.....-.- 3, 000 13, 500 154, 892 555, 011 853, 659 1,102,380 _ 1, 178,130.27 | 2, 500, 000. 00 | 2, 619, 713.49 | 2, 729,169.15 | 3, 217,770. 84
Orégen.........---.- 56, 873 77, 592 108, 881 146, 232 196, 787 461, 422 602, 239.00 | 2,085, 168.50 : 2, 334, 931. 25 3, 340, 519. 58 |} 4, 069, 609. 40
Pennsylvania.-_...-. 841, 062 1, 185, 039 1, 665, 276 2, 325, 057 3, 268, 025 4, 048, 186 5, 090,921.00 | 8, 090, 873. 04 9, 470, 174. 31 | 12, 575, 380, 56 | 15, 844, 303. 80
Rhode Island_..___. 129, 851 157, 020 206, 440 264, 737 346, 117 385, 608 | 477, 223, 25 531, 402. 75. : 848, 723. 59 1, 139, 742. 77 1, 286, 659. 47
South Carolina.____- 10, 000 14, 000 15, 000 10, 000 1138, 557 300, 217 | 389, 034. 68 527, 868. 13 | 741, 114. 79 | 734, 856. 18 | 902, 608. 69
South Dakota__..-.-- 89, 170 125, 000 3 180, 000 140, 746 210, 592 | Oe, ise | 322, 340. 50 | 784, 000. 00 : 720, 587. 00 743, 232.00 1, 180, 959. 27
Tennessee__.-----.-- 3 9, 000 39, 538 3 34, 000 186, 953 322, 200 390, 000 | 585, 181. 95 1, 215, 776.04 ; 1, 387,870.10 | 1, 592, 230. 14 . 2, 049, 653. 27
(a 16, 000 20, 000 20, 000 20, 000 858,978 | 2, 039, 589 2, 624, 334. 29. 3,510, 355.97 , 3, 806, 395. 25 4, 261, 488. 67 | 5, 441, 508. 59
Wea. ---.---- 3, 000 4, 852 3 60, 000 93, 494 170, 707 | 229, 203 | 291, 325. 96 : 390, 933. 29 | 441, 359. 88 | 729, 455. 00 | 430, 104. 72
ecrwmomy......-.-.-. 111, 460 154, 267 218, 480 297, 992 363, 541 398, 856 460, 190. 87 | 959, 422, 38 | 668, 288. 50 781, 982. 35 938, 860. 30:
YV iia. _ - we. - - - 83, 611 120, 814 176, 875 271, 266 518, 566 684, 636 — 900, 000. 00 1, 822, 736.16 ; 2,021, 146. 09 2, 467, 346. 93 | 3, 200, 161. 66
Washington_.____-.-.- 48, 356 60, 506 238, 717 350, 052 519, 526 | 875, 391 2, 325, 323. 53 | 2, 828,896.10 | 3, 140, 730.74 | 3, 291, 671. 70 3, 898, 597. 77
West Virginia.____-- 40, 000 60, 648 128, 952 198, 436 359, 339 447,705 ' 1, 008, 083. 31 1, 280, 193.28 | 1, 260, 525. 82 1, 936, 079. 29 , 2, 608, 508. 37
VpasSconsin._......... 190, 770 293, 580 431, 977 615, 721 861,278 | 2,076,701 ' 2, 502,852.00 | 3, 127,073.00 | 3, 671,645.50 | 4, 088,570.00 | 4, 958, 933. 55
Le 7, 920 12, 140 19, 880 35, 625 57, 421 80, 000 102, 114. 50 | 267, 179. 35 288, 121. 88 316, 849. 50 | 414, 096. 39
Total. .....-.- 8, 192, 253 | 12, 382, 031 | 18, 245, 711 | 25, 865, 369 | 37, 501, 233 | 51,477,419 , 64, 697, 255. 48 102, 546, 212. 25 |122, 478, 654. 33 152, 047, 823. 74 | 188, 970, 992. 24

? State registrations only. 4 Estimated. 4 Registration law held unconstitutional.

TaBLE 1V.—Gasoline taxes, 1923.

i Approximate.

|

Soret - F Ano
applicable ax in ax in applicable Taxin Taxin
to Bie ey cents | cents a oe to iighway | cents ! cents ae
work by or per per . work by or . per per
State. Berrios under gallon |-gallon | Change in State. Hgbap eness under gallon ' gallon | Change in
Mee supervision on on becniis a supervision , on on ae hoa
of State fan.i, | Jan, 1, effectine 6f State + Janot,.° Jan. 1, ieee :
highway | 1923. 1924 highway 1923. 1924. sis salle
department. department.
Alabama.......-..--- Siotao, Ome. 49 |.-2-.-_-_ 2. Paeerss 2 | Meer. 1. NeVvat ase. nce as ae 115, 843. 24 @9; 000,00 '.......-.. 2 | Mar. 20.
ego A.......------- 474, 123.04 | $118, 530. 76 | it 3 | June 9. , New Hampshire °__._| 5 163, 064. 64 16], 323510 .2......- 2°) Jans 4d, 19en
Arkansas 1__.._.....-.. 1, 219, 198. 75 301, 094. 76 1 AD) Die TORE. Mine Warm oe a etre Se elena cee:
Calffornia......._...- 2, 518, 893. 00 | 1, 259, 446. 00 |..._...-- 2 | Sept. 30. - New Mexico__---.-_-- 165, 000. 00 156, 750. 00 1 1
Colorado_...........- 846, 353.12} 402, 017. 73 1. 2 | Asngesl.. Noo gi: i err eae Cee
Commecticut.s.......- 880, 222. 70 880, 222. 70 1g 1 : North Carolina__---_- 2, 909, 904. 74 |72, 900, 000. 00 1 a Apr 1.
Delaware?_._.___....- 88, 579. 28 88, 579. 28:|_..-..--- 2 | Jam, 1, 1924. |) North Dakota_....... 0 a il | oe 1 1
oemal Gonmipia |.-..-_.__.____|_..-2.....-26-|-..-.----l.---.---- fou ie |S ae ee Se ae. a
Figfida«............-- 1, 641, 042. 25 | 1, 150, 355. 99 1 3 July 1. Giklalomia._.....--.-- 599, 000. 00 Doe, GGO700 0... il July 1.
Georgia. ..._..__...-- 1, 502, 503. 49 247, 666. 55 | 1g 3 Oct, m0 ).0) 0 ri 1, 958, 141. 37 | 1, 885, 421. 15 2 3 May 24.
1 9eho .....--..--~- me 396, 487. 18 pee aot. 19 |. ...-..~2 2 | Amr. 1. Pennsylvania_-____-__- Oo, 491, Geen66 |..........---- 1 2. oaly 1
a a Oe ee ee, aa as OB IS Oe 0 eat Oo es eee ee ee ee en
Imd@iana_............. 2, oe, des, 25 | 2,514, 756. 83 |_..-..--- 2 | June l, i Seuth Carolina....... 1, 511, 452. 56 411, 327. 78 | 2 3 | Mar. 23.
Ties 2<.--_.--- wel eae es 2. South Dakota_._....- 624, 692. 44 | 7 565, 000. 00 | 1 2
EE ee Se ee Tennessee_.__._.----- 812, 356. 68 Ml, G02, d0) 2.2.5. 2. 1 Aperi.
Kentueky........_... 680, 435. 30 680, 435. 30 | 1 ] TERS) oc oo a ee | 1, 215, 623. 36 GU, Zivsoe Wun. na i June 15°
Louisiana______---_-: 754, 437. 85 754, 437, 85 | 1! i © Ui 42> o2 ose eee 404, 085. $1 li, 92, 75 t.....--.. 23 | Mar. 8.
Nias... ..--.-- | 286, 076. 97 285, G39, 84 |_......-- 1 July 7. i, VieBmiOnt....-..22.-22 168, lgz. 81 fA | 1 Agr. 4.
Maryland_....__.-_-- 688, 304. 02 688, 304. 02 l@ 2 | Jam. 1, [92a | Vipeie........_...- 1, 556, 920, OO |51, @a7, G47. 32 j..___.... 3 June 27.
Massachusetts 3___._- [o,f [a <| ea een 2 | eee || Waistigeton.._......- 1, 225, 149. 66 | 1, 225, 149. 66 1 2 | Jan. 1, 1924.
Michigan____... as ee Oi ttt ee rr i; ae oa _ West Virginia.____..- 9 366, 490. 00 366, 490. 00 |._____._- 2 | Juby 27.
Minnesota !._..._..--- Uno ee a View ee ee ee AR Se
Mississippi_-......--- | 467, 855. 53 187, 142. 21 1 1 | W¥Griage.......-..- 140, 161. 62 140g GIFO2 Mg Soe ns 1 | Mar. 1,
rene I i omen we aloe aso nes - ance os eS
Montana...._.-..._-. | 441, 249. 10 7, 911,10 1 2 July 1. | ovale ........--|80, Sis, Se anG we), oes, Ged, 18 °.......-.|.---....--
Nebraska_.__.._...__- eeeeenene Conroe nee Peer eae ne | l

5 To Dec. 1, 1923.

6 Tax of 1 cent per gallon effective July 1 to Dec. 31, inclusive.

7 Approximate.

§ One-third of total receipts returned to counties for county highway work.
® Collections from July 27, when tax became effective, to Nov. 1.

1 One cent from Jan. 1 to Apr. 1; 3 cents Apr. 1 to Dec. 31, inclusive.

2 One cent from Apr. 22 to Dec. 31, inclusive.

3 Act passed by legislature, but referendum invoked. Election November, 1924.

4 Constitutional amendment permitting a tax on gasoline to be voted on Nov-
ember, 1924.

18

THE BRICK ROADS OF FLORIDA.

OBSERVATIONS OF THE BEHAVIOR OF BRICK SURFACES LAID ON CONFINED SAND SUBGRADES.

By C. A. HOGENTOGLER, Highway Engineer, U. S. Bureau of Public Roads.

Brick roads in Florida are generally laid directly upon the sand subgrade.
grout, or a bituminous filler, and are retained at the sides of the road by cypress, vitrified brick, or concrete curbs.

shoulders are sand, shell, clay, or limerock.

Brick pavements of this type have practically no ‘“‘beam strength.”

The brick are filled with sand, cement
The

Traffic loads are supported by the confined sand

of the subgrade, the brick surface serving chiefly as a wearing course.
The cement-grout filled pavements offer less tractive resistance and more resistance to deterioration than the sand-

filled roads.

They distribute the wheel loads over a wider area of subgrade, but when they do break up, as they do when
laid directly on the sand subgrade, the relaying value of the brick is much less than those of sand-filled pavements.

If in

the future this type of surface is laid with adequate base and shoulders and provision for expansion, it should make a very

satisfactory pavement.

Sand-filled pavements in service from 8 to 14 years, receiving little or no intelligent maintenance, have 70 per cent of
their surface functioning as fair and good road. The remaining 30 per cent, while in need of reconstruction, has a recon-

struction value of 80 per cent of the new construction cost.

Pavements of this type are believed to have been economical

and well adapted to a State in which uncertain development precluded a forecast of future traffic conditions.

Sand is ineffective as a filler.
and it can not be retained in place.

Bituminous fillers have desirable waterproofing and plastic properties.

pavement.

It is not waterproof; it offers but little frictional resistance to the movement of the brick;

They do not reduce the salvage value of the

Indications are that limerock dust, sand mixed with limerock dust or clay, or sand treated with a light oil, would make

satisfactory fillers.

Indications are that the brick roads can be strengthened to accommodate heavy traffic or to hold up in locations where
good drainage is impracticable by laying a base course of compacted limerock which will provide additional confinement of

the sand subgrade.

Such bases are not like rigid slabs which have ‘‘beam strength’’; their strength does not lie in the

bond between the individual stones as in the macadams; their chief value lies in their ability to remain at all times In con-

tact with the sand subgrade.
support of the subgrade.

They have little supporting power in themselves, but they do make available the maximum
They also prevent loss of sand through the crevices between the brick. -

Shoulders of limerock or other material capable of providing side support for the pavement are more necessary than

thick bases.

Florida State Highway Commission reports indicate a maximum daily traffic over such roads amounting to 200 motor
trucks on the two-way road between Lakeland and Tampa and 157 on the narrow one-way road between Sanford and Kissim-

mee.

The number of trucks averaged from 10 to 30 per cent of the total number of vehicles.

It is important to note that practically all of the Florida road traffic is carried on pneumatic tires, for it is quite probable
that equally good results as herein reported would not have been secured had the heaviest trucks operated on solid tires.

It should also be noted that Florida traffic is comparatively light.
tired vehicles and 8,000 pounds on vehicles having solid tires

able information concerning the strength and

wearing properties of rigid surfaces possessing
what is called beam strength when such surfaces are
laid on subgrades of questionable bearing value.

This article presents the results of a number of
observations of a kind of road which is the exact anti-
thesis of such construction. The brick roads of Florida
have little or no beam strength, but they are laid on a
subgrade which, when properly confined, has high
supporting value.

The unpaved sand roads are exceedingly unstable.
Their tractive resistance 1s high. Yet the surfacing of
such roads with a pavement of brick, in many instances
without other filler than the sand itself, and the in-
stallation of a curb along the edges of the brick surface
converts them into excellent thoroughfares which have
been a source of great satisfaction to thousands of
winter visitors to the “Land of Easter.’

The Florida sand soils lack stability because of the
poor gradation of the sand particles and their low clay
content. When properly compacted and confined, how-

R’ CENT highway research has developed consider-

The gross load limitation is 16,000 pounds on pneumatic

ever, they offer high resistance to volume change, a
fact which, with the absence of frost, accounts for their
extensive use as bases for brick pavements. ‘The
characteristic instability of the soil is indicated by
Figure 1, which shows the result of the passage of a
few vehicles. That sand-filled brick surfaces have
little or no beam strength is apparent in Figure 2,
which shows the separation of brick and loss of filler
on State route No. 1 between Jacksonville and Lake
City. This surface, which is representative of the
Florida construction, has withstood traffic for 14
years, including the war traffic of truck trains, gun
mounts, and carriages. While this surface is not in
perfect condition, its principal defects are directly
traceable to lack of stability, the one undesirable
characteristic of the sand subgrade. It is clear from
a study of these roads that when subgrades have sta-
bility and high supporting power and are subject to
little volume change the chief function of the
surface is that of a wearing course, capable of
utilizing the maximum support offered by the
subgrade.

I

STAGES OF DETERIORATION NOTED.

The rural brick surfaces of Florida are usually 9
or 15 feet wide and are supported by cypress,vitrified
brick, or concrete curbs. Sand, cement-grout, and
bituminous fillers are used, and the shoulders consist
of sand, shell, clay, or limerock.

The deterioration of sand-filled surfaces is first in-
dicated by a more or less uniform settlement along the
curbs, accompanied in some instances by transverse
separation of the brick.

The second stage of deterioration is indicated by
well-defined grooves or edge depressions, loss of filler,
transverse and longitudinal movement of the brick,
and, in some cases, slight unevenness of surface.
Looseness causes the bricks to rattle during the pas-
sage of vehicles, and broken bricks are often displaced.

The third stage of deterioration or failure of sand-
filled pavements is indicated by excessive rutting,
separation and displacement of bricks, and unevenness
of surface.

The progress of deterioration in bituminous-filled
surfaces could not be determined because of the new-
ness of this type of construction in Florida. All the
observed surfaces of this type, however, showed separa-

Fic. 1.—Graded natural Florida soil ped State Route No. 2, south of Crescent
ity.

tion of brick, accompanied in some instances by slight
erooving. The latter was found principally on curves.

In cement-grout-filled surfaces the first signs of de-
terioration noted were cracks, which in some cases,
were so frequent as to divide the pavements into small
blocks. These cracks, which generally were found only
on close inspection, while they did not change percep-
tibly the contour of the surface, did change the pave-
ment from a rigid to a more or less flexible top.

When the cracks became noticeable due to shght
feathering of the edges or separation of the pavement
blocks, and when these blocks were not displaced ver-
tically, a second stage of deterioration was indicated.

When excessive cracking separated practically every
brick, or when individual areas became so displaced
that traffic was seriously hindered, the third stage of
deterioration or failure was indicated.

Surfaces showing only the first indications of dete-
rioration offered all of the advantages that could be
expected from the best paved roads.

n the second stage of deterioration, though the
pavements showed plainly the effects of climate and
traffic, and in many cases indications of gross neglect,
they offered but little inconvenience to traffic and in

Fic. 2.—State Route No. 1 between Jacksonville and Lake City, showing lack of
“beam strength.”

general functioned as first-class roads. One of the in-
teresting features of the narrow, sand-filled surfaces was

that even dee ‘ooves dic as a rule impair the
that even deep grooves did not as a rul pair tl

smooth riding qualities of the pavement. Thev incon-
venienced traffic to some extent, however, when ve-
hicles passed each other.

The roughness of surfaces in the third stage of dete-
rioration seriously inconvenienced traffic which, to pre-
vent accident, was forced to move at considerably re-
dueed speed.

EXAMPLES OF PAVEMENTS IN FIRST STAGE OF DETERIORATION.

The following pavements were representative of those
which showed no greater deterioration than that de-
scribed as the first stage:

Park Avenue, Sanford, a view of which is shown in
igure 3, is a residential street constructed in 1906,
with sand-filled, repressed brick, laid on edge. The
pavement was still giving excellent trafhe service.

The Boulevard, DeLand, is representative of 4 miles
of cement-grout-filled. wire-cut-lug pavement con-
structed in 1916-17, at a cost of $1.65 per square yard.
Ranging from 24 to 44 feet in width, these pavements
were laid in business as well as residential streets. The
main business street carried also the trafhe of State
route No. 2, Orlando to DeLand. The principal de-
fects noted were one blow-up at a street and grade
intersection, one longitudinal crack caused by the fail-

Fic. 3.—Park Avenue, Sanford—A sand-filled pavement in the first stage of deteri-
oration, still giving excellent traffic service.

Fic. 4.—Bituminous-filled relaid brick surface between Jacksonville and Atlantic
Beach, giving good service though in the first stage of deterioration.

ure of a fill, and several cracks adjacent to a railroad
crossing.

The bituminous-filled pavement between Jacksonville
and Atlantic Beach, a view of which is shown in Figure
4,is 18 feet wide. It was relaid in 1919 with repressed
bricks from the sand-filled pavement constructed in
1909. When observed it showed slight transverse
separation of the brick and indications of grooving,
especially on curves.

A section of State route No. 1, in Jacksonville, a
cement-grout-filled, wire-cut-lug surface, shown in
Figure 5, was in excellent condition after four years of
service.

A section of State route No. 2, between Orlando and
Sanford, was another cement-grout-filed pavement of
31%-inch wire-cut-lug brick, the surface being 8 feet
wide. It was laid in 1917 with concrete curbs and
showed behavior typical of narrow pavements of this
type. In a length of 7.6 miles 16 breaks were noted.
Five of these were blow-ups which occurred at grade
apexes. Two breaks were adjacent to railroad cross-
ings and five occurred at curves. Figure 6 shows a
break near a curve in this pavement. Water can be
seen in the crack between the curb and the shoulder.
The surface had been pushed outward 5 inches from the
inside curb on a 90° turn, and about 21% inches on a 30°
turn. The outside curb had been broken off in the
latter case.

Fie, 5.—Cement-grout-filled brick surface, State Route No. 1, near Jacksonville,
giving excellent service after four years, though in the first stage of deterioration.

20

THE SECOND STAGE OF DETERIORATION ILLUSTRATED,

Pavements in the second stage of deterioration were
represented by the following:

The section of State route No. 4, Jacksonville to
Waycross, 15 feet wide, consisting of sand-filled, re-
pressed brick, laid on the side, with 4 by 10 inch con-
crete and brick curbs, was constructed in May, 1910,
at a cost of $1.48 per square yard. It is about 5 miles
long, beginning 31% miles from the city limits of Jack-
sonville. As shown in Figure 7, a good, even riding
surface was presented in spite of the fact that the
curbs were pushed out of line, that a considerable
transverse separation of the brick existed, and that
along the side edge there were depressed areas which
held water after rains. Increased settlement was
noted on fills through cypress swamps. Relaying of

Fic. 6.—Break on curve of cement-grout-filled surface—State Route No. 2, between
Orlando and Sanford.

uneven areas over culverts and salamander holes and
mounds, caused probably by stumps in the subgrade,
and appheation of additional filler would make this a
Ae lous road.

Two sections of the above road each one-half mile in
length were constructed with depressed centers, as
shown in Figure 8. More or less uniform depression of
brick along the edges was noted, as well as a slight de-
pression several feet from the left-hand edge. The
curbs were pushed out of line, but the sand filler seemed
to be intact. These depressed-center sections were
constructed in 1909, after serious washing of the
shoulder of the previous pavement. Although water
had been flowing down the middle of the road for some-
thing like 14 years, these sections presented very good
riding surfaces. They also elimmated the trouble
found on the majority of Florida roads—that of water
standing in depressions along the curb. |

THE THIRD STAGE OF DETERIORATION,

The following surfaces were representative of those
in the third stage of deterioration:

A section of sand-filled brick surface with wooden
curbs between Orlando and Sanford, a view of which is
shown in Figure 12. In this pavement, which was laid
in 1916, a very uneven surface was caused by excessive
brick movement.

Orange Park Road, passing the United States Gov-
ernment reservation, south of Jacksonville. The un-
evenness and brick separation in this sand-filled surface,
which was constructed in 1910-11, 15 feet wide with
brick curbs, are shown in Figure 13.

Sections of narrow, sand-filled brick surface between
Hastings and Ormond Beach, a typical view of which is

Fic. 7.—Sand-filled brick surface, north of Jacksonville. In the second stage of
deterioration but still giving good service.

Figure 9 illustrates the loss of filler and the brick
movement characteristic of the second stage of de-
terioration in a sand-filled pavement.

The section of State route No. 4, south of St. Augus-
tine, is 16 feet wide. It was graded in 1908, paved in
1909-10 with sand-filled, repressed brick laid on the
side, and retained by brick curbs. This road carries
practically all of the tourist traffic between north and
south Florida, including busses which have a capacity
of 35 passengers and run at a speed of about 35 miles
an hour. In some places this road has grass shoulders
(fig. 10), and considerable grass grows in the filler be-
tween the brick. There is more or less depression of
the sides in all sections, which is particularly noticeable
in the lower view, Figure 10. In addition to the de-

ression of the sides a longitudinal movement of the
fick: amounting to about three-fourths of an inch was
observed.

Representative also of the second stage of deteriora-
tion were the sections of sand-filled brick surfaces 9 feet
wide between St. Augustine and Hastings. The typi-
cal condition of these pavements is shown by Figure 11.

Fic. 9.—Section of sand-filled surface between Jacksonville and Atlantic Beach,
showing movement of brick and loss of filler.

shown in Figure 14. This road was in worse condition
than any other seen in Florida. In some places the
concrete curbs were 1 foot out of line. The base and
shoulders consisted of typical “ball-bearmg”’ sand, and
water stood along the sides 6 to 18 inches from the
surtace.

TRAFFIC SERIOUSLY INCONVENIENCED ON ONLY 25 PER CENT OF

PAVEMENTS INSPECTED.

Exclusive of city streets, about 300 miles of brick
pavement were inspected. About 35 per cent of this
length consisted of excellent surfaces, which either
showed no signs of deterioration or in which brick
movement, settlement, or cracking had not developed
to an extent requiring immediate repair except in small,
isolated areas. About 40 per cent consisted of roads
which showed marked loss of filler, appreciable crack-
Fic. 8.—Section of sand-filled brick pavement with depressed center—State Route No. ing, brick movement, SCTOOVINE, and spread of curbs.

— acksonville. Although water has re mm the middl his aut Cee eee . ae r a
ent lsdeatl asain feel teiiceenaitec down the middle of this Some of these pay ements retained remarkably smooth

29

riding qualities, while in others, such unevenness as
existed, inconvenienced traffic but little. The re-
maining 25 per cent consisted of surfaces on which
traffic was seriously inconvenienced or hindered by
marked brick movement, loose bricks, peaked centers,
nonuniform grooving or displacement of individual
parts.

The above percentages are based on a classification
of whole sections. If the general characteristics of a
section were such as to place it within the third class
the length of the whole section was used in determining
the percentage. If considered foot by foot, the first-
class percentage would be increased, since there were
short lengths of excellent surface in many sections
whose general condition indicated second and third
stages of deterioration.

INADEQUATE SIDE SUPPORT THE CAUSE OF MAJOR DEFECTS.

It is apparent that inadequate confinement of the
sand subgrade was responsible for the major defects

Fig. 10.—(UPPER) SANOD-FILLED SURFACE
ON STATE ROUTE NO. 4 JACKSON-
Vitis TO ST. AUGUSTINE, SHOWING
DEPRESSION OF THEeP@GE sO rs Tie
PAVEMENT. (LOWER) ANOTHER VIEW
OF THE SAME ROAD SHOWING
MARKED UNEVENNESS.

in the Florida pavements, and also that,
in the main, this inadequate confinement
was due to insufficient side support. De-
fects not attributable to the above cause
were initial settlement, cracking and breakage, and
unevenness found in lowland and swamp locations.

Initial settlement in both sand and_ bituminous-
filled surfaces was probably due to settlement of the
sand subgrade and can not be eliminated in this type
of construction. That even a nonrigid base course
will not entirely eliminate this defect is indicated by
Figure 15, a view of a sand-filled, repressed brick sur-
face, with conerete curbs, shell base and shoulders,
laid between Jacksonville and St. Augustine in 1916.
This minor defect can be reduced to a minimum by
adequately compacting the subgrade prior to laying
the base and by sufficiently rolling the bricks before
applying the filler. Retention of rain water on the
surface, the chief inconvenience caused by slight settle-
ment will be avoided by laying the bricks so that their
tops are slightly above the top of the curb.

Cracking and breakage in cement-grout-filled pave-
ments were due to surface movement caused by expan-

~

sion and the adjustment of the rigid slabs to their new
positions. These defects can not be eliminated in this
type of pavement.

Unevenness of surfaces in lowland and swamp loca-
tions was attributed both to the character of the sand
and the presence of water. The sand in these locations
is excessively fine and especially when wet has con-
siderably less stability than normal soil. There was
some indication also that this type of sand works up
through the crevices between the brick and is either
washed or blown away. The injurious effect of water
in all types of sand was plainly evident, although in
some cases, very good road surfaces were found in
locations where elimination of water was impracticable.

Where good drainage existed, the effect of curbs and
shoulders on the behavior of the pavements was very
apparent. In some cases, total absence of shoulders
alent! the subgrade to be washed away. Neglect
of this kind was undoubtedly responsible for non-
uniform settlement in sand-filled, and displacement
of blocks in cement-grout-filled surfaces.
In other cases, insufficient side resist-
ance allowed the curb movement which
was primarily responsible for grooves
and excessive separation movement
and unevenness of the brick. )

Figure 16, a view of the Tildenville
Road, relaid April, 1923, shows the
absence of shoulders and a space one-
half inch wide between sections of relaid

paves

= < = i 7
‘ ’ 7 ici r
wee . os {
D4 — a.
-. Nee
’ ie

curbing. Within a radius of 18 inches around the
joint the sand filler as well as about one inch of the
subgrade had been washed away. When this amount
of displacement occurs in several months, one can
easily conjecture what would happen in a period of
years.

TYPICAL DEFECTS OF A CEMENT-GROUT-FILLED SECTION.

A cement-grout-filled, wire-cut-lug surface between
Orlando and Bithlo showed very clearly the influence
of shoulders on the behavior of pavements. The first
100 feet, beginning at the end of East Colonial Street,
Orlando, had good sand shoulders flush with the pave-
ment and was practically free from cracks. Slightly
beyond this, there were indications that water flowed
along the north side, and coincident with this condition
a longitudinal crack 18 inches from the north edge of
the pavement was noted. Some distance farther

as

along the route poor drainage, mucky sand soil, in-
efficient shoulders, and practically no curbs were en-
countered, and, as would be expected, considerable
breakage of surface. Figure 17 shows the absence of
shoulders and the remains of the old cypress curb.
Although the pavement had little support this section
was in very good condition. Figure 18 shows the
breakage which occurred where shoulders were absent
and water stood within 6 inches of the top of the sur-
face. The displacement of surface shown in Figure 19
could not have occurred had the sand subgrade not
been removed, and since the shoulders adjacent to this
and to several other similar breaks were from 6 to 8
inches below the surface, water probably was the cause
of the settlement.

In 2.2 miles there existed several depressed areas
such as the one shown in Figure 19, several locations
where edge breaks occurred, such as the one shown
in Figure 18, and four blow-ups extending from 50
to 150 feet each. The combined length of all breaks
was somewhat less than 10 per cent of the length of
the surface. The remainder of the road, although
considerably cracked, was in the good riding condition
shown in Figure 17. Traflic failures were noted only
where no shoulders existed. The breakage in this
road occurred between April and July, 1923, during
which time about 5,000 loads of limerock were hauled
over it. Figure 20 shows one of these loads consisting
of three cubic yards of rock on the truck and two on
the trailer.

In passing from the cars to the road these trucks
passed over Mills and East Colonial Streets in Orlando,
and the indications were that they traveled in the same
path on each trip. Both street surfaces were sand-
filled, repressed brick, laid flat. In some places on
the former, which had been in service for about one
year, slight indications of settlement in the wheel
tracks were found on close examination. In the latter,

which had been in service about two years, the inside

Fig. 11.—Grooves in a narrow sand-filled brick surface between St. Augustine and
Hastings.

path was over a gas or water main trench and there
was settlement ranging in depth from one to two inches.
Rigid examination, however, failed to disclose any
indication of settlement in the outer wheel path.
At the intersection of the two streets, appreciable
settlement was noted where the wheel paths crossed
a gutter which carried surface water during rains.

Fic. 12.—Sand-filled brick surface with wood curbs, between Orlando and Sanford.
This surface is in the third stage of deterioration. Note the settlement and separa-
tion of the brick.

VALUE OF SIDE SUPPORT ILLUSTRATED.

The effect of side support in sand-filled pavements
was ‘illustrated by the road between Orlando and
Kissimmee, which was constructed 9 feet wide, with
4 by 10 inch curbs in 1916. On the first section,
between Orlando and Pine Castle, a distance of 3
miles, clay shoulders were laid immediately after con-
struction; on the second section 2 miles south from
Pine Castle the shoulders were laid with rock be-
tween 18 months and 2 years later; and along the
third section, rock shoulders were laid partly last year
and partly this year. That portion where shoulders
were not laid until this year was more rutted than
any other part of the Orlando-Kissimmee Road.
While rutting and separation seemed more pronounced
in the second than in the first section, it was only in
the third section that many areas were relaid, these
areas being principally where the road was subjected
to action of surface water.

Displacement of the sand subgrade due to vertical
movement of curbs was noted on the Orlando-Winter
Garden Road and was probably responsible for the
failure shown in Figure 21. Only two conditions of
this kind were found in a length of 3.2 miles of this
sand-filled, repressed-brick surface with concrete curbs,
which was laid in 1916. Bulging of the curbs began
soon after construction and was caused by expansion.
Until spaces were found under the curb, the pave-
ment was thought to have settled. This upward
movement of the curbs was increased by pressure of the
subgrade sand, which was forced into the spaces _be-
neath them, causing variation in the curb hne and set-
tlement of adjacent bricks. Although deeply grooved
as shown in Figure 22, a smooth-riding surface existed.
This surface is now being relaid, 15 feet wide.

The Orlando-Kissimmee Road referred to above is
part of the Sandford-Plant City Road, which, accord-
ing to a traffic census taken by the Florida State high-
way commission, January to June, 1923, carried heavier
truck traffic than any of the other roads observed.
Because all parts of this road received the same intel-
ligent maintenance, the behavior of its various sur-
faces was considered indicative of their adequacy for
Florida conditions. Considermg only those surfaces
9 feet wide which had been in service about eight

24

years, it was noted that of the cement-grout-filled
surfaces, all of which had 4 by 10 inch concrete curbs,
95 per cent were in class 1, 24 per cent in class 2, and
24 per cent, due to failure of the sand fill, were in class
38. Of the sand-filled surfaces, those which had 4 by
10 inch concrete curbs and limerock shoulders laid at
the time of construction were in class 1, those which
had 4 by 10 inch concrete curbs and sand shoulders
were in class 2, and those with wood curbs as well as
a short section through a swamp with concrete curbs
were in class 3. Short sections of the sand-filled sur-
faces with concrete curbs and sand shoulders, especially
at locations subjected to water action, had been relaid.

RELAYING VALUE OF SAND-FILLED SECTIONS HIGH.

Apparently the cement-grout-filled offered great re-
sistance to deterioration than the sand-filled surfaces.
The present value of the surfaces, however, depends
not alone on their condition, but also upon the relay-

FIG. 13.—(UPPER) LONGITUDINAL MOVE-
MENT OF BRICK IN THE ORANGE PARK
ROAD. NOTE GRASS GROWING IN THE
SAND FILLER. (LOWER) TRANSVERSE
SEPARATION OF BRICK PERMITTED BY
SPREADING OF CURBS.

ing value of the brick. This relaying value is of spe-
cial importance in Florida since, at 1923 prices, the
cost of brick was about 73 per cent of the total cost of
the surface. There was but little salvage value in
cement-grout-filled pavements, while in sand-filled
pavements there was considerable.

On a sand-filled seetion of the Jacksonville-Atlantic
Beach Road, laid in 1909 and relaid in 1919, the break-
age of brick was less than 1 per cent. On one contract
in Orange County 650 square yards of new brick were
required in relaying 90,000 square yards of surface
originally constructed in 1916. When relaid without
disturbing the curbs, a greater percentage of new
brick was required because of increased pavement
width. Owing to the very small breakage, however,
practically the entire cost of the brick ean be consid-
ered as a permanent investment. The conclusion
drawn from the observations was that even when a
sand-filled pavement had deteriorated to a condition
characteristic of the third stage, at present rates about
70 per cent of the initial investment. still remained,
the remaining 30 per cent representing the price of the

service afforded by the road. When, however, failure
occurs in & pavement of low salvage value, such as a
cement-grout-filled brick, almost the entire first cost
is lost. This pertinent fact must be given proper
consideration in the selection of a pavement.

The high salvage value of sand-filled brick was
indicated also by the difference between bids for new
and relaid pavements. This difference indicated a
relaying value of about $1.95 per square yard, or about
80 per cent of the total cost of new construction. It
is interesting to note that because of present high prices,
the indicated relaying value ($1.95) of bricks 1n the
Orlando-Winter Garden Road was 40 cents greater
than the cost ($1.55) per square yard of laying the
surface seven years ago.

CONCLUSIONS AND RECOMMENDATIONS.

It is believed that the foregoing descriptions and
discussion of the behavior of Florida brick pavements
warrant the following conclusions and
recommendations:

In general, cement-¢grout-filled surfaces
offered less tractive resistance and more
resistance to deterioration than those in
which sand filler was used. The bond

between bricks minimized the danger of separation
and, when adequate shoulders existed, required only

wooden side forms. Figure 23 shows that cement-
srout-filled surfaces conformed to changing subgrade
profiles without becoming rough. This type of sur-
face, because of its rigidity, distributed wheel loads
over larger areas of subgrade and consequently sub-
jected the soil to vertical pressure of less intensity
than other types. It is not believed, however, that
this advantage was of sufficient importance to compen-
sate for the breakage caused by blow-ups and the loss
of relaying value of the brick which cement-grout
filler causes. If in the future this type of surface is
laid with adequate base and shoulders and provision
for expansion, it should make a very satisfactory
pavement.

Because of the high salvage value of the brick and
the small cost of relaying, the sand-filled pavements
were economical and especially well adapted to a State
in which uncertain development precluded a forecast
of future traffic conditions. When pavements which
have been in service from 8 to 14 years, and which in

*) 1a
fom ©

that time in many cases have received little or no in-
telligent maintenance, have 70 per cent functioning as
fair and good roads and the remaining 30 per cent,
though in need of reconstruction, has a relaying value
equivalent to 80 per cent of the new construction cost,
such pavements can not be considered as other than
satisfactory.

By making a few changes in future construction,
however, it 1s believed that many of the defects at
present existing in the flexible brick tops can be con-
siderably reduced or entirely eliminated.

Sand as filler is very ineffective. It is not water-
proof; it affords but little frictional resistance to the
movement of the brick, and it can not be retained in
place. As a rule, the sand-filled pavements observed
were but half filled. Indications were that limerock

dust, sand mixed with limerock dust or clay, or sand
treated with a light oil, would make satisfactory fillers.

Bituminous fillers seem desirable because of their
waterproofing and plastic properties, and also since
they do not reduce the salvage value of the pavements.

Fic. 14.—Failure of narrow, sand-filled surface between Hastings and Ormond
Beach. This is a third-stage pavement.

While it was evident that 4 by 10 inch curbs (concrete
or vitrified brick) were ate of resisting without
movement the pressure to which they were subjected,
it is believed that, rather than increase the curb size,
special shoulders should be laid to furnish the required
additional side support.

Sand shoulders, like sand filler, many times meant no
shoulders at all. Especially along the narrow roads
which carried considerable traffic, sand shoulders could
not be retained in place. When covered with grass,
they could be retained along the wide roads, but even
so, their resistance was insufficient to prevent curb
spreading and the accompanying defects.

LIMEROCK A USEFUL MATERIAL FOR SHOULDERS AND BASE.

Indications were that limerock shoulders were very
effective and desirable not only on account of their
additional resistance but also for the additional effective
road width which they furnish.

_ Where heavy traffic is to be accommodated, and also
in all locations where good drainage is impracticable,
additional confinement of the soil foundation by means
of a base course is believed desirable. For these base
courses also the Florida soft limerocks are the most

Fic. 15.—Showing settlement in a narrow, sand-filled surface laid on a shell base
This is a section of the Jacksonville-St. Augustine road.

accessible materials. A piece of limerock placed in
water will disintegrate, but when thoroughly puddled
and rolled, it forms a smooth surface which apparently
is little affected by moisture. These surfaces are not
hard enough to resist surface wear but seem to have
considerable resistance to internal disintegration.

Figure 24 shows a limerock base before rolling.
Figure 25 shows the smooth surface obtained by
rolling and also its lack of beam resistance. This
case on the Tildenville-Black Lake Road was down
two weeks when the sand subgrade was washed out,
allowing the limerock base to fall. Figure 26 shows a
limerock surface which was laid in 1914 by placing the
material on the road and allowing traffic to compact it.
Figure 27 is a view of the first limerock road con-
structed in Florida. This section of State-aid Route
No. 5 between Ocala and Tampa was properly com-
pacted by a power roller in 1913 and has been main-
tained with sand. It has resisted both trafic and
climate remarkably well and at present is hard and
compact and undoubtedly has considerably more slab
strength than the base shown in Figure 25.

There is no criterion at present to indicate how thick
soft limerock bases should be. They are not like the
macadams which depend upon the bond between
individual stones, nor are they like rigid slabs which
have definite beam resistance. They are more or less

Fic. 16.—View showing absence of shoulder and wide, open curb joint on the Tilden-
ville road.

FIG, 17 (LEFT) =SHOWING GOOD se@enpiL

ae: TION OF CEMENT-GROUT-FILLED SURFACE

~ — ey NOTWITHSTANDING THE LOSS OF THE
— i SHOULDERS AND WOODEN CURBS.

Ee

FIG. 18 (RIGHT).—SHOWING HOW EDGES FAILED
WHERE WATER STOOD NEAR THE ROAD SUR-
FACE AND SHOULDERS WERE WASHED AWAY,

FIG. 19 (RIGHT).—THIS BREAK COULD NOT HAVE OCCURRED HAD NOT THE SAND
SUBGRADE BEEN DISPLACED.
FIG. 20 (ABOVE).—THE KIND OF TRAFFIC WHICH CAUSED THE DAMAGE.

VIEWS ILLUSTRATING THE DETERIORATION OF THE CEMENT-GROUT-FILLED ORLANDO-BITHLO ROAD AND THE CHARACTER OF THE
TRAFFIC WHICH PROBABLY WAS RESPONSIBLE FOR THE DAMAGE.

27

plastic layers whose function is to confine and utilize
the maximum bearing value of the soil rather than to
support the load.

Mado into slabs, cubes, or cylinders, limerock could
meet none of the requirements of concrete. Tests of
this character, however, do not indicate the relative
value of these materials as Florida pavement. bases.
Concrete because of its rigidity, expansion, contraction,
and warping, can not have uniform and continuous
subgrade support and therefore must have beam
strength to distribute the load. It fails by cracking
and shattering. The action and the function of lime-
rock bases are different. While in themselves they
have little supporting value, they at all times retain
contact with and make available the maximum sub-
grade support. If the sand settles slightly the lime-

rock does also, and if proper side support exists the
road should be more resistant than before.

Failure

Fig. 21.—Depression in Orlando-Winter Garden road, probably caused by displace-
ment of the sand subgrade, due to vertical movement of the curb.

Fic. 22.—Grooves in Orlando-Winter Garden road which do not impair the smooth
riding qualities of the surface.

occurs by excessive settlement, but this can not happen
unless the sand base is first displaced. It is possible
that if proper side support is supplied a comparatively
thin layer of limerock will suffice to prevent loss of
sand through the crevices between bricks and to supply
additional confinement. Referring to the descriptions
of the wider sand-filled roads, it will be cae that
the loose 3-inch brick tops were sufficient to confine
the sand subgrade to a remarkable degree, which seems
to warrant the above assumption. In the absence of
additional side support, a base of considerable thickness
will probably be required to carry heavy traffic. *

FIG. 23.—Section of a cement-grout-filled surface laid through a swamp section
south of Kissimmee which has conformed to changes in the sand subgrade without
becoming rough.

CONCRETE BASES VIEWED AS UNNECESSARY IN FLORIDA.

The use of limerock is warranted only because of the
high supporting value of the sand subgrade. If the
subgrade support were so low as to require a base
course having beam resistance equivalent to that fur-
nished by a 6-inch thickness of concrete, it is questioned
whether 10 or even 12 inches of limerock would be ade-
quate.

The behavior of the Florida surfaces, however, has
not indicated that such a base is required. Notwith-
standing considerable opinion to the contrary, there
was ample evidence to show that grooving and settle-
ment were not caused by recent traffic conditions.
These defects began to form in many cases soon after
completion of the road. In 1918 the grooves on the
Orlando-Winter Garden Road had so changed the
transverse profile of the surface that the rear wheels of
a passing road rollerhad contact only at their inner edges
and thus cracked a number of bricks. The bricks in
the Jacksonville-St. Augustine Road rattled during the
passage of vehicles in 1918 just as they did in 1923.
Naturally, where the roads were entirely neglected,
deterioration developed rapidly with increase of traflic,
but this was a fault of the organization in charge rather
than of the surface.

Fic. 24——Limeroek base before rolling.

28

Although little could be learned of the traffic which
the various roads had accommodated, a most important
factor noted was that, to facilitate travel through sand
and, in some instances, to comply with traffic regula-
tions, but few trucks were equipped with other than pneu-
matic tires. In this discussion of base courses it is
assumed that this type and not solid-tired trafhic 1s
to be accommodated in the future. The gross load
limitation of the State law is 16,000 pounds on pneu-
matic-tired vehicles and 8,000 pounds on solid-tired

vehicles.
THE VOLUME OF TRAFFIC.

As to the number of vehicles carried, it 1s indicated
by information supplied by the Florida State Highway
Commission that between January and June, 1923,
considering only trucks, the road between Lakeland
and Tampa ranked first, with 200 per day; that be-

* *& F _ . '
| awe - ; 4
a ee . a e

7
Saal

Cia, Tae

FIG.

Note the

25.—Failure of limeroek base due to washout of sand subgrade.
smooth surface obtained by rolling.

tween Orlando and Kissimmee, second, with 169; and
that between Sanford and Orlando, third, with 157
trucks per day. The number of trucks averaged from
10 to 30 per cent of the total number of vehicles. Since
the road between Lakeland and Tampa carried traffic
in two lines, it is apparent that the narrow road between
Sanford and Kissimmee received the greater intensity
of traffic since it was carried in one line.

Current opinions in regard to the necessary thickness
of limerock bases are reflected by the bases employed
in present construction. Many of the counties and
towns are laying a 6-inch layer, in some instances cov-
ered only by a bituminous surface treatment. The
Jacksonville-Atlantic Beach Road is being constructed
with 7 inches of loose material, or about 5 inches of
compacted base. The present Federal-aid specifica-
tions require 8 inches. As previously noted, the writer
does not beheve that a base of uniform thickness is
the most economic preventive of the Florida brick road
defects. No matter how thick the base is made, the

Laid in 1914.

Fic. 26.—Limerock road compacted by traffic.

sides will be relatively weaker than the middle. With
few exceptions the condition of the pavements observed
indicated that additional shoulder resistance is most
essential. There is reason to believe that with a given
quantity of lmerock, if adequate shoulders are first
laid and a confining base layer is made of the material
that is left, a considerably more resistant surface will
be secured than if all of the rock is used for a base of
uniform thickness. On a road 18 feet wide, for in-
stance, a 4-inch base and shoulders 24 by 8 inches will
possibly offer greater resistance than a 6-inch base.
By this means effective additional road width is also
secured.

In those surfaces along which curbs are not used,
increasing the width of base with material secured by
reduction of thickness is recommended. A base 21 feet
wide by 6 inches thick might be more effective under
a road 18 feet wide than a base 18 feet wide and 7
inches thick.

The most economic distribution of limerock between
base course and shoulders can be determined only by
construction and observation of experimental sections.
By this means also can be determined the advisability
of using wooden curbs when limerock bases and
shoulders are employed.

In connection with the use of the lhmerocks, it is to be
emphasized that they must be thoroughly puddled
and compacted in order that danger of uneven settle-
ment in the future may be prevented.

Fic. 27.—Limerock road compacted by road roller.
maintained, it is now a very satisfactory, hard, and compact road.

Built in 1913 and carefully

°) g

ROAD MATERIAL TESTS AND INSPECTION NEWS

WATER REQUIRED FOR STANDARD MORTAR CONSISTENCY DETER-
MINED BY NEW METHOD.

To determine the amount of water required for
standard consistency of mortars made with natural
sand is the purpose of one of the investigations now
being conducted by the physical laboratory of the
United States Bureau of Public Roads.

The greatest problem in connection with the strength-
ratio test for concrete sands has been that of properly
gauging the amount of water for the natural sand
mortar for comparison with standard, Ottawa-sand
mortar. Each laboratory acts according to its own
judgment and, on account of the large personal equa-
tion involved, the result has been a wide variation in
test results.

Studies made in the bureau’s laboratory have in-
cluded a number of methods such as computation of
surface area, determination of point of maximum
density, measurement of consistency by the flow table.
and various modifications of each of these methods.
Lately the problem has been attacked from a new
angle in that an effort is being made to determine
experimentally the amount of water required to cover
the surfaces of the sand grains and to provide for
absorption. Knowing this it is only necessary to add
cement and the additional water for normal-consist-
ency cement paste to put the mortar in a standard
condition.

Briefly, the method is as follows: A representative
sample of the sand passing the one-fourth-inch screen
and retained on the 100-mesh sieve is dried, weighed,
and saturated with water; it is then transferred to a
filtering tube of special design and a suction of 15
inches vacuum applied for 10 minutes, moist air
being supplied to the sample during suction. The
water retained by the sample is determined by weigh-
ing. By comparison of this method with the usual
method on a number of samples a constant of 1.6 has
been found necessary as a multiplier to give an adequate
percentage of water for the sand. All material pass-
in¢ the 100-mesh sieve is considered as of cement
size and is treated accordingly. The formula is:

N=1.6rW+n (C+w)
in which

N=rcquired weight of water for mortar mix in
crams. .

r=percentage by weight of water retained by
test of 4-100 sand.

W=weicht in grams of 4-100 sand in mortar mix.

n=normal consistency of cement.

C=weight of cement in mix in grams.

w=weight of sand passing 100-mesh sieve in
mortar m1X in grams.

This method promises to be more rehable than any
heretofore tried out, but the amount of data available
is as yet not sufficient to form the basis of definite
recommendations.

BETTER CONCRETE ROADS.

_ The conviction prevails that there is room for marked
improvement in the methods employed in the con-
struction of conerete roads and the manipulation of the
materials used. This view is supported by the results
of compression tests on cores drilled from pavements
which indicate a wide variation in strength, the maxi-
mum being often from 50 to 100 per cent greater than
the minimum. A number of factors are known. to
contribute to the strength of the concrete, but in most
instances the cause of defects can not be attributed to
any specific deficiency of construction.

It is the common belief that there is great need for
the introduction of a more accurate control of the
construction process. Certain principles have been
evolved through research which are generally accepted.
The present problem is one of practically applying
these principles to construction. In an attempt to
solve this problem, the United States Bureau of Public
Roads has in prospect the construction of an experi-
mental conerete pavement cooperatively with one of
the Eastern States.

Assuming that the design and specifications are
established and that the materials have been selected
for the job, the mechanical factors which are frequently
neglected and which have an important influence on
the resulting concrete are as follows: The accurate
measurement of aggregates which involves the bulking
of fine aggregates due to moisture content, the correct
grading of the coarse aggregate, a uniformly proper
consistency and adequate curing of the pavement.
With an accurate control of these factors together with
certain refinements of construction, it 1s expected to
secure an improved workability of the mixture, a
homogeneous concrete of more uniform strength, a
smoother riding surface and perhaps an increased
yield for a given mix.

In order to obtain a control of this kind and apply it, a
study of road-building equipment is being made by the
bureau with a view to selecting or modifying available
equipment, or devising equipment particularly suited
to the requirements. J*or a more precise means of
measuring aggregates a comparison of the weight and
volumetric methods is being made. An investigation
of the bulking of sand due to moisture content is being
conducted with a modern volumetric plant. With
regard to the grading of coarse aggregates, consid-ra-
tion is being given to the idea of delivery to the job in
screened sizes and combining them at the central
proportioning plant. It is also important that some
effective means of controlling the consistency be
devised.

By means of this experimental construction which is
proposed for the coming season, it is hoped to develop
the necessary equipment and a practical control of
construction which will produce a pavement of better
quality and uniformity without adding greatly, if at
all, to the cost.

30

A NOTE ON THE DISTILLATION TEST FOR ROAD TARS.

Considerable variations in the results obtained from
this test by different laboratories are caused by the
use in some laboratories of uncorrected thermometers,
and in others of thermometers calibrated in the vapors
of pure substances with known boiling points. The
yrocedure used by almost all producers and State
ee testing laboratories for this test 1s that adopted
by the American Society for Testing Materials, serial
designation D20-18, which requires that the thermo-
meter shall be set up in the apparatus as in the test,
with water, napthalene and benzophenone as distilling
liquids. However, the standard method does not
state clearly how the temperatures indicated by these
calibrations are to be used, and the result has been that
only a minority of the laboratories engaged in testing
tars make use of this method of determining correc-
tions to be applied to the thermometer in arriving at
the true temperature of the distilling vapors. Other
laboratories take actual readings of the thermometer
as fractionating points. The corrections by the first
method may amount to from 5° to 10° at 300° C.

The difference in percentage of total distillate to
300° C. is not a very serious matter, ranging up to
3 or 4 per cent; but when the effect of this dis-
tillate on the softening point of the residue is con-
sidered, it is often found to be sufficient to place the
material tested either within or without the require-
ments of the specification, depending upon whether a
corrected or uncorrected thermometer 1s used in the
test. A variation of 8° or 10° C. in softening point
may readily occur.

There are good arguments in favor of either use of
the thermometer. The object here is merely to call
attention to the influence a variation in practice may
have on test results, and point out that its bearing on
the interpretation of distillation results and on the
selection of specification requirements should be kept
in mind. It is obviously desirable that all producers
and consumers of road tar products shall agree upon
a uniform procedure.

SOFTENING-POINT TEST.

The ring-and-ball method for conducting the soften-
ing-point test on bituminous road materials is used by
the majority of State testing laboratories, but some
States use the cube method in at least some softening-
point determinations.

The use of two different methods makes for con-
fusion and lack of uniformity. The universal use of
one method is highly desirable, especially in view of the
difference in results obtained by the two methods. The
committee on tests and investigations of the American
Association of State Highway Officials has reeommended
the use of the ring-and-ball method (see Department
of Agriculture Bulletin No. 949, p. 52) and the Bureau
of Public Roads in its Typical Specifications for Bi-
tuminous Road Materials (Department of Agriculture
Bulletin No. 691) stipulates the use of the ring-and-ball
method.

TESTING SIEVES.

An effort is being made by the American Society for
Testing Materials working in cooperation with the
United States Bureau of Standards, United States
Bureau of Public Roads, American Association of State
Highway Officials, and the several manufacturers, to
adopt a practical standard screen scale for testing
sieves. Several meetings have been held and enough
progress made to indicate that in all probability the
screen scale of the United States Bureau of Standards,
somewhat modified as to permissible tolerances in both
average opening and wire diameter, will be adopted.
The general adoption of such a screen scale by all users
and manufacturers of testing sieves will greatly sim-
plify the use of the sieves in the laboratory, because it
will be possible in all cases to correlate the sieve num-
ber with the size of the actual opening and thus defi-
nitely fix the size of material under examination.

Should this screen scale be adopted it has been sug-
gested that the Bureau of Standards be requested to fur-
nish sieve correction factors for sieves other than the
standard No. 200, m order that anyone who desires to
have a sieve calibrated for special purposes can do so

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ROAD PUBLICATIONS OF BUREAU OF PUBLIC ROADS.

Applicants are urgently requested to ask only for those publications in which they are
particularly interested. The Department can not wndertake to supply complete sets,
nor to send free more than one copy of any publication to any one person. The editions
of some of the publications are necessarily limited, and when the Department's free supply
is exhausted and no funds are available for procuring additional copies, applicants are
referred to the Superintendent of Documents, Government Printing Office, this city, who
has them for sale at a nominal price, under the law of January 12, 1895. Those publica-
tions in this list, the Department supply of which is erhausted, can only be secured by

urchase from the Superintendent of Documents, who is not authorized to furnish pub-
ications free.

REPORTS.

Report of the Director of the Bureau of Public Roads for 1918.
Report of the Chief of the Bureau of Public Roads for 1919.
Report of the Chief of the Bureau of Public Roads for 1920.
Report of the Chief of the Bureau of Public Roads for 1921.
*Report of the Chief of the Bureau of Public Roads for 1922. 5c.
*Report of the Chief of the Bureau of Public Roads for 1923. 5c.

DEPARTMENT BULLETINS.

No. 105. Progress Report of Experiments in Dust Prevention
and Road Preservation, 1913.
*136. Highway Bonds. 20c.
220. Road Models.
257. Progress Report of Experiments in Dust Prevention
and Road Preservation, 1914.
*314. Methods for the Examination of Bituminous Road
Materials. 10c.
*347. Methods for the Determination of the Physical
Properties of Road-Building Rock. 10c.
*370. The Results of Physical Tests of Road-Building
Roek, 5c.
386. Public Road Mileage and Revenues in the Middle
Atlantic States, 1914.
387. Public Road Mileage and Revenues in the Southern
States, 1914.
388. Public Road Mileage and Revenues in the New
England States, 1914.
*389. Public Road Mileage and Revenues in the Central,
Mountain, and Pacific States, 1914. 15c.
390. Public Road Mileage in the United States, 1914. <A
Summary.
*393. Economic Surveys of County Highway Improve-
ment. 5c.
407. Progress Reports of Experiments in Dust Prevention
and Road Preservation, 1915.
*463. Earth, Sand-Clay, and Gravel Roads. 15c. .
*532. The Expansion and Contraction of Concrete and
Concrete Roads. 10c.
*537. The Results of Physical Tests of Road-Building Rock
in 1916, Including all Compression Tests. 5c.
*555. Standard Forms for Specifications, Tests, Reports,
and Methods of Sampling for Road Materials. 10c.
583. Reports on Experimental Convict Road Camp, Fulton
County, Ga.
*586. Progress Reports of Experiments in Dust Prevention
and Road Preservation, 1916. 10c.
*660. Highway Cost IKkeeping. 10c.
670. The Results of Physical Tests of Road-Building Rock
in 1916 and 1917.
*691. Typical Specifications for Bituminous Road Ma-
terials. 15c.
*704. Typical Specifications for Nonbituminous Road Ma-
terials. 5c.
*724. Drainage Methods and Foundations for County
Roads. 20c.
*949 Standard and Tentative Methods of Sampling and

Testing Highway Materials, Recommended by the
Second Conference of State Highway Testing Engi-
neers and Chemists, February 23 to 27, 1920, 25c.
*1077. Portland Cement Conerete Roads. 15c.
*1132. The Results of Physical Tests of Road-Building Rock
from 1916 to 1921, Inclusive. 10c.

* Department supply exhausted.

DEPARTMENT CIRCULAR

No. 94. TNT as a Blasting Explosive.

FARMERS’ BULLETINS. :

338. Macadam Roads.
*505. Benefits of Improved Roads. ic.
597. The Road Drag. .

No.

SEPARATE REPRINTS FROM THE YEARBOOK.

IN ORE L 21.
TSO.

*849,

Design of Public Roads. 5c.
Federal Aid to Highways, 1917. 5c.
Roads. 5c.

OFFICE OF PUBLIC ROADS BULLETIN.

*45. Data for Use in Designing Culverts and Short-span

Bridges. (1913.) 15c.

OFFICE OF THE SECRETARY CIRCULARS.

49. Motor Vehicle Registrations and Revenues, 1914.
59. Automobile Registrations, Licenses, and Revenues in
the United States, 1915.

63. State Highway Mileage and Expenditures to January
1, 1916.

Width of Wagon Tires Recommended for Loads of
Varying Magnitude on Earth and Gravel Roads. 5c.

73. Automobile Registrations, Licenses, and Revenues in
the United States, 1916.

74. State Highway Mileage and Expenditures for the Cal-
endar Year 1916.

161. Rules and Regulations of the Secretary of Agriculture
for Carrying out the Federal Highway Act and
Amendments Thereto.

Public Roads Vol. III, No. 25. Automobile Registrations, Li-

censes, and Revenues in the
United States, 1919.
Vol. ITI, No. 29. State Highway mileage, 1919.
Vol. III, No. 36. Automobile Registrations, Li-
censes, and Revenues in the
United States, 1920.
5. Automobile’ Registrations,
January 1 to July 1, 1921.

ait

Vol. IV, No.

REPRINTS FROM THE JOURNAL OF AGRICULTURAL

RESEARCH.

Vol. 5, No. 17, D- 2. Effect of Controllable Variables Upon the
Penetration Test for Asphalts and
Asphalt Cements.

Vol. 5, No. 19, D- 3. Relation Between Properties of Hardness
and Toughness of Road-Building Rock.

Vol. 5, No. 20, D- 4. Apparatus for Measuring the Wear of
Concrete Roads.

Vol. 5, No. 24, D- 6. A New Penetration Needle for Use in
Testing Bituminous Materials.

Vol. 10, No. 7, D-13. Toughness of Bituminous Aggregates.

Vol. 11, No. 10, D-15. Tests of a Large-Sized Reinforeed-Con-
crete Slab Subjected to Eecentric Con-

centrated Loads.

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1924

é

FUNDAMENTAL PRINCIPLES OF HIGHWAY FINANCE

The wide variation in the present status of highway development in the several States prevents the
adoption of a uniform policy for securing the funds necessary to the annual highway budget and expending
these funds. Generally speaking, however, these principles may be enunciated.

(a) States in the initial stage of highway development should issue bonds to defer that portion of the
annual charge for construction which would overburden either property or the road user.

(6) States where original construction programs are well under way can, in the main, finance further
expenditure for construction by bond issues devoted to deferring the cost of special projects.

(c) States where original construction is practically completed are concerned chiefly with maintenance
and reconstruction and should depend on current funds, save in cases of emergency.

(¢) The maintenance of interstate and State roads should be a charge against the road user.

(€) Roads serving a purely local purpose will generally require only light upkeep, and this should
properly be a charge against the adjacent property, which in this case is the first and often the only beneficiary.

(f) No road should ever be improved to an extent in excess of its earning capacity. The return to the
public in the form of economic transportation is the sole measure of the worth of such improvements.

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