28 BULLETIN 257, U. S. DEPARTMENT OF AGRICULTURE. 
TaBLEe 19.—Average and maximum distance between cracks in concrete experiments at 
Chevy Chase, Md., March 10, 1915. 
Character of pavement. 
Average = 
distance iceeien 
Length. | between SS 
Concrete. Aggregate. - 
Surface coated with bituminous material: 
Cas 76 2 11 Pee ee ee a oe eee a cp Mee le SR Necks Gravel 22 
Heys Pee ee ae ee ee a ee ee eee Limestone 
OTEPCCMeN fle ee 5 ee as Se ea a ee ee Gravel... .:... 
UE Sr ce ss Se te eee ce ee Re eee aR ee Limestone. 
Surface exposed 
@LITIG NE Gee ee ee ee ee ae ee ee Grayelscas: 5 
Oe eee Ce ee ee ee Limestone. 
RSS an CR ee ee eee Wraps so. S23* 
GHEGEMCGH iS Se <= ee hes SS ice Scie ere ee Gravel... <2. 
Dears re BS 2 LB ce 2 kee Bee ea Limestone 
TB) OS Ree ne Ss SEN See ee a Ce iErap reece 
As noted in the previous progress report, the relative distances 
between cracks continue greater on sections constructed with a 
limestone aggregate than on those where trap rock or gravel were 
used, 
EXPERIMENT No. 6 (ViTRiFieD Brick). 
An inspection of this experiment showed no appreciable difference 
in wear between the several brands of brick. Three longitudinal 
eracks were noted, as follows: 
In section D, a crack about one-third the length of the section 
and about 6 feet from the west curb. Im section F, a crack about 
half the length of the section, beginning at the south a and about 
6 feet from the east curb. In section G, a crack about 6 feet long 
and about the same distance from the east curb as that in section F. 
These cracks are practically straight and so fine that they would — 
hardly be distinguished in a casual observation. Their cause has 
not thus far been clearly ascertained. 
A traffic census on this experimental road is taken every 13 days 
for a 24-hour period. A tabulation of the maximum and average 
of each class of traffic for the period between March 1, 1914, and 
March 1, 1915, is given in Table 20. The east side of the road carries 
outgoing traffic and the west side incoming traffic. 
“7 4k 
oa nee nnn nea ge a ee ah a ar 
ae ae le 
wa Chey 
