22 
BULLETIN 532, U. S. DEPARTMENT OF AGKICULTUEE. 
the solid concrete show a slight contraction, while the joints show 
an expansion, or, in other words, they have opened slightly. The 
contraction of the concrete took place notwithstanding the fact that 
it was wet continually. It is to be noted, however, that the tempera- 
ture fell from 82° on July 7 to 75° on July 8,' and this probably ac- 
counts for the slight contraction observed. 
Up to July 22 the road was kept covered with wet clay, and the third 
set of readings was taken on this date. Here it is noticed that there 
is a slight expansion of the concrete with a large ccntr action at three 
of the joints and an expansion at two. The temperature at these 
readings was slightly higher than that taken during the initial read- 
ings. This, combined with the moisture expansion, could account 
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JULY 8.1914 
JULY 22,1914 
OCTOBER 31.1914 
MARCH A, 1919 
JUNE 19.1915 
FEBRUARY 25.1918 
OCT. 31 - 50° 
Road. Section near national road station. Laid July 6, 
1914. Section I. 
for the slight expansion noted in the concrete. But during this 
period of initial hardening, while the concrete was kept wet, it is seen 
that very little change took place in its length. It is important to 
note, however, that even on the second day, when the readings 
showed a slight contraction of the concrete, a transverse crack ap- 
peared. The slight tensile stress induced in the weak green concrete 
by the contraction evidently was enough to produce rupture. 
Just after July 22 the earth covering was removed from the road 
surface, and it was subjected directly to atmospheric influences. On 
October 31, with the pavement temperature at 50° (32° lower than 
the initial temperature) , the uncracked concrete showed large con- 
traction, while the cracks and joints opened or gave an expansion 
