26 
BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 
sions at some of the expansion joints, and the joint which had pushed 
together and overrode during the preceding summer remained in the 
same condition. 
In an effort to determine whether atmospheric moisture or tem- 
perature played the most important part in influencing the expansion 
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Fig 19. — Curves of unit of expansion and contraction of uncracked portions 
of concrete road, Ohio Post Road. 
and contraction of the Ohio road, the curves shown in figure 19- 
were plotted. The unit expansions and contractions shown were 
obtained by summing up the changes in the concrete in the uncracked 
portions. Each curve represents the unit deformation in a different 
slab of concrete included between different joints or cracks. In the 
same section of road these curves should be of practically the same 
