22 



BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 



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 contraction 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 fl, 1914 



JULY 22.1914 



OCTODtR 31.1914 



MARCH A. 



1913 



JUNE 19.1915 



FEDRUARY 23,1910 



TEMPCRATURE OF PAVEMENT 



JULY 7 - 82 "F 



JULY - 75* 



JULY 22 - 85" 



OCT Jl - SO* 



MAR. A - 30* 



JUNC 19 - 66° 



rts. 2» - 3*° 



Fig. 16. — Expansion and contraction of concrete, Ohio Tost 

 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 Avet, 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 81, 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 



