EXPANSION" AND CONTRACTION' OF CONCRETE. 



9 



way and are subjected to no other influences. Recent researches * have shown 

 that under constant stress concrete exhibits a slow yielding, or " flow," making 

 the deformation "produced by constant stress very much greater than that 

 produced by a static stress of short duration. In the curves on figure 7 it is 



seen, again, that there is very little 

 difference between the contraction 

 and expansion of 1 : 2 : 4 and 1:3:6 

 concrete, whether wet or dry. Ap- 

 parently there is not enough dif- 

 ference in the degree of richness 

 of the mixture to cause a differ- 

 ence in the contraction and expan- 

 sion of concrete. The maximum 

 contraction obtained in this set. of 

 experiments was about 0.0008 inch 

 per inch of length. 



GRAVEL CONCRETE, STORED 

 OF DOORS. 



OUT 



On figure 8 is shown the effect 

 of exposure to the atmosphere of 

 a specimen made of 1:2:4 gravel 

 concrete. This specimen was 

 stored in a vertical position out of 

 doors at a place where it was in 

 shade for perhaps three or four 

 hours every day. No effort was 

 made to protect it from rain or 

 sun. This curve, like the preced- 

 ing ones, simply shows the effect 

 of moisture, all temperature effects 

 having been eliminated. It is seen 

 that there has been but very little 

 change in the length of the con- 

 crete due to moisture changes in 

 the specimen. This seems reason- 

 able to expect in a specimen cured 

 out of doors, as the alternate wet- 

 ting and drying to which it was 

 subjected, due to changes in the 

 weather, occurred with such fre- 

 quency that there was little chance 

 for moisture changes to be effec- 

 tive, and it has been pointed out 

 already that large changes in 

 length, due to moisture changes, 

 are apt to be slow and progressive, 

 although changes of 0.0001 to 

 0.0002 inch per inch of length may 

 occur in the course of a few days. The influence of moisture on this specimen 

 cured out of doors probably is somewhat typical of the behavior of concrete in 



roads that have a well-drained subbas e. 



1 " Flow of Concrete under Sustained Loads," by E. B. Smith, Proceedings of American 

 Concrete Institute, 1916. 



80045°— 17— Bull. 532 2 



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