EXPANSION" AND CONTRACTION OF CONCRETE. 
9 
way and are subjected to no other influences. Recent researches 1 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 
a, difference between the contraction 
=i and expansion of 1 : 2 : 4 and 1:3:6 
v 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- 
ds 
& sion of concrete. The maximum 
* contraction obtained in this set of 
>i experiments was about 0.0008 inch 
h 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 subbase. 
0.0002 
0-0001 
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00001 
00002 
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NOU.3Va.LNOD 
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1 " Flow of Concrete under Sustained Loads," by E. B. 
Concrete Institute, 1916. 
80045°— 17— Bull. 532 2 
Smith, Proceedings of American 
