BULLETIN 532, U. S. DEPARTMENT OE AGEICULTUEE. 
1 : 2 AND 1 : 3 MORTAR, STORED IN AIR AND ALSO IN WATER. 
The 
water 
shrinkage of mortar when stor 
are shown clearly on the diagr 
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ed in air and the expansion when stored in 
•mis in figure 4. Note that the changes are 
somewhat greater in the 1 : 2 than in the 
1 : 3 mortar. The shrinkage of air-cured 
1 : 3 mortar which has been allowed to dry 
out is approximately 0.078 per cent at the 
age of 6 months, and that of 1 : 2 mortar 
at the same period is 0.0S5 per cent, which 
figures are quite like those of other in- 
vestigators. It will be noted that both the 
1 : 2 and 1 : 3 mortars have expanded 
when immersed in water, and at 6 months 
the values for the respective mortars are 
0.015 per cent for 1 : 3 and 0.025 per cent 
for 1:2. 
CONCRETE STORED IN AIR. 
On figure 5 is shown the behavior of 
concrete when it is allowed to dry out 
immediately after molding. The speci- 
mens are 1:2:4 and 1:3:6 mixtures of 
very wet and of very dry consistencies. 
It is seen that contraction takes place 
almost immediately, due to drying out of 
the water, and at the age of 1 week the 
approximate contraction is from 0.01 to 
0.03 per cent, or from 0.0001 to 0.0003 
inch per inch of length. If the modulus 
of elasticity of concrete is assumed to be 
2,000,000 pounds per square inch in ten- 
sion, the tensile stress that would be de- 
veloped by a contraction of only 0.0001 
inch per inch of length would be 200 * 
pounds per square inch. Unless free con- 
traction of the concrete were provided 
some of this stress would be developed 
and cracking surely would result, as the 
tensile strength of the concrete then 
would be exceeded. These curves repre- 
sent merely the contraction due to change 
in moisture, and all temperature effects 
are eliminated. 
1:2:4 AND 1:3:6 CONCRETE, ALTER- 
NATELY WET AND DRY. 
The curves on figure 6 show very clearly 
the effect of changes in moisture content 
on the change in length of concrete. The 
specimens were mixed in different pro- 
portions and consistencies, and all were 
kept wet for 15 days after pouring the 
1 Tin 
later. 
Bow" effect of concrete probably will decrease tbis figure. This is mentioned 
