BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 



1 : 2 AND 1 : 3 MORTAR, STORED IN AIR AND ALSO IN WATER. 



The shrinkage of mortar when 

 water are shown clearly on the d 



t '- = = 

 *■>*■> 



U „ u K 



i a J o 



OOB 













! / 

















,' 





































OOi 



























v- 





099 













f- 1 















t 



> 













I 

















/ 







' 1 





oes 



099 

 0*5 

 019 

 005 

 08* 











■S 



/ 













c 



i 

 i 













," 



// 













'i'q 1 



/ 











1 1 



> ?1 



I 











' < 













1 -I 















•''1 



j 



It 











1 •' 

















» 





2 

 oec 



< 











t 













i 













*<, 















• 













1 



i r 















 1 



B 













• 



r ' 













, 



f] 





























& 



08i 











^ > 



I 













°! 















f 













;7I 



j 











«r 



//;' 



r 











<l 



/•/ 













I 













i 



f * 



i 









,/> 



i. 



/A 









*2 



?« 



t> 









NOI.L7VtiA.NO?' XllMfV 



stored in air and the expansion when stored in 

 Lagrams 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 0.07S 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 1 

 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 The " flow" effect of concrete probably will decrease Ibis figure. This Is mentioned 



Inter. 



