BULLETIN 532, U. S. DEPARTMENT OP AGRICULTURE. 



out, after several weeks, they shrink and develop tension, but they are then 



somewhat fortified by 



019 



their maturity and are better 



able to resist the tensile 

 stresses developed. The 

 practice of keeping con- 

 crete wet must be em- 

 phasized from this 

 standpoint, as well as 

 from the fact that by 

 so doing a more com- 

 plete hydration of the 

 more sluggish particles 

 of cement is effected and 

 the strength increased 

 somewhat thereby. The 

 practice of subjecting 

 the concrete to an ini- 

 tial period of wetting 

 can not wholly prevent 

 cracking, but it does aid 

 in decreasing the num- 

 ber of cracks that form 

 in concrete pavements. 



1:2:4 AND 1:3:6 CON- 

 CRETE; LONG INITIAL 

 WETTING. 



On figure 7 are shown 

 four curves giving the 

 expansion and contrac- 

 tion of 1:2:4 and 

 1:3:6 concrete of very 

 wet and very dry con- 

 sistencies. These speci- 

 mens differ from the 

 others in that they 

 were kept in water for 

 a period of about six 

 months, then removed 

 and allowed to dry in 

 the warm, dry air of the 

 laboratory. Note that 

 concrete under con- 

 stantly moist conditions 

 maintains almost con- 

 stant expansion while it 

 is moist, and that the 

 amount equals approxi- 

 mately 0.0001 inch, or 

 0.01 per cent. Theoreti- 

 cally, when the ends of 

 ~SoSsSs3S2SS2a concrete structure are 



Id o©ooo ooooe>o 



Sj SSaSdSSggggS restrained from move- 



NOiQNvaxa NOiiC^/axmoo iind ment, this would pro- 



duce a compressive stress of 3,000.000 pounds per square Inch, multiplied by 0.0001 

 inch, or 300 pounds per square inch, provided stresses can be figured in this 



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