Effect of Vibration on Air Content of Mass Concrete
Walter O. Crawley
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Tests were made to observe the effect of high-frequency (13,000 vpm and moderate-frequency (6800 vpm) vibration on concrete ranging from 1/2 to 4-in. slump, containing 6-in. coarse aggregate, and having nominal air contents of 3, 6, and 9 percent in that portion of the mix smaller than the 1 1/2-in. sieve. Cores drilled from hardened specimens of the concrete with 6 percent air content were examined micrometrically for amount and distri-bution of air and coarse aggregate. The high-frequency vibrator was found to cause more rapid loss of entrained air than the moderate-frequency vibrator. However, either vibrator could cause a 50 percent loss in air from nominal 3 percent-air-content concrete in 30 sec. The rate at which air was lost generally increased with slump, but not to a marked degree. The high-frequency vibrator had more effect in causing movement, and escape of air, while the moderate-frequency vibrator caused more movement and segregation of the coarse aggregate.