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Effects on Air Entrainment on Portland Cement Concrete
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1991-12-01
[PDF-2.24 MB]
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Edition:Interim: September 1990 October 1991
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Abstract:Experience in Texas suggests problems may occur in stabilizing the air content of entrained concrete during and after pumping operations. In one instance, normal air entraining dosage rates were significantly exceeded in an effort to maintain the desired amount of air content in the concrete immediately after discharge. It was determined subsequently from hardened samples that the loss air was fully recovered and actually was 50 percent greater than the desired levels. Several factors have been noted in the literature to affect the level of entrained air in concrete. Factors such as cement content and fineness, coarse aggregate size, amount of fine aggregate, slump, type of admixture, etc. have been identified as factors affecting entrained air content. Preliminary test results indicate an apparent loss of air occurs immediately after discharge from the pump and tends to return after a period of time. This noted variation of air follows a dissolution process suggesting a shifting of the air-void system from smaller bubbles to larger bubbles. A test program is suggested to identify significant factors in this process.
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