INVESTIGATION OF RESISTANCE OF PREPLACED-AGGREGATE CONCRETE TO FREEZING AND THAWING.

The objectives of this investigation were to establish whether variations in manufacturing procedures may be expected to include some which affect the frost resistance of preplaced-aggregate concrete, to identify such procedures if they exist, to determine if the hardened concrete can be rendered more resistant to freezing and thawing by the addition of an air-entraining admixture AEA to the grout mixture, and to make appropriate recommendations for means by which any adverse effects encountered may be avoided in practice. Results indicate that the resistance of conventional preplaced-aggregate concrete at an age of 28 days to accelerated freezing and thawing is much less than that of concrete containing AEA both conventionally mixed and preplaced. Apparently, this relatively low resistance of the preplaced-aggregate concrete containing no added AEA was due chiefly to the low air content, which was contributed to by the relatively small amount of fines in the mixture. The results of tests of the preplaced-aggregate concrete containing AEA for resistance to freezing and thawing were approximately the same as concrete conventionally mixed containing AEA the addition of AEA increases these values regardless of delay time between mixing and pumping of grout. The air-void spacing-factor values of the preplaced-aggregate hardened-concrete specimens containing similar amounts of entrained air as the conventionally prepared specimens indicated that the concrete would be durable. The durability test data agree with this prediction. Author