Effects of Duration of Moist Curing on Concrete Made with Blended Cements or Pozzolans. Report 1. Laboratory Investigations of 3/4-In.-Aggregate Concrete

摘要

Tests were made to determine if the 21-day moist-curing requirement for concrete containing a pozzolan, or natural cement, or made using type IV portland cement could be reduced to 14 days as required for type II portland cement and portland blast-furnace slag cement concrete. Seven air-entrained concrete mixtures containing 3/4-in.-maximum-size limestone aggregate were proportioned with 4 bags of cement per cu yd, an air content of 6%, and a slump of 2-1/2 in. Specimens made from each mixture were cured under six different curing conditions and tested for dynamic modulus of elasticity, compressive strength, and resistance to freezing and thawing. The results of the freezing-and-thawing tests indicated that there was no significant difference between the 14- and 21-day moist-cured specimens tested at both 28 and 90 days ago regardless of the cementing material of the mixtures. The strength values for the 21-day moist-cured specimens were somewhat higher than those of the specimens moist-cured 14 days. The results also indicated that low-strength air-entrained concrete can be durable if it has had an opportunity to dry before it is frozen. (Author)