Curing of high-performance concrete:

Abstract

This report summarizes the results of an exploratory study on the effects of curing duration on the variation of mortar strength with distance from the drying surface. The study was sponsored by the Partnership for High-Performance Concrete Technology, which is a coordinated research effort by the Building and Fire Research Laboratory to provide the bases for reliable application of high-performance concrete in construction. In this study, a novel, notched cylindrical test specimen was used to measure tensile strength at different depths. Two mortar mixtures with w/c of 0.30 and 0.45 were used; the former was assumed to be representative of the paste system in a high-performance concrete. Specimens were moist cured for (1, 3, or 7) d and then exposed to air at 25 C and 50 % or 70 % RH. The cylinders were sealed to simulate one-dimensional drying in a large member. Tensile strengths were measured at 28 d. Relationships between tensile strength and depth were compared with those of specimens continuously moist cured. The data tended to show that 1 d of moist curing might be sufficient to ensure adequate strength development at a depth of 25 mm from the exposed surface. The phenomenon of increasing strength with drying may have confounded the results, and recommendations for additional studies are provided.