Internal curing in cementitious systems made using saturated lightweight aggregate

Ryan Henkensiefken, Purdue University

Abstract

Low water-cement ratio concrete mixtures have been increasingly promoted for use in civil engineering infrastructure due to potential improvements in strength and durability. Despite their increased strength and reduced permeability, these mixtures are susceptible to early-age cracking caused by autogenous shrinkage. Methods have been developed to reduce the cracking susceptibility of these mixtures. One such method is internal curing. Internal curing uses water-filled lightweight aggregate to supply water to counteract the effect of self-desiccation after the initial pore structure of the paste has formed. This project evaluated the shrinkage cracking performance and fluid transport properties of mixtures containing internal curing. This thesis describes how chemical shrinkage results in internal vapor-filled void creation which leads to self-desiccation. The use of internal curing agents can provide a sufficient volume of water in the lightweight aggregate (LWA) to counteract the effects of self-desiccation. In addition to the volume of water provided by the LWA, the distribution of the LWA plays an integral role in the effectiveness of internal curing. X-ray absorption measurements indicate that the water can travel up to 1.8 mm during the first 75 hours. These results are combined with a hard core soft shell model developed at NIST to determine the spacing between lightweight aggregate particles to indicate an efficient aggregate size and grading. Measurements of unrestrained length change were performed for mortars made using different volume replacements of LWA under sealed and unsealed curing conditions. The cracking potential of sealed and unsealed mixtures is presented when the mixtures are restrained from shrinking freely using the restrained ring test. The results indicate that if a sufficient volume and an appropriate spacing of lightweight aggregate are used, shrinkage cracking can be significantly reduced or eliminated for both sealed and unsealed curing conditions. The results of this study indicate that when internal curing is used, the overall water absorption and electrical conductivity is reduced. This is shown to be due to the increased degree of hydration and a depercolation of the interfacial zones around the aggregate. As a result, mixtures with internal curing may have a w/c of 0.30 but exhibit the performance of a concrete with a lower w/c (e.g., 0.23).

Degree

M.S.C.E.

Advisors

Weiss, Purdue University.

Subject Area

Civil engineering|Materials science

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