Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage

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Title: Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage

Author(s): JoAnn Browning, David Darwin, Diane Reynolds, and Benjamin Pendergrass

Publication: Materials Journal

Volume: 108

Issue: 6

Appears on pages(s): 638-644

Keywords: Bridge decks; cracking; curing; drying shrinkage; lightweight aggregate; slag cement; vacuum saturation.

Date: 11/1/2011

Abstract:
The effectiveness of prewetted, vacuum saturated (PVS) lightweight aggregate (LWA) as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days. Normalweight aggregate is replaced by LWA at volume replacement levels ranging from 8.9 to 13.8%. Some mixtures contain a partial replacement of portland cement with slag cement while maintaining the paste content at approximately 24.1% of concrete volume. Comparisons are made with mixtures containing low-absorption granite and high-absorption limestone normalweight coarse aggregates. At the replacement levels used in this study, PVS LWA results in a small reduction in concrete density, no appreciable effect on concrete compressive strength, and a substantial decrease in concrete shrinkage for drying periods up to 365 days. Increasing the curing period from 7 to 14 days reduces concrete shrinkage. Thirty and 60% volume replacements of portland cement by slag cement result in reduced shrinkage when used with a porous LWA or normalweight aggregate. After 30 and 365 days of drying, all mixtures with LWA exhibited less shrinkage than the mixtures with either low- or high-absorption normalweight aggregates.