LWA as Internal Curing Agent to Control Availability of Internal Curing Water in Concrete
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LWA as Internal Curing Agent to Control Availability of Internal Curing Water in Concrete Luis Emilio Rendon1, Montserrat Rendon2 and Norma Ramirez1 1 Mexican Institute of Water Technology, Jiutepec, Morelos, México 2 Centre of Arts of the State of Morelos, Cuernavaca, Morelos, Mexico. ABSTRACT The effectiveness of lightweight aggregate (LWA) as an internal curing agent (ICA) to reduce concrete shrinkage is evaluated for repair concrete used in cultural heritage works (RCCHW) using curing periods of 30 days. Normal weight aggregate is replaced by LWA at volume replacement levels ranging from 10 to 14%. The mixtures contain Portland cement maintaining the paste content at approximately 24.1% of concrete volume. Comparisons are made with mixtures containing low-absorption granite and high-absorption limestone normal weight coarse aggregates. At the replacement levels used in this study, LWA results in a small reduction in concrete density, no appreciable effect on concrete compressive strength, and a decrease in concrete shrinkage for drying periods up to 30 days. With a curing period of 14 days, all mixtures with LWA exhibited less shrinkage than the mixtures with either low- or high-absorption normal weight aggregates. INTRODUCTION Drying shrinkage is a principal cause of cracking in concrete structures. For a wide variety of structures, however, the cracking can be accommodated (such as with joints in slabs-on-ground) or modified (such as through minimum reinforcement in structural slabs) so that the performance of the overall structure is not affected. One significant case where this is not true are concrete cultural heritage works, archaeology and historical collections, where drying shrinkage cracking combines with plastic shrinkage, settlement, and thermal cracking to lower the durability of the cultural heritage by allowing water, pollutants and atmospheric present chemicals to penetrate the concrete. This study demonstrates that a partial replacement of normal weight aggregate with LWA will reduce drying shrinkage in (RCCHW). This study also demonstrates the positive impact of extended curing on reducing shrinkage. Taken together, the results provide the basis for a combined strategy to reduce drying shrinkage —and by extension, the cracking that some times accompanies it— in (RCCHW) to repair all kind of cultural heritage works concrete. MATERIALS Basic materials for the production of concrete are cement, aggregates, and water. Up to certain limits, additional compounds –concrete additives– may be used to control some properties of the fresh or hardened concrete. These materials must meet
specifications set forth in standards or in approval documents. The compatibility of all of the compounds used must also be considered.
Figure 1. Crushed pumice and expanded shale internal structure. When using a LWA as ICA to be the primary responsible for the availability of internal curing water. The overriding parameter seems to be the internal structure of the LWA. Figure 1, after [1] the internal structure of the t
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