| Abstract | Internal curing of concrete can be achieved by soaking porous lightweight aggregate (LWA) in water before its introduction into the concrete mix as a partial replacement for normal density aggregate. This technique is particularly useful for low water-cement ratio concrete, for which self-desiccation can lead to autogenous shrinkage, tensile stresses and cracking at early ages. A research project has been undertaken to develop low-shrinkage high performance concrete for the design of concrete structures with long service life. One specific objective was to optimize the concrete mix design by introducing selected chemical admixtures into the concrete mix by using porous lightweight aggregate as a carrier. Expanded shale lightweight aggregate sand was soaked in a solution of water and given admixtures, such as a shrinkage-reducing admixture (SRA) and/or a corrosion inhibitor (CI), prior to mixing. Several fresh and hardened concrete properties were measured and compared to those of a similar concrete mix, in which the given chemical admixtures were added directly into the mix according to the manufacturer?s specifications. The results showed that this new admixture delivery method produced no adverse effects on the desired fresh and hardened concrete properties, including compressive strength and autogenous shrinkage. The addition of SRA through LWA mitigated chemical interactions between the air entraining admixture and the SRA, which was previously found to reduce the effectiveness of the air entraining admixture. For instance, when SRA was delivered through LWA, it was found that the target air content of 5% could be achieved with 10 times less air entraining admixture. |
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