Wood ash versus expanded clay aggregate as internal curing water reservoirs in high performance concrete

The performances of expanded clay aggregate and wood ash as internal curing water reservoirs were studied in the mortar phase of a hypothetical high performance concrete with a low water-to-binder ratio. The two materials substituted the 15 and 30% of the sand volume. Two different binders, Portland cement and high-volume fly ash blended cement, were used. The compressive strength and the volume stability of the mortars in sealed and air-drying conditions were studied. Furthermore, the desorption capacity of the internal curing water reservoirs and the internal humidity inside the mortars during the first days after casting were analysed. The results shown that the reduction in the self-desiccation shrinkage was higher when the expanded clay aggregate was used, even in air-drying curing conditions, due to its higher desorption capacity in low-relative-humidity environments in comparison to that of the wood ash. However, wood ash had a stronger beneficial effect on early age autogenous shrinkage without significantly increasing the drying shrinkage. The two alternative aggregates influenced the strength moderately. Considering the technical, economic, and environmental implications of using the two lightweight aggregates, wood ash is recommended.

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