Impacts of metakaolin on lightweight concrete by type of fine aggregate

Metakaolin is a widely used admixture known to be highly effective in enhancing compressive strength and durability. Previous studies, however, have mainly focused on comparing metakaolin with other admixtures, with little research being directed toward the correlation between metakaolin and aggregates. Against this backdrop, this study performs experimental research on the impacts of metakaolin on lightweight concrete according to different types of fine aggregate currently available. For this purpose, three types of fine aggregate, two types of bottom ash (by-product of power plant) and one type of artificial expanded shale, were used. Metakaolin was mixed with each fine aggregate at cement replacement ratios of 0%, 5%, 10%, 15%, and 20% by weight. The effects of metakaolin on the workability, density, porosity, compressive strength, and modulus of elasticity of lightweight concrete are addressed in detail. It was found that the compressive strength of lightweight aggregate concrete, which had 1790 kg/cm3 density and 15 ± 1 cm slump, was increased by up to 74.2% when 20% of metakaolin was replaced by metakaolin. The test results also show that the effects of metakaolin vary significantly according to the replacement ratio and types of aggregates. This implies that, in order to enhance the effects of metakaolin on lightweight concrete, careful consideration is necessary with respect to the mutual impacts between lightweight aggregate and metakaolin.