Effects of Micro- and Ultrafine Metakaolin on Compressive Strength and Water Sorptivity of High Volume Fly Ash Concrete

The experimental study on the effect of using micro- and ultrafine metakaolin incorporated with Portland cement composite for the improvement of compressive strength and water sorptivity of high volume fly ash concrete is presented in this paper. Mixture proportions was prepared where metakaolin in micro- and ultrafine sizes was used to replace cement in high volume fly ash concrete mixtures (40 and 60% by wt.). Phase identification and the hydration products were obtained through X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The results reveal that the inclusion of micro- and ultrafine metakaolin offsets the inferior characteristics of high volume fly ash concrete by accelerating the hydration products, contributes the formation of additional CSH through the reaction with calcium hydroxide and densifies the microstructure of sustainable high volume fly ash matrix, particularly at the 7th day after water curing. Furthermore, the utilization of high volume fly ash containing micro- and ultrafine metakaolin is potential for the application of eco-friendly concrete.