Fresh, micro- and macrolevel studies of metakaolin blended self-compacting concrete

• Fresh concrete properties were achieved for metakaolin blended SCC.
• MK significantly enhanced the compressive and split tensile strengths at early ages.
• Inclusion of MK reduces the microcrack width and calcium:silicate ratio.
• MK reduces calcium hydroxide and increases calcium–silicate–hydrate.
• Optimum replacement of MK was 10 wt.%.

This investigation focuses on the effect of metakaolin (MK) on the fresh, micro- and macrolevel properties of self-compacting concrete (SCC). Cement content of 500 kg m− 3 was considered, while the MK was used to replace cement by 5, 10 and 15 wt.%. To assess the fresh concrete properties tests like slump flow, T50 cm time, V-funnel flow times, L-box and blocking ratio were performed. The macrolevel properties studied were compressive strength and split tensile strength. The microstructural changes were studied using a Scanning Electron Microscope (SEM), X-ray Diffraction Analysis (XRD) and Energy Dispersive X-ray Analysis (EDX). The fresh concrete results show that SCC mixes prepared at different Water:Powder (W:P) ratios satisfied the rheological properties without addition of Viscosity Modifying Admixture (VMA). MK inclusion enhanced the macrolevel properties. The microlevel studies indicated that microcrack width was reduced due to inclusion of MK in the control mix. In addition pozzolanic action of MK reduces the calcium hydroxide (CH) and lowers the calcium:silicate (Ca:Si) ratio of calcium silicate hydrate (C–S–H). The optimum replacement of MK was 10 wt.% regarding micro- and macrolevel properties. As a result of this evaluation, inclusion of MK improved the micro- and macrolevel properties.