This paper shows the effect of metakaolin with different amorphous phase content on 2 and 7 day compressive strengths and microstructure of MK-blended cement pastes. The cement pastes that contained 0%, 10% and 50% MK were prepared at a constant water/binder ratio of 0.35 and cured at 22 °C for 2 days and 7 days. It was found that cement paste with high-quality MK (high amorphous phase content) resulted in a higher early age compressive strength than pastes with lower amorphous phase contents and this was attributed to high initial reactivity. The lowest amorphous phase content MK/cement blends achieved early age compressive strengths comparable to higher amorphous phase content MK/cement blends. The MK-blended pastes, prepared without a plasticizer, had higher degrees of agglomeration and lower strengths.
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