The deterioration and spalling frequency of metakaolin (MK) blended concrete subjected to high temperature is analyzed and compared with the equivalent silica fume (SF), fly ash (FA) and pure OPC concretes. Normal and high strength concrete mixes incorporating 0-20% MK were prepared and exposed to a series of high temperatures till 800°C. The residual compressive strength, porosity and pore size distribution were determined. It was found that after an increase in compressive strength at 200°C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and pure OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents. It is concluded that the dense micro-structure and low porosity are the main reasons of the poor performance of MK concrete at high temperature.
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