Effect of Fire on Microstructure and Mechanical Properties of Blended Cement Pastes Containing Metakaolin and Silica Fume

The influence of high temperature on microstructure and mechanical properties of cementpaste is vital to characterize fire resistance. Some experimental investigations on themicrostructure and compressive strength of pre-heated metakaolin-silica fume blendedcement pastes are presented in this paper. The aim of this investigation is to study the effect of substitution of metakaolin (MK) by silica fume (SF) on thermal stability of Portlandcement-MK blended pastes. The kaolinte was thermally activated at 850°C for 2 hours. The cement pastes were prepared using standard water of consistency. The pastes were kept in moulds at 20°C and 100% relative humidity for 24 hours and then hydrated for 28 days under water. The hydrated pastes were exposed for 2 hours to temperature 200, 400, 600 and 800°C. The pre-heated specimens were tested for compressive strength, thermal stability, microstructure and phase composition. The thermal shock resistance were performed on cement pastes after hydration. The results of investigation showed that the compressive strength of pre-heated blended cement increases with temperature up to 400°C and then, it decreases as the pre-heated temperatures increase up to 800°C. The replacement of Portland cement, PC, by 15% MK and 15% SF in cement pastes increases the thermal shock resistance by about 20 times than control