Effect of silica fume and metakaoline pozzolana on the performance of blended cement pastes against fire

The aim of this investigation is to study the effect of the subsititution of metakaoline (MK) by silica fume (SF) upon the thermal stability of Portland cement -MK blended pastes. The kaoline was thermally activated at 850 degrees C for 2 hours. The cement pastes were prepared with constant consistency. The pastes were kept in moulds at 20 degrees C/100 % relative humidityfor 24 hours and then hydrated for 28 days under water The hydrated pastes were exposed for 2 hours to temperatures of 100, 200, 400, 600 and 800 degrees C. The hydrated specimens were tested for compressive strength, thermal stability and phase composition after heat treatment. It was found that, after increase of compressive strength of control cement paste up to 200 degrees C, the paste suffers a more loss of compressive strength with further increasing treatment temperatures. But, it was evidenced that the compressive strength of blended cements increases with temperature up to 400 degrees C and then, it decreases as increase the treatment temperatures up to 800 degrees C. The replacement ofPortland cement (PC) by 15 % MK and 5 % SF in cement pastes increases the thermal shock resistance by about 10 times.