High temperature durability of fiber reinforced high alumina cement composites

The effect of high temperature exposure on the durability of fiber-reinforced composite materials based on high alumina cement is studied. A combination of X-ray diffraction- and thermal analyses of hydrated phases shows a simultaneous presence of all principal hydrates (CAH10, C2AH8, C3AH6, AH3) in significant amounts during the whole 2-28 days hydration period. The application of basalt aggregates and basalt fibers is found to improve significantly the high-temperature durability, in a comparison with the cement paste. The residual values of compressive and bending strength of the most successful mix with the combination of longer and shorter basalt fibers in a 90:10 ratio are 50% and 34%, respectively, after 1000 °C exposure. The fiber reinforced composite material with the most favorable mechanical properties exhibits also the highest resistance to water and water vapor transport and the lowest water vapor adsorption after 1000 °C pre-heating, which correlates well with its lowest amount of pores bigger than 100 nm. The thermal conductivity and specific heat capacity of all analyzed composites show a significant increase with the increasing moisture content; the differences between the values in dry and water saturated state are up to 100% and 65%, respectively. The thermal strain of all studied materials is almost linear within the whole 20-1000 °C range, with the basalt fibers being able to decrease it by up to 7% at 1000 °C.