Use of Carbon Microfibers for Reinforcement of Calcium Aluminate-Class F Fly Ash Cement Activated With Sodium Meta-Silicate at up to 300°C

摘要

This study assessed the carbon microfiber (CMF) for improvement of the compressive-toughness and steel-cement shear bond strength of sodium metasilicate-activated calcium aluminate/Class F fly ash foamed cement at hydrothermal temperatures of up to 300°C. In contact with cement pore solution the CMFs surfaces undergo alkali-caused oxidation, leading to the formation of metal (Na, Ca, Al)-complexed carboxylate groups. The extent of this oxidation is higher at higher temperature where the fibers incorporate more oxidation derivatives, such as complexed carboxylate groups, which play a pivotal role in improving the adherence of fibers to the cement matrix. Such fiber/cement interfacial bonds contributed significantly to the excellent bridging effect of fibers, resistance to the cracks development and propagation, and to improvement of the post-crack material ductility. Consequently, the compressive toughness of the 85°-, 200°-, and 300°C-autoclaved foamed cements reinforced with 10 wt.% CMF was 2.4-, 2.9-, and 3.1-fold higher than for cement without the reinforcement. Additionally, the fibers not only increased steel-cement shear bond strength but more importantly significantly improved the resistance of this bond to a thermal shock (350°C heat followed by 25°C water cooling) allowing only 35% decrease in it after 7 thermal shock cycles vs. 64% strength decrease in the bond strength without fiber reinforcement.