Effect of high temperature on morphologies of fibers and mechanical properties of multi-scale fiber reinforced cement-based composites

By experimental research on the steel- polyvinyl alcohol (PVA) fibers- calcium carbonate whisker (CW) multi scale fiber-reinforced cement-based composites (MSFRC) after exposure of temperatures up to 900 degrees C, the flexural, compressive strength, and microstructures of multi scale fibers were investigated in this paper. The incorporation of steel-PVA fibers-CW can effectively improve the flexural and compressive strength of mortar after elevated temperatures. Compared with normal concrete, hybrid fiber reactive powder concrete (RPC) and engineered cement-based composites (ECC), the MSFRC present better capacity of high temperature resistance. The flexural and compressive strength increase first and then decrease with the increasing temperature, and the critical temperatures are 200 degrees C and 400 degrees C respectively. Models for describing the relationship between strength, CW content and temperature are proposed. The good high temperature resistance of MSFRC relates to the hybrid effect of melt of PVA fiber, good heat conduction of steel, and the phase transformation from aragonite to calcite of CW. Comprehensive morphology observations by digital camera and optical microscope are simple and useful way to evaluate the changes of fibers and CW at high temperature. This research is very beneficial for the applications of MSFRC in construction project with fire risk. (C) 2020 Elsevier Ltd. All rights reserved.