Microstructure and residual strengths of limestone cement rendering mortars exposed to elevated temperatures

Purpose Portland-limestone cement (PLC) is a low-carbon, green alternative binder that can substitute for ordinary Portland cement (OPC) to support the development of eco-friendly infrastructure solutions. The building's energy consumption and strength retention efficiency can be improved by effectively enhancing the cementitious matrix properties of the rendering materials. Design/methodology/approach In this study, the residual mechanical strengths and microstructure of OPC and PLC mortars before and after exposure to elevated temperatures of up to 800 °C were experimentally investigated. Tested specimens were prepared using 0%, 5%, 10% and 15 wt.% of limestone as a replacement for OPC. The fire-resistance performance of the prepared rendering mixtures was evaluated through their residual strengths, X-ray diffraction, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Findings Based on the results, the mechanical properties of all mortars improved at 250 °C, due to internal autoclaving and pore pressure effects. At 800 °C, the major phases observed in OPC and PLC mortars were calcium silicate and quartz. Large wollastonite and gehlenite crystalline phases were observed in PLC mortars; thus, the matrix structure was severely damaged, and this damage was more pronounced in PLC mortars. Originality/value Several studies have concentrated on this area, and numerous investigations into the fire-resistance performances of cement-based mortars have been reported. Nevertheless, limited investigations focused have focused on the residual strengths of rendering mortars made with PLC as a sustainable alternative to Portland cement; and therefore, have not been acknowledged to date.