Effect of Varying Glass Powder Size on Performance of Cement Mortar: Microstructural and Compressive Strength Assessment at High Temperatures

This study employs fine glass powder as a partial replacement for ordinary Portland cement in order to better understand the complex effects of high temperature on the microstructure and compressive strength of cement mortar. The study aims to identify the optimal mix that maximizes the benefits of glass powder incorporation by experimenting with different glass powder sizes (38 µm, 53 µm, and 75 µm) and replacement rates (10%, 20%, and 30%). At 25oC, 200oC, 400oC, 600oC, and 800oC, mortars containing glass powder were subjected to compressive strength tests. Mortar samples were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Thermo Gravimetric analysis (TGA) to gain insight into their behavior at high temperatures. Mortar mixes containing 10% glass powder (38 µm size) performed best at temperatures below 400oC, with an average residual strength index value of 90.7% compared to 87.8% in the reference sample. The glass powder mortars with 10% and 20% replacement rates functioned better at higher temperatures of 800oC, losing just 52-57% of their strength as opposed to 72% in the control sample. The increased pozzolanic activity attributable to the addition of glass powder is shown by XRD and SEM analyses to account for the increased strength of mortar by consuming more portlandite (Ca(OH)2). TGA study has shown that at temperatures exceeding 400oC, to bermorite and other hydrated products become dehydrated, which may account for the strength reduction.