High temperature performance of mortars containing fine glass powders

This paper reports on the high-temperature performance of cementitious materials containing fine glass powders (GP) as a partial replacement for ordinary Portland cement. Various mixes were prepared in which cement was replaced by GP in 3 different proportions, i.e., 5 wt%, 10 wt% and 20 wt%. Compressive strength tests were carried out at various temperatures (20, 500 and 800 °C) for mortars containing GP. To have a fundamental understanding of the material behaviour at elevated temperatures, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal strain tests were conducted on the corresponding pastes. Results show two distinct temperature ranges regarding effects of GP on the strength of mortars. At temperatures below 500 °C, a mortar mix with 20% GP (Type I) showed the best performance with an average strength loss of 15% compared to 33% strength loss in reference samples. The XRD analysis shows a reduction in the calcium hydroxide (CH) content in mortars with GP. At temperatures below 500 °C, the strength loss is believed to be due to the dehydration of CH. Therefore, the low strength loss of mortars with GP is associated with their low CH content. In the temperature range of 500-800 °C, the average strength loss was 56% in the GP mortar and 35% in the reference mortar. The thermal shrinkage of GP paste is higher than the reference paste. This can be attributed to softening of glasses. The higher strength loss of GP mortar is due to the higher thermal incompatibility which arises because the paste shrinks while sand particles expand.