Experimental evaluation of alkali-activated and portland cement-based mortars prepared using waste glass powder in replacement of fly ash

The decreasing trend in coal fly ash production has led to a rapidly growing interest in finding alternative materials to replace fly ash in concrete. In this study, the use of glass powder to replace fly ash in concrete was investigated. The performance of portland cement and alkali-activated slag-based mortars containing fly ash (class F) or glass powder (aluminosilicate-based) was evaluated via a series of experiments, including fresh, physical, mechanical, and restrained cracking tests. Notably, a customized restrained shrinkage test was used to investigate the cracking potential. Results showed that the ultra-fine glass powder performed differently in the two binding systems. In the portland cement system, the use of glass powder yielded higher concrete mechanical performance compared to the concrete containing fly ash, while the opposite conclusion was obtained for the alkali-activated system. Comparing the alkali-activated system with the portland cement system, the alkali-activated materials with either fly ash or glass powder had higher free shrinkage and developed cracks much earlier under the restrained drying shrinkage. However, the alkali-activated materials maintained a high level of strain in the steel ring, which was primarily attributed to the development of multiple cracks and their different bonding at the mortar and steel interface.