Glass powder as a partial precursor in Portland cement and alkali-activated slag mortar: A comprehensive comparative study

Abstract

Prior studies were conducted in an isolated manner for the use of glass powder (GP) either as ordinary Portland cement (OPC) replacement material in blended cement or as a precursor in AAM material. There was no reported literature that made a direct comparison on the properties of blended cement and AAM containing GP with an equivalent mix composition. The present study was aimed to evaluate and compare the effects of GP as a partial precursor on properties of both OPC and alkali-activated slag (AAS) mortars. For this purpose, cement and ground granulated blast furnace slag (GGBFS) was partially replaced with 10%, 20%, 30%, and 40% (by weight) GP in OPC and AAS mortars, respectively. The mortar mixes were prepared for a fixed water-to-solid (W/S) ratio to make them equivalent. The evaluation was carried out on the workability, mechanical strength, water absorption, alkali-silica reaction (ASR) response and ecological analysis of the mortar. According to the test results, the flow of the fresh mortar increased monotonically with GP content, and AAS mortars showed a higher flow value than OPC mortars. Based on the mechanical properties, the optimum GP content in OPC and AAS mortars was found to be 20% and 30% by the total weight of the binder, respectively. In general, the inclusion of GP was more effective in enhancing the strength properties of AAS mortars as compared to OPC counterparts. Furthermore, the use of GP led to a systematic increase in the water absorption of mixes due to moisture instability of the sodium silicate gel produced by GP activation. According to the results of SEM analysis, AAS mortars showed a higher degree of micro-cracking, which resulted in higher water absorption and a lower flexural strength as compared to OPC mortars. Also, the incorporation of GP densified the pore system of the paste. The potential of ASR was evaluated via the accelerated mortar bar test. The OPC mortars showed up to a 55% reduction in the ASR expansion at 40% GP content. The AAS mortars, on the other hand, showed shrinkage during the first days and then started to show expansion with increasing GP content, which was beneficial as it compensated the shrinkage. The ecological analysis of mixes revealed that the carbon footprint of AAS mortars was about 60% lower than that of OPC counterpart mixes, and the use of GP reduced the CO2 emissions and energy demand of mixes.