Hybrid portland cement-slag-based geopolymer mortar: Strength, microstructural and environmental assessment

Abstract

The aim of the current work is to investigate the strength, microstructure, environmental and economic effects of hybrid ordinary portland cement (PC) and ground granulated blast-furnace slag (GGBS) based geopolymer mortar as an alternative to ordinary cement mortar. Eleven mixtures were prepared for this. In this regard, PC was blended with GGBS content of 0-90 wt% in these mixtures. The designed mortar samples were cured at ambient temperature (20 +/- 2 degrees C) to be more applicable in the construction industry, unlike most geopolymer productions and ordinary PC mortar samples were also produced to be comparable to the designed hybrid PC/ GGBS-based geopolymer mortars. The compressive strength (fc) development, ultrasonic pulse velocity (UPV), and dynamic modulus of elasticity (Edyn) values of these ten-hybrid PC/GGBS-based geopolymer mortars were compared with the designed ordinary PC mortar. The results indicated that the incorporation of 20 % PC with 80 % GGBS in the alkali-activated system had the best 28-day compressive strength value with 74.26 MPa, which was 91.07 % higher than that of the designed ordinary PC mortar. The techniques of scanning electron microscopy (SEM)-EDS, Fourier transform-infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to identify the microstructural changes caused by the use of ambient temperature cured hybrid 20 % cement-80 % GGBS based alkali-activated mortar. The relatively higher ratios of Ca/Al and Ca/Si compared to ordinary PC mortar proved the more excellent binding property of the C-A-S-H gel, and a denser microstructure was observed in the SEM results. The superior strength development of the hybrid 20 %cement-80 %GGBS alkaliactivated mortar was confirmed by the formation of highly cross-linked C-S-H and C-A-S-H gels due to the higher degree of polymerization and hydration. Additionally, the designed hybrid 20% cement-80 % GGBS geopolymer mortar presented significant environmental and economic benefits compared to those of ordinary PC mortar, with 32.6 % and 23.5 % lower CO2 emission and cost intensity values, respectively.