Mechanical Characteristics of GGBFS/FA-Based Geopolymer Concrete and Its Environmental Impact

Abstract

Geopolymer concrete is considered to be one of the best alternatives to portland cement concrete, partially or totally, not only because it decreases the CO2 emissions released during ordinary portland cement (OPC) production, but also due to its acceptable mechanical and durability properties. This study presents the experimental results of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) on fresh and hardened geopolymer concrete properties, considering the effects of several parameters such as binder type and content, alkaline binder ratio, molarity, Si/OH ratio, cement ratio in the binder, water addition, and curing temperature. These parameters were studied over a wider range than in previous research using local by-product waste to determine the validity of the additives for massive production of geopolymer concrete. The studied properties were the slump, 7- and 28-day cube compressive strength, tensile strength, and modulus of elasticity. For all studied mixes, the increase of the binder content, sodium hydroxide concentration, and cement ratio of the binder enhanced the concrete properties, whereas the increase of the alkaline binder ratio, Si/OH ratio in the solution, and additional water decreased the concrete properties. An increase of curing temperature from 30°C to 90°C improved the fly ash–based geopolymer concrete mechanical properties by an average of 35%; in contrast, the same increase in temperature decreased the concrete mechanical properties of GGBFS-based geopolymer concrete by an average of 22%. Equations for tensile strength and modulus of elasticity in terms of compressive strength were proposed and were compared with equations from standards and equations previously proposed in the literature. Finally, the environmental impact in terms of CO2 emissions was found to be on average 90% less than that of conventional concrete of the same grade.