Development and Mechanical Performance of Sustainable Geopolymer Concrete

Abstract

Concrete production has always been a main source of carbon dioxide (CO2) emissions. These emissions come mainly from Ordinary Portland Cement (OPC), which releases an average of 0.83 tons of CO2 /t. Researchers have been trying to find a suitable substitute for the OPC as a binding material in concrete to meet sustainability requirements. Therefore, this study focuses on developing and evaluating sustainable geopolymer concrete. Three cementitious materials, Class F fly ash, ground granulated blast furnace slag (GGBS), and silica fume, were used with different combinations to replace all cement in the mix. A 10 M sodium hydroxide solution was prepared and used to activate the cementitious materials and form geopolymer paste. Seven different concrete mixes were developed and analyzed in terms of strength, durability, microstructural performance, and carbon footprint with the aim of choosing the geopolymer concrete mix with the best performance. A total of 102 concrete samples, including cubes, beams, and cylinders were casted and tested for compressive strength, tensile strength, flexural strength, and modulus of elasticity. A durability test was performed on the geopolymer concrete specimens using rapid chloride penetration test. A microstructural analysis was also performed on the specimens using scanning electron microscope (SEM) coupled with energy dispersive X-ray spectra (EDS) to evaluate the geopolymer concrete microstructure. The experimental results of geopolymer concrete were compared with a control mix that had 100% OPC. Results showed good performance of geopolymer concrete with 100% replacement of cement by GGBS in compressive strength, flexural strength, tensile strength, and chloride penetration tests. It showed a compressive strength of 36 MPa at 28 days without the need for heat curing, and a tensile strength that was higher than the control mix by 12%. SEM images showed high compactness and no cracks in the ambient cured specimens of the mix with 100% GGBS, and the EDS images showed high traces of both alumino-silicate and calcium silicate gels responsible for strength gain in geopolymer concrete. Furthermore, analysis of the concrete mixes showed that the use of geopolymer concrete has the potential to decrease the carbon footprint of concrete production for up to 60%.