Stiffness and strength properties of spent coffee grounds-recycled glass geopolymers

Spent coffee ground (CG) geopolymers are novel cementitious materials, which utilise industrial wastes such as fly ash and ground granulated blast furnace slag as precursors. Several past studies have investigated the strength development of these recycled products, and established their suitability as road subgrade construction materials. This paper evaluates the incorporation of recycled glass (RG) into the CG geopolymer blend to further enhance the strength of the mix, as well as investigates the resilient modulus (MR) properties of CG+RG. Repeat Load Triaxial (RLT) tests were undertaken to investigate the flexibility and deformation pattern of CG+RG geopolymer subgrades under repeated traffic loading. The relationship between RG replacement ratio and material stiffness was furthermore established. California Bearing Ratio (CBR) tests on the CG+RG geopolymers indicate that the CBR value of these materials exceeds those of naturally occurring subgrade materials. The CBR and MR values of the CG+RG geopolymers are essential design parameters for the usage of this novel construction material in subgrades.