Characteristics of metakaolin-based geopolymer concrete for different mix design parameters

Geopolymer is emerging as a potential alternative material to the ordinary Portland cement (OPC) owing to its energy efficiency and environmental protection. However, the effect of the mix design parameters on the behavior of geopolymer concrete (GPC) produced using local metakaolin (MK) is not well established. This paper presents findings from a comprehensive experimental program to study the effect of various mix design parameters on the properties of fresh and hardened MK-based GPC. Seventeen mixes were cast in four groups to investigate the effect of four parameters, including sodium silicate to sodium hydroxide ratio, alkaline solids to MK ratio, aggregate content, and water to solids ratio on the properties of GPC. The investigated properties included workability, density (wet and dry), development of compressive strength with age, splitting tensile strength, ultrasonic pulse velocity, water absorption, and horizontal abrasion resistance. Besides, two reference OPC concrete mixes, equivalent to two MK-based geopolymer mixes, were tested for the sake of comparison. The test results were helpful in developing a better understanding of the behavior of MK-based GPC. Some useful models are proposed for predicting workability, splitting tensile strength, water absorption, and weight loss in abrasion for MK-based GPC. The test results were supplemented and confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analysis performed on some selected GPC mixes.