Investigation of the density, ultrasonic pulse velocity and strength properties of metakaolin based geopolymer mortars

Abstract. Ordinary Portland Cement (OPC) remains a cornerstone of construction, but its production carries a significant environmental burden due to greenhouse gas emissions. This paper investigates Metakaolin-based geopolymer mortar (GPM) as a promising replacement for OPC mortars, focusing on its potential for reduced environmental impact. The study explores the influence of two main factors on the properties of geopolymer mortar: the Alkaline to Metakaolin ratio (A/M) and the Sodium Silicate to Sodium Hydroxide solution ratio (SS/SH). The molarity of sodium hydroxide was fixed at 16 for all samples, and the curing temperature was maintained at 60°C for 24 hours after demolding. The effect of these variations on the unit weight, ultrasonic pulse velocity, and compressive strength of the geopolymer mortar was evaluated. Notably, geopolymer mortars have been shown to exhibit compressive strengths exceeding those of traditional OPC mortars. The investigation focuses on the interplay between A/M and SS/SH ratios. A higher A/M ratio, with a higher amount of alkaline activator in the mix, can enhance the mechanical properties of geopolymer mortars. Moreover, the additional alkalinity promotes further geopolymerization and the formation of crystalline materials within the geopolymer structure, ultimately leading to improved strength. However, maintaining a controlled amount of silica is crucial. While sodium silicate is a necessary component of the activator solution, an excessive amount of soluble silicate can hinder the formation of these geopolymer mortars for achieving desired mechanical properties and durability while contributing to the development of more sustainable construction materials. The findings will highlight the delicate balance between the A/M and SS/SH ratios for maximizing the potential of geopolymer mortars as a viable and environmentally friendly alternative to traditional cement-based materials.