Enhancing the mechanical and thermal properties of geopolymers prepared by refractory brick dust: An investigation into optimal mix ratios and curing conditions

Abstract

This study proposes the development of a novel geopolymer by investigating the feasibility of using refractory brick dust (RBD), a waste product from brick manufacturing. The focus was on exploring the trade-off between waste incorporation and high-temperature resistance in geopolymer pastes. Throughout the experiments, the NaOH solution concentration was consistently maintained at 10 M. The primary goal was to examine how varying the ratios of Na2SiO3/NaOH (NS/NH) and RBD/alkaline activator (AS) on the geopolymers’ characteristics. A series of meticulous tests were conducted using various curing methods, ranging from room temperature to high temperatures between 100 °C and 140 °C, with curing times extending up to 72 h. It was observed that geopolymers exhibit the highest compressive strength after being precured at 100 °C for 72 h, achieving a maximum compressive strength of 15.40 MPa. SEM microstructure analysis revealed a correlation between the curing regime, material density and porosity. Specifically, at 140 °C, the data indicated that more porous structures have lower compressive strength. Geopolymers exhibited good mechanical properties at low curing temperatures, but exposure to temperatures above 1200 °C resulted in significant deterioration. For example, Mix 3.0RBD2.0, with a higher RBD/AS and NS/NH ratio, experienced the greatest compressive strength loss of 61.3% and a mass loss of 15.5% at these elevated temperatures. Interestingly, a geopolymer composition of 2.0RBD0.5 showed high-temperature-induced physical changes that might alter its strength and stability, yet it retained its overall structure. This study provides an in-depth explanation of the importance of optimising waste utilization to develop resilient geopolymer materials. It demonstrates how the composition – specifically, a Si/Al ratio of approximately 2.26, which is preferred based on EDS results – along with the curing methods, significantly influences the performance and high-temperature resistance of geopolymers.