Freeze-thaw Performance and Microstructural Mechanisms of Hybrid OPC-Alkali Activation as a Route to Durable Red Mud-based Non-Fired Bricks

Abstract

This paper discusses the increasing issues of urbanization and industrialization by creating compressed non-fired solid waste bricks (CNFSWB) under 10 MPa uniaxial pressure and without heat treatment with red mud (RM), fly ash (FA), and silica fume (SF) as the main materials with less ordinary Portland cement (OPC) and alkali (NaOH) activation, providing an alternative construction material which is sustainable. Effects of combinations of OPC-NaOH on early-age and 28-day compressive strength were also systematically examined, as well as their freeze-thaw resistance in order to determine durability behavior under cyclic environmental factors. Findings indicate that cement hydration and alkali activation have a synergistic effect on mechanical performance, leading to enhancement of the dissolution of aluminosilicate phases and consequent formation of C–S–H, C–A–S–H and N–A–S–H gels. The specimens with a moderate level of NaOH dosage (8.4 g) had the highest 28-day compressive strength (52.24 MPa) and better freeze-thaw resistance, which showed that there is an optimal level of OPC content and alkali activation ratio, which is important in densifying the microstructure, mechanical strength and long-term stability. These results indicate the possibilities of using strategic blending of industrial solid wastes with controlled chemical activation in the production of sustainable, high performance, and durable non-fired bricks to be used in construction.