Mechanical properties and microstructure of red mud-coal metakaolin geopolymer concrete based on orthogonal tests

Abstract

Red mud, an industrial solid waste, can be used as a raw material for geopolymer concrete to reduce its environmental damage and achieve resource utilization. Nonetheless, the performance of red mud-based geopolymer concrete is influenced by various factors, and its overall sustainability remains to be comprehensively evaluated, limiting its widespread application. For this reason, this study systematically investigated the effects of water-binder ratio, aggregate-binder ratio, curing conditions, and Na2O/H2O on the water absorption, mechanical properties, and efflorescence degree of geopolymer concrete using Taguchi's orthogonal method. The optimal mixture for maximization of mechanical properties was determined using Design-Expert software. Subsequently, the microscopic properties of the samples were evaluated. In addition, an AHP-CRITIC-TOPSIS model was used to construct a sustainable assessment framework for geopolymer concrete including environmental, social, and economic indicators. The results indicated that the water-binder ratio is the main influencing factor. Excessive water increases the length of interfacial transition zone, coarsens the pore structure, and hinders the condensation process, leading to a degradation of material properties. In terms of sustainability, both M30 and M40 grade geopolymer concretes obtained significantly higher scores than cement concrete, and therefore it is considered a greener alternative.