Impact of bauxite residue and fly ash on Portland cement hydration

Abstract

The use of by-products from industrial processes, such as bauxite residue (BR) and fly ash (FA), as SCMs with Portland cement is a strategy that promotes waste reuse and reduces cement production's environmental impact. Additionally, a ternary system fosters chemical interactions among materials, mitigating BR's harmful effects (leaching of hazardous elements and high alkalinity) without requiring energy-intensive processes. This study evaluates the influence of BR and FA on Portland cement hydration through three systems: a reference paste (cement only), two binary pastes (70% cement, 30% SCM), and a ternary paste (70% cement, 15% BR, and 15% FA). The hydration process was analyzed using isothermal calorimetry, XRD, and TGA. Results show SCMs accelerate hydration, shortening induction periods and increasing reaction rates. FA, with its high shape factor, enhances early hydration by facilitating hydrate precipitation, while BR contributes chemically, increasing Portlandite and chemically bound water. Both SCMs accelerate hydration through the filler effect due to their larger specific surface areas. These findings highlight the potential of ternary systems for the safe, sustainable application of SCMs in construction.