The workability of the castables bonded with hydrated magnesium carboxylate–organic acid

Abstract This study modifies the hydration process of hydrated magnesium carboxylate (HMC) by organic acids to improve the workability of HMC‐bonded castables (HMCC), while comprehensively analyzing the effects of organic acids on the mechanical properties and thermal shock resistance of HMCC. Results demonstrate that lactic acid significantly increases the setting time and rheology of HMCC by 738% and 217.8%, respectively. This is due to lactic acid inhibiting HMC ionization and delaying hydration, as evidenced by hydration kinetics experiments. Furthermore, lactic acid could also reduce the degree of polymerization of HMC hydration products. Notably, lactic acid increases the cold modulus of rupture by 593.7%, 100%, and 95.7% at 500°C, 800°C, and 1100°C, respectively. This performance improvement is attributed to lactic acid's promotion of the sintering process of HMCC, possibly due to its effect on improving castable uniformity. However, lactic acid results in an 18.1% reduction in the green body strength, potentially due to the weakened three‐dimensional network structure of HMC hydration products. Additionally, lactic acid increases the residual strength ratio of HMCC by 4.3% and enhances crack propagation resistance ( R ‴) by 45%. These improvements result from an optimized microstructure, characterized by smaller, more uniformly distributed particles with regular shapes and tighter interparticle connections.