The effect of hydroxides on the workability of the castables bonded with hydrated magnesium carboxylate

Abstract This study investigates the effect of Al(OH) 3 , Mg(OH) 2 , or Ca(OH) 2 on the performance of HMC‐bonded castables (HMCC), aiming to synergistically improve the workability and medium‐temperature mechanical properties of HMCC. The results indicate that Al(OH) 3 synergistically improves the medium‐temperature mechanical properties, workability, and thermal shock resistance of HMCC. Specifically, Al(OH) 3 prolonged the setting time from 21 to 27 min, whereas Mg(OH) 2 and Ca(OH) 2 reduced it to 19 and 7 min, respectively, due to the low solubility of aluminum citrate formed by Al(OH) 3 , which inhibits HMCC ionization. Additionally, Al(OH) 3 increases the aspect ratio of hydration products, resulting in a 29.8% decrease in flowability compared with the control sample N. The addition of these compounds significantly improves medium‐temperature mechanical properties, with Al(OH) 3 increasing the cold modulus of rupture from .17 to 1.74 MPa at 500°C and from 1.24 to 2.51 MPa at 800°C. Moreover, Al(OH) 3 improves the the residual strength ratio after thermal shock from 26.16% to 28.70%, unlike Ca(OH) 2 , which lowers it to 19.02%, by enhancing resistance to microcrack propagation.