Thermal shock resistance properties of refractory castables bonded with a CaO-free binder

Abstract

The potential of hydratable magnesium carboxylate compounds (HMC) combined with MgO powder as a binder of castables was evaluated. The green mechanical and thermal shock resistance properties of HMC-bonded castables (HMCC) and calcium aluminate cement-bonded castables (CACC) were compared. The green mechanical strength of the HMCC reached the mechanical strength of the CACC. The residual strength ratio of the HMCC is higher than that of the CACC and increases first and then decreases with the MgO/HMC ratio. The residual strength ratio's highest value is 56.8% (MgO/HMC ratio is 2/3), which is 1.8 times that of CACC. Interestingly, the microcracks in the HMCC after thermal shock are radial, while those in CACC are linear. The micromechanical testing on the matrix of castables after thermal shock showed that the ratio of the energy for crack initiation to the work of fracture of the HMCC is lower than that of the CACC, but its fracture toughness is higher than that of the CACC, indicating that the microcracks in the HMCC initiate easily but propagate hardly.