Fracture behavior of Al2O3–SiO2 castables by the wedge splitting test and digital image correlation technique

Abstract The elucidation of fracture mechanisms is helpful for the optimization and design of toughness and microstructure of refractories. Fracture behavior of ultra-low cement bonded Al2O3–SiO2 castables was researched using the wedge splitting test coupled with digital image correlation technique (WST-DIC). Britleness of Al2O3–SiO2 castables is reduced by introducing andalusite aggregates into the castables. The characteristic length LCH, a parameter used to assess flexiblity of materials, was observed to reach 287.2 mm in andalusite-containing Al2O3–SiO2 castables, more than 5 times that of reference castables. Microcracks toughening is the main toughening mechanisms for flexibility improvement of the Al2O3–SiO2 castables containing andalusite. Microcrack network in microstructure of the Al2O3–SiO2 castables could be designed by exploiting the volume expansion caused by mullitization of andalusite and the the coefficient of thermal expansion (CTE) mismatch between the andalusite aggregate and the matrix. Unlike andalusite-free castables, castables containing andalusite possess a distinct fracture process zone (FPZ), the crack branching and deflection phenomena can be observed around the main crack during the fracture process, which leads to the prolong of the crack propagation path, the increase of the dissipation energy during the fracture, and the enhancement of resistance to crack propagation.