Using recycled brick powder in slag based geopolymer foam cured at ambient temperature: strength, thermal stability and microstructure

To recycle waste clay bricks and alleviate the physical and mechanical performance degradation of slag-based geopolymer foam concrete (SGFC) in thermal exposure, the brick powder (BP) was utilized to prepare slag-brick powder based geopolymer foam. The thermal stability of SGFC was evaluated comprehensively by introducing the strength and volume loss rate, and surface crack area after thermal exposure. Additionally, the composition and transformation of the phases before and after fire were quantitatively characterized by XRD, TG-DSC and FTIR. The results showed that the addition of BP significantly could greatly improve the thermal stability of SGFC, subsequently alleviate the volume shrinkage and reduce surface cracks after thermal exposure. The reason was that the BP changed the reaction products of SGFC and the phase transitions during thermal exposure. Specifically, the brick powder introduced a new phase, yoshiokaite, and decreased the melting sintering temperature (sintering point) of SGFC in fire. The SGFC with 20 wt% brick powder exhibited the optimal comprehensive thermal stability after 800℃ thermal exposure: the surface crack area decreased by 21.00 %, and the volume shrinkage reduced by approximately 10 %, with a residual strength of 1.06 MPa. This study demonstrates that ambient cured geopolymer foams prepared with slag and BP can achieve excellent thermal stability under temperature over 800℃.