Uncover the thermal behavior of geopolymer: insights from in-situ high temperature exposure
Y. Luo, K.M. Klima, Stefan Melzer, H.J.H. Brouwers, Qingliang Yu
Abstract
The understanding of geopolymers' behavior at elevated temperatures is lacking due to the most focuses on post-situ research, leading to unsubstantiated expectations of in-situ thermal performance. This work systematically investigates the in-situ thermal behavior of geopolymers, including phase changes, deformation, and mechanical performance, following a comparison between in-situ and ex-situ properties. The results reveal a notable discrepancy between the in-situ and ex-situ thermal performance of geopolymers. During heating, geopolymers shift from a brittle to a ductile state by physicochemical transformation, facilitating accommodation of thermal incompatibilities. As we observed, the in-situ mechanical strength and creep strain increase until partial melting, with higher Na 2 O% accelerating melting of geopolymer. During cooling, geopolymers undergo matrix shrinkage and cracking, which impairs ex-situ performance. A denser matrix provides superior in-situ strength, while its high stiffness negatively impacts structural integrity during cooling, further reducing residual strength. These findings highlight the limitations of ex-situ experiments in estimating high-temperature performance of geopolymers. To accurately predict the in-situ thermal performance, future ex-situ research must account for partial melting during heating and deterioration induced by cooling.