Understanding the thermal behavior of geopolymeric composites designed by packing model

The interaction between geopolymer binder and aggregates has a significant impact on thermal performance, which however still lacks sufficient understanding. In this study, a novel approach for designing high temperature resistant geopolymer composites is introduced. The microstructural-thermophysical properties and heat transfer pattern of the developed geopolymer composites are investigated and further linked to the progressive evolution up to 800 °C. Results reveal that the optimized packing contributes to a significantly high porosity from 48.6% to 52.8% and large moisture permeability in lightweight aggregate incorporated geopolymer (LWAG). A much lower thermal conductivity but comparable mechanical strength is achieved in LWAG as compared to sand aggregate incorporated geopolymer (SAG). At elevated temperatures, sand incorporation results in a fast heat transfer, and lightweight aggregates lead to a large temperature gradient within geopolymer composites. Compared to SAG, LWAGs show a lessened microstructural degradation with noticeable strength gain at 800 °C. Increasing the distribution modulus from 0.2 to 0.3 eases the thermal deterioration thanks to the decreased temperature gain rate and thermal diffusivity, resulting in low thermal shrinkage and high residual strength.