Thermal and Mechanical Properties of Geopolymers Exposed to High Temperature: A Literature Review

Abstract

Geopolymers are prepared by alkali solution-activated natural minerals or industrial waste materials, which have been widely used as new sustainable building and construction materials for their excellent thermal and mechanical properties. The thermal and mechanical properties of geopolymers at high temperature have attracted great attention from many researchers. However, there are few systematic works concerning these two issues. Therefore, this work reviewed the thermal and mechanical behaviors of geopolymers at high temperature. Firstly, the thermal properties of geopolymers in terms of mass loss, thermal expansion, and thermal conductivity after high temperature were explained. Secondly, the mechanical properties of residual compressive strength and stress-strain relationship of fly ash geopolymers and metakaolin geopolymers after high temperature were analyzed. Finally, the microstructure and mineralogical characteristics of geopolymers upon heating were interpreted according to the changes of microstructures and compositions. The results show that the thermal properties of geopolymers are superior to cement concrete. The geopolymers possess few mass loss and a low expansion ratio and thermal conductivity at high temperature. The thermal and mechanical properties of the geopolymers are usually closely related to the raw materials and the constituents of the geopolymers. Preparation and testing conditions can affect the mechanical properties of the geopolymers. The stress-strain curves of geopolymer are changed by the composition of geopolymers and the high temperature. The silicon-type fillers not only improve the thermal expansion of the geopolymers but also enhance mechanical properties of the geopolymers. But, they do not contribute to reducing the thermal conductivity. the different raw materials, aluminosilicate precursor and reinforcement materials, result in different geopolymer damage during the heating. However, phase transitions can occur during the process of heating regardless of the raw materials. The additional performance enhancements can be achieved by optimizing the paste formulation, adjusting the inner structure, changing the alkali type, and incorporating reinforcements.

Study on Concrete Deterioration in Different NaCl-Na2SO4 Solutions and the Mechanism of Cl− Diffusion

“…Najjar [ 33 ] found that the deterioration of concrete’s mechanical properties after sulfate corrosion was mainly due to reactions between SO 4 2 − and the aluminates (e.g., tricalcium aluminate, tetra-aluminate, and calcium monothioaluminate) of cement hydration products in concrete to produce ettringite (Aft) [ 34 , 35 , 36 ]. Additionally, sulfate corrosion tests revealed that the corrosion product Aft could be distributed throughout the ITZ and the internal concrete pores [ 37 ]. After Na 2 SO 4 eroded concrete under a dry-wet cycle, the evolution of Aft was studied via thermal difference-thermogravimetry [ 38 ].…”

Comparison of the Thermal Properties of Geopolymer and Modified Gypsum

“…The researchers obtained thermal conductivity of the foamed geopolymers at 0.12 W/(m·K) in the case of a density of 0.36 kg/m 3 [ 30 ], and 0.10 W/(m·K) in the case of a density of 0.55 kg/m 3 [ 31 ]. The authors of paper [ 32 ] improved the thermal conductivity of geopolymer by simultaneously foaming it and introducing a hollow glass bead (HGB) into it. The products received in this way had a low density, and at the same time, a low value of the thermal conductivity coefficient.…”

Process Design for a Production of Sustainable Materials from Post-Production Clay

“…During the annealing of the samples above 1000 °C, a glass-like structure appeared on the surface of the material, and pore pressure grew gradually as a result of heat transfer and gas evaporation. When the vapor pressure exceeds the limit of the matrix, intensive thermal cracking and spalling, the pore structure collapsing, and further contraction could be observed [ 38 ].…”