Synthesis Of Fly Ash—metakaolin Based Straw-geopolymer Building Insulation Materials And High Temperature Performance

Geopolymers possess many excellent properties for its unique inorganic three-dimensional network structure and have also shown potential applications in many areas.Metakaolin based systems are regarded as an‘ideal'system,but more researchers agree that the utilization of waste precursor materials in geopolymer synthesis,such as fly ash.This will enhance both the environmental and economic credentials of the end product,and in many cases,improves the performance.Comprehensive utilization of the fly ash of industrial by-product and straw fiber of agricultural crops in the geopolymer provide a new way for reuse of them and put forward a new idea for thermal properties of building materials.This paper presents a study on the mechanical and physical properties and high temperature performance of a range of geopolymers were synthesized from four alkali solution with different components in order to obtain the optimal design mixture and assess their suitability for high temperature applications.The results showed that geopolymer containing 15%fly ash and 4%straw fiber exhibited the best mechanical and physical properties,and the particle nature of solid materials have an important effect on the physical properties of geopolymer,such as particle morphology and fineness.The workability of geopolymer in fresh state varied with the increasing of fly ash content in synthesis test.It was found that the Na₂O/SiO₂ ratio in the alkali solution and liquid to solid ratio?L/S?strongly influenced the formation of geopolymer gel and the geopolymeric reaction extent.Geopolymers derived from fly ash and metakaolin have the representativeinhomogeneousstructurewithunreactedand partially-reacted solid particles scattered within geopolymer gels.The matrix was visibly porous and remained the amorphous microstructure of metakaolin.The microstructure evolution,pore size distribution,thermal behavior and phase changes of geopolymer before and after 800\1000?were measured by scanning electron microscopy?SEM?,Mercury intrusion porosimetry?MIP?,thermoanalysis?TG-DSC?,X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?analysis.Geopolymer exhibited obvious apparent physical change with color,size and cracks,the microstructure of matrix while the nature and content of gel had a significant change,which caused the degradation of compressive strength,density and porosity.It was worth highlighting that the category of pore changed mesopore to macropore.Although the geopolymer experienced a significant continuous weight loss,but still remain a good thermal performance and thermal stability after high temperature exposure.