Strength and microscopic mechanism analysis of CFBCA-based geopolymer-Pisha sandstone cement composite soil

Solidification of soil mass by geopolymer is a novel technology that can be used to prevent soil and water loss in the Pisha sandstone area of the middle reaches of the Yellow River. In this paper, to realize the effective utilization of a large number of loose Pisha sandstone and circulating fluidized bed combustion fly ash by adding combustion fly ash into Pisha sandstone cement-soil by alkali excitation, we prepared CFBCA-based geopolymer-Pisha sandstone cement composite soil, which is often used in agricultural engineering. The results show that the content of (C, N)-A-S-H gel in composite soil is affected by alkali equivalent and alkali excitation temperature, while the content is the main factor affecting the strength of composite soil. However, (C, N)-A-S-H gel will gradually transform into chabazite (gmelinite) crystal in a high-alkali environment, which will eventually lead to expansion and cracking occurring in the samples. When the alkali excitation temperature is 20 °C, and the alkali equivalent is 5%, the CFBCA-based geopolymer-Pisha sandstone cement composite soil is the optimal physicochemical reaction condition. At this time, the strength of the composite soil is 6.85 MPa; the porosity is 23.88%; and the proportion of internal micro-pores is 16.32%. The results of this study can provide a theoretical basis for the practical application of CFBCA-based geopolymer-Pisha sandstone cement composite soil, and also provide a scientific basis for the local resource utilization of Pisha sandstone and bed combustion fly ash.