Preparation and properties of high-temperature-resistant grout using orthogonal tests

The properties of cement grout significantly deteriorate at high temperatures, making it unable to meet the demands for reinforcement in deep engineering projects. This study employed plastic polycarboxylic superplasticiser (PCS), ground granulated blast-furnace slag (GGBS), fly ash (FA) and silica fume (SF), using the orthogonal test design method, to improve the properties of cement at high temperatures. Laboratory tests, including viscosity, mechanical strength, stone rate and porosity, were carried out, and a comprehensive performance index was established to determine the optimal mix proportion. The results showed that the PCS significantly reduced the viscosity, enhanced compressive strength and decreased porosity, but also decreased the stone rate. GGBS could reduce the viscosity, improve compressive strength and decrease the stone rate, but it increased porosity. FA and SF could improve the compressive strength and stone rate, but impaired the pore structure and increased its viscosity. The viscosity of the new grout at 80°C was decreased by >90%, and the compressive strength improved by >180%, while the porosity was also slightly increased. The hydration of mineral admixtures generated calcium-poor calcium silicate hydrate gels and calcium aluminium silicate hydrate gels, which inhibited the decalcification effect of gels at high temperatures, while the morphology and size of the gels remained essentially unchanged.