Development and Characterization of Cement-Based Grout for Fracture Grouting under Subzero Temperature Conditions

Abstract Highway infrastructure in the permafrost regions of the Qinghai–Tibet Plateau frequently experiences structural deterioration, creating a pressing need for trenchless rehabilitation through grouting. Traditional cement-based grouts exhibit severe strength loss and poor freeze–thaw resistance at subzero temperatures, limiting their field applicability. In this study, a customized cement-based grout was formulated for fracture grouting at −3°C, incorporating ordinary portland cement, sulphoaluminate cement (SAC), polycarboxylate ether (PCE) superplasticizer, defoamer, and calcium chloride (CaCl 2 ). The grout was systematically evaluated for flowability, initial setting time, bleeding rate, unconfined compressive strength (UCS), and freeze–thaw resistance. A combination of orthogonal testing, range analysis, and multiple linear regression was used to quantify the influence of each mix variable. The optimal composition was identified as 20% SAC proportion, a water–cement ratio of 0.6, 0.5% PCE content, and 0.3% defoamer content. Under these conditions, the grout reached a 28-day UCS of 16.17 MPa at −3°C and maintained 84.3% of its strength after 25 freeze–thaw cycles. Microscopic analyses further revealed that early hydration of SAC formed a dense microstructure dominated by needlelike ettringite (AFt). AFt dissolution–recrystallization produced reprecipitated AFt that partially hindered water migration, thereby mitigating freeze–thaw degradation rather than acting as a strengthening phase. Furthermore, the defoamer contributed to a more uniform pore structure, reducing freeze–thaw damage and improving durability. By limiting SAC to 20% of the binder while maintaining high subzero strength and freeze–thaw resistance, this study not only proposes a cost-effective solution for trenchless repair of highway foundations in cold regions but also establishes a rational design approach for high-performance cementitious materials used in extreme thermal environments.