Novel selection of environment-friendly curing agents for thawing permafrost: Alkali-activated ground granulated blast-furnace slag

Abstract

Permafrost thawing deformation due to the climate warming has been continuously increasing in the Qinghai-Tibet Plateau, which may influence the stability of local infrastructures and cause frequent subgrade diseases. Although the effectiveness of cement has been certified to solidify thawed permafrost, the usage of cement is gradually limited due to its energy consumption and CO2 emissions. The alkali-activated ground granulated blast-furnace slag (GGBS), as waste by-products, has been widely used in the application of soil stabilization under normal temperature, but there exist few investigations on its application in cold regions, such as permafrost regions. The study aims to investigate the effectiveness of calcium carbide residue (CCR)-GGBS and NaOH-GGBS as curing agents to solidify thawing permafrost cured at low temperature. Simultaneously, the conventional Portland cement (PC) is also selected as the comparison. Laboratory tests, containing the unconfined compressive strength (UCS), pH, electron microscopy (SEM)/ energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests, were carried out to investigate the effect of different influence factors including alkali activator types, activator content, and curing time on the strength development. The experiment results showed that alkali-activated GGBS with the optimum activator content can effectively improve the strength of thawing permafrost at low temperature. Furthermore, on the basis of strength difference (ΔUCS) and strength growth rate (UCSgr), it demonstrates that the best approach to development strength is to combine 30% GGBS with 20% CCR or NaOH. The microstructure analysis showed that alkali-activated GGBS is conducive to the polymerization reaction, and the strength development is attributed to the formation of the dense skeleton structure. Finally, the efficacy of alkali-activated GGBS as an alternative and green curing agent to solidify thawing permafrost was confirmed based on the stabilization mechanism and analysis of environmental benefit.