Performance of BFS-OPC-RSAC Ternary Composite Cementitious Anchoring Material

During tunnel construction in the southwestern region of China, it is common to traverse soft-rock geological areas. To minimize deformation after tunnel excavation, anchoring materials need to exhibit properties such as high strength, rapid setting, and slight expansion. Meanwhile, to address the high carbon emissions and cost issues associated with cement-based anchoring materials in tunnel construction, and in response to the national requirements for ecological construction and the 2030 carbon peak plan, we developed an environmentally friendly anchoring material based on blast-furnace slag (BFS)–ordinary portland cement (OPC)–rapid-hardening sulfoaluminate cement (RSAC) ternary system, using the theory of synergy. This study systematically investigated the effects of BFS, lithium carbonate, and united expansive agent (UEA) on the setting time, mechanical strength, and linear expansion of the OPC-RSAC binary system. Micromechanism analysis was conducted through hydration heat analysis, X-ray diffraction, and scanning electron microscopy. The pullout model tests on the anchoring body verified the bonding performance and engineering application potential of the new material. The experimental results indicate that the optimal mix ratio, determined through range analysis of orthogonal test data, is 100 parts OPC-RSAC binary cement (with a ratio of 2∶8), 10% slag powder, 0.1% lithium carbonate, and 2% UEA expansion agent. The 24-h compressive strength is 34.85 MPa, which is an increase of 0.26 MPa compared to RSAC special cement. The initial setting time is 1.74 min, which is 47% faster, with a cost reduction of 30% and a threefold increase in hydration heat within 3 h. Microanalysis shows that the BFS-OPC-RSAC ternary cement–based environmentally friendly material exhibits sufficient hydration reactions, with ettringite crystals interwoven with calcium silicate hydrate (CSH) gel, calcium hydroxide (CH), and calcium aluminate hydrate (CAH) gels to form a dense and stable network. The filling effect of slag particles further densifies the material. Compared to RSAC, the higher aluminum and lower calcium content in slag powder enhances early strength hydration within a certain range, promoting the formation of ettringite and hydrated metal oxides, thereby improving the expansion rate and mechanical strength of the anchoring material. Based on synergy theory, BFS-OPC-RSAC material uses RSAC as the primary base material, fully utilizes BFS waste resources, and combines low-cost OPC materials, reducing the production cost of similar anchoring materials by 30% and lowering carbon emissions. This promotes the green and sustainable development of cement materials.