عملکرد بتن خودمتراکم کم‌سیمان با استفاده از لجن سنگ به‌عنوان جایگزین ماسه

The production of sustainable and high-performance concrete has become a global necessity due to the increasing demand for construction materials and the significant environmental burden associated with cement manufacturing and natural aggregate extraction. In this research, self-compacting concrete (SCC) was developed by partially substituting natural sand with stone-cutting sludge derived from marble, granite, and travertine at three replacement levels: 10%, 15%, and 20%. A low-cement ternary binder system was adopted, consisting of 85% ground granulated blast furnace slag (GGBFS), 10% ordinary Portland cement (OPC), and 5% hydrated lime, to drastically reduce cement consumption and CO₂ emissions while maintaining adequate mechanical strength. The experimental program included both fresh and hardened concrete tests. Fresh properties such as slump flow diameter, T500 time, V-funnel flow, and segregation resistance were assessed to evaluate workability, viscosity, and stability in line with EFNARC guidelines. Hardened properties included compressive and flexural strength at 7 and 28 days. In addition to mechanical and rheological testing, durability aspects such as resistance to segregation and cohesion were qualitatively assessed. Life cycle assessment (LCA) was also conducted to quantify the environmental benefits of the proposed mixtures compared with conventional SCC made with OPC. By linking laboratory-scale performance with broader sustainability indicators, the study provides an integrated evaluation of technical feasibility and environmental compatibility. Results showed that 10% replacement of sand with any type of stone sludge, especially marble, enhanced flowability and viscosity while significantly improving resistance to segregation without increasing the dosage of superplasticizer. At 15% and 20% replacement levels, marble and travertine sludge maintained acceptable rheological and mechanical behavior, whereas granite sludge exhibited a negative influence, reducing workability and mechanical strength at higher dosages. The optimum replacement level was found at 10%, which yielded up to 5.9% improvement in compressive strength over the control. Flexural strength was unaffected at 10% and even increased with marble sludge, but noticeable reductions occurred at 15% and 20%, with marble again showing the least adverse effect compared to granite and travertine. From an environmental perspective, the use of the ternary binder drastically reduced the global warming potential (GWP), energy demand, and acidification potential relative to OPC-based SCC. The LCA results indicated that GWP decreased by as much as 71.9% compared to conventional mixtures. Moreover, replacing sand with stone sludge contributes directly to the circular economy by diverting industrial waste from landfills and natural water bodies, thereby reducing pollution and ecological degradation. Beyond numerical reductions in environmental indicators, the valorization of stone sludge alleviates waste disposal challenges, minimizes dust and runoff contamination, and preserves limited natural sand resources. These broader sustainability impacts demonstrate that the benefits of stone sludge utilization extend beyond concrete performance and can influence waste management strategies at the industrial scale. Overall, the study demonstrates that the synergy between partial sand substitution with marble, granite, and travertine sludge and the adoption of a low-cement ternary binder offers a promising pathway toward eco-efficient SCC. This approach not only enhances certain rheological and mechanical properties but also provides substantial environmental and economic benefits, making it a viable strategy for future sustainable construction practices.