Rock fracturing using soundless cracking agents produced from freshwater sludge and carbide sludge

Rock fracturing plays a crucial role in mining, civil engineering, and infrastructure development; however, conventional techniques such as blasting often involve the release of uncontrollable energy, resulting in adverse environmental and safety impacts. To address these limitations, soundless cracking agents (SCAs) have emerged as a promising non-explosive alternative. Nevertheless, conventional SCAs production relies heavily on non-renewable resources and therefore lacks sustainability. In this context, this study explored using freshwater sludge (FS), carbide sludge (CS), and gypsum (Gy) for sustainable synthesis of SCAs, addressing the limited research on their effectiveness in rock fracturing applications. This strategy is based on harnessing the aluminum (Al) and sulfur (S) richness of FS, the Ca abundance in CS, and the supplemental S provided by Gy to formulate Ca-Al-S system-based SCAs (FS-CS-Gy SCAs). FS-CS-Gy SCAs with varying Ca:Al:S ratios were synthesized and tested for expansive pressure in a steel mold under different water contents to determine the optimal formulation and curing conditions. Chemical and microstructural analyses were performed to elucidate the hydration mechanisms. Granite fracturing experiments were conducted to validate the practical applicability of the developed SCAs. The results indicated that the optimal formulation, with a CaO/(CaO+Al 2 O 3 +SO 3 ) ratio of 93.6% and a water content of 30%, achieved a maximum expansive pressure of approximately 19.17 MPa after hydration for 4 h. The primary hydration products, ettringite and portlandite, govern the expansive behavior and contribute to internal pressure through volumetric crystallization under confined conditions. Under these optimized conditions, the FS-CS-Gy SCAs successfully fractured granite in the laboratory.