Sustainable Reuse of Sand Hydrocyclone Washing Wastes (SHWW): A Case study on Flowable Fills Applications in Coimbatore

The circular economy promotes sustainability by recycling waste and byproducts, offering an alternative to the conventional linear "take-makeconsume-dispose" model. Achieving Sustainable Development Goals (SDGs) in the building sector requires the adoption of sustainable construction materials, exploring the possibilities for recycling wastes from urban domestic and industrial sectors. The granite quarries in India generate approximately 68 million tonnes of mining products annually, of which a significant portion is discarded as Sand Hydrocyclone Washing Wastes (SHWW), being unsuitable for construction works due to poor strength and workability. The present study investigates a confirmatory approach for recycling SHWW as an innovative flowable fill, also known as Controlled Low Strength Material (CLSM). An optimum mixture ratio is arrived for the CLSM from the silt fraction obtained from a sand mining unit in Coimbatore, India along with fly ash (15%) based on laboratory-scale batch tests. The CLSM is evaluated for its flowability, stiffening time, and strength properties in both fresh and hardened states in compliance with national and international standards. The results indicate that an optimized CLSM can achieve about 200 mm of flowability and 0.7 to 1.12 MPa of compressive strength (for 28 days curing) by adjusting the fly ash-tocement ratio. Additionally, pilot-scale tests were conducted by constructing contour bunds to manage erosion in sloped terrains. Based on the strength and durability of the prepared CLSM, it is recommended for backfilling and contour bonding applications. The proposed approach demonstrates that SHWW can be effectively repurposed into durable CLSM, supporting sustainable construction and environmental conservation.