Prospects of sustainable geotechnical applications of manufactured sand slurry as controlled low strength material

Rapid changes in the construction industry for infrastructure development require extensive use of building materials from a variety of sources. As natural resources deplete at a faster rate in recent years, new materials are being explored, and recycled materials are being discovered for various applications. The slurry obtained during the washing of mined quarry sand (also called as M Sand Slurry or MSS) is found to be disposed as mining waste causing environmental pollution. In the present study, we propose an innovative methodology to recycle the MSS as a suitable replacement of fine aggregate by imparting sufficient strength and workability to produce a com-posite, commonly called as controlled low strength material (CLSM). We have optimized the mix proportioning of MSS by adding fly ash (up to 15%) and Portland cement (up to 10%). Various tests on the plastic properties (flowability, bleeding, hardening time) and hardened properties (ultimate compressive strength or UCS) were performed on the selected mixtures. The optimum mixture of CLSM with MSS provided excellent flowability (at 200 mm), bleeding rate (3-5%) and UCS up to 1.12 MPa. The improved binding effect on the poor-graded MSS has been attributed to the pozzolanic reaction in presence of fly ash and cement, as evident from the micro -structural analysis. Based on the excavation criteria (ACI 229R), the selected mixtures have high removability modulus (1.2-2.5) except for two proportions (with only MSS, and with very low fly ash) while all combinations have sufficient strength (UCS < 2.1 MPa), making them suitable for various geotechnical applications. Further, to address the sustainability aspects of MSS-based CLSM utilization, a strategic framework is proposed based on the Life Cycle Assessment (LCA) approach for the mining industries. It is observed that MSS-based CLSM can reduce the cost of earthworks approximately by 62% (compared to the river sand) and 32% (compared to the available alternate sand). Hence, based on the environmental, economic and mechanistic aspects, we demonstrate that MSS-based CLSM can be effectively adopted for sustainable geotechnical applications.