Behavior of controlled low-strength material incorporating industrial by-products fly ash, quarry waste and concrete waste

The widespread generation of concrete waste from demolished structures presents a significant challenge in construction waste management. However, its integration into Controlled Low Strength Material (CLSM) presents a promising avenue for sustainable construction for utility fill or backfilling applications when suitable granular fills are not available. A low strength flowable fill mix necessitates a mix design that achieves a compressive strength below 0.7 MPa after 28 days for easy excavatability using hand tools. This study delves into the feasibility of replacing fly ash by incorporating concrete waste and quarry waste into CLSM formulations with minimal amounts of cement through laboratory investigations to engineer CLSM blends optimized for easy excavation, particularly for utility fills. Results indicate that the inclusion of concrete waste reduces the water demand and mitigates bleeding in CLSM, thereby enhancing the overall stability of the mix. Moreover, CLSM compositions exhibit densities akin to the density of sand. The addition of 10 % and 20 % of concrete waste led to substantial increases in unconfined compressive strength (UCS). The impact was more pronounced at lower cement contents, with significant early strength development observed when concrete waste was included.The split tensile strength was found to have a linear correlation with the UCS and the dry density of the mix. The formation of pozzolanic hydration products, particularly in mixes with higher fly ash content, was identified as a key factor contributing to strength development, while increased friction between particles of quarry waste further increased the strength and the same has been confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The findings also revealed that a CLSM blend composed of, 30 % fly ash, 50 % quarry waste and 20 % concrete waste supplemented with an extra 3 % cement at 250 mm flowability could be used for backfilling applications where sufficient strength and excavatablity with hand tools is required.