Abstract: A solid waste controlled low strength material (CLSM) was prepared using engineering waste soil and construction waste sand as fine aggregates. The fluidity, bleeding rate, and unconfined compressive strength of the CLSM were studied by considering the substitution rate of the engineering waste soil, particle/powder ratio of the engineering waste soil, water-solid ratio, and binder-aggregate ratio as influencing factors. The hydration and hardening characteristics of the CLSM were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the fluidity of the CLSM decreases with an increase in the engineering waste soil content; however, it can effectively control bleeding, and it promotes early strength but weakens later strength. The smaller the particle/powder ratio, the more water is needed for the CLSM to reach the same fluidity, which has little effect on the 28 d strength. Under the influence of the watersolid ratio, the fluidity and 28 d strength of the CLSM are negatively correlated, whereas the two indexes are positively correlated under the influence of the binder-aggregate ratio. The results of microscopic analyses show that the formation of CLSM hydration products was mainly owing to the hydration reaction of cement and slag powder, whereas the ion exchange and granulation of engineering waste soil had limited influence on the hydration system. In this experimental system, the solid-waste CLSM slurry not only has excellent working performance with a high fluidity (>200 mm) and low bleeding ratio but also can satisfy backfill engineering applications requiring secondary excavation (<2.1 MPa), which provides a new idea for the resource utilization of low-quality building solid waste.

Key words: engineering waste soil, controlled low strength material, fluidity, unconfined compressive strength, microscopic analysis