Assessing Workability of Ready-Mixed Soils Derived from Excess Spoil

Abstract

Civil excavation projects frequently produce significant amounts of excess spoil. Repurposing this spoil into usable backfill material instead of disposing of it offers economic and environmental benefits. This study explores the prospect of converting red-bed mudstone construction waste, a type of soil frequently found at shallow depths, into a ready-mixed soil material (RMSM). It assesses the fresh mixture’s workability characteristics (initial flowability, bleeding rate, and density) and the hardened material’s mechanical properties (compressive strength and stress-strain relationship) by adjusting the water-to-solid ratio (W/S) and cement-to-soil ratio (C/S). The study investigates the impact of W/S, C/S and time on RMSM’s flowability loss and proposes an empirical formula to provide a scientific reference for RMSM’s flowability design in engineering applications. Findings highlight the significant influence of W/S on flowability, bleeding rate, and compressive strength, while showing C/S has a limited effect on flowability and bleeding. A negative exponential relationship is observed between flowability and time for all mixes, with the flowability loss ratio increasing over time, ranging from 22.9% to 35.6% after 1 h and stabilizing after 3 h. These insights are crucial to optimize RMSM’s performance and suggest the need to further improve the flowability retention of RMSM. Furthermore, in comparison to soil cement and concrete, RMSM reduces backfill costs by 30.8% and 80.0%, respectively, while also achieving a reduction in CO2 emissions by 25.9% and 69.2%. Therefore, RMSM presents as an economically and environmentally friendly alternative for backfill applications.