Preparing controlled low strength materials (CLSM) using excavated waste soils with polycarboxylate superplasticizer

The disposal of massive waste soils is troublesome during urban excavation projects, which is commonly dumped temporarily and transported to the suburban landfills. Meanwhile, energy-intensive materials (e.g. plain concrete) are being used in the foundation trench backfill, resulting in high engineering costs and carbon emissions. Therefore, it is of significant economic and environmental benefits to try to convert waste excavated soils into qualified materials for trench backfill. To satisfy engineering requirement, the contradiction between flowability and strength of very fine aggregates should be addressed. This paper examines the feasibility of preparing controlled low strength material (CLSM) using excavated waste soils, where polycarboxylate superplasticizer (PCE) is used to improve workability of the materials. The engineering properties of soil-based CLSM are experimentally investigated. The results indicate that PCE improves the flowability of CLSM remarkably, which increases by half with addition of 1.0% PCE. The used dosage of PCE is higher than those in concretes due to intercalation behavior with clay minerals. The PCE has a negative effect on early strength of CLSM but the effect becomes positive with increasing curing time and more sufficient hydration reactions. The positive effect of PCE on hydration reactions has been demonstrated by XRD and SEM analysis. Moreover, construction cost analysis shows that to use waste soils to prepare CLSM has significant economic benefits, in spite of the high price of PCE.