Multi-scale laboratory evaluation of the physical, mechanical, and microstructural properties of soft highway subgrade soil stabilized with calcium carbide residue

Calcium carbide residue (CCR) is an industrial by-product, stockpiles of which are rapidly accumulating worldwide. Highway embankment construction has been identified as an avenue to consume huge quantities of CCR as an economical, less energy intensive, and environmentally friendly chemical additive for soil stabilization. Previous studies have investigated the mechanical behavior of soils stabilized by CCR or blends of CCR with other additives; however, interpretation of the macroscale geomechanical behavior of CCR-stabilized soft soils from a systematically microstructural observation and analysis is relatively unknown. This paper presents a multi-scale laboratory investigation on the physical, mechanical, and microstructural properties of CCR-stabilized clayey soils with comparison to quicklime-stabilized soils. Several series of tests were conducted to examine the Atterberg limits, particle-size distribution, compaction characteristics, unconfined compressive strength, California Bearing Ratio, and resilient modulus of the CCR-stabilized clayey soils. The influences of binder content, curing time, and initial compaction state on the physical and mechanical properties of treated soils are interpreted with the aids of physicochemical and microstructural observations including soil pH, soil mineralogy obtained from X-ray diffraction and thermogravimetric analysis, and pore-size distribution obtained from mercury intrusion porosimetry. Soil particle flocculation and agglomeration at the early stage and pozzolanic reactions during the entire curing time, which originate from the finer particle size, greater specific surface area, and higher pH value of CCR, are the controlling mechanisms for the superior mechanical performance of CCR-stabilized soils. The outcomes of this research will contribute to the usage of CCR as a sustainable and alternative stabilizer to quicklime in highway embankment applications.