Mechanical and shrinkage behavior of hydraulically bound mixtures with sulfate saline soil lightweight aggregates: effects of replacement ratio and method

The shortage of high-quality aggregates and the environmental risks associated with sulfate saline soils constrain infrastructure development in high-altitude cold plateau regions. To address this challenge, cold-bonded sulfate saline soil lightweight aggregates (SSSLAs) were developed as a low-carbon material derived from locally available sulfate saline soils. Their feasibility as partial replacements for mineral aggregates in hydraulically bound mixtures (HBM) was evaluated in Qinghai, China. Different replacement ratios and incorporation strategies were examined to investigate their effects on compaction behavior, mechanical performance (unconfined compressive strength and compressive resilient modulus), and volumetric stability (drying and thermal shrinkage). Incorporating SSSLAs reduced the maximum dry density and increased the optimum moisture content, while the UCS, splitting tensile strength, and compressive resilient modulus decreased with increasing replacement ratio. At 50% replacement, the 7 d UCS decreased by approximately 27%–34% compared with the control mixture, depending on the replacement method. Drying shrinkage strain (DSS) reached approximately 400 × 10 -6 at 100% replacement and followed a power-law relationship with cumulative water loss, whereas the temperature shrinkage coefficient (TSC) reached its minimum within the 40%–60% replacement range. SEM observations showed that multi-size replacement improved particle filling and skeleton continuity, whereas single-size replacement produced more open pores and discontinuous particle contacts. Considering strength, stiffness, shrinkage behavior, and microstructural characteristics, an SSSLA replacement ratio not exceeding 50% is recommended. These findings establish a performance-oriented framework for incorporating sulfate-saline-soil-derived lightweight aggregates into structural HBM systems and support the development of ecological road materials in environmentally sensitive plateau regions.