Characterization of controlled low-strength materials from waste expansive soils

Abstract

Expansive soil from civil excavation projects is often considered waste material due to its propensity to swell. This study pioneers a novel approach to sustainable infrastructure by exploring the viability of repurposing expansive soils in the production of controlled low-strength materials (CLSM), incorporating sand and cement into the mix. Laboratory tests were conducted on CLSMs with varying mix proportions to assess their fresh (flowability, bleeding rate, and setting time) and hardened (swelling, unconfined compressive strength, and dry-wet durability) properties. The investigation focuses on three critical parameters: sand-to-soil ratio (S), cement-to-aggregate ratio (C), and water-to-solid ratio (W). Experimental results indicate the problematic swelling behavior of CLSM is mitigated when C surpasses 18%, at an S value of 10%. Adjusting either W or S enhances flowability but also elevates the bleeding rate. An increase in C has a marginal effect on flowability and bleeding rate, but markedly accelerates the setting time. Flowability follows a negative exponential relationship with time. Furthermore, increasing C or decreasing W markedly enhances both residual strength after dry-wet cycles and compressive strength. When S is below 10%, both compressive and residual strengths show a positive correlation with S. Conversely, when S exceeds 10%, a negative correlation is observed with compressive strength. A predictive model for the compressive strength and flowability of CLSM made from expansive soil has been developed, utilizing data normalization techniques. This model assists in determining the optimal mix proportions appropriate for applications in narrow backfills.