Strength Development and Hydration Behavior Analysis of Sand-Bentonite and Sand-Bentonite-Cement Composites

Sand-bentonite (SB) and sand-bentonite-cement (SBC) mixtures are widely used in geotechnical applications such as liners, cut-off walls and soil stabilization. This study investigates the strength and moisture retention behavior of SB and SBC mixtures at different curing periods (7, 14, and 28 days). A total of six mix ratios were tested, with three from each group (SB and SBC). The best-performing mix was identified from each group based on compressive strength and compaction characteristics. The compressive strength of the optimal SBC mix (with 5% cement) was approximately 7.5 times higher than the optimal SB mix after 28 days. Future strength development was predicted using best-fit equations generated in MS Excel and implemented in Python to estimate hydration times (t₅₀ and t₉₀). Water Retention Curves (WRCs) were developed using the filter paper method and fitted with the van Genuchten equation. The SBC mix exhibited a higher ‘α’ value (0.0009 kPa-1 vs. 0.0007 kPa-1), indicating it holds water longer before drying, while the SB mix had a higher ‘n’ value (1.60 vs. 1.425), suggesting it releases water more quickly. The results show that cement not only enhances long-term strength but also changes the moisture retention pattern due to C-S-H gel formation.