Water-regulated processing window of soil–cement–epoxy hybrid binders for cohesive soil interface applications

This study investigates a water-regulated soil–cement–epoxy hybrid binder developed for cohesive silty clay interface applications. The work aims to identify a preliminary processing window that provides adequate workability, dimensional stability, and soil-contact continuity under moisture-sensitive conditions relevant to bored-pile construction. A laboratory-based iterative mixture-screening approach was conducted using fixed proportions of soil, cement, and epoxy while varying water dosage and epoxy resin-to-hardener ratio. Nine mixtures were prepared using 200 g soil, 40 g cement, and 80 g epoxy, with water contents ranging from 200 to 560 mL and resin-to-hardener ratios of 2:1 and 1:1. The main evaluation parameters were liquid-phase duration, shrinkage response, phase stability, and visual bonding classification. Among the tested mixtures, the formulation containing 210 mL of water and a 2:1 resin-to-hardener ratio was identified as the best-balanced mixture, providing a liquid-phase duration of approximately 64 min, controlled shrinkage of about 1.0 cm, stable paste morphology, and favorable visual bonding behavior. Mixtures within the 200–220 mL water range remained relatively stable, whereas water contents above 230 mL promoted water migration, phase separation, and reduced bonding classification. The findings indicate that water content is a critical processing variable governing workability, shrinkage stability, and hydration–polymerization balance in soil–cement–epoxy hybrid binder. However, the visual classification used in this study should not be interpreted as confirmed interfacial bonding strength. These results provide a preliminary materials-design framework for developing water-regulated cement–polymer hybrid binders for moisture-sensitive cohesive soil interface applications. Further mechanical, microstructural, durability, and field-scale validation is required before practical bored-pile performance can be confirmed.