Optimization of mechanical properties of modified rammed earth materials using cement-aggregate-fiber composites: an experimental study

Traditional rammed earth materials often suffer from low strength and high shrinkage, limiting their structural applicability, especially in seismic-prone regions. This study investigates the mechanical properties of modified rammed earth reinforced with sand-aggregate, cement, and fiber composites. Through orthogonal experimental design, the effects of aggregate content, sand ratio, maximum aggregate size, cement content, and fiber type on compressive strength and drying shrinkage were quantified. Results indicate that aggregate content is the dominant factor controlling shrinkage, with a 70% content reducing shrinkage by 52.0% compared to 30%. Cement content significantly enhances compressive strength, reaching 4.47 MPa at 15% content. Rice straw fiber at 0.15% dosage showed the best reinforcing effect, with a synergistic strength enhancement factor of 1.88 when combined with cement. Layered compaction with a 100 mm × 100 mm tamper improved density by 15.2%, increased compressive strength to 3.3 MPa, and reduced shrinkage by 96.1%. The optimal mix ratio recommended is 15% cement + 0.15% rice straw fiber + 30% aggregate, providing a reliable material basis for rammed earth in high-seismic-intensity areas.