Research on capillary water absorption properties of multi-material composite modified rammed earth

Rammed earth materials are generally poor in water resistance. Studying the moisture transport process and pore structure characteristics—particularly capillary absorption behavior and its rate—is of great value for enhancing the water resistance of rammed earth. In this study, rammed earth was modified with cement, recycled powder, and jute fiber. Strength tests and softening coefficient measurements were carried out to evaluate the modification effect, and further analyses were conducted on the capillary absorption rate, moisture penetration depth, and pore structure. The microscopic mechanism of multi-material composite modification was explored. The results indicate that jute fiber can significantly enhance the compressive and flexural strength of raw soil materials, whereas alkali-activated recycled micro-powder has a limited effect on strength improvement. Recycled micro-powder can effectively improve moisture transport performance; compared with the cement-modified group, the cumulative water absorption per unit area, moisture transport rate, and porosity are reduced by 42%, 32.7%, and 13%, respectively. Compared with pure cement-modified raw soil, the softened coefficient of the jute fiber-modified group is consistently above 0.83; however, its porosity is 1.8% higher than that of the cement group, with most pore sizes ranging from 50 to 200 nm. The jute fiber-modified group exhibits greater moisture penetration depth, capillary absorption rate over 60–300 min, and cumulative water absorption per unit area, reflecting the typical feature of fiber modification—altering water transport paths while maintaining high strength. Composite modification with recycled powder and jute fiber effectively optimized pore structure, enhanced material compactness, and achieved the best water resistance. The moisture transport rate and penetration depth of the composite-modified group were between those of the two single-material groups.