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Partial soil replacement in soil cement using bentonite and polyurethane foam
Author(s)
Rattanapitak, Pornkanok
Shelina, Aza
Ayawanna, Jiratchaya
Kingnoi, Namthip
Mase, Lindung Zalbuin
Date Issued
June 1, 2026
Type
Article
Abstract
This study evaluates the effects of partially replacing soft clay with Ca-bentonite or polyurethane foam in soil-cement mixtures to improve geotechnical performance in soft soils. Cement content was fixed at 20% by total mix weight (% wt), while soft clay was partially replaced with Ca-bentonite or polyurethane foam at 20% wt, 30% wt, and 40% wt. Density, weight, and compressive strength were evaluated at curing ages of 7 and 28 days. The optimal mixture, determined based on compressive strength, was subsequently selected for the permeability test and compared with natural soft clay and a conventional soil-cement mixture. Moreover, scanning electron microscopy was conducted to characterize particle morphology and pore structure, providing microstructural insight into the strength behaviour of mixtures incorporating both Ca-bentonite and polyurethane foam replacements. The results indicate a clear contrast between the two replacement materials. Ca-bentonite increases density and compressive strength through pozzolanic and filling effects. The optimal sample, consisting of 50% soft clay, 20% cement, and 30% Ca-bentonite (S5C2B3) by weight, achieves a 28-day compressive strength of 9.71 MPa with stiff and brittle behaviours. Weight increase is associated with Ca-bentonite swelling, which enhances impermeability. In contrast, polyurethane foam reduces density and strength, producing a lightweight, ductile material due to its porous structure and water loss. Ca-bentonite is suitable for high-strength or low-permeability applications, whereas polyurethane foam is appropriate for lightweight fill where reduced weight is required.
Citation
Results in Engineering, 30, 2026