Soil improvement using biopolymers has attracted considerable attention in recent years, with the aim to reduce the harmful environmental effects of traditional materials, such as cement. This paper aims to provide a review on the environmental assessment of using biopolymers as binders in soil improvement, biopolymer-treated soil characteristics, as well as the most important factors affecting the behavior of the treated soil. In more detail, environmental benefits and concerns about the use of biopolymers in soil improvement as well as biopolymer–soil interaction are discussed. Various geotechnical properties are evaluated and compared, including the unconfined compressive strength, shear strength, erosion resistance, physical properties, and durability of biopolymer-treated soils. The influential factors and soil and environmental conditions affecting various geotechnical characteristics of biopolymer-treated soils are also discussed. These factors include biopolymer concentration in the biopolymer–soil mixture, moisture condition, temperature, and dehydration time. Potential opportunities for biopolymers in geotechnical engineering and the challenges are also presented.

Biopolymers have recently shown great potential to replace traditional binding materials in geotechnical engineering; however, more research is required to reach a deeper understanding of biopolymer-treated soil behavior. The objective of this study was to investigate the most important parameters that affect the behavior of biopolymer-treated soil, including biopolymer content, dehydration time, soil type effect, and durability. Sodium alginate and agar biopolymers were used due to their stability under severe conditions and the reasonable costs to study these parameters. A broad range of soil particle sizes was used to optimize the kaolinite-sand combination. As one of the main concerns in the behavior of biotreated soils, durability was investigated under five cycles of wetting and drying. In addition, a comprehensive microstructural study was performed by FTIR analysis and SEM images, as well as chemical interaction analysis. The results indicated that the optimized biopolymer content was in the range of 0.5–1% (to soil weight) and the dehydration time was 14 days. A soil combination of 25% kaolinite and 75% sand provided the highest compressive strength. Under wetting and drying conditions, biopolymers significantly increased soil resistance against strength reduction and soil mass loss. This study provides an understanding how agar and sodium alginate changes the behavior of the soil and can be used as a reference for further studies in the future.

Improvement of soil characteristics has always been of interest to civil engineers. This research aims to propose an environmentally-friendly material to improve dune sand strength using sodium alginate biopolymer. For this purpose, unconfined compressive tests were performed. The effect of temperature on the variation of compressive strength was also studied. It was shown that curing at temperatures of higher than 45°C led to a gradually decrease of compressive strength up to 80°C. Curing time was also an effective parameter on the compressive strength which considerably increased until 7 days and samples reached to 90% of their total strength. CBR tests were also conducted to evaluate the ability of using sodium alginate for base and subbase of road stabilization. The results indicated that sodium alginate as a biodegradable material greatly increased the CBR strength in comparison to pure sand. A microstructural analysis was also carried out through SEM images which showed that sodium alginate effectively linked soil articles together through different types of chemical bonds. Consequently, it was pointed out that sodium alginate has a good potential to improve the mechanical properties of poorly graded sand, and also it has no detrimental effects on the environment.