Shear strength behavior and parameters of microbial gellan gum-treated soils: from sand to clay

Abstract

Microbial biopolymers have recently been introduced as a new material for soil treatment and improvement. Biopolymers provide significant strengthening to soil, even in small quantities (i.e., at 1/10th or less of the required amount of conventional binders, such as cement). In particular, thermo-gelating biopolymers, including agar gum, gellan gum, and xanthan gum, are known to strengthen soils noticeably, even under water-saturated conditions. However, an explicitly detailed examination of the microscopic interactions and strengthening characteristics between gellan gum and soil particles has not yet been performed. In this study, a series of laboratory experiments were performed to evaluate the effect of soil-gellan gum interactions on the strengthening behavior of gellan gum-treated soil mixtures (from sand to clay). The experimental results showed that the strengths of sand-clay mixtures were effectively increased by gellan gum treatment over those of pure sand or clay. The strengthening behavior is attributed to the conglomeration of fine particles as well as to the interconnection of fine and coarse particles, by gellan gum. Gellan gum treatment significantly improved not only interparticle cohesion but also the friction angle of clay-containing soils.

Soil consistency and interparticle characteristics of xanthan gum biopolymer–containing soils with pore-fluid variation

“…3d. All kaolinite-sand soils show a peak LL DI at m b /m c = 0.5%, which is in accordance with the previous finding from Chang and Cho (2019) addressing m b /m c to mainly govern biopolymer-clay matrix formation and relevant shear strength properties (i.e., cohesion and friction angle) (Chang and Cho 2019). As the content of xanthan gum increases, xanthan gum initiates kaolinite aggregation via ionic or hydrogen bonding (Laird 1997;Sastry et al 1995;Theng 2012), which accompanies a decrease in LL DI (③ in Fig.…”

“…However, application of biopolymers to soil treatment requires considerations of the biopolymer rheology, phase transfer with water content variation, biopolymer to soil ratio, soil type, and pore-fluid condition, which affects the biopolymer-soil matrix formation (Chang and Cho 2019;Chang et al 2015cChang et al , 2017. Biopolymer-treated soils with a high water content show low strength due to the low viscous biopolymer hydrocolloids surrounding soil particles (Chang et al 2017), while dehydration increases the soil strength due to the condensation of the biopolymer hydrogels forming high-tensile-strength biofilms through the soil particulate network (Chang et al 2016a).…”

“…For biopolymertreated sands, the concentration of biopolymer hydrogels be-comes the dominant factor controlling the strength behavior of sands (Chang et al 2016a;Lee et al 2017). Meanwhile, electrostatic and chemical bonding characteristics between biopolymers and clayey particles become important for fine soils, where the "biopolymer-to-clay content" (in mass) becomes more critical than the "biopolymer-to-total soil content" (in mass) in terms of the strengthening purpose for biopolymer-treated soils (Chang and Cho 2019;Chang et al 2015a).…”

A Review of the Application of Biopolymers on Geotechnical Engineering and the Strengthening Mechanisms between Typical Biopolymers and Soils

“…Gellan gum in the polysaccharide group is a high-molecular-weight polymer produced by the bacterium Sphingomonas elodea (formerly known as Pseudomonas elodea) [27,31,32]. Also, gellan gum is generated by four molecules: (1,3)-β-D-glucose, (1,4)-β-D-glucuronic acid, (1,4)-β-D-glucose, and (1,4)-α-L-rhamnose as shown in Figure 3 [27].…”

Sustainable utilization of biopolymers and biocement in aggregation of granular materials

“…The strength of sand-clay mixtures has been reported to increase by the addition of biopolymers unlike that of pure sand or clay alone Cho, 2018, Cabalar et al, 2018). The synergistic effect is due to the flocculation of fine particles as well as the interconnection between fine and coarse particles (Chang and Cho, 2018). Studies have also demonstrated the importance of complete drying in order to achieve maximum strength for biopolymer treated soils (Swain et al, 2018) as the strength of biopolymers has been found to be dependent on water content (Chang et al, 2015).…”