Soil strengthening using thermo-gelation biopolymers

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

“…These results suggest the potential utility of these biopolymers as a new construction material for environmentally friendly geotechnical engineering [5,13,14,18,19]. Among biopolymers suitable for soil treatment, gel-type biopolymers, such as gellan gum, agar gum, and xanthan gum, have several advantages, including quick (rapid) setting (gelation) [17], the ability to reduce hydraulic conductivity via bio-clogging [21], improving the shear resistance of soils [38,52] and a unique gel-structure formation process that reveals high gel strength even under fully saturated conditions [22]. Soil type and soil particle composition (i.e., coarse and fine composition) are basic properties that affect soil index parameters, such as Atterberg limits [67,80], and geotechnical engineering behaviors, such as undrained shear strength [73,82], soil stiffness and compressibility [12,15] and hydraulic conductivity [56].…”

Introduction of Microbial Biopolymers in Soil Treatment for Future Environmentally-Friendly and Sustainable Geotechnical Engineering

“…SEM images of sand-clay-biopolymer mixtures show that biopolymers directly bond with kaolinite particles, producing accumulated face-to-face clay layers, while sand surfaces remain clean or only film-type coats form around particles (Figure 4). Thus, the strengthening is maximized in the presence of clayey particles due to the hydrogen and ionic bonding between the biopolymers and clay particles, which have electrical charges [103,106]. However, this does not mean that biopolymers have a negligible impact in terms of their use with sand particles, because well-graded soil with coarse particles treated with biopolymers shows higher strength than that obtained with pure clay, such as kaolinite [103].…”

“…Gellan gum shows great promise for application as an engineered soil material due to its high strengthening effect [110]. A recent study showed that 3% of gellan gum dispersed within a clayey soil exhibited a maximum unconfined compressive strength of 12.6 MPa [106]. Although gellan gum has a similar gelation rheology and strengthening effect to agar gum, gellan gum is preferred for future mass commercialization because it can be easily produced via microbial fermentation, whereas agar gum has to be extracted from seaweed (i.e., algae).…”

“…The elastic properties of biopolymer hydrogels, such as their tensile strength and stiffness, diminish exponentially with increased water content [113], resulting in a remarkable reduction in soil strength, to approximately 1/10th of the strength of the dried state in a fully saturated condition. However, the unconfined compressive strength of re-wetted biopolymer soil mixtures (i.e., clayey soil ě 200 kPa; sandy soil ě 50 kPa) is much higher than that of untreated soils, and is immeasurable in most cases [106].…”

“…Moreover, agar gum has a thermogelation property that allows the formation of strong gels when cooled back to room temperature after being dissolved in boiling water [104]. Agar gum effectively improves the strength of sand (especially cohesion) without environmental risks [105] Recently, researchers attempted to use agar gum to enhance the strength of soils, showing that the use of 3% (to soil mass) thermal treated agar gum enhanced the unconfined compressive strength of soil up to 10 MPa under a dried condition [106].…”