Inulin biopolymer as a novel material for sustainable soil stabilization

Abstract

The development of new urban areas necessitates building on increasingly scarce land, often overlaid on weak soil layers. Furthermore, climate change has exacerbated the extent of global arid lands, making it imperative to find sustainable soil stabilization and erosion mitigation methods. Thus, scientists have strived to find a plant-based biopolymer that favors several agricultural waste sources and provides high strength and durability for sustainable soil stabilization. This contribution is one of the first studies assessing the feasibility of using inulin to stabilize soil and mitigate erosion. Inulin has several agricultural waste sources, making it a sustainable alternative to traditional additives. Soil samples susceptible to wind erosion were collected from a dust-prone area in southwest Iran and treated with inulin at 0%, 0.5%, 1%, and 2% by weight. Their mechanical strength was evaluated using unconfined compressive strength tests and a penetrometer. In addition, wind tunnel tests (at 16 m/s) were performed to investigate inulin's wind erosion mitigation potential. The durability of treated samples was evaluated after ten wetting-drying cycles to assess the effect of environmental stressors. The results indicated a 40-fold increase in the unconfined compressive strength (up to 8 MPa) of the samples treated with 2% inulin and only 0.22% weight loss after ten wetting-drying cycles. SEM images revealed the formation of biopolymer-induced particle-to-particle bonds. Moreover, Raman spectroscopy indicated molecular (hydrogen) bonding of the biopolymer hydrogel-soil particles facilitated by the hydroxyl groups of inulin. The deterioration in stiffness and strength of treated samples was less noticeable after 3rd dry-wet cycle, indicating the durability of the samples. The durability of samples against wet-dry cycles was attributed to molecular bonding of soil-biopolymer hydrogel, as revealed by FTIR analysis.

Keywords: Carbohydrate biopolymer; Durability tests; Green soil stabilization; Inulin; Soil erosion control; Sustainable geoengineering.

Fig. 1

Sustainable development goals (SDGs) achieved through the use of carbohydrate biopolymers^{,,,,,,,,–,,,,–}.

Fig. 2

Map of sand and dust storm sources in Iran.

Fig. 3

Maximum monthly temperature, relative humidity and UV level of the dust source region in 2023.

Fig. 4

Particle-size distribution of soil used in this study.

Fig. 5

Schematic of Armfield subsonic wind tunnel system used in this study.

Fig. 6

Variation of penetration force versus penetration depth for treated and untreated soil samples (a) after the 1st wet–dry cycle (b) after the first and 5th wet–dry cycles.

Fig. 7

Variation of maximum penetration force versus wet–dry cycles after 1st to 5th wet–dry cycles.

Fig. 8

Variation of the normalized soil weight with time for treated and untreated soil samples during (a) the first wet–dry cycle and (b) the tenth wet–dry cycle.

Fig. 9

Weight loss of samples improved with water and biopolymer solution in concentrations of 0.5% and 2% after wind tunnel tests.

Fig. 10

Normalized soil weight loss (erosion ratio) of samples improved with water and biopolymer solution in concentrations of 0.5% and 2% during wet–dry cycles after the wind tunnel test.

Fig. 11

Variation in cumulative weight loss of inulin-treated soil by number of wet–dry cycles.

Fig. 12

Stress-stain curves of UCS tests on samples treated with different inulin content.

Fig. 13

Durability results of 28-day cured samples improved with 2% inulin after 1 to 5 wet–dry cycles (a) Stress–strain curves obtained from unconfined compressive tests for after each cycle, (b) q_u, (c) E₅₀.

Fig. 14

Consistency limits, liquid limit (w_L) and plastic limit (w_P) of the soil treated with varying percentages of inulin to soil mass.

Fig. 15

SEM of samples treated with (a) 2% inulin (b) 1.5% inulin (c) 1% inulin (d) 0.5% inulin.

Fig. 16

(a) The Raman spectra of the untreated soil specified by (1) and three points inside the carbohydrate biopolymer-treated soil specified by (2, 3 and 4). (b) The Raman image of the point (4) in the soil sample, where the Raman shift range of 3400–3700 (cm⁻¹) is colored in green, and the Raman shift range of 2800–3000 (cm⁻¹) is depicted in red.

Fig. 17

(a) The bonds between inulin and water and hydrogel formation. (b) Development of the bonds within soil matrix (inulin, water and soil elements) )one of the most prevalent chemical constituents of the studied soil, namely, SiO₂, has been presented in the soil along with its associated bonds with the considered biopolymer, namely, inulin).

Fig. 18

SEM of the surface of samples treated with 2% inulin (a) before wet–dry cycles (b) after 1st wet–dry cycle (c) after 3rd wet–dry cycle (d) after 5th wet–dry cycle.

Fig. 19

The Fourier-Transform infrared spectroscopy (FTIR) of the inulin-treated soil (a) before the wet–dry cycle, (b) after 3rd wet–dry cycle, (c) after the 5th wet–dry cycle.

Fig. 20

Comparison of unconfined compressive strength between traditional additive (T.A.) and biopolymer soil treatment (BPST) for fine soil at dry condition^,,,,,,–.