Sustainable biopolymer soil stabilisation: the effect of microscale chemical characteristics on macroscale mechanical properties

Abstract

Sustainable biopolymer additives offer a promising soil stabilisation methodology, with a strong potential to be tuned to soil’s specific nature, allowing the tailoring of mechanical properties for a range of geotechnical applications. However, the biopolymer chemical characteristics driving soil mechanical property modifications have yet to be fully established. Within this study we employ a cross-scale approach, utilising the differing galactose:mannose (G:M) ratios of various Galactomannan biopolymers (Guar Gum G:M 1:2, Locust Bean Gum G:M 1:4, Cassia Gum G:M 1:5) to investigate the effect of microscale chemical functionality upon macroscale soil mechanical properties. Molecular weight effects are also investigated, utilising Carboxy Methyl Cellulose (CMC). Soil systems comprising of SiO2 (100%) (SiO2) and a Mine Tailing (MT) exemplar composed of SiO2 (90%) + Fe2O3 (10%) (SiO2 + Fe) are investigated. The critical importance of biopolymer additive chemical functionality for the resultant soil mechanical properties, is demonstrated..For Galactomannan G:M 1:5 stabilised soils the ‘high-affinity, high-strength’, mannose-Fe interactions at the microscale (confirmed by mineral binding characterisation) are attributed to the 297% increase in the SiO2 + Fe systems Unconfined Compressive Strength (UCS), relative to SiO2 only. Conversely for SiO2 Galactomannan-stabilised soils, when increasing the G:M ratio from 1:2 to 1:5, a 85% reduction in UCS is observed, attributed to mannose’s inability to interact with SiO2. UCS variations of up to a factor of 12 were observed across the biopolymer–soil mixes studied, in line with theoretically and experimentally expected values, due to the differences in the G:M ratios. The limited impact of molecular weight upon soil strength properties is also shown in CMC-stabilised soils. When considering a soil’s stiffness and energy absorbance, the importance of biopolymer–biopolymer interaction strength and quantity is discussed, further deciphering biopolymer characteristics driving soil property modifications. This study highlights the importance of biopolymer chemistry for biopolymer stabilisation studies, illustrating the use of simple low-cost, accessible chemistry-based instrumental tools and outlining key design principles for the tailoring of biopolymer–soil composites for specific geotechnical applications. Graphical abstract

A State-of-the-Art Review of Organic Polymer Modifiers for Slope Eco-Engineering

“…Biopolymers can occupy part of the pore space of the soil and reduce its water retention capacity. The water absorption of the biopolymers is reduced due to the limitation of soil particles compared with that of pure biopolymers [49,[123][124][125].…”

Strengthening mechanisms of clay building materials by starch

“…Indeed, starch increases the mechanical behavior of earth-based building materials with only 1 wt% addition [17,18]. The stabilization of earth-based building materials with biopolymers is assumed to depend on the nature of the clay minerals by modifying mainly layer thickness and chemical composition [19][20][21][22][23]. It is also assumed that starch influences the rheology of fresh mixes depending on the clay nature of the earth-based building material [24].…”

Stabilisation of Soft Clay, Quick Clay and Peat by Industrial By-Products and Biochars

“…In the soil stabilisation industry, research and testing on a laboratory scale have been conducted using a wide variety of IBPs, e.g., cement kiln dust [3][4][5], lime kiln dust [6,7], fly ash [8][9][10], bottom ash [11], gypsum [12,13], ground-granulated blast-furnace slag (GGBS) [14][15][16][17][18] and ladle slag [12]. In addition, other binders or additives have been studied, such as biopolymers [19,20], geopolymers [21], fibres [22], reactive magnesia [5], colloidal silica [23] and natural or synthetic zeolites [24,25]. These studies have illustrated the potential to reduce emissions when using IBPs.…”