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

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. Supplementary Information: The online version contains supplementary material available at 10.1007/s11440-022-01732-0.

Sustainable biopolymer soil stabilization in saline rich, arid conditions: a 'micro to macro' approach.

Water scarcity in semi-arid/arid regions is driving the use of salt water in mining operations. A consequence of this shift, is the potentially unheeded effect upon Mine Tailing (MT) management. With existing stabilization/solidification methodologies exhibiting vulnerability to MT toxicity and salinity effects, it is essential to explore the scope for more environmentally durable sustainable alternatives under these conditions. Within this study we investigate the effects of salinity (NaCl, 0-2.5 M) and temperatures associated with arid regions (25 °C, 40 °C), on Locust Bean Gum (LB) biopolymer stabilization of MT exemplar and sand (control) soil systems. A cross-disciplinary 'micro to macro' pipeline is employed, from a Membrane Enabled Bio-mineral Affinity Screen (MEBAS), to Mineral Binding Characterisation (MBC), leading finally to Geotechnical Verification (GV). As predicted by higher Fe2O3 LB binding affinity in saline in the MEBAS studies, LB with 1.25 M NaCl, results in the greatest soil strength in the MT exemplar after 7 days of curing at 40 °C. Under these most challenging conditions for other soil strengthening systems, an overall UCS peak of 5033 kPa is achieved. MBC shows the critical and direct relationship between Fe2O3-LB in saltwater to be 'high-affinity' at the molecular level and 'high-strength' achieved at the geotechnical level. This is attributed to biopolymer binding group's increased availability, with their 'salting-in' as NaCl concentrations rises to 1.25 M and then 'salting-out' at higher concentrations. This study highlights the potential of biopolymers as robust, sustainable, soil stabilization additives in challenging environments.

Biopolymer Stabilization/Solidification of Soils: A Rapid, Micro-Macro, Cross-Disciplinary Approach.

In this study, we describe a novel high throughput, micro-macro approach for the identification and efficient design of biopolymer stabilized soil systems. At the "microscopic" scale, we propose a rapid Membrane Enabled Bio-Mineral Affinity Screening (MEBAS) approach supported by Mineral Binding Characterization (MBC) (TGA, ATR-FTIR and ζ Potential), while at the "macroscopic" scale, micro scale results are confirmed by Geotechnical Verification (GV) through unconfined compression testing. We illustrate the methodology using an exemplar mine tailings Fe2O3-SiO2 system. Five different biopolymers were tested against Fe2O3: locust bean gum, guar gum, gellan gum, xanthan gum, and sodium carboxymethyl cellulose. The screening revealed that locust bean gum and guar gum have the highest affinity for Fe2O3, which was confirmed by MBC and in agreement with GV. This affinity is attributed to the biopolymer's ability to form covalent C-O-Fe bonds through ß-(1,4)-d-mannan groups. Upon their 1% addition to a "macroscopic" Fe2O3 based exemplar MT system, unconfined compressive strengths of 5171 and 3848 kPa were obtained, significantly higher than those for the other biopolymers and non-Fe systems. In the current study, MEBAS gave an approximately 50-fold increase in rate of assessment compared to GV alone. Application of the proposed MEBAS-MBC-GV approach to a broad range of soil/earthwork components and additives is discussed.

Automatic yield-line analysis of slabs using discontinuity layout optimization.

The yield-line method of analysis is a long established and extremely effective means of estimating the maximum load sustainable by a slab or plate. However, although numerous attempts to automate the process of directly identifying the critical pattern of yield-lines have been made over the past few decades, to date none has proved capable of reliably analysing slabs of arbitrary geometry. Here, it is demonstrated that the discontinuity layout optimization (DLO) procedure can successfully be applied to such problems. The procedure involves discretization of the problem using nodes inter-connected by potential yield-line discontinuities, with the critical layout of these then identified using linear programming. The procedure is applied to various benchmark problems, demonstrating that highly accurate solutions can be obtained, and showing that DLO provides a truly systematic means of directly and reliably automatically identifying yield-line patterns. Finally, since the critical yield-line patterns for many problems are found to be quite complex in form, a means of automatically simplifying these is presented.

An investigation of the significance of Actinomycosis in tonsil disease.

OBJECTIVES: The objective of the study was to establish the incidence of Actinomycosis in the tonsils of children undergoing tonsillectomy or adenotonsillectomy, and to evaluate its role in clinical tonsillar disease. METHODS: This was a prospective controlled study done at the Red Cross Children's Hospital in Cape Town, South Africa over an 8-month period and included all children undergoing tonsillectomy or adenotonsillectomy. All resected tonsils were examined for the presence of Actinomycosis and any signs of significant cryptitis or active tonsillitis. A comparison was made in the incidence of Actinomycosis in children with obstructive sleep apnoea, recurrent tonsillitis or obstructive sleep apnoea and recurrent tonsillitis. The data was further analysed to determine the statistical significance of the association between Actinomycosis of the tonsils and age, sex and histopathological and clinical diagnosis. RESULTS: A total of 344 tonsils were analysed on 172 patients. We found 20 patients (11.6%) with Actinomycosis in the tonsils. The mean age of patients with Actinomycosis was 7.25 years and without Actinomycosis was 5.4 years (p=0.002). Most specimens (16) had no evidence of tissue reaction to Actinomyces, and their presence was found to be due to colonisation of the tonsils only. Actinomycosis was present in 11% of patients with obstructive sleep apnoea, 11% of patients with recurrent tonsillitis and in 9% with obstructive sleep apnoea and recurrent tonsillitis. The difference in incidence of Actinomycosis between these three groups (p=0.94), and between the recurrent tonsillitis group alone compared to the obstructive group (p=0.83), was not statistically significant. There was therefore no statistical significance found between Actinomyces and OSA+/- recurrent tonsillitis. CONCLUSIONS: There was no correlation found between the presence of tonsillar Actinomycosis and recurrent tonsillitis and/or obstructive tonsillar hypertrophy. Histopathologic findings showed no evidence of tissue reaction to Actinomyces and its presence was found to be due to colonisation of the tonsils only. The series did however show a statistically significant correlation between Actinomycosis colonisation and age with Actinomycosis being more common in older children, especially those over 5 years of age.

Is diagnostic tonsillectomy indicated in all children with asymmetrically enlarged tonsils?

OBJECTIVES: The aims of the study were: (i) to determine the necessity for diagnostic tonsillectomy in children with asymmetrically enlarged tonsils; (ii) to determine the accuracy of clinical assessment of tonsillar asymmetry; and (iii) to determine how to manage children with clinical tonsillar asymmetry in a developing-world practice. METHODS: A prospective study was carried out at Red Cross War Memorial Children's Hospital in Cape Town, over an 8-month period. All children undergoing tonsillectomy or adenotonsillectomy had a clinical assessment of tonsil symmetry done, and all tonsil and adenoid specimens were examined histologically. The maximum diameter and volume of the resected tonsils were measured. A comparison was done of true tonsil asymmetry in patients with asymmetrical tonsils and a subgroup of matched controls with symmetrical tonsils. RESULTS: A total of 344 tonsils were analysed (172 patients). The 13 patients (7.6%) diagnosed as having clinically asymmetrically enlarged tonsils had no significant pathological diagnosis. In the patients with symmetrical tonsils there were 2 abnormal pathological findings (tuberculosis of the adenoids and T-cell lymphoma of the tonsils and adenoids). In the clinically asymmetrical tonsil group, true tonsillar asymmetry was 3 mm (maximum diameter), and 2.2 cm(3) (volume), compared with 1.9 mm and 1.5 cm(3) in the symmetrical tonsil group. When patients with clinical tonsillar asymmetry and symmetry were compared, the difference in maximum diameter (p = 0.62) and volume (p = 0.73) was not significantly different. CONCLUSIONS: Clinical tonsillar asymmetry is usually apparent rather than real. The incidence of significant pathology in children with asymptomatic, asymmetrical tonsils is low. Diagnostic tonsillectomy is indicated in children with asymmetrically enlarged tonsils associated with constitutional symptoms, cervical lymphadenopathy, rapid tonsil enlargement or significant tonsillar asymmetry.

Non-equilibrium partitioning tracer transport in porous media: 2-D physical modelling and imaging using a partitioning fluorescent dye.

This paper describes an investigation into non-equilibrium partitioning tracer transport and interaction with non-aqueous-phase liquid (NAPL) contaminated water-saturated porous media using a two-dimensional (2-D) physical modelling methodology. A fluorescent partitioning tracer is employed within a transparent porous model which when imaged by a CCD digital camera can provide full spatial tracer concentrations and tracer breakthrough curves. Quasi one-dimensional (1-D) benchmarking tests in models packed with various combinations of clean quartz sand and NAPL are described. These modelled residual NAPL saturations, S(n), of 0-15%. Results demonstrated that the fluorescent partitioning tracer was able to detect and quantify the presence of NAPL at low flow rates. At larger flow rates and/or higher NAPL saturations, the tracer increasingly underpredicted the NAPL volume as expected and this is attributed primarily to non-equilibrium partitioning. Despite little change in permeability, change in NAPL saturations from 4% to 8% resulted in significant NAPL saturation underestimates at the same flow rates implying coalescence of NAPL into wider separated but larger ganglia. A 2-D investigation of an idealised heterogeneous residual NAPL contaminated flow field indicated little permeability change in the NAPL contaminated zone and thus little flow bypassing, leading to reduced underpredictions of NAPL saturations than for equivalent quasi 1-D cases. This was attributed to increased 'sampling' of the NAPL by the tracer. The process is clearly visually identifiable from the experimental images. This rapid and relatively inexpensive experimental method is of value in laboratory studies of partitioning tracer behaviour in porous media; in particular, the ability to observe full field concentrations makes it valuable for the study of complex heterogeneous systems.

Dissolved oxygen imaging in a porous medium to investigate biodegradation in a plume with limited electron acceptor supply.

A novel combination of noninvasive imaging with an oxygen sensitive fluorescent indicator was developed to investigate the biodegradation processes occurring at the fringe of a solute plume, where the supply of oxygen was limited. A thin transparent porous matrix (156 x 120 x 3 mm) was made from quartz plates and quartz sand (212-300 microm) and enriched with acetate-degrading bacteria. A degrading plume developed from a continuous acetate source in the uniform flow field containing dissolved oxygen. Ruthenium (II)-dichlorotris(1,10-phenanthroline) (Ru(phen)3Cl2), a water-soluble fluorescent dye, was used as an indicator of dissolved oxygen. The fluorescence intensity was dependent on the concentration of oxygen because the dissolved oxygen acted as collisional quencher. The oxygen distribution was interpreted from images recorded by a CCD camera. These two-dimensional experimental results showed quantitatively how the oxygen concentrations decreased strongly at the narrow plume fringe and that oxygen was depleted at the core of the plume. Separately, dispersivity was measured in a series of nonreactive transport experiments, and biodegradation parameters were evaluated by batch experiments. Two-dimensional numerical simulations with MT3D/RT3D used these parameters, and the predicted oxygen distributions were compared with the experimental results. This measurement method provides a novel approach to investigate details of solute transport and biodegradation in porous media.

Physical modelling of solute transport in porous media: evaluation of an imaging technique using UV excited fluorescent dye.

The development and evaluation of a 2-dimensional physical model, which is designed to assist in the characterisation of complex solute transport problems in porous media, is described. The laboratory model is a transparent 2-dimensional porous media of nominal thickness and uses a non-invasive imaging technique in conjunction with a fluorescent dye tracer (sodium fluorescein) to monitor solute movements. Under ultraviolet (UV) illumination the dye emits visible light which is imaged by a CCD (Charge Coupled Device) camera. The image is processed to estimate the 2-dimensional distribution of tracer concentrations. The system can successfully model a simple contaminant plume within a homogenous porous matrix constructed from glass beads (60-100 microm). Experimental results show that transverse dispersion coefficient was 3.9 x 10(-10) m2/s when sodium fluorescein transported in porous matrix with a walter velocity of 5.71 x 10(-6) m/s. The low transverse dispersion coefficient suggests that the molecular diffusion of solute cannot be neglected under low velocity of the water. The advantages of using UV rather than an ordinary light system are a reduction in noise and experimental errors. Errors due to light dispersion within the model are shown to be negligible for the current model. Since contaminant with aromatic rings are usually fluorescent and biological samples can be labelled by fluorescent dye, this imaging technique using UV excited fluorescent dye will be used to investigate biodegradation process in porous media.