Rubber powder−polymer combined stabilization of South Australian expansive soils

This study examines the combined capacity of rubber powder inclusion and polymer–treatment in solving the swelling problem of South Australian expansive soils. The rubber powder was incorporated into the soil at three different rubber contents (by weight) of 10%, 20% and 30%. The preliminary testing phase consisted of a series of consistency limits and free swell ratio tests, the results of which were analyzed to arrive at the optimum polymer concentration. The main test program included standard Proctor compaction, oedometer swell–compression, soil reactivity (shrink–swell index), cyclic wetting and drying, crack intensity, and micro–structure analysis by means of the scanning electron microscopy (SEM) technique. The improvement in swelling potential and swelling pressure was dependent on the rubber content, with polymer–treated mixtures holding a notable advantage over similar untreated cases. A similar dependency was also observed for the crack intensity factor and the shrink–swell index. The beneficial effects of rubber inclusion were compromised under the cyclic wetting and drying condition. However, this influence was eliminated where the rubber powder was paired with the polymer agent. A rubber inclusion of 20%, preferably paired with 0.2 g/l polymer, was suggested to effectively stabilize South Australian expansive soils

A sulphonated oil for stabilisation of expansive soils

© 2017 Informa UK Limited, trading as Taylor & Francis Group The efficiency of a commercially manufactured sulphonated oil (SO) agent in treating a highly expansive soil was investigated through an extensive experimental program. A total of six SO to water mass concentrations, i.e. 0.25, 0.5, 0.75, 1, 1.25 and 2.5%, were examined. The test program included swell–load oedometer, unconfined compressive strength and cyclic wetting and drying tests. SO-stabilisation amended the soil’s mechanical behaviour through improvements achieved in swelling and strength characteristics. The reduction in swelling potential and swelling pressure was dependent on SO concentration, while the effect of curing time was found to be insignificant. A similar dependency was concluded for the unconfined compressive strength and stiffness of the stabilised soil. Both dependencies suggested an SO concentration of 1.25% capable of yielding an optimal stabilisation scheme. Results of the cyclic wetting and drying tests indicated that the beneficiary effects of SO-stabilisation at optimum concentration, particularly in ameliorating the adverse effects of swell–shrink-related volume changes and to some extent increasing the strength, are strongly preserved under the influence of alternate wetting and drying

Quasi-solid-State Electrolytes for Low-Grade Thermal Energy Harvesting using a Cobalt Redox Couple

Quasi-solid-State Electrolytes for Low-Grade Thermal Energy Harvesting using a Cobalt Redox Coupl

Application of a water-soluble cobalt redox couple in free-standing cellulose films for thermal energy harvesting

Thermal energy harvesting using thermoelectrochemical cells (thermocells) is a sustainable method to produce electricity without carbon dioxide emissions. The solvent and redox couple used in the electrolyte play an important role in determining both the safety and performance of thermocells, and development of leak-free electrolytes with high performance is particularly important for transportable devices. Here, the application of aqueous and non-aqueous electrolytes containing the [Co(bpy)]2+/3+ redox couple in both liquid and solid forms was studied. Cellulose was used as an environmentally friendly material for solidification of the different liquid electrolytes. The properties and performance of the new aqueous [Co(bpy)]2+/3+ electrolytes was compared to those containing the Fe(CN)63−/4− couple, both in liquid and quasi-solid state electrolytes. Higher diffusivity for the cobalt redox ions was observed in the aqueous electrolyte compared to the non-aqueous electrolytes, while the Seebeck coefficient of the redox couple, which determines the open circuit voltage of the thermocell, was largest in the organic solvents. No significant effect of solidification on the Seebeck coefficient was observed

Improved shear strength performance of compacted rubberized clays treated with sodium alginate biopolymer

This study examines the potential use of sodium alginate (SA) biopolymer as an environmentally sustainable agent for the stabilization of rubberized soil blends prepared using a high plasticity clay soil and tire-derived ground rubber (GR). The experimental program consisted of uniaxial compression and scanning electron microscopy (SEM) tests; the former was performed on three soil–GR blends (with GR-to-soil mass ratios of 0%, 5% and 10%) compacted (and cured for 1, 4, 7 and 14 d) employing distilled water and three SA solutions—prepared at SA-to-water (mass-tovolume) dosage ratios of 5, 10 and 15 g/L—as the compaction liquid. For any given GR content, the greater the SA dosage and/or the longer the curing duration, the higher the uniaxial compressive strength (UCS), with only minor added benefits beyond seven days of curing. This behaviour was attributed to the formation and propagation of so-called “cationic bridges” (developed as a result of a “Ca2+/Mg2+ ⟷ Na+ cation exchange/substitution” process among the clay and SA components) between adjacent clay surfaces over time, inducing flocculation of the clay particles. This clay amending mechanism was further verified by means of representative SEM images. Finally, the addition of (and content increase in) GR—which translates to partially replacing the soil clay content with GR particles and hence reducing the number of available attraction sites for the SA molecules to form additional cationic bridges—was found to moderately offset the efficiency of SA treatment

The effect of solvent on the seebeck coefficient and thermocell performance of cobalt bipyridyl and iron ferri/ferrocyanide redox couples

© 2019 CSIRO. The conversion of thermal energy to electricity using thermoelectrochemical cells (thermocells) is a developing approach to harvesting waste heat. The performance of a thermocell is highly dependent on the solvent used in the electrolyte, but the interplay of the various solvent effects is not yet well understood. Here, using the redox couples [Co(bpy)3][BF4]2/3 (bpy = 2,2′-bipyridyl) and (Et4N)3/(NH4)4Fe(CN)6, which have been designed to allow dissolution in different solvent systems (aqueous, non-aqueous, and mixed solvent), the effect of solvent on the Seebeck coefficient (Se) and cell performance was studied. The highest Se for a cobalt-based redox couple measured thus far is reported. Different trends in the Seebeck coefficients of the two redox couples as a function of the ratio of organic solvent to water were observed. The cobalt redox couple produced a more positive Se in organic solvent than in water, whereas addition of water to organic solvent resulted in a more negative Se for Fe(CN)63-/4-. UV-vis and IR investigations of the redox couples indicate that Se is affected by changes in solvent-ligand interactions in the different solvent systems

Swell–shrink behavior of rubberized expansive clays during alternate wetting and drying

The present study examines rubber’s capacity of improving the swell–shrink potential of expansive clays. Two rubber types of fine and coarse categories with different geometrical features were considered. The test program consisted of standard Proctor compaction and cyclic wetting–drying tests. Scanning electron microscopy (SEM) analysis was also performed to identify the soil–rubber amending mechanisms, and to observe the evolution of fabric in response to alternate wetting and drying. Cyclic wetting–drying led to the reconstruction of the soil/soil–rubber microstructure by way of inducing aggregation and cementation of the soil grains. The greater the number of applied cycles, the lower the swell–shrink features, following a monotonically decreasing trend, with the rubberized blends holding a notable advantage over the virgin soil. The tendency for reduction, however, was in favor of a larger rubber size, and more importantly the rubber’s elongated form factor; thus, predicating a rubber size/shape-dependent amending mechanism. The soil–rubber amending mechanisms were discussed in three aspects—increase in non-expansive content, frictional resistance generated as a result of soil–rubber contact, and mechanical interlocking of rubber particles and soil grains. The swell–shrink patterns/paths indicated an expansive accumulated deformation for the virgin soil, whereas the rubberized blends manifested a relatively neutral deformational state, thereby corroborating the rubber’s capacity to counteract the heave and/or settlement incurred by alternate wetting and drying

Swell–shrink behavior of rubberized expansive clays during alternate wetting and drying

The present study examines rubber’s capacity of improving the swell–shrink potential of expansive clays. Two rubber types of fine and coarse categories with different geometrical features were considered. The test program consisted of standard Proctor compaction and cyclic wetting–drying tests. Scanning electron microscopy (SEM) analysis was also performed to identify the soil–rubber amending mechanisms, and to observe the evolution of fabric in response to alternate wetting and drying. Cyclic wetting–drying led to the reconstruction of the soil/soil–rubber microstructure by way of inducing aggregation and cementation of the soil grains. The greater the number of applied cycles, the lower the swell–shrink features, following a monotonically decreasing trend, with the rubberized blends holding a notable advantage over the virgin soil. The tendency for reduction, however, was in favor of a larger rubber size, and more importantly the rubber’s elongated form factor; thus, predicating a rubber size/shape-dependent amending mechanism. The soil–rubber amending mechanisms were discussed in three aspects—increase in non-expansive content, frictional resistance generated as a result of soil–rubber contact, and mechanical interlocking of rubber particles and soil grains. The swell–shrink patterns/paths indicated an expansive accumulated deformation for the virgin soil, whereas the rubberized blends manifested a relatively neutral deformational state, thereby corroborating the rubber’s capacity to counteract the heave and/or settlement incurred by alternate wetting and drying

Interfacial shear strength of rubber–reinforced clays: A dimensional analysis perspective

The present study aims towards the development of practical dimensional models capable of simulating the interfacial shear strength of rubber–reinforced clays. Two types of recycled tire rubbers (of fine and coarse categories) were each incorporated into the soil at four different contents (by weight), and statically compacted at their respective Proctor optimum condition for direct shear testing. The rubber inclusions amended the soil through improvements achieved in two aspects: i) frictional resistance generated as a result of soil–rubber contact; and ii) mechanical interlocking of rubber particles and soil grains. In general, both amending mechanisms were in favor of a higher rubber content, and to a lesser degree a larger rubber size. The dimensional analysis concept was extended to the soil–rubber shear strength problem, thereby leading to the development of practical dimensional models capable of simulating the shear stress–horizontal displacement response as a function of the composite's basic index properties. The predictive capacity of the proposed models was examined and validated by statistical techniques. The proposed dimensional models contain a limited number of fitting parameters, which can be calibrated by minimal experimental effort and hence implemented for predictive purposes

Probing the molecular interactions and physicochemical properties of a cobalt-based redox electrolyte system for thermo-electrochemical cells

Redox-active materials play a primary role in the high-performance electrochemical device research field. Their bulk ion dynamics and performances can be studied using different electrochemical analysis methods, but their molecular level interactions and dynamics on which these depend are often not well understood. Here, nuclear magnetic resonance (NMR) relaxation and double-stimulated echo pulsed field gradient (PFG) techniques have been used to gain insights into the molecular level interactions, exchange dynamics and self-diffusivity of the various species present in a cobalt-based redox active electrolyte system used for thermo-electrochemical applications, including how these factors depend on the oxidation state and concentration of the redox species. A series of liquid electrolyte samples consisting of a Co2+/3+(bpy)3(NTf2)2/3 redox couple (where bpy = bipyridyl and NTf2 = bis(trifluoromethanesulfonyl)imide) in 3-methoxypropionitrile (MPN) have been investigated using NMR as well as viscosity and conductivity measurements carried out over a temperature range 293 to 353 K. The results provide insights into the mobilities and interactions between the various species present, including the exchange of the NTf2− anions between the solvation shells of the Co(bpy)3 species. Such information will be useful in understanding the behaviour of these electrolytes in devices such as thermo-electrochemical cells