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The use of non-conventional additives in soil stabilisation has increased significantly in recent years. Nevertheless, the effectiveness of alternative additives, which can be determined by the impact promoted on the pH of the soils, could be limited due to insufficient time for the pozzolanic reaction (associated with a quick decrease of pH). Thereby, this paper focuses on the study of the efficacy of using different dosages of innovative industrial wastes in both clayey and marly soils. The additives studied were dolomitic lime (from residual quarry sludges), biomass fly ash, steel slag (from Electric Arc Furnace), and conventional lime which was used as a control. The effectiveness of these additives was evaluated by measuring the evolution of pH, carbonate content and particle size at 0, 7, 14 and 28 days. Results showed that residual dolomitic lime can be as effective as commercial lime in soil stabilisation, while the biomass ash used in this work was found to be the least effective additive. All additives used in this study led to greater changes in soil properties for clayey samples. [ABSTRACT FROM AUTHOR]

Conflicting recommendations and opinions can be found in literature concerning the effects of a delayed compaction of lime-stabilized soils. This study was carried out to evaluate such effects on a clayey soil (CH) with 5% of quicklime and hydrated lime. One-dimensional consolidation and hydraulic conductivity tests were carried out on samples compacted soon after lime addition and after 48 h. Analysis of results, helped by scanning electron microscopy and mercury intrusion porosimetry, shows that, for the tested soil, delayed compaction causes a reduction of the dry unit weight up to 11% with hydrated lime and to 18% with quicklime and a greater compressibility of the mixtures at high pressures (at 800 kPa the compression index of samples compacted with delay is doubled relative to that of the immediately compacted ones). However, pozzolanic reaction was found to progress with curing time, even in the case of delayed compaction. The hydraulic conductivity is not significantly modified by a delayed compaction; it is strongly affected by the wetting conditions of curing in the case of hydrated lime. In general, a prompt compaction is always recommendable after addition of hydrated lime whereas the use of quicklime mitigates the influence of a delayed compaction. [ABSTRACT FROM AUTHOR]

Abstract: One of the major setbacks of road construction in most flood plains is their geological incompetence. They are hardly able to form soils with the right engineering profile for use as foundation soils for road construction. This has undoubtedly made the prospects of improving natural soils an attractive option, coupled with the ever increasing zest of zero waste, reduction in energy usage, reduction in natural resource depletion and lowering carbon dioxide emissions to the atmosphere. To avoid the strain associated with material haulage over long distances—increased costs and carbon foot prints. Soil stabilisation with by-product materials has proved to be a useful cost effective option. This paper hence, presents a detailed investigation of the viability of using waste materials, Ground Granulated Blastfurnace Slag (GGBS), gotten from the steel making processes, activated by lime (CaO), in the stabilisation of low bearing capacity clay soils (Lower Oxford Clay). Particularly, where flooding is envisaged to be of utmost concern, as facilities hosted by scenarios of this type are imminent environmental concerns and undermines cost efficiency. This was achieved by the laboratory simulation of flooding scenarios in which 50mm diameter and 100mm long cylindrical specimens were exhaustively investigated. The assessment involved soaking samples in water, for 4- and 10-days after different days of moist curing (7, 14, 28, 56 and 90days), durability index test and unconfined compressive test for up to 90days of these samples were assessed. The results achieved, show that road structural layers/embankments constructed on floodplains could be durable with the application of industrial by-product material (GGBS) activated by lime. This has the implication of combining cost effectiveness with improved quality of the materials formulated, thereby enhancing the environmental friendliness of construction processes on flood plains. This sustainability implication provides the impetus for the current research. [Copyright &y& Elsevier]

Abstract: The topsoil of clayey slope is easy to erosion because it is weak in its strength, water stability and erosion resistance. A new organic polymer soil stabilizer, which was developed for the stabilization treatment of clay slope topsoil and was named as STW, was introduced in this study. In order to understand the effect of STW on the stabilization of clayey soil, laboratory tests on the unconfined compressive strength, shear strength, water stability and erosion resistance of untreated and treated soil specimens are performed, The results indicated that STW soil stabilizer can significantly increased the unconfined compression strength, shear strength, water stability and erosion resistance of clayey soil. The unconfined compression strength increased with the increasing of curing time and the variation mainly occurs in the first 24-hour. With the addition amounts of STW increasing, the strength, water stability and erosion resistance increased at the curing time being 48h, but in the case of friction angle, no major change was observed. Based on the scanning electron microscopy (SEM) analysis of the stabilized soil, the stabilization mechanisms of STW soil stabilizer in the clayey soil were discussed. Finally, a field test of the stabilization treatment of clay slope topsoil with STW was carried out, and the results indicated that the STW soil stabilizer on the stabilization treatment of clay slope topsoil is effective for improving the erosion resistance of slope topsoil, reducing the soil loss and protecting the vegetation growth. Therefore, this technique is worth popularizing for the topsoil protection of clay slope. [Copyright &y& Elsevier]

Abstract: In the French model of deep nuclear wastes repositories, the galleries should be backfilled with excavated argillite after the site has been filled. After thousands of years, the degradation of the concrete lining of the galleries will generate an alkaline solute (pH>12) that would circulate through the backfill. The goal of this paper is to describe the impact of such solute circulation on the properties of compacted argillite. Since additives (bentonite, sand or lime) are often introduced in the remoulded argillite for the backfill, such mixtures were also studied. Saturated-portlandite water was circulated through compacted samples for 3, 6 and 12months at 60°C. The shear strength behaviour of the samples was determined with triaxial tests. The microstructure of the samples was analysed via mercury intrusion porosimetry tests and scanning electron microscopy. The results showed that the influence of the alkaline fluid on the properties of the argillite is a function of the nature of the additive. In the case of the calcareous sand, no major changes were observed. The pure argillite underwent a slight decrease in its cohesion due to limited dissolution of its clayey particles. Conversely, intense alteration of the bentonite–argillite mixture was observed, and the shear strength behaviour was modified. Lime addition improved the mechanical characteristics of the argillite. [Copyright &y& Elsevier]

The technique of carbonated stabilization is an innovative method to improve the engineering performance of soft soils. However, the improvement in the engineering performance of stabilized soils with carbonized steel slag has not been studied. In addition, the effect of clay minerals on carbonation parameters and D-W cycle performance remains unknown. To this end, in this paper, three types of synthetic soils containing different clay minerals were prepared to be stabilized by carbonated steel slag. The strength performance and microstructural evolution of carbonated steel slag stabilized soils were investigated by drying-wetting (D-W) cycle tests, unconfined compression strength (UCS) tests, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM). The results showed that the compressive strength after and resistance to D-W cycles of carbonated steel slag stabilized soils were significantly improved due to carbonation treatment. The presence of clay minerals in stabilized soils led to the high values of optimum moisture content for carbonation (C-OMC). The C-OMC value of stabilized soils containing montmorillonite was higher than that of stabilized soils containing kaolinite. Montmorillonite had a higher negative effect on the D-W cycle performance of soils compared to kaolinite. This fact could be reflected by the fluctuation of UCS and mass change ratio (R m). The main carbonation product by three types of carbonated steel slag stabilized soils was calcite, which remained stable after D-W cycles. After carbonation for 18 h, the generated calcite and carbonation degrees for three types of stabilized soils were obtained. In the microstructures of carbonated steel slag stabilized soils, the spindle-like clusters of the generated calcite appeared, which adhered to the surface of mineral particles. The aggregated degrees of the generated calcite in stabilized soils containing clay minerals tended to decrease after D-W cycles. In this work, a new type of carbonated steel slag stabilized soil was studied. The results indicated that the effect of clay minerals on the engineering characteristics of soil should be considered. • Carbonated steel slag is used to stabilize three types of artificial soils. • Influence of clay minerals on performance and microstructure of carbonated steel slag stabilized soils is investigated. • The existence of clay minerals leads to increasing values of the optimum moisture content for carbonation. • The main carbonation product is calcite which remains to be stable after drying and wetting cycles. [ABSTRACT FROM AUTHOR]

There are various methods for improving the engineering properties of weak soils among which the usage of chemical additives is one of the most important ones. Considering sepiolite as an environmental friendly material and its unique physiochemical characteristics, this substance has been used as an additive for soil improvement in this study. For this purpose, in addition to soil identification tests, in order to examine the effect of changes in the percentage of sepiolite additive, a set of tests has been done including Atterberg limits, modified compaction, uniaxial compressive strength, pH, direct shear and permeability test on sandy clay and clayey sand soils. Furthermore, scanning electron microscopy (SEM) and x-ray diffraction (XRD) tests have been performed to investigate the microstructure of non-stabilized and stabilized soil. According to the results, with increasing the additive percentage and the curing time, the uniaxial compressive strength of the soil increased. The uniaxial strength in the clayey sand soil rose up to six times larger than that of the initial strength of the soil. However, the maximum strength enhancement in the sandy clay soil was up to three times the initial value. Sepiolite (above 5%) has improved soil shear strength parameters including cohesion and internal friction angle. The increase in the additive content led to diminished permeability in soil. Further, the elevation of the sepiolite content in the soil resulted in enhanced liquid and plastic limits of soil. Microstructural investigations indicated that the reason of improvement in strength parameters of soil was the incidence of chemical reactions including ion exchange, flocculation and production of calcium-silicate-hydrate (CSH) and calcium-aluminate-hydrate (CAH) gels. Further, sepiolite fiber resulted in enhanced strength by filling the pores and void spaces of soil. • Sepiolite is an environmentally friendly material to stabilize the soils. • Increasing the sepiolite content during the curing time, increases UCS of the soil. • Sepiolite fibers act like bridges and connect different parts of soil. • CSH and CAH are products of chemical reactions between sepiolite and soil. [ABSTRACT FROM AUTHOR]