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Red mud and bottom ash are two industrial wastes generated in huge quantities by the aluminum industry and coal-based power plants, worldwide. The high alkaline nature and high specific gravity of red mud are the major hindrances in utilizing as constructional geomaterial. The manuscript aims to utilize these two wastes as subgrade material in pavement by mixing different proportions of red mud with bottom ash. The physical behavior i.e., specific gravity, grain size pattern, and chemical characterization i.e., pH of all the mixes were assessed. Geotechnical properties such as compaction, compression, strength, and permeability tests were conducted to investigate the efficiency of different mixes as suitable geomaterial. The California bearing ratio, cyclic triaxial test under different confining pressure, resilient modulus, and nonactivity of clays by methylene blue test results provide the proficiency of different mixes in utilizing as subgrade material. The highest strength, high CBR, and resilient modulus values suggest that the mixture of 70% HRM with 30% HBA is suitable and strength gain upon drying suggests that it can be used as a structural subgrade material. Further, a leachate analysis of all the mixes concluded that the chemicals are within permissible limits and hence not hazardous to the ecosystem. [ABSTRACT FROM AUTHOR]

Abstract The disposal of magnesite mine tailings (MMT), a by-product of magnesite mining, raises significant environmental concerns due to its adverse effects on soil, water and air quality. Likewise, the improper disposal of used face masks exacerbates environmental burdens. The innovative use of polypropylene fibres (PPF) derived from disposable face masks to reinforce. This study explores the compaction and strength characteristics of PPF-MMT composites with varying fibre content to develop a sustainable composite for subgrade construction. The findings indicate that the addition of PPF increases optimal moisture content and decreases maximum dry density. Shear strength analysis reveals a linear failure envelope for both MMT and PPF-MMT, with initial angle of internal friction improvement at lower PPF content (0.25% and 0.5%) but a decline at higher contents (0.75% and 1%). Importantly, PPF-MMT consistently exhibits a unique strain-hardening behaviour across all stress levels, distinguishing it from MMT, which only transitions to strain-hardening at higher stresses. Under vertical load, MMT shows contraction, while the PPF-MMT composite initially contracts but later dilates due to increased fibre-MMT interaction during horizontal displacement. Furthermore, California bearing ratio (CBR) tests demonstrate increased dry CBR with PPF, reaching a peak of 33.85% at 0.5% fibre content. The soaked CBR tests affirm the remarkable durability of PPF-MMT, maintaining significantly higher values than MMT even after 60 days of soaking. The study concludes that 0.5% fibre content as optimum dosage.

The research demonstrates the geotechnical properties of tropical soils and their implications for road construction. A series of standardized geotechnical and geochemical laboratory tests on lateritic soils of Bahir-Dar (Ethiopia) were conducted. Soil samples at depths of 0.6 m and 1.5 m were collected from five sites. The silica to sesquioxide ratio indicated that soils are lateritic. The findings show invariable particle-size distribution and Natural Moisture Content range between 4.53 to 12.2%. Average Maximum Dry Density and Optimum Moisture Content were 1.563 and 20.58, respectively. The specific gravity ranges from 1.95 to 3.09. The LL, PL, and PI range from 42 to 86.3%, 28.38 to 38.4%, and 13.12 to 49.7%, respectively. The unsoaked CBR and corresponding soaked CBR values range from 4.86 to 14.36% and 1.22 to 3.88%, respectively, at 65 blows of the modified proctor. The results evaluated the suitability of soils according to the Ethiopian Roads Authority standards and implicated that partially Test Pits-C, D & E soils satisfy to be a sub-grade or embankment material. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the feasibility of the large-scale application of steel slag (SL) in subgrade. Subgrade materials with three kinds of SL proportions were first prepared. Then, a compaction test, liquid-plastic limit combined-measurement test, and a California bearing ratio (CBR) test were applied to determine the best proportion between SL and intact soil (S), i.e., SL/S. Subsequently, static and dynamic tests and a volume stability test were carried out for soil mixed with SL at the optimum proportion (SSL). In addition, a composition analysis of infiltration fluid and a permeability test of SSL were performed. The test results showed that compared to S, the physical properties of SSL were significantly improved, especially the liquid-plastic limit, as well as the soil water stability. The optimum proportion of SL was determined as 50% of soil by mass. At the optimum proportion, SSL had the highest CBR value of 60%, which had both economic and engineering compaction performance, leading to a large-scale utilization rate of SL. The static and dynamic characteristics showed that the addition of SL would greatly improve the shear strength and dynamic modulus of soil, mainly expressed as the increase of internal friction angle. The volume stability of SSL could also meet the requirements of the Chinese specification. After adding 2% cement, the strength and stability of SSL was further improved. In addition, the environmental impact test proved that the infiltration liquid did not pollute surface water nor underground secondary water. Although the permeability coefficient of SSL with the optimum proportion of 50% was higher than that of pure soil, it still belonged to the normal value of clay and silty clay, and good impermeability would ensure the controllability of potential trace elements. Based on the test results of mechanical properties and environmental impact, SSL proved to have the potential for green road material engineering properties. This study proposes a reliable and practical method to promote the utilization of steel slag. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the feasibility of the large-scale application of steel slag (SL) in subgrade. Subgrade materials with three kinds of SL proportions were first prepared. Then, a compaction test, liquid-plastic limit combined-measurement test, and a California bearing ratio (CBR) test were applied to determine the best proportion between SL and intact soil (S), i.e., SL/S. Subsequently, static and dynamic tests and a volume stability test were carried out for soil mixed with SL at the optimum proportion (SSL). In addition, a composition analysis of infiltration fluid and a permeability test of SSL were performed. The test results showed that compared to S, the physical properties of SSL were significantly improved, especially the liquid-plastic limit, as well as the soil water stability. The optimum proportion of SL was determined as 50% of soil by mass. At the optimum proportion, SSL had the highest CBR value of 60%, which had both economic and engineering compaction performance, leading to a large-scale utilization rate of SL. The static and dynamic characteristics showed that the addition of SL would greatly improve the shear strength and dynamic modulus of soil, mainly expressed as the increase of internal friction angle. The volume stability of SSL could also meet the requirements of the Chinese specification. After adding 2% cement, the strength and stability of SSL was further improved. In addition, the environmental impact test proved that the infiltration liquid did not pollute surface water nor underground secondary water. Although the permeability coefficient of SSL with the optimum proportion of 50% was higher than that of pure soil, it still belonged to the normal value of clay and silty clay, and good impermeability would ensure the controllability of potential trace elements. Based on the test results of mechanical properties and environmental impact, SSL proved to have the potential for green road material engineering properties. This study proposes a reliable and practical method to promote the utilization of steel slag.

The application of industrial waste in construction reduces the dependency on natural resources. The materials, including red mud (RM) and fly ash (FA), proved to be favorable materials. However, the materials potential together as a geopolymer composite for road applications has rarely been explored. This study will examine the possibility of the replacement of natural materials in subgrade applications. To achieve this, the geopolymer compositions will be prepared by replacing RM with FA at replacement rates of 10%, 20%, and 30% by dry weight basis. The alkaline activator solution of 8 M will be prepared using sodium hydroxide (NaOH) and sodium silicate to develop geopolymer composites. The strength properties will be studied using the California Bearing Ratio (CBR) and unconfined compression strength (UCS) and validated with microstructural analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results reveal that geopolymer composites could achieve a maximum CBR value of 12% and UCS of 2,700 kPa. The microstructural analysis revealed that the formation of dense calcium aluminate hydrate (C-A-H) and calcium silicate hydrate (C-S-H) are the reason for strength improvement. The leaching studies show that the toxic elements were within the permissible limits. Overall, the test results confirmed that the geopolymer composites meet the required strength and could be used as a subgrade material in road construction. [ABSTRACT FROM AUTHOR]

Highlights • A novel subgrade material that modifying SC (silty clay) by waste FA (fly ash) and OSA (oil shale ash) was prepared. • The optimum ratio of OSA/FA/SC in the modified soil was determined. • The mechanical properties of the modified soil at the optimum ratio of OSA/FA/SC were measured. • The environmental impact of the modified soil subgrade leachates on water was assessed. Abstract The objective of this study was to evaluate the viability of utilizing waste fly ash (FA) and oil shale ash (OSA) to modify silty clay (SC) as a subgrade material. First, the modified soils at five different ratios of OSA/FA/SC were prepared. Second, the compaction, Atterberg limits and CBR (California bearing ratio) tests were conducted to determine the optimum ratio of OSA/FA/SC. Third, the static and dynamic mechanical characteristics of the modified soil at the optimum ratio of OSA/FA/SC were measured. Subsequently, the environmental impact of the modified soil subgrade leachates on water was assessed. The results show the physical properties of SC are improved by the addition of FA and OSA. The modified soil at the OSA/FA/SC ratio of 40:20:40 possesses the highest CBR value, propriate physical properties and the balanced usage ratio of FA, OSA and SC. The triaxial tests demonstrate that the static strength parameters and dynamic fracture strength of SC are significantly increased by FA and OSA. The obtained dynamic modulus could be valuable for evaluating the deformation and stability of this modified soil in geotechnical engineering. The main ions and trace elements concentration analysis results indicate that the modified soil leachates have no pollution on Class II surface water and Class III ground water. Based on these results, SC modified by FA and OSA has the potential to be used a viable subgrade material. [ABSTRACT FROM AUTHOR]

This paper assesses the stabilizing effect of powdered glass on clay soil. Broken waste glass was collected and ground into powder form suitable for addition to the clay soil in varying proportions namely 1%, 2%, 5%, 10% and 15% along with 15% cement (base) by weight of the soil sample throughout. Consequently, the moisture content, specific gravity, particle size distribution and Atterberg limits tests were carried out to classify the soil using the ASSHTO classification system. Based on the results, the soil sample obtained corresponded to Group A-6 soils identified as ‘fair to poor’ soil type in terms of use as drainage and subgrade material. This justified stabilisation of the soil. Thereafter, compaction, California bearing ratio (CBR) and direct shear tests were carried out on the soil with and without the addition of the powdered glass. The results showed improvement in the maximum dry density values on addition of the powdered glass and with corresponding gradual increase up to 5% glass powder content after which it started to decrease at 10% and 15% powdered glass content. The highest CBR values of 14.90% and 112.91% were obtained at 5% glass powder content and 5mm penetration for both the unsoaked and soaked treated samples respectively. The maximum cohesion and angle of internal friction values of 17.0 and 15.0 respectively were obtained at 10% glass powder content.

In order to reuse red mud and bauxite tailings mud (two typical aluminum industrial wastes) to reduce the occupation of land resources and environmental damage, these two wastes were combined to develop subgrade materials for the first time. With different combinations, the effects of the amounts of red mud, tailings mud, and cementitious materials on the strength of tested subgrade materials were investigated. The mechanism of strength growth was analyzed by a micro-test. The test results showed that the material strength of three combinations met the requirements when the unconfined compression strength (UCS) of all combinations increased with age. The UCS of the A1BC2 combination (the mass ratio of red mud and tailings mud was 2:1, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2) was the best, with the UCS being 3.03 MPa in 7 days. Microscopic imaging showed that specimens with high red mud contents had compact structures without cracks. The strength of these materials is mainly due to hydration reactions and pozzolanic reactions; the cementitious products generated by the reactions solidify Na+ and inhibit the release of OH−, while the addition of tailings mud can reduce the content of Na2O in the material, which makes the environmental compatibility of the A3BC2 combination the best (the mass ratio of red mud and tailings mud was 1:2, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2). Its pH value was 8.75. This experiment verifies the feasibility of the combined application of red mud and tailings mud in subgrade materials. To this end, a feasible scheme for the simultaneous consumption of these two kinds of aluminum industrial wastes has been proposed. [ABSTRACT FROM AUTHOR]

The current paper reports an experimental investigation that aims to determine the effects of freeze-thaw cycles (cycle number and freezing low temperature) on the dynamic responses of frozen subgrade soil. The test results indicate that the curve level for the dynamic shear modulus (damping ratio) first decreases (increases) and then remains approximately stable at a small strain range with increasing freeze-thaw cycles. These critical cycle numbers for the dynamic shear modulus (damping ratio) are different at the three freezing low temperatures. A theoretical model is developed to describe the evolutionary features of the dynamic shear modulus (damping ratio) under different conditions. The development of accumulative plastic deformation is strongly sensitive to freeze-thaw cycles and freezing low temperatures. Two-stage evolutionary features for the resilient modulus with a loading cycle number were experimentally verified under different conditions. The freeze-thaw attenuation coefficient was adopted to evaluate the property deterioration with increasing freeze-thaw cycles. The comparison results display good agreement between the experimental data and the predicted curve determined from this proposed theoretical model. This investigation provides a useful and important reference for assessing the degeneration of engineering properties for frozen subgrade soil exposed to freeze-thaw cycles. • The development features for dynamic shear modulus and damping ratio are dependent to freeze-thaw cycles. • The evolution characteristics of accumulative plastic deformation and resilient deformation are sensitive to freeze-thaw cycles. • The freeze-thaw attenuation coefficient is presented to characterize the degenerations of dynamic properties. [ABSTRACT FROM AUTHOR]