Indigenous Technique of Biochar Production and Effect of Biochar Application on the Geotechnical Properties of the Expansive Soils

Various remedial measures adopted to overcome the problems posed by expansive soils like soil replacement, moisture control, prewetting, and lime stabilization have been practiced with varying degrees of success. However, these techniques suffer from certain limitations with respect to their adaptability. Stabilization using solid wastes is one of the emerging techniques to improve the engineering properties of expansive soils to make them suitable for use in construction. This paper presents an attempt made to study the influence of two wastes, rice husk ash (RHA), an agro-waste, and phosphogypsum (PG), an industrial waste from fertilizer industry, in different percentages, as stabilizing materials to improve the properties of problematic expansive soil. The percentage of phosphogypsum (PG) was varied from 0 to 8% with an increment of 2% in combination with 0, 5, and 10% percentages of rice husk ash (RHA). Different tests in the laboratory were conducted to evaluate the characteristics of treated expansive soil. The analyzed results clearly depict that the combination of 10% RHA + 6% PG had significantly improved the soaked CBR value and unconfined compressive strength (UCS) by about 3 times and 96%, respectively, when compared to that of virgin expansive soil. The parametric evaluation summarizes that the combined effect of waste materials phosphogypsum (PG) and rice husk ash (RHA) had shown promising influence on the strength characteristics of expansive soil, thereby giving a twofold advantage in improving problematic expansive soil and also solving a problem of waste disposal.

Utilization of waste materials in the stabilization of expansive pavement subgrade: An extensive review

Forests play a critical role in terrestrial ecosystem carbon cycling and the mitigation of global climate change. Intensive forest management and global climate change have had negative impacts on the quality of forest soils via soil acidification, reduction of soil organic carbon content, deterioration of soil biological properties, and reduction of soil biodiversity. The role of biochar in improving soil properties and the mitigation of greenhouse gas (GHG) emissions has been extensively documented in agricultural soils, while the effect of biochar application on forest soils remains poorly understood. Here, we review and summarize the available literature on the effects of biochar on soil properties and GHG emissions in forest soils. This review focuses on (1) the effect of biochar application on soil physical, chemical, and microbial properties in forest ecosystems; (2) the effect of biochar application on soil GHG emissions in forest ecosystems; and (3) knowledge gaps concerning the effect of biochar application on biogeochemical and ecological processes in forest soils. Biochar application to forests generally increases soil porosity, soil moisture retention, and aggregate stability while reducing soil bulk density. In addition, it typically enhances soil chemical properties including pH, organic carbon stock, cation exchange capacity, and the concentration of available phosphorous and potassium. Further, biochar application alters microbial community structure in forest soils, while the increase of soil microbial biomass is only a short-term effect of biochar application. Biochar effects on GHG emissions have been shown to be variable as reflected in significantly decreasing soil N2O emissions, increasing soil CH4 uptake, and complex (negative, positive, or negligible) changes of soil CO2 emissions. Moreover, all of the aforementioned effects are biochar-, soil-, and plant-specific. The application of biochars to forest soils generally results in the improvement of soil physical, chemical, and microbial properties while also mitigating soil GHG emissions. Therefore, we propose that the application of biochar in forest soils has considerable advantages, and this is especially true for plantation soils with low fertility.

The expansive soil under investigation has caused damage to lightweight structures due to its swelling and shrinkage characteristics in response to changing moisture content. The study aims to assess the impact of municipal solid waste (MSW) fly ash on the engineering properties of subgrade expansive soils and its influence on pavement structure deformation. The influence of municipal solid waste fly ash on expansive soils was evaluated using laboratory tests and finite element methods. The Abaqus software was used to investigate the effects of MSW fly ash on pavement structure deformation. The input parameters employed for this analysis were elastic modulus, Poisson ratio, load, contact area dimension, and pavement layer thickness. To mitigate this issue, MSW fly ash was used as a stabilizing agent at varying percentages (5 %, 10 %, 15 %, 20 %, 25 %, and 30 % of the dry mass of the soil sample).According to the AASHTO soil classification, the soil is classified as A-7, has a high free swell, a low soaked CBR value, and a high soaked CBR swell, and does not meet the ERA manual standard for subgrade materials. The laboratory tests shown several improvements in the engineering properties of expansive soil when MSW fly ash were mixed. These improvements included a reduction of soaked CBR swelling, free swell index, plasticity index, specific gravity, optimum moisture content. Additionally, the maximum dry density and soaked CBR values increased. Numerical analysis using Abaqus software focused on vertical deformation of the pavement structure. The results showed that as the percentage of MSW fly ash in form 0 % to 25 % of soil dry weight, the vertical deformation of the pavement structure decreased from 0.84 mm to 0.67 mm. This demonstrates that the addition of MSW fly ash reduced the deformation of expansive sub-grade soil and improved the engineering qualities of pavement structure. In conclusion, the study revealed that the use of MSW fly ash as stabilizing agent effectively reduced the deformation of expansive subgrade soil and improved the engineering qualities of pavement structure.

Expansive soil shows dual swell–shrink which is not suitable for construction. Several mitigating techniques exist to counteract the problem promulgated by expansive clayey soils. This paper explored the potential mecho-chemical reinforcement of expansive clayey soil to mitigate the effect of upward swelling pressure and heave. The polypropylene fiber is randomly distributed in the soil for mechanical stabilization, and the industrial residual silica fume is used as a chemical stabilizer. The experimental analysis was made in three phases which involved tests on mechanically-reinforced expansive soil, using randomly distributed polypropylene fibers with different percentages (0.25%, 0.50%, and 1.00%), and which were 12 mm length. The second phase of experiments was carried out on chemical stabilized expansive soil with different percentages (2%, 4%, and 8%) of silica, and the next phase of the experiment focused on the combination of mecho-chemical stabilization of the expansive soil with different combinations of silica (i.e., 2%, 4%, and 8%) and polypropylene fibers (i.e., 0.25%, 0.50%, and 1.00%). Maximum dry density (MDD), optimum moisture content (OMC), liquid limit (LL), plastic limit (PL), plastic index (PI), grain size, and constant volume swelling pressure tests were performed on unreinforced and reinforced expansive soil, to investigate the effects of polypropylene fiber and silica fume on the engineering properties of expansive clayey soil. The experimental results illustrate that the inclusion of polypropylene fiber has a significant effect on the upward swelling pressure and expansion property of expansive soil. The reduction in the upward swelling pressure and expansion is a function of fiber content. These results also indicated that the use of silica fume caused a reduction in upward swelling potential, and its effect was considerably more than the influence of fiber.

The weak engineering properties of black cotton soil can cause instability and failure of structures built upon it. Thus, the improvement of its properties is of utmost importance. The present research is to investigate the effect of integrating sawdust ash and rice husk ash on the engineering features of black cotton soil. The soil samples were collected from Guntur KL University, Andhra Pradesh, at a depth of 1-2 meters. Rice husk ash was added to the soil in varied percentages of 0, 3, 6, 9, 12, and 15% by weight of black cotton soil, whereas sawdust ash was added to all mixed samples at 6% by weight of soil. To analyze the engineering properties of the soil and its mixtures, laboratory tests such as Atterberg’s Limits, Specific Gravity, Particle Size Distribution, Standard Proctor test, Unconfined Compressive Strength (UCS), and California Bearing Ratio (CBR) were performed. Results showed that adding a combination of 9% Rice husk and 6% sawdust ash to the weight of black cotton soil notably improves its engineering properties. Therefore, sawdust and rice husk ash have the potential as soil stabilizing agents, making black cotton soil a more suitable foundation material for construction.

Biochar from agricultural crop residues: Environmental, production, and life cycle assessment overview

Expansive soils are the soils which have tendency to increase the volume in the presence of water and decrease in the volume in the absence of water. This expansive behavior in the soil is due to the presence of clay minerals like montmorillonite, illite, and kaolinite. These soils have distributed almost all locations in India and cause troublesome from engineering conditions. To overcome the same, soil properties can be modified with the use of modern techniques. Among the methods, stabilization of expansive soil by using different additives is an appropriate method for the improvement of soil by changing the behavior and properties of expansive soil. The present study is to investigate the effect of calcium chloride and terrasil on the strength properties of soil. Different laboratory experiments conducted on expansive soil mixed with different percentages of calcium chloride and terrasil with a view to determine the optimum percentage. The results yielded an encouraging performance and the efficiency of the added materials. The optimum combination was 1.5% of calcium chloride and 0.10% terrasil which gave the ultimate results in the strength properties of the problematic expansive soil. Hence, the present paper summarizes the use of calcium chloride and terrasil as stabilizing materials for improving the strength properties of expansive soil.KeywordsExpansive soilCalcium chlorideTerrasilStabilization and strength characteristics

Optimization of Atterberg limits of treated expansive soils with Taguchi method

Combined biochar and double inhibitor application offsets NH3 and N2O emissions and mitigates N leaching in paddy fields

Expansive soils are known to show significant volumetric changes in response to changes in the moisture content. Such soils swell when the moisture content is increased and shrink when the moisture content is decreased, thereby causing distress and damages to structures founded on them. Construction developments on naturally occurring expansive soils are usually problematic. This study examines the properties of expansive soil obtained from the city of Muscat in Oman. The expansive soil samples were further treated with gypsum, which was obtained from waste plasterboards, at varying quantities of 3%, 6%, 9% and 12% by mass in an attempt to stabilize the soil. Based on USCS classification system, the expansive soil was identified a poorly clay with high plasticity (CH) with AASHTO classification of A-6. The pH test confirms the reaction between expansive and gypsum, while both the compaction and unconfined compression strength (UCS) tests revealed the optimum percentage of gypsum required to enhance the properties of expansive soil to be 9% by mass. The unconfined compression strength (UCS) test yielded a 37.7% increase over that of untreated expansive soil at 28 days of curing. The California Bearing Ratio (CBR) test of the treated soil yielded a 57% increase in CBR value for expansive soil treated with 9% of waste gypsum over untreated expansive at the unsoaked state and 70% at soaked state. Overall, a solid understanding of the physical and engineering properties of expansive soil, and the confirmation of the potential use of gypsum for its stabilization, was achieved in this study.

The use of cheap and waste materials in bricks production have been encouraged as an alternative to industrial stabilizers due to high cost of cement or lime for production of stabilized bricks. This study looks at the potential of using wastes like saw dust ash (SDA) and rice husk ash (RHA) mixture in treatment of Makurdi clay for burnt bricks production and its subsequent assessment for structural building bricks. Makurdi clay was treated with SDA and RHA mixture, each at 0%, 2%, 4% and 6% respectively. The compressive strength of the burnt bricks increased from 9.40 MN/ for untreated brick to a maximum value of 11.29 MN/ for 2%SDA+2%RHA treated burnt bricks. Treatment with waste mixtures above this content resulted in decreased strength. The water absorption of 14.9% for untreated burnt brick increased to a value of 16.2 % for 2%SDA+2% RHA treated burnt brick. Treatment with higher waste mixture additions resulted in increased water absorption up to 19.4% for 6%SDA+6% RHA treated burnt brick. Energy Dispersion X-ray Spectrometer results showed the presence of calcium, silicate and aluminate as a cementitious compound in the 2%SDA+2%RHA treated burnt brick. The compressive strength value of 11.29 MN/ is greater than 10.3 MN/ which is the minimum value suitable for structural building bricks in grade negligible weather based on ASTM C62-99. Thus 2%SDA+2%RHA treated burnt brick from Makurdi clay is recommended for structural building bricks in grade negligible weather

The study focusses on comparative analysis of mechanical properties of Bentonite (expansive soil) and Kaolinite (non-expansive soil) treated with Lime and Rice Husk Ash (RHA). Unconfined Compressive Strength (UCS) tests were carried out for different curing periods of 0, 3, 7, 21 and 28 days. X-ray Diffraction and Scanning Electron Microscope tests were carried out to study the mineralogical and microstructural properties of the soil. Beyond optimum content the strength was found to decrease for all cases. In case of Lime the reduction in strength may be due to formation of the silica gel or excess Lime content beyond the optimum content may act as a lubricating agent between two-soil particle and reducing the shear resistance. In case of RHA the reduction in strength may be due to the formation of coarse particles which results in lower densities and more void formation. It was observed that UCS of Lime treatment is approximately 3 times higher than that of RHA treatment. In case of non-expansive soil, it was 3.5 times higher in Lime than RHA treatment.

ABSTRACTBiochar amendments can reduce greenhouse gas (GHG) emissions from agricultural soils while helping to maintain food security. However, whether the effect of biochar application on emission intensity (EI) of non‐CO2 greenhouse gas emissions (including methane (CH4) and nitrous oxide (N2O)), per unit of crop caloric content, varies for different crops and its driving mechanism remains unclear. Here, we conducted a meta‐analysis of EI changes (ΔEI) with biochar application for three major cereal crops: rice, wheat, and maize, based on 202 observations from 41 research publications from Monsoon Asia. Our results showed that biochar application reduced the EI for all three crops by an average of −14.6 kg CO2 eq M cal−1, with the greatest reduction in ΔEI for rice (−28.9 kg CO2 equation M cal−1). Biochar application‐induced reduction in CH4 emissions (−0.4 Mg CO2 eq ha−1) was the main contributor to ΔEI for rice, which was greater than those for upland crops: maize and wheat (−0.1 Mg CO2 eq ha−1 and 0.3 Mg CO2 eq ha−1, respectively). Crop type directly affected ΔEI after biochar application. Additionally, crop type indirectly influenced ΔEI by associating with soil organic carbon and clay contents for N2O emission and CH4 emission, respectively. This study highlights that biochar application to soil reduces EI across the globally important agricultural region, and these reductions were most pronounced for rice compared to wheat and maize. Our study provides a better understanding of the effects of biochar on GHG emissions for three important crops and can facilitate the development of new strategies for agricultural GHG mitigation while maintaining food security for the future.

The presence of expansive soils on construction sites is problematic in geotechnical engineering. The swell-shrink behaviour makes these soils not suitable to be used in their natural state. The expansive soil damages cause financial loss yearly more than floods, hurricanes, tornadoes, and earthquakes combined. Moreover, the cost of cut to spoil of expansive soils during construction projects has continued to rise because of the high cost of earthworks, haulage, and the increasing scarcity of spoil areas because of the built environment. Nonetheless, a proper stabilization technique can significantly enhance the expansive soil's properties. The research project attempts to review, report the limits and merits of mechanical and chemical methods utilized to stabilize expansive soils in line with their efficiency, environmental concerns, and cost-effectiveness. A review of mechanical and chemical treatment techniques is conducted in this regard. Ultimately, each stabilization method exhibits its merits and limitations. The lack of standards for the treatment of swelling soils is a significant problem in engineering practice. Specialists in the domain of soil treatment must work together to obtain an optimized stabilization approach and protocol. Moreover, engineers should perform a geoenvironmental assessment appropriate for chemical stabilization methods and additives utilized. This research work contributes as a guideline in the selection and application of chemical and mechanical stabilization methods.