2. Thesis and Dissertations
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Item Investigation on Synergistic Effect of Biomineralization and Ash-Based Soil Stabilization(National Institute of Technology Karnataka, Surathkal, 2023) Kothuri, Mahindra; Devatha, C. P.Waste management is an intricate and pressing global challenge that demands our immediate attention and concerted efforts to address the environmental impacts resulting in widespread pollution and adverse effects on human health. To combat these challenges, it is imperative to develop innovative and eco-friendly solutions that mitigate the negative consequences of waste and promote sustainable practices for a cleaner and healthier future. Waste materials, including biomedical ash and ferrochrome ash, contain toxic heavy metals such as Pb, Ni, and Cr, which pose risks to the environment and human health. Hence, the present study aims to assess the effect of biomineralization to immobilize the heavy metals and allowing the safe application of biomedical ash (BMA) and ferrochrome ash (FCA) in enhancing the properties of black cotton soil (BCS). The research objectives encompass evaluating microbial growth in waste ashes, identifying the optimal protein source for bacterial urease production, optimizing nutrient medium composition for enhanced biomineralization, and analyzing the impact of biomineralization on the engineering properties of waste ashes as environmentally friendly soil stabilizers. To address these objectives, a three-stage methodology has been adopted. In the first stage, the investigation focused on the presence of bacteria in waste ashes. Indigenous urease-positive bacteria were isolated using the serial dilution technique with Christensen's agar medium and identified through 16SrRNA analysis. The study identified Bacillus cereus and Lysinibacillus sphaericus as suitable urease-positive bacteria for biomineralization in BMA and ferrochrome ash FCA, respectively. The performance of different legumes as protein sources were compared by monitoring pH, optical density, and urease activity over time. Blackgram and soybean were identified as the most suitable protein sources for bacterial growth and urease activity. The second stage of the research involved integrating biomineralization into biomedical ash for stabilizing black cotton soil. Response surface methodology (RSM) using a central composite design (CCD) was employed to model the role of protein, vitamin, and carbon sources in urease activity. The study determined the optimal combination ii of 23.47 g/L black gram, 3.45 g/L yeast extract, and 0.03 g/L dextrose while also observing that the dosage of protein and vitamin sources significantly impacted bacterial growth and urease activity. The production of mineralized biomedical ash consisted of combining equimolar urea & calcium chloride (1 M) and the acquired bacteria with biomedical ash. Leachate extracted from mineralized biomedical ash demonstrated reduced concentrations of Hg (97 %), Cr (96 %), Zn (97 %), Pb (93 %), Fe (94 %), Cu (93 %), Cd (98 %), Ba (87 %), As (96 %), Ti (88 %), and Se (86 %), indicating the effectiveness of biomineralization in immobilizing heavy metals. To assess the influence of mBMA on soil characteristics, black cotton soil (BCS) was subjected to different proportions (10 %, 20 %, 30 %, and 40 %) of mBMA. At 40 % soil replacement (m40) by mBMA, the soil’s liquid limit (LL), plastic limit (PL), plasticity index (PI), and free swell index (FSI) were 47 %, 34 %, 13 %, and 14 %, respectively. The corresponding values in the same order are 53 %, 25 %, 27 %, and 114 % for BCS. The optimal moisture content (OMC) shifted from 22 % for BCS to 26 % for m40. The corresponding maximum dry density (MDD) reduced from 1.596 g/cm3 for BCS to 1.458 g/cm³ for m40. These values indicate improved soil consistency and reduced compressibility due to adding mBMA to BCS. Notably, the highest unconfined compressive strength (UCS) of 147 kPa was observed for m30 (30 % BCS replaced with mBMA). UCS of BCS was determined as 35 kPa. Characterization studies (XRD, FEGSEM, FTIR, TGA) were conducted on mBMA. X-ray diffraction analysis detected significant amounts of calcite while scanning electron microscope images revealed the presence of dense matter connecting the ash particles, which was identified as calcite formed during biomineralization. Fourier transform infrared absorption bands corresponding to carbonates further supported the occurrence of biomineralization. A 10 % weight reduction in the characteristic thermal decomposition range for calcium carbonate also confirmed its presence due to biomineralization. Calcite was identified in mBMA through XRD, with peaks observed at 23.03 °, 29.38 °, 25.47 °, 31.34 °, 35.98 °, 39.41 °, 43.15 °, 45.44 °, 48.48 °, and 57.40 °. Dense matter connecting the ash particles was observed in FESEM images of mBMA. It is believed to be the calcite formed during biomineralization. The carbonate presence was backed iii by the FTIR absorption bands at 711.6 cm-1, 873.6 cm-1, and 1420.3 cm-1. A 10% weight reduction in the characteristic thermal decomposition range (570 °C to 660 °C) for calcium carbonate confirmed its advent during biomineralization. In the third stage of the present study, FCA was employed in conjunction with biomineralization to stabilize BCS. Through optimization of the quadratic model, an ideal combination of 20 g/L soybean, 3 g/L yeast extract, and 0.125 g/L dextrose was determined for maximum optical density (1.946) and urease activity (27 m.mol urease/min). To stabilize the black cotton soil, soil bacteria were used with ferrochrome ash. The study involved assessing the extent to which ferrochrome ash could replace the black cotton soil and analyzing the impact of bacterial optical density, urea, and calcium chloride on enhancing the soil's unconfined compressive strength. The soil composite with the highest UCS of 350 kPa (TC5) comprised 40 % FCA, a bacterial medium with an optical density of 1.12, 0.5 g urea, and 0.5 g calcium chloride. A quadratic model was employed to investigate the impact of ferrochrome ash, bacterial density, calcium chloride, and urea concentrations on the unconfined compressive strength. The model indicated FCA as the primary contributor for the UCS improvement. The leachate of TC5 demonstrated reductions in heavy metal concentrations with efficiencies of 95% for Ni, 97% for Cu, 98% for Fe, 99% for Cr and Zn, and 100% for Pb, Cd, Ti, Hg, and As. The XRD analysis of TC5 revealed peaks at 20.61 °, 26.39 °, 28.08 °, 29.20 °, 31.08 °, 36.29 °, 39.21 °, 42.20 °, 43.16 °, 49.92 °, and 55.17 °. Additionally, peaks of FCA were observed at 28.32°, 40.54 °, and 50.23 °, while peaks of BCS were observed at 20.96 °, 26.72 °, 36.63 °, 39.58 °, 40.41 °, 42.53 °, 45.92 °, and 50.24 °. SEM of TC5 contained rhombohedral crystals of calcium carbonate and spherical particles of FCA on the flaky surface of the clayey soil. The FTIR profile of TC5 contained a characteristic absorption band for carbonate at 1457 cm-1, which was absent in the spectra of BCS and FCA. Other bands at 993 cm-1 and 1633 cm-1 indicate C-S-H formation. TGA analysis of TC5 exhibited an 18% weight loss in the temperature range iv of 590 °C to 810 °C, indicating the decomposition of calcium carbonate formed during biomineralization. These findings have important implications for waste management strategies, providing valuable insights into the potential of BMA and FCA with biomineralization in mitigating environmental risks and deriving value from waste.Item Laboratory Investigations on Black Cotton Soil Stabilized With Inorganic Additives and Marginal Materials(National Institute of Technology Karnataka, Surathkal, 2022) B A, Chethan; A. U., Ravi ShankarMany roads constructed over the Black Cotton (BC) soil in Chikmagalur district, Karnataka, India, face many problems due to the seasonal variation of the moisture in the subgrade and observed swelling and shrinkage. Therefore, in the present investigation, BC soil obtained from the Chikmagalur district is mixed with different marginal materials, viz, class F fly ash, limestone powder, construction demolition waste (CDW), coconut, and arecanut fibers. These marginal materials used are not capable of improving the strength properties of soil. Therefore, two types of binders, viz, ordinary Portland cement (43 grade) and alkali solution (NaOH solution of 8 molar concentration mixed with Na2SiO3 solution to obtain SS/SH (Na2SiO3 solution/NaOH solution) ratios of 0.5, 1.0, and 1.5), were used to improve the strength (viz, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), flexural strength) and durability properties of the soil. When durability tests were conducted, the BC soil treated with 3, 6, 8, 10, 12, and 14% cement could not resist the soil loss under Wetting-Drying (WD) and Freezing-Thawing (FT) cycles. If stabilized materials are to be used in pavement, as per IRC 37: 2018, WD and FT durability tests are mandatory. FT test is essential for cold regions like Arunachal Pradesh, Jammu & Kashmir, Ladhak, etc. However, to study the behavior in adverse conditions, both tests were conducted. The soil properties were further im- proved by adding class F fly ash and cement. The cement dosages of 3, 4, 5, 6, and 7%, along with fly ash dosages of 0 to 32%, improved soil strength but could not control the soil loss within 14% when the durability tests were conducted. The BC soil stabilized again with 8, 10, 12, and 14% cement and fly ash dosage from 10 to 42%. The BC soil stabilized with 8% cement, and a high fly ash dosage of 42% failed in the WD test. At (cement+fly ash) dosages of (10+30), (10+35), (10+40), (12+30), (12+34), (12+38), (14+25), (14+30), and (14+36)% the BC soil exhibited soil loss of <14% after 12 WD and FT cycles. When the UCS test was conducted, there was an improvement in UCS at standard Proctor compaction. The mixes that passed durability tests (both WD and FT) were also evaluated at modified Proctor density and found improvement in UCS values. The stabilized BC soil exhibited higher resistance to weathering actions under FT cycles compared to WD cycles. The soil stabilized with higher cement content iv (14%) and fly ash dosage (>30%) exhibited a maximum retained UCS after subjecting to durability tests. At a higher dosage of fly ash (>30%), the mix exhibited low plasticity with uniform distribution of cement cluster formations based on the Scanning Electron Microscopy (SEM) images and led to significant volume stability with improved soaked California Bearing Ratio (CBR(soaked)). The above mixes with high-volume stability are preferred for pavements. The mixes that passed durability tests were further blended with 0.50% coconut fibers to study the further improvement in strength properties. The inclusion of fibers slightly reduced the density of stabilized soil mixes and thereby a marginal decrease in UCS values; however, the flexural strength of specimens increased. All the mixes exhibited significant improvement in retained UCS after durability tests. Due to the densest compact soil mix, the resistance to penetration has improved and exhibited higher CBR values. The BC soil is further strengthened by adding an alkali solution. Initially, the BC soil was treated with class F fly ash (<50%) and activated using the alkali solution. There is a marginal improvement in strength due to less dissolution of aluminosilicate materials at a lower SS/SH ratio. The strength gain is more at a high SS/SH ratio of 1.5 due to increased dissolution. To improve the strength further, 5% limestone powder was added with fly ash. However, there is no enhancement in strength. Further to en- hance the strength properties, arecanut fibers were added, the stabilized soil resulted in a marginal decrease of UCS values, with improvement in flexural strength. Again when the soil was replaced with CDW (<50%), there was a significant improvement in UCS and CBR(unsoaked) values for all alkali-activated mixes. At the same time, the CBR(soaked) values are in the range of 5–8% for various mixes. All alkali-activated specimens failed during the durability test due to mineral constituent leaching from the set soil. The alkali solution could not retain bonding due to the high moisture affinity of BC soil present in the mix. SEM images showed formations of cemented intercluster. Hydration products formed resulted in strength improvement, as observed from X-Ray Diffraction (XRD) patterns. As per IRC SP-72: 2015, the only durability passed soil mixes can be used as a modified soil layer or as an improved subgrade. The critical strain values obtained by considering the stabilized soil as subgrade, Cement-Treated Sub-Base (CTSB) for high-volume pavements were within limits as per the IRC 37: 2018. However, these mixes are generally not preferred as a Cement-Treated Base (CTB) due to the complications involved in mixing, compaction, low interface friction, etc., requiring complete quality control.Item Laboratory Investigation on Lateritic and Black Cotton Soils Stabilised With GGBS and Alkali Solutions(National Institute of Technology Karnataka, Surathkal, 2020) Amulya S.; Ravi Shankar, A. U.The natural aggregates are depleting in developing countries due to the excessive usage in road and building construction. The present work investigates the improved properties of lateritic and Black cotton (BC) soils stabilized with Ground Granulated Blast Furnace Slag (GGBS) and alkali solutions such as sodium hydroxide and sodium silicate. The lateritic and BC soils are stabilized with 15, 20, 25 and 30% of GGBS and the alkali solutions consisting of 4, 5 and 6% of Sodium Oxide (Na2O) having Silica Modulus (Ms) of 0.5, 1.0 and 1.5 at a constant water binder ratio of 0.25. The Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) are obtained for both untreated and stabilized soils from standard and modified Proctor tests. The stabilized samples were air-cured for 0 (immediately after casting), 3, 7 and 28 days at ambient temperature. In case of stabilized lateritic soil, the maximum strength is achieved at 30% of GGBS and alkali solution consisting of 6% Na2O and 1.0 Ms whereas, in case of stabilized BC soil, the maximum strength is achieved at 30% GGBS and alkali solution consisting of 6% Na2O and 0.5 Ms at both standard and modified Proctor densities. The stabilizedlateritic soil with 25 and 30% of GGBS and alkali solution consisting of 5 and 6% of Na2O having 0.5 and 1.0 Ms is found to be durable after 28 days curing at both densities. Whereas, the stabilized BC sample having 25 and 30% of GGBS and alkali solution consisting of 5 and 6% of Na2O with Ms of 0.5 only at modified Proctor density have passed durability. The stabilized lateritic soil with 30% of GGBS and alkali solution consisting of 6% of Na2O having Ms of 1.0 at both densities and the stabilized BC soil with 25% of GGBS and alkali solution consisting of 5% of Na2O having Ms of 0.5 only at modified Proctor density achieved the highest flexural strength, fatigue life and the densified structure. Thex formation of calciumsilicate hydrate and calcium aluminosilicate hydrate structures resulted in a remarkable improvement of compressive strength, flexural and fatigue life of the stabilized soils due to the dissolved calcium ions from GGBS, silicate and aluminium ions from alkali solutions. The design of high and low volume roads is proposed by replacing the conventional granular layer with the durable stabilized soil and stress-strain analysis is carried out using pavement analysis software. The comparison of the cost of the conventional material with the proposed stabilized soils are carried out.