1. Ph.D Theses
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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.Item Performance of Alkali Activated Concrete Mixes with Steel Slag as Coarse Aggregate for Rigid pavements(National Institute of Technology Karnataka, Surathkal, 2016) Palankar, Nitendra; Ravi Shankar, A. U.Improved road connectivity is very essential for any countries progress. Well designed and constructed concrete pavements have been identified component for the development of a sustainable highway infrastructure. The higher demand for concrete roads and other construction purposes has resulted in the increased production of Ordinary Portland Cement (OPC), which is one of the basic constituents required for concrete production. However, the production of OPC is associated with emissions of large amounts of CO2, with the cement industry accounting for about 5-8% of worldwide CO2 emissions. In addition to CO2 emissions, the production of OPC requires considerable amounts of natural raw materials and energy. The present research community is focused on the development of alternative binders, with the aim of minimization of production of OPC. Alkali Activated Binders (AABs) such as Alkali Activated Slag (AAS), Alkali Activated Slag Fly Ash (AASF), Geopolymers, etc. can be considered as potential alternatives to OPC. Steel slag, an industrial by-product obtained from manufacture of steel can be identified as an alternative to natural aggregates for concrete production, since there is a possibility of acute shortage of natural aggregates for concrete in future. The present study is conducted to evaluate the performance of steel slag as coarse aggregates in Alkali Activated Slag Concrete (AASC) and Alkali Activated Slag Fly Ash Concrete (AASFC) by replacing natural granite aggregates. AASC and AASFC mixes are designed to attain a minimum strength of M40 grade and compared with conventional OPC concrete mix of similar grade. AASC mixes are prepared with 100% GGBFS as sole binder, while AASFC mixes are prepared by mixing GGBFS and FA in different proportions, i.e. 75:25, 50:50 and 25:75. Preliminary tests are carried out to identify the optimal activator modulus and dosage of alkaline activators for each of the AASC and AASFC mixes. Steel slag as coarse aggregates are incorporated in the AASC and AASFC mixes by replacing the natural coarse aggregates by volume replacement method at different levels of replacement, i.e. 0%, 25%, 50%, 75% and 100%. The fresh and hardened properties such as workability, compressive strength, split tensile strength,flexural strength, and modulus of elasticity of different concretes are evaluated as per standard test procedures. The durability of concrete mixes, in terms of resistance to sulphuric acid, magnesium sulphate, water absorption and Volume of Permeable Voids (VPV) are investigated. Flexural fatigue performance of various concrete mixes is evaluated by carrying out repeated load tests on beam specimens using repeated load testing equipment. The fatigue life data obtained are represented and analyzed using S-N curves to establish fatigue equations. Probabilistic analysis of fatigue data is carried out using two parameter Weibull distribution method. Further, the goodness-of-fit test is done to ascertain the statistical relevance of the fatigue data using Weibull distribution model. Survival probability analysis to predict the fatigue lives of concrete mixes with required probability of failure is carried out. The impact of the properties of AASC and AASFC mixes on the rigid concrete design is analyzed by carrying out standard pavement design. The ecological and economical benefits of AASC and AASFC mixes in comparison with conventional OPC concrete are analyzed and discussed. The results indicated that incorporation of steel slag in AASC and AASFC mixes resulted in slight reduction in mechanical strength. Reduction in number of cycles for fatigue failure was observed in AASC and AASFC mixes containing steel slag as compared to granite aggregates. Two parameter Weibull distribution was used for statistical analysis of fatigue data and it was observed that the fatigue data of concrete mixes can be approximately modelled using Weibull distribution. The inclusion of steel slag aggregates slightly reduced the durability performance of AASC and AAFC mixes. The higher water absorption and subsequent VPV increase, with inclusion of steel slag in both AASC and AASFC mixes, due to higher water absorption of steel slag as compared to normal aggregates. Alkali activated concrete mixes with natural aggregates exhibited better resistance to sulphuric acid and magnesium sulphate environments as compared to OPCC, which may be attributed to properties/structure of binders. The acid and sulphate resistance of alkali activated concrete mixes decreased with replacement of natural aggregates with steel slag. The Embodied Energy (EE), Embodied Carbon Dioxide Emission (ECO2e) and cost of alkali activated concrete with natural aggregates are foundto be quite lower as compared to OPCC. Incorporation of steel slag in alkali activated concrete mixes led to further reduction in EE, ECO2e and cost as compared to OPCC. Steel slag aggregates reported acceptable performance in AASC and AASFC mixes for its use in pavement quality concrete.Item Performance Studies on Pavements Using Chemically Stabilized Soils(National Institute of Technology Karnataka, Surathkal, 2016) B. M, Lekha; Ravi Shankar, A. U.Pavements constructed on weak soils can cause significant distress due to moisture-induced volume changes and low strength, thereby reducing the pavement life. Soil stabilization is the alteration of one or more soil properties, by mechanical or chemical means, to obtain an improved soil material possessing the desired engineering properties. Subgrade soils may be stabilized to increase the strength and durability or to prevent erosion and dust generation. In the present study two types of soils, Lateritic Soils (LS1 and LS2) and Black cotton soil and were stabilized with five different stabilizers viz. Terrasil, Terrabind, Cement, Road Building International grade 81, and marginal materials like Fly ash, Arecanut coir and aggregates. These additives can be used with a variety of soils to improve their native engineering properties, but their effectiveness depends on the amount of additive and the nature of soil. The laboratory investigations were conducted for different curing days to determine the basic and engineering properties of soil such as Atterberg’s limits, grain-size distribution, Maximum Dry Density (MDD), Optimum Moisture Content (OMC), California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), Indirect Tensile (IDT) Strength, Durability, Fatigue and Resilient Modulus (E). The investigations are also carried out to study the effect of addition of 12.5 mm down aggregates to the soil with optimum content of Cement and RBI 81 to evaluate the extent of modification in the Compaction, CBR, IDT strength and resilient modulus tests. The experimental investigations indicate that there is a good improvement in the engineering properties of the soils treated with different stabilizers. KENPAVE software was used for stress strain and damage analyses of both natural and stabilized soils and also to prepare pavement design sections for low and high volume pavements. For low volume pavements, CBR 3% and traffic T4 to T7 conditions were considered as per IRC-SP-72:2007. For high volume pavements, analyses were carried out for CBR 8% and traffic 2 to 150 million standard axles, using the standard design thickness as per IRC-37:2012 guidelines. Trial and error method was adopted to determine the thickness for treated soil aggregate mixture, by keeping the strain value within permissible limits. For stabilized soil, rutting and fatigue lives and damage ratio were also observed to be significantly improved. From the results of theexperimental research and KENPAVE analysis, it has been observed that modified soil can be effectively used as a modified subgrade and base layers. Analysis was also performed in IITPAVE for high volume roads under dual wheel loading. Cost analysis was carried out as per the Schedule of Rates (SOR) 2014-2015 for stabilized and unstabilized materials.