Browsing by Author "Yaragal, Subhash C."

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Optimization Studies on One-Part Geopolymer Mixes (Pastes, Mortars and Concretes)
(National Institute of Technology Karnataka, Surathkal, 2024) S, Anil Sagar; Yaragal, Subhash C.; Swaminathan, K.
The consumption of ordinary Portland cement (OPC) to meet the enormous need for concrete production all over the world, is a global threat for climate change. To reduce massive carbon dioxide emissions associated with the manufacturing of OPC, the geopolymerization process has given rise to the transformation of industrial wastes into strong and durable construction materials such as geopolymer binders. However, these geopolymer binders are based on aluminosilicate by-products and alkali activators. The activators involved in alkali activation process are concentrated aqueous solutions, which are viscous, corrosive and caustic. In addition, complexity in transportation and impracticalities in site such as, difficulty in handling, not user friendly, and hard to use for mass production. This study reports on development of a novel ‘one-part’ or ‘just-add water’ geopolymer binder produced by dry blending the solid aluminosilicate precursors, solid alkali source and then adding free water to the blended dry mix to produce a binder as similar to OPC. One-part geopolymers (OPG) have immense potential in large-scale structures owing to their improved safety and convenience of handling over the conventional geopolymer mixing procedure. This study aims to optimize the mixes by understanding, assessing the influence of binder content, activator dosage and water to geopolymer solids (W/GS) ratio on the fresh and hardened properties of one-part geopolymer mixes (namely pastes, mortars and concretes). Various fly ash and slag-based OPG mixes have been developed and studied. The GGBS substitution was chosen as 25, 50, and 75% by volume of fly ash. The activator dosage was taken as 8, 12, and 16% by mass of total binder content and at varied W/GS ratios of 0.35, 0.40, and 0.45. The test results were utilized to develop models which can predict the desired properties of mixes and optimize the mix proportions of OPG mixes using the response surface method (RSM). The microstructural characterization adopting techniques like Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA) and Fourier Transform Infrared (FTIR) was carried out to study microstructural changes, mineral phases, thermal mass loss and molecular bonding of OPG mixes. The elevated temperature studies, ecological and cost analysis studies were also performed. x Based on the material characterization observations, the change in GGBS addition, activator dosage, and W/GS ratio were observed to have a considerable impact on both the fresh and hardened properties. The optimum mix proportion of OPG paste obtained was 51.4% GGBS substitution, 12.4% activator content, and 0.32 W/GS ratio with 191 mm flow, 68.6 MPa of compressive strength, 59 and 191 mins of initial and final setting times, respectively. The optimum mix proportion of OPG mortar obtained consists of 49.8% GGBS, 13.6% activator dosage, and 0.37 W/GS ratio. This mix achieved 170.4 mm flow, 57.8 MPa and 5.9 MPa compressive and flexural strengths, respectively and also 1626 microstrain of 180 days drying shrinkage. The optimum mix composition of OPG concrete for achieving a 125 mm slump while maximizing strengths comprises of 75% GGBS, activator dosage of 13.8%, and W/GS ratio of 0.34. This optimized mix achieved compressive, flexural, and split tensile strengths of 73 MPa, 6.2 MPa and 3.9 MPa, respectively. The verification of experimental values of proposed optimized mix are within the absolute deviation of 10% of predicted values, indicating the accuracy of the models and effectiveness of RSM in designing the optimum mix proportions of OPG mixes. Elevated temperature endurance of OPGC mixes increases with both GGBS content and activator dosage. Embodied CO2eq (ECO2eq) and embodied energy (EEeq) increases with increase in activator dosage. The ECO2eq and EEeq of OPG concrete mixes are lower compared to OPC based concrete mixes. Hence the OPG mixes can be considered as more eco-friendly and sustainable materials, as against conventional OPC based mixes.
Performance Evaluation of Ferrochrome ASH Based Alkali Activated Slag Mortars
(National Institute of Technology Karnataka, Surathkal, 2022) B, Chethan Kumar; Yaragal, Subhash C.; Das, B. B.
The use of ground granulated blast furnace slag (GGBS), fly ash (FA), silica fume (SF), etc. are gaining importance as cementitious materials for researchers, as these reduce carbon footprint, indirectly providing a viable solution to the threat of global warming and waste disposal problems. In particular, industrial byproducts are very promising in their use, due to their mechanical strength and long-term durability performance under aggressive conditions. Hitherto, one of the industrial byproducts not largely researched is ferrochrome ash (FCA). FCA is obtained from the gas cleaning plant of ferrochrome industries during the production of chromium. One of the possible ways of utilizing FCA is as a binder in the alkali activated slag (AAS) binder system. The addition of FCA in the AAS system addresses one of the important issue of the landfill problem and associated cost reduction. The main aim of the present study is to synthesize an AAS system using FCA as a binder material. Three important factors, including alkaline dosage (Na2O = 4-6% of the binder), modulus of silica (Ms = 0.75-1.75), and FCA replacement in the AAS binder system (0-50%) were considered for the experimental design. The microstructure and mineralogical studies were performed using scanning electron microscopy - energy dispersive spectroscopy (SEM-EDAX) image analysis and X-ray diffraction (XRD), respectively. Functional group identification was carried out using the Fourier Transform Infrared (FTIR) spectroscopy. Durability studies like, volume of permeable voids (VPV), sulphate attack, acid attack, elevated temperature studies, and ecological studies were also carried out. Optimization of FCA based AAS mortars were done based on grey relational analysis (GRA), technique for order preference by similarity to ideal solution (TOPSIS), and desirability function approach (DFA). As the replacement of FCA increases in the AAS mortars, N-A-S-H is observed to be predominant with the co-existence of C-S-H, C-A-S-H, and gismondine. The reduction of C-S-H, C-A-S-H, and gismondine is the main reason for the reduction in compressive strength in FCA based AAS mortars compared with 100% GGBS based AAS mortars. As the amount of Na2O dosage increases, compressive strength of FCA based AAS mortar mixture also increases. VPV of FCA based mortar mixture decreases with increase in Na2O dosage. Sulphate and acid resistance of FCA based AAS mortar mixture increases with increase in Na2O dosage. VPV also increases with increase in FCA content. Sulphate and acid resistance decreases with increase in FCA content in AAS mortar mixtures. Elevated temperature resistance of AAS mortar mixture increases with increase in both FCA content and Na2O dosage. ECO2eq and EEeq increases with increase in Na2O dosage. However, ECO2eq and EEeq decreases with increase in FCA content. Ranking obtained from DFA method is found to be best alternative for optimal mixture identification in terms of VPV, sulphate resistance, and acid resistance of FCA based AAS mortar mixtures. TOPSIS method ranking order can be used for obtaining optimal mixture identification of these mortar mixtures in terms of elevated temperature resistance, ECO2eq and EEeq.
Potential Use of Processed Lateritic Fine Aggregates in Cement Mortars and Concretes for Sustainable Development
(National Institute of Technology Karnataka, Surathkal, 2020) S. N., Basavana Gowda; Rajasekaran, C.; Yaragal, Subhash C.
Availability of river sand is becoming scarce, due to rapid increase in infrastructure projects in India. Acute shortage of river sand, has led to indiscriminate sand mining. Adverse effect of sand mining includes river bank erosion, river bed degradation, loss of biodiversity and deterioration of river water quality and ground water availability. To address the above issues, research efforts are on, to find substitutes for river sand to be used as fine aggregate in mortars and concretes. One among the locally available resources is laterite. Laterite is a product of tropical or sub-tropical weathering, which is an abundant soil material available in many parts of India. An attempt has been made to characterize the processing technique to obtain good quality lateritic fine aggregates (lateritic FA). Experiments were designed and conducted to study the performance of lateritic FA as replacement to river sand, in cement mortars and concretes. Processed lateritic FA in replacement levels of 0, 25, 50, 75 and 100 wt.% to river sand at all fineness levels (Zone I to Zone IV as per Indian standards) is considered. The workability and compressive strength characteristics of cement mortars and concretes are evaluated. Laterized mortars with Zone III and Zone IV fine aggregates, at all replacement levels, result in the same compressive strengths as those of control mortars. Suitable strength enhancement technique has been attempted to achieve strengths of Zone I and Zone II lateritic fine aggregates based mortars at 100 wt.% replacement, to achieve strength at least equal to or more than those of control mortars. Laterized concretes have achieved nearly the same strengths as those of control concretes, at all replacement levels and for all fineness levels (Zone I to Zone IV). Microstructure studies were also conducted to understand the arrangement of river sand and lateritic FA with cement matrix and their Interfacial Transition Zones (ITZ) using Scanning Electron Microscope (SEM). In the second phase, performance evaluation of laterized mortars blended with GGBS and fly ash at elevated temperatures was studied. The study was carried out in three stages, in the first stage effect of elevated temperatures on laterized mortar with different proportions of fly ash and GGBS were evaluated with constant retention period and varying exposure temperature. In the second stage, the best performing laterized mixes with GGBS and fly ash were examined for different retention periods of 30, 60 and 90 minutes. The effect of retention period on the physical and mechanical properties are investigated. In the third stage, the effect of different cooling regimesii on the residual properties of laterized mortar specimens when subjected to elevated temperatures are assessed. In the present study, three cooling regimes namely furnace cooling, ambient air cooling and water quenching were adopted. Microstructure analysis of specimens subjected to different exposure temperatures was done through SEM image analysis using image J software. In the third phase, usage potential of recycled concrete aggregates (RCA) along with lateritic FA in concrete was studied. Mechanical properties of RCA based laterized concretes were examined. Suitable strength enhancement methodology is adopted to overcome the decrement in strength caused by the usage of RCA in concrete. Finally, sustainability in the production of concrete is achieved by using GGBS as sole binder and lateritic FA as fine aggregates and RCA as coarse aggregates along with alkali solution as an activator. The resultant alkali activated slag concrete with lateritic FA and RCA shows almost similar results in terms of mechanical properties when compared to control concrete.