Faculty Publications
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Item Influence of Solid Activator on Setting Time and Compressive Strength Properties of Fly Ash/Slag-Based One-Part Geopolymer Pastes(Kalpana Corporation, 2022) Srinivasa, A.S.; Swaminathan, K.; Yaragal, S.C.Geopolymerization has transformed industrial wastes into strong and durable construction materials such as geopolymer binders to minimise CO2 emissions during ordinary Portland cement (OPC) production. These geopolymer binders, on the other hand, are derived from aluminosilicate waste products and alkali activators. The activator solutions show some drawbacks in transportation, storage, preparation and execution stage. In this research, a new one-part or just-add water geopolymer binder was developed by dry blending the aluminosilicate precursors, alkali activators in powder form and free water, similar to OPC. The impact of solid activator on the fly ash/slag based OPG mixes with respect to setting time and compressive properties was studied. The solid activator content was considered from 6 to 16% at an interval of 2%. Microstructure and mineral phase evolution of the mixtures were investigated using scanning electron microscopy and x-ray diffraction. The test results revealed that prolonged setting times were recorded at lower activator content. The lower compressive strength was recorded at 6% activator and higher strength was noticed at 12% activator content. The mix with 12% activator performed better than all other mixes with respect to setting time and compressive strength properties and also exhibits dense and compacted microstructure properties. © 2022 - Kalpana Corporation.Item Optimisation of recycled concrete aggregates for cement-treated bases by response surface method(Taylor and Francis Ltd., 2023) Chiranjeevi, K.; Kumar, D.H.; Srinivasa, A.S.; Ravi Shankar, A.U.Sustainability is a primary concern that needs to be addressed since infrastructure development requires significant natural resources. Using Recycled Concrete Aggregates (RCA) for road construction has numerous benefits in saving natural resources and the environment. In the present investigation, the demolition waste is being used for road construction, partially/fully replacing natural aggregates. The Cement Treated Recycled Concrete Aggregate (CTRCA) specimens were prepared at 3%, 5%, and 7% cement with various blends of RCA and Natural Coarse Aggregates (NCA) ranging from 0 to 100%. The strength characteristics in terms of Unconfined Compressive Strength (UCS), Flexural Strength (FS), Elastic Modulus, Indirect Tensile Strength (ITS) and durability tests were conducted on cured samples. Microstructural analysis using Scanning Electronic Microscope (SEM) revealed that the pores and cracks in the old mortar have a detrimental influence on the mechanical properties of CTRCA mixes. However, Energy Dispersive Spectroscopy (EDS) and durability tests have shown positive results. The Response Surface Method (RSM) was utilised to optimise the RCA and cement content in CTRCA mixes. The research resulted in the maximum possible RCA of up to 70% with a cement content of 5.8%, which met the Indian Road Congress (IRC) specifications for Cement Treated Bases (CTB). © 2023 Informa UK Limited, trading as Taylor & Francis Group.Item Effect of slag and solid activator on flowability and compressive strength of fly ash based one-part geopolymer pastes(Elsevier Ltd, 2023) Srinivasa, A.S.; Swaminathan, K.; Yaragal, S.C.The geopolymerization process has led to the transformation of industrial by-products into sturdy and long-lasting construction materials, such as geopolymer binders, which can be used to mitigate the massive CO2 emissions associated with the production of Ordinary Portland Cement (OPC). These binders are produced from aqueous solutions of alkali activators and alumina and silica rich industrial waste materials. Strong, caustic, and viscous aqueous solutions are used in alkali activation. Its handling, usability, and mass production are all tough, even transport and site difficulties compound these issues. The solid alumina-silica rich components, solid alkali activators, and free water are dry mixed in this work to create a unique “one-part” or “simply add water” geopolymer binder that is equivalent to OPC in its manufacture. Researchers looked at the flowability and compressive strength properties of fly ash based one-part geopolymer mixes while adding ground granulated blast furnace slag and a solid activator (anhydrous sodium metasilicate powder). At the 25 and 50% replacement levels, GGBS was used in place of fly ash. Solid activator content varied from 8 to 16% at an interval of 2% for each replacement level of GGBS. Microstructural and mineralogical alterations were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. According to the findings of the tests, the flowability and compressive strength improved with decreasing slag and solid activator concentration. It was found that activator content increments beyond 12% result in minor reduction in compressive strength, and that the highest compressive strength was measured at 50% GGBS and 12% activator content. Both flowability and compressive strength were improved by the 50% GGBS and 12% activator mixture, which also displayed symptoms of having a dense and compacted microstructure. © 2023Item Microstructural and optimization studies on novel one-part geopolymer pastes by Box-Behnken response surface design method(Elsevier Ltd, 2023) Srinivasa, A.S.; Swaminathan, K.; Yaragal, S.C.This paper reports the work on developing an optimized mix proportion of novel one-part geopolymer (OPG) binder produced by dry blending the solid aluminosilicate precursor and solid alkali source and then adding free water to the blended mix similar to the preparation of Ordinary Portland Cement (OPC). A three-level Box-Behnken Response Surface Method (RSM) design was used to study the properties of OPG mixes at fresh and hardened state and to test and develop the regression models. The Ground Granulated Blast Furnace Slag (GGBS) substitution, water to geopolymer solids (w/s) ratio, and the activator dosage were considered as the independent variables. The response target values were the flow value, initial and final setting time, and compressive strength. The multiple regression analysis with the quadratic polynomial model was used to fit the data, which offered an accurate and reliable match to the actual data. Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were used to study changes in microstructure, mineral phase, and molecular bonding of OPG mixes, respectively. Based on the material characterization observation, the change in GGBS addition, w/s ratio, and activator dosage were discovered to have a considerable impact on both the fresh and hardened properties. The optimum mix proportion obtained was 51.39% GGBS substitution, 0.32 w/s, and 12.35% activator content, with 191 mm flow, 68.56 MPa of compressive strength, 59 and 191 mins of initial and final setting time, respectively. The target values obtained using the one-part geopolymer mix with 50% GGBS substitution, 0.3 w/s, and 12% activator content were in close agreement with the target values predicted by the optimized mix, confirming the efficiency of RSM in obtaining the optimum one-part geopolymer mix proportion. © 2023 The AuthorsItem Physicomechanical Properties and Characterization of Gold Ore Tailings and the Utilization in Manufacturing of Geopolymer Concrete with Class F Fly Ash and Recycled Coarse Aggregates(American Society of Civil Engineers (ASCE), 2023) Lokesha, E.B.; Mangalpady, M.; Kumar Reddy, S.K.; Srinivasa, A.S.The mining industry generates a large amount of waste, particularly in the form of tailing dumps, which creates major environmental difficulties such as air pollution, water pollution, soil erosion, and acid mine drainage. Previous studies confirmed that the mine waste could be used in making building materials, such as bricks, tiles, concrete blocks, pavement blocks, and precast concrete elements. However, gold ore tailings (GOTs) are recognized as major mine residues in the mining industry. In this study, GOTs were utilized as partial replacement material (0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight) to fine aggregates such as river sand (RS) and low calcium fly ash (FA) as binder material in the manufacture of geopolymer concrete (GPC) along with recycled coarse aggregates. The GPC samples were cast and cured at room temperature until the curing ages; subsequently, the compressive strength of the samples was determined. This study demonstrated that the RS can be partially substituted in the manufacture of GPC by GOTs up to 15% with a slump value of 38.6 mm and the maximum compressive strength of 35.8 MPa. The mineralogical and chemical composition of raw materials (i.e., GOTs and FA) was analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. The XRD analysis revealed that the quartz has the highest peak intensity of 55% in GOTs and 50% of corundum in FA. The XRF analysis exhibited that GOTs and FA have high silicon oxides up to 39% and 38%, respectively. The crushed GPC samples were analyzed using field emission scanning electron microscopy to observe the morphological changes. The GPC sample comprised 15% GOTs exhibited denser and compacted microstructures. © 2023 American Society of Civil Engineers.Item Development of Regression Model and Optimization of Mechanical Properties of Geopolymer Concrete Prepared Using Gold Ore Tailings(American Society of Civil Engineers (ASCE), 2023) Lokesha, E.B.; Mangalpady, M.; Kumar Reddy, S.K.; Srinivasa, A.S.In this study, 11 mix proportions of geopolymer concrete (GPC) beam and cylinder samples were prepared by partially replacing the class F fly ash (FA) as the binder with ground granulated blast furnace slag (GGBFS) in steps from 10% to 100%, along with gold ore tailings (GOTs) [as a partial substitute to the river sand (RS) in steps from 5% to 30%] and recycled coarse aggregates (RCAs). The laboratory tests demonstrated a maximum split tensile strength of 5.99 MPa and flexural strength of 7.98 MPa for Sample GOT-11-15 (11 indicates Mix Proportion-XI and 15 indicates 15% of GOTs) of Mix Proportion-XI. In addition to the previous 11 mix proportions, one more set of cylinders and beams was prepared using FA, GOTs, and natural coarse aggregates (NCAs), which are designated as Mix Proportion-XII. For Mix Proportion-XII, the highest split tensile strength of 4.17 MPa and flexural strength of 6.13 MPa was achieved for Sample GOT-15 (15 indicates 15% of GOTs). Among the 12 types of mix proportions, Sample GOT-0 of Mix Proportion-XII (i.e., FA 100%, GOT 0%, and NCAs 100%) showed a maximum slump value of 89.3 mm. Sample GOT-1-0 of Mix Proportion-I (i.e., FA 100%, GOT 0%, and RCA 100%) exhibited the maximum slump of 65.3 mm. The field emission scanning electron microscopy (FESEM) analysis indicated that silicon (Si) and aluminum (Al) were the two main constituents of the GOTs and FA. In addition, this analysis revealed the existence of uneven forms of quartz particles in GOTs and the spherical shapes of the FA particles that adhered to the RCAs. The multiple regression analysis exhibited the root mean square (R2) values of 89.0% and 85.5%, respectively, for the split tensile and flexural strengths. The p-value for the developed model was <0.05; therefore, the developed model was considered significant and the best-fit model. © 2023 American Society of Civil Engineers.Item One-part eco-friendly alkali-activated concrete – An innovative sustainable alternative(Elsevier Ltd, 2023) Rakesh Kumar Reddy, R.; Yaragal, S.C.; Srinivasa, A.S.The primary objective of this study is to develop an eco-friendly one-part alkali-activated concrete (OPAAC) by incorporating a combination of fly ash (FA), ground granulated blast furnace slag (GGBS), and micro silica (MS). In this investigation, the proportion of MS is maintained at 20% of FA, while the maximum replacement of FA with GGBS is set to 60%, varying in 20% intervals (i.e., 0%, 20%, 40%, and 60%). Further, the natural aggregates (NA) are substituted with recycled coarse aggregates (RCAs), ferrochrome slag aggregates (FCSAs), or a combination of both. The influence of GGBS and alternative aggregates (RCAs, FCSAs) on the mechanical properties of OPAAC is thoroughly examined. To provide a comprehensive assessment, the properties of OPAAC are compared against Ordinary Portland Cement (OPC) concrete (CC) of equivalent grades. Additionally, microstructural and mineralogical investigations are conducted to determine the formation of distinct hydration products, utilizing scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques. In OPAAC containing FA, the primary hydration products identified are alkaline alumino silicate hydrates (CASH and NASH). As the GGBS content increases, calcium silicate hydrate (CSH) becomes the predominant hydration product. Furthermore, in order to assess the sustainability of OPAAC, an analysis of embodied CO2 emissions is performed, and the results are compared with CC and alkali-activated concrete. Notably, OPAAC comprising 40% FA replaced with GGBS, 50% RCAs, and 50% FCSAs demonstrates the most favourable mechanical properties and exhibits lower CO2 emissions. © 2023 Elsevier LtdItem Multi-objective optimization of one-part geopolymer mortars adopting response surface method(Elsevier Ltd, 2023) Srinivasa, A.S.; Yaragal, S.C.; Swaminathan, K.; Rakesh Kumar Reddy, R.One-part geopolymers have immense potential in large-scale structures owing to their improved safety and convenience of handling over the conventional geopolymer mixing procedure. Thus, this study aims at optimizing the mixes by assessing the influence of binder content, activator dosage and water to geopolymer solids (W/GS) ratio on the flowability, strength, and shrinkage properties of one-part geopolymer mortars (OPGM). The test results were utilized to develop models that could predict the desired properties of mixes and optimize the mix proportions of OPGMs using the response surface method. The fly ash and slag-based OPGMs were developed. 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 at varied W/GS ratios of 0.35, 0.40, and 0.45. The responses considered were flowability, compressive and flexural strengths at 7 and 28 days, and drying shrinkage of up to 180 days. Total of 504 specimen were cast to record the observations for this optimization study. The GGBS content, W/GS ratio, and combined effect of these factors were found to be the most influential factors affecting the responses. The optimal mix proportion 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 microstructural characterization adopting techniques like SEM, XRD, TGA and FTIR was carried out to study microstructural changes, mineral phases, thermal mass loss and molecular bonding of OPGM mixes. This study revealed that mix with 50% GGBS, 12% activator dosage and 0.40 W/GS ratio can better be characterized compared to other mixes. © 2023 Elsevier Ltd