Faculty Publications

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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. © 2023
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 Authors
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

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