Browsing by Author "Prakash, G.B."

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Durability performance of one-part alkali-activated self-compacting concrete mixes under aggressive and elevated temperature conditions
(Elsevier B.V., 2025) Mahendra, K.; Narasimhan, M.C.; Rathod, S.; Das, A.K.; Prakash, G.B.
The growing demand for sustainable, high-performance materials in modern construction has driven the development of advanced concrete technologies. This study introduces one-part alkali-activated self-compacting concrete (OPASC) as a practical, safe, and user-friendly alternative to conventional Portland cement-based concretes. Selected mixes with compressive strengths exceeding 70 MPa were evaluated for durability under aggressive conditions, including extended exposure to 5 % sulfuric acid and 5 % magnesium sulfate up to 180 days. The thermal stability of these candidate mixes was also assessed by subjecting the mixes to sustained temperatures ranging from 200 °C to 800 °C. Chloride-ion resistance of these mixes was examined under bulk diffusion tests. Key durability indicators, including water absorption, permeable voids, and sorptivity, were quantified to evaluate matrix impermeability. The results revealed compressive strength losses of 25–32 % under acid exposure, 7–15 % under sulfate exposure, and 30–42 % under thermal exposure, with chloride diffusion coefficients ranging from 0.21 × 10?12 to 0.32 × 10?12 m2/s, indicating high resistance to ionic ingress. The mixes also exhibited low water absorption (3–4.5 %), lower soptivities (0.0024–0.0013 mm/s1/2), and much reduced permeable voids (4.3–5.5 %), reflecting an impermeable, dense matrix. Microstructural analyses using SEM-EDS and XRD revealed that degradation under acid and sulfate conditions is primarily attributable to the decalcification of C/N-A-S-H gels, accompanied by the recrystallization of stable aluminosilicate phases. Finally, the environmental sustainability evaluation, which considered both embodied energy and carbon footprint, verified the superior environmental friendliness of OPASC mixes relative to conventional concrete. These findings confirm that OPASC exhibits superior chemical and thermal durability, reduced permeability, and enhanced resilience, thereby establishing it as a sustainable and practical solution for modern infrastructure applications. © 2025 Elsevier B.V.
Experimental investigation and optimization of one-part alkali-activated self-compacting concrete mixes
(Elsevier Ltd, 2024) Mahendra, K.; Narasimhan, M.C.; Prakash, G.B.; Das, A.K.
Emphasizing the growing importance of sustainability, alkali-activated materials (AAMs) have emerged as a revolutionary alternative for cement in the construction sector. This study delves into the fresh, mechanical, and microstructural properties of One-Part Alkali-activated Self-compacting Concrete (OPASC) mixes. While mixtures of Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash (FA) were utilized as the precursors, powdered sodium metasilicate was employed to function as the activator. To streamline experimental design and reduce the economic demands of extensive testing, the Taguchi-Grey Relational Analysis (GRA) was utilized to identify optimal multi-response parameter levels. This method considered binder content (B) within a range of 700–800 kg/m³, water-to-binder (W/B) ratios between 0.38 and 0.42, and Na2O percentages from 5 % to 7 % as key input variables. Results indicated that the designed mixes recorded workability values satisfying the EFNARC guidelines, compressive strengths greater than 60 MPa, split-tensile strengths in the range of 3.5–4.6 MPa, and flexural strengths varying between 5.5 and 7.2 MPa. The mix parameters for the optimal mix, with the highest mean grey relational grade, were identified from the Taguchi-GRPA approach as B = 750 kg/m3, W/B = 0.4, and N = 6 %. Microstructural analysis revealed the formation of C/N-A-S-H type gels, which are instrumental in developing a compact matrix enhancing the mechanical properties. A good agreement between actual experimental results obtained for a different set of verification mixes with those predicted by regression-equations confirmed the potency of the Taguchi-GRA approach in optimizing the OPASC mix parameters. © 2024 The Authors
Flexural and fracture performance of fiber reinforced self compacting alkali activated concrete– A DOE approach
(Elsevier B.V., 2024) Prakash, G.B.; Prashanth, M.H.; Narasimhan, M.C.; Mahendra, K.; Das, A.K.
Owing to their much-reduced carbon footprint and lower embodied energy, compared to conventional Portland Cement (OPC-based) Concrete mixes, Alkali Activated Concrete (AAC) mixes represent a pivotal advancement towards achieving sustainability goals. The fracture properties were investigated using Three-Point Bending Tests (3-PBT) under the mode I failure mechanism. This study utilises Taguchi analysis to analyse and optimise Self-Compacting Alkali-Activated Concrete (SAAC), focusing mainly on its flexural strength and fracture characteristics. An L-16 orthogonal array of experiments with three input parameters − replacement of Blast Furnace Slag (BFS) with Fly ash (FA) (0 %, 30 %, 40 %, and 50 %), Steel Fibers (SF) volume content (0 %, 0.25 %, 0.5 % and 0.75 %) and Notch to Depth (a0/d) ratio (0.2,0.3,0.4 and 0.5), at four levels each, was adopted. The Work of Fracture Method (WFM) and Double K Fracture Criterion (DKFC) were utilised to determine the Fracture Energy (GF) and fracture toughness, respectively. The results obtained from all the sixteen mixes showed that the F0-S0.75-N0.5 mix demonstrated better values in several parameters, such as flexural strength of 7.82 MPa,KICini of 0.928 MPa√m, KICuns of 6.99 MPa√m and KICini/ KICuns of 0.133. A maximum GF of 2350 N/m was obtained with F50-S0.75-N0.2 mix. However, all the inferior values of these parameters were observed with F50-S0-N0.5 mix, which recorded a flexural strength of 4.90 MPa, KICini of 0.612 MPa√m,KICuns of 1.16 MPa√m, KICini/ KICuns of 0.528 and GF of 125 N/m. Through Taguchi analysis, the optimal combination for flexural strength was identified as FA 0 %, SF 0.75 %, and a0/d 0.5 and for both Initial Fracture Toughness (KICini) and Unstable Fracture Toughness (KICuns) at FA 0 %, SF 0.75 % and a0/d 0.4. For both the ratio of initial to unstable fracture toughness (KICini/ KICuns) and fracture energy (GF), the optimum combination was FA 0 %, SF 0.75 % and a0/d 0.2. Furthermore, the results indicate that FA significantly influences KICini, while SF predominantly affects all other parameters. The predictive performance of the regression equations demonstrates good agreement with experimental outcomes. © 2024 Elsevier Ltd
Performance evaluation of fiber reinforced self compacting alkali activated concrete mixes—a DoE approach
(Springer Nature, 2025) Prakash, G.B.; Prashanth, M.H.; Narasimhan, M.C.; Mahendra, K.; Das, A.K.
Alkali-activated concrete (AAC) has emerged as a sustainable alternative to conventional concrete due to its lower carbon emissions and effective use of industrial by-products. Several studies have explored the performance of AAC in both fresh and hardened states. However, the broader application of these mixes in real-time applications can be enhanced through further modifications to meet current needs. Fiber-reinforced self-compacting alkali-activated concrete (FSAAC) mixes represent one such class of innovative concrete mixes. This study evaluates the fresh-state, mechanical, and fracture properties of FSAAC mixes optimized using Taguchi’s design of experiments (DOE) methodology. An L9 orthogonal array was employed with three variables at three levels: fly ash (FA) content (30%, 40%, 50%) as partial replacement of blast furnace slag, steel fiber (SF) content (0.25%, 0.5%, 0.75% by concrete volume), and fiber aspect ratio (AR) (40, 60, 80). A control mix without FA and SF was included in the comparison study. All FSAAC mixes satisfied EFNARC guidelines for fresh-state properties. Fracture parameters were determined through three-point bending (TPB) tests. The F30-S0.75-A80 mix exhibited superior performance with compressive strength of 66.33 MPa, flexural strength of 7.05 MPa, initial fracture toughness (KICini) of 0.813 MPa?m, unstable fracture toughness (KICuns) of 6.123 MPa?m, fracture energy (GF) of 5513.80 N/m, and a toughness ratio of 0.133. Compared to the control mix, the mix F30-S0.75-A80 showed 22.6%, 14.35%, 313.15% and 2518% rise in flexural strength, KICini, KICuns and GF, respectively. Taguchi analysis identified optimal mix proportions for slump flow at FA 50%, SF 0.25%, AR 40, and for KICini at FA 30%, SF 0.75%, AR 60. For other properties, proportions were optimized at FA 30%, SF 0.75%, AR 80. Regression models developed exhibited high degree of predictive accuracy, closely aligning with experimental outcomes. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.
Performance of Alternate Superplasticizers on Performance of Self-compacting Geopolymer Mortarsâ€”An Experimental Study
(Springer Science and Business Media Deutschland GmbH, 2024) Prakash, G.B.; Mahendra, K.; Tanush, L.; Narasimhan, M.C.
Geopolymer binders are the best alternatives to Ordinary Portland cement in the view of carbon impact on the environment. The effect of addition of different types of superplasticizers (SPs) on the flow and compressive strengths of a class of self-compacting geopolymeric mortar (SCGM) mixes is investigated in the present study. Three different kinds of SPs, namely modified Polycarboxylate Ether (MPCE), Polycarboxylate Ether (PCE), and Sulfonated Naphthalene Formaldehyde (SNF), were used in the production of SCGM with varying proportions at 1, 1.5, and 2% by weight of the binder. Results revealed that modified PCE-based SP showed better results in flow and compressive strength (CS) in comparison to PCE and SNF-based SPs. However, an increase in the dosage of SP had less/adverse effect on the flow properties. A maximum slump flow of 270Â mm was observed for a modified PCE-based SP at 1.5% dosage, while the highest CS of 34Â MPa was observed at 1.5% dosage of the same SP. Scanning electron microscope (SEM) analyses were carried out on a few selected SCGM mixes. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
Shear Strength Characteristics of One-Part Alkali Activated Concrete Mixesâ€”A DOE Approach
(Springer Science and Business Media Deutschland GmbH, 2024) Mahendra, K.; Prakash, G.B.; Shetty, S.; Narasimhan, M.C.
Utilization of one-part alkali-activated concrete (OPAAC) mixes is an advantageous option for large-scale construction applications. In the present investigation, the main objective was to investigate the shear strength characteristics of OPAAC mixes that were made using GGBFS and fly ash as precursors and sodium meta-silicate as solid activator. Taguchiâ€™s DOE approach has been used to reduce the experimental effort and to find the optimum parameters. An initial set of nine OPAAC mixes was identified based on an L-9 array, with three representative levels considered for each of three principal mix parameters and experiments were conducted to test their compressive and shear strengths. The test results revealed that the OPAAC mixes exhibited 28-day compressive strength values ranging from 55 to 70Â MPa, with shear strengths varying in the range of 8.5â€“12.67Â MPa. Multi-linear regression equations were then developed to predict the 28-day compressive and shear strengths using MINITAB 21 statistical software. The predictions of these were verified by conducting actual strength experiments on a new set of three verification mixes. Further, additionally, a generalized correlation was developed to predict the 28-day shear strength of OPAAC mixes based on the known 28-day compressive strength. Again, an examination of microstructures was carried out through the utilization of FESEM analysis, to get a general appreciation of the microstructure (morphology) and elemental composition using EDX analysis of these mixes. The outcomes of this study are anticipated to promote the extensive adoption of environmentally friendly and sustainable materials within the construction industry. The findings of this study are anticipated to promote the extensive adoption of environmentally friendly and sustainable materials in the construction industry. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.