Faculty Publications
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Item An experimental investigation on self-compacting alkali activated slag concrete mixes(Elsevier Ltd, 2018) Manjunath, R.; Narasimhan, M.C.In present work, an attempt has been made to develop self-compacting, alkali activated slag concrete mixes, using steel slag sand as fine aggregate and EAF (Electric Arc Furnace) slag as coarse aggregate. The study investigates the properties such as compressive strength, splitting tensile strength and water absorption of these mixes. Development of Self-Compacting Alkali Activated Slag Concrete mixes (hereafter referred to as SCAASC mixes) was made with GGBFS (Ground Granulated Blast Furnace Slag) as the binder, with its content varying between 700 kg/m3 and 900 kg/m3 of fresh concrete. The net W/B (water to binder) ratio of the mixes was varied between a narrow 0.47 – 0.48 range. The alkaline solutions had Na2O percentages in the range 7 – 9%, but a constant activator modulus was maintained at 1.0 in all the mixes. In order to optimise the number of trial mixes to be tested, Taguchi's design of experiments methodology was adopted. A total of nine mixes were formulated using Taguchi orthogonal L9 array. Results showed the slump flow values for the mixes greater than 700 mm, with their L–Box ratios and V-Funnel values ranging between 0.90 and 0.95 and 9 – 11 s respectively, satisfying the EFNARC guidelines. Results also showed good compressive strengths (65–80 MPa), split-tensile strengths (2–4 MPa) and low water absorption values in the range of (2%–3%). The microstructural studies such as SEM, EDX and XRD analysis were also carried out, showing denser morphologies clearly indicating effective activation of slag by the alkaline solution. © 2018 Elsevier LtdItem Studies on development of high performance, self-compacting alkali activated slag concrete mixes using industrial wastes(Elsevier Ltd, 2019) Manjunath, R.; Narasimhan, M.C.; Umesh, K.M.; Kumar, S.; Bala Bharathi, U.K.In the present study, development of a class of High Performance Alkali Activated Slag Concrete mixes (hereafter referred to as HPAASC mixes) is discussed. These mixes are developed using three industrial wastes from Iron and Steel industry. While Ground granulated blast furnace slag (GGBFS) was used as the main binder, in the development of these HPAASC mixes, steel slag sand and Electric Arc Furnace slag (EAF slag) have been employed in the fine aggregate and coarse aggregate fractions of them. Higher flow characteristics, as those of self-compacting concrete mixes, as well as enhanced mechanical strength properties of these mixes are discussed in detail. The alkaline solutions used consist mixtures of sodium hydroxide and sodium silicate solutions, with a constant activator modulus (ratio of SiO2/Na2O) of one maintained in them. Taguchi’ design of experiments methodology was used to reduce the experimental efforts. The formulation of all the mixes developed herein was based on Taguchi's L-9 orthogonal array. Flow and strength properties of a set of nine mixes were used for performance evaluation purposes in an initial, calibration phase. Strength prediction equations were derived based on such results, the predictive capability of which were then assessed and ascertained with actual results of experiments on the next six new mixes, in the prediction phase. Test results indicated a higher flowability values for all the mixes (with slump flows greater than 700 mm), good filling and passing abilities, all satisfying the EFNARC (European Federation of Specialist Construction Chemicals and Concrete Systems) recommendations for SCC mixes. Higher compressive strengths (65–90 MPa), split-tensile strengths (4.8–5.3 MPa), flexural strengths (6.5–7 MPa), and Modulus of Elasticity (30.4–36.2 GPa) were observed along with lower water absorption values (2.1–2.7%) for all the HPAASC mixes tested herein. Microstructure studies were conducted on samples from the fractured surfaces of test specimens from different mixes, using advanced SEM, EDX and XRD analyses and the results are discussed. © 2018 Elsevier LtdItem Effects of fiber addition on performance of high-performance alkali activated slag concrete mixes: An experimental evaluation(Taylor and Francis Ltd., 2022) Manjunath, R.; Narasimhan, M.C.; Kumar, S.There is an ever-increasing awareness on issues connected with emission of high amounts of greenhouse gases from various industries, including that from the concrete construction industry. Performances of alternative binder systems including geopolymers and alkali activated slag concretes are being investigated in this context. There is again a continuous drive to enhance their performances, both when green and on getting hardened and so also, simultaneous efforts are being made to take advantage of all the various fast-track, state-of-art construction technologies, leading to efficient, eco-friendly and economical infrastructure projects. The present authors have developed and evaluated a new set of such alkali activated slag concrete mixes having self-compacting property, along with higher mechanical properties (hereafter referred to as HPAASC mixes) using three industrial by-products, all obtained from iron and steel industry. While these HPAASC mixes have higher compressive strengths (in the range of 70–90 MPa), reasonable split and flexural strengths and are self-compacting, they continue to be brittle just as other high strength concrete mixes. In order to improve their cracking behaviour during failure, either under mechanical loads or on exposure to higher temperatures, addition of increasing amounts of steel fibers in HPAASC mixes is contemplated. Hence in the present study, the attempt is to study the effect of incorporation of fibers (within a small range of 0.4 ? 0.8%) in the new class of high-performance, fibre reinforced. Self-compacting alkali-activated slag concrete mixes–(referred to as HFSASC hereafter). The present study evaluates the properties such as flow ability, compressive strength and flexural toughness performances for these mixes. Results in the present study indicate that, while all the HFSASC mixes exhibit satisfactory passing and flowing abilities specified as per EFNARC standards for self-compacting mixes, they exhibit enhanced toughness characteristics too. © 2020 Informa UK Limited, trading as Taylor & Francis Group.Item Multi-objective optimization of one-part alkali-activated mortar mixes using Taguchi-Grey relational analysis(Elsevier Ltd, 2024) Mahendra, K.; Narasimhan, M.C.; Bhanu Prakash, G.; Das, A.K.In the context of the contemporary emphasis on sustainability within the realm of construction, there is a notable surge in attention towards one-part alkali-activated (OP-AA) materials. This is primarily attributed to their enhanced performance and reduced carbon emissions as compared to conventional OPC-based concrete. In the present investigation, Taguchi and Taguchi- Grey relational analysis (GRA) methodologies were employed to execute the experimental design, involving three input parameters, each considered at three levels, to generate an L9 orthogonal array. An attempt was made to assess the impact of different parameters, such as ground granulated blast furnace slag (GGBFS) to fly ash (FA) ratio - (S/F), water-to-binder ratio - (W/B), and percentage of Na2O - (N), on the slump flow, setting time, and compressive strength characteristics and hence to optimize the proportions of the OP-AA mortar blends. The results revealed that optimum parameter levels for multi-objective optimization corresponded to S/F = 1, W/B = 0.45, and N = 5%. For these parameter levels specified, the corresponding values of slump flow, initial setting time, final setting time, and 28 days compressive strength were 208 mm, 285.4 min, 990.4 min, and 36.52 MPa, respectively. In addition, to gain insights into their mineral composition, morphology, and chemical bond characteristics, microstructural characterization such as X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), and Fourier transform infrared spectroscopy (FTIR) were also conducted on selected OP-AA mortar mixes. The microstructural examination unveiled the predominant formation of hydration products, such as C/N -A-S-H gels, in OP-AA mortar blends, resembling those found in conventional alkali-activated materials (AAMs). During the validation phase, an assessment was conducted by comparing the actual experimental results with the predicted values obtained through regression equations. The outcome of this comparison revealed that the proposed optimum mix parameter levels demonstrated the effectiveness of both the Taguchi and Taguchi-GRA approaches. © 2024 Elsevier LtdItem 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 LtdItem 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