Journal Articles
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Item Influence of fineness of fly ash on compressive strength and microstructure of bottom ash admixed geopolymer mortar(Associated Cement Companies Ltd., 2018) Shivaprasad, K.N.; Das, B.B.; Renjith, R.Investigations were conducted to find out the suitability of bottom ash as a possible replacement to fine aggregates in geopolymer mortar. Experimental work was done to study the influence of fineness of fly ash (with three levels of Blaine's fineness, 2043 cm2/g, 2602 cm2/g and 3113 cm2/g on compressive strength and microstructure development of fly ash based geopolymer mortar with natural river sand and bottom ash as fine aggregates. three different water to solids ratios of 0.246, 0.349, and 0.443 were chosen for this study and the curing of the specimens was at ambient temperature (28 ± 3°c). compressive strength development for all eighteen mortar mixes was measured at 7, 14, 28 and 56 days. Further, the effect of fineness of fly ash on degree of polymerization, microstructure and properties of geopolymers was studied using Fourier transform Infrared Spectroscopy (FtIR) and Scanning Electron Microscopy (SEM). It was observed from the compressive strength of the geopolymer mortar that the degree of polymerization is gradual for both types of mortar. there is a continuous increase in the development of compressive strength noticed till the age of 56 days for both types of mortar, sand as well as bottom ash admixed. However, the increment of compressive strength for bottom ash found to be significantly less as compared to natural sand. Improvement in compressive strength due to fineness of fly ash were characterised by SEM and FtIR and it is revealed that with increase in fineness levels, the microstructure significantly enhanced the characteristics of geopolymer mortar. © 2018 Associated Cement Companies Ltd.. All rights reserved.Item Early age, hydration, mechanical and microstructure properties of nano-silica blended cementitious composites(Elsevier Ltd, 2020) Snehal, K.; Das, B.B.; Akanksha, M.This study was carried out to understand the influence of nano-silica on hydration properties of binary, ternary and quaternary blended cement paste and mortar containing micro to nano sized admixtures including fly ash (FA), ultrafine fly ash (UFFA) and nano-silica in colloidal form (CNS). Characterization methods such as thermogravimetric analysis (TGA), X-ray diffraction studies (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) was employed to quantify the hydration products. Further, early age and mechanical properties were also investigated for binary, ternary and quaternary cementitious system blended with nano-silica. The optimized proportions of blended paste and mortar are designed through modified Andreasen and Andersen particle packing model. The experimental test results revealed that the optimum dosage of CNS in binary blended cement composites is 3%. The presence of nano-silica in cementitious system amplified the hydration and pozzolanic activity, thereby promoting densified microstructure at nano scale. The flow test indicated the intensified demand for water absorption and reduced workability with the rise in level of incorporation of CNS particles in cement paste. Quaternary blended mix performed superior hydration along with strength properties amongst all the blended samples. © 2019 Elsevier LtdItem Influence of Integration of Phase Change Materials on Hydration and Microstructure Properties of Nanosilica Admixed Cementitious Mortar(American Society of Civil Engineers (ASCE) onlinejls@asce.org 1801 Alexander Bell DriveGEO Reston VA 20191 Alabama, 2020) Snehal, K.; Das, B.B.; Kumar, S.The present study demonstrates the influence of integrating phase change materials (PCMs) on hydration and microstructure properties of nanosilica admixed cementitious mortar. First, the optimized dosage of nanosilica in correspondence to compressive strength was determined. Subsequently, the desired proportion of PCMs was identified pertaining to a designated compressive strength of 35 MPa at the curing age of 28 days. The hydration and microstructure studies were carried out through thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Further, thermal properties were determined by means of differential scanning calorimetry (DSC). Incorporation of nanosilica into the cementitious mortar was found to have a positive influence on early strength development and durability, however, there was found to be an increase in chemical shrinkage as compared to the control mixture. PCMs integrated cementitious mortar improved the thermal efficiency as well as reduced the chemical shrinkage, but adversely affected the mechanical, hydration, and durability properties. With respect to development of compressive strength of the cementitious mortar, it is found that n-octadecane PCMs performed better amidst other PCMs, such as paraffin and sodium carbonate hydrates. Further, studies were carried out on cementitious mortar having both nanosilica (optimized proportion) and PCMs (the best performing). From the results, it is found that cementitious mortar comprising of both nanosilica and PCMs have compensated the drawbacks of one another. Blended mortar (having both nanosilica and PCMs) showed superior strength gain at early age, better durability resistance, low chemical shrinkage, and superior thermal performance. © 2020 American Society of Civil Engineers.Item Influence Of Marine Environment Exposure On The Engineering Properties Of Steel-concrete Interface(Bentham Science Publishers, 2022) Goudar, S.K.; Sumukh, E.P.; Das, B.B.Aims: A detailed and reformed service life prediction model needs to be developed by considering the non-uniform distribution of the porous zone and the non-uniform distribution of the corrosion products layer. Background: The microstructure of the steel-concrete interface (SCI) plays an important role in corrosion initiation and concrete cover cracking. The porous zone around SCI is one of the vital engineering properties that influence the service life of corroding reinforced concrete structures in service life prediction models. Objective: The SCI properties are sensitive to the sample preparation technique of reinforced concrete (RC) samples for studying with the aid of scanning electron microscopy (SEM). A simple step-wise sample preparation technique of RC samples for SEM analysis is proposed where there is minimal damage to the properties of SCI. The development, distribution, and propagation of corrosion products at SCI are investigated for RC samples exposed to the marine environment for different exposure periods. The service life of RC structures was assessed through experimentally determined porous zone thickness (PZT) values. Assuming a uniform and constant value of PZT and uniform distribution of corrosion products around SCI might lead to variation or misinterpretation of the service life of structures. The same is explored in the present study. Methods: In this research investigation, backscattered electron images were obtained for the analysis of porous zone thickness around SCI. The distribution and propagation of corrosion products around SCI were investigated for different mineral admixed reinforced concrete samples exposed to the marine environment. Also, porous zone thickness values were used experimentally measured, and the time from corrosion initiation to corrosion cracking was estimated using a service life prediction model. Results: Results show that porous zone thickness is not uniform around SCI. Once the corrosion is initiated, the corrosion products accumulate in the SCI's porous region. Further, the non-uniform porous zone thickness directly influenced the non-uniform distribution of corrosion products. Assuming a constant or uniform porous zone thickness and uniform distribution of corrosion products around SCI leads to misinterpretation of the service life of corroding reinforced concrete structures. Conclusion: The porous zone thickness values around the steel-concrete interface and corrosion current density play an important role in predicting the service life of reinforced concrete structures exposed to the marine environment. © 2022 Goudar et al.Item Pozzolanic Reactivity, Hydration and Microstructure Characteristics of Blended Cementitious Composites Comprising of Ultrafine Particles(Springer Science and Business Media Deutschland GmbH, 2022) Snehal, K.; Das, B.B.; Sudhi, A.; Pandey, D.Performance of ultrafine fly ash (UFFA, 5–10 µm) and fly ash (FA, 45–50 µm) particles in cementitious composites was investigated individually as well as in combination. To study the physicochemical behaviour of blended cementitious composites, engineering properties and pozzolanic reactivity test were conducted. Further, characterization techniques such as thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) were employed. The results showed good amplification in the development of early compressive strength and durability on admixing ultrafine particles of fly ash (UFFA) in cementitious system. Particle size and specific surface area of UFFA greatly influenced on the phase assemblages of cementitious composites, i.e. due to enriched pozzolanic reactivity which reduced Ca/Si atomic ratio (≤ 1.82) in the pore solution of cementitious matrix. On contrary, the presence of UFFA particles in cementitious composite mix developed disjoining pressure in addition to self-desiccation thereby induced early age cracks and also reduced the workability in correspondence to that of FA particles. Further, use of UFFA in conjunction with FA particles, cementitious composites showed much superior performance in terms of both physical and chemical characteristics, which necessitates the crucial need of admixing micron and submicron size particles in the design of sustainable and high-performance cementitious composites at this point of time. © 2022, The Author(s), under exclusive licence to Shiraz University.Item IMPLICATION OF HIGH-VOLUME MINERAL ADMIXTURE ON MECHANICAL PROPERTIES AND MICROSTRUCTURE AT STEEL-CONCRETE INTERFACE(Associated Cement Companies Ltd., 2023) Goudar, S.K.; Sumukh, E.P.; Das, B.B.The existence of a non-homogeneous unique zone in concrete along the periphery of steel surface is being referred as steel-concrete interface (SCI). The interface between steel and concrete exhibits a porous zone, with a thickness measuring several micrometers. This porous zone thickness around SCI plays a crucial role in influencing bond strength, durability, and is a significant parameter used in service life prediction models for reinforced concrete structures. The value of porous zone thickness around SCI is being assumed and adopted without any practical studies in service life prediction models as well as in reinforced concrete mesoscale structure modelling. In the present study, porous zone thickness was experimentally measured through obtaining backscattered electron images around SCI. Gray scale-based thresholding technique was employed to ascertain the porous zone thickness (PZT) around SCI. Furthermore, the influence of incorporating ground granulated blast furnace slag (GGBS) in high-volume on the interfacial transition zone (ITZ) between steel reinforcement bars and the surrounding concrete was investigated. It was observed that porous zone thickness around SCI varies in every other point along the periphery of reinforcement bar. The pozzolanic reaction in high volume GGBS concrete resulted in a substantial decrease of porous zone thickness (PZT) and reduced the accumulation of Portlandite around SCI with the progress in curing age. The factors contributing to the enhanced ultimate bond strength of high volume GGBS concrete compared to control concrete are the decrease in the Porous Zone Thickness (PZT) along with the reduced Ca/Si ratio around the SCI. © 2023, Associated Cement Companies Ltd.. All rights reserved.Item Influence of multi-stage processing and mechano-chemical treatments on the hydration and microstructure properties of recycled aggregate concrete(Elsevier Ltd, 2023) Trivedi, S.S.; Sarangi, D.; Das, B.B.; Barbhuiya, S.On account of the shortage of naturally occurring coarse aggregate, recycled aggregate (RA) made from crushed concrete debris is now used in the construction industry. With this rise in the utilisation of recycled aggregate in the construction sector, there has been extensive research into ways to improve its quality. The significant fraction of mortar remains that are left on the RA surface is the primary factor that affects its quality. Concrete made from RA loses strength and mechanical performance due to the attached mortar's increased porosity and water absorption values and the frailer transition region between the new mortar and aggregates. In order to minimise the old cement fractions and increase the quality, this paper studies the effect of concrete incorporating multi-stage processed RA from demolished concrete waste, followed by treatment with mechanical abrasion and sodium silicate immersion. The recycled aggregates were produced through multi-stage jaw crushing, followed by utilising natural aggregate, recycled aggregate, and recycled aggregate obtained after mechanical abrasion, followed by sodium silicate treatment for concrete mix design at various substitution percentages as coarse aggregates. The experimental investigation further progresses with the evaluation of mechanical and durability properties of concrete mixes, which is additionally followed by microstructural studies such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetry-differential thermal analysis (TG-DTA). The outcomes demonstrate that two-stage treatment, such as mechanical abrasion followed by sodium silicate immersion, yields superior-quality RA. Recycled aggregate concrete (RAC) made with these treated aggregates illustrated an increase in workability and density with respect to an untreated RAC mix. Furthermore, comparable strengths in compression, flexure, and tension are found in treated RAC mixes, particularly at 35% replacement levels, with respect to concrete mixes comprised of natural aggregates. A similar trend is detected in the chloride penetration tests and water sorptivity tests. In addition, the microstructural investigation confirmed the formation of additional calcium silicate hydrate for treated RAC mixes, particularly for the 35% substituted RA mix. On the basis of the results, it is suggested that multi-stage jaw crushing followed by treatment through mechanical abrasion and sodium silicate can potentially enhance the mechanical, microstructural, and durability performance of RAC. © 2023 Elsevier LtdItem Synergy of Hydration and Microstructural Properties of Sustainable Cement Mortar Supplemented with Industrial By-Products(Springer Science and Business Media Deutschland GmbH, 2024) Sumukh, E.P.; Das, B.B.; Barbhuiya, S.The present research assists in resolving the issues allied with the disposal of industrial solid wastes/industrial by-products (IBPs) by developing sustainable IBPs based cement mortars. The applicability of IBPs as a feasible alternative to river sand in cement mortar has been evaluated by investigating the synergy among the ingredients, resulting engineering properties and microstructural developments at early and late curing ages. The study could effectively substitute 30% volume of river sand with bottom ash and 50% in the case of slag sand mortars. The experimental outcomes disclose that the practice of IBPs as fine aggregate enhances the engineering properties of mortar and the optimum replacement level lies at 10% and 40% usage of bottom ash and slag sand, respectively. The advanced characterization studies and particle packing density illustrate the refinement of pores by void filing action and accumulation of additional hydration products through secondary hydration reactions. The consumption of portlandite followed by increased hydration products formation observed through thermogravimetric analysis, X-ray diffraction analysis and energy dispersive X-ray spectroscopy that confirmed the contribution of finer fractions of IBPs to secondary hydration reactions. This constructive development was also observed from the lowering of wavenumber corresponding to Si–O–Si/Al vibration bands in Fourier transform infrared spectroscopy spectra. The improved microstructure resulted in enhancing the compressive strength by 9.01% and 18.18% in optimized bottom ash and slag sand mortars, respectively at the curing age of 120 days. Similarly, the water absorption reduced by 1.03% and 1.24% in bottom ash and slag sand mortars, respectively. © The Author(s), under exclusive licence to the Iran University of Science and Technology 2024.Item Combined Effect of Multistage Processing and Treatment Methods on the Physical, Chemical, and Microstructure Properties of Recycled Concrete Aggregates(ASTM International, 2024) Trivedi, S.S.; Dixit, K.; Das, B.B.; Barbhuiya, S.This research aims to examine the effects of multistage processing on reducing the old cement fractions and enhancing the quality of concrete recycled aggregate (CRA). The investigation involves the use of demolished concrete debris and subsequent treatments in both single and multistage processes. The recycled aggregates (RAs) were obtained using a multistage jaw crushing process followed by utilizing natural aggregate, untreated RA, RA treated with hydrochloric acid (HCl) and sodium silicate (SS) immersion (single-stage treatment), and RA treated with mechanical scrubbing and SS immersion in two separate stages (multistage treatment). The subsequent phase of the experimental inquiry involves assessing the physical attributes of both treated and untreated RA. This is followed by conducting microstructural examinations utilizing techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and thermogravimetry-differential thermal analysis. The findings indicate that employing a two-step process, involving mechanical abrasion followed by immersion in SS, yields high-quality CRA. This conclusion is reinforced by the favorable physical performance observed. The water absorption values of CRA were lowered by 78 % through single-stage treatments such as immersion in HCl. The similar treatment is found to show densest concrete with calcium/silicon ratio reduced to around 81 % to that of untreated CRA. Additionally, for single-stage treated CRA samples, microstructural study using FTIR verified the creation of additional hydration products, whereas for two-stage treated CRA specimens, thermogravimetric analysis demonstrated the formation of stable CSH. According to the findings, it is advised to use a multistage process of jaw crushing, then treating it with mechanical abrasion and SS. This has the ability to improve the physical, chemical, and microstructural properties of CRA. © © 2024 by ASTM International,Item 3D printing aspects of fly ash and GGBS admixed binary and ternary blended cementitious mortar(Taylor and Francis Ltd., 2025) Mishra, S.K.; Upadhyay, B.; Das, B.B.This study investigates the integration of Ground Granulated Blast Furnace Slag (GGBS) and fly ash to sustainably reduce the usage of Ordinary Portland Cement (OPC) in 3D printable mortar to enhance printability and engineering performance. Four mortar mixes were developed, and their printability parameters, such as flowability, extrudability, open time, yield stress, shape retention, and buildability, were assessed. Among mixes, O70G30 (70% OPC, 30% GGBS) showed the best printability, with an 18.3% and 54.3% higher shape retention factor than the control and O70F30 mixes, respectively, which can be attributed to improved particle packing and 5.5% higher yield stress. However, its open time was 22.2% lower than the control. This reduction can be attributed to the finer particle size and higher specific surface area of GGBS, which increased water demand and accelerated the loss of workability. In the hardened state, O70G30 exhibited 24% lower water absorption and 18.5% reduced permeable porosity than the control, indicating a denser microstructure. Printed specimens exhibited anisotropic strength, with the highest values observed on the YZ plane and the lowest on the ZX plane. Depending on the loading direction and mix composition, their compressive strength was 9.4–35.6% lower than that of mould-cast samples, while the flexural strength improved by 16.19% to 40.18%. Microstructural analysis revealed a denser matrix with a lower Ca/Si ratio and enhanced secondary hydration, evidenced by stronger C–S–H peaks in XRD, pronounced Si–O–Si/Al bands in FTIR, and 41.22% higher bound water (WH) with reduced portlandite (CH) in TGA compared to O70F30. These promising results can be attributed to GGBS’s role in enhancing hydration, refining the microstructure, and improving the performance of 3D printable mortar, offering a sustainable and effective pathway for digital construction. Also, the Life Cycle Impact Analysis (LCIA) revealed that the incorporation of supplementary cementitious materials (SCMs) significantly reduces environmental impacts compared to the control mix. © 2025 Informa UK Limited, trading as Taylor & Francis Group.