Faculty Publications
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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 Effect of elevated temperatures on ferrochrome ash based mortars(Associated Cement Companies Ltd., 2019) Kumar, B.; Yaragal, S.C.; Das, B.B.Due to boom in construction sector, large amount of Ordinary Portland Cement (OPC) is being consumed. Cement production is energy intensive and releases large amount of CO2 into atmosphere. Efforts are on to bring down cement consumption by the use of secondary cementitious materials. An attempt is made to study the influence of combined effect of various levels of ferrochrome ash (FCA) and lime, as replacement to OPC for different cement mortar mixtures at elevated temperatures. FCA replacement considered is in the range of 0% to 20% and along with 7% lime as replacement to cement. Compressive strength of cementitious materials is being an important parameter in the design of structures. The main objective of this work is to assess the residual compressive strengths at different levels of temperatures (200, 400, 600, and 800ºC) for a retention period of half an hour. Residual strengths of mortar mixtures produced, using FCA, have shown a good performance. Upto 20% FCA and 7% lime, mixture turns out to be a good elevated temperatures enduring material. This would increase the suggested application for environmental friendly materials. Important differences were seen in microstructural observations with scanning electron microscope (SEM) for various levels of FCA and lime incorporated mortars. © 2019, 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 Ferrochrome ash – Its usage potential in alkali activated slag mortars(Elsevier Ltd, 2020) Kumar, K.B.; Yaragal, S.C.; Das, B.B.This study is an attempt to develop a sustainable construction material, i.e., alkali activated slag (AAS) in combination with ferrochrome ash (FCA) as a replacement to ordinary Portland cement (OPC). The effect of the various levels of FCA (0, 25, and 50%) replacing ground granulated blast furnace slag (GGBS) in AAS mortars with 4% of Na2O dosage is studied. Further, five levels of the modulus of silica (Ms = 0.75, 1.00, 1.25, 1.5, and 1.75) are chosen to achieve targeted compressive strength at 28 days under ambient temperature curing conditions. The compressive strength decreases with the increase in level of the FCA replacement. The targeted design compressive strength is achieved with 25% FCA replacement to GGBS in the AAS mortar system with Ms = 1.25. In addition, microstructure and mineralogical studies are undertaken to ascertain the formation of different hydration products with the aid of the scanning electron microscope (SEM) and the X-ray diffractometer (XRD). Gismondine and calcium aluminate silicate hydrate (C-A-S-H) are the major hydration products in the AAS mortar mixes. Sodium aluminate silicate hydrate phases (N-A-S-H) are also observed prominently as the FCA replacement level increases in the AAS mortar mixes. The Fourier-transform infrared spectroscopy (FTIR) confirms the presence of the Si–O-(Si or Al) functional group. The addition of FCA in the AAS system is of vital significance in the reduction of the embodied carbon dioxide (ECO2eq), embodied energy (EEeq) and cost. © 2020 Elsevier LtdItem Effect of phase-change materials on the hydration and mineralogy of cement mortar(ICE Publishing, 2020) Snehal, K.; Das, B.B.The influence of direct incorporation of thermally efficient phase-change materials (PCMs) on the hydration and mineralogical properties of cement mortar was investigated. To assess the viability of bulk addition of PCMs to a cementitious system, tests of the early age, hydration, mechanical, durability and mineralogical properties were carried out. Organic PCMs showed an increase in setting time, while inorganic materials exhibited fast setting characteristics. Surface temperature was also found to be lower for cement paste with incremental dosages of PCM. However, chemical shrinkage was found to be reduced in the presence of PCM except for the inorganic type. It was observed from the results that PCMs negatively influenced the rate of strength development of a cementitious mortar. The slow rate of strength development was found to be attributed to interrupted hydration, which was confirmed through mineralogical studies. Further, from the thermo-gravimetric analysis, it was observed that the presence of PCMs in a cementitious system increased calcium hydroxide content and reduced the content of water related to hydration products. © 2020 ICE Publishing: All rights reserved.Item Acid, alkali and chloride resistance of binary, ternary and quaternary blended cementitious mortar integrated with nano-silica particles(Elsevier Ltd, 2021) Snehal, K.; Das, B.B.This paper investigates the quantification of ettringite (Ca6Al2(SO4)3(OH)12.26H2O, AFt), gypsum (CaSO4.2H2O, Gy) and Friedel's salt (Ca4Al2(OH)12Cl2.4H2O, Fs) formed for binary, ternary and quaternary blended cementitious mortar mixes that were exposed to acid (H2SO4), alkali (Na2SO4) and chloride (NaCl) solutions. Quantification was carried out through a thermogravimetric analyzer by characterizing the mass loss associated to the decomposition of these compounds at specific boundaries of temperature (50–120 °C for AFt, 120–150 °C for Gy and 230–380 °C for Fs). Binary, ternary and quaternary blended cementitious mortar mixes were designed by adopting modified Andreasen and Andersen particle packing model. A long-term exposure period was spanned to the duration of 180 days for all kind of aggressive media and its effect on engineering properties of blended cementitious mortar were measured. Deterioration due to acid (H2SO4) exposure is found to be more intense due to the synergistic action of acid and sulfates. It is to be noted that for acid exposure period of 180 days, control mortar underwent an acute density and strength losses of 18% and 59%, respectively. However, cementitious mortar mix consisting of 3% nano-silica performs the best against aggressive media. The optimistic resistance to the formation of AFt and Gy was also found to be offered by quaternary blended mix. A similar trend was also observed in the formation of Fs for the mortar mixes exposed to NaCl solution. Significant improvement in particle packing density by the inclusion of micron to nano sized finer particles for quaternary blended mortar mix has minimized the permeable porosity, thus reduced the susceptibility to the formation of voluminous compounds. Enhanced pozzolanic activity due to the presence of nano-silica could be one of the primary reasons for quaternary blended mortar to perform better against the aggressive media that can be adopted in the practice considering sustainability and economical point of view. © 2021 Elsevier LtdItem Potential utilization of regional cashew nutshell ash wastes as a cementitious replacement on the performance and environmental impact of eco-friendly mortar(Elsevier Ltd, 2023) Manjunath, B.; Ouellet-Plamondon, C.M.; Das, B.B.; Bhojaraju, C.Globally, agro-waste ashes are increasing significantly due to the rapid implementation of biomass-based power plants. In the present trend, agro-wastes are disposed of in an unsustainable manner. The recycling of agro-waste has significantly contributed to sustainable goals. In the construction sector, it is possible to dispose of waste more efficiently. However, the efficiency of locally available agro-residual waste in cementitious composites is not well understood. In the present investigation, the practicability of using agro-residual ash obtained from the burning of cashew nutshells on the properties of eco-friendly blended cement paste and mortars is explored. Blended cement mixtures containing cashew nutshell ash (CNSA) were prepared at five replacement levels, 5, 10, 15, 20, and 25%, relative to the weight of the cement. To understand the characteristics of CNSA, microstructure investigations such as X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy, and energy-dispersive spectroscopy analyses were performed. Paste properties of CNSA-based cement are observed through consistency, setting time, mini-slump flow, and expansion tests. For the CNSA-based mortars flow table, compressive strength, ultrasonic pulse velocity (UPV), electrical resistivity (ER), water absorption, bulk density, and porosity tests were performed to understand its efficiency. The strength indices of mortars were used to quantify the pozzolanic effect of CNSA. With the incorporation of CNSA, water demand increased by 57%, initial and final setting time decreased by 90% and 83%, respectively. Results showed that CNSA-based mortars absorbed more water and had higher porosity, which reduced compressive strength, UPV, and ER values. CNSA blended mortar is more suitable for applications that do not require high compressive strength. Results indicated that the compressive strength, UPV, and ER are within the limit specified. Strength indices indicated that CNSA has a positive and negative pozzolanic effect during early and later ages, respectively. Further, the sustainable assessment showed that the introduction of CNSA in mortar could substantially reduce embodied carbon, embodied energy, and strength efficiency over the control mortar. The inadequate amount of SiO2, Fe2O3, and Al2O3 in CNSA makes it an unsuitable pozzolanic material. However, it can be utilized in smaller amounts as a fractional replacement of cement and is found to be promising for specific desired properties of cement as a cost-effective accelerator. © 2023 Elsevier LtdItem Synergistic effect of nano silica on carbonation resistance of multi-blended cementitious mortar(Elsevier Ltd, 2023) Snehal, K.; Das, B.B.; Barbhuiya, S.Confiscation of alkaline buffer in a blended cementitious system surges the risk of carbonation. Understanding the carbonation mechanism and kinetics of multi-blended cementitious systems in correspondence to microstructural properties is the need of the hour. In this context, the change in the microstructure of binary, ternary, and quaternary blended cementitious mortar mix comprising of fly ash or/and ultra-fine fly ash or/and nano-silica upon accelerated carbonation (3.5% CO2; 70% RH) was studied. All multi-blended mixes were proportioned using modified Andreasen and Andersen particle packing theory. Permeable porosity and carbonation parameters such as carbonation depth, rate of change in compressive strength, and carbonation shrinkage were measured. Further, qualitative/quantitative estimation of carbonation phases was done using characterization techniques such as TGA and FTIR. In control mix with solely OPC, the reaction of CO2 with calcium-bearing phases showed chemo-mechanical changes leading to 18% improvement in strength at 30 days of exposure. The optimized multi-blended cementitious systems with nano-silica exhibited higher resistance to carbonation kinetics. Phase assemblages quantified through TGA within depth of carbonation imply a negligible concentration of portlandite (CH). However, mixes without nano-silica exhibited a significant reduction in bound water content associated with C–S–H/AFt/AFm phases and intensified the precipitation of calcium carbonate (CaCO3) phase. Asymmetric stretching band of C–O–C at 1424 cm−1 corresponding to calcite phase measured using FTIR validates the outcomes of TGA. © 2023 Elsevier LtdItem 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 Ltd