Browsing by Author "Lahoti, Mukund"

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Alternative materials for wearing course of concrete pavements: A critical review
(Elsiever, 2020-03-10) Singh, Ajit Pratap; Sarkar, Askoke Kumar; Lahoti, Mukund
The existing worldwide road length of concrete pavements is significant. Furthermore, concrete pavements have a number of specific applications, even though they are second to asphalt pavements in terms of current popularity. Besides, asphalt is a rapidly depleting resource, which might mean that concrete is the chief material for the future. However, concrete pavements have their drawbacks, such as high construction cost, low tensile strength, and significant contribution to global carbon-di-oxide emissions. The present study aims to address these drawbacks by reviewing the prominent alternative materials that may be utilized to replace cement and/or aggregates in concrete. The potential of alternatives such as coal ash, silica fume, nano-silica, fly ash, slag, and recycled concrete aggregate is investigated. In addition, the effects of adding fibers (as both fiber-reinforced concrete and engineered cementitious composite) to concrete pavements are discussed. This review will also help pavement engineers and researchers to ascertain which combination of materials to use so that mechanical properties better than conventional concrete are achieved. The specific advantages and disadvantages due to various combinations of materials, in several types of concrete pavements such as conventional concrete, roller-compacted concrete, and self-compacting concrete are discussed in detail.
Bioconcrete-Enabled Resilient Construction: a Review
(Springer, 2023-03) Lahoti, Mukund; Srivastava, Anshuman
Concrete, the ubiquitous cementitious composite though immensely versatile, is crack-susceptible. Cracks let in deleterious substances causing durability issues. Superseding conventional crack-repair methods, the innovative application of microbially induced calcium carbonate precipitation (MICCP) stands prominent, being based on the natural phenomenon of carbonate precipitation. It is eco-friendly, self-activated, economical, and simplistic. Bacteria inside concrete get activated by contacting the environment upon the crack opening and filling the cracks with calcium carbonate—their metabolic waste. This work systematizes MICCP’s intricacies and reviews state-of-the-art literature on practical technicalities in its materialization and testing. Explored are the latest advances in various aspects of MICCP, such as bacteria species, calcium sources, encapsulations, aggregates, and the techniques of bio-calcification and curing. Furthermore, methodologies for crack formation, crack observation, property analysis of healed test subject, and present techno-economic limitations are examined. The work serves as a succinct, implementation-ready, and latest review for MICCP’s application, giving tailorable control over the enormous variations in this bio-mimetic technique.
Clinker-free CaO-activated silica fume as a cementitious binder for pavement application
(Elsevier, 2024-10) Lahoti, Mukund
Ordinary Portland cement (OPC) production requires heating limestone up to 1450 °C and produces 0.5–0.9 kg of carbon dioxide for every 1 kg produced. Moreover, the massive volume of cement manufactured around the world every year adds to the urgent need to look for sustainable alternatives. This work proposes a novel calcium oxide (CaO)-activated high-volume silica fume mixture as a cementitious binder for pavement application that can address the sustainability concern with cement (because producing CaO requires a much lower calcination temperature than OPC, and that CaO is also used in low-volume in the binder). The combination of low-volume CaO and high-volume silica fume, particularly as a pavement binder has not been studied in the literature before. The compressive and flexural strength results showed that even by using a small fraction of CaO in the binder, it is possible to obtain acceptable strengths that satisfy ASTM pavement design guidelines, while OPC is unable to provide similar strengths at such low dosage. The mix having CaO content as 30 % of the silica fume content (CSF-30) shows the highest compressive strength (28d: 18.4 MPa) and flexural strength (28d: 4 MPa). In contrast, the maximum OPC-silica fume compressive and flexural strengths observed are 13.9 MPa and 2.9 MPa respectively at 28d From the microstructural results, it was seen that CaO–silica fume develops strength due to formation of calcite and calcium silicate hydrate. Almost all CaO–silica fume mixes exhibited lower porosity compared to their OPC-silica fume counterparts; CSF-30, the mix having the best mechanical performance showed the lowest porosity at 28d (2.8 %). A comparative sustainability analysis followed by a 5D analysis considering all the parameters studied in this work revealed that CSF-30 is the best binder alternative (overall score: 5.24). The results of this work will be useful for pavement users, designers, researchers, engineers, and relevant government officials, in having a sustainable clinker-free alternative pavement binder to OPC, particularly for low-volume roads, that satisfies the pavement design guidelines.
Comprehensive assessment of leaching characteristics in electric arc furnace slag-based alkali-activated mortar
(Springer, 2025-03) Lahoti, Mukund
This study investigates the leaching resistance and environmental performance of electric arc furnace slag (EAFS) as a precursor in alkali-activated materials (AAMs), contributing to sustainable construction practices and reducing reliance on conventional cement. The research employs detailed leaching analysis to evaluate the chemical stability, environmental impact, and long-term performance of EAFS-based AAMs (EFAM). Key findings reveal stable pH values in leachate samples, indicative of precursor properties and effective alkali activation, alongside increasing electrical conductivity over time due to the formation of durable ionic bonds. The release of heavy metals, such as Zn, Cu, and Cr, decreases significantly after 60 days, highlighting effective stabilization mechanisms. Distinct leaching patterns of oxyanions like arsenic and chromium, coupled with minimal leachability of elements such as molybdenum and barium, emphasize the material’s environmental safety. Additionally, calcium in the system reduces the mobility of certain elements, ensuring compliance with environmental standards. All leached metals remain below detection limits across samples, confirming the suitability of EFAM for construction applications without adverse ecological effects. This study underscores the relevance of thorough leaching analysis in validating the safety and sustainability of novel construction materials, paving the way for their broader adoption in eco-friendly construction.
A comprehensive review on applications of engineered cementitious composites in pavements
(Elsevier, 2023-12) Lahoti, Mukund; Muthukumar, G.
A significant proportion of the pavement network around the world uses asphalt as the construction material. However, asphalt reserves are expected to last no more than 50 years. The apparent alternative, Portland Cement Concrete, has its limitations, such as environmental emissions and poor riding quality. Since its inception, Engineered Cementitious Composite (ECC) has been suggested as an alternative pavement material in scattered studies over the years. This study aims to compile and present the state-of-art in ECC-related pavement applications and clearly define the research gaps so that future researchers in this area can carry out their work efficiently. It is observed that ECC has primarily been used as an overlay over both asphalt and concrete substrates rather than as a full-depth pavement material. Other application areas include bridge deck pavements, repair works, multi-layer pavements, and special function applications. Research related to the comparative life cycle and life cycle cost assessment of ECC pavements is also reviewed in this study. One significant benefit of using ECC in pavements that is noted is that slab joints can be eliminated due to the high ductility of ECC. ECC also has the potential to greatly reduce pavement reflective cracking and life-cycle environmental impacts. While the absence of coarse aggregates produces a smooth surface for excellent riding quality, it also poses the risk of low pavement skid resistance. Another important and well-known drawback of ECC, especially for such a large-scale application, is the high construction cost. Some of these problems have been solved to a certain degree using waste alternative materials and rough fine aggregates such as corundum. More research is needed to understand the prospects of ECC as a full-depth pavement material rather than just an overlay. Future work revolving around more large-scale field demonstration, durability enhancement, further cost reduction, and life-cycle impact reduction is desirable for enhanced applicability of ECC in road infrastructure.
Computational design of fly ash geopolymer mortar using experimental and attribute evaluation approaches
(Springer, 2024-10) Lahoti, Mukund; Srivastava, Anshuman
Geopolymer is a ceramic-like inorganic material synthesized at room temperature and is a potential sustainable replacement of Portland cement. In the present work, a comprehensive experimental program was designed to evaluate the relative importance of mix design factors controlling the strength of fly ash geopolymer mortar. Restrained factors, namely, temperature of curing; alkaline solution to fly ash (L/FA) ratio; sodium silicate to sodium hydroxide (SS/SH) ratio; sodium hydroxide molarity; and fly ash to sand (FA/Sand) ratio, and unrestrained factors, namely, H2O/Na2O; SiO2/Al2O3; SiO2/Na2O; and Al2O3/Na2O molar ratios, were considered for evaluation. Feature subset selection and multivariate adaptive regression splines (MARS) techniques were used to determine the significance of these factors. Results show that temperature of curing is the most significant factor. FA/Sand and L/FA are found to affect compressive strength more significantly than sodium hydroxide molarity and SS/SH. Except for H2O/Na2O molar ratio, other molar ratios were observed to be very less significant. It is noted that mix design of geopolymer mortar should not be based on the molar ratios, instead mix design must be prepared by controlling the restrained factors. The findings of this study should be helpful in optimization of design factors leading to a robust geopolymer mix.
Concrete Compressive Strength Prediction Using Boosting Algorithms
(Springer, 2023-02) Lahoti, Mukund; Muthukumar, G.
This study proposes intelligent machine learning (ML)-based methods for concrete compressive strength prediction by utilizing a publicly available dataset. The methods employed are the XGBoost, CatBoost and TabNet algorithms. A total of 1030 data points are collected wherein the independent input variables are the amounts of the different components of the concrete mix design and the output variable is the compressive strength at different curing ages. The proposed boosting algorithm approaches are contrasted with a few other popular ML techniques used in this field, such as logistic regression, classification and regression tree, and artificial neural networks. It is found that XGBoost and CatBoost show significantly lower mean errors between predicted values and actual observations of the compressive strength than the contemporary architectures, while TabNet is not so efficient. TabNet’s lower efficiency of prediction can be attributed to the relatively small dataset that was used for this study.
A critical review of geopolymer properties for structural fire-resistance applications
(Elsevier, 2019-10) Lahoti, Mukund
Protection of structures from fire is of extreme importance. Geopolymer is a novel material that has wide-ranging applications, and this review article focuses on assessing the potential of geopolymers towards enhancing the structural fire resistance by critically reviewing its properties subjected to elevated temperature exposure. The properties of geopolymers are categorized into three scales, namely, micro-scale, meso-scale and macro-scale, and are discussed at length. It is noted that geopolymers are chemically stable and do not undergo breakdown of chemical structure in contrary to OPC hydration products. Thermal deformations occurring in geopolymers, which cause macro-cracking, are discussed. Compressive strength of geopolymers is observed to be affected by microstructural changes (including crack formation, pore structure changes, densification, sintering, and melting) and phase composition changes (such as growth or destruction of crystals and transformations in geopolymer paste). Geopolymer-based binders show inherently superior fire resistance as compared to Portland cement-based binders. However, it requires careful mix design, to achieve substantial chemical stability, low volume changes, strength endurance, and spalling resistance. Factors such as choice of precursor, use of aggregates, total alkali content in geopolymer, water content, etc. are critical and should be controlled. The influence of these factors is discussed at length in this article. The current applications of geopolymers for heat and fire resistance have also been briefly presented.
Economic input-output LCA of precast corundum-blended ECC overlay pavement
(Elsevier, 2022-09) Muthukumar, G .; Lahoti, Mukund
Many studies have explored the prospect of using Engineered Cementitious Composites (ECC) in rigid pavements by looking at aspects such as mechanical performance, temperature susceptibility, cost, and environmental impact. Although ECC is an excellent choice because of its high tensile capacity, its major drawback for pavement applications is that it lacks roughness because of no coarse aggregates. Recently, an ECC mix containing corundum fine aggregates has shown remarkably higher skid resistance and drainage performance for pavement applications. The current study attempts to perform a comprehensive Economic Input-Output Life Cycle Analysis (EIO-LCA) of a concrete pavement having a precast corundum-blended ECC overlay. This LCA is compared with the LCA of a conventional rigid pavement and a full-depth conventional ECC pavement. The study includes both an inventory analysis using EIO-LCA and an impact assessment at midpoint and endpoint level on selected impact categories. It is found that the pavement having a precast corundum-blended ECC overlay is more economically and environmentally sustainable than the full-depth concrete and ECC pavements, and also has lower life-cycle impacts overall.
Effect of alkali cation type on strength endurance of fly ash geopolymers subject to high temperature exposure
(Elsevier, 2018-09) Lahoti, Mukund
Choice of alkali cation in mix design of geopolymers is critical for their thermal performance. However, the influence of alkali cation type on strength endurance of geopolymers subject to high temperature exposure and the underlying governing mechanisms have not been studied. This study investigated the effects of alkali cation type on high temperature response of fly ash geopolymers aiming towards structural applications. In-depth investigation was carried out to discover the underlying mechanisms governing the strength endurance of fly ash geopolymers subject to high temperature exposure and its correlation with their volume stability and chemical stability. Results showed that potassium geopolymer exhibited significant strength enhancement (30–40%) and sodium geopolymer displayed reduced strength (10%), and the strength of mixed sodium and potassium geopolymer remained unchanged after exposure to elevated temperature. While the binders were chemically stable without deterioration and formation of new crystal phases after high temperature exposure, the volume stability varied with the type of alkali cation used. Formation of cracks and gel densification due to shrinkage, and healing of micro-cracks and change of pore sizes due to sintering were identified as responsible mechanisms at different temperature ranges. While crack development and enlargement of pores lowered the strength, densification of matrix and healing of micro-cracks favored strength gain. These competing mechanisms determine the strength endurance of geopolymers depending on the type of alkali cation used. Overall, it shows that geopolymers can be tailored, such that stable (or even enhanced) strengths upon thermal exposure are realized, for structural applications.
Effect of sodium hydroxide concentration on EAFS based alkali activated binder
(Elsevier, 2023-04) Lahoti, Mukund
The emission of greenhouse gases primarily CO2 during the production of cement is a substantial global threat. Along with this the disposal of industrial waste is also a key concern due to leachate. In order to lower the emissions and make better use of industrial waste, a novel technology termed alkali-activated binder (AAB) can be a potential alternative to ordinary portland cement. In the past few years, AAB’s have been a phenomenon of remarkable interest to the construction sector because of their exceptional mechanical qualities and sustainability. The selection of the source material is a critical factor to develop AAB’s. This research attempts to utilize the electric arc furnace slag (EAFS) generated from the production of steel through EAF route as the primary precursor. Four different variations of sodium hydroxide (SH) molarity (8, 10, 12, and 14) were used to investigate its effect on the fresh and mechanical properties of EAFS-based AAB. The alkali to binder ratio of 0.40, curing temperature 80 °C, and 85% humidity were used for preparing the AAB. Scanning electron microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray fluorescence (XRF), and X-Ray diffraction (XRD), are used for material characterization and for analyzing microstructural development.
Effects of aircraft operating fluids and environmental thermal fatigue on fly ash and steel slag based cementitious composites
(Springer Nature, 2024-06) Lahoti, Mukund
This paper investigates the performance of concrete incorporating high-volume fly ash (HVFA) and steel slag aggregates against the detrimental effects of combined cycles of environmental thermal fatigue and exposure to leaked aircraft fluids. A total of 128 cubes and 90 prisms were cast for five mixes and exposed to 60, 120, 180, 240 and 300 combined cycles. The results demonstrate the positive effect of utilization of HVFA which reduces the total amount of portlandite available in the system. The SS aggregates demonstrate a strong interlocking with the surrounding matrix and supply the necessary portlandite for continued pozzolanic reaction. However, their reaction with aircraft fluids causes significant degradation to flexural strength initially, which is redeemed by pozzolanic reaction at a later stage. Hybrid basalt and polypropylene fibres were successful in enhancing the flexural strength and reducing the cracking. The mercury intrusion porosimetry revealed a reduction in pore volume because of HVFA. Scanning electron microscopy and differential scanning calorimetry were also employed to uncover the underlying mechanisms of damage and assess the performance of the cementitious composite.
Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature
(Elsevier, 2018-04) Lahoti, Mukund
Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900 °C. Although, the geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6 MPa) because viscous sintering of geopolymer mixes with high Si/Al ratio at temperature beyond 600 °C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900 °C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin geopolymers for structural fire resistance applications.
Enhanced thermal performance of fiber-reinforced cementitious composite with high-volume fly ash and steel slag aggregates
(ACS, 2025-04) Lahoti, Mukund
Existing cementitious composites often undergo severe degradation when exposed to high temperatures. The present study proposes utilization of high-volume fly ash (HVFA) and steel slag (SS) aggregates to address this issue. Hybrid fiber reinforcement in the form of basalt fibers and polypropylene (PP) fibers have also been utilized. A total of 120-cylinder specimens were cast for the elevated temperature testing between 200°C and 800°C, and the residual compressive and microstructural properties were analyzed. Results indicate that the HVFA mixes with 100% SS fine aggregates and hybrid length basalt fiber yield optimal performance at elevated temperatures. Specifically, the mix containing 100% SS aggregates retained 101%, 115%, 113%, and 55% of its compressive strength at 200°C, 400°C, 600°C, and 800°C, respectively. Microstructural analysis further revealed that the use of HVFA-SS system enhanced the elevated temperature performance by promoting the pozzolanic reaction of slow reacting fly ash particles, tobermorite formation, and improvement in the interfacial transition zone. Also, excellent resistance to cracking and spalling was observed. Overall, this study provides new perspective on the design of sustainable fiber-reinforced cementitious composites with excellent thermal endurance.
Enhancing the resistance of cementitious composites to environmental thermal fatigue using high-volume fly ash and steel slag
(Elsevier, 2024-10) Lahoti, Mukund
Daily fluctuations in environmental temperature induce thermal fatigue and cause degradation in concrete structures. This study introduces a novel approach of utilizing high-volume fly ash, steel slag fine aggregates, and basalt-polypropylene fibres to prevent degradation against environmental thermal fatigue (ETF). Five mixes were considered with variations in fine aggregate type, fibre length and volume. The compressive and flexural strengths were analysed after exposure to 60, 120, 180, 240, and 300 ETF cycles between 20 and 60 °C (at constant relative humidity). The residual compressive strength of mix with 100 % river sand and 100 % steel slag as fine aggregates was ∼106 % and ∼112 % respectively after 300 ETF cycles. The developed cementitious composites performed significantly better than the mixes utilized in the existing literature. The mix with 100 % steel slag aggregate even demonstrated a continual rise in compressive strength as opposed to mixes with river sand whose strength declined after 180 or 240 ETF cycles. Flexural strength also improved up to 180 ETF cycles and then started to decline in all mixes. A thorough microstructural analysis was also conducted using scanning electron microscopy, differential scanning calorimetry, and mercury intrusion porosimetry to gain further insights into the underlying mechanism of the newly introduced matrix composition against ETF.
Exploratory study on concrete incorporating copper tailings and marble dust as partial substitutes for ordinary portland cement
(Springer, 2025-07) Lahoti, Mukund; Srivastava, Anshuman
Supplementary cementitious materials are crucial to reduce costs and carbon footprint, as traditional cement production emits greenhouse gases. This study explores using copper tailings and marble dust as substitutes for Ordinary Portland Cement (OPC) in concrete. In this investigation, three concrete mixes were designed, and tests were carried out to compare their tensile and compressive strengths. C0M0 served as the control mix, i.e., mix with no replacement of OPC. While in C5M5 mix, 10% OPC was replaced by 5% copper tailings and 5% marble dust. While in mix C5M10, 15% OPC was replaced by 5% copper tailing and 10% marble dust. Experimental observation was that the control mix (C0M0) exhibited highest compressive strength, which then declined for C5M5 mix and further retreated in increasing path in C5M10 mix, with almost reaching compressive strength of the C0M0 (control) mix. The compressive strength as compared to the control mix was reduced by about 24.8% for C5M5 mix and close to 0.9% for C5M10 mix. The observed decrease in strength was attributed to the moisture-absorbing nature of copper tailings and marble dust, which limited water availability for OPC hydration, while marble dust's filler action contributed to strength gain. Ultrasonic Pulse Velocity (UPV) tests established a relationship between compressive strength and sound velocity. Economic analysis revealed the cost-effectiveness of concrete incorporating copper tailings and marble dust. The study highlights the potential for developing concrete strength with these waste materials, promoting environmentally friendly and cost-effective construction practices.
A Feasibility Study on the Potential Usage of Engineered Cementitious Composites in Indian Pavements
(Springer, 2022-09) Lahoti, Mukund
The global concrete consumption has been rising at over 2.8% per annum, reaching as high as 4.08 billion metric tons in FY-2021 alone. A significant chunk of this is being used in pavement construction to eventually reduce the usage of traditionally utilized asphalt and RCC in pavements and to improve environmental impact, pavement performance, and life. This study addresses the potential of using engineered cementitious composites (ECC) in comparison with traditional materials like RCC. The scope of this paper includes an in-depth analysis of material properties, economic benefit, and the lifecycle assessment of ECC, in comparison with RCC and an another alternative fiber-reinforced concrete (FRC). The framework thus established to analyze the feasibility of ECC in the Indian context is based upon the use case of FRC as discussed subsequently in the form of a case study. A similar basis has been utilized to discuss a case study on an M45 ECC mix. A similar skeleton approach can be followed to comprehend and analyze the cases of ECC usage in any alternative geography or climatic condition by choosing a mix suitable to the respective location, material availability, and logistics. It is found that ECC offers a 30% reduction in total lifecycle costs as compared to conventional concrete if a 50-year analysis period is considered.
Fired clay bricks synergistically valorizing hazardous nickel chrome-plating sludge and fly ash: Performance assessment
(Elsevier, 2024-04) Singhal, Anupam; Routroy, Srikanta; Bhunia, Dipendu; Lahoti, Mukund
Nickel Chrome Plating Sludge (NCPS) is a hazardous waste containing 25%-30% nickel and chromium. Previous attempts to immobilize NCPS into fired clay bricks resulted in weakened strength due to porosity and microstructure deterioration. This study introduces co-valorization of NCPS and fly ash in fired clay bricks to address these issues. Factory-scale firing of green bricks, alongside conventional clay bricks, assessed the commercialization potential. The optimal proportion of NCPS, fly ash, and clay was found to be as 12.5:37.5:50.0, respectively. Fly ash addition significantly improved brick properties, causing compressive strength to increase from 3.2 MPa to 11.6 MPa for a NCPS content of 12.5%. Microstructural analysis highlighted fluxing oxides in NCPS, amorphous silica-alumina in fly ash, synergistic ceramic bond formation, enhanced sintering and pore filling during vitrification. The study also demonstrated substantial fuel savings of 40%-50% due to NCPS's high heat of combustion causing internal firing of green bricks. The developed bricks exhibited almost double linear attenuation coefficients, indicating enhanced gamma radiation shielding. Leaching tests confirmed successful heavy metal immobilization. This co-valorization approach not only overcomes previous drawbacks but also offers significant environmental and economic benefits in utilizing NCPS in brick production.
High volume fly ash and basalt-polypropylene fibres as performance enhancers of novel fire-resistant fibre reinforced cementitious composites
(Elsevier, 2023-11) Lahoti, Mukund
This study attempts to address the fire resistance of fibre reinforced cementitious composite (FRCC) while considering sustainability. Sustainable FRCC mixes were developed by varying the contents of silica fume and high-volume fly ash (up to 60% by wt.), along with a hybrid combination of basalt and polypropylene fibres. The FRCC was exposed to temperatures up to 800 °C, and its appearance, mass loss, and compressive properties were analysed. Exceptional performance in terms of resistance to cracking and strength retention was observed. The relative residual compressive strength of one of flyash based mixes was found to be 93.46%, 117.48%, 102.03% and 38.48% between 200 and 800 °C. Also, fly ash enhanced the mass retention properties especially with higher replacement levels and at higher temperatures. The influence of temperature on hydration products in the system has been explained using scanning electron microscope, X-ray diffraction, and thermogravimetric analysis. Furthermore, the improvement in thermal performance is demonstrated as a novel incentive for addition of fly ash in high volumes.
Influence of activator ratios and concentration on the physio-mechanical and microstructural characteristics of the geopolymers derived from sandstone processing waste
(Springer, 2024-03) Bhunia, Dipendu; Lahoti, Mukund; Chakraborty, Sayantan
Natural stones have been utilized to meet various needs of human civilization since ancient times. The exploitation of any resource is associated with the production of redundant materials called wastes. Sandstone waste (SW) is one such waste obtained during the industrial processing of sandstones. Due to its siliceous composition, extensive yield, and disorganized dumping, noxious conditions related to land and human health are promoted. However, the lack of comprehensive engineering studies, mineralogical analysis, and design methodologies associated with the utilization of sandstone processing wastes restricted their applicability only to fillers or partial substitutes with pozzolans and traditional cement in meager volumes. In the past, limited efforts have been made to utilize SW as a construction entity, particularly for binding purposes. Thus, to enhance the scope of its utilization, a comprehensive investigation has been performed in this research to transform sandstone waste into a novel construction material by geopolymerization. Mix design tailoring and laboratory tests were implemented to understand the effects of sodium hydroxide concentration and sodium silicate to sodium hydroxide ratio on the dissolution and physio-mechanical characteristics of SW-based geopolymers. The activator-to-binder ratio was restricted to 0.4 to obtain pastes with sufficient workability without hindering the properties of the matrix. Besides, a high temperature-curing regime was selected based on SW's crystallographic and reactivity analysis. Subsequently, a total of 48 samples were prepared and tested at the curing age of 28 days. Detailed characterization of SW and SW-based geopolymer samples was performed using optical, X-ray, and infrared spectroscopies aided by electron imaging and thermogravimetric techniques. SW-based geopolymer samples showed compressive strengths in the range of 6-12 MPa, ~2 to 3 times higher than those obtained in previous experimentations. Phase analysis and microstructural examinations confirmed SW's participation in geopolymerization. Overall, it could be advocated that geopolymerization is an innovative approach for solving issues related to the disposal and re-utilization of SW, extending its possible application to the fields of cement mixes, wall tiles, mortars, and masonry as per the commendations of ASTM and ACI committee.