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Author: search.filters.author.Pradhan, Subhasis

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    Particle packing method for recycled aggregate concrete
    (Springer, 2024) Pradhan, Subhasis; Barai, Sudhir Kumar
    This book highlights the use of commercially available recycled aggregate concrete (RAC) extracted from multiple construction and demolition sites, considering it as a viable alternative to conventional aggregate. It further describes the advanced techniques, such as, scanning electron microscopy, nanoindentation, thermogravimetric analysis and X-ray microtomography shedding light on the deep-rooted causes of inferior macro-mechanical performance of RAC and the advantages of particle packing method design approach in this regard. It then describes the improved properties of RAC with the help of macro-mechanical performance studies, microstructural characterization and fracture analysis. The systematic and in-depth presentation of the use of recycled coarse aggregate as an alternative to conventional aggregate for the preparation of structural concrete will guide researchers on subsequent research in RAC and provide assistance to structural engineers and concrete manufacturers for the usage of RAC.
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    Reaction kinetics and thermodynamic modeling of alkali-activated calcined marine clay with mechanical activation
    (Elsevier, 2025-09) Pradhan, Subhasis
    A clinker-free, one-part alkali-activated materials (AAM) using calcined marine clay (CMC) and Ca(OH)2 (CH) was developed in this study. The influence of mechanical activation on the mechanical properties, morphology, and the microstructure of one-part AAM was explored. Chemical dissolution test elucidates the relationship between reacted SiO2/Al2O3 content, CH content, and pH values throughout the reaction process. Leveraging these experimental and statistical analysis results, a novel quantitative study on the kinetics of alkali activation process and the impact of milling on one-part AAM was conducted through thermodynamic modeling. CH dissolution-controlled reaction kinetics was revealed through experimental and modeling equilibrium comparisons. It demonstrates that the co-milling of CMC and CH can facilitate the alkali activation by synergistically improving the reacted CaO, SiO2, and Al2O3 content via accelerated dissolution of CH and CMC. This research advances understanding for one-part AAM design by optimization of precursor/activator content and mechanical activation time via experimental and modeling approaches
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    Synergistic effect of particle packing method, aggregate saturation levels, and paste content in improving the performance of high volume fine recycled aggregate concrete
    (Springer Nature, 2025) Pradhan, Subhasis
    Using fine recycled concrete aggregate (FRCA) is challenging because of the presence of mortar fines in higher quantities. Past studies have reported a few approaches (Presoaking FRCA, surface treatment of FRCA, use of mineral admixture, method of mix proportioning, and mixing FRCA concrete) to improve the performance of FRCA concrete. However, these studies recommend the deployment of 30–50% FRCA as a substitute for natural fine aggregate. Additionally, the treatment methods are not cost-effective. To address these limitations and upscale the use of FRCA, this study introduces the particle packing method (PPM) for mix proportioning, a modified presoaking method for concrete mixing, and presents the effect of aggregate saturation level and paste content on the performance of concrete. Concrete mixes with 0–100% FRCA, 15% and 20% extra paste contents, and different aggregate saturation levels (50–100%) were prepared. The mechanical and durability properties of concrete, such as compressive strength, flexural strength, modulus of elasticity, abrasion resistance, sorptivity, water permeability, and chloride ingress, were analysed by replacing 0–100% crushed stone sand (CSS) with FRCA. The initial results showed a significant reduction in the mechanical and durability properties of fully saturated 100% FRCA concrete than the control mix. However, substantial improvement was seen by using partially saturated (50%) FRCA, and 20% paste content. The effect of decreasing FRCA saturation level was prominent. On using 50% saturated FRCA, the compressive strength, flexural strength, static and dynamic modulus of elasticity, and abrasion resistance, improved by 16%, 14%, 14%, 8%, 13%; and exhibited a lower sorptivity, water permeability, and chloride ingress of 56%, 14%, and 34%, respectively. The microstructural analysis showed that by reducing the saturation level and increasing the paste content a denser interfacial transition zone can be obtained. Furthermore, using PPM for mix proportioning is beneficial in minimizing the cement content for FRCA concrete mixes. The study demonstrates the synergistic effect of the PPM mix proportioning method, modified mixing method, 20% extra paste content, and partially (50%) saturated FRCA in improving the performance of untreated high-volume FRCA concrete, thereby supporting a sustainable approach.
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    Novel LCA-centric mix design approach for alkali-activated EAF slag with hybrid optimization techniques
    (Springer, 2024-12) Lahoti, Mukund; Pradhan, Subhasis
    This study presents an innovative life cycle assessment (LCA)-centric approach for optimizing the mix design of alkali-activated materials (AAMs) as sustainable alternatives to ordinary portland cement (OPC). The AAMs are developed using electric arc furnace slag (EAFS) and fly ash as precursors. The environmental performance is evaluated using the ReCiPe midpoint methodology, considering both mass and economic allocation methods. The results indicate that global warming potential and terrestrial ecotoxicity are the primary environmental impact categories across all mixes and allocation scenarios. A Taguchi-based hybrid optimization technique, integrating gray relational analysis (GRA) and analytical hierarchical process (AHP)-weighted GRA, is employed to determine the optimal mix design based on fresh properties, mechanical performance, durability, and sustainability indices. The AHP-GRA analysis reveals that mixes containing at least 50% EAFS perform better than OPC in terms of overall sustainability. A blend of 75% EAFS and 25% fly ash is recommended for achieving the best balance between performance and environmental impact, offering a promising alternative for sustainable construction practices.
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    Experimental and numerical study of recycled aggregate concrete column
    (Wiley, 2023-02) Pradhan, Subhasis; Barai, Sudhir Kumar
    The improved mechanical properties of recycled aggregate concrete (RAC) by employing the particle packing method (PPM) of the mix design approach encourages its application to study the performance of structural members. The experimental investigation is conducted on the axial compressive behavior of reinforced natural aggregate concrete (NAC) and RAC columns using two different tie spacing conditions. A reduction of 18% in the axial load of RAC columns is observed with respect to the NAC columns and only 2.7% improvement in axial load is recorded as the tie spacing reduces by 22.5%. Subsequently, the finite element (FE) analysis is conducted to investigate the axial compressive strength of both NAC and RAC columns using different tie spacing conditions. The FE analyses of RAC columns with different tie spacing support to modify the spacing of transverse reinforcement as half as that of the spacing specified in the prevailing design for NAC columns.
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    A thermo-mechano-chemical activation technique to use quartz rich marine clay for one-part geopolymer preparation
    (Elsevier, 2023-07) Pradhan, Subhasis
    This research aims to prepare one-part geopolymer by using the quartz rich marine clay available in Singapore. The higher quartz and lower kaolinite mineral (∼29%) in marine clay is not ideal for a precursor material in geopolymerization. Hence, a novel thermo-mechano-chemical activation process is employed. The process of thermal activation (calcination at 850 C) transforms kaolinite into reactive metakaolin form. The mechanical activation by ball milling alters the surface group of quartz by forming non-bridging oxygen. The chemical activation process is promoted by adding alkali materials, such as NaOH, Na2CO3, and Ca(OH)2. XPS results inform the presence of higher non-bridging oxygen content in Na2CO3 and NaOH based mixtures than Ca(OH)2 based mixture. However, more reactive Q0(0Al) and Q1(1Al) states of 29Si are observed in Ca(OH)2 based mixture from NMR spectra. This resulted in higher compressive strength of Ca(OH)2 based one-part mixture. A temperature curing (at 80 C) is required to facilitate the geopolymerization process.
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    Particle Packing Method for Recycled Aggregate Concrete
    (Springer, 2024) Pradhan, Subhasis; Barai, Sudhir Kumar
    This book highlights the use of commercially available recycled aggregate concrete (RAC) extracted from multiple construction and demolition sites, considering it as a viable alternative to conventional aggregate. It further describes the advanced techniques, such as, scanning electron microscopy, nanoindentation, thermogravimetric analysis and X-ray microtomography shedding light on the deep-rooted causes of inferior macro-mechanical performance of RAC and the advantages of particle packing method design approach in this regard. It then describes the improved properties of RAC with the help of macro-mechanical performance studies, microstructural characterization and fracture analysis. The systematic and in-depth presentation of the use of recycled coarse aggregate as an alternative to conventional aggregate for the preparation of structural concrete will guide researchers on subsequent research in RAC and provide assistance to structural engineers and concrete manufacturers for the usage of RAC.
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    Characterization of Materials
    (Springer, 2024-02) Pradhan, Subhasis; Barai, Sudhir Kumar
    Concrete is a composite material and a heterogeneous mixture of cement, coarse aggregate, fine aggregate, water, and chemical admixture. The behaviour and performance of concrete in the fresh as well as hardened stages largely depend on the physical, mechanical, and chemical properties of its constituents. Hence, it is important to determine the characteristics of the raw materials prior to the designing of concrete mix for their intended application. This book aims to compare the performance of concrete, prepared using two different types of coarse aggregates (natural coarse aggregate (NCA) and recycled coarse aggregate (RCA)). The subsequent sections exclusively discuss the differences in physical and mechanical properties between NCA and RCA.
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    Structural Applications: Beam
    (Springer, 2024-02) Pradhan, Subhasis; Barai, Sudhir Kumar
    The fundamental characteristics of RCA and how it is used to create RAC were covered in prior chapters. In this context, the influence of the PPM mix design technique was explored.
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    Life Cycle Assessment and Cost Analysis
    (Springer, 2024-02) Pradhan, Subhasis; Barai, Sudhir Kumar
    The researchers suggested various mix design techniques and mixing strategies to prepare RAC with acceptable mechanical characteristics.