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Author: search.filters.author.Barai, Sudhir KumarSubject: search.filters.subject.Recycled aggregate concrete (RAC)

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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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    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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    Beam-column joints made of self-compacting concrete containing recycled coarse aggregates and nano-silica
    (Inderscience, 2020-03) Barai, Sudhir Kumar
    This research focuses on the analysis of beam-column joints prepared using self-compacting concrete (SCC) incorporated with nano-silica (NS) and recycled coarse aggregates (RCA). For this purpose, beam-column joint behaviour of normal concrete, SCC incorporating RCA and NS was examined under static loading condition. Analysis of the experimental results indicates that the performance of the joints made with RCA is comparable with that of normal concrete in terms of cracking and ultimate load-carrying capacity. This study also depicts that compressive strength (CS) of SCC made with 100% RCA is somewhat higher than that of SCC made with normal aggregates. Moreover, enhancement in CS can be obtained with the introduction of NS in SCC containing 100% RCA.
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    Recycled aggregate concrete: a sustainable built Environment
    (ICSBE, 2010) Barai, Sudhir Kumar
    In the present study the influence of recycled coarse aggregate (RCA) obtained from three different sources having different ages of structures are on the properties of recycled aggregate concrete (RAC) are investigated. RAC mixes are prepared with each source of RCA separately. In order to assess the performance of RAC in comparison with normal concrete, two normal concrete mixes prepared with 100% natural coarse aggregate. Locally available natural sand is used in all mixes. The compressive strength and the characteristics of interfacial transition zone (ITZ) viz. porosity and microhardness of RAC are studied. The results reveal that the ITZ of RAC is relatively loose and porous than the ITZ in normal concrete.
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    Shear performance of recycled aggregate concrete beams: An insight for design aspects
    (Elsiever, 2018-07-30) Barai, Sudhir Kumar
    The shear failure of reinforced concrete beam is a brittle type of failure and can be dangerous if it is not properly designed. The inherent inferior quality of recycled coarse aggregate (RCA) makes the recycled aggregate concrete (RAC) beams even more vulnerable in shear resistance. This persuades the structural designers to account each of the contributing components in the shear resistance mechanisms seriously, especially that of concrete. In this regard, an experimental investigation was carried out on fourteen beams to examine the shear performance of RAC beams in the absence and presence of transverse reinforcement. Six numbers of beams without transverse reinforcement were tested to examine the contribution of RAC in shear resistance mechanisms and eight beams with shear reinforcement were tested to verify the applicability of the prevailing shear design provisions for RAC beams. The inferior mechanical properties of the RAC are improved satisfactorily by implementing the Particle Packing Method of mix design approach along with the established Two Stage Mixing Approach. However, even with the improved mechanical properties of RAC, the poor performance of RAC beams in shear could not be avoided and a drop of 14% was recorded in the ultimate shear strength of RAC beams without stirrups. A database is prepared by compiling the reported test results of RAC beams with and without transverse reinforcement. An alternative equation is proposed to predict the diagonal tension cracking strength of RAC beams, by using the database of RAC beams without transverse reinforcement and it exhibits a better correlation with the experimental results. Further, in the shear resistance mechanisms of RAC beams the effectiveness of stirrups is studied using the database of RAC beams without and with transverse reinforcement.
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    Multi-scale characterisation of recycled aggregate concrete and prediction of its performance
    (Elsiever, 2020-02) Barai, Sudhir Kumar
    The inherent inferior quality of recycled coarse aggregate (RCA) influences the microstructural characteristics and consequently, the macro-mechanical properties of recycled aggregate concrete (RAC). The present paper investigates the influence of aggregate properties, degree of hydration (), and micro and meso level characteristics of concrete on its compressive strength. Moreover, the influence of different mix design methods (conventional and Particle Packing Method) and mixing approaches (normal mixing approach and two stage mixing approach) on , and micro and meso level properties of concrete are analysed. In addition to the crushing value and water absorption of coarse aggregate, thermogravimetric analysis, nanoindentation and image analysis of back-scattered electrons images and X-ray microtomography images are performed to measure , interfacial transition zone (ITZ) thickness, voids content in the ITZ and interface of concrete, respectively. However, none of these parameters can be singled out to demonstrate its major or significant contribution to the compressive strength of concrete. Hence, the influence of each parameter must be appreciated. An expression is proposed by accounting each of these parameters and also the cement content and coarse aggregate fraction to predict the compressive strength of concrete, which exhibits good correlation with the experimental results.
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    Characteristics of sustainable concrete incorporating recycled coarse aggregates and colloidal nano-silica
    (Techno Press, 2015-09) Barai, Sudhir Kumar
    The present study addresses about the development of sustainable concrete utilizing recycled coarse aggregates manufactured form waste concrete and colloidal Nano-Silica. Experimental investigations are carried out to determine compressive and tensile strength of concrete mixes designed with recycled coarse aggregates and different percentages of Nano-Silica. Moreover, water absorption, density and volume voids of concrete mixes are also examined to ascertain the influence of Nano-Silica on behavior of recycled aggregate concrete. The outcomes of the research depict that properties of concrete mixes are significantly affected with the introduction of recycled coarse aggregates in place of the natural coarse aggregates.However, the study reveals that the depletion of behavior of recycled aggregate concrete could be restored with the incorporation of little amount (3%) of Nano-Silica.
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    Performance of fly ash incorporated recycled aggregates concrete column under axial compression: Experimental and numerical study
    (Elsiever, 2019-10-01) Barai, Sudhir Kumar
    The reinforcing steel properties and concrete constituents such as binder materials as well as type and geometry of coarse aggregates influence performance of a reinforced concrete column under uniaxial compression. This paper investigates full-scale reinforced concrete (RC) column specimens comprising 100% recycled coarse aggregates and fly ash as partial replacement of cement. Two cement replacement ratios such as 20% (FA20RAC) and 30% (FA30RAC) are considered. Particle packing method is used for proportioning of concrete. This mix design method leads to dense packing with minimized voids in fly ash incorporated recycled aggregate concrete (FARAC) mix requiring less fresh binder content. As compared to natural aggregate concrete (NAC), the load carrying capacity of FA20RAC and FA30RAC column specimens are higher by about 4% and 9% respectively. Prediction of full-scale column behaviour from the standard cylinder test highlights size effect that affects the peak load less in FARAC as compared to NAC. Two-dimensional numerical analysis of a transverse tie confined concrete is carried out using fibre element method. The effect of core concrete on the development of confining pressure is examined for RC columns with similar arrangement and properties of lateral ties.
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    Petrographic investigation on recycled coarse aggregate and identification the reason behind the inferior performance
    (Elsiever, 2019-10-10) Barai, Sudhir Kumar
    Recycled concrete aggregate (RCA) shows more complex behavior in fresh and hardened concrete due to its higher water absorption, weak bonding capacity, poor interfacial transition zones (ITZs) and other uncertainties. The old attached mortar (AM) of RCA is the primary reason behind this. Petrographic analysis is normally assessed for construction aggregate to evaluate the physical and mineralogical characteristics, along with these the prediction of aggregate behavior in concrete. The same methodology is applied here for RCA and demanding to investigate the reason behind the inferior performance of it into fresh concrete. Optical microscopy, thin section, and Scanning Electron Microscopy (SEM) analysis are carried out in order to solve the addressed issue. Both the qualitative and quantitative petrographic analysis is conducted in order to identify the inferior properties of RCA. Micropores and microcracks are very common for RCA surface which propagates the failure of recycled aggregate concrete (RAC) under load. The experimental observation is suggested that the RCA is different kind of aggregate for sustainable construction material and cannot comparable with natural aggregate (NA) without proper understanding the type of parent aggregate or source of RCA. The range of aggregates between 20 and 10 mm can give good quality RCA after additional crushing and suitable treatment is required on RCA for strengthening the old ITZ and AM in order to achieve high-quality RCA.
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    Nano-engineered concrete using recycled aggregates and nano-silica: Taguchi approach
    (Techno Press, 2015-12) Barai, Sudhir Kumar
    This paper investigates the influence of various mix design parameters on the characteristics of concrete containing recycled coarse aggregates and Nano-Silica using Taguchi method. The present study adoptsWater-cement ratio, Recycled Coarse Aggregate (%), Maximum cement content and Nano-Silica (%) as factors with each one having three different levels. Using the above mentioned control parameters with levels an Orthogonal Array (OA) matrix experiments of L9 (34) has selected and nine number of concrete mixes has been prepared. Compressive Strength, Split Tensile Strength, Flexural Tensile Strength, Modulus of Elasticity and Non-Destructive parameters are selected as responses. Experimental results are analyzed and the optimum level for each response is predicted. Analysis of 28 days CS depicts that NS (%) is the most significant factor among all factors. Analysis of the tensile strength results indicates that the effect of control factorW/C ratio is ranked one and then NS (%) is ranked two which suggests thatW/C ratio and NS (%) have more influence as compared to other two factors. However, the factor that affects the modulus of elasticity most is found to be RCA (%).Finally, validation experiments have been carried out with the optimal mixture of concrete with Nano-Silica for the desired engineering properties of recycled aggregate concrete. Moreover, the comparative study of the predicted and experimental results concludes that errors between both experimental and predicted values are within the permissible limits. This present study highlights the application of Taguchi method as an efficient tool in determining the effects of constituent materials in mix proportioning of concrete.