Department of Civil Engineering
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Item Environmental impact of concrete(Springer, 2025-10) Barai, Sudhir KumarSustainable concrete production demands satisfaction of the two most important criteria such as optimization of resources and minimization of end-of-life wastes. As discussed in the previous chapters, one of the important ways in which this can be achieved is by using coarse recycled concrete aggregates (RCAs) as an alternative to natural coarse aggregates and other industrial wastes as supplementary cementitious materials (SCMs). In this regard, the role of a suitable mix design method for obtaining an optimum combination of concrete constituents is also significant. In this chapter, sustainability of 100% recycled coarse aggregate concrete (RAC) along with SCMs in concrete is explored through performing life-cycle assessment, especially focusing on concrete with coarse RCA and low-volume fly ash as cement substitute (denoted as FARAC) in concrete. The effect of particle packing method (PPM) of mix proportioning on the environmental impact of FARAC is assessed for a case study of India.Item Behaviour of reinforced concrete slabs under punching shear(Springer, 2025-10) Barai, Sudhir KumarFlat slab supported by an interior column is a complicated problem due to the most likely phenomenon of punching shear failure. This chapter discusses the punching shear behaviour of recycled aggregate concrete with coarse RCA. In the context of using SCMs in concrete, we address the following question: How does low-volume fly ash as a cement substitute alter the punching shear of RAC flat slabs? Another aspect while using any recycled material is maintaining the level of structural safety as that of the already existing material. The punching shear resistance design equation, available for the standard reinforced concrete slabs, may not yield a safe design for RAC slabs due to greater uncertainties. The reliability of standard punching shear models is assessed and modified to ensure equivalent safety for RAC and NAC flat slabs. It is crucial to conduct this reliability analysis in order to confidently establish fly ash and 100% coarse RCA as alternative concrete constituents in practice.Item Behaviour of reinforced concrete beams(Springer, 2025-10) Barai, Sudhir KumarIn the preceding chapters, we have discussed the properties of concrete, specifically focussing on the material behaviour of SCM and recycled coarse aggregates. The primary challenge in incorporating this sustainable recycled material is to fulfil the performance requirements of structural elements subjected to flexural, shear, and compression. The behaviour of reinforced concrete RAC beams under bending and shear is discussed in this chapter. Load carrying capacity, failure pattern and effects of material parameters are examined for fly ash incorporated 100% RAC beams. We evaluate the suitability of current code provisions for natural aggregate concrete to be used in RAC with fly ash beams. Furthermore, reliability of structural elements is evaluated, considering the variabilities associated with these recycled materials. Necessary modifications are suggested to achieve the same level of safety as conventional concrete.Item Performance assessment and life cycle analysis of concrete containing ferrochrome slag and fly ash as replacement materials – A circular approach(Elsevier, 2022-09) Barai, Sudhir KumarClimate change mitigation and resource efficiency have emerged as crucial challenges for long-term sustainability of concrete. Implementing circular approach through waste valorisation in concrete production with eco-efficient mix design is an efficient mitigation pathway to combat natural resources depletion and environmental issues. This paper investigates techno-environmental sustainability of concrete utilizing 100% ferrochrome slag as alternate coarse aggregate and fly ash as partial cement substitute (0–40%) adopting particle packing optimization technique (PPOT) as a sustainable mix design method. Total of ten types of concrete mixtures were prepared using the alternate materials and mix design methods (PPOT and IS:10262(2009)). Natural aggregate concrete prepared by IS:10262(2009) mix design was considered as the reference mixture. Technical assessment of concrete was performed experimentally in terms of compressive strength and tensile strength. Environmental performance was investigated through life cycle assessment (LCA) as per ISO 14040-44 guidelines using cradle-to-gate system boundary and two functional units: 1 m3 concrete and 1 MPa compressive strength. Results revealed that ferrochrome slag aggregate concrete (FCSAC) containing fly ash up to 30% prepared by PPOT has enhanced strength than reference concrete. Regardless of the functional units used, FCSAC with 30% fly ash designed by PPOT was ranked as the most sustainable mix with significant environmental savings (around 50–70%) without compromising desired requirements. Sensitivity analysis was performed by varying transportation distance, mode of transport and energy mix. Results showed that FCSAC with 30% fly ash is not sensitive to the scenarios investigated. The outcomes will be helpful for decision-makers to develop policy directives and frameworks on synergistic use of ferrochrome slag and fly ash towards concrete sustainability.Item Flexural behaviour of fly ash incorporated ferrochrome slag aggregate reinforced concrete beam(Elsevier, 2023-10) Barai, Sudhir KumarThe structural behaviour of fly ash integrated ferrochrome slag aggregate concrete (FCSAC) is not widely understood owing to lack of research, although some studies have focused on its mechanical and environmental performance. The real-world use of FCSAC relies on its large-scale structural tests. This research investigates the flexural response of reinforced concrete beams fabricated with fly ash and ferrochrome slag (FCS) aggregate. A total of sixteen full-scale beams were built and tested. The beams were cast using four different concrete compositions: natural aggregate concrete (NAC) without any fly ash and FCS as the reference; FCSAC comprising 100% FCS as coarse aggregate and fly ash as partial substitution of cement at different percentages: 0%, 20% and 30%. The beams were fabricated with two different longitudinal reinforcement ratios of 0.69% and 1.86%. An eco-efficient mix proportioning method based on Particle packing optimization technique (PPOT) was adopted aiming to develop sustainable concrete. The effect of alternate resources (FCS and fly ash) and reinforcement ratios on the flexural response, cracking, ultimate load, failure pattern, ductility and toughness were examined. The experimental outcomes were compared to the predictions derived from the existing code provisions. Results revealed that the flexural performance of the FCSAC with fly ash beams was superior to that of NAC beam, despite having a lower flexural capacity than the FCSAC without fly ash beams. Moreover, the comparative study demonstrated that the fly ash-based FCSAC beams may be designed in accordance with the same guidelines as conventional concrete.Item 8 - Fly ash-incorporated recycled coarse aggregate-based concrete(Elsiever, 2021) Barai, Sudhir KumarThis chapter focuses on the feasible use of partial cement substituted by fly ash in 100% recycled coarse aggregate-based concrete (feasible use of fly ash in recycled aggregate concrete [FARAC]). The effect of particle packing method of mix proportioning is explored. Performance of such sustainable concrete is assessed for both strength and durability. At material level, this chapter examines fresh and hardened concrete properties. Microstructural analysis provides some insights for macrolevel behavior. Finer spherical fly ash particles and triple mixing method improve workability of recycled aggregate concrete (RAC). The negative effects of RAC on compressive strength (CS) is only significant at early ages (7 days), which reduces with adequate curing in RAC with 30% fly ash. Split tensile strength and the ratio of split tensile to CS decreases, which implies reduction of the rate of development of tensile strength at higher CS in RAC. Presence of fly ash in RAC causes densification of pores, thereby increasing the resistance to chemical attack. Fly ash used as cement substitution also proves to be beneficial as far as the creep and shrinkage of concrete is concerned. Adverse effects at material level can be accounted for with necessary design considerations for safe application of FARAC as structural components (beam, column, and slabs).Item Flexural performance and tension-stiffening evaluation of reinforced concrete beam incorporating recycled aggregate and fly ash(Elsiever, 2018-06) Barai, Sudhir KumarThis paper presents the effect of fly ash in recycled aggregate concrete (RAC with 100% recycled coarse aggregates) on the flexural performance of reinforced concrete (RC) beam. Particle packing method (PPM) of mixture proportioning is used in a novel way for the flexure study. This method by principle accounts for the excess adhered mortar present on the outer surface of recycled coarse aggregates (RCA) while calculating maximum packing density and consequently minimize the requirement of fresh mortar. The parameters such as materials (aggregate type and fly ash), mix design method and reinforcement percentages are considered for evaluation of moment carrying capacity, deflection, and failure pattern. Based on experimental results, the constitutive relation for cracked RAC and natural aggregate concrete (NAC) is evaluated numerically showing tension stiffening effect. The results conclude mostly comparable moment carrying capacity of RAC incorporating fly ash beams and NAC beams at ultimate limit state. The maximum mid-span deflection has been observed to be higher, but the variation is not substantial at service load due to the effect of fly ash and PPM in RAC. The reduced tension-stiffening effect, as observed from the derived stress–strain relation of cracked concrete justifies the higher mid-span deflection in RAC. The applicability of existing code provisions for NAC beam is assessed for RAC with fly ash beams. The results suggest the potential application of 100% recycled coarse aggregates and up to 30% fly ash in a reinforced concrete beam without compromising its flexure performance.Item Recycled aggregate concrete incorporating fly ash: Comparative study on particle packing and conventional method(Elsiever, 2017-12-15) Barai, Sudhir KumarIn the present study, particle packing method (PPM) of mix proportioning is applied in a novel way for recycled aggregate concrete (RAC) incorporating fly ash as a partial replacement of cement. Lesser fresh mortar content was achieved by PPM which resolves the major concern of excess adhered mortar in RAC. Theoretical packing density (PD) obtained using compaction-interaction packing model was compared with experimental PD. 18% and 28% reduction in cement content was observed for RAC with 20% and 30% fly ash replacement respectively due to PPM mix proportions as compared to conventional method at water-binder ratio of 0.45. Compressive strength, flexural strength and modulus of elasticity of RAC with fly ash showed comparable results with natural aggregate concrete in PPM. The rate of long term compressive strength gain was about 11%–20% and 30% in RAC and natural aggregate concrete (NAC) respectively. Split tensile strength and modulus of elasticity in RAC was comparable in both the conventional as well as PPM methods. Flexural strength was improved in RAC incorporating fly ash mix due to PPM. Statistical analysis showed better tensile strength for RAC as compared to NAC up to the characteristic compressive strength of 25 MPa. Poor tensile behaviour was reported for high strength recycled aggregate concrete. The results suggest that, the particle packing method can be used in RAC with fully replaced recycled aggregates incorporating fly ash (up to 30% replacement) for sustainable construction practices.Item Performance of fly ash incorporated recycled aggregates concrete column under axial compression: Experimental and numerical study(Elsiever, 2019-10-01) Barai, Sudhir KumarThe 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.Item Partially fly ash incorporated recycled coarse aggregate based concrete: Microstructure perspectives and critical analysis(Elsiever, 2021-04-05) Barai, Sudhir KumarThis paper presents experimental investigation of the microstructure of partial cement substituted fly ash incorporated recycled aggregate concrete (FARAC). Testing techniques such as thermo-gravimetric analysis, scanning electron microscopy, nano-indentation and X-ray tomography were adopted for this study. Effects of parameters like (i) percentage of fly ash (20% and 30% as cement replacement by weight), (ii) particle packing mix design and conventional method, (iii) curing ages (7, 28 and 90 days), and (iv) coarse aggregate types (100% natural or recycled) are examined. Degree of hydration of FARAC, though higher than natural aggregate concrete, did not translate directly into compressive strength due to formation of more loosely connected low density C-S-H confirmed by SEM images. It is observed that micro-cracks pass mostly through the old and fresh bulk paste rather than the old ITZ in 90 days cured concrete. Thickness of the old ITZ as well as heterogeneities of the new ITZ reduced in FARAC. Upto 30% fly ash can compensate higher porosity of RAC through formation of spherical smaller-size pores.