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    Development of stress-strain models for glass fiber reinforced polymer composites confined sustainable concrete made with natural and recycled aggregates
    (2024-02-16)
    Yooprasertchai, Ekkachai
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    Hussain, Qudeer
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    Khan, Kaffayatullah
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    Ejaz, Ali
    This study addresses the mechanical limitations of concrete fabricated with recycled brick and concrete as partial replacement of coarse aggregates, which exhibit inferior strength and stiffness compared to those with natural aggregates. To rectify this, a cost-effective approach involving low-cost glass fiber-reinforced polymer composites (LOC-GFRP) is proposed. The key parameters considered were the plain concrete compressive strength and the quantity of LOC-GFRP layers. The compressive strength of LOC-GFRP-confined concrete increased with the number of layers, with greater improvements observed in lower-strength plain concrete. Moreover, the improvement in ultimate strain was more significant than the improvement in compressive strength. The compressive strength and ultimate strain were improved by 271% and 478%, respectively. LOC-GFRP confinement resulted in a bilinear compressive stress vs. strain response, showcasing increased ductility and strength with more LOC-GFRP layers. The study evaluated various existing analytical expressions for fiber-reinforced polymers but found them inadequate in predicting parameters accurately. As a result, nonlinear regression analysis was carried out to propose expressions for predicting compressive strength and ultimate strain of LOC-GFRP-confined concrete for different aggregate types. The calculated coefficient of determination values ≥ 0.90 confirmed the good correlation among experimental and predicted values.
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    Axial stress versus strain responses of CFRP confined concrete containing electronic waste aggregates
    (2023-12-01)
    Ullah, Saad
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    Qureshi, Muhammad Irshad
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    Hussain, Qudeer
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    Khan, Kaffayatullah
    This research work investigates the axial stress versus strain responses of un-strengthened and carbon fiber reinforced polymer (CFRP) composites strengthened concrete specimens made with electronic waste coarse aggregates. For this purpose, 36 circular and non-circular 300 mm high concrete specimens constrained with CFRP sheets and partially replaced with E-waste coarse aggregates were prepared. The effect of cross-sectional geometry, 20% partial substitution of natural coarse aggregates with E-waste aggregates, corner effect of non-circular concrete specimens, confinement of specimens with CFRP sheets, and effect of the number of confinement sheets were also studied. In control concrete specimens, the coarse aggregates were 848 kg/m<sup>3</sup> and E-waste aggregates were 212 kg/m<sup>3</sup>. The cement was 475 kg/m<sup>3</sup> and fine aggregates were 655 kg/m<sup>3</sup>. Test results indicated that compressive strength is reduced by substituting natural coarse aggregates with E-waste aggregates. At the same time, compressive strength increased to 71%, 33%, and 25% for circular, square, and rectangular concrete specimens, respectively, by CFRP confinement. Whereas the axial strain increased to 1100%, 250%, and 133%, for circular, square, and rectangular concrete specimens, respectively, by CFRP confinement. CFRP sheets also enhanced the Poisson's ratio. Because of the greater confinement given by a double CFRP layer, it is more effective than a single layer. Furthermore, results also indicated that strength reduction in non-circular concrete specimens was greater than in circular concrete specimens for all studied cases. In the end, for theoretical calculations, strength and strain models for confined concrete suggested by different researchers were applied and compared with experimental results. In comparison to the experimental findings, theoretical data showed that most of the models were either on the higher or on the lower side, while only some model results matched well with the experimental data.
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    Cyclic Behavior of Different Connections in Precast Concrete Shear Walls: Experimental and Analytical Investigations
    (2023-06-01)
    Yooprasertchai, Ekkachai
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    Wiwatrojanagul, Pongsak
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    Khan, Kaffayatullah
    This study investigated the grouted sleeve splices and corrugated duct splices between shear walls and footing. In this regard, three shear walls were experimentally tested. One wall was cast monolithically with the foundation (RCWS), whereas two walls were precast. One wall was connected to the foundation using splice sleeves (PGWS), and another with corrugated duct splices (PCWS). All the walls were tested under reverse cyclic loading and a constant axial load. It was observed that the performance of specimen PGWS was controlled by rocking, and a premature connection loss was observed at one of the grouted sleeve splices. The hysteretic performance of specimen PCWS was close to that of specimen RCWS, whereas extensive pinching was observed in the hysteretic response of specimen PGWS. The peak load, ductility, secant stiffness, and energy dissipation of specimens RCWS and PCWS were in good agreement, whereas the energy dissipated by specimen PGWS was considerably lower than the corresponding values of specimens RCWS and PCWS. Nonlinear fiber-based modeling in OpenSees was performed using SFI-MVLEM elements. The predicted hysteretic response of the OpenSees model was in close agreement with the experimental response.
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    Enhancing the flexural response of RC one-way slabs using low cost fiberglass chopped mat sheets and anchors
    (2025-07-01)
    Yooprasertchai, Ekkachai
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    Ejaz, Ali
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    Chatveera, Burachat
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    Sua-iam, Gritsada
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    Hussain, Qudeer
    This study experimentally evaluated the effectiveness of Carbon Fiber Reinforced Polymer (CFRP) and Fabric Cementitious Matrix (FCSM) sheets in enhancing the structural performance of one-way reinforced concrete slabs under three-point bending. Fourteen slabs were tested, considering key variables such as the number of FCSM sheets, type, size, and spacing of anchors to mitigate debonding. Results revealed that slabs strengthened with FCSM sheets and epoxy anchors demonstrated peak capacity improvements of up to 151 %, while mechanical anchors yielded a peak improvement of 95 %. Epoxy anchors also enhanced energy dissipation by up to 222 %, surpassing the 76 % maximum improvement observed with mechanical anchors. However, slabs with more than two FCSM layers required robust anchorage systems to maintain increased capacity without significant drops due to debonding. Slabs with epoxy anchors showed higher peak capacities but were more prone to abrupt post-peak losses than those with mechanical anchors. These findings underline the critical role of anchor type and configuration in optimizing the flexural and energy dissipation performance of strengthened slabs, providing valuable insights for sustainable and effective retrofitting strategies. Finite element modeling of slabs strengthened with FCSM, assuming no debonding, was carried out using ATENA software. The adopted modeling approach yielded slightly overestimated predictions of ultimate loads. As this represents initial research in the field, further investigations are recommended to develop more accurate and refined constitutive laws for FCSM to enhance the reliability of FEM simulations.
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    Axial compressive performance of sustainable BFRP-confined rectangular columns using recycled brick aggregates
    (2025-10-01)
    Suthumma, Chisanuphong
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    Ejaz, Ali
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    Iqbal, Muhammad Jawed
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    Yooprasertchai, Ekkachai
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    Hussain, Qudeer
    This study examines the mechanical behavior of basalt FRP confined rectangular concrete columns using crushed brick aggregates, addressing a research gap. While previous work focused on circular and square columns, this is the first to explore rectangular ones. The use of waste brick aggregates promotes sustainability. The study aims to assess the mechanical properties, expecting improvements in strength and ductility, and could lead to broader applications of basalt FRP. A total of 32 rectangular specimens were tested to evaluate the influence of aggregate type, concrete grade, and number of BFRP layers (0, 2, 4, and 6) on axial compressive performance. Results showed that BFRP confinement significantly enhanced strength and ductility, with maximum gains of 81% in strength and 230% in strain observed in low-strength natural aggregate concrete. Although recycled brick aggregate concrete (RBAC) exhibited lower stiffness, BFRP still provided up to 23% strength improvement. The effectiveness of confinement reduced with increasing unconfined strength. Post-peak analysis revealed that additional BFRP layers delayed stiffness degradation, promoting more ductile failure. Experimental elastic modulus closely matched ACI predictions in natural aggregate (NA) specimens but was overestimated in RBAC due to its higher porosity. The findings demonstrate the viability of BFRP confinement for enhancing the structural performance of sustainable concrete, while emphasizing the need for aggregate-specific design considerations. Design-oriented modelling was adopted to predict the complete stress-strain response of BFRP-confined concrete incorporating both natural and recycled brick coarse aggregates. A two-branch idealization of the compressive response was performed. Several key points were identified and predicted by using nonlinear regression analysis. The proposed approach closely predicted the response of BFRP-confined concrete.
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    Development of stress-strain models for concrete columns externally strengthened with steel clamps
    (2023-05-09)
    Yooprasertchai, Ekkachai
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    Ejaz, Ali
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    Ng, Anne Wai Man
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    Joyklad, Panuwat
    A robust and sustainable solution is required to tackle the ever-growing generation of construction waste worldwide. It has been known that construction waste yields concrete with substandard mechanical properties when used as a replacement for natural aggregates. With attributes like easy application and low cost, this study investigated the performance of low cost and easily available steel clamps to improve the compressive stress–strain properties of concrete fabricated with recycled concrete and brick aggregates. Results demonstrate that steel clamps effectively improved the stress–strain behavior of recycled aggregate concrete, and this improvement was more pronounced in concrete with a higher percentage of recycled aggregates. Steel clamps confinement increased the compressive strength by up to 242% and 252% for recycled concrete and recycled brick aggregate concrete, respectively, whereas the corresponding strain was increased by up to 448% and 414%, respectively. The stress–strain response of steel clamp-confined RAC was idealized into two branches: the first branch was assumed to be parabolic in shape till the peak strength, and a linear degrading branch was assumed for the post-peak region. Separate equations were proposed using regression analysis for peak strength, strain, initial modulus, and post-peak degradation modulus. The complete stress–strain curves of steel clamp-confined RAC were generated by utilizing existing equations. The proposed regression equations were combined with existing equations to generate complete stress–strain curves of steel clamp-confined RAC. In general, good agreement between experimental and predicted stress–strain curves was obtained.
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    Incorporation of Steel Fibers to Enhance Performance of Sustainable Concrete Made with Waste Brick Aggregates: Experimental and Regression-Based Approaches
    (2023-11-01)
    Yooprasertchai, Ekkachai
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    Bahrami, Alireza
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    Hussain, Qudeer
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    Ejaz, Ali
    Each year, an enormous amount of construction waste is produced worldwide. The reuse of construction waste in construction works is a sustainable solution. The present research work utilized recycled brick aggregates in the production of concrete. The resulting concrete exhibited substandard splitting tensile, flexural, and compressive properties. Steel fibers were used to improve these substandard properties of recycled brick aggregate concrete. The volume fractions of 1%, 2%, and 3% for steel fibers were mixed in concrete, whereas recycled brick aggregates were obtained from solid fired-clay bricks, hollow fired-clay bricks, and cement–clay interlocking bricks. The compressive strength was enhanced by up to 35.53% and 66.67% for natural and recycled brick aggregate concrete, respectively. Strengthened flexural specimens demonstrated up to 8765.69% increase in the energy dissipation. Specimens strengthened with steel fibers showed substantially improved splitting tensile, flexural, and compressive responses. Separate equations were proposed to predict the peak compressive strength, strain at peak compressive strength, elastic modulus, and post-peak modulus of recycled brick aggregate concrete. The proposed regression equations were utilized in combination with an existing compressive stress–strain model. A close agreement was observed between experimental and predicted compressive stress–strain curves of recycled brick aggregate concrete.
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    Sustainable development of concrete through treated and untreated plastic waste aggregates
    (2024-12-01)
    Yooprasertchai, Ekkachai
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    Khursheed, Ahsan
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    Qureshi, Muhammad Irshad
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    Ejaz, Ali
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    Hussain, Qudeer
    This study focused on sustainable and novel development of concrete through treated and untreated plastic waste aggregates. In this study, the surface of Elec-waste coarse aggregates was treated with sulfuric acid, marble dust coating, silica fume coating, and alkaline bleach. Elec-waste aggregates were used in concrete by replacing natural coarse aggregates in amounts of 10%, 20%, and 30%. The 10%, 20%, and 30% Elec-waste replacement ratios resulted in the compressive strength reduction of 8.97%, 27.99%, and 42.01%, respectively. The same percentage of Elec-waste aggregates reduced the splitting tensile strength by 21.77%, 35.89%, and 47.89%, respectively. However, the slump was observed to increase by 41.4%, 52.1%, and 68.8%, respectively. All the considered treatments enhanced the performance of Elec-waste aggregate concrete (E-WAC). Overall, the best improvement in the performance of E-WAC was imparted by silica fume coating, irrespective of the quantity of Elec-waste aggregates. The present study proposed an expression to estimate the reduction of the compressive strength of E-WAC. It was demonstrated that the equation by JCI-08 predicted splitting tensile strength of E-WAC close to experimental results.