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Temperature-resilient performance of hemp rope–Confined recycled aggregate concrete in axial compression
(2026-07-01)
Thansirichaisree, Phromphat
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Ejaz, Ali
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Chaimahawan, Preeda
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Hussain, Qudeer
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Jirasakjamroonsri, Amornthep
This study addresses the growing need for sustainable and cost-effective alternatives to conventional fiber-reinforced polymer (FRP) confinement systems, particularly for recycled aggregate concrete (RAC) subjected to elevated temperatures. The axial compressive behavior of hemp rope-confined RAC cylinders was experimentally investigated under ambient and moderate thermal exposure (150°C). Two strength grades were considered, with confinement applied using one to three layers of hemp rope. The results demonstrate that hemp confinement significantly enhances both compressive strength and axial strain, with improvements increasing with the number of layers, while strain enhancement was consistently more pronounced than strength gain. The stress–strain response exhibited a characteristic two-stage behavior, consisting of an initial unconfined-like region followed by a confinement-activated ascending branch. The elastic modulus of RAC was found to be approximately 21.9% to 29.7% lower than ACI 318-19 predictions, suggesting a reduction factor of about 25% for practical applications. Thermal exposure had a limited effect on normalized strength and strain parameters, although post-peak stiffness showed some sensitivity. Notably, confinement proved even more effective in thermally damaged specimens due to increased lateral deformability. A regression-based analytical model was developed to predict the complete stress–strain response, showing close agreement with experimental results. This study is among the first to evaluate the performance of hemp rope confinement for RAC under elevated temperature conditions and to propose a unified predictive framework. Overall, the findings confirm that hemp rope confinement is an effective, sustainable, and reliable technique for enhancing both the strength and ductility of RAC, with strong potential for structural applications, including post-fire rehabilitation.
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Hybrid B-CSM Composites Strengthening Approach for Improved Stress–Strain Behavior of Concrete Columns and Development of Analytical Models
(2025-02-01)
Thansirichaisree, Phromphat
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Mohamad, Hisham
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Zhou, Mingliang
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Ejaz, Ali
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Saingam, Panumas
The brittle behavior of concrete under axial compressive loading has been a persistent issue. This study investigates the effectiveness of a hybrid Basalt-E-glass confinement (B-CSM) in improving the compressive behavior of concrete. The B-CSM confinement demonstrates a considerable improvement in ultimate strength and strain capacity by over 250 and 500%, respectively, making it a favorable solution for enhancing the ductility of concrete structures. Specimens at 18.43 MPa unconfined strength, confined with 3-layer B-CSM, demonstrated a 258% ultimate strength enhancement. For 24.43 MPa specimens, the same confinement resulted in a 207% increase in ultimate strength. Specimens with an initial ultimate strain of 18.43 MPa, when confined with 3-layers, showed a notable 516% increase. Likewise, for 24.43 MPa specimens, the same confinement led to a significant 395% improvement in ultimate strain. The use of B-CSM confinement is also effective in terms of cost compared to synthetic fiber-reinforced polymer jackets, and its availability is widespread. Existing analytical models for fiber-reinforced polymer confinement were evaluated, and it was found that these models could not predict the ultimate strength and strain of B-CSM-confined concrete. Therefore, this study proposes a unique regression-based approach for predicting the various points of the compressive stress vs. strain curve of B-CSM confinement. These points are then used to trace the complete stress vs. strain curve, which matches closely with experimental results. This work contributes to the development of new design recommendations for B-CSM confined concrete structures, which can enhance the performance of concrete structures and potentially reduce construction costs.
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Stress-strain behavior of square concrete columns confined with hybrid B-CSM composites and development of novel prediction models
(2024-07-01)
Thansirichaisree, Phromphat
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Mohamad, Hisham
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Ejaz, Ali
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Saingam, Panumas
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Hussain, Qudeer
This paper presents a comprehensive investigation into the behavior of concrete confined with hybrid Basalt and Chopped Strand Mat (B-CSM) fibers. The newly proposed B-CSM confinement technique substantially enhances the brittle compressive stress-strain behavior, leading to a noteworthy increase in peak strength (approximately 90%) and ultimate strain (approximately 461 %). The efficiency of B-CSM confinement is affected by the strength of plain concrete, with lower-strength specimens indicating a more pronounced enhancement. The performance of existing analytical models for FRP confinement in predicting ultimate strength and strain in B-CSM confined concrete is assessed, highlighting the need for tailored models. Regression-based equations are proposed for characteristic points along the stress-strain curve, enabling accurate prediction of material behavior. The predicted stress-strain curves exhibit a high level of agreement with experimental results. These findings provide valuable insights for the design and application of B-CSM confinement techniques in structural engineering, facilitating improved performance and ductility of concrete structures under compressive loading conditions.
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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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Saingam, Panumas
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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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