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Green reinforcement techniques: Using natural hemp and cotton ropes to enhance the structural integrity of short-span RC beams
(2025-09-01)
Thansirichaisree, Phromphat
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Ejaz, Ali
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Saingam, Panumas
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Mohamad, Hisham
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Hussain, Qudeer
This study evaluates the structural performance of natural fiber ropes—hemp and cotton—as sustainable strengthening materials for short-span reinforced concrete (RC) beams. A total of 15 beams were tested under four-point bending: one unstrengthened control beam and 14 strengthened beams divided into three groups. Group I included three cotton-strengthened beams using two strip configurations (Type A: 50 mm wide, Type B: 100 mm wide) and one full wrap (Type C). Group II comprised nine hemp-strengthened beams reinforced with 1, 2, or 3 layers in various configurations, while Group III included two CFRP-strengthened beams using a single layer of CFRP strips (Types A and B). Beams strengthened with a single cotton or hemp rope layer exhibited inadequate shear resistance, showing concrete crushing or diagonal cracking. In contrast, two-layer hemp confinement led to more vertical cracking, indicating improved ductility. Results showed that cotton- and hemp-strengthened beams improved peak load capacity by 17 %–40 % and 22 %–78 %, respectively, compared to the control beam, while CFRP offered 36 %–51 % gains. Deflection capacity, indicating ductility, increased by 58 %–95 % for cotton, 42 %–155 % for hemp, and 71 %–145 % for CFRP. Full wrap configurations consistently provided the highest enhancements in both load and ductility, while among strip configurations, Type B outperformed Type A. Hemp ropes delivered higher load capacity due to their superior tensile strength, whereas cotton ropes exhibited greater ductility because of their higher fracture strain (13.5 % vs. 3.5 %). Energy dissipation improved with increased rope quantity and tighter strip spacing. The study also found that conventional FRP-based shear prediction models significantly overestimated the contribution of hemp confinement due to its larger diameter (2.1 mm), underscoring the need for revised modeling approaches. These findings demonstrate the technical feasibility, cost-effectiveness, and environmental advantages of using natural fiber ropes as alternative strengthening materials in structural retrofitting.
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Modeling and comparative analysis of sustainable cotton rope confinement: Full vs. STrip wrapping for enhanced concrete strength and ductility
(2025-07-01)
Saingam, Panumas
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Gadagamma, Chaitanya Krishna
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Hussain, Qudeer
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Hlaing, Hnin Hnin
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Suwannatrai, Rawirot
The rise of natural FRPs as ecological alternatives to synthetic ones has highlighted the need for studies on partial confinement using cotton ropes, which offer cost-effective, low-carbon solutions with high rupture strain. Unlike full confinement, partial confinement through cotton rope strips can efficiently strengthen deteriorated concrete sections with reduced material usage. Despite possessing several advantages, the partial confinement by cotton on concrete has not been investigated. This study addresses the gap by investigating the performance of cotton rope strips and developing analytical models to predict their structural impact. This study tested cylindrical concrete specimens of two strengths, strengthened with cotton rope in either complete wrapping (Group 1) or strip wrapping (Group 2). Each group was further divided by concrete strength and included one unstrengthened specimen, and three strengthened with one, two, or three layers of cotton rope. Experimental results revealed that cotton rope wraps effectively confined the concrete, enhancing load-bearing capacity and improving ultimate compressive strength by 9.97–152.10 % and ultimate strain by 188.00 % to 1488.89 %. The compressive stress vs. strain behavior exhibited an initial stiff elastic ascent followed by a parabolic transition. The second branch of the response, either ascending or descending, was significantly improved with an increased confinement ratio. Type-I failure was characterized by an ascending second branch in the compressive stress vs. strain curve, while Type-II failure exhibited a descending second branch. Four specimens demonstrated Type-I failure (L-2F, L-3F, H-3F, and L-3S), predominantly in full configurations and with lower unconfined compressive strength. The modulus of the second branch improved with an increased confinement ratio, transitioning from Type-II to Type-I failure near a ratio of approximately 0.50. Regression analysis provided equations of various key points along the compressive response with R² values greater than 0.90, highlighting a strong dependence on the confinement ratio. The Popovics model effectively predicted the first part of the compressive response, with predicted curves closely matching experimental results.
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Bond strength of lap spliced steel bars in RC beams strengthened with low-cost natural FRP composites: Experimental and theoretical study
(2025-07-01)
Hussain, Qudeer
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Ruangrassamee, Anat
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Ejaz, Ali
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Jirawattanasomkul, Tidarut
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Zhang, Dawei
Natural FRPs have proven their prospective in enhancing the compressive behavior of concrete. However, their effectiveness in preventing brittle steel lap splice failure has not been investigated. This study utilizes low-cost hemp and cotton eco-friendly ropes for the first time and proposes a bond strength-based model for its design. Twenty-six RC beams in three groups were tested, with varying lap splice lengths and layers of Natural Fiber Reinforced Polymers. The study reveals that Natural FRP effectively reduces concrete cover delamination and improves structural performance, while reinforced beams still exhibit noticeable cracks at lap splice ends upon failure. Notably, hemp and cotton configurations demonstrate effectiveness in enhancing load capacity, with hemp showing superior ductility restoration, especially for lap splices of 28d<inf>b</inf>. The peak load and ultimate deflection (i.e., the deflection against a 20 % drop in peak load) improved between 17.6 % and 73.6 % and 36.9–837.2 % compared to the control beam without strengthening, respectively, with hemp confinement configuration Type B enhancing peak load by 73.6 % and 73.1 % for lap splice lengths of 20d<inf>b</inf> and 28d<inf>b</inf>, respectively. The inclusion of extra Natural FRP length on both sides of the lap splice appeared to impede vertical crack propagation, delaying beam failure. Furthermore, the paper addresses the challenge of predicting bond strength improvements under Natural FRP confinement due to the significant difference in elastic moduli between Natural FRP and synthetic FRPs. It proposes a strain-based approach to predict bond strength enhancements, yielding close agreement with experimental results, suggesting its potential in Natural FRP confinement design to prevent lap splice failures, albeit with consideration of lap splice properties matching those in the study.

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