Effects of Sand-Coated and Ribbed GFRP Bars in Hybrid GFRP-Steel-Reinforced Concrete Beams

Rajeev Devaraj; Ayodele Olofinjana; Christophe Gerber

doi:10.3390/ma19071372

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Effects of Sand-Coated and Ribbed GFRP Bars in Hybrid GFRP-Steel-Reinforced Concrete Beams

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Effects of Sand-Coated and Ribbed GFRP Bars in Hybrid GFRP-Steel-Reinforced Concrete Beams

Rajeev Devaraj, Ayodele Olofinjana and Christophe Gerber

Materials, Vol.19(7), pp.1-16

2026

DOI: https://doi.org/10.3390/ma19071372

PMID: 41976659

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Abstract

GFRP-concrete bond

hybrid GFRP-steel beams

sand-coated and ribbed surface profiles

The integration of glass fibre-reinforced polymer (GFRP) and steel reinforcement in hybrid RC beams offers durability benefits, yet the specific influence of GFRP surface treatments on bond mechanics remains critical. This study experimentally investigates the performance of hybrid GFRP-steel-reinforced beams under three-point bending, comparing sand-coated and ribbed GFRP bars, while maintaining a constant total reinforcement ratio of 1.4% to isolate interface mechanics. Due to the exploratory nature of the study and the specific specimen matrix, the results are interpreted as observed experimental trends rather than statistically generalised performance metrics. The results indicate that ribbed GFRP bars provide enhance mechanical interlocking; in this specific experimental program, the ribbed GFRP hybrid beam exhibits an observed load capacity approximately 11% greater than the sand-coated specimen in this study and surpassing comparable steel-only beams. Additionally, ribbed configurations demonstrated an observed 15% higher toughness. In contrast, sand-coated hybrid beams exhibited signs of premature bond degradation, quantitatively captured by strain gauge monitoring; sand-coated bars plateaued at 14,000 µε, reaching only 79% of their theoretical rupture capacity. This strain limitation indicates failure by internal slippage rather than material rupture, further evidenced by a 50% reduction in crack propagation compared to ribbed beams. While energy-based ductility indices suggest a marginal 6% advantage for sand-coated bars, both hybrid systems exhibited relatively low energy-based ductility indices (μ < 2), reflecting the linear-elastic nature of GFRP reinforcement. These findings suggest that the mechanical interlock of ribbed surface treatments is more resilient under the combined stress states typical of hybrid configurations, providing a foundational baseline for the development of future numerical models and reliability-based design frameworks for hybrid GFRP-steel-RC systems.

Details

Title: Effects of Sand-Coated and Ribbed GFRP Bars in Hybrid GFRP-Steel-Reinforced Concrete Beams
Authors: Rajeev Devaraj (Corresponding Author) - University of the Sunshine Coast
Ayodele Olofinjana - University of the Sunshine Coast
Christophe Gerber - University of the Sunshine Coast
Publication details: Materials, Vol.19(7), pp.1-16
Publisher: MDPI AG
Date published: 2026
DOI: 10.3390/ma19071372
ISSN: 1996-1944
PMID: 41976659
Copyright note: © 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
Data Availability: The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.
Organisation Unit: School of Science, Technology and Engineering
Language: English
Record Identifier: 991222619302621
Output Type: Journal article

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