Elsevier

Engineering Structures

Volume 241, 15 August 2021, 112429
Engineering Structures

Experimental and finite element analysis of flexural performance of RC beams retrofitted using near-surface mounted with CFRP composites and cement adhesive

https://doi.org/10.1016/j.engstruct.2021.112429Get rights and content

Highlights

  • Significant flexural performance of modified cement based adhesive with CFRP composites.

  • Effective contribution of CFRP textile and laminate in the ultimate capacity of concrete members.

  • Excellent mechanical bonding properties have been achieved compared to epoxy adhesives.

Abstract

Fiber reinforced polymer (FRP) composite has been used effectively for the rehabilitation of concrete and steel structures in the last decades due to its excellent properties compared with conventional reinforcing materials such as steel. Despite the major role of epoxy resins as a bonding material between fibre and substrate, the rapid deterioration of the mechanical properties at elevated temperature is the critical issue for the epoxy matrix. Therefore, substitution of epoxy adhesive with cementitious bonding agent will be beneficial in order to provide more resistant systems at elevated temperatures. Near-surface mounted (NSM) strengthening technique with cement adhesives has only been investigated for torsion. Flexural performance is a significant factor in the strengthening of different structures. This paper reports the experimental study on the behavior of small scale retrofitted beams using Near-Surface Mounted strengthening system with carbon fiber reinforced polymer (CFRP) textile and laminate and cement-base adhesives for flexure. The beams retrofitted with modified cement-based adhesive achieved 98% to 100% ultimate loads of that beams strengthened with epoxy adhesives. Numerical analyses is utilized to evaluate the experimental results, and comparable results were observed between the experimental results and finite element analysis.

Introduction

The demand for rehabilitation of and increased load capacity for different structures has grown around the world during the last decades, due to design faults, increasing load capacity, and the degradation of structures with time resulting from harsh environments. The high strength of FRP composites compared to their weight and their ease of application have attracted researchers to employ this material in civil engineering applications, especially for the reinforcement of of concrete and steel structures. The most commonly-used bonding materials are epoxy adhesives. Different structures have been retrofitted using CFRP with epoxy adhesive around the world [1]. However, the epoxy matrix has disadvantages associated with its application, including flammability, moisture impermeability, the negative effects of emission of toxic fumes with curing, and skin irritation [1], [2]. In addition, the most critical factor is the degradation of mechanical properties of the epoxy resins when exceeding the glass transition temperatures (60–82C°), as reported in ACI 440.2R 2008 [3].

Since the major role in determining of bonding properties is the bonding material [4], the resistance of the adhesive to temperature plays the major role in the strengthening performance of structures exposed to high temperature. It would be beneficial to replace the epoxy with cementitious adhesives to enhance the resistance at high temperatures. The most investigations on strengthening of RC structures using cementitious adhesives as a bonding agent have been conducted for externally-bonding with CFRP textile and fabrics [1], [2], [5], [6], [7], [8]. Few of research have been conducted on the use of NSM strengthening systems with cementitious adhesives [9].

The application of cement adhesives for NSM strengthening systems has been studied by Al-Abdwais and Al-Mahaidi. A modification has been conducted to provide specific physical characteristics for this type of strengthening system [11]. The bond characteristics with concrete using different types fibers (textile and laminates) have been studied and excellent results have been reported [12], [13]. This strengthening technique using the cemenitious adhesive has been investigated on the torsional performance of RC beams by Ghaidak and Al-Mahaidi [14], [15]. In literature, different investigation has been reported on flexural strengthening with NSM CFRP using epoxy adhesives [16], [17]. The performance of flexural strengthening with NSM technique using modified cement-base adhesives has been investigated for large scale beams, and different modes of failure have been observed [18]. In order to study the effect of beam size on the behavior and modes of failure, this investigation on flexural performance of small-scale RC beams retrofitted with modified cement-based adhesive is assessed and compared with the last study conducted on large-scale beams [18].

Section snippets

Specimen details

Eight beams were used in this investigation. The beams were 120 mm wide, 180 mm deep and 1600 mm long. The main reinforcement of two N12 steel bars was used at each compression and tension reinforcement zone of the beams. The shear reinforcement was designed with N10 steel stirrups spaced at 125 mm along the beam length. The reinforcements were designed for shear to resist the total loads to ensure flexural failure prior to shear. The beams’ geometrical details are illustrated in Fig. 1.

Two

RC beams and cementitious adhesive

The finite element analysis was conducted using ATENA software by Cervinks consulting [23]. Fracture-plastic constitutive model for brittle material was used for modelling of the concrete and cement mortar according to the exponential softening in tension and Rankine failure criterion (Fig. 31) [23]. The formulation of crack opening in the concrete was modelled using a fictitious crack model based on opening law and fracture energy.

Interface model between adhesive and fibre

Modelling of bond between CFRP textile and the RC substrate was

Conclusion

The results showed considerable flexural performance using modified cement-based adhesive compared to previous experimental investigations using other types of cementitious adhesives. The ultimate load was about 98% to 100% of that gained by beams strengthened using epoxy resin.

The mode of failure developed in three stages, the first stage started by yielding of bottom steel reinforcement layer at maximum moment and secondly with crushing in compressive zone of concrete followed by fibre

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The support and funding for this research provided by Swinburne University of Technology is acknowledged. The technical support of the Smarts Laboratory team is also acknowledged.

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