Experimental and finite element analysis of flexural performance of RC beams retrofitted using near-surface mounted with CFRP composites and cement adhesive
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.
References (24)
- et al.
Cementitious composites reinforced with continuous carbon fibres for strengthening of concrete structures
Cem Concr Compos
(2003) - et al.
Experimental and finite element analysis of flexural behavior of FRP-strengthened RC beams using cement-based adhesives
Constr Build Mater
(2012) - et al.
A review on the bond behavior of FRP NSM systems in concrete
Constr Build Mater
(2015) - et al.
Modified cement-based adhesive for near-surface mounted CFRP strengthening system
Constr Build Mater
(2016) - et al.
Bond properties between carbon fibre reinforced polymer (CFRP) textile and concrete using modified cement-based adhesive
Constr Build Mater
(2017) - et al.
Performance of NSM CFRP strengthened concrete using modified cement-based adhesive at elevated temperature
Constr Build Mater
(2017) - et al.
Mineral-based bonding of carbon FRP to strengthen concrete structures
J Compos Constr
(2007) - Hashemi, S. and R. Al-Mahaidi, Investigation of bond strength and flexural behaviour of FRP strengthened RC beams using...
- ACI Committee 440. Guide for the design and construction of concrete reinforced with FRP rebars, American Concrete...
- et al.
Behavior and Modeling of Bond of FRP Rebars to Concrete
J Compos Constr
(1997)
Strengthening of Concrete Beams Using Cementitious Carbon Fiber Composites
Cited by (7)
Steel-concrete composite beams strengthened with NSM CFRP systems at the hogging-moment regions
2023, Engineering StructuresEffect of fatigue loading on flexural performance of NSM CFRP-strengthened RC beams under different service temperatures
2022, Engineering StructuresCitation Excerpt :Due to the nature of epoxy adhesives typically used in the NSM FRP-strengthening technique, their mechanical properties can be affected by the application of temperature variations or constant temperature approaching the glass transition temperature (Tg) of the adhesive [9–12]. Although a significant amount of work on the flexural behavior of NSM FRP-strengthened RC beams under short-term loading exists [7,8,13–17], few studies addressing the effect of high service temperature have been published [18–20]. Regarding the fatigue behavior of the FRP-strengthened RC beams, a significant amount of work has been done for the EBR FRP-strengthening system [21–29], whereas less literature exists for the case of NSM FRP-strengthening [30–34].
Evaluation of high temperature endurance of RC beams retrofitted with NSM technique using CFRP composites and modified cement-based adhesive
2022, Engineering StructuresCitation Excerpt :The experimental program comprised seven reinforced concrete beams tested under high temperature exposure. Full scale beams were designed with dimensions of 120 × 180 × 1600 mm to fit with the dimensions of the furnace and similar to that used at normal temperature tests [22] to utilize the ultimate loads for calculation of the service loads applied in this test. The minimum concrete cover according to ACI-318 [32] was selected to evaluate the strengthening efficiency at this critical case in practice when using small beam dimensions or due to construction mistakes in practice in addition to assess the maximum effect of temperature on the fibre since the concrete cover can provide a protection layer against the temperature.
Deterioration of mechanical properties of basalt/carbon hybrid FRP bars in SWSC under seawater corrosive environment
2022, Construction and Building MaterialsCitation Excerpt :This limitation can be overcome by introducing non-corrosive materials into SWSC. Fiber reinforced polymer (FRP) bars have outstanding advantages, including high strength-to-weight ratios, non-corrosive nature, and easy processing, and have been used in various corrosive environments [1,2,13–17]. Therefore, FRP bars can be used as promising materials to replace steel bars in SWSC.