Assessment of glass fibre-reinforced polymer concrete bond strength after high-temperature exposure

External wrapping with fibre-reinforced polymer (FRP) sheet has become a promising solution for retrofitting of damaged reinforced concrete slab in reinforced concrete framed structures as well as brick masonry structures due to various advantages. In particular, the flexural strength of a slab can be significantly increased by application of FRP sheets adhesively bonded to the tension face of the slab. It has been tried in the present work to study the behaviour of reinforced concrete slab strengthened with glass fibre-reinforced polymer (GFRP) laminates following the finite element approach using the software ANSYS. Previous research work based on the experimental observation reveals the fact that the extent of repair or strengthening of reinforced concrete slab with FRP laminates in terms of the load-carrying capacity or deformation under service load depends on different parameters such as the location of FRP laminate, the width of the FRP strips and thickness of the FRP.

Bond behaviour of staggered/non-staggered lap-spliced GFRP bars in concrete

This study investigated the mechanism of stress transfer between glass and carbon fiber-reinforced polymer (FRP) laminates and concrete beams with deteriorated surfaces. Thirty-six beams were prepared with either a solid concrete cross section, or with a weak concrete layer at the surface, simulating the state of a deteriorated surface. The beams were reinforced with glass or carbon FRP sheets and tested in flexure. Strain development in the laminate and in the concrete layers was recorded and analyzed. The mode of failure changed from shear within the deteriorated layer of concrete to delamination at the interface between the resin and the concrete in the solid high-strength concrete. A significant amount of stress was transferred between the FRP laminates and the concrete surface probably by residual frictional stresses after shear cracks developed in the deteriorated layer, leading to a remarkable load bearing capacity of these beams.

In spite of many benefits, FRP materials are susceptible to elevated temperatures. On the other hand, because FRP laminates are different from other FRP materials, data acquired from investigations concerning FRP materials cannot be suggested for FRP laminates. An assessment of the tensile performance of fibers impregnated by epoxy resin as binder is needed. In recent decades, many methods have been presented to protect fiber reinforced polymer (FRP) composites against high temperatures. The application of fire protection mortar is a low-cost and easy technique among all methods. In this investigation, the influence of fire protection mortar on the improvement of the tensile strength of glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) laminates was evaluated. For this object, over 200 FRP laminates with or without fire protection mortar were tested at various elevated temperatures. Investigated temperatures varied from 25°C to 500°C. According to the results obtained from this study, the strength of FRP laminates considerably reduced following the laminates experienced the temperatures higher than 400°C. However, the samples covered with fire protection mortar underwent lower the tensile strength decrements. Eventually, a linear model was presented to estimate the strength of FRP laminates including or excluding protective mortar at elevated temperatures on the basis of linear regressions carried out on test data.

Behavior of GFRP bar-reinforced hollow-core polypropylene fiber and glass fiber concrete columns under axial compression

Concrete, when exposed to elevated temperatures, undergoes deterioration and loses much of its strength. The strengthening of heat-damaged concrete is possible with the help of external reinforcing materials such as fiber-reinforced polymers (FRPs). The strength of FRP-strengthened flexural concrete members depends on the bond between the FRP and the concrete. The purpose of this experimental study was to investigate the behavior of the bond between the glass fiber-reinforced polymer (GFRP) laminate and the heated concrete using a single-shear test (SST). The specimens were initially heated to temperatures of 200, 400, 600, and 800°C. The heat-damaged specimens were subsequently bonded with FRP sheets with various bond lengths (100, 150, and 200 mm). The test variables were bond length and elevated temperatures. The results show that bond strength increased with increasing bond length and noticeably decreased as temperatures exceeded 400°C. The thickness of the delaminated concrete layer with GFRP...

Research on the bond performance between glass fiber reinforced polymer (GFRP) bars and Ultra-high performance concrete(UHPC)

Performance of reinforced concrete beams strengthened by hybrid FRP laminates

Structural health monitoring (SHM) of composite materials is of great significance in various practical applications. However, it is a challenge to accurately monitor the damage of composites without affecting their mechanical properties. In this paper, an embedded sensing layer based on carbon nanotube-coated glass fiber is designed, combined with electrical resistance tomography (ERT) for in situ damage monitoring. Multi-wall carbon nanotube-coated glass fiber (MWCNT-GF) is prepared and embedded into laminates as an in situ sensing layer. Low-velocity impact experiments demonstrate that the embedded sensing layer has high compatibility with the composite laminates and has no adverse effect on its impact response; although, the energy absorption behavior of glass fiber-reinforced polymer (GFRP) laminates containing MWCNT-GF occurs about 10% earlier than that of GFRP laminates overall. ERT technology is used to analyze the laminates after a low-velocity impact test. The results show that the in situ monitoring method with the embedded MWCNT-GF sensing layer can achieve high precision in imaging localization of impact damage, and the error of the detected damage area is only 4.5%.

Composite beams consisting of pultruded glass fibre-reinforced polymer (GFRP) I-beams and ultra-high-strength fibre-reinforced concrete (UFC) slabs have been developed for use in short-span bridges. Fibre-reinforced polymer bolts (fibre-reinforced polymer threaded rods) and epoxy adhesive were used to connect the UFC slab to the GFRP I-beam. The authors conducted material tests and large-scale static bending tests at room and elevated temperatures (less than 90°C) to investigate the flexural behaviour of GFRP-UFC composite beams subjected to elevated temperature. The test results demonstrated that the mechanical properties of the GFRP I-beams, fibre-reinforced polymer bolts and epoxy adhesive were significantly deteriorated at elevated temperatures due to the glass transition of their polymer resin matrices. As a result, the stiffness and ultimate flexural capacity of the GFRP-UFC composite beams under elevated temperatures were significantly reduced. More than 85% of the flexural capacity of the GFRP-UFC composite beams was retained up to 60°C but that was decreased to 50% at 90°C. Fibre model analysis results confirmed that the stiffness of the GFRP-UFC composite beams is not significantly affected by actual hot environments, where there is a moderate temperature gradient across the beam cross-section.

The adoption of fiber-reinforced polymer (FRP) bars in concrete structures has increased due to their superior mechanical properties and durability. However, the compressive response of FRP bars at high temperatures remains unclear. This article presents an experimental study on the behavior of glass FRP (GFRP) and basalt FRP (BFRP) bars subjected to compressive loads at different elevated temperatures and deformation rates. The study considers four different temperature conditions: ambient temperature (25 °C), 50 °C, 100 °C, and 150 °C, and two different deformation rates: 0.5 mm/min and 1000 mm/min. Digital Image Correlation (DIC) was used to accurately measure strains at high temperatures by generating a suitable speckle pattern over the specimen surface for full-field deformation measurements. The study results revealed that the modulus of elasticity and compressive strength of both GFRP and BFRP bars degraded as the temperature increased from 25 °C to 150 °C. The compressive strength reduction was higher at 150 °C compared to 100 °C, and the reduction was more significant for BFRP bars than GFRP bars. The compressive strength of GFRP bars was comparable under both strain rates for all temperature conditions. However, the elastic modulus of the bars showed a slight variation between the different load rates, especially at an elevated temperature of 150 °C. For the BFRP bars, the study found that different strain rates at ambient temperature resulted in significant deviation in the compressive strength and modulus of elasticity results. At higher temperatures, the reduction in mechanical properties was more pronounced. In summary, the study provides valuable insights into the behavior of GFRP and BFRP bars under compressive loads at elevated temperatures, which is useful for designing and assessing the performance of FRP-reinforced structures under fire conditions.

Bond failure of steel beams strengthened with FRP laminates – Part 2: Verification

Bond strength of GFRP bars to high strength and ultra-high strength fiber reinforced seawater sea-sand concrete (SSC)

Significant issue in reinforced concrete (RC) structures is corrosion of steel. High alkalization of cement matrix, low permeability, and sufficient cover plays an important role to shield from corrosion of steel. There is a replacement material for steel is fiber‐reinforced polymer (FRP) bars as reinforcement. The FRP bars are nonconductive and durable material and they are composited from fibers and polymers matrix. In this study, new technology geopolymer concrete (GC) was used along with glass fiber‐reinforced polymer (GFRP) and basalt fiber‐reinforced polymer (BFRP) bars. GC is produced from industrial by‐product materials such as fly ash and ground granulated blast furnace slag (rich in silica and alumina) and treated as sustainable material. The long term durability of many RC structures affects drastically by the reinforcement corrosion. Main aspect of bond behavior is tension stiffening as it has capability to control the reinforcement to shift the tensile stresses to concrete. This paper evaluates the bond strength between the GC reinforced with GFRP/BFRP and the results were evaluated with conventional concrete (CC) reinforced with steel. The pullout test method was used to determine the bond between FRP and steel bars with the surrounding concrete based on IS: 2770 (part I)‐1967. The comparison of bond strength GC with FRP almost same as CC with steel. The tension test and double shear test were also carried out in FRP and steel bars based on IS 432–1982 and 5242–1979, respectively.

This paper focuses on the interlaminar shear behavior of basalt fiber reinforced polymer (FRP) laminates impregnated with epoxy and vinyl ester resins as well as hybrid basalt and carbon FRP laminates. Meanwhile, the interlaminar shear behavior of carbon and E-glass FRP laminates was also studied for comparison. The experiments were conducted according to the ASTM-D-2344 standard, and the failure modes, load–deformation (L–D) relationships, and interlaminar shear stress to normalized deformation relationships of various FRP laminates were analyzed. The differences in interlaminar shear behavior among different fibers and resins were identified. The fracture surfaces of the laminate specimens with different fibers were examined by scanning electron microscopy. Furthermore, the hybrid effect on interlaminar shear behavior was discussed and the interlaminar shear strength was predicted based on above analysis. The results show that the L–D relationships of FRP laminates can be classified into three types, which are determined by the interlaminar shear strength between fiber layers and the resin as well as by the failure modes. The interlaminar shear strength of basalt FRP with vinyl ester resin is higher than that of the glass FRP but less than that of the carbon FRP. The adoption of epoxy resin and the hybridization of basalt and carbon fibers can enhance the interlaminar shear strength of basalt FRP. In addition, the scanning electron microscopy images of fracture surfaces of the laminate specimens confirm the differences of interlaminar behavior of various composites. The hybrid effect on the interlaminar shear behavior is reflected in the integration of both advantages of basalt FRP and carbon FRP in the interlaminar shear stress to nominal deformation relationship, which results in both higher interlaminar shear strength at the cracking and the final stages. Finally, the interlaminar shear strength of different FRP laminates can be accurately predicted by the proposed model.