Between Basalt Fibre Reinforced Polymer Research Articles

Study on the bond properties between BFRP bars and hybrid fibers reinforced recycled concrete under freeze-thaw cycles

To study the bond properties between basalt fiber reinforced polymer (BFRP) bars and hybrid fibers which were basalt fiber (BF) and polypropylene fiber (PF) reinforced recycled concrete under freeze-thaw cycles, conducting center pull-out tests to study the effects of three factors on the bond properties: the number of freeze-thaw cycles, the volume fractions of single fiber, and the volume fractions of hybrid fibers. Based on the data obtained from the test, establishing a four-stage bond-slip constitutive relationship model. The results showed that the failure modes were pull-out failure and splitting failure. The bond strength decreased when adding the single fiber, with a maximum reduction of 13.18%, but the peak slip increased, with a maximum increase of 69.92%. When the volume fraction of BF was 0.3%, it achieved the optimal effect. The bond strength and peak slip increased when adding hybrid fibers, with maximum increases of 13.47 and 130.08%, respectively. However, excessive fiber content will reduce the increase of bond strength. The bond strength between BFRP bars and hybrid fiber-reinforced recycled aggregate concrete (HFRAC) increased when the number of freeze-thaw cycles increased but decreased when the number of freeze-thaw cycles exceeded 50. The four-stage bond-slip constitutive relationship model fitted well with the bond-slip curves. Compared with other fiber-reinforced recycled concrete specimens, this model fitted better with the curves of HFRAC specimens after freeze-thaw cycles and had the best fitting effect for the internal crack slip stage of the curves.

Investigation of the bond properties between hybrid fiberreinforced concrete and BFRP bars after exposure to high temperature

This research investigated the bond properties at high temperatures and with hybrid fiber addition between basalt fiber reinforced polymer (BFRP) bars and hybrid fiber-reinforced concrete (HFRC). The tensile strength and appearance morphology of BFRP bars were analyzed. Used scanning electron microscopy (SEM) to examine the microscopic morphology and used the bond-slip constitutive model to fit the bond-slip curves. When BFRP bars after exposed to 300 °C, their tensile strength dropped by 42%. With the increasing temperature, the bond strength and stiffness of normal concrete (NC) specimens decreased by 27.3 % and 67.5 %, respectively, while HFRC specimens decreased by 20.8 % and 55 %, respectively. Hybrid fibers increased the bond strength and stiffness of HFRC specimens by 27.1 % and 49.1 %, respectively. The best fitting models were the Malvar model and the Continuous Curve model.

An experimental investigation of the bond performance of BFRP bars with recycled-aggregate concrete of different particle sizes

The pull-out test was performed in this study to investigate the bond performance between basalt fiber reinforced polymer (BFRP) bars and recycled concrete. Three factors were considered: aggregate size (5–10 mm, 11–15 mm, and 16–20 mm), bond anchorage length of bars (3D, 5D, and 7D), and the recycled aggregate replacement rate (0%, 30%, 60%, and 100%). The bond–slip mechanism, failure mode, bond stress distribution, and bond–slip curves were all analysed. Based on the results, it was found that situations with a high recycled aggregate replacement rate, large aggregate particle sizes, or long bond lengths have an increased likelihood of experiencing splitting failure. As the aggregate size increases, the bond strength between the BFRP bars and the concrete would also increase, in ordinary concrete, a 22.54% increase was observed, whereas in recycled concrete, the maximum increase reached 48.20%. The effect would be more pronounced on recycled concrete compared to ordinary concrete, and it would also be more significant in specimens with BFRP bars compared to steel bars. Additionally, the optimal bond anchorage length was determined to be 5D. The bond strength exhibited a trend of decrease followed by an increase as the recycled aggregate replacement rate increased. The maximum reduction of 59.7% in bond strength was observed when the replacement rate of recycled aggregate reached 60%. Moreover, when the replacement rate of recycled aggregate increased to 100%, there was a decrease of 19.05% in bond strength compared to the specimen without recycled aggregates. Based on the experimental test data and existing models, an improved two-stage bond–slip constitutive model was proposed.

Bond durability between BFRP bars and recycled aggregate seawater sea-sand concrete in freezing-thawing environment

Fibre reinforced polymer (FRP) bar reinforced recycled aggregate seawater sea-sand concrete (RASSC) structures can reasonably solve the two key problems of reinforcement corrosion and resource shortage. In this paper, the bond durability between basalt fibre reinforced polymer (BFRP) bars and RASSC in freezing-thawing environment was studied by eccentric pull-out tests. The research parameters were freezing-thawing cyclic numbers and concrete cover thicknesses. The results revealed that the bond strength between BFRP bars and RASSC decreased significantly with the increase in freezing-thawing cyclic numbers. Additionally, the bond strength increased with concrete cover thicknesses. The variation laws of slip at bond strength and bond stiffness were similar to those of bond strength. Considering the effect of freezing-thawing cyclic numbers, the equations for relative compressive strength and relative dynamic elastic modulus of RASSC were established. Considering the effects of freezing-thawing cyclic numbers and concrete cover thicknesses, the equations for bond strength, slip at bond strength, and bond stiffness between BFRP bars and RASSC were given. Furthermore, mBPE model and CMR model were calibrated.

Numerical analysis of bonding interface of basalt fibre-reinforced polymer and concrete

The bonding between basalt fibre-reinforced polymer (BFRP) and concrete has a crucial effect on the durability of externally retrofitted concrete structures, because the BFRP–concrete interface is the element most vulnerable to failure. Although numerous experiments have investigated the tensile bonding strength of the FRP–concrete interface, there have been only a limited number of numerical simulations of crack propagation. Therefore, in this study, the tensile bonding strength between BFRP and concrete was analysed numerically using a cohesive zone model (CZM). To validate the numerical modelling results, experiments were conducted under different initial crack widths. To clarify the crack propagation, the representative fracture area technique was applied. According to the numerical and experimental results, the CZM is appropriate for simulating the BFRP–concrete interface. The results also indicate that specimens with no initial cracks suffer only limited cracking at the edge of the surface, whereas the specimen with an initial 10 mm crack width suffered cracking across almost all of its surface. This is due to the reduced effective bonding area of the BFRP–concrete interface.

Experimental study on fatigue bond behaviour between basalt fibre-reinforced polymer bars and recycled aggregate concrete

The bond performance between fibre-reinforced polymer (FRP) bars and recycled aggregate concrete (RAC) affects their combined working ability and further influences the bearing capacity and deformation resistance of FRP bar-reinforced RAC structures. In addition to static loads, many structures such as roads, bridges and subways usually bear fatigue loads during their service periods. Therefore, to provide theoretical and experimental references to the fatigue bond design of FRP bar-reinforced RAC structures, this study systematically investigated the fatigue bond behaviour between basalt fibre-reinforced polymer (BFRP) bars and RAC. Pull-out tests were carried out considering the effects of the surface shapes of BFRP bars, bar diameters, concrete types, fatigue stress levels, and fatigue cycles. Based on the damage at the bond interface, the corresponding bond mechanism was analysed and the bond stress–slip characteristics were summarised. Furthermore, the effect of design parameters on the bond stiffness, slip, bond strength, and residual bond strength was revealed. Different surface shapes of BFRP bars induced different bond mechanisms. Moreover, fatigue loads mainly affected the bond behaviour by eliminating the imperfections and accumulating the damage.

Bond performance between BFRP bars and 3D printed concrete

To improve the design and construction of three-dimensional (3D) printed concrete structures, the bond performance between basalt fibre reinforced polymer (BFRP) bars and 3D printed concrete were analysed via pull-out tests. It is found that the bond strength of 3D printed specimens was lower than that of mould-cast specimens, while the failure mode of BFRP bar-reinforced printed concrete was similar to that of reinforced common concrete. The bonding of sand-coated BFRP bars to 3D printed concrete was superior to that of smooth bars. The printing direction of concrete also affected bond performance, with the bond strengths of parallel and 45° inclined specimens exceeding that of vertically printed specimens. By identifying defects at printed and bonding interfaces, the bond degradation mechanism was determined. Furthermore, a continuous bond–slip model was established to predict the bonding strength between BFRP bars and printed concrete, which agreed well with the experimental results.

Effect of Different Bond Parameters on the Mechanical Properties of FRP and Concrete Interface.

This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC (digital image correlation) technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types.

Bond behavior between basalt fiber-reinforced polymer bars and concrete under cyclic loading

Concrete structures reinforced with fiber-reinforced polymer (FRP) bars are frequently subjected to cyclic loadings. The bond behavior between FRP bars and concrete under cyclic loading is important in evaluating the seismic and fatigue performance of concrete structures reinforced with FRP bars. Although the bond stress-slip relationship between basalt FRP (BFRP) bars and concrete under static loading has been investigated, investigations on the bond behavior between BFRP bars and concrete under cyclic loading remain lacking. The present study presented experimental investigations on the bond behavior between BFRP bars and concrete under cyclic loading using a pull-out test. Test results showed that: (1) the bond stress-slip relationship between BFRP bars and concrete revealed the behavior at different phases: the elastic phase, the cracking propagation phase, the cracking closure phase, and the friction phase; (2) the bond strength between BFRP bars and concrete under cyclic loading decreased with the increase of number of cycles; (3) the slip corresponding to bond strength between BFRP bars and concrete under cyclic loading increased with the increase of number of cycles; (4) the hysteretic curve area between BFRP bars and concrete under cyclic loading decreased with the increase of number of cycles; (5) several prediction models for bond strength, slip corresponding to bond strength and hysteretic curve area between BFRP bars and concrete under cyclic loading were proposed considering number of cycles; (6) the residual bond strength between BFRP bars and concrete decreased while the slip corresponding to residual bond strength increased after cyclic loading.

Effect of Temperature Variation and Pre-Sustained Loading on the Bond between Basalt FRP Sheets and Concrete.

The coupled effects of temperature variation and pre-sustained loading on the bond between basalt fiber reinforced polymer (BFRP) sheets and a concrete substrate were studied. Single lap-shear test specimens were exposed to temperatures of 15, 30, 40, 50, and 60 °C for 3 h with pre-sustained loading at 35% of the ultimate load capacity (Fu). Compared with the case of 15 °C, the interfacial fracture energy of the specimens at 30 and 40 °C increased by 46% and 11%, respectively, whereas those reduced by 73% and 77% at 50 and 60 °C, respectively. The coupled effects of temperature and pre-sustained loading on the effective bond length are insignificant for the specimens at both 15 and 30 °C and the effective bond length increased to 300 mm when the temperature exceeded 40 °C. The failure crack still occurred in the concrete substrate at the temperatures of 15 and 30 °C, and changed to the debonding of the adhesive layer from the concrete substrate at the temperature above 30 °C.

New epoxy anchor for better bonding between FRP sheets and concrete

This study carried out an experimental investigation on the effectiveness of newly proposed epoxy anchors on the interfacial bond performance between basalt fibre reinforced polymer (BFRP) sheets and concrete. The parameters examined included the size of epoxy anchors and the number and spacing of anchors. It is concluded that the proposed epoxy anchors remarkably enhanced the shear resistance while the progressive FRP debonding was significantly postponed. The experimental results showed an average 77.49% increment in the bond strength, 86.71% increment in the utilization of BFRP sheets, and 78.10% increase in the peak shear stress. A bond strength model by incorporating the effects of strain energy and bonding area of epoxy resin was proposed to analyse the effect of anchorage. The predicted debonding load showed good agreement with the testing data.

Influence of concrete strength on dynamic interfacial fracture behaviour between fibre reinforced polymer sheets and concrete

This study experimentally investigates the effect of concrete strength on the dynamic interfacial bond behaviour between basalt fibre reinforced polymer (BFRP) sheets and concrete under different loading speeds (i.e. 8.33E−6 m/s, 0.1 m/s, 1 m/s, 3 m/s, 5 m/s, and 8 m/s) by using single-lap shear tests. Three concrete strengths (i.e. C20, C30, and C40) were considered to examine the influence of concrete strength and strain rate on the interfacial bond-slip responses under dynamic loadings. The test results including the strain distributions, interfacial fracture energy, and bond-slip response were evaluated and discussed. The test results showed that the BFRP-concrete interface exhibited sensitivity to strain rate and the bond strength and shear resistance of the interface enhanced with strain rate. Compared with high strength concrete, low strength concrete showed higher strain rate sensitivity, which is induced by the different interfacial fracture mechanisms under different strain rates. An empirical bond-slip model incorporating strength effect of concrete and strain rate was proposed based on fracture mechanics.

Bond behavior between basalt fiber‐reinforced polymer rebars and coral‐reef‐sand concrete conditioned in saline solution

AbstractThis paper studies the bond behavior between basalt fiber‐reinforced polymer (BFRP) rebars and coral‐reef‐sand (CRS) concrete exposed to a saline environment. The gradation and mix proportion of CRS concrete was firstly selected, through compressive tests on CRS concrete cubes. A series of pullout tests were conducted on a total of 84 pullout specimens after conditioning in a saline solution. The experimental variables included type of rebar (steel and BFRP), diameter of BFRP rebar, conditioning duration and temperature, and type of conditioning (continuous immersion and wet–dry cycle). The stress–slip curves and bond strength of the pullout specimens were analyzed and discussed. The results show that 0.54 is selected as the water/cement ratio for CRS concrete, among the range of analyzed concrete mixes. The bond behaviors of BFRP rebars depend on their diameter. BFRP rebars with 12‐mm‐diameter have the best bond durability after conditioning in a saline solution, when compared with their counterparts with 8‐ and 16‐mm‐diameters. The effects of conditioning temperature and type of conditioning on the bond behavior of 12‐mm‐diameter BFRP rebar are negligible. A design‐oriented formula was proposed for the prediction of the development length of a BFRP rebar in CRS concrete based on the experimental data. Furthermore, modified BPE models were calibrated to describe the bond–slip relationship of BFRP rebars in CRS concrete in a saline environment.

Bond-slip behaviors of BFRP-to-concrete interfaces exposed to wet/dry cycles in chloride environment

Fiber-reinforced polymer (FRP) has been employed as an alternative for strengthening and rehabilitation of deteriorated civil infrastructure, which can effectively prolong service-life and provide lower life-cycle costs than conventional materials. The present paper devotes attention to the influence of chloride environmental aging (wet/dry cycles) on the bond-slip characteristic of interface between basalt FRP (BFRP) sheet and concrete substrate. The four-point bending beam specimens were adopted to evaluate the durability of BFRP-concrete interfaces. The aging condition imposed on the BFRP beams was wet/dry cycles in salt water with 3.5% sodium chloride. After exposure, small beam tests were carried out to investigate the bonding behaviors of BFRP-concrete interfaces. The results indicate that the residual strength, ductility, and fracture energy of the bonded interfaces substantially decreased with increasing wet/dry cycles; the failure mode changed from the cohesive fracture of concrete in the ambient environment to the combined failure of BFRP fracture and adhesive debonding in aging condition; the effective bond length of BFRP where the tension force delivers from fiber fabric to cohesive interface was shortened under wet/dry cycles. Finally, a modified model was also proposed to predict the bond-slip relationship of the BFRP-concrete interface after wet/dry cycles exposure in a chloride-containing environment.

Effect of high temperature on the bond performance between basalt fibre reinforced polymer (BFRP) bars and concrete

The use of basalt fibre reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. However, few studies have reported on the bonding performance of the bars in concrete when exposed to high temperatures. This paper investigates the effects of seven variable parameters, namely, temperature, bonded length, diameter and type of FRP bars, concrete strength, concrete cover thickness and a fireproof coating material on the concrete surface, on the bond stress-slip curves, failure modes, and bond strength of the BFRP bars. Glass fibre reinforced polymer (GFRP) bars were used for comparison. BFRP bar pullout specimens exhibited similar bond stress-slip curves at both room and high temperatures, but the peak bond stress and the slope decreased when the temperature increased. The bond strength declined gradually with the increase of the temperature, and the effect of temperature on the bond strength of the GFRP bar pullout specimens was more severe than that of the BFRP bar pullout specimens. At temperatures from 70°C to 220°C, the bond strength decreased by 2.45–14.24%. At 270°C, the bond strength declined by approximately 32%. At 350°C, the residual bond strength was 12.20–23.14% of their original values.

Strain rate effect on effective bond length of basalt FRP sheet bonded to concrete

Reinforced concrete structures strengthened by fiber-reinforced polymer (FRP) always suffer dynamic loadings. The success of this strengthening method relies on the effectiveness of the bond between the FRP sheet and concrete. Determination of the bond strength between FRP and the concrete substrate is an important issue in this technology because the typical failure mode of FRP-to-concrete joints involves the debonding of the sheet from the concrete substrate. Most theoretical bond strength models are established based on effective bond length. Therefore, determination of the effective bond length is necessary to determine bond strength. Although numerous experimental studies have investigated this effective bond length, experimental data from dynamic tests on the effective bond length of the interface between basalt fiber-reinforced polymer (BFRP) sheets and concrete under different strain rates remain lacking. This paper presents an experimental investigation of the dynamic effective bond length between BFRP sheets and concrete under different strain rates. Double-lap shear specimens were utilized in the tests. Results of dynamic tests were discussed to evaluate and compare the influence of strain rate on the dynamic effective bond length between BFRP sheets and concrete. Data show that bond stress and effective bond length are sensitive to strain rate. The dynamic effective bond length of the BFRP–concrete interface is affected by both BFRP stiffness and concrete strength. The dynamic elastic modulus of BFRP increases with the increase in strain rate, and the failure mode under different strain rates involves debonding in the concrete layer. The dynamic effective bond length of the BFRP–concrete interface decreases with the increase in strain rate as a logarithmic function. A calculation model of dynamic effective bond length in consideration of the influence of strain rate was established through regression analysis of bond length data.

Bond Behavior between Basalt Fiber–Reinforced Polymer Sheet and Concrete Substrate under the Coupled Effects of Freeze-Thaw Cycling and Sustained Load

AbstractThis paper presents an experimental investigation on the bond behavior between basalt fiber–reinforced polymer (BFRP) sheet and concrete substrate under the coupled effects of freeze-thaw cycling and sustained load. Test variables were freeze-thaw cycles, level of sustained load, and adhesive type. Double-lap shear specimens were used in the tests, and a specially designed reaction-loading system was used to apply the sustained load during freeze-thaw cycles. Specimens with or without sustained load were exposed to up to 300 freeze-thaw cycles. A modified epoxy resin, made by adding a toughening agent to the original epoxy resin, was used in the test to study the effect of adhesive type on the durability of the BFRP–concrete interface. Coupon tests were also conducted to determine the freeze-thaw resistance of the constituent materials of the BFRP–concrete interface. After exposure, double-lap shear tests were carried out to investigate the residual bond capacity of the BFRP–concrete interface. Di...