CFRP Grid Research Articles

Flexural Behavior of Concrete Beams Reinforced with a CFRP Grid Exposed to Chloride-Containing Environments: An Experimental Study

Flexural Behavior of Concrete Beams Reinforced with a CFRP Grid Exposed to Chloride-Containing Environments: An Experimental Study

Strength calculation method and numerical simulation of slender concrete shear walls with CFRP grid-steel reinforcement

A series of experimental research has demonstrated superior hysteretic behavior, damage mitigation, and self-centering properties of concrete shear walls incorporating CFRP grid-steel reinforcement. Developing comprehensive theoretical and numerical models becomes crucial to assess the performance of these novel walls for structural design and application purposes. Based on the preliminary experimental investigation, a strength calculation method and numerical model for slender concrete shear walls with CFRP grid-steel reinforcement were proposed in this study. The calculation method provided a stable estimation for the loading capacity and ultimate compressive strain of edge concrete for the slender CFRP grid shear wall. The fracture strain of outermost longitudinal CFRP grid and ultimate compressive strain of edge concrete were suggested for design. The numerical model integrated hybrid reinforcements and utilized MVLEM to simulate the nonlinear hysteretic behavior of CFRP grid shear walls, effectively considering specimen failure mechanisms. The model can well capture the hysteretic behavior of the specimen, involving the peak loading, envelope curve, residual deformation, and stiffness degradation. Finally, the parametric analysis was conducted to further investigate the effects of axial compressive ratio and aspect ratio on shear walls with CFRP grid-steel reinforcement.

Bend behavior of CFRP grid fabrics UHPC panels with serpentine connectors: Experiments, simulations and calculation formula

CFRP-UHPC panel is an essential type of lightweight concrete structure that can be applied in many cases, such as protective structures, warehouses, and offshore structures. However, further research is needed to achieve the CFRP grid fabrics widely applied in concrete structures. This work proposes a CFRP-UHPC panel with serpentine connectors and conducts three/four-point bending tests, DIC, and finite element methods to reveal its bend behavior. This work also presents the formula for calculating the ultimate moment, considering the stress-strain relationship of UHPC and the interaction of CFRP grid fabrics-UHPC. In summary, this work reveals the failure mechanism of CFRP-UHPC panels with serpentine connectors and proposes a formula for calculating bending capacity.

Tensile behavior of ultra-high-performance concrete (UHPC) strengthened with fiber reinforced polymer (FRP) grid

In order to enhance the tensile strength and toughness of Ultra-High Performance Concrete (UHPC) at the macro level, this study developed Fiber-Reinforced Polymer (FRP)-reinforced UHPC composite materials. The steel fibers and FRP grids in UHPC play a reinforcing and toughening effect on UHPC at two different levels. Therefore, this paper examined, evaluated 48 FRP grid-UHPC specimens. The study includes independent parameters such as grid type (Carbon-FRP, Basalt-FRP, stainless steel wire mesh), grid size (5 × 5 mm, 10 × 10 mm, 20 × 20 mm), steel fiber content (0 %, 0.5 %, 1.0 %, 1.5 %, 2.0 %), grid layers (1 layer, 2 layers, 3 layers, 4 layers), and the fiber bundle impregnation status. Based on the test results, a simplified tensile stress-strain relationship for FRP grid-UHPC was proposed. The test results show that when the steel fiber content is less than 1 %, the FRP grid does not exert its reinforcing effect. The FRP grid-UHPC composite material exhibits strain-softening behavior. However, when the steel fiber content is greater than 1 %, the FRP grid-UHPC specimens all exhibit strain-hardening phenomena. Compared to other grids type, the enhancement and toughening effects on UHPC are more pronounced when using CFRP grids. Specifically, when using a 20 × 20 mm CFRP grid, the tensile stress can be increased by 30.36 %. Regardless of whether dry grids or impregnated grids are used, increasing the grid layers greatly improves the peak strain and stress of UHPC. Compared to dry grids, impregnation with epoxy resin further improves the stress state between fiber filaments in FRP grids, resulting in a more significant improvement in the tensile performance of FRP grid-UHPC composite materials. Finally, based on experimental data, a tensile stress-strain model for FRP grid-UHPC considering different mesh ratios was proposed and validated against experimental results. These conclusions and findings are of great significance for understanding and optimizing the performance of FRP grid-UHPC composite materials, providing valuable references for the future research and application of FRP grid-UHPC composite materials.

Axial behavior of concrete cylinders retrofitted with a hybrid system of CFRP textile grid and engineered geopolymer composite

Fiber-reinforced polymer (FRP) textile grid-reinforced engineered cementitious composites (ECCs) are effective in strengthening concrete structures. Considering environmental interest, engineered geopolymer composites (EGCs) have been employed as an alternative to ECC. In this study, we present a retrofit scheme for CFRP textile grid-reinforced EGC matrix composites for concrete cylinders and compare the axial behavior of strengthened concrete cylinders with a conventional FRP-reinforced ECC strengthening system. Axial compressive specimens were tested for various parameters, including the number of FRP textiles, original concrete strength, and damage level of the original concrete cylinder. The results indicated that the strengthened concrete cylinders failed in a ductile manner owing to the progressive rupture of the CFRP textile grids. The CFRP-EGC strengthening layers improved the axial bearing capacity, stiffness, and ductility of the concrete cylinders. The axial bearing capacity increased by 89.4%–170.4 %; therefore, the contribution of enhanced confinement effect was 36.7–113.6 %. The confinement effect provided by the grids ranged from 0.805 to 1.958 MPa and played a major role in the CFRP-EGC strengthening layers. Comparatively, the CFRP grid utilization is more efficient in the EGC matrix than in the traditional ECC matrix. Moreover, the influence of the pre-damage on the behavior of the concrete cylinders was compensated for by the strengthening layers.

Axial compression performance of underwater columns reinforced with stainless steel tube-FRP grids

Stainless steel tubes have excellent plasticity and ductility, and FRP grids have favorable advantages for application in specific structural reinforcements. For systems including underwater construction without drainage, underwater columns reinforced with stainless steel tube-FRP grids are proposed using nondispersive mortar (NDM) as the reinforcement layer to best leverage the material properties of all elements. This paper carried out axial compression tests on 18 underwater columns reinforced with stainless steel tube-FRP grids (SS-FGWCs), 6 columns reinforced with stainless steel tube-FRP grids on land (SS-FGLCs), 3 underwater columns reinforced with stainless steel tubes (SSWCs), and 3 unreinforced concrete columns. The research parameters include the number of FRP grid layers, the types of FRP grids, and the reinforcement layer mortar pouring environments. The test results showed that FRP grids can be combined with stainless steel tubes (SSs) and nondispersive mortar (NDM) to reinforce concrete columns in underwater construction without drainage. In addition, compared with those of the SSWC specimens, after the BFRP grid and CFRP grid were built in, the ultimate stresses of the specimens increased by 13.4% ∼ 20.8% and 19.5% ∼ 25.4%, respectively, and the ultimate strains increased by 6.8% ∼ 31.7% and 21.8% ∼ 59.1%, respectively. Compared to BFRP grids, CFRP grids provide better reinforcement of the underwater columns. Existing prediction models were evaluated for ultimate stress calculations, the calculation methods for the ultimate stress and ultimate strain applicable to the SS-FGWCs and SS-FGLCs were revised, and a calculation model for the FRP grid failure point was proposed. Finally, a corresponding full stress–strain curve model was established.

Flexural Behavior of Concrete Members based on Development Length of CFRP Grid

Flexural Behavior of Concrete Members based on Development Length of CFRP Grid

Polymer cement mortar strengthened RC beams with/without silica fume as repair material

Polymer cement mortar (PCM) overlaying methods leads to brittle interfacial debonding before its classical failure causing a sudden decrease of the load-carrying capacity. For a reliable design procedure for the practitioner, a need exits to prevent the interfacial debonding. The proposed modified 5 % silica fume (M) PCM overlay is intended to delay debonding because it increased the concrete-PCM bond (confirmed in our previous study). Fourteen RC beams (size-150x150x1440 mm, a/d – 3.5) using C40 concrete (mix proportion – 1:2.1:2.6) were prepared and strengthened with rebar (2D6 and 2D10), CFRP grid with changing stiffness (low, medium and high), and CFRP strand sheet (50 mm and 150 mm width) as strengthening reinforcement that embedded with normal (N) PCM and MPCM overlay of thickness 20 mm to investigate the effectiveness of silica fume. Four-point bending test were made at room temperature to evaluate the flexural performance. Compared to NPCM, MPCM with all cases of strengthening reinforcement enhanced the crack numbers, ductile behavior, peak load (12–25 %) and debonding load (3–33 %), proving MPCM as ideal cementitious matrix for strengthening. The flexural strengthening configuration using MPCM and reinforcement amount (area x tensile strength) ratio of 0.5 between strengthening and main bar proved to be more efficient as this configuration delayed the debonding failure, shifted fracture to classical mode and confirmed uniform shear stress transfer at the overlay-concrete interface. Conclusively, MPCM overlay nearly achieved a full-strength composite action which is effective to prevent the debonding that benefits practitioners.

Axial Compression Performance Test and Bearing Capacity Calculation of RC Square Column Strengthened by FRP Textile Grid-reinforced ECC

In order to investigate the strengthening effect of FRP textile grid reinforced ECC composite (abbreviated: TRE) restrained RC columns, this study conducted experimental and theoretical studies on the axial compression performance of TRE strengthened RC square columns with RC square columns as the research object. The effects of the chamfer radius of the original column, the type of FRP grid and the number of layers of the grid on the axial compression performance of the TRE-strengthened RC square column were considered. The axial compression tests showed that the strengthened layer exhibited excellent crack control, the reinforced column cracked as a whole without breaking when it was damaged, and the strengthened layer adhered well to the core concrete. Compared with unstrengthened specimens, the compressive strength, ductility and deformation capacity of the RC square column under TRE restraint were significantly higher. The increase of chamfer radius of square column makes the TRE restraint effect better. Increasing the number of grid layers can significantly improve the ultimate bearing capacity and ductility of the strengthened specimens. The effects of TRE strengthening methods with different FRP grids differed, with the same number of grid layers, the ultimate bearing capacity of the specimens strengthened with CFRP grid reinforced ECC was higher, and the cracking load of the specimens strengthened with BFRP grid reinforced ECC was higher. A model for calculating the ultimate bearing capacity of the TRE-constrained RC square column was established, and the validity of the model was verified by comparing the results of this test.

Low-velocity impact performance of orthogonal grid reinforced CFRP-foam sandwich structure

Orthogonal grid structures, which are widely used in engineering, are incorporated into the foam to form the grid reinforced core. However, the impact resistance of this type of sandwich structure varies with position. In this paper, the low-velocity impact performance of orthogonal grid reinforced CFRP-foam sandwich structure at different positions was investigated. The drop hammer low-velocity impact tests were conducted at 30 J, 50 J and 80 J energy for the intersection, rib, and center positions, respectively, and the impact resistance of the three positions was further compared with the impact data. The test results showed that the intersection and rib exhibited fiber fracture and delamination of CFRP face and grid, as well as foam crushing and cracking. The center position showed face perforation and foam crushing. At the same impact energy, the intersection position had the strongest impact resistance, with an initial stiffness about 18 % higher than that of the rib, and their peak load per unit mass was higher than that of CFRP-foam sandwich panels, and the center was the weakest. In addition, numerical simulations were performed which were in good agreement with the tests, and the damage processes at different stages were discussed. The lightweight, high impact resistant sandwich structure proposed can provide a reference for structural design.

Flexural Behavior of Concrete Beams Reinforced with CFRP Grid

Flexural Behavior of Concrete Beams Reinforced with CFRP Grid

Comparison of Punching Shear Behaviour of Two-Way Concrete Slab Reinforced with CFRP Grid and Steel Bars

Two punching shear failure tests of two-way concrete slab reinforced by CFRP grid and HRB 400 steel were studied in this paper. The reinforcement ratio of slab reinforced with CFRP grid and HRB400 is 0.33% and 0.37 respectively. The upper and lower surfaces of the concrete slab’s tensile and compressive strains, the reinforcement strains, the load deflection of the slabs, and the applied load value were analyzed. The results show that under approximately the same reinforcement ratio, the concrete slab reinforced with CFRP grid has higher bearing capacity. Both slab failure formed with punching cones, the punching cone angle of CFRP grid slab is 24.1°, which is far less than 38° for reinforced concrete slabs. The tests results indicated that there is a cooperative between longitudinal and transverse limb of CFRP grid.

Prediction of Flexural Behavior of Concrete Members Reinforced with CFRP Grid

Prediction of Flexural Behavior of Concrete Members Reinforced with CFRP Grid

EXPERIMENTAL STUDY OF RC BEAM REINFORCED BY EXTERNALLY BONDED FRP GRID

Fiber Reinforced Polymer (FRP) material which exhibits light weight, high strength, and high stiffness was developed. It has been actively experimentally utilized in the construction field. FRP fibers are mostly made of Carbon, Aramid, and Glass. However, another material named basalt has been recently developed because it is more eco-friendly compared to the existing materials. Therefore, in this study, a four-point bending test was performed on reinforced concrete (RC) beams strengthened with CFRP and BFRP grids. As a result, the behavior changes of the specimen were observed due to the differences of the material properties. It confirmed that the specimen reinforced with BFRP grid was more ductile than that reinforced with CFRP grid even after the yield of rebar. It is because BFRP material possesses lower stiffness and longer elongation compared to CFRP. Moreover, reinforcing with BFRP can prevent brittle failure of the beam compared to CFRP even CFRP is more expensive and harmful to environment.

A Study on Tensile Behavior According to the Design Method for the CFRP/GFRP Grid for Reinforced Concrete.

In the present study, fiber-reinforced plastics (FRP) grid-reinforced concrete with very rapid hardening polymer (VRHP) mortar composites were fabricated using three types of design methods for the FRP grid (hand lay-up method, resin infusion method, and prepreg oven vacuum bagging method), along with two types of fibers (carbon fiber and glass fiber) and two types of sheets (fabric and prepreg). The FRP grid was prepared by cutting the FRP laminates into a 10 mm thick, 50 mm × 50 mm grid. The tensile behavior of the FRP grid embedded in composites was systematically analyzed in terms of the load extension, fracture mode, partial tensile strain, and load-bearing rate. The CFRP grid manufactured by the prepreg OVB method showed the best tensile behavior compared to the CFRP grid manufactured by the hand lay-up and resin infusion methods. The load-bearing of each grid point was proportional to the height from the load-bearing part when reaching the maximum tensile load. In addition, finite element analysis was conducted to compare the experimental and analysis results.

Bond Stress and Development Length Calculation of CFRP Grid through Direct Pullout Test

Bond Stress and Development Length Calculation of CFRP Grid through Direct Pullout Test

Study on the shear behavior of RC beams strengthened by CFRP grid with epoxy mortar

In this paper, an experimental and theoretical study on the shear behavior of rectangular reinforced concrete (RC) beams strengthened by CFRP grid with epoxy mortar was investigated. Based on the test parameters including the reinforcement ratio of CFRP grid, the shear span-to-effective depth ratio and the concrete strength, six beam specimens were prepared and carried out to reveal the their strengthening mechanism and performance improvement. In addition, a prediction model of shear capacity of strengthened beams was proposed for more reasonable prediction. The research results indicated that the shear capacity and crack patterns of RC beams strengthened with CFRP grid in shear can be effectively improved. There was a substantial influence on the shear strengthening effects under the same reinforcement ratio of CFRP grid, as changing the shear span-to-effective depth ratio and concrete strength, which should be paid more attention. A novel shear model was proposed to evaluate the shear capacity of CFRP grid-strengthened RC beams, and this proposed model appeared as a good predictor of shear capacity with sufficient accuracy and smaller dispersion, when compared to other four existing models.

Bond durability of epoxy and cement- bonded CFRP reinforcement to concrete interfaces subject to water immersion

Durability is a critical concern for concrete structures externally bonded with fiber-reinforced polymer reinforcement. This paper presents the results from an experimental study which compared the bond durability of epoxy-bonded CFRP sheets and cement-bonded CFRP grids to concrete interfaces subjected to water immersion. Totally twelve groups of CFRP sheet or grid-strengthened concrete beams with a notch at their midspan were carefully fabricated through epoxy- and cement-based bonding systems and tested under monotonic loading before and after water immersion exposure, respectively. The cement binder included polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC). The CFRP grids and sheets were designed with the similar tensile stiffness. The duration of water immersion ranged from 0 to 6 months. The test results indicated that debonding in concrete adjacent to the concrete-adhesive interface in accompany with a diagonal concrete crack near the notch was the main failure mode of the beams strengthened with epoxy-bonded CFRP sheet and ECC-bonded CFRP grid, while the tearing off of CFRP grids from the PCM matrix was the main failure mode of the beams strengthened with PCM-bonded CFRP grids. After water immersion exposure, the ultimate loads of the beams with cement-based CFRP grids were at least 50% higher than their epoxy-bonded counterparts, confirming the superior moisture durability of cement based bond to epoxy-bonded ones. The interfacial fracture energy was found to exhibit an exponential decline trend with water immersion duration.

Experimental verification of a novel anchorage method of CFRP grid in mortar

A novel anchorage method of CFRP grid in mortar named intersect-type anchorage method was proposed in this paper. In order to verify the application feasibility of this novel anchorage method in practical engineering, two phases of pull-out tests including single-direction pull-out tests and bidirectional pull-out tests were carried out. The number of grid points and anchorage conditions were selected as changing parameters. The maximum tensile loads, failure patterns, load–displacement curves of test specimens and load–strain curves of CFRP grids were obtained. The ultimate resistant actions, tensile bearing modes of grid points, tensile stress transfer process, coupling effect between the bond action of vertical grid and the resistant action of grid points and the failure mechanism were discussed. The research results showed that the intersect-type anchorage method is a favorable anchorage method for CFRP grid in mortar and the bond action of vertical grid play a dominant role for the anchorage action of CFRP grid in mortar rather than the resistant action of horizontal grid. In order to make full use of the tensile strength of CFRP grid, the number of grid points in intersecting part was not less than two.

Study on the flexural strengthening effect of RC beams reinforced by FRP grid with PCM shotcrete

Recently a new repair and retrofit method of reinforced concrete (RC) members that uses fibre-reinforced-polymer (FRP) grid with polymer-cement-mortar (PCM) shotcrete has been proposed. Four RC beams externally strengthened with CFRP grid-PCM at the bottom and one non-reinforced RC beam were tested to reveal their flexural behaviour and strengthening effect. The number of FRP layers and reinforcement amount per unit length of the CFRP grid were selected as the two main parameters in the test programme. The test results indicated that the flexural strengthening effect of the CFRP grid-PCM was sufficient; moreover, two-layer reinforcements were effective as one-layer ones under similar unit-reinforcement values. Furthermore, a new analytical model was proposed to evaluate the flexural capacities of RC beams strengthened with CFRP grid, and the predicted values were well matched to the test results and collected data.