Basalt Fiber Reinforced Polymer Sheets Research Articles

Behavior of a Precast Bridge Pier with Basalt Fiber-Reinforced Polymer (BFRP)-Strengthened Segments under Seismic Loading.

The precast segmental column (PSC) has been proposed for reducing onsite construction time and minimizing impacts on traffic and the environment. It has been proven to have good seismic performance according to previous studies. However, due to the rocking behavior of the column, the toe of the bottom segment could experience excessive compressive damage. In addition, the commonly used steel rebars in the PSC could experience corrosion problems during the service life of the structure. Moreover, ordinary Portland cement concrete (OPC) is normally used in the construction of the PSC, but the manufacturing processes of the OPC could emit a lot of carbon dioxide. This paper investigates the seismic performance of PSCs incorporating Basalt Fiber Reinforced Polymer (BFRP) bars and geopolymer concrete (GPC) segments. To mitigate the concrete crushing damage of the segment, the BFRP sheet was used to wrap the bottom segment of one of the specimens. The results revealed that the BFRP-reinforced geopolymer concrete PSC exhibited good seismic performance with minimal damage and small residual displacement. Strengthening the bottom segment with BFRP wrapping proved to be effective in reducing concrete damage. As a result, the column with BFRP wrap demonstrated the ability to withstand ground motions with higher Peak Ground Acceleration (PGA) compared to the column without strengthening.

Study of the flexural behavior of UHPC-HPC composite beams strengthened with BFRP sheet after chloride secondary erosion

To solve the issue of insufficient durability of reinforced concrete (RC) structures, a new structure of ultra-high performance concrete (UHPC)-high performance concrete (HPC) composite beam was designed, and the flexural performance of the composite beam strengthened with basalt fiber reinforced polymer (BFRP) after pre-damage was investigated. Results indicate that main cracks are formed and developed after the secondary erosion of chloride salt, leading to three forms of failure modes of the beams: BFRP sheet fracture and concrete crushing, BFRP sheet debonding and concrete crushing and BFRP sheet debonding. The test beam failure process can be classified into three stages: linear elasticity, crack development and yield. The maximum cracking and ultimate loads increased by 27.9 % and 35.8 %, respectively. The crack load growth rate of the beam decreased after 7 days (d) of secondary chloride salt erosion. The formula for calculating the peel strength of the UHPC-HPC composite beam was modified. The calculated bending capacity of the beam agrees well with the measured value. This study provides a reference for enhancing the lifespan and calculating the flexural bearing capacity of structures in corrosive environments.

Enhancing Flexural Behavior of Reinforced Concrete Beams Strengthened with Basalt Fiber-Reinforced Polymer Sheets Using Carbon Nanotube-Modified Epoxy.

The external bonding (EB) of fiber-reinforced polymer (FRP) is a usual flexural reinforcement method. When using the technique, premature debonding failure still remains a factor of concern. The effect of incorporating multi-wall carbon nanotubes (MWCNTs) in epoxy resin on the flexural behavior of reinforced concrete (RC) beams strengthened with basalt fiber-reinforced polymer (BFRP) sheets was investigated through four-point bending beam tests. Experimental results indicated that the flexural behavior was significantly improved by the MWCNT-modified epoxy. The BFRP sheets bonded by the MWCNT-modified epoxy more effectively mitigated the debonding failure of BFRP sheets and constrained crack development as well as enhanced the ductility and flexural stiffness of strengthened beams. When the beam was reinforced with two-layer BFRP sheets, the yielding load, ultimate load, ultimate deflection, post-yielded flexural stiffness, energy absorption capacity and deflection ductility of beams strengthened using MWCNT-modified epoxy increased by 7.4%, 8.3%, 18.2%, 22.6%, 29.1% and 14.3%, respectively, in comparison to the beam strengthened using pure epoxy. It could be seen in scanning electron microscopy (SEM) images that the MWCNTs could penetrate into concrete and their pull-out and crack bridging consumed more energy, which remarkably enhanced the flexural behavior of the strengthened beams. Finally, an analytical model was proposed for calculating characteristic loads and characteristic deflections of RC beams strengthened with FRP sheets, which indicated a reasonably good correlation with the experimental results.

Durability performance of BFRP-confined coal gangue concrete exposed to the sulfate-rich mine environment

The combination of basalt fiber reinforced polymer (BFRP) confinement and coal gangue concrete (CGC) is an economical and innovative approach for serving as a supporting structure in the underground mine. Nevertheless, the sulfate-rich mine water and mist exist in the mine environment, which may cause the performance deterioration of structures. Thus, the long-term behavior of BFRP-confined CGC in the sulfate-rich environment was systematically explored, based on the sulfate durability investigation of BFRP sheets and CGC. The tensile test of BFRP sheets and the compressive test of CGC were first carried out to evaluate their deterioration laws and mechanism in different sulfate environment. More importantly, axial compression test of FRP-confined concrete cylindrical specimens after sulfate attack were conducted, considering the effect of inner concrete, FRP layer, sulfate concentration and corrosion time on the stress-strain response and dilation properties. The results indicate that the tensile strength of BFRP sheet declined to a small extent with the extension of sulfate corrosion due to the degradation of epoxy resin and matrix-fiber interface. Additionally, the compressive strength of CGC exhibits a first increase and then decrease trend as the secondary hydration occurs and the sulfate ions react with the hydrated production to form expansive gypsum and ettringite crystals. The strength and ductility of CGC were improved by FRP confinement regardless of sulfate attack or not, whereas sulfate corrosion degraded the improvement ratio, especially the deformation capacity. Most importantly, the sulfate degradation coefficients were introduced into ultimate strength and strain models for sulfate-attacked BFRP-confined CGC, providing a basis for its design and life cycle assessment in the underground mine.

Damage assessment of concrete beams repaired with basalt fiber-reinforced polymer sheets through digital image correlation and acoustic emission

Basalt fiber-reinforced polymer (BFRP) has high mechanical strengths as a repairing material but exhibits low ductility. This paper investigates the damage process of reinforced concrete beams repaired using BFRP sheets, aimed at understanding the underlying mechanisms of achieving structural ductility when BFRP sheets are used. The damage process was assessed using digital image correlation (DIC) and acoustic emission (AE) techniques applied to monitor surface and internal damages of three full-scale concrete beams subjected to four-point bending. A beam was first loaded to crack, then repaired with BFRP sheets, and finally reloaded to failure. Surface strain fields and cracks were monitored using a DIC method, and cracking events were monitored using AE sensors deployed at different positions of the beams. The AE signals were analyzed to assess the damage process. The test results indicated that (1) tensile cracks predominated throughout the loading process; (2) the BFRP sheets hindered the widening of cracks and promoted the generation of fine cracks; and (3) the development of concrete cracks promoted interfacial debonding at steel-concrete and BFRP-concrete interfaces. A combination of different types of cracks and interfacial debonding helped the repaired beam achieve ductile flexural behaviors.

Enhancing bonding behavior between basalt fiber-reinforced polymer sheets and concrete using resin pre-coating method and multi-wall carbon nanotubes

There is a crucial problem of premature debonding failure in fiber-reinforced polymer (FRP) sheet external bonding reinforcement for concrete structures. Using anhydrous ethanol as solvent instead of acetone, the effect of resin pre-coating (RPC) technique with neat resin-ethanol solution and multi-wall carbon nanotubes (MWCNTs)-resin-ethanol solution on the bonding behavior of the FRP-concrete joints was investigated by single-shear tests. Experimental results indicated that RPC technique significantly enhanced the bonding properties, especially when the pre-coating was MWCNTs-resin-ethanol solution. In the case of using neat epoxy resin as adhesive, compared with the control specimens without RPC treatment, the ultimate bearing capacity, ultimate global slip, maximum bond stress and interface fracture energy of the basalt fiber-reinforced polymer (BFRP)-concrete joints using RPC treatment with MWCNTs-resin-ethanol solution increased by 32.6 %, 48.4 %, 68.3 % and 88.8 %, respectively. MWCNTs could be seen in scanning electron microscopy (SEM) images of the fracture surface, which indicated that they could penetrate into the concrete and the crack bridging and pull-out of MWCNTs could enhance the interfacial adhesion of the FRP-concrete joints. Compared with the RPC treatment using the restricted acetone, the RPC treatment with MWCNTs-resin-ethanol solution can more significantly enhance the bond properties of the interface between concrete and FRP sheet, and it is suitable for large-scale practical engineering applications on site. This study demonstrated the great promise of the RPC technique with MWCNTs-resin-ethanol solution toward practical engineering application in reinforcement and repair of concrete structures.

Assessment of damage evolution of concrete beams strengthened with BFRP sheets with acoustic emission and unsupervised machine learning

Basalt fiber reinforced polymer (BFRP) is an emerging material that can be used to strengthen or repair concrete structures. This paper experimentally investigates the flexural failure process of concrete beams strengthened by BFRP sheets under four-point loading conditions using acoustic emission (AE)-based nondestructive evaluation and unsupervised machine learning techniques. Both damaged beams and repaired beams were tested and compared with intact beams regarding their mechanical performance and AE signature. Test results showed that BFRP sheets enhanced the load-bearing capacity of the beams significantly, and AE signals were sensitive to the initiation and development of damages. The damage process and mechanisms of different beams have been investigated by analyzing AE signals regarding various AE parameters, and particularly, the failure process and damage mechanisms were investigated via b-value and k-means clustering analyses. This research provides theoretical guidance for evaluating the reinforcing effect of BFRP sheets for concrete beams based on AE techniques.

Strength of Hybrid Steel-BFRP Reinforced Concrete Beams with Openings in the D-Region Strengthened Internally and Externally

The opened beams always confused the designers due to the guidelines missing. In this research, six hybrid beams reinforced with mixed steel and basalt fiber-reinforced polymer (BFRP) bars and having constant cross-sections of 150 mm × 300 mm and a clear span of 1800 mm were cast and tested under a four-point loading setup. Generally, five beams had symmetrical rectangular openings with dimensions of 150 mm × 250 mm located at a distance of 250 mm (equivalent to the beam effective depth) from the beam support, while an additional solid beam served as a control. The studied parameters included the effect of using internal reinforcement (steel or BFRP bars) provided adjacent to the opening sides or by incorporating an external BFRP sheet around the opening corners. Also, double enhancement with internal steel reinforcement bars together with external strengthening BFRP sheet was investigated. The relevant results showed that the opened beam without enhancement lost 75% of the maximum load compared with the solid beam. Placing internal steel or BFRP bars around the openings increased the maximum load by 62% and 60%, respectively, compared to the non-enhanced opened beams. Using an external BFRP sheet to strengthen the opening corners of the beam enhanced the maximum load by 76% compared with the non-enhanced opened beam. Consequently, by combining both the internal steel reinforcement and external BFRP sheet around the openings, the maximum load increased by 137% compared with the non-enhanced opened beam. Ultimately, a numerical analysis of the three-dimensional finite element model was performed to confirm the experimental findings, and the relevant results showed compatibility correlations with the experimental ones. Also, the effect of various parameters such as BFRP reinforcement ratio and number of BFRP sheet layers around the openings was investigated by adapting the validated numerical model.

Effects of seawater on durability of hybrid C/BFRP-confined seawater–sea sand concrete columns under axial compression

A carbon-fiber-reinforced polymer (CFRP) sheet is wrapped around the basalt-fiber-reinforced polymer (BFRP) to develop a hybrid carbon/basalt-fiber-reinforced polymer (C/BFRP) so as to protect the basalt fibers in touch with chloride ions. Tensile testing is conducted on the BFRP and hybrid C/BFRP sheets. The effect of the durability of the fiber-reinforced polymer sheet on the behavior of the seawater–sea sand concrete (SSC) columns confined by the BFRP and hybrid C/BFRP sheets is examined using axial compression testing. The tensile strength retention and elongation at break retention of the hybrid C/BFRP sheet improve by 41% and 24% higher than those of the BFRP sheet after 12 months in seawater. The ultimate strength of the BFRP-confined SSC column decline by 40% more than those of the hybrid C/BFRP-confined SSC column respectively, after 12 months of seawater immersion, resulting from the reduction of lateral pressure provided by the BFRP and hybrid C/BFRP sheets in seawater. A formula for calculating the long-term ultimate strength and ultimate strain of the FRP-confined SSC column is proposed, and its predictions agree well with the test results. The hybrid C/BFRP sheet proves more efficient than the BFRP sheet in confining the seawater–sea sand concrete columns.

Investigation on bonding behavior of basalt fiber reinforced polymer (BFRP) sheet reinforced concrete beam

Although basalt fiber reinforced polymer (BFRP) sheet offers promising benefits including environmental friendliness and excellent mechanical performance in concrete reinforcement, its full potential is still hindered by the lack of understanding about their bonding mechanism. Therefore, the comprehensive investigation of the bonding behavior of BFRP sheet reinforced concrete is necessary. This work aims to address the research gap between the analytical design and industrial application of BFRP sheet reinforced concrete due to the complicated bonding behavior. Analytical method, experimental measurement, and numerical simulation are employed to comprehensively investigate the bonding behavior of BFRP sheet reinforced concrete. According to the mechanical model and assumptions of the reinforcement, analytical solutions for interfacial stress and strain are derived. In addition, four-point bending test are conducted on specimens, and multi-view digital image correlation (DIC) technique is used to analyze the deformation on concrete part and BFRP sheet simultaneously. Based on analytical and experimental results, finite element model (FEM) is applied to simulate mechanical behavior of BFRP sheet reinforced concrete beam, and parametric analysis is further conducted. Results reveals that the maximum interfacial stress appears at the end of bonding region so that BFRP debonding at the end is the main failure mode. The strain distribution of BFRP sheet obtained by multi-view DIC indicates that there is an effective bonding region. Besides, strain can be used as a variable to validate numerical model by analytical and experimental results. The validated numerical simulation could be conducted for the internal response study and application design of BFRP sheet reinforcement.

Flexural performance and damage evaluation on basalt fiber reinforced polymer (BFRP) sheet reinforced concrete

Basalt fiber reinforced polymer (BFRP) is a promising composite material for concrete restoration as an external sheet reinforcement. This work aims to propose a methodology that can effectively monitor and evaluate the damage of external BFRP sheet reinforced concrete during its industrial service life. For better understanding of flexural performance and damage evaluation on BFRP sheet reinforced concrete, four-point bending tests were conducted on specimens produced with different bonding conditions (bonding BFRP sheet at 0%, 80%, 90%, and 95% of failure load) to explore suitable repair strategies for engineering. Multi-view digital image correlation technique is used to analyze the deformation on concrete part and BFRP sheet simultaneously. Such a non-contact measurement makes it possible to observe crack development and evaluate damage degree of concrete beams during loading process and could be applied in industrial measurement. In addition, crack development could be characterized by length and width, which is calculated by strain distribution of both concrete part and BFRP sheet. Results reveal that BFRP sheet could improve about 78.56% of flexural strength and 304.38% of ductility. Besides, it is found that the growth of damage degree is steadier in BFRP reinforced specimens. According to the early warning levels proposed in this work, it is suggested that BFRP reinforcement should be adopted before concrete is loaded to 90% of failure load to allow for timely repair and facilitate subsequent health monitoring.

Improving bonding behavior between basalt fiber-reinforced polymer sheets and concrete using multi-wall carbon nanotubes modified epoxy composites

Premature debonding failure is a critical problem in the reinforcement of concrete structures using fiber reinforced polymer (FRP) sheets with externally bonded reinforcement (EBR) technique. The usual anchoring methods are likely to cause damage to the concrete. The effect of incorporating various amounts of carboxyl (COOH)-functionalized MWCNTs in the epoxy resin on the bonding behavior of the basalt fiber-reinforced polymer (BFRP)-concrete joints was detailed studied by single-shear tests and the digital image correlation (DIC) technique. Experimental results indicated that adding the functionalized MWCNTs into the epoxy considerably enhanced the bonding properties. In comparison with the BFRP-concrete joints using neat epoxy, the effective bond length, bond strength, ultimate global slip, interface fracture energy, and BFRP strain of the BFRP-concrete joints using 0.8 wt% MWCNTs modified epoxy increased by 96 %, 55 %, 39 %, 172 %, and 114 %, respectively. The scanning electron microscope (SEM) images of debonded BFRP surface revealed that the MWCNTs could penetrate into concrete along with epoxy resin, and the MWCNTs pull-out and crack-bridging could indicate a reinforcing effect to prevent premature adhesive failure. This study demonstrated the great promise of the MWCNTs modified epoxy composites toward practical engineering application in reinforced concrete (RC) structures. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Effect of bond length on bond behavior between basalt fiber-reinforced polymer sheet and concrete

Many reinforced concrete structures are always damaged due to material aging during service life. Reinforced concrete structures can be retrofitted by fiber-reinforced polymer (FRP) sheets to improve load carrying capacity and extend the service life. The bond behavior between the FRP sheet and concrete is important for assessing the load carrying capacity of reinforced concrete structures retrofitted with FRP sheets, and the effective bond length is often used in determining the bond behavior. Basalt FRP (BFRP) has excellent properties, such as light weight and high tensile strength. Although the effective bond length between carbon FRP sheets and concrete has been studied, study on the effective bond length between BFRP sheets and concrete remains lacking. The effect of bond lengths on the bond behavior between BFRP sheets and concrete was investigated in the present study. The results revealed that: (1) the failure load between the BFRP sheets and concrete increased with the increase of the bond length when the bond length was not beyond the effective bond length; (2) the effective bond length of the interface between BFRP sheet and concrete was not beyond 80 mm obtained from the failure load; (3) the effective bond length of the interface between BFRP sheet and concrete was obtained from the bond stress; and (4) models for the failure load and the effective bond length were established.

Experimental Study on Shear-Peeling Debonding Behavior of BFRP Sheet-to-Steel Interfaces.

In order to study the failure mode and debonding behavior of the interface between BFRP (basalt fiber reinforced polymer) sheet and structural steel under mixed-mode loading conditions, eighteen specimens with different initial angles were tested in this study. The specimens were designed with different initial angles to ensure that the interface performed under mixed-mode loading conditions. The relations between the bond strengths, failure modes, and initial angles were investigated. A new evaluation method to predict the interfacial bond strength under shear-peeling loading mode was proposed. The test results show that specimens with a smaller initial angle are more likely to exhibit a shear debonding failure at the interface between the steel plate and adhesive. In contrast, specimens with a larger initial angle are more likely to exhibit peeling of the interface. The ultimate tensile strength of the specimen is higher with a smaller initial angle. The results predicted by the proposed method are in good agreement with the experimental results.

Behavior of Reinforced Concrete Beams without Stirrups and Strengthened with Basalt Fiber–Reinforced Polymer Sheets

This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams’ shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface’s normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams.

Effect of corroded reinforcement on capacity of square reinforced concrete columns confined with FRP sheets under eccentric loads

Steel corrosion is one of the primary causes which significantly degrade the load-carrying capacity and FRP (fibre reinforced polymer) strengthening efficiency of FRP-strengthened reinforced concrete columns under eccentric loading. However, this issue has not been studied comprehensively and systematically in the literature. Particularly, there has been no study on the strengthening efficiency of basalt FRP (BFRP) which is becoming popular due to its excellent performance and affordable price. This study experimentally investigates the effect of corrosion level of reinforcement by mass (0%, 15% and 30%), relative eccentricity (e/h = 0.125 and 0.375), type of FRP (CFRP and BFRP) and FRP thickness (1 or 3 layers) on the load-carrying capacity and deformation of corroded-reinforcement reinforced concrete (RC) columns. The experimental results showed that steel corrosion reduced the load-carrying capacity of the unstrengthened RC columns up to 23% and this degradation increased with the corrosion level. Both CFRP and BFRP have proven excellent strengthening efficiency since the capacity of the FRP-strengthened corroded-reinforcement RC columns increased up to 47%. Particularly, the strengthening efficiency of BFRP sheets was slightly lower than that of CFRP sheets (<7%). On the other hand, the increase of the relative eccentricity from e/h = 0.125 to e/h = 0.375 reduced the strengthening efficiency of FRP. In addition, a semi-empirical model was proposed to predict the capacity of corroded-reinforcement RC columns strengthened with FRP under eccentric loading. The predictions match well with the experimental results with a small coefficient of variation.

Effectiveness of reinforcing methods in enhancing the lateral impact performance of geopolymer concrete column reinforced with BFRP bars

To achieve more sustainable and durable structures, geopolymer concrete (GPC) structures reinforced with non-corrosive basalt fiber-reinforced polymer (BFRP) bars have been proposed to replace conventional steel reinforced ordinary Portland cement concrete (OPC) structures. The performances of GPC structures reinforced with BFRP bars under static loading conditions have been studied and engineering structures might be subjected to impact loading during their service life, which can cause severe damage to the structures. Therefore, it is important to also investigate the impact-resistant performance of structures. The impact-resistant response of BFRP-GPC columns under lateral impact loading has been recently investigated, and different response characteristics were observed from those of steel-OPC columns due to the different material properties. To enhance the impact resistance capacity, this study investigates the effectiveness of various reinforcing methods of BFRP-GPC columns. One BFRP-GPC column from our previous study was used as the reference column, and four BFRP-GPC columns were cast and tested by using a pendulum impact testing rig in this study. The four columns were respectively reinforced or strengthened with four different methods (i.e., increasing the longitudinal reinforcement ratio to enhance the flexural strength of the column, increasing the stirrup ratio to enhance the shear strength of the column, adding steel fibers to increase the tensile strength of GPC material, and wrapping the column with BFRP sheet). The columns under lateral impact loading were compared and analysed with respect to the failure mode, failure progress, impact force, and midheight deflection. It was found that increasing the longitudinal reinforcement ratio and using the external BFRP sheet wrapping led to better improvement in the impact resistance of the column. In addition, numerical simulations were carried out to investigate the response mechanism of the BFRP-GPC column, and a simplified model was proposed to predict the maximum shear force distribution of the column under impact for design analysis.

Seismic performance of earthquake-damaged corroded reinforced concrete beam-column joints retrofitted with basalt fiber-reinforced polymer sheets

This present research conducted an experimental study on the influence of different earthquake damages on the seismic performances of aged reinforced concrete (RC) beam-column joints retrofitted with basalt fiber-reinforced polymer (BFRP) sheets under cyclic loadings. Six beam-column joints included one benchmark specimen, one uncorroded specimen retrofitted with BFRP sheets, and four earthquake-damaged corroded specimens with the corrosion rates of 0% and 9% retrofitted with BFRP sheets. Test results demonstrated that the seismic performances of earthquake-damaged corroded specimens effectually improved after retrofitting with BFRP sheets, and the retrofitting effectiveness was significantly affected by the earthquake-damaged levels. The bucking of stirrups, spalling and crushing of concrete of retrofitted specimens were effectually postponed, while the ductility of corroded and uncorroded specimens under the earthquake damages increased after retrofitting with BFRP sheets. The total cumulative energy dissipation and final stiffness of retrofitted specimens considerably improved with the maximum increase of 22.3% and 14.3% comparing to those of benchmark specimen, respectively. Besides, the models for predicting the shear strength of RC beam-column joint cores considering the influences of earthquake damage, reinforcement corrosion, and FRP retrofitting were proposed.

Behavior of pre-damaged normal-strength concrete prisms repaired with basalt FRP sheets under axial compressive monotonic and repeated loading

The damaged concrete columns under earthquake can be retrofitted with fiber-reinforced polymer (FRP) and the axial mechanical properties of the strengthened columns can be greatly enhanced. In the present study, monotonic and repeated axial compressive behavior of damaged concrete prisms repaired by basalt FRP (BFRP) was investigated. Pre-damage tests were performed on plain concrete prismatic specimens under three axial compressive loading levels. Then, the damaged specimens were repaired with 1-, 2-, 4-, and 6-layer BFRP composites, followed by monotonic or repeated compression tests. The test results showed that the compressive strength and axial deformation capacities of the damaged prismatic specimens under monotonic compressive loading were improved remarkably after repairing. However, in the stress–strain curves of BFRP-repaired specimens, the initial elastic modulus, and the strength at the turning and ultimate states decreased with the increase of initial damage. Based on the test results of this study and existing literature, the strength and strain at the turning and ultimate states were estimated, and a monotonic stress–strain relationship was proposed for BFRP-repaired concrete prisms considering the adverse effect of pre-damage level. Further, a modified repeated compressive stress–strain model was proposed for BFRP-repaired damaged concrete prisms. The proposed models predicted well the test results.

Structural behavior and vibration characteristics of geopolymer composite lightweight sandwich panels for prefabricated buildings

In this study, two new types of geopolymer composite lightweight sandwich panels are developed for prefabricated buildings. The first one has Fiber-reinforced Geopolymer (FRG) composite skin layers and polyurethane (PUR) foam core, and the second one is based on the first panel but strengthened with Basalt fiber reinforced polymer sheet (BFRP). Experimental studies are conducted to investigate the structural behavior and vibration characteristics of these panels. The failure mechanisms and capacity of the developed lightweight sandwich panels under flexural and compressive loads are studied by experimental quasi-static tests. Experimental results from flexural and compressive loading tests match well those from analytical calculations. The experimental studies show that the lightweight sandwich panel has a competitive capacity for prefabricated buildings. The vibration characteristics of the developed lightweight sandwich panels are obtained by hammer impact vibration tests. The finite element models are developed to predict the vibration characteristics of the tested sandwich panels. The obtained natural frequencies and mode shapes from numerical analysis and experimental tests show that the developed finite element models can be used to predict the vibration characteristics of geopolymer composite lightweight sandwich panels accurately. The addition of BFRP sheet does not significantly change the vibration characteristics of the panels, but changes the failure mode of the developed sandwich panel from skin tension failure to PUR foam core shear failure.