Journal of Composites for Construction

This paper presents an overview of the experimental results obtained by combined in-plane/out-of-plane (IP/OOP) tests carried out on reinforced concrete (RC) frames infilled with thin clay masonry walls. After preliminary characterization tests on building materials, combined IP/OOP tests on eight full-scale, one-bay, one-story infilled RC frames were carried out. Three external strengthening solutions were investigated considering three types of lime-based plasters, reinforced by means of dispersed fibers and/or bidirectional basalt meshes, applied on both sides of each wall. The experimental results of the tested frames are presented, discussed, and compared to evaluate the performance and the effectiveness of each strengthening solution.

Many studies exist on carbon fiber-reinforced polymer (CFRP) strengthening of cracked steel details (e.g., cracks in riveted or welded bridge connections). The majority of these studies used CFRP sheets without prestressing. The efficiency of such systems for fatigue strengthening is often limited because the high strength of CFRP materials is not utilized under service loads. However, prestressing small CFRP sheets is very difficult and requires hydraulic jacks and mechanical clamps, which makes the strengthening process very complicated or even impossible. Therefore, in this study, NiTi shape memory alloy (NiTi-SMA) wires and CFRP sheets were used to produce a heat activated prestressed SMA-CFRP composite patch. This composite patch offers both the benefits of the prestress of SMA and the high elastic modulus of CFRP. The proposed patch is relatively small (300 × 45 mm) and can be prestressed, which makes it a good solution for the strengthening of cracked bridge connections, for example, welded connections. In this study, the composite patch is used to enhance the fatigue performance of central cracked steel plates. Because the SMA wires were small (1 mm in diameter), firstly 45 SMA wires were converted into a sheet of SMA strands and then embedded into multiple CFRP layers, forming an SMA-CFRP composite patch, which offers an easy manufacturing process. Eight central cracked steel plates were tested under cyclic loading. For the specimens strengthened by prestressed SMA-CFRP composites, the fatigue lives were extended to 2.7 times (with normal modulus CFRP) and 6 times (with high modulus CFRP), respectively. A finite element (FE) simulation was employed to better understand and interpret the test results. The decreased effective stress intensity factor (SIF) range was the reason for the prolonged fatigue life of the cracked specimens.

The need for an effective method for the restoration of corrosion-damaged reinforced-concrete elements cannot be overemphasized. In this investigation, the use of textile-reinforced mortar (TRM) for external strengthening of corroded reinforced-concrete beams in flexure is examined. The degrees of corrosion considered were 10% and 20% mass losses of the tension steel at midspan. Sixteen beams were tested in four-point bending; eight beams were cast using normal grade 35 concrete and eight beams were cast with a special high-strength concrete with steel fibers. Three strengthening schemes of a single-ply basalt TRM, covering an equal area on individual beam surfaces, were employed. As expected, the corrosion had a detrimental effect on load-carrying capacity, ductility, energy absorption, and flexural stiffness of RC beams. The strengthening schemes increased the load capacity of the 10% corroded beams within a range of 7.5%–26%, thereby yielding a restoration ranging from 105% to 112% of the peak load capacity. Full recovery of load capacities was not achieved for the 20% corroded beams. The ultimate failure mode observed in all strengthened specimens was fiber rupture, indicating full utilization of composite action of basalt TRM. A U-wrap scheme gave the best load–displacement response and energy absorption recovery.

To realize lightweight and corrosion resistance, a novel hybrid pultruded fiber-reinforced polymer (PFRP)-aluminum space truss system is proposed, which adopts the pretightened teeth connections (PTTCs) and aluminum–bolt–ball connecting system (ABCS). The diagonal and chord members of the system are joined by the ABCSs to form a free-form space truss. To identify possible failure modes, reveal the bearing mechanism, and investigate suitable design methods, compression experiments were separately conducted on two square pyramid substructures. Two loading scenarios were designed for the compression experiments, with top ball rotation unconstrained and constrained denoted as loading scenarios 1 and 2, respectively. Different failure modes, load–strain, and load–displacement responses were recorded. The joint instability phenomenon occurred in loading scenario 1, resulting in the bending failure of the ABCSs around the top ball. Buckling induced splitting failure of the PFRP tube occurred in loading scenario 2. In addition, the pyramid substructure was numerically modeled by a series of line elements and this model could accurately and directly predict the nonlinear compression behavior of the square pyramid substructure. Finally, a direct second-order analysis was recommended for the design of PFRP space truss structures, which could avoid the difficulty in determining the effective length factor and yield a more accurate and reliable structural design.

This is the first study on the effectiveness of nonuniform fiber-reinforced polymer (FRP) wrapping to strengthen and prevent the sudden failure of a square reinforced concrete (RC) column. The behavior and performance of square RC columns strengthened with nonuniform carbon FRP (CFRP) wrapping were critically investigated in comparison with the behavior and performance of square RC columns strengthened with full and intermittent CFRP wrapping. The results from the experimental study revealed that nonuniform wrapping enhanced the strength and improved the ductility of square RC columns. Also, nonuniform wrapping was effective in preventing the sudden failure of the FRP confined square RC columns. The strength enhancement of square RC specimens due to the nonuniform wrapping was higher than that due to the intermittent wrapping but lower than that due to the full wrapping when an equivalent amount of CFRP was used. The failure envelopes (axial load–bending moment interactions) were analytically developed for the test specimens. It was found that the analytical failure envelopes agreed well with the experimental failure envelopes.

This paper suggests using a combination of steel and fiber-reinforced polymer (FRP) reinforcements to introduce sustainable reinforced concrete moment-resisting frames (RC-MRFs) characterized by damage-controlled seismic performance, cost-effectiveness, and postearthquake recoverability. The aim of this study is twofold. First, according to a predefined seismic performance of RC-MRFs, this study introduces the optimum replacement ratio of the longitudinal FRP reinforcement of FRP RC-MRFs with steel bars. Second, this study investigates the application of FRP-steel reinforcement details to alleviate damage in the plastic-hinge zones of the beams. A detailed three-dimensional finite-element model (3D-FEM) of an RC-MRF is developed and validated against the experimental results of a large-scale, two-bay, two and half story MRF entirely reinforced with FRP rebars and stirrups. Results indicate that compared with FRP RC-MRFs, for a replacement ratio of FRP reinforcement ≤42%, the serviceability state of the proposed steel–FRP RC-MRFs is characterized by a controlled deformability, and the ultimate state is characterized by an acceptable residual lateral strength ensuring safe exit of the structure from its functionality. Furthermore, when steel reinforcements are only provided at the ends of the beams, the frame lateral deformability is based on the development of two sequential plastic hinges at each end of the beams, leading to higher deformability and lower damage levels.

Fiber-reinforced polymer (FRP) near-surface mounted (NSM) reinforcement represents an effective solution for strengthening and retrofitting existing concrete structures. As it is embedded into concrete, NSM reinforcement is protected from accidental impact, high temperature, and vandalism and it is less prone to debonding than externally bonded reinforcement. However, debonding of the NSM reinforcement remains the main issue associated with this strengthening technique. Numerous studies have focused on the bond behavior of NSM-concrete joints and in some of them analytical models for the prediction of NSM-concrete joint bond capacity were proposed. However, these models are often based on a few experimental results of a specific strengthening configuration. In this paper, a new analytical model to estimate the effective bond length and the bond capacity of NSM-concrete joints that fail due to cohesive debonding within concrete is proposed. The model is based on a pure fracture mechanics Mode-II loading condition and can be applied to either NSM strips, round bars, or rectangular bars. The accuracy of the model proposed and of existing analytical models was assessed by comparing analytical and experimental results of 117 NSM-concrete joints collated from the literature. The assessment showed that the model proposed provided accurate estimations of the NSM-concrete bond capacity for all types of reinforcement considered.

This paper presents a generalized evaluation method for determining the bond slip relationship of an external reinforcement bonded to concrete based on the experimental global force versus the displacement curve. The proposed method also provides several advantages, including predicting the global force versus displacement curve with any bond slip relationship, deriving the bond strength model, predicting the strain distribution along the fiber reinforced polymer (FRP)–concrete interface, and evaluating the effective bond length. An introductory example shows detailed implementation of the proposed method on an FRP–concrete interface reported in the literature. Since no prior assumption is made on the detailed configuration of the bond slip relationship using the proposed method, the obtained bond slip relationship can be seen more generalized and representative. The obtained bond slip relationship differs from the available bond slip models and leads to predictions that best approximate the experimental results. In addition, the reliability of the proposed method in determining the effective bond length is also verified against the experimental and analytical results.

Brick waste is the second-largest source of China's construction and demolition waste. Reprocessing brick waste into recycled brick aggregate (RBA) to fabricate new concrete [i.e., recycled brick aggregate concrete (RBAC)] has proved to be an effective solution. RBAC is generally used as nonstructural concrete owing to its inferior mechanical and durability properties compared with natural aggregate concrete (NAC). To achieve substantially enhanced properties that would qualify RBAC for potential structural use, fiber-reinforced polymer (FRP) jacketing will be adopted in this study to provide confinement and corrosion resistance to the concrete core. A total of 60 standard cylinder specimens will be tested under monotonic axial compression with the replacement ratio of RBA (0%, 15%, 30%, 60%, and 100%) and the FRP jacket stiffness (0, 1, 2, and 3 plies) as variables. The test results will be analyzed and compared with existing strength and stress–strain models, and based on this it is concluded that although the compressive behavior of FRP-confined RBAC is similar to that of FRP-confined NAC, in general, a high RBA content tends to reduce the effectiveness of FRP confinement.

Fiber-reinforced polymers (FRPs) have been used for repairing chloride-induced corrosion in steel for more than 40 years. Since FRP is a barrier element, it cannot stop electrochemical reactions responsible for corrosion of steel in concrete. The effect of ongoing corrosion can only be detected by inspectors after it has reached such an advanced state that rust stains become visible. This paper presents a predictive framework to estimate the rate of chloride-induced corrosion inside an FRP-concrete repair. Statistical methods were used to extend experimental data on oxygen permeation for one- and two-layer configuration to multilayer configurations. The model was calibrated by comparing its prediction against measured metal loss in specimens repaired using one to four FRP layers that were kept outdoors and subjected to simulated tidal cycles for longer than three years. The application of the model is illustrated by a numerical example.

In this paper, the role of masonry joints in the textile reinforced mortar (TRM)-to-substrate bond is investigated through an experimental program employing double-lap/double-prism (DL/DP) shear bond tests. The TRM system is composed of a dry glass fiber textile and a cementitious mortar applied as an overlay onto unreinforced wall prisms made from solid clay bricks and a cement/lime based masonry mortar. Specimens with different bond lengths (BLs) and various mortar joints-to-bonded area ratios are examined. For all specimens, the shear bond strength of the TRM/masonry interface is larger than the respective strength of the textile/matrix interface the shear failure of which was the governing failure mechanism. For the BLs considered, an increase in the mortar joints/BL surface ratio led to an increase in the transferable shear load of the joints indicating a substrate dependent behavior. A critical discussion on the characteristics of this dependence is included in this paper highlighting the effect of the substrate on the modification of the in situ properties of the composite's matrix. Finally, for BLs larger than the effective BL an existing indirect bond-slip model was applied, therefore, a cohesive material law could be determined for each substrate modified textile/matrix combination.

The performance of steel structures strengthened with externally bonded fiber-reinforced polymer (FRP) rely heavily on the interfacial shear stress transfer mechanism of the FRP-to-steel bonded interface. Much is known about the behavior of FRP-to-steel bonded joints under mechanical loading, but little is known about the performance of this type of bonded joints at elevated temperatures. Almost all adhesives typically used in FRP-to-steel applications experience a change in their mechanical behavior at temperatures <70°C. Therefore, gaining a sound understanding of the behavior of FRP-to-steel bonded joints at elevated temperatures is necessary. This paper presents a series of tests where carbon FRP (CFRP)-to-steel bonded joints are subjected to elevated temperatures. The outcomes of this paper showed that, at elevated temperatures, the dominant failure mode of the CFRP-to-steel bonded joints is the cohesion failure within the adhesive. The bond strength was found to increase with the temperature until the heat deflection temperature (HDT). The bond–slip behavior of the interface was found to undergo significant changes with increasing temperature. Specifically, the initial elastic stiffness and the peak shear stress were found to decrease as the temperature increases. The fracture energy was found to increase at temperatures below the HDT but then decrease drastically when the temperatures exceed the HDT.

Experimental research and real-case applications are demonstrating that the use of fiber–reinforced polymer (FRP) composite materials can be a solution to substantially improve circular cross section concrete columns in terms of strength, ductility, and energy dissipation. The present study is dedicated to developing a new model for estimating the dilation behavior of fully and partially FRP-based confined concrete columns under axial compressive loading. By considering experimental observations and results, a new relation between secant Poisson's ratio and axial strain is proposed. In order for the model to be applicable to partial confinement configurations, a confinement stiffness index is proposed based on the concept of confinement efficiency factor. A new methodology is also developed to predict the ultimate condition of partially FRP confined concrete taking into account the possibility of concrete crushing and FRP rupture failure modes. By comparing the results from experimental tests available in the literature with those determined with the model, the reliability and the good predictive performance of the developed model are demonstrated.

In this paper, the experimental behavior of short and slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars under eccentric compression loading is presented. A total of 10 large-scale concrete column specimens with a rectangular cross section (205 × 306 mm) were tested under a single curvature condition with equal load eccentricities at both ends of the column. Four slenderness ratios of 16.6, 21.5, 39.7, and 59.5 and two reinforcement ratios of 2.78% and 4.80% were considered. The results showed that no crushing of GFRP bars occurred prior to concrete spalling. The columns were able to sustain load, moment, and deformation after the concrete spalling up to the crushing of GFRP bars in compression. The latter was attributed to the contribution of GFRP bars in compression. An analytical model was also adopted to predict the behavior of the test specimens and to evaluate the effect of load eccentricities beyond the one considered in the experimental program. Also, the flexural stiffness and moment magnification factor obtained from the experimental program were compared with those calculated using equations from the literature. The results showed that most of the equations underestimated the flexural stiffness and the magnified moment.

The realistic seismic response of two damaged reinforced concrete (RC) shear walls repaired using externally bonded carbon fiber-reinforced polymer (CFRP) sheets was evaluated using hybrid simulation. The CFRP repair used horizontal and vertical CFRP layers applied to a single side of the wall that were anchored with a steel tube anchor system and CFRP fan anchors. The objective of the CFRP repair was to restore the initial stiffness and restore or increase the strength, ductility, and energy dissipation capacity of the damaged walls. Hybrid simulation was used to evaluate the effectiveness of the repair strategy under real earthquake ground motion records with realistic boundary conditions, including the effects of axial load, shear force, and overturning moment. The results show that the single-sided application of the CFRP sheets restored the seismic performance of the damaged RC shear walls tested in this study. Hybrid simulation is shown to be an efficient test method to experimentally study the seismic response of a structural component with realistic boundary conditions over a range of earthquake hazard levels.

Fabric-reinforced cementitious matrix (FRCM) composites are thin laminates of mortar that embody synthetic and mineral-based continuous fabrics. FRCM materials are proven to be an effective strengthening and rehabilitation technique for concrete structures under flexural, shear, and axial stresses. This paper reports analytical and experimental studies of the mechanical performance of glass FRCM (GFRCM) strengthened RC beams subject to monotonic and cyclic loads. First, material properties of the GFRCM system were determined according to “Acceptance Criteria AC434.” The material properties were then used to analytically determine the capacity of strengthened reinforced concrete (RC) beams, using ACI 549.4R design guidelines. RC beams were strengthened with the GFRCM system and tested under monotonic and cyclic loads to determine ultimate flexural capacity, concrete cracking pattern, failure mode, bond performance, and fatigue threshold. Under monotonic loading, GFRCM increased the steel yielding and ultimate flexural capacity of the strengthened RC beams, but did not change their stiffness. Thus, GFRCM had a minimal effect on serviceability. Fatigue failure of the GFRCM-strengthened beams resulted from progressive cracking and rupture of the steel rebars, followed by fabric slippage within the GFRCM system and rupture of fibers. The GFRCM restrained crack width in concrete, and cracks were more distributed over the length of strengthened beams.

The performance of fabric with lime mortar (LM) as the cementitious matrix was investigated for the strengthening of lime masonry wallettes, which were compared with the respective cement-based matrix. Based on the material composition identified at selected heritage sites, a set of 54 clay brick–LM masonry assemblages were constructed and strengthened using glass fabric and two different grades of the cementitious matrix. Diagonal, four-point bending, and column uniaxial compression tests were performed to evaluate the shear, flexural, and axial behavior of the strengthened lime masonry specimens. The test results show that the fabric with compatible mortar could be used to improve the strength and ductility of old lime masonry structures. In addition, the experimental results were compared with the respective theoretical predictions estimated using the available analytical models.

This paper presents the results of the flexural testing to destruction of two cast iron girders preserved during the demolition of a railway bridge in Scotland. The 151-year-old girders were reinforced with ultrahigh modulus carbon fiber polymer composite (CFRP) plates in 2004. The CFRP plates on one girder were damaged during the demolition and were rendered completely ineffective before testing. The girders were 9 m long and were be tested in four-point bending to failure which gave a unique opportunity to compare the behavior of unreinforced and reinforced cast iron at full-scale. Fragments of cast iron and CFRP that remained after the flexural testing were be used to prepare test specimens and were used to determine material properties. The tests demonstrated the considerable benefits of CFRP strengthening (an increase in load-bearing capacity of 43.9% and an increase in stiffness of 31%) and confirmed that the CFRP was fully bonded to the cast iron until close to the point of failure. The test results have been compared with theoretical and original design predictions that showed that the theoretical predictions were remarkably accurate and the design predictions were conservative as is required for a safe design. This paper includes details of the girders, the test rig, and test procedure, and presents in detail the test results that include the failure mechanisms and will discuss the benefits obtained from the CFRP strengthening of cast iron girders.

New guidelines require that sand particles used to provide a bond between the FRP reinforcing bars and concrete to be free of any expansion due to alkali–aggregate reactions. The current study aims at establishing the preliminary groundwork for assessing the potential alkali–silica reactivity (ASR) of sand particles used as sand coating for FRP bars. Two sand types widely used as sand coating were examined with three testing methods to determine their ASR. Mortar-bar samples prepared with the two sands were monitored for length change for 14 days and compared to reference bars produced with innocuous sand. Analysis under a stereomicroscope and scanning electron microscope (SEM) was performed to detect any signs of silica gel or microcracks in the mortar bars. The long-term reactivity of the sands was assessed by immersing glass-FRP (GFRP) bars in concrete cylinders exposed to an aggressive environment of 1 N NaOH solution at 80°C. The cylinders were then cut into small slices and examined under a stereomicroscope to detect any formation of silica gels between the sand particles and the surrounding concrete. Petrographic examination of the conditioning cylinders after 6 months of exposure revealed no gaps at the GFRP–concrete interface. The three testing methods were found to be suitable for examining the sand-coated bars to ensure fine aggregates free of expansive reactions.