International Concrete Abstracts Portal

Fiber-reinforced polymer (FRP) composite materials been widely used in civil engineering new construction and repair of structures due to their superior properties. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published reports, guides, and specifications on the use of FRP materials for may reinforcement applications based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

This volume represents the thirteen in the symposium series and could not have been put together without the help, dedication, cooperation, and assistance of many volunteers and ACI staff members. First, we would like to thank the authors for meeting our various deadlines for submission, providing an opportunity for FRPRCS-13 to showcase the most current work possible at the symposium. Second, the International Scientific Steering Committee, consisting of many distinguished international researchers, including chairs of past FRPRCS symposia, many distinguished reviewers and members of the ACI Committee 440 who volunteered their time and carefully evaluated and thoroughly reviewed the technical papers, and whose input and advice have been a contributing factor to the success of this volume.

This paper investigates experimentally the effect of sand coating bond enhancer on the flexural behavior of circular concrete-filled FRP tube (CFFT) by testing two full-scale CFFT cantilevers under lateral cyclic load. The full-bond between concrete and any kind of reinforcement is one of the main factors affecting on its flexural behavior. Limited research has investigated the bond effect on CFFT flexural behavior. The bond between the concrete core and the interior surface of the FRP tube is the main parameter of this study. Embedded-concrete strain gauges were used to measure the strain values inside the concrete core, then compared with the strain values measured from the electric strain gauges installed on the tube outer surface. The observed experimental results illustrate that the sand coating increases the flexural strength and stiffness of circular CFFT members. No slippage was observed on the sand-coated specimen; while 6 mm (0.24 in) slippage was measured on the specimen without sand coating. The internal and external strain curves are identical for the sand-coated specimen; while these curves are incompatible for the specimen without sand coating. The experimental results demonstrate the significance of investigating the bond effect and the sand coating contribution to improve the bond between the concrete core and the FRP tube, and assure a good composite action under flexural loads.

Flexural strengthening of reinforced concrete (RC) beams with fiber reinforced polymer (FRP) composites and two different bonding agents were investigated in this research. The bonding agents used in this research consisted of an epoxy paste and a sprayed polyurea. When polyurea was used as the bonding agent, it was sprayed to specific regions on the RC beams. Three RC beams were flexural strengthened with FRP composites according to the following techniques: (a) sprayed polyurea with and without glass FRP (GFRP) grid reinforcement, and (b) manual layup using one GFRP grid. Experimental results clearly indicate that flexural strengthening with the un-reinforced or reinforced polyurea technique is an effective strengthening scheme. Advantages of using polyurea over other epoxy based methods are that the application process requires significantly less time and the polyurea cures within minutes. Furthermore, no debonding of the un-reinforced or reinforced polyurea system was observed, suggesting a further benefit of this technique. Application of the polyurea system and key experimental results are presented and discussed herein.

The elastic nature of fiber-reinforced polymer (FRP) reinforcement raises concerns about the feasibility of using this type of reinforcement in reinforced concrete (RC) structures in seismic regions. To date, no studies have been conducted to investigate the seismic response of GFRP-RC slab-column connections. This paper presents the results of an experimental program carried out to assess the lateral displacement deformability of slab-column edge connections reinforced with GFRP reinforcement. Two full-scale connections were tested under gravity and reversed-cyclic lateral loading. One connection was reinforced with steel reinforcement, while the other one was reinforced with the same reinforcement ratio of GFRP reinforcement. The GFRP-RC connection was able to sustain a 2.5% drift ratio, which is higher than the 1.5% minimum drift ratio for the steel-RC counterpart. This indicates the ability of GFRP-RC edge connections to undergo or exceed the suggested seismic drifts while maintaining their gravity load carrying capacity.

Utilization of fiber-reinforced polymers (FRPs) in concrete structures, particularly bridges, has promised a safe and satisfactory performance. However, the structural performance of FRP-reinforced bridges can be affected by occurrence of various types of damage. This paper presents structural damage identification in FRP-reinforced bridge truss girders tested under static and fatigue loading. The proposed technique combines discrete wavelet transforms (DWTs) and spectral entropy in a relative procedure to detect and quantify the damage-induced disturbances in the measured vibrational signals of the girders. Various types of test-induced damage were identified using the vibrational signals obtained only from the damaged state of the girders. Results of damage identification were verified by data obtained through instrumentations and by visual inspection of the actual state of damage in the girders during and after the tests. The results show that the technique can be implemented in a protective structural health monitoring (SHM) system to identify imminent failure. It can also help with the decision-making process regarding maintenance of FRP-reinforced concrete bridges. The technique is a practical means for damage identification in in-situ cases, where the normal operation of bridges cannot be interrupted, and the data obtained from a reference state of bridges are not available.

This paper presents an investigation on deterioration of tensile and shear properties of GFRP bars. Composite bars, contrary to conventional steel, when used in structures exposed to aggressive environments can significantly increase their durability and lifetime. However, the use of GFRP bars in concrete structures is still limited due to unspecified durability properties of this relatively new material. Since long-term durability data are not readily available, accelerated aging tests have been used in this research to study GFRP bar degradation. GFRP bars were kept in a highly alkaline solution heated to 50, 60 and 70°C for 1, 3 and 5 months, respectively, and after each immersion period, bars were taken out and tested in tension and shear. The test results show that the high pH of the alkaline solution has an adverse influence on GFRP properties, and the speed of degradation depends on the temperature of the solution. Also, the effect of bar size and surface finishing on the degradation speed was analyzed, and the results are presented in the paper.

FRP is customarily used to wrap concrete columns to increase their strength and strain capacities by providing extra confinement. Typically, steel hoops or spirals are used in constructed columns as mandated by codes. The behavior of retrofitted columns becomes thoroughly different because there are two systems with different mechanical response and interaction engaged in confinement. While most of the literature addressed concrete confined with FRP only, a limited number of studies and experimental cases accounted for both actions. This paper developed an axial stress-strain model which utilized geometric and mechanical properties of concrete, steel and FRP. The proposed work adopted Lam and Teng model for concrete confined with FRP, originally implemented in ACI 440.2R-17 guide, and calibrated its parameters against experimental curves. The proposed model correlates well with experimental cases that were collected from the literature.

The use of Fibre Reinforced Polymer (FRP) reinforcement has been widely adopted in the construction industry. This paper presents the findings of an experimental program undertaken to examine the use of small-diameter Carbon Fiber Reinforced Polymer (CFRP) strands for shear strengthening of concrete beams, not in a U-shape form confinement, but in a discrete form; sheets are applied to beam sides only. Nine concrete beams were constructed and tested to evaluate the effectiveness of the strengthening scheme. The considered parameters included the width and spacing of the CFRP strands strips. The research was extended to examine the feasibility of additional anchorage system, in form of longitudinal strips, to better resist the shear diagonal cracks in both components directions (vertical and horizontal), to delay premature failure due to delamination of the strands. Test results revealed that the use of small-diameter CFRP strands for shear strengthening of concrete beams is simple, easy to install and efficient in increasing the shear capacity by around 23% compared to the control specimen. It was also shown that presence of the longitudinal CFRP strands enhanced the shear behavior of the beams by providing more resistance to the induced diagonal tension and delayed delamination of the strands.

In recent research, the use of the near-surface mounted (NSM) technique has been proven to increase the torsional strength of reinforced concrete (RC) members. In this paper, an investigation into the torsional deformation characteristics of the ten RC beams strengthened using the NSM technique is reported and evaluated using photogrammetry. The experimental results of two control beams and eight beams strengthened using CFRP laminate embedded into pre-cut grooves using epoxy and mortar are evaluated. The Digital Image Correlation Photogrammetry (DIC) is used to determine the three-dimensional displacement of targets placed on the north and south faces of the beams at selected load levels up to failure. The main aim of this study was to measure the propagation of torsional crack width with increasing torque for each beam. The torsional deformations of the beams are evaluated and verified with the photogrammetry measurements and the differences in the width of the large torsional cracks across the tested beams are highlighted and compared. The width of the torsional cracks for the strengthened beams was smaller than that that of the control beams at the same load level. Similar deformation mechanisms were observed for the strengthened and control beams.

The objective of the work presented in this paper is to develop an image analysis methodology for evaluating the fracture surfaces of concrete-epoxy interfaces (CEI). The CEI is formed at the interface between epoxy and concrete and is influenced, as is the interface between fiber reinforced polymer composite bonded to concrete, by environmental and loading conditions in service. The developed image analysis methodology was used to characterize CEI debonding failure by one of three possible modes: cohesive failure in the concrete (CC), interfacial failure (IF), and cohesive failure in the epoxy (CE). Quantitative digital image analysis coupled with a set of rules for failure mode classification enabled the correlation of CEI failure mode with bond performance metrics such as fracture energy and lap shear pull-off force. The results show a strong correlation between failure mode and bond performance. Extended periods of sustained loading decrease bond performance and shift the dominant failure mode from CC to IF.