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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-10 of 331 Abstracts search results
February 1, 2019
Ian Shaw, Hang Zhao and Bassem Andrawes
Fiber reinforced polymer (FRP) composites have emerged as a lightweight and efficient repair and retrofit material for many concrete infrastructure applications. FRP can be applied to concrete using many techniques, but primarily as either externally bonded laminates or near-surface mounted bars or plates. This paper presents the results of direct shear pull-out tests performed on aged concrete specimens reinforced with glass FRP (GFRP) and carbon FRP (CFRP) externally bonded laminates and near surface mounted (NSM) bars. An accelerated aging scheme consisting of freeze/thaw cycling in the presence of a deicing salt solution is implemented to determine the effect of long-term environmental exposure on the FRP/concrete interface in regions that experience aggressive winter environments. The results show that the NSM bar technique is superior to externally bonded laminates in terms of efficiency in the use of FRP material and the effects of accelerated aging. Generally, the performance of GFRP is affected less than CFRP after freeze/thaw cycling for both externally bonded laminates and NSM bars. For high strength NSM FRP bar applications, a spalled or cracked concrete surface caused by freeze/thaw cycling may drastically reduce the capacity of the FRP/concrete interface by inducing failure at the concrete/epoxy filler interface.
November 1, 2018
Piyong Yu, Pedro F. Silva and Antonio Nanni
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.
Ghaidak Al-Bayati, Riadh Al-Mahaidi and Robin Kalfat
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.
Yoseok Jeong, Maria M. Lopez and Charles E. Bakis
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.
Salah Altoubat, Abdul Saboor Karzad, Mohamed Maalej
This paper is part of an on-going research project on the behavior of damaged Reinforced Concrete (RC) beams repaired and strengthened with Externally Bonded Fiber Reinforced Polymer (EB-FRP). A total of seven full-scale rectangular beams; fully-damaged in a previous study, were repaired and retested to failure. The repair methodology consists of filling the cracks with epoxy, and then wrapping the beams with FRP discrete strips with two different thicknesses (1 layer and 2 layers). Out of the seven beams, four beams were strengthened using 2 layers of EB-FRP discrete strips; two beams were strengthened with 1 layer of EB-FRP; and the remaining beam was only repaired by crack injection with epoxy without wrapping with FRP. The beams were instrumented and tested to failure in three-points loading setup. The measured test parameters were the beams deflection and the maximum load-carrying capacity. Furthermore, the mode of failure was also observed and reported in this study. The test results revealed that the use of EB-FRP strips along with epoxy injection is an effective repair method that not only recovers the original strength (strength of the beams tested in previous study, considered as the reference beams), but also significantly increases their shear capacity. Comparing the shear capacity of the repaired beams to that of the reference beams, revealed that 2 layers of EB-FRP increased the shear strength by up to 95%, while the use of 1 layer of EB-FRP increased the shear strength by up to 66%. Moreover, comparison of the test results with existing predictive models (ACI 440.2R and fib TG-9.3) showed that both models reasonably predict the EB-FRP contribution to the shear strength of repaired and strengthened damaged beams.
Cheng Jiang, Baolin Wan and John Omboko
The bond between external bonding (EB) of fiber reinforced polymer (FRP) composite materials to concrete is the weakest link in the strengthened concrete flexural members. There are three mechanisms to transfer the interfacial shear between FRP and the concrete substrate, i.e., adhesion, interlocking and friction. This paper proposes a new approach by grooving on the concrete surface before applying epoxy to make epoxy ribs to increase interlocking. An experimental program was conducted to verify the effectiveness of the proposed epoxy ribs. Six grooves perpendicular to the fiber direction were cut on the bonding surface of the concrete blocks. The grooves were filled by wax in the unfilled specimens and with epoxy primer in the epoxy filled specimens before CFRP plate was installed. The experimental results show that epoxy-filled grooves can significantly improve the bond between FRP and concrete.
Jaime Gonzalez-Libreros, Cristian Sabau, Lesley H. Sneed, Carlo Pellegrino, and Gabriel Sas
Fiber reinforced cementitious matrix (FRCM) composites have gained popularity for strengthening of concrete structures due to their capacity to overcome some drawbacks of fiber reinforced polymer (FRP) composites, mainly related to the use of epoxy resins. Research on the topic has shown that FRCM composites can increase the axial, flexural, shear, and torsional capacity of concrete elements. However, experimental studies are still limited, and an important effort is required to develop accurate and reliable design models to predict the contribution of the system to the capacity of strengthened elements. In this paper, a quantitative review of experimental studies of axially loaded concrete elements confined with FRCM composites is presented. The influence of selected variables on the increase in axial capacity of the strengthened specimens is evaluated. Three available design models for predicting the increase in axial capacity of FRCM-strengthened concrete are assessed using a database compiled by the authors. Results show that confinement with FRCM composites can provide a significant increase in axial strength for both cylindrical and prismatic concrete specimens. Further efforts are needed to improve the performance of models to predict the axial strength and behavior of FRCM-confined concrete.
Ruo-Yang Wu and Chris P. Pantelides
A rapid repair or replacement method is developed for severely damaged concrete bridge columns due to cyclic loading. A carbon fiber-reinforced polymer (CFRP) shell and headed steel bars are used to relocate the column plastic hinge. The technique employs a steel collar with steel studs to increase bond of the original column to repair concrete inside the CFRP shell. Two bridge columns were damaged including concrete crushing and longitudinal steel bar pullout under quasi-static cyclic loads. One of the specimens required additional epoxy injection of the cracks; for the other specimen, the column and cap beam were decoupled before repair to simulate replacement of a column which sustained unrepairable damage. The technique successfully relocated the plastic hinge and restored strength and displacement capacity. Failure of the repaired specimens included concrete crushing and bar fracture. The technique is an accelerated bridge construction method and could be used to repair columns with repairable damage or replace columns with unrepairable damage.
September 12, 2018
Rico J. Massa, William D. Cook and Denis Mitchell
An experimental program was carried out on full-scale precast pretensioned I-girders to study the influence on the shear response of carbon fiber reinforced polymer (CFRP) shear strips epoxied to the sides of the girders. The test program demonstrated that the CFRP shear strips were effective in increasing the shear strength of the webs and in controlling the shear crack widths. The shape of the I-girders makes it difficult to properly anchor the vertical shear strips. The curved epoxy transitions between the web and the flanges at the re-entrant corners together with the use of horizontal CFRP strips in the regions of the re-entrant corners helped to improve the anchorage of the vertical CFRP strips. The shear resistance components from the concrete, the stirrups and the CFRP shear strips, were determined experimentally and compared with analytical predictions. The results from this experimental study are compared with the test results from other researchers. The design approach of the 2014 Canadian Highway Bridge Design Code provides conservative estimates of the shear strength of the webs.
August 10, 2018
Experiments were performed on two RC columns taken from a school building that was originally constructed in 1963. The columns were subjected to reverse loading with displacement control under constant axial load. Both columns were designed with a common shear span length of 1200 mm for the validation of shear capacity equations currently used for seismic evaluation. The concrete of both columns exhibited honeycombs. Thus, one column was repaired with epoxy resin injection, and the effect of retrofitting was investigated. The columns did not exhibit significantly different crack patterns. The collapse mechanism of the two columns were shear failure, and the shear force drift angle response was considerably brittle. The observed values of the original column could be predicted by the recommended standard equations for the strength of shear crack and shear capacity. The maximum strength and the initial stiffness of the retrofitted column were 1.18 times and 1.40 times, respectively, of those of the original column. Results indicated that epoxy resin injection improves the seismic performance of columns of the existing buildings.
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