This paper deals with two main topics. The first topic is the development ofglass fiber-reinforced plastics (GFRP) rebar with ribs composed of both epoxy resin andmilled fibers. The milled fibers are used to improve the interaction of the ribs undermechanical, thermal, and environmental loading states. The ribs, which contain milledfibers, are attached to the surface of the core section and molded using a pressmachine. The second topic is the bond performance of the proposed GFRP rebar.Pullout tests were conducted to investigate the effect of the milled fibers on the bondstrength of the proposed GFRP rebar and to evaluate the bearing resistance offered bythe ribs containing the milled fibers. The test results were compared with those ofother commercially available GFRP rebar. The results showed that the GFRP rebar withribs containing milled fibers was more effective at enhancing the bond performance.The tests confirmed that the bond performance of the proposed GFRP rebar wassuperior to that of other commercially available GFRP rebar.

Fiber Reinforced Polymers have proven to be effective strengtheningmaterials in the construction industry, due to their low weight (easy to apply), non-corrosiveness and high strength. Extensive research has been carried out into thestrengthening of concrete structures with externally bonded FRP. It turned out thatdebonding of the FRP is governing the design of most FRP strengthening applications.One of the parameters, which may affect the bond properties of the FRP-concrete joint,is the ambient temperature. Only little research into the influence of temperature onthe bond behavior has been carried out so far. This paper presents the results of anexploratory experimental and numerical investigation in which the influence oftemperature on the debonding behavior of externally bonded CFRP was investigated.Two different test setups were applied. Results showed that the failure load of CFRPstrengthened concrete structures was affected by the temperature, but depended onthe used test setup. Two types of failure were observed. For low to moderatetemperatures (-10°C to +40°C), failure occurred in the concrete, leaving 1-3 mm ofconcrete attached to the adhesive. For elevated temperatures (50°C to 75°C), failure ofthe adhesive-concrete interface occurred, without leaving any concrete attached to theadhesive.

For under-reinforced concrete sections reinforced with FRP, failure of amember is initiated by rupture of the FRP bar and the typical ACI compression stress-block might not be applicable. This is because of the fact that the corresponding strainat the extreme fiber of the concrete will not reach the ultimate strain in concrete.Therefore, accurate computation of flexural capacity requires developing equivalentstress-block parameters that represent the stress distribution in the concrete at aparticular strain level. While the ACI 440 permits the use of a simplified approach tocalculate moment capacities that do not require equivalent stress-block calculations,the significance of this simplification needs to be examined. This paper suggests afamily of curves based on the extreme fiber strain in concrete using three existingstress-strain models. The paper highlights the significance of these curves for differentvalues of compressive strengths of concrete.

Fiber reinforced polymer (FRP) casings, in the form of stay-in-placeformwork, provide an attractive alternative to conventional confinement reinforcementfor concrete columns. These casings can fulfill multiple functions of; i) formwork, ii)confinement reinforcement, and iii) protective shell against corrosion, weathering andchemical attacks. This paper investigates the use of stay-in-place FRP formwork asconcrete confinement reinforcement for HSC columns with circular and square cross-sections. Large-scale specimens with 270 mm cross-sectional dimension and up to 90MPa concrete strength, were tested under combined axial compression andincrementally increasing lateral deformation reversals. FRP casings were manufacturedfrom carbon fiber sheets and epoxy resin. One of the square columns was providedwith internal FRP crossties, a new technique introduced by the authors, to provide well-distributed lateral restraints along the column face, thereby improving the mechanismof confinement. The results indicate that the deformation capacity of HSC columns canbe improved significantly by using FRP casings. The results further indicate that theconfinement effectiveness of casings of square columns is significantly affected by thecorner radius of casings. Confinement efficiency of these casings improves with the useof FRP crossties.

Limited information is known about the effects of environmental conditionsduring installation on quality and performance of the bond between carbon fiberreinforced polymer (CFRP) reinforcement and substrate material. This research studyinvestigates the effect of surface moisture, relative humidity and temperature on thebond strength between concrete and CFRP reinforcement. Three test methods includinga surface pull-off bond test, a surface shear-torsion bond test, and a flexural test wereused to evaluate the bond performance of the FRP fabric under various installationconditions. Test results revealed that the high surface moisture content, extremehumidity and extreme low temperature can be detrimental to bond strength. Althoughthe high temperature improved the bond strength, it is not recommended because ofdecreased set-time and saturant workability. Based on the results presented in thispaper, a maximum allowable limit on surface moisture content, relative humidity, andtemperature of 4.3%, 82%, and 90oF, respectively, at installation is recommended.