International Concrete Abstracts Portal

A study on glass FRP-bonded RC beams subjected to sustained loadingunder tropical weathering is reported. Beams were observed for long-term deflectionsand cracking due to sustained loading over different periods of time, after which theywere unloaded and subsequently tested to failure. Beams subjected to outdoortropical weathering for six months showed 8% larger deflections and 15% larger crackwidths compared to those kept under ambient laboratory condition. Under acceleratedweathering in a chamber, similar increase in deflections and crack widths wereobserved. Also, after six months of accelerated weathering, the ultimate flexuralstrength was about 17% and 12% less for beams bonded with uni- and bi-directionalglass FRP laminates, respectively, compared to the un-weathered reference beams.The failure mode changed from concrete crushing to FRP rupture with weatheringperiod, indicating the deterioration of FRP laminates. The effect of weathering wasmore detrimental in the presence of sustained loads.

Although fiber reinforced polymer (FRP) composites are increasingly beingused in civil infrastructure applications, there is still a lack of well documented data andunderstanding regarding their long-term performance especially under combinedexposure to environmental conditions and sustained load. This paper presents theresults of an investigation into synergistic effects of hygrothermal exposure andsustained strain on pultruded E-glass/vinylester composites. It is seen that effects ofincreasing strain levels can be significant and can lead to changes in damagemechanisms, especially in conjunction with moisture uptake. High strains incombination with moderate to elevated temperatures resulted in substantially morecatastrophic failure than elevated temperatures in combination with lower strains.These effects were noted in tension and short-beam-shear modes, and overalldeterioration was corroborated by moisture uptake, Dynamic Mechanical ThermalAnalysis (DMTA) and Fourier Transform Infrared Spectroscopy (FTIR) investigations.

Over the last few years, the use of composite materials has become anincreasingly popular method of repairing and strengthening ageing civil engineeringstructures. However, despite the efficiency and attractiveness of this technique, itsmarket progression has been impaired by the relative lack of knowledge on the long-term behavior of the FRP materials themselves and, by extension, on the behavior ofthe structures strengthened with such products. The authors are conducting a 10-yearexposure test program on FRP products, and this paper provides midway results fromthe first 5 years of exposure data. There was no significant change in the tensilestrength of the CFRP laminates after a 5-year exposure, however in-plane shearstrength showed a slight decrease. Bending strength of matrix resin also decreased inthe early exposure stage. The results suggest a reduction of the bonding propertiesbetween carbon fibers and resin.

This research program was initiated to examine the feasibility of assessingthe blast-resistant capacity of reinforced concrete (RC) slabs using the displacementbased design (DBD) method. In order to achieve this objective, five RC slabs weretested under real blast loads in the out-of-plane direction. One of the slabs was usedas the control unit to establish a baseline for comparison in terms of performance forthe other four slabs, which were strengthened with fiber reinforced polymer (FRP) andsteel fiber reinforced polymer (SRP). The explosive charge weight and stand-offdistance required to impose a given damage level were predicted by the DBD method.Test results showed that the blast loads were effectively estimated and the damagelevels observed from the field tests correlated well with the predicted levels. Inaddition, test results corroborated that the blast-resistant capacity of RC slabs can beeffectively increased by strengthening using FRP composites. The main conclusion thatcan be drawn from these tests using improvised explosive devices (IDE) is that RC slabsretrofitted on both sides have a higher blast resistance capacity than those slabsretrofitted only on one side. This paper discusses these experimental results alongwith the analysis steps used to predict the blast charge and standoff distance toimpose a given damage level.

Recently, ISIS Canada studied the durability of GFRP in concrete in severalfield structures across Canada. The objective of the study was to provide theengineering community with the results of the performance of GFRP materials that havebeen exposed to the concrete environment in built structures. Cores of GFRP-reinforcedconcrete were removed from five field structures. Analytical methods, namely opticalmicroscopy, scanning electron microscopy and energy dispersive x-ray, differentialscanning calorimetry and infrared spectroscopy, were used to determine thecomposition of GFRP after being subjected to the alkaline environment of concrete forfive to eight years. Three research teams from four Canadian universities performedmicroanalyses of the GFRP and surrounding concrete independently. Results indicatethat no deterioration of GFRP took place in any of the field structures. No chemicaldegradation processes occurred within the GFRP due to the alkalinity of the concrete.The overall conclusion of the study is that GFRP is durable in concrete. Also, it wasconcluded that the CHBDC was conservative in its first edition by not permitting GFRP asprimary reinforcement. As a result of the study, the second edition of the CHBDC,currently in the final stages of approval, permits the use of GFRP as primaryreinforcement.