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Strain hardening and multiple cracking behavior of hybrid fiber reinforced cement composites containing different hybrid combinations of steel and polyethylene (PE) fibers under four-point bending are reported. The total volume fraction of fibers was kept constant at 2.5% to maintain a workable mix. Effects of increase in fly ash content as partial replacement of cement beyond 50%, such as 60% and 70% on the flexural response of hybrid steel-PVA (Polyvinyl Alcohol) and steel-PE fiber composites are also evaluated here. Among composites with different volume ratios of steel and PE fibers, the composite with 1.0% steel and 1.5% PE was found to show the highest flexural strength and that with 0.5% steel and 2.0% PE exhibited highest deflection and highest flexural toughness. Generally, the steel-PE hybrid composites exhibited lower flexural strength but higher deflection capacity than steel-PVA hybrid composites. The rate of strength loss after peak load in steel-PE hybrid composites was found low compared to steel-PVA hybrid system. The 50% replacement of cement by fly ash is found to be an optimum fly ash content in hybrid fiber composites.

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This paper reports the results of an experimental program on the effectiveness of a Ductile Fiber Reinforced Cementitious Composite (DFRCC) material, which exhibit strain-hardening and multiple-cracking bahavior under flexural loadings, in retarding the corrosion of steel in Reinforced Concrete (RC) beams. Based on the collective findings from theoretically-estimated steel losses, rapid chloride permeability tests, pH value tests, as well as structural tests, it was concluded that Functionally-Graded Concrete (FGC) beams, where a layer of DFRCC material was used around the main longitudinal reinforcement, had a noticeably higher resistance against reinforcement corrosion compared to a conventional RC beam. The better performance of the FGC beams was also evident from the absence of any corrosion-induced cracking and the very low tendency of the concrete cover to delaminate as measured by a concrete-embeddable fiber optic strain sensor.

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Plastic optical fibre sensors offer remarkable ease of handling, and recent research has shown their potential as a low-cost sensor for damage detection and structural health monitoring applications. This paper presents details of a novel extrinsic polymer-based optical fibre sensor and the results of a series of mechanical tests conducted to assess its potential for structural health monitoring. The intensity-based optical fibre sensor proposed in this study relies on the modulation of light intensity as a function of a physical parameter (typically strain) as a means to monitor the response of the host structure to an applied load. Initially, the paper will reveal the design of the sensor and provide an outline of the sensor fabrication procedure followed by a brief description of its basic measurement principle. Two types of sensor design (fluid type and air type) will be evaluated in terms of their strain sensitivity, linearity and signal repeatability. Results from a series of quasi-static tensile tests conducted on an aluminium specimen with four surface-attached optical fibre sensors showed that these sensors offer excellent linear strain response over the range of the applied load. A comparison of the strain response of these sensors highlights the significant improvement in strain sensitivity of the liquid-filled-type sensor over the air-filled-type sensor. The specimens were also loaded repeatedly over a number of cycles and the findings exhibited a high degree of repeatability in all the sensors. Free vibration tests based on a cantilever beam configuration (where the optical fibre sensor was surface bonded) were also conducted to assess the dynamic response of the sensor. The results demonstrate excellent agreement with electrical strain gauge readings. An impulse-type loading test was also performed to assess the ability of the POF sensor to detect the various modes of vibration. The results of the sensor were compared and validated by a collocated piezofilm sensor highlighting the potential of the POF sensor in detecting the various eigen-frequencies of the vibration. Finally, preliminary results of a loading-unloading test of the same sensor design encased within a metal tube will be presented. The results obtained were encouraging offering the possibilities of employing the proposed device as an embedded sensor for damage detection in concrete beams.