Information regarding the early strength gain of fresh concrete determines the time for the removal of form work and the transfer of pre-stressing forces for pre-stressed concrete. An ultrasonic based non-destructive evaluation of early strength gain may not work for concrete in fluid and semi-solid phases. A possible alternative is a lead zirconate titanate (PZT)-based smart aggregate embedded in concrete, which can evaluate the micro-structural and rheological properties right from the fluid phase. A set of five smart aggregates embedded in a concrete cube were investigated for their suitability to evaluate electromechanical impedance (EMI) signatures. Cubes were loaded to failure and the EMI during progressive strength loss under compressive loads was studied. To show the generalized applicability of this, experimental results for the performance of typical smart aggregates on a larger specimen, namely a concrete beam, are also discussed. Different statistical metrics were examined computationally on a three peak admittance curve with a parametric variation of stiffness, damping and simple scaling. The root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), cross correlation (CC) and modified cross correlation (MCC) were investigated, in addition to the rate of change of the RMSD. Variations between the reference and modified states were studied. Both stiffness and mass gains occur for the smart aggregates, resulting in an increase or decrease of frequency and amplitude peaks due to progressive C-S-H gel formation. The trend of increasing stiffness and the consequent rightward shift of the resonant peaks and decrease of damping, with the consequent upward shift of amplitudes that happens during curing and strength gain, was observed to be reversed during the application of damaging loads.
In the present study, an experimental investigation was carried out to evaluate the flexural and shear capacity of near surface mounted (NSM) reinforced concrete (RC) beams using carbon fibre reinforced polymer (CFRP) rebars. A total of 16 half scale beams were tested to study the flexural and shear responses of strengthened RC beams. The CFRP rebars were manufactured at structural testing centre using locally developed twisting equipment to strengthen the RC beams. Also, new anchor system was locally developed to predict the tensile characteristics of CFRP bars using universal testing machine. To examine the flexural and shear behaviour, all beams were tested under two-point loading system. It was observed that the NSM strengthened RC beams have higher load carrying capacity than the corresponding control beam in flexure and shear by 68% and 35.6%, respectively. Typical failure modes of the beams during the experimental investigation were CFRP rupture, CFRP debonding, crushing of concrete and shear failure. Finally, a design example has been presented for better understanding in the analysis and design of NSM FRP strengthened RC beams. Further, the values obtained from the analytical study are in good agreement with the experimental values.Keywords: beam; composite; design example; flexure; NSM-FRP; performance; strengthening; shear; sustainable materials.Reference to this paper should be made as follows: Singh, S.B., Sivasubramanian, M.V.R., Likhith Reddy, A., Chandra Prakash, K., Nagarjuna, K. and Hima Kiran, A. (2012) 'Performance of NSM-FRP RC beams in flexure and shear using locally developed CFRP rebars', Int.
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