DYNAMICAL MECHANICS OF CONCRETE
Moufaq J. Katwan. B.Sc.. ph. D. . Director General of NCCL.Baghdad.. Iraq .
Sabah S. Abdulnoor. B.Sc.. MSc.,ph. D.. University of Technology.
Yasir K. AL-Ani, B. Sc. M Sc.. University of Baghdad.
Received 26/10/1999 Accepted 6/5/2000
Various concrete composites were developed, where plain concrete was reinforced with crimped steel fibers and with fibrillated Polypropylene fibers separately. It was only possible to introduce 0.5 % and 1 % volume fraction of steel fibers, while the polypropylene fibers was mixed in (0.5%, 1%, 1.5% and 2%) volume fraction.
The dynamical mechanics of these composites in addition to that of plain concrete was investigated using two different techniques. In the first, measurements were made using the resonant frequency technique in determining the fundamental longitudinal and Torsional resonance frequency of the composites bulk. The second was done by measuring the transverse (shear) and longitudinal (compressional) velocities of ultrasonic waves using the pulse velocity technique.
Basic mechanical parameters like dynamic young modulus, dynamic shear modulus, and dynamic Poisson's ratio were deduced from the above measurements in a separate manner. Generally the values of young and shear moduli deduced from both techniques were found to be nearly identical.
However, they were all found to decline with increased reinforcement volume fraction. This in fact agrees very well with theoretical predictions which indicate that the reinforcing fibers are increasing their share in bearing the externally applied stresses with matrix.
Moreover, the dynamic Poisson's ratio values deduced from both techniques were found to be identical for individual composites. And that this ratio was enhanced with increased reinforcing fibers presence. Suggesting that this presence of reinforcing fibers is encouraging the concrete matrix to maintain a reasonably constant volume when undergoing an elastic deformation.