International Concrete Abstracts Portal

Fiber-reinforced cement for piezoelectricity and pyroelectricity is introduced, as these phenomena are useful for the sensing of strain and temperature. The use of short steel fibers (8 µm diameter), together with polyvinyl alcohol, as admixtures greatly enhances these effects, thereby attaining longitudinal piezoelectric coupling coefficient 3 x 10-" mN (10kHz), and pyroelectric coefficient 6 x 10$ C/mz.K (10 kHz). The piezoelectric effect is comparable in magnitude to that of PZT. However, due to the high value (2,500) of the relative dielectric constant, the piezoelectric voltage coefficient and pyroelectric voltage are comparable to or even lower than those of plain cement paste or carbon fiber (15 µm diameter) cement paste. Carbon fiber cement paste and plain cement paste are comparable in the piezoelectric coupling coefficient, piezoelectric voltage coefficient and pyroelectric voltage, though the pyroelectric coefficient is higher for carbon fiber cement paste than plain cement paste.

This paper reports on a series of dynamic splitting tensile tests on 70 mm diameter cored concrete and steel fiber reinforced concrete (SFRC) specimens at moderate strain rates. A modified split Hopkinson pressure bar (SHPB) was specifically developed to test such large diameter heterogeneous specimens. Details of the modified SHPB and a novel striker bar are presented. Dynamic strength magnification of up to 4.5 times the static strength at moderate strain rate was obtained. For the SFRC specimens, hooked-end steel fibers were used with 0.3% fiber volume concentration. A high-speed camera with framing rate up to 106 frames per second was used to record the crack propagation mechanism and the progressive fracture of the specimens in tests. Numerical simulation of the test is briefly presented and discussed. Good approximation of the response is obtained.

The objectives of this paper are to present experimental evidence and to offer an explanation of the size effects on structural strength and post-peak behavior observed in high strength concrete beams under three point bending. The materials had an aggregate/binder ratio of 1.5, a microsilica/binder ratio of 0.1, a water binder ratio of 0.22, and different steel reinforcing microfibers content (0-1 and 2% by volume). Beams of different length-to-depth ratio and different sizes were considered. The tests were monitored with interferometric measurements that detect the full displacements field on the surface and with acoustic emission that reveals inelastic phenomena related to damage that develops in the specimen. Test results showed that when steel fibers are introduced in the concrete mix, the size effects on the structural strength and ductility usually are less pronounced. However, the considered size ranges show that the fiber length should be chosen adequately relative to the size of the specimen. The proposed model shows that an asymptotic value of strength is reached sooner in fiber-reinforced material.

During the last 4 years a large testing program has been carried out in order to investigate the shear capacity of concrete beams containing longitudinal reinforcement and steel fibers. The results of this research program are presented here and compared with calculated values. For the calculations two models were used: the model proposed by RILEM TC 162-TDF and the model of Imam which is originally derived from a formula proposed by Bazant and Sun. The results of this comparison indicate that the RILEM method is a conservative approach. Especially the contribution of the stirrups and the influence of the shear span to depth ratio are underestimated. In the formula of Imam the contribution of the stirrups is calculated in the same way as in the RILEM method and consequently underestimated. However, for SFRC beams containing longitudinal reinforcement but without stirrups the correlation between experimental results and values calculated with the formula of Imam is fairly good.

This narrative discusses design and construction aspects related to a steel fiber reinforced concrete bonded overlay repair project on the existing Houston Beltway 8 Freeway. Several previous steel fiber reinforced paving projects are reviewed. An experimental program involving steel fibers complete in 1983 (1-610 Overlay Project in Houston) is comprehensively reviewed with special attention paid to reflective cracking reduction. Design considerations such as mix design, modulus of rupture, residual strength factors, overlay bond performance, and evaporation rate are discussed. Fatigue endurance limit laboratory test data are presented and a correlation to design applications using residual strength factors is suggested.