The purpose of the present investigation was the study of the effect of specimen size on the compressive strength of concrete reinforced with steel spirals and with fibers. Concrete cylinders of different sizes were loaded under uniaxial compression. The cylinders, ranging in size from 60 x 120 mm to 100 x 400 mm, were reinforced with short fibers (steel and polyolefin) at volume percentages of 1% and 2%. Some specimens also contained transverse steel reinforcement (0 5 mm) at pitches of 25 and 50 mm. There was a reduction in compressive strength as the specimen size increased in all cases (plain concrete, fiber reinforced concrete or spirally reinforced concrete). The effect of the fibers and of the steel spirals was a reduction in the brittleness of composite with increasing size of the specimens. The experimental results confirm that the size effect laws proposed in the literature for compressive strength provide a satisfactory prediction of the reduction in compressive strength with increasing specimen size.

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.

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.

A design method for determining the capacity of slab-column connections made with steel fibre concrete at ultimate load is presented. The proposed design equation is based on the authors' theoretical analysis, which considers the physical behaviour of the connections under load and is therefore applicable to both lightweight and normal weight concrete as well as to concrete without fibres. The design equation incorporates the effects of fibre reinforcement on resisting the upward movement of flexural cracking and of increasing the concrete tensile stress. Furthermore, it simplifies the calculation of the neutral axis depth still accounting for the steel strain hardening effect. The approach does not employ fitting factors to match the predictions to experimental data. However, a depth correction factor is used to account for the size effects. The proposed design equation is applied to predict the ultimate punching shear strength of sixty two slab-column connections tested by authors and other investigators, involving a wide range of fibre variables, concrete type and strength, tension steel ratio, size of slab and loaded area. The comparisons between computed values and the experimentally observed values are shown to validate the proposed design equation.

The tensile stress-strain response of cement composites reinforced with newly developed twisted polygonal steel fibers (identified here as Torex fibers) is investigated in this study. The new fibers are produced from a prototype machine developed for this research. Parameters investigated are: 1) volume fraction of the fibers (Vf=1 % to 4%); 2) fiber equivalent aspect ratio (L/de = 60, 80 and 100); and 3) the compressive strength of the mortar matrix (20, 44, 68 and 84 MPa). It is observed that high performance fiber reinforced cement composites that exhibit strain hardening and multiple cracking behaviors can be obtained with a proper combination of these parameters. A comparison with hooked and straight steel fibers is also provided. The new Torex fibers leads to a significantly higher composite performance in terms of strength, ductility and cracking behavior.