International Concrete Abstracts Portal

This paper presents an overall evaluation of the observed behavior of fiber reinforced concrete under dynamic loading. The term dynamic loading is used to describe either high strain rate monotonic loading (impact) or cyclic loading under high stress range, high strain rates (simulating earthquake loading). Particular emphasis is placed on the evaluation of the fracture energy (or toughness) and fatigue life of this composite. The research program comprises four related parts dealing re-spectively with: 1) the effect of strain rate on the pull-out behavior of fibers in mortar, 2) the surface energy of fiber reinforced mortar prisms in tension, 3) the energy absorbed by fiber reinforced mortar beams subjected to impact loading and 4) the behavior in compression of fiber reinforced concrete cylinders under high strain rates monotonic and cyclic loadings. While Parts 2 and 3 of the program deal with steel fibers only, Parts 1 and 4 involve also glass, polypropylene and polyester fibers.

This paper reports a few results of the experiments carried out in order to investigate the characteristics of deflection of the polymer fiber and the hybrid fiber reinforced concrete beams under bending load. Some results on the dynamic strength test for the polymer and hybrid fiber reinforced concrete beams by a Charpy impact tester modified for concrete specimens are also refered in this paper. The polymer fibers used in polymer fiber reinforced concrete are generally filaments with extremely small diameter. The fibers used in this study are relatively thick with the rectangular cross section of 2 by 0.6 mm. From these experiment, it may be found that the flexural strength of concrete is improved by the addition of the polymer fibers. The polymer fiber reinforced concrete beams showed great endurance after the initiation of cracks in the specimens. A method by a modified Charpy impact tester was proposed in this study for evaluating the resistance of concrete against impact load. According to the results obtained using this method, the resistibility of the polymer and the hybrid fiber reinforced concrete against impact load is about double that for fiber-free concrete.

A method for adapting existing pavement thickness design curves and formulas for "special" concretes is presented. The need for doing this is discussed; i.e., special concretes made, for example, with fiber reinforcement or high-range water reducers have material properties (specifically changed fatigue endurance and the effects of maturity) which are different from the long-assumed properties that "normal concretes" possess and upon which current design curves are based. Without making these adaptions, wasteful over-design or failures from underdesign can occur. An example is given

A polypropylene-reinforced cement composite has been developed which is considered to be an economic alternative to asbestos-cement. A major application of the composite will be as corrugated sheeting for roofing and cladding. Comparative tests on the behaviour of full-size polypropylene reinforced cement corrugated sheet and asbestos-cement sheet under simulated uniformly distributed loads are reported. The results indicate that the new sheeting of similar profile to a typical asbestos-cement sheet profile and tested over the span recommended for the asbestos-cement profile can sustain the loads in International Standards recommendations and remain serviceable. Furthermore, the quasiductile behaviour of the sheeting and consequent excellent impact resistance are considerable advantages over the brittle behaviour of asbestos-cement.

Increase of steel fiber reinforced concrete structures requires a simple test method for measuring steel fiber content in concrete. The measurement of steel fiber content is considered important as the fiber content is the most important index for quality control of steel fiber reinforced concrete. The prominent test methods which have been presented so far are washing analysis and X-ray image test. Both of these tests are too troublesome to be applied for field tests. Measurement of fiber content using electro-magnetic method is not only applicable to hardened concrete but also to fresh con-crete. The measurement can be done within a few minutes whether the test is performed in laboratories or on the fields. A special electro-magnetic apparatus is made and the problems encountered are investigated. The problems are such as the effects of distribution and orientation of steel fibers, the effects of the distance from the apparatus to the test specimen, etc.. A practical method to measure steel fiber content is clarified and the measured values showed good agreements with the washing analysis. Application of the apparatus for estimation of rupture sections of beams is also investigated.