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.

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.

It is well accepted that fiber-reinforced concrete exhibits superior impact resistance than does plain concrete and numerous tests have been employed to evaluate its impact resistance. These include explosive tests and impact tests using projectiles and drop weights. Some of these tests and their results are described in this paper. Attempts to obtain more basic material parameters, by conducting instrumented impact tests, are described next and problems associated with the interpretation of their results are discussed. Finally a testing method developed by the authors, which appears to yield basic mechanical properties of fiber-reinforced concrete subjected to impact is presented.

Plain and mesh reinforced shotcrete have been used for many years for ground support in tunnels, mines, excavations and rock slopes. Since the early 1970's steel fiber shotcrete has enjoyed increasing use in such applications. The question has often been asked how steel fiber reinforced shotcrete performs under loading in such applications compared to plain and mesh reinforced shotcrete. There is a dearth of published literature on this subject and this study seeks to help fill this void. In this study, 1.52 m x 1.52 m x 64 mm (5 ft. x 5 ft. x 21/2 in.) shotcrete panels were fabricated using plain shotcrete, plain shotcrete reinforced with 2 in. x 2 in. x 12/12 wire mesh, and shotcrete with two concentrations of steel fiber. The panels were anchored at 1.22 m (4 ft.) centers with two different conditions of restraint and loaded to destruction with continuous monitoring of the load versus deflection and fracture characteristics of the panels. Under the conditions of test, the improved residual load carrying capacity of the mesh and steel fiber reinforced shotcrete after first cracking, compared to the plain shotcrete, was well demonstrated. The steel fiber reinforced shotcrete panels also displayed improved residual load carrying capacity after first crack compared to the mesh reinforced shotcrete at deformations up to 10 mm (1/2 in.), and equivalent residual load carrying capacity at deformations up to 50 mm (2 in.). The inherent toughness and ductility characteristics of the steel fiber reinforced shotcrete were enhanced by increasing the volume concentration of steel fiber from 0.75 percent to 1.25 percent by volume.

Research and development regarding fiber reinforced materials (FRC) has evolved steadily with most notable progress having been made with the periodic introduction of new fiber types; including materials and form or shape. The attendant interest associated with new fibers has invariably led to an improved understanding of the mechanics of behavior of FRC and to new applications. The use of collated fibrillated polypropylene fibers (CFP) at low fiber volumes improves many aspects of the production and application of FRC including mixing and placement. Plastic state rheological and hardened state mechanical behavior are quite different from those properties which have been reported in the literature for FRC systems using rigid metallic or more brittle glass fibers and for which fiber volumes are normally about ten times the fiber volume of CFP fibers used in this research. A series of tests are designed to assess the basic properties of CFP fibrous concrete in both the plastic and hardened state. As much as possible these tests were conducted in accordance with recommended ASTM and ACI Committee 544 procedures including tests for compression, flexure, impact, split cylinder, and rebar pullout. Other specially designed tests include flexure of composite steel deck and concrete overlay specimens to affect the replacement of weld wire fabric in such applications, and shrinkage testing. Results indicate the benefit derived from the use of CFP fibers is significant as a secondary reinforcement and for crack control. A significant reduction in shrinkage is found and there are positive contributions in other strength performance areas.