International Concrete Abstracts Portal

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.

The main purpose of this project was to explore the feasibility of using newly developed polypropylene (PP) fibers as reinforcement for portland cement concrete and to compare their reinforcing effectiveness with asbestos, glass and steel fibers. The PP fibers used were made of a high tensile strength (up to 80 ksi), high modulus (up to lo6 psi), high stretch ratio (up to 12 to 1) polypropylene ribbon yarn supplied by AMOCO Synthetic Fabrics. The fibers were cut from a continuous strand obtained by properly twisting two PP ribbon yarns together. Twisting led to a substantial increase in the bonding properties of the fibers (mechanical bond) and their rigidity considered important during mixing. Different fabrication procedures and mortar mixes are described. Salient results of an extensive series of tests on flexural beams and pull-out tests to improve bonding properties are reported. Because steel, glass, asbestos and polypropylene have substantially different specific gravities, performance com-parison is made not only on the basis of volume fraction of fibers but also weight fraction and related costs. It stresses the potential merits of using PP or equivalent organic fibers in concrete matrices and suggests exciting research directions to pursue.

Experiments concerning the bearing capacities of thin steel fiber-reinforced concrete (SFRC) slabs which are most important in using SFRC for over-lays on asphalt pavements are reported and installation operations and serviceabilities of actual overlays are described. According to loading tests, SFRC slabs with crushed-rock and asphalt-concrete bases possess bearing capacities of about 17 to 22 tons and it is thought actual traffic loads can be amply supported. Consequently, it is considered the use of SFRC immune to rutting and distortion would Drovide excellent resurfacing, smooth and durable, and economical as well. It is further shown that the "Yield Line Theory" can be applied to design of resurfacing using SFRC. Actual overlays were constructed on asphalt pave-ments in the northern city of Sapporo where extreme de-formation occurs due to wear in winter and plastic flow in summer. The overlays were of fiber contents of 2 percent and 1.4 percent measuring 3x130x0.05 and 3x200x 0.05 meters, respectively, and were among the first SRFC overlays in Japan. Until the fall of 1981 they had been in service 4 years and 2 years (5 and 3 win-ters), respectively, and worn down 1 to 2 centimeters, with a fair amount of cracks traversing the overlays. However, most of the cracks are connected well by steel fibers, while the wear is of a degree not to impede traffic. Overall, it may be judged that serviceability under traffic is good and that economic losses due to repairs of asphalt pavements at least every 2 to 3 years can be alleviated to a considerable extent.

The performance of most of the fiber-reinforced concrete pavement projects in the United States (34 projects built since 1971) are reported. These include experimental street and highway projects as well as more recently constructed fullscale airport pavements. While a few have performed well, many have developed defects early in their service lives. The lessons learned should help engineers to design future projects that will provide better service. Careful consideration, and perhaps additional research, is needed in the areas of joint design and spacing, load transfer at joints, fiber content, and thickness design.

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.