International Concrete Abstracts Portal

Results of an experimental investigation of the properties of steel fiber reinforced structural lightweight concrete are presented. The concrete was proportioned to obtain a compressive strength of about 6000 psi (41.3 Mpa). The targeted values for slump and air content were 4 to 8 in. (100 to 200 mm) and 8 percent, respectively. Collated fibers 30 mm long with hooked ends were used for the entire investigation. The fresh concrete was tested for temperature, slump, V-B time, flow table spread, air content, and unit weight. The hardened concrete was tested for dry unit weight, compressive strength, flexural strength, splitting tensile strength, and shrinkage. In addition to these results, a comparative evaluation of normal-weight and lightweight fiber reinforced concretes is also presented. Study results show that highly workable, high-strength, lightweight fiber reinforced concrete can be produced successfully. The lightweight concrete has as much energy absorption capacity as the normal-weight concrete.

The U.S. Navy is evaluating jet-blast and heat-resistant materials for high-temperature pavements. The research program includes laboratory and jet exhaust blast tests. Paper describes the jet exhaust blast tests on heat-resistant pavement materials reinforced with stainless steel fiber. The optimum steel fiber content for jet blast-resistant pavement was about 0.8 to 1.2 percent by volume. The test panels prepared by casting were stronger than those by gunning. The results from the jet exhaust blast tests were used in the design of a full-scale V/TOL test pad, AV-8B power check pads, and fire-fighting training facilities.

Use of reinforced fiber concrete in buildings, for construction of an adequate section to resist a flexural failure, has been under investigation by engineers in the past decade. Design and analysis methodologies are discussed in the paper so this type of construction can be developed successfully by engineers. In the first part of the paper, results from 13 beams that were tested at New Jersey Institute of Technology are presented to show the nature of the flexural behavior. These beams are for: 1) normal concrete, 2) high-strength concrete, and 3) lightweight concrete with and without fibers. Most of the results from these tests have not been reported previously. A computer program will also be shown that accurately predicts the flexural behavior of these beams and other reinforced fiber concrete members. Using these test results and the computer program, inelastic and elastic behavior in flexure are discussed. The majority of the paper deals with analysis and design methods. All past methods of analysis are discussed briefly. A method that has been developed by NJIT is explained for analyzing regular singly reinforced, doubly reinforced, and T-beams. The {rho}b criteria is explained for each case, and analysis equations and design methodology are shown for each type of beam. Hence, the paper shows the state-of-the-art in analysis with the examples, and presents a rational design scheme for use by the design engineer that will help in the adoption of such a construction material.

Behavior of soil-cement that has been modified by the addition of fiber reinforcing is investigated. Two different soil mixtures were used--one containing a sand aggregate and the other containing a clayey sand aggregate. Four different types of fibers were examined--straight steel, hooked steel, polypropylene, and fiberglass. All fiber mixtures were evaluated based on a comparison with a control mixture containing no fiber reinforcing. The material properties examined were: 1) compressive strength; 2) splitting tensile strength; 3) shear strength; 4) compressive stress-strain behavior; 5) wet-dry durability; and 6) freeze-thaw durability. Overall, fiberglass reinforcing was found to be most effective in improving the strength properties of the soil-cement. An increase in tensile splitting strength of up to 140 percent was observed. Ductility was greatly enhanced for all the fiber mixtures, as indicated by higher post-peak strengths. Also because of the presence of fibers, the confinement of specimens was improved. For some fiber/soil combinations, increases in compressive strength and shear strength were also observed. The wet-dry and freeze-thaw tests showed that all the fiber types except fiberglass improve the durability of soil-cement. Fiberglass fibers, however, were generally found to be detrimental to durability. In view of substantial increases observed in tensile splitting strength, ductility, durability, and confinement, it is suggested that fiber reinforced soil-cement might be applied in the construction of soil-cement liners for reservoirs and landfills.

Restrained shrinkage tests were carried out on ring specimens of concrete reinforced with polypropylene fibers. These fibers had a relatively improved modulus of elasticity and enhanced bond with portland cement matrix. To achieve uniform dispersion for the relatively high fiber content (2 percent volume fraction) employed, a conventional pan mixer was attached with a high-speed activator. It was observed that even after severe drying, no visible cracks (cracks wider than 0.01 mm) appeared on the polypropylene fiber reinforced specimen.