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.

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.

Paper focuses on technological aspects of steel fiber reinforced concrete (SFRC) related to the workability improvement, unconventional compaction techniques, and low-pressure steam curing. Major research data are presented, along with suggestions for future applications of some of the techniques discussed.

Paper presents extensive data on the influence of steel fibers, alone or in conjunction with conventional stirrups, on shear transfer in concrete. The test specimens used in this study were of the push-off type with an initially uncracked or cracked shear plane. The main variables investigated include fiber volume, amount of stirrups, and the type of concrete. The results show that fibers enhance the ultimate shear transfer strength in both uncracked and precracked specimens. In the latter, the ultimate shear strength can be expressed on the basis of Coulomb's criterion. Fibers increase the residual shear transfer strength, and the shear transfer stiffness can be related to crack width. The shear transfer strength was generally lower in lightweight concrete than in normal-weight concrete.

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.