International Concrete Abstracts Portal

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.

Paper presents the results of an experimental investigation to determine the flexural fatigue strength of concrete reinforced with collated fibrillated polypropylene fibers. The performance of fresh concrete and the elastic and mechanical properties of hardened concrete are compared for concretes with and without fibers. The test program included 1) flexural fatigue and endurance limit; 2) static flexural strength including load-deflection curve, determination of first-crack load, and toughness index; 3) compressive strength; 4) static modulus; 5) pulse velocity; 6) unit weight, workability, and finishability of fresh concrete. The complete series of tests was run for three concentrations of fibers. Special care was taken to insure consistency with cement, aggregates, admixtures, procedure, and mix temperatures. There was no "balling" or tangling of the fibers during mixing and placing. Fiber reinforced concretes had better finishability and were easy to work with even at higher fiber concentrations. Due to the addition of fibers, the ductility and the post-crack energy absorption capacity was increased. There was a slight increase in the static flexural strength and a moderate increase in the flexural fatigue strength. When compared to plain concrete, there was a positive improvement in the endurance limit (for 2 million cycles).

By lightening the weight of the building material, the vertical load can be decreased. This minimizes the quantity of material required for earthquake resistance. Furthermore, it increases on-site productivity. The objective of this study is to develop lightweight, durable L-FRC, and to apply it to the exterior walls of buildings. Structural design demands many performance specifications for the exterior walls--specific gravity, panel weight, flexural strength for maximum wind pressure, fireproofing, drying shrinkage, and freeze-thaw durability. The physical properties of L-FRC are produced by calcium-silicate-slag-type low alkaline cement, anti-alkali glass fiber, and a special chemical admixture that includes a superplasticizer, foaming agent, and other additives. The physical characteristics of L-FRC are obtained from laboratory tests, actual-size experiments, and construction work using L-FRC. The main results are: 1) The specific gravity is nearly 1.28, and the unit weight of the panel is 115 kg/mý (1.13 kN/mý) (7 days); 2) The flexural strength of specimens is 12.8 MPa (14 days) and that of full-scale panels is 8.80 MPa (28 days); 3) The compressive strength is 21.6 MPa (14 days); 4) L-FRC is officially recognized as a fireproof material; 5) The rate of drying shrinkage is less than 5 x 10-4 (180 days); 6) The durability factor is more than 90 percent. The physical characteristics of L-FRC were sufficiently greater than the specified standards for these characteristics. Therefore, exterior wall work can be satisfactory and successfully completed in a shorter period.

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.

Several types of failure mechanisms and fracture of fiber reinforced concrete (FRC) composites are discussed. These include: multiple fracture of the matrix prior to composite fracture; catastrophic failure of the composite immediately following matrix cracking due to inadequate reinforcing; fiber pullout following matrix cracking providing significant energy absorption with or without substantial strengthening of the matrix; and fracture of short fibers bridging the matrix crack without multiple fracture of the matrix. Aspects relating to the modeling of the two major causes for nonlinearities associated with fiber concrete composites, namely interfacial bond-slip and matrix softening, are also discussed. Analytical models available for predicting the tensile response of such composites are examined in light of the above mechanisms of failure.