International Concrete Abstracts Portal

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.

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.

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.