International Concrete Abstracts Portal

Experiments were performed on concrete specimens reinforced randomly with polypropylene fibers. To obtain the true properties of the fibers, their tensile stress-strain diagram was obtained through tests. The fibers used had a tensile strength of 2800 kgf/cm 2 (40,000 psi), a failure strain of about 11 percent, and a modulus of elasticity of 2.55 X 10 5 kgf/cm 2 (3,642,857 psi). Then, the 7- and 28-day polypropylene fiber reinforced concrete (PFRC) samples with 0, 0.5, 1.0, 1.5, 2.0, and 2.5 percent by volume of fibers were tested in splitting tensile and compressive strength tests, and the tensile strength, maximum tensile strain, and compressive strength versus percentage by volume of fibers diagrams were plotted. The results show that compressive strength did not change significantly, but tensile strength had an increase of about 80 percent. Significant improvement in ductility was also achieved. The tests also showed that the best improvement was obtained at an optimum percentage by volume of fibers of about 1.5 percent.

Relatively low-cost and energy-efficient materials with desirable short-term mechanical properties can be constructed using cellulose fibers as cement reinforcement. There are, however, concerns regarding the long-term performance of cellulose fiber reinforced cement composites; some cellulose fibers tend to disintegrate in the alkaline environment of cement. The growth of cement hydration products within the hollow cellulose fibers may also lead to excessive fiber-to-matrix bonding and brittle failure after exposure to natural weathering. This paper presents the results of an experimental study concerned with the long-term performance of cellulose fiber reinforced cement composites. Cellulose fiber reinforced cement composites were investigated, using accelerated weathering conditions representing repeated wetting and drying of materials in outside exposure conditions. The cement composites considered in this investigation incorporated 2 percent mass fractions of kraft pulp. Comprehensive replicated flexural test data were generated for various test ages at different wetting-drying cycles and were analyzed statistically. The analysis of variance and multiple comparison techniques were employed to derive reliable conclusions regarding the effect of accelerated wetting-drying cycles on flexural strength and toughness characteristics of cellulose fiber reinforced cement composites. The results generated in this study showed, at 95 percent level of confidence, that accelerated aging under repeated wetting-drying cycles had negligible effects on flexural strength, but led to reduced toughness and embrittlement of cellulose fiber reinforced cement composites.

Describes improvements in the performance characteristics of cements due to carbon fiber reinforcement. In particular, the structure, physical properties, mechanical behavior, and durability aspects of carbon-cement composites using pitch-based fibers are discussed. The various possible applications of these composites in structural and nonstructural applications are enumerated and future research needs to be identified.

Carbon fiber reinforced cement composite (CFRC) has outstanding advantages in its dynamic characteristics and durability. Among other characteristics, it has a flexural strength three to four times higher than that of ordinary concrete. Taking advantage of these characteristics of CFRC in designing curtain walls, the manufacturing of thin, lightweight curtain walls becomes possible. This paper describes experimental studies conducted using CFRC specimens to examine the effects of mixing and placing conditions upon the flexural strength of CFRC, scale effects, and the fatigue of CFRC subject to repetitive loads. Furthermore, based on the results of these experiments, allowable bending stress in designing curtain walls was determined and its authenticity verified by having a full-scale composite panel undergo a wind resistance test. Several examples of CFRC used as curtain walls are also introduced.

The effectiveness of steel fibers as shear reinforcement to replace and/or augment conventional stirrups in concrete beams with flexural reinforcement has been demonstrated by Batson, et al. (1972), J. Craig (1984), and other researchers. The current thinking within ACI Committee 544 is to adjust the limiting values of the empirical equations for shear design in ACI 318. However, a rational basis for the design or analysis of steel fibers as shear reinforcement has not been developed. Possible approaches can be based on the plasticity of concrete, Chen (1978) and Nielsen (1984); and limit state analysis and the modified compression field theory, Marti (1986) and Collins (1984). Test data for flexural reinforced concrete beams using steel fibers as the shear reinforcement match the lower bound solution for the shear strength as a function of the shear span-depth ratio, based on limit states analysis of concrete by Nielsen and Braestrup (1978) and Kemp and Al-Safi (1981). The test data agree well with the theoretical predicted strength, assuming the steel fiber concrete is rigid-plastic with a modified Coulomb failure criterion for the yield condition, no tensile strength, and the compressive strength is the effective compressive strength. The plasticity assumption for steel fiber reinforced concrete is supported by research reported on its torsional strength by Narayanan et al. (1979 and 1983), in which the torsional strength was best predicted by the Nadai's "sand heap" plastic model for a variety of steel fiber volumes in the concrete. The random distribution of the steel fibers at relatively close spacing provides a very ductile mode of failure that is in good agreement with strength theories based on plasticity theory and limit states. The initial test results suggest that a rational design procedure for the shear strength of steel fiber concrete can be based on a modified compression field theory that will be accepted by design engineers. This paper briefly reviews the current thinking on shear design of beams using steel fibers as the shear reinforcement, plastic material response of steel fiber concrete, and test data that agrees with the plasticity properties and limit theorems proposed by Nielsen and Braestrup and by Kemp and Al-Safi for reinforced and prestressed concrete beams without shear reinforcement.