International Concrete Abstracts Portal

Strength properties of steel fiber reinforced concrete and plain concrete specimens subjected to normal atmospheric exposure and accelerated cyclic testing in marine environment were examined. The concrete mix design consisted of cement:sand:aggregate in ratio of 1:1.96:3.01 with water-cement ratio of 0.6. The steel fibers, 10 mm in length, were added in volume of 0.0, 0.6, and 1.2 percent of the mix. Strength properties--compressive, flexural, and tensile strength of the concrete specimens containing steel fibers--showed considerable improvement over those obtained in the plain concrete exposed to the normal atmospheric condition. Both steel fiber reinforced and plain concrete specimens subjected to accelerated cyclic testing at 60 C, 24-hr cycle in marine environment, showed that the addition of fibers provided considerable improvement in strength properties. However, corrosion of the fibers was observed at or near the surface, and continued to worsen after 20 cycles. Specimens with 1.2 volume percent of steel fibers exhibited the largest increase in compressive and flexural strength in both test conditions, normal atmospheric and accelerated cyclic testing.

Treatments of AR glass fibers in silica fume slurry prior to their incorporation in cementitious matrix was found to be an effective means for improving the durability performance of GFRC composites. The improvement was found to be dependent on the extent of penetration of the silica fume particles into the spaces between the filaments during the slurry treatment. In a glass fiber fabric, heavily coated with polymer, the penetration was hindered and therefore the advantage offered by the silica fume treatment was not as great as in continuous glass fiber strands that were more readily wetted by the slurry.

Traditionally, the first cracking strain of plain matrix is used as the material property in the fiber reinforced cement-based composites. It is used to indicate the tensile strength, and thus termination of the contribution of the matrix phase. In the presence of high volume fraction of fibers, formation of the first crack does not necessarily lead to the fracture instability; thus, matrix is able to carry increasing loads. The strength of the matrix is thus dependent on the type, volume fraction, bond, and strength of the fibers. Paper investigates the tensile stress-strain response of cement paste in the presence of glass fibers. A test procedure is described that can characterize the toughening effect of various fiber types on the matrix properties.

Fibers are added to concrete to improve several of its properties. The ability of polypropylene fibers to modify different characteristics of concrete is controversial. This paper presents results on the influence of adding polypropylene fibers (0.1 to 0.2 percent by volume) on mortar permeability and plastic shrinkage. The influence of adding polypropylene fibers on the early stages of shrinkage is studied with 120 x 15 x 3 cm specimens. These were fabricated in mortar and then held in a chamber with controlled temperature and ventilation. The specimens have a special geometry to enable the shrinkage measurement in the plastic state, and the influence of this on mortar cracking. The variables studied were: water-cement ratio, sand-cement ratio, and fiber content. In addition, the ability of fiber concrete to absorb water and its permeability to CO2 were tested. Water absorption was measured in accordance with French standard NFB 10.502. Carbonation was studied by introducing fiber mortar specimens in a chamber saturated with CO2 and comparing the results with natural carbonation. Results show that the addition of fiber reduces plastic shrinkage when compared with the same type of mortar without fibers. Concerning water absorption, it is reduced when water-cement ratio is about 0.5; however, when the water-cement ratio is higher than 0.5, this behavior is reversed and the fiber mortar is more water absorbent. Accelerated and natural carbonation show that CO2 diffusion increases in mortar with the highest amount of fibers.

A brief review of the literature on cellulose fiber reinforced cement is presented, followed by the results of an experimental study concerned with the effects of mechanical and chemical pulps on the performance characteristics of neat cement paste in the fresh and hardened states. The mix proportions and manufacturing techniques used in this study for the production of cellulose-cement composites are reviewed. The air content, setting time, and drop in workability with time are compared for plain cementitious materials and those reinforced with 1 and 2 percent mass fractions of mechanical and chemical pulps. The flexural and compressive strength and toughness characteristics, impact resistance, specific gravity, and water absorption capacity of plain and fibrous materials are also compared. Effects of moisture content on the flexural performance of plain cementitious materials and those reinforced with mechanical pulp are discussed.