International Concrete Abstracts Portal

The fabrication, properties, and application of carbon fiber reinforced cement (CFRC) product made of coal tar pitch-based high-performance carbon fiber are presented. The experiments were conducted by mixing the chopped carbon fiber strands with cement and sand to obtain CFRC. The mixing test results revealed that this type of carbon fiber disperses quickly and uniformly in ordinary mortar. No special type of mixer is required. To optimize the characteristics of CFRC, experimental analysis was conducted on batches made in a mortar mixer regarding the fiber properties and mix proportion. The relationships of these parameters to the mechanical properties were examined. It was revealed that the parameters determining the apparent viscosity F (flow index) of CFRC slurries are fiber diameter í1, filament number n, specific surface area S, and fiber volume fraction Vf. It was also revealed that the parameters determining the strength of the hardened body were fiber tensile strength TS and Vf. The flexural strength of the 20 mm thick CFRC is about 3 to 4 times greater than that of plain mortar. This CFRC is also stronger and more durable than other FRC under the same conditions. High productivity, light weight, and weatherability characterize this new CFRC. These characteristics being appreciated, precast CFRC products have been increasingly used in construction in Japan. Some detailed descriptions of the practical applications are also made.

Researchers have developed a new form of fibrous polyethylene to replace asbestos fibers in asbestos-cement composites. This very fine, short, molecularly oriented polyethylene pulp was tested in cement at various levels of incorporation and in combination with other fibers. Most of the initial investigation was focused on the pure cement matrix normally used for asbestos-cement products; however, this paper includes preliminary work with cast cement-mortar matrixes. The polyethylene pulp can be used effectively for reinforcing cement. Flexural strengths can be increased by more than 200 percent. The pulp induces excellent ductility. Accelerated aging studies indicate that the pulp is durable in alkaline cement matrixes.

A cementitious matrix capable of dispersing fibers using conventional mixing techniques was developed. The effects of reinforcing this matrix with different volume fractions (0 to 2 percent) of aramid fibers ranging in length from 1/8 to 1/2 in. (3 to 12.7 mm) on the composite material performance in the fresh and hardened states were assessed experimentally. The effects of matrix mix proportions on the fibrous material properties were also investigated. The test data generated in this study indicated that improvements in strength and toughness characteristics of cementitious materials can be achieved through aramid fiber reinforcement, with no need to use specialized manufacturing techniques.

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.

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.