International Concrete Abstracts Portal

Describes the investigation of a new range of cellulose fibers suited to the reinforcement of a portland cement matrix. This investigation indicated that fibers selectively derived from high-density summerwood are better suited for reinforcement than is the unmodified pulp that contains a large measure of fibers derived from springwood as well as summerwood. Another cellulose fiber material, termed expanded fiber because of its finely fibrillated microstructure, was indicated to have potential as a processing aid. Expanded fiber displayed excellent suspending and retention properties and imparted relatively high uncracked strength to finished composites. Overall, substantial performance differences were observed comparing, tests on wet versus dry specimens and the long-term durability was not evaluated. Despite these limitations, flexural stress/strain performance of the cellulose reinforced composites compared quite well to asbestos and glass fiber reinforced composites. The cellulose composites had substantially more ductility than asbestos cement; in this regard, the load-deflection curve was similar to glass reinforced cement.

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.

Thin-walled, nonload-bearing exterior building facade panels of glass fiber reinforced concrete (GFRC) are manufactured by the spray-up process. Controlled factory conditions with strict attention to quality control are essential to help assure manufacture of a high-quality product. Furthermore, careful attention to installation and erection procedures cannot be overlooked. Paper describes the authors' experiences during their involvement in several major GFRC facade installations. Observations made during successful GFRC panel applications, and lessons learned in evaluation of GFRC facade failures, have formed the basis for development of an effective Quality Control/Quality Assurance (QC/QA) program that has been successfully implemented. Paper addresses QC/QA aspects of panel manufacture and installation that go beyond guidelines given in the PCI Recommended Practice. Methodologies presented in this paper will be a valuable tool for owners, designers, manufacturers, and contractors participating in the manufacture and installation of GFRC facades.