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.

The production of a polypropylene-reinforced cement material marketed as an alternative to asbestos-cement is outlined. Typical tensile stress-strain curves of a number of alternative materials are compared with asbestos-cement. The load-deflection characteristics of corrugated sheets made from nonasbestos materials are also presented and discussed. The nonasbestos materials are generally much less brittle than asbestos-cement, although they have a lower first-cracking strength. The pseudo-ductile behavior exhibited, with multiple cracking before the ultimate load is reached, means that permissible loads in service must not be based solely on ultimate loads but on cracking and possible deflection criteria. Less well-defined stresses arising during installation and from restrained moisture movements, which may crack the nonasbestos materials, are likely to be critical for the effective performance of new sheeting materials.

Flexural behavior of sandwich beams reinforced with thin layers of steel-fiber reinforced mortar was studied in this investigation. The effect of variations in thickness of the reinforced layer on the modulus of rupture, Young's modulus, and toughness of the member was investigated. This investigation considered one single specimen size with fiber reinforced mortar using one fiber geometry and content. Steel fibers with 0.6 x 0.3 mm cross section and 18 mm long were used. The specimens were cast in 100 x 100 x 350 mm molds. Eight series of sandwich beams with different thicknesses of the reinforced layer were tested. Experimental results indicated that sandwich beams can have strength and toughness comparable to fully fiber reinforced beams. The minimum thickness of the fiber reinforced layer required to impart ductile behavior to the sandwich beam was found to be about one-sixth of the beam depth.

Reports on the performance of semi-full scale pavement and overlay slabs under static loads. The test results of 60 mm SFRC pavement slabs having 0.5 percent fibers by volume have been presented under different loading and subgrade conditions. The test results of 100 mm PCC (plain cement concrete) pavement slab resting over a well-compacted subgrade have also been presented. The performance of 201 mm ferro-fibro overlay cast over 60mm cracked SFRC pavement has been reported and compared with a 40 mm SFRC overlay slab cast over 60 mm SFRC pavement. The experimental results of semi-full scale overlay and pavement slabs have been validated by infinite element analysis, a numerical technique developed for the analysis of unlimited domain of a layered system consisting of an overlay, pavement and subgrade of known properties. A comparative study has been presented with respect to Ferro-fibro and SFRC overlays.