International Concrete Abstracts Portal

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.

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.