Synthetic fibers and cementitious systems including same

Abstract

The present invention discloses novel fibers for use as secondary reinforcement materials in cementitious composites, which fibers are effective in preventing cracking far better than prior art fibers. Also disclosed are methods of producing the fibers and methods for producing cementitious composite containing the fibers.

Description

[0001] This application is a Continuation application Ser. No. 09 / 958,320, filed Oct. 9, 2001, which is a National Stage Application of PCT / US00 / 08168, filed Mar. 28, 2000, which is a Non-Provisional of U.S. Ser. No. 60 / 128,126, filed Apr. 7, 1999.FIELD AND BACKGROUND OF THE INVENTION [0002] The present invention relates to specific fibers suited for use as secondary reinforcement materials of cementitious matrices in cementitious composites and, more particularly, to acrylic fibers, melt spun synthetic fibers and precursor low orientation nylon fibers for use as secondary reinforcement materials in cementitious composites. The invention further relates to methods [0003] More particularly, the present invention relates to improvement of the efficiency of short cut acrylic fibers for reinforcement of cementitious composites via adjustment of their friction and surface tension characteristics to obtain superior fibers dispersion in a cementitious matrix and greater reinforcement and c...

AI Technical Summary

Benefits of technology

[0055] According to still further features in the described preferred embodiments the upgraded fibers acquire superior basic hydrolysis resistance.

[0062] According to still further features in the described preferred embodiments the fibers are coated with a typical spin finish imparting lower interfiber cohesion by increasing kinematic viscosity to at least 150 cstokes and surface tension to at least 60 dynes / cm.

[0064] According to still further features in the described preferred embodiments the fibers are characterized by superior plastic cracking inhibition capacity while maintaining higher slump values relative to standard fibers for concrete and cementitious system reinforcement such that 400 grams of fibers per cubic meter of concrete reduces the degree of cracking of a cementitious matrix in the concrete relative to a non-reinforced equivalent cementitious matrix by more than 80%, while reducing the slump of the reinforced concrete to less than 15%.

[0065] According to still further features in the described preferred embodiments the fibers are characterized by superior plastic cracking inhibition capacity while maintaining higher slump values relative to standard fibers for concrete and cementitious system reinforcement such that 400 grams of fibers per cubic meter of concrete reduces a degree of cracking of a cementitious matrix in the concrete relative to a non-reinforced cementitious matrix by more than 90%, while reducing the slump of the reinforced concrete to less than 9%.

Problems solved by technology

As is well known in the art, cementitious composites, such as concrete, are prone to self-induced cracking, as such composites are brittle by nature.

Thus, concrete fails in tension by progressive crack development.

Plastic shrinkage cracking of the concrete occurs when the rate of water evaporation exceeds the rate of water displacement.

As mentioned above, these cracks, which are formed while the concrete mix settles, affect the strength and durability of the concrete during service.

However, as watering concrete products while hardening does not completely eliminate microcracks and cracks formation and calls for special care, the search for concrete additives which reduce cracks formation has begun.

Thus, nylon fibers assist in the prevention of microcracks during settling of concrete, which microcracks form flaws which, long after settling and during service, tend to develop into bigger cracks and fractions, which weaken the concrete and reduce its durability.

This prior art patent does not teach the use of low orientation precursor nylon or of acrylic fibers.

However, according to the mechanical behavior models for fiber reinforced concrete, the fibers discontinuously distributed in the cement system contribute to its load carrying capacity via load transformation to the fibers by shear deformation at the fiber / matrix interface.

The failure in cementitious systems is typically initiated by tensile fracture of the matrix that yields cracks propagating throughout the system.

Use of nylon, acrylic and polyvinyl alcohol fibers is taught by Goldfine's U.S. Pat. No. 3,645,961 in order to meet these criteria, however this patent does not teach any lubrication or surface treatment in order to improve surface properties of fiber.

Techniques for improvement of fibers mixability in the concrete by premoisturizing are taught by WO83 / 00324 but these teachings are limited to olefinic fibers.