Graded fiber design and concrete reinforced therewith

A method for improving the crack resistance of concrete comprising the steps of:

• adding to a selected amount of concrete, a mixture of at least a first, second and third plurality of fibers, each of said first, second and third plurality of fibers having deniers ranging from about 15 to about 3000 and lengths ranging from about 1/16 to about 1 inch;
• at least three pluralities of fibers having deniers different from each other such that one plurality of fibers has a denier at the lower end of the range, one plurality has a denier at the upper end of the range and one plurality has a denier in the middle of the range;
• at least three pluralities of fibers having lengths different from each other such that one plurality of fibers has a length at the lower end of the range, one plurality has a length at the upper end of the range and one plurality has a length in the middle of the range;
• and
• mixing said components sufficiently to distribute said fibers uniformly throughout said concrete, said fibers being made of synthetic material, whereby initiation of cracking of the concrete is inhibited and flexural properties of the concrete are improved as compared to concrete reinforced by the addition of single length fibers.

A method for inhibiting the initiation of cracking in concrete during curing stages comprising the steps of:

• adding to a selected amount of concrete, a mixture of at least a first, second and third plurality of fibers, each of said first, second, and third plurality of fibers having deniers ranging from about 15 to 3000 and lengths ranging from about 1/16 to about 1 inch:
• at least three pluralities of fibers having deniers different from each other such that one plurality of fibers has a denier at the lower end of the range, one plurality has a denier at the upper end of the range and one plurality has a denier in the middle of the range;
• at least three pluralities of fibers having lengths different from each other such that one plurality of fibers has a length at the lower end of the range, one plurality has a length at the upper end of the range and one plurality has a length in the middle of the range;
• and
• mixing said components sufficiently to distribute said fibers uniformly throughout said concrete, said fibers being made of synthetic material.

Concrete consisting essentially of:

• concrete;
• and
• from about 0.025 to 1 percent by volume of a graded, synthetic fiber mixture, said graded fiber mixture containing, prior to its addition to said concrete, at least a first, second, and third plurality of fibers, each of said first, second and third plurality of fibers having deniers ranging from about 15 to 3000 and lengths ranging from about 1/16 to 3 inches;
• wherein said first, second and third plurality of fibers have deniers different from each other;
• and
• wherein at least three pluralities of fibers have lengths different from each other;
• whereby initiation of cracking of the concrete is inhibited and flexural properties of the concrete are improved as compared to concrete reinforced by the addition of single length fibers.

Concrete having improved crack resistance consisting essentially of:

• concrete;
• and
• from about 0.025 to 1 percent by volume of a synthetic fiber mixture, having deniers ranging from about 15 to about 3000 and lengths ranging from about 1/16 to about 3 inches, graded to provide a plurality of different lengths, widths, thicknesses, deniers, fibrillation, cross-sections or aspects ratios, prior to its addition to said concrete, so as to accommodate the mortar factions within said concrete and provide a continuous distribution of fibers therein;
• whereby initiation of cracking of the concrete is inhibited as compared to concrete reinforced by the addition of single length fibers.