Fibers having improved sinusoidal configuration, concrete reinforced therewith and related method

Concrete having improved crack resistance comprising:

• concrete;
• and
• from about 0.25 to about 5 percent by volume of sinusoidally configured thermoplastic fibers having a profile geometry defined by the equation, ##EQU27## wherein the amplitude a.sub.0 falls within a range of from about 0.1 d.sub.f to 2 d.sub.f and the period .lambda. falls within a range of from about 2 d.sub.f to 15 d.sub.f for fibers having a diameter d.sub.f of from about 0.5 to about 1 mm;
• the peak pull-out stress .sigma..sub.peak and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm .psi..sub.peak, both increase linearly with a deformity factor defined by the equation, ##EQU28## where .alpha.=0.8 and .beta.=-1, such that the peak pull-out stress is defined by the equation, ##EQU29## and the specific pull-out energy is defined by the equation, ##EQU30## said fiber additives having an optimum deformity,
• D.sub.optimum .apprxeq.(0.5 to 1)D.sub.critical,
• D.sub.critical being that deformity where the ultimate tensile strength of the fiber equals k.sub.1 D.sub.critical +C, and where loads are measured in N;
• energy in N-mm;
• length dimensions are in mm, and the values of k.sub.1, k.sub.2, C and C.sub.1 are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D.sub.critical.

A method for improving the bond slip performance of fibers in concrete comprising the steps of:

• adding to a selected amount of concrete, from about 0.25 to about 5 percent by volume, of sinusoidally configured thermoplastic fibers having a profile geometry defined by the equation, ##EQU31## wherein the amplitude a.sub.0 falls within a range of from about 0.1 d.sub.f to 2 d.sub.f and the period .lambda. falls within a range of from about 2 d.sub.f to 15 d.sub.f for fibers having a diameter d.sub.f of from about 0.5 to about 1 mm;
• the peak pull-out stress .sigma..sub.peak and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm .psi..sub.peak, both increase linearly with a deformity factor defined by the equation, ##EQU32## where .alpha.=0.8 and .beta.=-1, such that the peak pull-out stress is defined by the equation, ##EQU33## and the specific pull-out energy is defined by the equation, ##EQU34## said fiber additives having an optimum deformity,
• D.sub.optimum .apprxeq.(0.5 to 1)D.sub.critical,
• D.sub.critical being that deformity where the ultimate tensile strength of the fiber equals k.sub.1 D.sub.critical +C, and where loads are measured in N;
• energy in N-mm;
• length dimensions are in mm, and the values of k.sub.1, k.sub.2, C and C.sub.1 are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D.sub.critical ;
• and
• mixing said components sufficiently to distribute said fibers uniformly throughout said concrete, whereby energy absorption capability of concrete is improved as compared to concrete reinforced by fibers having a geometry other than said geometry.