Quantitative description of the pull-out behavior of crimped yarns from cement matrix

The object of the present paper was to quantify the effect of crimping of a low modulus polymer yarn on the bonding with a cement paste matrix. Crimping of this kind has been evaluated within the context of optimizing the structure of woven fabric to obtain a strain hardening composite. The concept applied here was based on existing models developed for straight yarns. These models resolve between two stages: the elastic stage (adhesion) and the slip stage (friction). A similarity in the shape of the pull-out load versus slip curve of straight yarns and crimped yarns was found, suggesting that a modeling approach for straight fibers, which consider adhesional and frictional resistance, can also be applied for the crimped yarns. The effect of the yarn crimping on calculated adhesional and frictional components, τ_au and τ_fu, was estimated, showing a marked increase with yarn density for both types of bonding mechanisms. These values are considered as equivalent values since their physical significance is limited. Empirical linear correlations was found between the equivalent adhesional and frictional bond strengths and the crimp density. These empirical relations were combined with equation describing the shape of pull-out curves, to calculate the pull-out curves of the crimped yarns. The agreement with the experimental curve was reasonably good.