The nature of bonding between monofilament polyethylene yarns and cement matrices

The bond performance of monofilament polyethylene yarns embedded in a cement matrix was studied to resolve yarn-matrix interaction mechanisms. Pull-out tests were carried out to determine the mechanical characteristics of bonding. Pre-tensioning of the yarns was applied prior to the production of the composite specimens. The tension loads were removed at different stages, during the hardening process and at a later stage. Two types of specimens were designed for a pull-out test: (i) the yarn is fully embedded in the specimen and extends at the rear side with a tail; (ii) the yarn is fully embedded but has no tail. The microstructure of the yarn's groove in the matrix and the yarn's surface prior to and after the pull-out were examined by a scanning electron microscope. It was found that the pull-out resistance of the straight yarn was controlled by frictional as well as anchoring effects. When the pulled yarn length was equal to the matrix length, the pull-out resistance was found to decrease with increasing the initial tension, due to Poisson's effect on the yarn-matrix interaction. When the pulled yarn was longer than the embedded length, the yarn's tail was found to considerably improve the pull out resistance due to wedging induced by the Poisson effect.