Study of the pull-out test of multifilament yarns embedded in cementitious matrix

Abstract

In order to understand the impregnation mechanism of a yarn by a cementitious matrix and its influence on the mechanical properties of a yarn/cement composite, pull-out tests have been performed on samples of yarn/cement. Two embedded lengths for the yarn and different rheological and mechanical properties for the matrix were tested. Two pull-out modes were distinguished according to the compressive strength of matrices. For matrices with a compressive strength between 60 and 70 MPa the pull-out mode is characterized by a behaviour close to the tensile behaviour of the yarn, with maximum load values reaching approximately 60% of the tensile maximum load because of filaments damages. For matrices with compressive strength inferior to 60 MPa, the pull-out mode exhibits a residual phase linked to a slippage and an extraction of a variable number of filaments, with lower maximum load values than the first pull-out mode. After pull-out test, for some samples with filaments extraction, an innovative method based on a double impregnation with resin enables to visualize the yarn/matrix interface and identify the level of impregnation of the filaments by using confocal microscopy. It is concluded that this level of impregnation has a direct influence on the mechanical behaviour of the embedded yarn, except for the slippage and extraction phase, but the rheological properties of the matrix has no significant influence on this impregnation.