New visualization method to characterize the impregnation of a multifilament yarn in a cement matrix

Composites of textile structure embedded in concrete matrix have a complex mechanical behaviour because it depends mainly on the bonds between the textile and the matrix. Those bonds cannot be controlled because they are determined by the impregnation degree of the yarn by the matrix, which is highly irregular in the cross section but also along the yarn. To quantify the impregnation degree of the yarn, a new visualization method was set up, using a double resin impregnation technique followed by confocal microscopy observations. Pull-out tests were performed on several samples with different matrices and different embedded lengths, before resin impregnation and observation. The physical parameters of the impregnation of the yarn were then linked to the pull-out mechanical parameters. The results show that the maximum load is directly linked to the number of filaments that are fully impregnated by the matrix, and this number depends on the composition of the matrix. The length and the shape of the filaments bundle pulled out without failing during the test were also determined and linked to the mechanical behaviour of the composite.