Bond Properties of Carbon Fibers in Cementitious Matrix

Abstract

The interfacial bond properties of two carbon fibers, having diameters of 10 μm and 46 μm, were tested for cement matrices of different water-to-binder ( w /b) ratios and silica-fume contents. The pullout test was conducted using a special technique that prevented the brittle fiber from breaking during specimen handling. An environmental scanning electron microscope (ESEM) was used to determine the nature of the fiber-matrix bond. The results show a friction-based bond mechanism for the fiber of 10 μm, with a bond strength of 0.5 MPa for the high w /b matrix and without silica fume. Densifying the matrix by lowering the w /b ratio or by using silica fume improved the bond by 50–100%. For the larger-diameter fiber, silica fume had a very strong effect on the bond (an increase of 370–670%). It appears that long grooves along the fiber surface creates a mechanical anchorage, which is strongly affected by the presence of silica fume.