BOND PROPERTIES OF CARBON-FIBERS IN CEMENTITIOUS MATRIX

The interfacial bond properties of two carbon fibers, having diameters of 10 mu m and 46 mu m, were tested for cement matrices of different water-to-binder (w/b) ratios and silica-fume contents. The pullout tes t was conducted using a special technique that prevented the brittle f iber from breaking during specimen handling. An environmental scanning electron microscope (ESEM) was used to determine the nature of the fi ber-matrix bond. The results show a friction-based bond mechanism for the fiber of 10 mu m, 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 t he 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 affec ted by the presence of silica fume.