Mechanical Properties of SiO2-Coated Carbon Fiber-Reinforced Mortar Composites with Different Fiber Lengths and Fiber Volume Fractions

In the present study, SiO2 particles were coated on the surface of carbon fibers by means of chemical reaction of silane coupling agent (glycidoxypropyl trimethoxysilane, GPTMS) and colloidal SiO2 sol to improve the interfacial bonding force between fibers and matrix in cement matrix. The surface of the modified carbon fibers was confirmed through a scanning electron microscope (SEM). The mechanical properties of SiO2-coated carbon fiber mortar and uncoated carbon fiber mortar with different fiber lengths (6 mm and 12 mm) and fiber volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) were compared and analyzed. The experimental results show that the flow values of the carbon fiber mortar were greatly disadvantageous in terms of fluidity due to the nonhydrophilicity of fibers and fiber balls, and the unit weight decreased significantly as the fiber volume fractions increased. However, the air content increased more or less. In addition, regardless of whether the fibers were coated, the compressive strength of carbon fiber-reinforced mortar (CFRM) composite specimens tended to gradually decrease as the fiber volume fractions increased. On the other hand, in case of the SiO2-coated CFRM composite specimens, the flexural strength was significantly increased compared to uncoated CFRM composite specimens and plain mortar specimens, and the highest flexural strength was obtained at 12 mm and 1.5%, particularly. It can be seen that the new carbon fiber surface modification method employed in this study was very effective in enhancing the flexural strength as cement-reinforcing materials.