CARBON SPHERES AS POSSIBLE MICRO-REINFORCEMENT OF CEMENT- BASED COMPOSITES Jan M. SKOWROēSKI 1 , Agnieszka ŚLOSARCZYK 2 PoznaĔ University of Technology, 1 Institute of Chemistry and Technical Electrochemistry, ul. Piotrowo 3, 60-965 PoznaĔ, Poland, e-mail: jan.skowronski@put.poznan.pl 2 Institute of Structural Engineering, ul. Piotrowo 5, 60-965 PoznaĔ, Poland, e-mail: agnieszka.slosarczyk@put.poznan.pl ABSTRACT In this research, the influence of carbon spheres additive on mechanical properties of cement-carbon composites, such as flexural strength, flexural toughness and compression strength, were investigated. Carbon spheres were added to cement mortars in amount of 0.5 wt. %. Chemical treatment in hot nitric acid was applied in order to improve interfacial bonding between carbon fibres and cement mortar. It was found that the addition of carbon spheres in the amount of 0.5 wt.% to cement matrix improved its flexural toughness. The best results were obtained for cement composites subjected to chemical treatment. As proved by electrochemical measurements, during modification of carbons in nitric acid the functional groups, such as carboxyl, hydroxyl or phenol, were build up on the surface of carbon spheres. Consequently, the bonding between carbon fibres and cement matrix was enhanced. Keywords Carbon spheres; cement-carbon composites, chemical treatment, cyclic voltammetry; mechanical properties. INTRODUCTION While PAN- or pitch-based carbon fibres used as reinforcement in cement-carbon composites have been advanced over the past twenty years [1-5], no attention has been devoted to cement composites modified with carbon spheres (CS) obtained from mesophase pitch. Carbon spheres are commonly used as precursor to obtain high-performance carbon materials or active carbons with high developed specific surface, among others as the components of carbon/carbon composites [6,7]. Carbon spheres are composed of microcrystallites, in which numerous spaces are created during solvent extraction. Due to their specific structural properties, among others spherical shape, carbon spheres enable the formation of isotropic properties of composite. This article focuses on the improvement of mechanical properties, especially flexural toughness, of cement matrix due to the addition of carbon spheres. Carbon spheres were chemically oxidised in nitric acid at the temperature of 12Ń°C in order to enhance the interfacial bonding between carbons and cement paste. Cyclic voltammetry measurements were applied to evaluate the surface properties of unmodified and modified carbon spheres.