The Chemically Modified Vapour Grown Carbon Fibres as Micro-reinforcement in Cement-Carbon Composites

摘要

This research discusses the influence of amount and chemical treatment of very short vapour grown carbon fibres (VGCFs) on mechanical properties of cement-carbon composite, such as flexural strength, flexural toughness and compression strength. VGCFs were added to cement mortars in amount of 1, 2 and 3 vol. %. For improving mechanical properties of VGCF-reinforced composites, different surface treatments such as oxidation with air, nitric acid and oxygen plasma can be used. By enrichment of the VGCFs with functional groups, especially those containing oxygen, on the VGCF surface, the bonding between matrix and VGCFs is enhanced. In presented research VGCFs were chemically oxidised by nitric acid treatment at 120oC, while cyclic voltammetry, BET and FTIR measurements were applied to evaluate the surface properties of unmodified and modified carbon fibres. It was found that the best parameters of cement – carbon composite, especially its flexural toughness, were obtained for mortars modified with the 0.2 vol.% additive of VGCFs. The additional improvement of flexural toughness was obtained for mortars modified with carbon fibres subjected to nitric acid treatment. As proved by electrochemical and FTIR measurements, during nitric acid treatment functional groups, such as carboxyl, hydroxyl, were build up on carbon fibres surface. Consequently, the bonding between carbon fibres and cement matrix was enhanced. The analysis of stress – deflection curves and SEM spectra indicates that very short carbon fibres act as micro-bridges across micro-cracks and pores and cause the increase of flexural parameters. Moreover presented results shown that unlike to long and aligned carbon fibres the influence of very short vapour grown carbon fibres on the mechanical properties of cement composite appears before the top of the first crack in the elastic range.