Agnieszka Ślosarczyk

Synthesis and characterization of silica aerogel-based nanocomposites with carbon fibers and carbon nanotubes in hybrid system

In presented research the silica aerogel nanocomposites with carbon microfibers and nanofibers, as well as carbon microfibers/carbon nanotubes hybrid system were investigated. It was shown, that an important element of tailoring the properties of silica aerogel nanocomposite was the right choice of the type and the length of the carbon material. In case of carbon nanofibers with length of 20 nm, the applied amount of fibers was too low to keep the silica aerogel frame in monolith and resulted in obtaining the nanocomposite in form of granulate. Only longer fibers with length of 700 µm gave the monolith structure of silica aerogel nanocomposite. As a result of hybrid reinforcement, which enables reduction of cracking on micro and nano level, a monolith nanocomposite was received, which had very good structural parameters and low contraction during drying. All the received nanocomposites were characterized by good thermal resistance and all applied carbon materials did not deteriorate the high thermal resistance of silica aerogel.Graphical Abstract

The influence of non-metallic and metallic fibres on the mechanical properties of cement mortars

Compared to concrete, the compressive strength is not a very important property of cement mortar. It is very important that mortar forms a complete, strong, and durable bond with the building material elements, because it is used as an adhesive and sealant material. The physical and mechanical properties of cement mortar, especially flexural strength, toughness, tensile strength, reduction of plastic as well as drying shrinkage, can be enhanced by the use of randomly dispersed fibres, such as steel, carbon or polymer. In the present research there were investigated cement mortars modified with randomly dispersed polypropylene and steel fibres in different volume fraction used both separately and in a hybrid system. The conducted research proved that the low modulus polypropylene fibres with good flexibility added to cement matrix resulted in good properties of fresh mortar and caused the reduction of early age cracking. The beneficial effects of flexible fibres could be attributed to their high aspect ratio and increased fibre availability at a given volume fraction due to their low density. Because of low stiffness, these fibres are particularly effective in controlling the propagation of micro-cracks. It was found that the hybrid combination of metallic and nonmetallic fibres can offer potential advantages in improving cement matrix properties, such as the ultimate strength and toughness of composites.

Carbon Spheres as Possible Micro-Reinforcement of Cement-Based Composites

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.