Investigation of different types of fibers to strengthen cement paste, mortar and concrete
The development of fiber reinforced concrete is for time being in an interesting promising stage. This report is a kind of state of the art statement on new directions in fiber research. Steel fiber reinforcement has been used to control and reduce crack widths in ordinary reinforced concrete structures. Now a development has started to produce structures of concrete reinforced only with steel fibers in amounts of 100 kg/m3 concrete. Appropriate codes are under development and necessary test methods used, evaluated and discussed. Full scale tests have been performed. Slabs with free span and size 6x6m have been constructed. Savings in extensive work with ordinary reinforcement are obtained. The development is just on its start.
The development of nano technique has also influenced the concrete industry. Carbon nanotubes (nanofibers) with 10-100 nm diameter and lengths of μm to some mm up to several cm are now available. The price is very high, but if extensive use can be found for the nanotubes the price will fall dramatically. The nanofibers are extremely strong and stiff, but thanks to their high aspect ration (length/diameter) they are flexible like strings. They have very good electric and heat conductive properties. Concrete with carbon nanotubes can obtain piezoresistivity enabling strain registration. Steady new properties of the nanotubes are found. The research on carbon nanotubes in concrete is just in starting phase. There has to be a follow up of controlling concrete structure on nano level to avoid porosity, disturbing bond of the tiny nanofibers. Therefore the report presents an overview of concrete technology and the necessary provisions to be able to use carbon nanofibers in cementitious matrix. It is essential to investigate the carbon nanotube influence on human health and the recirculation of the fibers and the final deposition parallel with the application research. A new asbestos disaster has to be avoided.