POSSIBILITY OF CONCRETE STRUCTURES STRENGTHENING WITH CONTINUOUS CARBON FIBRES

V tem diplomskem delu smo predstavili uporabo kontinuiranih snopičev iz ogljikovih vlaken za ojačitev tankih betonskih plošč. Nosilnost in trajnost z vlakni ojačenih betonskih konstrukcijskih elementov je poleg lastnosti betona in vlaken odvisna predvsem od spoja med vlakni in betonsko matrico. V diplomski nalogi smo raziskali vpliv mikrosilike, superplastifikatorja in aeranta na izboljšanje spoja med ogljikovimi vlakni in cementnimi matricami. Ugotovili smo, da dodatek mikrosilike utrjuje prehodno cono med matrico in vlakni z zmanjšanjem poroznosti in porabo kristalov kalcijevega hidroksida. Dodatek superplastifikatorja je sicer izboljšal obdelovalnost sveže malte, vendar pa ni vplival na kvaliteto spoja. Zračni mehurčki, ki so se formirali v matrici v neposredni bližini zunanjih vlaken kot rezultat delovanja aeranta, so povzročili hrapavost prehodne cone in mehansko sidranje vlaken, kar je bistveno povečalo trenje med izvlekom vlaken. Z dodanim aerantom smo dosegli najvišjo izvlečno silo in s tem najkvalitetnejši spoj med uporabljenimi ogljikovimi vlakni in cementno matrico. V nadaljevanju smo prikazali možnosti uporabe vlaknaste ojačitve tankih prerezov v primerjavi s klasično ojačitvijo z jekleno armaturo. Po izvedenih upogibnih preizkusih se je izkazalo, da ima vlaknasta ojačitev številne prednosti pred konvencionalnimi ojačitvenimi materiali (jeklena armatura). Prednosti z vlakni ojačanih betonskih kompozitov so predvsem bistveno stanjšanje prereza (celo do 5-krat), majhna masa, možnost poljubnega oblikovanja elementov zaradi fleksibilnosti vlaken ter povečana duktilnost in žilavost. Glede na predstavljene rezultate z veliko tanjšim prerezom dosežemo enako ali celo višjo upogibno trdnost v primerjavi s klasično armiranimi betonskimi elementi.In this diploma thesis we presented the use of continouos carbon fibres for reinforcement of thin concrete slabs. Carrying capacity and sustainability of fibre reinforced concrete structural elements, in adittion to the properties of concrete and fibres depends primarily on the bond between fibre and concrete matrix. This diploma thesis investigates the influence of admixtures – silica fume, superplasticizer and air entraining agent – on the improvement of the bond strength between carbon fibre yarn and cementitious mortars. An overall analysis has shown that added silica fume strengthens interface transition zone by reducing its porosity and consumption of CH crystals. The addition of a superplasticizer increased the workability of fresh mortars, but the bond improvement was insignificant. Air bubbles formed inside the mortar mix as a result of added air entraining agent and the ones formed in the vicinity of the fibre yarn were found to provide mechanical anchoring for fibres leading to a significant increase in interface friction. Based on the resulting load-displacement curves, air entraining agent was found to be the most effective in improving the bond strength of the studied carbon-fibre reinforced cementitous composite. Additionaly we showed the possibility of using fibrous reinforcement of thin sections compared to a conventional reinforcement with a steel rebars. After carried out bending tests it was proved that the fibrous reinfocement had several advantages over conventional reinforcement materials (steel reinforcement). The adventages of fiber-reinforced concrete composites are primarily essential thiness of the section (up to 5 time), low mass, the possibility to arbitrary create elements because of the fiber flexibility and increased ductility and toughness. According to the results we reach the same or even higher flexural strength with a much thinner section compared to conventional reinforced concrete elements