Hybrid fiber composite material with OSA mechanical load-bearing capacity after thermal heating

Fibre-reinforced concrete is now booming in the construction industry since it has various advantages over non-reinforced concrete. Important is the possibility of fibre concrete to withstand external mechanical loading after the first visible crack formation. Such possibility does not exist for non-reinforced concrete because it collapses. Competing with steel fibres, we have novel composite fibres (CF). In the single CF, glass or carbon or basalt etc. short microfibers are glued together with polymer resin, and in the hybrid composite fibre (HCF) combination of at least two or more short fibres of the following types — glass, carbon, basalt, etc. are glued together. In the present research, concrete with hybrid (Basalt-Carbon/Epoxy, Basalt-Glass/Epoxy, and Carbon Glass/Epoxy) fibres is being investigated and studied for its possibility to withstand thermal and mechanical loading. Hybrid fibres are prepared from yarns twisted together (Basalt-Carbon, Basalt-Glass, and Carbon-Glass) impregnating them with epoxy resin (Epoxy/hardener ratio — 3:1). Single fibre weight was the same for all HF. The concrete mixture contains Oil Shale Ash (OSA) in the ratio of 0%, 15%, and 35% to the cement, to analyse the strength of the obtained fibre concrete. In our investigated concrete mixes cement was replaced by OSA that came from Auvere (Estonia) thermal power plant. Pull-out samples were prepared to test the binding strength between the fibre and the concrete material. One set of samples was kept aside, and the other is subjected to heating for 100 °C, 200 °C, and 300 °C along with the fibres in the oven. After testing, the results were compared of the heated and non-heated specimens, as well as different concentrations of OSA. The single fibre pull-out tests were realized so that strength is reduced in variation of the concrete mixture and thermal load. Pulling–out displacement curves were obtained and analysed.