Behaviour of Tougher Coating with Concrete under Different Types of Loading

The beneficial effect of relatively thin tougher coating on the tensile strength and extensibility of concrete and other quasi-brittle materials was discovered by our ageing short-term static tests and explained by the energy absorption due to the deformation of the coating spanned over a critical crack. Afterwards, this approach was used in U.S.S.R. but another energy condition was considered, namely the improvement of the energy balance due to the debonding. Under this assumption, no improvement of mechanical properties of the brittle core can occur for the cases of the long-term static loading and of the repeated loading because the energy is consumed daring the whole loading process and is then not available at the moment of the sudden final failure. Nevertheless, our recent tests have confirmed our first statement, i.e. that the increase in tensile strength and in extensibility is similar like under short-term static loads. Therefore, the energy absorption due to the deformation of the coating prevails that-one due to the de-bonding. This conclusion is also in accordance with our theoretical results and will be used for the formulation of the new unified Czechoslovak-Soviet recommendation for so-called layered structures.