The effects of ageing can be positive (think on a excellent wine…) or negative (as usually associated with deterioration of reinforced structures). Ageing processes occur on the level of the material (nano- and micro-structural scale) or on the level of structures (meter and mega-scale) and are usually interacting with each other. First example presented is hydration of cement-based materials. This process increases compressive strength and reduces effective diffusion coefficient with time. The electrical resistivity is a key parameter describing all these ageing phenomena; determining electrical resistivity on structures can be used for on-site quality control of concrete and post-tensioned structures (electrically isolated tendons) as well as a early warning system for corrosion of the reinforcement. Second example is the ageing of the protective passive film on the reinforcement (thickness of some nm). Surface analytical studies have shown that the passive film evolves progressively to a less Fe(II) defects containing film, in the case of stainless steels changes also its composition showing an increase of chromium-oxyhydroxid with time. Both tend to a more pitting resistant passive film. Thus many properties in reinforced concrete “get better” with time, also on a quite long time scale. The problems of testing “young” laboratory samples is discussed, a new approach for testing real concrete is presented.
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