ENVIRONMENTAL AND CONCRETE AGEING EFFECTS ON TRANSPORT

摘要

Environmental conditions and material transport properties are rarely constant during the exposure of cement based materials. Ageing means a permanent change of transport properties caused by time- and environmental influences and not related to hydration. The environment (moisture, temperature, wind, salt etc) may also cause transcient changes of transport. Ageing and environmental effects are here divided in wetting/drying, temperature, carbonation, leaching and cracking/self-healing/-sealing. Permeation can be very sensitive to small changes in material and boundary conditions. Wetting/drying and self-sealing can change flow permanently by a factor of 100 for rather porous materials in highly saturated condition. Also leaching affects these materials significantly. Cracking can affect permeation even more in all materials, but may be transcient due to potential self-healing of cracks. Diffusion is affected by temperature due to change of Brownian movement, and due to vapour diffusion towards ice in the material. In wet freeze/thaw, 1-4 times increase is observed in short experiments. Chloride diffusivity can be reduced to 1/20 by marine self sealing and carbonation, whereas wetting/drying and leaching may increase diffusivity 10 - 100-fold. There are many effects of material (porosity, type of binder etc) and environment (marine, water hardness etc) on self-sealing. Generally diffusion gets slower in-situ than in laboratory tests.