Durability of Concrete
In terms of durability investigations are carried out on the thaw and freeze thaw resistance of concrete in particular. With the help of various test methods laboratory classification of concretes in exposure classes may take place. For areas with high water saturation – XF3 – and areas with additional de-icing agents – XF4 – the CF, CIF, CDF tests, the cube and slate tests can be applied. By determining the amount of scaling and the internal structural damage, the frost or freeze-thaw resistance of concrete is checked.
The method of the critical degree of saturation according to Fagerlund is another test method, which makes it possible to draw conclusions about the life expectancy of buildings under the anticipated conditions. By identifying the critical degree of saturation of the concrete and comparing it with the current level of saturation of the component the frost resistance is deduced .
In various research projects long-term measurements at different buildings in Germany will take place to capture the temporal evolution of the water content and the temperature stress in the concrete edge zone. With the most advanced multi ring electrode continuous measurement is performed at several buildings. The electrode allows a depth-dependent measurement. From sections of about 5 mm deep inside the concrete cover to depths of not affected concrete the respective electrolytic resistance is detected non-destructively and continuously. The electrolyte resistance of concrete is closely related to the water content of the concrete. By calibration of a measured resistance the actual water content can be deduced. In conjunction with the laboratory test methods the results of these investigations provide a basis to verify the transferability to practice conditions.
A future research focus is in the modeling of damage mechanisms in concrete by frost attack.