Testing and modelling chloride penetration into concrete

摘要

The design of concrete structures is usually made by means of a performance approach based on strength tests carried out following testing conditions agreed by convention. A similar approach should also be followed in the case of durability design regarding reinforcement corrosion. This type of consideration enables the establishment of verification of durability in categories. Three categories have been identified: (Ⅰ) it would be the prescriptive method already given in present codes based on "deemed-to-satisfy" rules, (Ⅱ) this is based in the testing through "durability indicators" that where still not quantification of the time to reach a limit state is explicit but the minimum life time is assured through performance based tests, (Ⅲ) it is the category in which the calculation of aggressive ingress through models having explicit the time is made including probabilistic treatments. In the paper in addition to the comment on the most common methods of calculation of the chloride ingress and their limitations it is illustrated how for level Ⅱ and Ⅲ the measurement of the electrical resistivity results a very suitable proposal due to this parameter can be measured in a non-destructive test and serves to quality control. It is not only a performance test (level Ⅱ) but it can be included in models of both the initiation and propagation periods. For the time to corrosion onset, the electrical resistivity represents the porosity and its connectivity and therefore can be used to model transport processes. It also results very suitable for measuring concrete aging and then accounting for the reduction of the diffusion coefficient with time. Concerning the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a certain relationship with the corrosion cement. A model is proposed in which the resistivity is introduced in the square root of time law. Finally the paper comments on the tests methods used for the measurement of the diffusion coefficient and of resistivity.