Performance of concrete exposed to natural carbonation: Use of the k-value concept

This work presents results of concrete carbonation after 10 years of exposure to a natural environment not sheltered from rain, and the values are utilized for the application of the k-value concept used within EN 206 for Type II additions to concrete. The concrete mixtures were prepared with Portland cement and different replacement levels of cement by fly ash (FA), ground granulated blast furnace slag (GGBFS), or both FA and GGBFS and using distinct water/binder ratios. The concrete performance is related with the binder constituents and dosages through the k-value concept. Thirty-three concrete mixtures were tested and the results show a consistent decrease of carbonation resistance when the water/clinker ratio increases, which is in accordance with the low k-values obtained for fly ash and slag. The analysis performed also shows that the mixtures with FA present lower carbonation resistance than those with GGBFS, for the same cement replacement level.