Carbonation rate in old structures assessed with air-permeability site NDT

In this paper, test results obtained on several old concrete structures (up to 60 years old), located in different regions of Japan, Portugal and Switzerland, arc presented. First, the coefficient of air-pcrmcability kT (Swiss Standard SIA 262/1) was measured at different locations of those structures, to be followed by the measurement of the carbonation depth CD on samples removed from the same locations. The CD values were "normalized" by converting them into carbonation rates CR (CR = CD/√Jage). The results highlight the following facts: There is a large scatter in both kT and CD within each structure, posing a challenge for prediction modeling There is a general trend of higher values of CR for higher values of kT If kT is low, CR is also low; however, there arc some cases of high kT and low CR (possibly due to micro- climatic exposure conditions and/or presence of cracks) There seems to be a threshold value of kT (~0.0l 10^-16 m2) below which the carbonation rate is negligible (less than 1 mm/√a, i.e. less than 10 mm in 100 years) The results presented are useful lo predict the carbonation rate on Ihe basis of non-deslruclive air-permeability measurements made on site, as has been done in some real cases.