ABSTRACT
Several laboratory investigations have shown that the coefficient of air-permeability kT correlates well with natural and accelerated carbonation rate CR of concrete (Fig. 1). Carbonation Rate measured in the lab under natural CO<sub>2</sub> exposure vs. <italic>kT</italic> values (predominantly OPC concretes). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig15_1.tif"/>
On the contrary, results obtained on site on old structures are scarce.
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, are presented. First, the coefficient of air-permeability 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/√age).
The consolidated results obtained in the three countries are presented in Fig. 2. <italic>CR</italic> and <italic>kT</italic> values measured on Swiss, Japanese and Portuguese Structures. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig15_2.tif"/>
The results highlight the following facts:
There is a large scatter in both kT and CD within each single 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 are some cases of high kT and low CR (possibly due to microclimatic exposure conditions and/or presence of cracks)
There seems to be a threshold value of kT (~ 0.01 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 to predict the carbonation rate on the basis of non-destructive air-permeability measurements made on site, as has been done in several real cases.
