PSI - Issue 11

Pablo Benítez et al. / Procedia Structural Integrity 11 (2018) 60–67 Benítez et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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The analysis is performed over carbonation depth reports relating to 206 tests in several different structures located in the city of Asunción. Despite the carbonation test with phenolphthalein, these reports include values of the cover thickness of structural elements and their characteristic strength. Likewise, the case studies correspond to structures whose service life at the inspection time were between 1 and 40 years. Considering only the classification of structural elements, the carbonation depth and cover thickness values are summarized in Table 1.

Table 1. Summary of results obtained from the intervention of concrete buildings in Asunción. Structural element N° of data Cover Thickness (mm)

Carbonation depths (mm)

Mean

Standard Deviation

Mean

Standard Deviation

Beam

87 88 31

18.4 19.2 12.2

9.61 10.78 5.52

12.9 17.6 12.0

7.92 10.07

Column

Slab 7.86 Performing a statistical analysis over all data, the structures considered showed a mean value for the cover thickness equal to 18.9 mm with a standard deviation equal to 8.04 mm; and carbonation depth mean value and its standard deviation equal to 16.5 mm and 7.25 mm respectively. However, the statistical mode for the same parameters was 10 mm and 15 mm respectively. This means that, in several cases, there is a carbonation depth value greater than the cover thickness, and taking into account the carbonation effect on RC structures, it can be expected that those structures are under a considerable corrosion risk. The normal distribution of all measurements made in the case study is depicted in Figure 1.

Fig. 1. Normal distribution of the test results

Although Figure 1 shows the test results in a general perspective, it should be mentioned that the cover thickness has been measured even with values of 1 mm at certain points. Even though it is an unthinkable case considering the durability of structures, it is usually a recurrent situation in structures not only in Asunción but throughout the country. The main cause of this problem is given by the lack of control during the execution of the structures, where the cover thickness established in the structural design are not respected at the time of the concreting process. On the other hand, an analysis where the corrosion risk was represented based on a correlation between the concrete cover and the carbonation depth was also performed. Thus, it was possible to classify three degradation conditions for the structures, which are shown in Figure 2: corrosion risk, without corrosion risk, and the condition of imminent corrosion initiation. The last condition considers what has been established in the literature, where corrosion begins when the carbonation front is at least 5 mm from the reinforcement (Yoon, Çopuroğlu, and Park 2007) .

DEGRADATION CONDITIONS

14.91%

Imminent Corrosion Corrosion Risk No Corrosion Risk

50.93%

34.16%

Fig. 2. Degradation conditions based on test results