Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016
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- Bu səhifədəki naviqasiya:
- Mean carbonation depth at locations shown in Figure 3
- Half-cell potential (mV) relative to Cu/CuSO 4 reference electrode (HCP) percentage chance of active corrosion
33 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark Monte Carlo simulation was used to simulate the limit state function and to calculate the probability of corrosion initiation using Eqs. (4) and (5) for the statistical characteristics of random variables given in Tab. 1. In this study, 10 6 simulations were performed using Matlab software to calculate the probability of corrosion initiation. The probability of corrosion initiation versus time (years) was plotted, as shown in Figure 2.
4.2 Determination of carbonation depths on-site Initially, the location of the reinforcement was identified, and 10 holes were chiselled into the concrete, as marked in Figure 3. The phenolphthalein test was carried out on site to measure carbonation depths. Tab. 2 shows the mean carbonation depths measured at test locations in each console, as indicated in Figure 3. The test locations ((a) to (j)) are chosen, about 22 cm from the closet edge. Test locations (a) to (e) are considered as sheltered from rain, whereas locations (f) to (j) are considered as partially exposed to rain.
110cm 22cm 55cm
22cm (a)
(b) (a)
(c) (f)
(g) (h)
(a)Front of a console (b)Back of a console 110cm (c)
(h) (e)
(d) (j)
(i) 55cm
Sheltered from rain Partially exposed to rain Sheltered from rain Partially exposed to rain
Figure 3: Sampling point of a console 0 0.5 1 1.5 2 2.5 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 Reliability Index Pr obability of corr osion initiation(% ) Time ( years) Corrosion initiation (sheltered from rain) Corrosion initiation(partially exposed to rain) 34 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark Table 2: Mean carbonation depth at locations given in Figure 2
Partially exposed to rain Location (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Console 1 (mm) 7 7 6
7 2 4 6 7 4 Console 2 (mm) 5 7
8 5 7 3 3 4 5 4 Console 3 (mm) 6 8 10
5 7 3 5 8 6 4
Half-cell potential mapping (HCP) is a non-destructive method, which is widely used for monitoring steel corrosion in concrete structures. However, there are no specific guidelines available in the literature to interpret HCP measurements due to carbonation. According to ASTM (1991) Standard [8], the results from a potential mapping process can be interpreted as shown in Tab. 3, which is based on the findings from laboratory testing (partial immersion in chloride solution) and outdoor exposure of various reinforced concretes structures above ground level. The standard states that criterion given in Tab. 3 should not be utilized if concrete is carbonated to the level of the embedded steel, unless either experience or destructive examination of some areas, or both, suggest their applicability. Considering measured carbonation depths (i.e. destructive examination) in Tab. 2, it can be seen that concrete is not carbonated to the level of embedded steel. This is because the average concrete cover to the reinforcement (25 mm) is deeper than the measured carbonated depths. Considering that fact, Tab. 3 was used to evaluate HCP values due to carbonation . At 53 years of service life, the three consoles had 36 HCP measurements taken at 200 mm intervals over each of their surfaces, using Cu/CuSO4 as reference electrode. Figure 4 shows the HCP measurement over the surface of Console 2 as an example.
Table 3: Interpretation of half-cell potential values as per ASTM C876 [8] Half-cell potential (mV) relative to Cu/CuSO 4 reference electrode (HCP) percentage chance of active corrosion <-350 > 90%
-300 to -200 50%
>-200 Less than 10%
Considering the mean value of each random variable in Eq. (1) and Tab. 2, the mean value of the carbonation depths vs time have been plotted as given in Figure 4 for the area sheltered from rain and the area partially exposed to rain. It can be seen that, at 53 years, the calculated mean value of the carbonation depth is 18 mm for the area sheltered from rain, which is higher than the measured average carbonation depth (X1=7 mm). For the locations in the area which is partially exposed to rain, the calculated mean carbonation depth is 8.7 mm, which is also higher than the measured carbonation depth (X2=4.5 mm, as shown in Figure 5). However, both measured and calculated carbonation depths are below the mean value of Yüklə 8,6 Mb. Dostları ilə paylaş:
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