PSI - Issue 64

Antonio Bossio et al. / Procedia Structural Integrity 64 (2024) 56–64 Author name / Structural Integrity Procedia 00 (2019) 000–000

61

6

2.00

Ω p,tr

1.00

MC10 SFM EC2

0.0

4.5

9.0

0.00

f l [N/mm

2 ]

4.00

x [µm]

8.00

Fig. 4. (a) Ω p,tr ratios and bar reduction, x , vs internal lateral pressure f l – concrete exposure class XC1, (b) Ω p,tr ratios vs bar reduction, x , – class XC1 (top) and XC4 (bottom).

4.3. Effect of creep Corrosion weakens RC structures over long time, so it's important to consider how creep affects the bond between the rebar and concrete. Creep is a phenomenon where concrete slowly deforms under sustained (constant) load. Creep reduces the stiffness of concrete, as measured by elastic modulus ( E c ). A creep reduction factor (1/(1+ ϕ )) is introduced that decreases with time and higher sustained loads (increasing ϕ ). A higher creep factor means that concrete gets softer. Creep affects the relationship between bar reduction ( x ) and internal pressure ( f l ) from oxide buildup. For a specific scenario (Figure 5b - exposure class XC2, 16mm rebar, 20mm concrete cover, and concrete strength class C25/30), maximum internal pressure ( f l ) is similar in all cases. However, this pressure occurs at different levels of bar reduction ( x ) depending on the creep factor. Higher creep (softer concrete) leads to more bar reduction for the same pressure. For a harsher exposure class (XC4), the bar thins more, overall. This is likely because there's more concrete cover (protecting the rebar slightly) and the concrete itself is stronger (taking longer to weaken from corrosion). 4.4. Effect of concrete strength While the strength of concrete plays a role in when cracks begin to form (crack initiation), it has little effect on how those cracks grow (crack propagation) according to Bossio et al. (2011). Figure 5c focuses on how the concrete's strength class affects the bond behavior between the rebar and concrete. As the concrete gets stronger (higher strength class), the ratio of Ω p,tr (related to bond improvement) and the stiffness of the concrete (represented by elastic modulus, E c ) needed to cause cracking in the concrete cover increase. It's important to note that Ω p,tr related the C40/50 strength class is significantly affected by a limitation of 1.4 imposed by Eurocode 2 (Eq. 1 § 3.1). This limitation likely restricts the bond improvement for this high-strength concrete compared to lower strength classes.