Corrosion pits in steel bars embedded in cracked concrete

Here is a short update on what I've found on inspecting the bars after extracting them from the specimens. The first image shows the size of pits found in a specimen with a 'smaller' crack width'.

The second image shows what happens when the crack width in increased. Both specimens were subject to the same amount of salt-dry cycles.

In both cases, the original image dimensions were 5600x4200 microns approx. However, these images have been resized for posting purposes.

There are very interesting findings that will be published in the near future.

Until next time,

Visual analysis of corroded bars

I've been working on the analysis of corroded reinforcing steel embedded in cracked concrete. The cubes were mechanically split so the reinforcement can be assessed. All images are taken with the stereomicroscope.

A layer of orange rust can be observed on the steel surface. However, there are still some corrosion free spots. The original image size was aprox. 17000 x 1300 microns*.

This last image shows the thickness of the oxide layer on the steel surface. 

Next step will involve the removal of the rust layers and assessing the size if pits, if any.

Until next time,

* Note: Images were resized for this post.

REPOST: I've just added two images of bars embedded on concrete samples with different crack widths. See the effect of the crack width on the deterioration.

Cheers

Bending cracks in reinforced concrete cubes

During the course of the M3C4 research, a Modified Wedge Splitting Test (MWST) was employed as the main source of getting controlled cracks in reinforced concrete specimens. For this purpose, we used concrete cubes that contained a recess, where the action of the wedges is applied; and two reinforcing bars embedded in concrete.

After cracking, one can only measure the COD (Crack Opening Displacement) at the concrete surface by means of LVDTs. After some other procedures, we're now able to visualise the shape of the crack inside the concrete cubes.

More results are about to come.
Until next,

Concrete cracking Pt1.

Cracks in concrete cover are definitely a concern for concrete infrastructure. The figure shows cracks propagate not only vertically, i.e. towards the reinforcement, but also horizontally once it has reached the steel bar position.  It is clear that the internal cracked concrete area is far larger the surface crack width. Hopefully, this will be taken into account in future durability design approach.

Until next time,

Jose

Cracked concrete infrastructure

Betondag 2012 is coming next Thursday November 15th to Rotterdam. A brief, but interesting presentation regarding the influence of cracks on concrete durability will be given by two PhD candidates of the M3C4 project. If interested, don't hesitate to attend the presentations given by PhDs during Betondag.

Until Thursday!

Corrosion rates of steel in cracked concrete

Cracks in concrete cover allow fast penetration of aggressive substances such as chlorides, leading to reinforcement corrosion. In the Figure 1, corrosion rates of embedded reinforcing bars in concrete with transverse cracks with widths ranging from 135 to 375 microns are shown. It seems that crack width has an effect on the  evolution of corrosion rate in laboratory conditions.

Figure 1. 

In Figure 2 corrosion potentials are shown, providing indication of the thermodynamical condition of the steel reinforcement. One interesting effect is found on crack width of 217 microns. Although potentials are significantly less noble than the rest, corrosion rates were found to be the lowest of all specimens. It is clear that the experimentation must go on, but so far interesting results have been obtained!

Figure 2. 

More results to be posted soon!