Best wishes from the M3C4 team

Finally 2014 has arrived. This is the last year for some of the PhD candidates so big plans are ahead. The blog is planned to be more active during this year so keep visiting if you are interested. On behalf of the M3C4 team, veel succes!

j

Structural synergy

Check out this cool video about the Structural Synergy event:

http://www.youtube.com/watch?v=mIe0Akn6aFw&feature=youtu.be

Thanks to the team for organizing the event!

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,

Corrosion of steel in concrete

Figuring out what is really going on during corrosion of steel in concrete is no easy task That's why we use advanced experimental techniques to characterize the process. Here's an example:

 

On the left, we see the concrete at the steel concrete interface (dark), in the middle, corrosion products are visible (gray), and on the right, we see the sound steel (white). Characterizing their mechanical properties is our task! Stay tuned for updates! 

Update 1:

How corrosion induced cracking takes place:

Also, different cross sections of the same beam can be observed (top - with PVA fibers; bottom - no fibers):

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

Calcareous aggregates on BSE mode

Studying the composition of concrete samples can be performed easily under the ESEM. Sometimes, the origin of the aggregates and their main composition must be determined. In this case is the presence of calcareous (CaCO3) aggregates in the concrete mix. In some countries, Aggregates are obtained from crushed rocks. Calcium carbonates have a similiar intensity under the BSE mode when compared to CSH. This quite be uncommon in places where aggregates are commonly from siliceous origin.

 Sample w/b ratio 0.45

 

Sample w/b ratio 0.65

A quick look on the previous images confirms the presence of calcium carbonate as the main aggregates in concrete samples. In the coming future, more explanations regarding the EDS analysis on this type of samples will be shown.

Until next time,

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,

Corrosion induced cracking

When steel corrodes, a rust layer is created around it which exerts pressure on the concrete cover. Although much is known about this process, it would be nice to be able to study it non-destructively. How? Well, we might have a trick up our sleeve! Keep checking the blog for news!

And here is an update:

Big city, big Conference

The view of Chicago's skyline from Jon Hancocks's Observatory.

 The 35th International Conference on Cement Microscopy was held from April 29th to May 1st in Chicago, Ill. The M3C4 had the opportunity to attend and show some of the research lines we've been currently looking into. The conferece had a lot of interesting presentations and extensive discussions regarding cement microscopy.

We also had the opportunity of visiting the headquarters of PCA (Portland Cement Association) based in Skokie, Ill. The facilities were excellent for research on cementitious materials.

From the M3C4 here's a big shout-out to the organizing team of ICMA and hopefully, we'll see you again next year in Italy.

Headquarters of PCA, Skokie, Ill.

Cracking of the concrete cover due to reinforcement corrosion

 Our paper titled "Cracking of the concrete cover due to reinforcement corrosion: A two-dimensional lattice model study"
 has just been published in Construction and Building Materials. It deals with numerical modelling of cracking of the concrete cover as a consequence of reinforcement corrosion, based on the Delft lattice model framework. Registered subscribers can download the article at: http://www.sciencedirect.com/science/article/pii/S0950061813002730
I hope you find it interesting and useful.
Cheers!