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! 

Concrete butchers

Chlorides in concrete can be washed away when concrete is sawn by employing water as lubricant. For this reason, we took some samples and sawn them in dry conditions. The experiment had an overall success, but the environmental conditions were the problem. It was really cold outside!

Branko as a concrete butcher

Chloride penetration fronts and profiles are about to be assessed from the sawn slices of concrete containing chlorides. Results will come soon.

Until next time.

FraMCoS-8

FraMCoS-8 came and went... One of the best conferences with regards to fracture mechanics of concrete was a great opportunity to get a sneak peak at the newest and most innovative research in the field. We had a great time, filled with nice presentations and fruitful discussions. The official website of the organization is now www.framcos.org (under development). The next one is in three years, somewhere in the US... We will try to perform even better in the next one! Till then!

Traffic-induced vibrations of frame structures

A paper titled "Traffic induced vibrations of frame structures" (Marija Nefovska-Danilovic, Mira Petronijevic, Branko Šavija) , related to Branko Šavija's diploma thesis work, has been published in Canadian Journal of Civil Engineering.
Abstract:
"Using the spectral element method (SEM), a 2-D numerical model of multi-storey frame structures has been developed. The model has been used to predict traffic-induced vibrations of two, six, and twelve-story concrete buildings measured along the route of a future metro line in Belgrade, the capital of Serbia. Vibration simulations of the six-storey frame match satisfactorily the measured dynamic response. However, there is a difference between numerical simulation and the actual measurements for the two-storey and twelve-story buildings. The results indicate a great potential of the proposed SEM to simulate ground-induced vibrations of frame buildings. However, more complex structural models should be developed to better replicate actual situations."
Subscribers can download the full paper at  http://www.nrcresearchpress.com/doi/abs/10.1139/cjce-2011-0247#.UUbKWGf4LTp

FraMCoS - 8 begins today!

The 8th International Conference on Fracture Mechanics of Concrete and Concrete Structures begins today in Toledo, Spain. Two members of the M3C4 team: Branko Šavija and Erik Schlangen will contribute with presentations. 

The major topics for FraMCoS-8 are as follows:

• Recent advances in fracture mechanics of concrete

• Fracture and cracking behavior of reinforced and prestressed concrete structures

• High-performance, high strength concretes and FRC

• Advances in structural design codes

• Structural monitoring and assessment

• Repair and retrofitting, practical application

• Durability and corrosion-induced cracking

• Interface fracture and debonding phenomena

• Constitutive relations, time-dependent effects, cyclic and fatigue behaviour

• Brick masonry, concrete-like and quasi-brittle materials

• Computational aspects in fracture mechanics of concrete

You can see the conference program here.

When the levee (or concrete) breaks

This week finished with a set of concrete specimens being cracked for chloride penetration and reinforcement corrosion tests. Overall, it was a successful experiment.
Cheers

The Cable Guy

Today in the lab, a set of specimens was prepared by Jose... These specimens used for the CTC Round Robin test somehow reminded me of the movie "The Cable Guy"... Don't you agree?

Of concrete and microscopes

The use of the scanning electron microscope (SEM) in concrete research is not new. One of the main advantages of using the SEM is the characterisation of elements in cement phases, hydration products (CSH) or deleterious reactions (ASR). Energy-Dispersive X-ray Spectrometry (EDS) is capable of detecting elements heavier than carbon (C), but in order to provide fully-quantitative analysis, a reference mineral must be employed.

Why is this reference mineral so important? Well, let me provide an analogy to explain it.

Imagine that your car's speedometer is not properly calibrated. It tells you that your speed is 60 mph, yet your driving speed is 100 mph. It would be hard to convince the police officer that you didn't intend to overspeed.

Going back to microscopes, the reference mineral will calibrate your EDS detector to acceptable values.  This will provide your research with strong scientific proof that the elements that you've encountered, and their atomic proportions, are correct. The selection of the reference mineral will depend on the elements you are interested in, their atomic ratios, etc. While it is not a simple task, it will improve your results dramatically.

Until next time,

SEM training at WHD Microanalysis

The first half of this week I had the opportunity of visiting Aldeburgh (see above) and Woodbridge, UK; working place of Nick B Winter of WHD Microanalysis Consultants. For two days, Dr. Oguzhan Copuroglu and myself could talk to Nick, an expert on SEM microanalysis, and engage in great discussions regarding the possibilities of SEM for concrete and cementitious materials. Nick is an expert on this field with more than 30 years of experience; he even had the opportunity of working with Hal Taylor, known author of Cement Chemistry book. On top of that, Nick owns a SEM (see below) which is probably one of the best to have fun with. Turning knobs and clicking buttons does make a difference when learning this stuff. He was so kind to let me use it for a while and do some EDS analysis. Hopefully our collaboration will continue in the future.

New simulation results

Rapid chloride migration (RCM) tests are often used to characterize the resistance of concrete to chloride ion ingress. In the framework of the lattice model, this test can be simulated using a characteristic Galerkin approach. Although the mesh needed for the simulation is very fine (0.25 mm voxel size), this approach can be used to successfully simulate the RCM test in heterogeneous (meso-scale) concrete. To date, the only simulation of the ionic migration with the heterogeneous material structure (known to us) was published by Liu et al (2012) {Multi-phase modelling of ionic transport in concrete when subjected to an externally applied electric field, Engineering Structures 42, pp. 201-213}. We will therefore continue with this approach. Check out the video!

Goodbye 2012, Hello 2013!

The year has come to an end. It was full of great experiences, exciting results, new destinations and fruitful discussions. For the next year, the M3C4 team has many things to do. First, ESEM training in UK; conference in Toledo, Spain; microscopy conference in Chicago, US; and more. The first set of publications might come to light in this 2013, so fingers crossed.
The M3C4 wishes all lots of health, successful research and exciting adventures.
Until next time,