When the reinforcing steel bar inside concrete corrodes, it starts expanding, since the volume of the oxides that form during the process is higher than the volume of the original steel. It, therefore, exerts pressure on the surrounding concrete, which eventually cracks. To study the mechanism, the lattice model can be used. Here is the result of the first simulation of corrosion induced cracking. Enjoy!

The "rebar effect"

It has been reported in the literature that the buildup of chloride ions occurs at the top of the rebar. This means that the higher chloride concentration can be observed at the top of the reinforcing steel, than at the same depth to the side. Since reinforcement is impermeable to chloride ions, this actually makes perfect sense. Therefore, sampling the chloride ions at the side of the rebar to study, for example, the chloride threshold concentration, can lead to serious errors. This has be proven experimentally by Yu et al. (2007) in their study. So, what is a simple way to check this hypothesis? Well, numerical simulation, of course!

First figure shows the setup. Part of the mesh was was made impermeable to simulate the effect of reinforcing steel, while the chloride can freely penetrate the other side of the sample. The specimen was then subjected to chloride penetration for a certain period.


And here is the result:

Clearly, the phenomenon does occur. And what are the implications for the Round Robin test of the CTC Rilem committee? I guess we'll just have to wait and see!

Reference: H. Yu, W.H. Hartt, Y.P. Virmani, "Effects of reinforcement and coarse aggregates on chloride ingress into concrete and time-to-corrosion: Part 1-Spatial Chloride Distribution and Implications", NACE Corrosion 2007 Conference & Expo

Chloride exposure of cracked concrete

Concrete specimens with controlled crack widths just started to be exposed to a chloride containing solution. This experiment will show how fast chlorides penetrate into concrete on the vicinity of the crack.
More results to be posted soon.

Photo by: B. Šavija

Chloride binding

As chlorides penetrate into the concrete, some of them are physically and chemically bound to the cement matrix. Therefore, only free chloride ions can promote the further penetration. Also, only free chloride ions are responsible for steel depassivation and initiation of the reinforcement corrosion. This effect needs, therefore, to be included in our predictions. The simplest way to do this is to consider binding as a linear phenomenon. Some authors suggested, however, that this assumption is not suitable for a wide range of chloride concentrations. Therefore, non-linear binding isotherms (mainly Freundlich and Langmuir) are often used. First trials with the both nonlinear and linear binding have been performed, and here are the results!

ESEM

Some interesting results were obtained on the ESEM on the past days. There is still a group of samples to be analyzed this week and results seem promising! Part of this work will be published soon. Keep in touch for more upcoming updates.
Adios

Click here to download the January 2012 Newsletter

January has come to an end. Now the M3C4 project is proud to announce the first monthly issue of the Newsletter. On January, some interesting results were found. More information regarding publications or presentations at Conferences will be published soon!

See ya,

Glowing concrete

It seems that concrete properties also include glowing under UV light! Cracks allow aggressive substances to reach into concrete. In this case, the crack pattern is visible when it has been filled with epoxy.


We would like to take this opportunity to wish you success in all your endeavors. Until next time!

Photo by: J. Pacheco

In 2011, it seems that the one question that was on everybody's mind was: is self-healing of concrete possible? Even though it is not directly related to our project, we've been asking ourselves the same thing. Here is our suggestion:

And with that, the M3C4 team would like to wish everyone Marry Christmas and a happy New Year! Till next year!

Chloride ingress in cracked concrete

First simulation of chloride penetration in cracked concrete has been performed. A specimen (top) has been subjected to tension (below it-cracked elements after 15000 steps). Subsequently, it has been subjected to chlorides from the left side. Below are the chloride profiles at 30, 90, 180, 365, and 730 days, respectively. Till next time!

RCM test

Rapid chloride migration testing is increasingly used in practice to assess the chloride resistance characteristics of a concrete mix. It is fast and simple, and can be performed with no fancy equipment whatsoever. Standardized as NT BUILD 492 in Scandinavia, it is also increasingly popular in the Netherlands. But, is there a faster way of testing? Well, of course there is: a numerical simulation! If we could simulate the test, different concrete mixes could be tried and the best one chosen. The first simulation of the test is here. Enjoy!

Here is the comparison of our simulations with some experimental data from the literature: