I have been recently busy with trying to improve damage model by implementing better ways to represent variety in material definitions. After finishing the analysis of NanoIndent results now we have the opportunity to assign this information (basically E-modulus and Strength values driven from hardness) for different phases in the system.
I recently introduced
Random distribution based on Nano Indent test results - using mean and variance of data
Triangular random generation of mesh with around 112000 elements to represent 10cm x 10cm sections
Probabilistic distribution of reaction (in this case expansion) based on petrographic identification of reactive phases in aggregates (different for each mix design)
and implementation of saturated cracks by updating the loading system while simulation is running (by introducing plastic behavior stage non elements stress strain curves)
Here are some representative images;
Histogram showing distribution of E values grouped by phases (Agg-Mortar-Bond-Void)
Heat map of E Mod values based on Digital image, Mesh geometry representing heterogeneity in aggregates and mortar
The viaduct Vlijmen-Oost, affected by Alkali-Silica Reaction, was proof loaded on 6 November 2013.
This tested was performed in order to asses the structural response of the bridge and the its current capacity.
The viaduct was already monitored from several years in the contest of the A59 project. The development of ASR was assessed in 1997, however the bridge expansion appear to be still limited.
This project was conducted by Rijkswaterstraat in collaboration with 3 IS2C project (PAT-ASR, Smart Proof Loading and InfraWatch).
Article in the local news paper.
The BELFA truck used to perform the proof loading.
Part of the team (from left to right): Rita Esposito (TUDelft), Max Hendriks (TUDelft), Johan De Boon (TUDelft), Sonja Fennis (TUDelft) and Ane de Boer (Rijkwaterstrat).
We are currently carrying out numerous Damage Rating index analysis on RILEM test (AAR-4.1 and AAR-3) samples. Along the process of images we frequently come along with text-book examples of ASR damage in our Lab samples. Here is one under UV light.
Sample info:
Prism from RILEM AAR-3 Test on Norwegian Aggregates (Original Mix)
Age 364 days old @ 38°C RH 100%. No Alkali boosting.
Editor's Note: It's weird how we (ASR researchers) enjoy cracks (evidences) in our samples, while it is absolutely bad news for structures and clients.
Today I have been busy with a trial CT-scan of RILEM AAR-4 samples. The Main aim was to get a 3-dimensional view on how cracks were distributed in concrete medium. Following 3 videos show Top, Front and side view respectively. While progressing through the sample, we can see how cracks are located and progressed.
Current sample size is 15mm x 15mm x 7 mm, resolution of images are around 13 microns\pixel. Largest observed crack width is roughly 80 microns.
By the end of 2012, (and no Apocalyptic events so far) I am trying to put together results of first set of Nano indentation.
As mentioned earlier, 4 specimens from 60°C testing (3 from original mix design + 1 RILEM standard mix design) are used for analyses. Main problem following indentation process is matching mechanical properties to exact locations on specimens. So far success rate of indent attempts are a bit low (around 55-70%). This was mainly due to some last minute revisions on samples and disturbing the flatness of our samples. Yet there are enough data for our purpose. With our new sample holders I believe this rate will raise drastically.
For the last week or so, I have been working on a Matlab code which gathers thousands of indent data, crunches the numbers and groups curves in to several E Modulus values (with 30GPa intervals). I have been working on a standardised way to identify (hypothesise) a way to identify locations of indents. As they are not (or very hardly visible) through light microscope, we needed to randomly distribute a grid on indent area, then check whether it is statistically comparable with NanoIndenter results.
Here is how it works.
\begin{example}
We had original documentation of our samples where interested indent areas are marked.
Micrograph image under stereo microscopy MagX0.63 - Each grid represents 4mm² area
After indentations is performed another micrograph is taken with a higher magnification (4X) for detailing indent area alone.
Micrograph image under stereo microscopy MagX4 - Each cross is placed 200microns from each other as indentation points were
It is hardly visible from this image but manual point counting is applied on this image where each 200 microns increment is marked digitally. Finally we end up with two images for matching and comparison purposes. First one representing hypothetical distribution of indent points and their corresponding material phases. Second one a representation of how E-modulus values vary through indentation grid.
Point count results
Surface map diagram of Indent results for E (GPa) values
This methods allows a standard way to overlay test results with real material properties. This can be further investigated by correlating findings with following subgroups of indent results shown in subplots.
\end{example}
Next set of experiments will start in Jan 3rd 2013. Till then,
Biannual Meeting with our academic and industrial partners was held today (04/10/2012) in TU Delft. It has been a fruitful meeting and many constructive discussions. We would like to thank all our Users for their participation...
Work in progress. Here is crack development for 3 different samples based on different loading conditions, various aggregate size and agg/paste ratio.
Currently working on quantification of damage obtained from simulations. Regarding our previous post these are attempts to understand the crack formation mechanism (and hopefully fitting on a timeline).
8th International Conference on Fracture Mechanics of Concrete and Concrete Structures will be held in Toledo Spain, March 2013. Deadline for Paper submission is 15 September, approaching.
Hopefully we will be there to present our findings.
ICAAR conference series continued in Austin, Texas. Thanks to University of Texas, it has been a remarkable organization from 21st to 25th May. It has been a warm but a knowledgeable week for PAT-ASR team. We had the opportunity to experience interesting researches from around the world. We have share knowledge and connected with researches from our field. Our team also presented 2 papers during the conference and collected useful feedback. one of the highlights of the conference was the visit to Texas University ASR Exposure site (see images). They showing a considerable effort and dedication to run this site.
Over all, it has been a informative week for everyone.
Crack formation changes according to localization of the gel. this correlation brings a challenge in modelling. Which loading point will successfully represent Gel expansion?
Recently explored various loading options on a hypothetical section with a low aggregate-paste ratio. Different images represent various loading points, On; aggregate, ITZ, aggregate+ITZ, respectively.
Also comparative stress distribution after certain amount of crack growth
Built
in 1964, over highway N206. Recently diagnosed with severe map cracking
and coloration under the deck and abutments. In 1999, several cores
have been extracted from the structure and ASR formations were observed.
Couple of months ago, administrative units concluded on demolition of
this structure. PAT-ASR team will be involved in further studies on
concrete cores from this structure. You can find images of our recent
site visit to this structure.
Built
in 1959, on road N216 is the first confirmed concrete structure in the
Netherlands which was severely damaged by alkali silica reaction. Bridge
demolished end of 2010.
Dr
Oguzhan Copuroglu studied several cores from this structure for the
investigation of microstructural features of the concrete and amorphous
and crystalline ASR product compositions.
This
study concluded that ASR and related damage were exclusively created by
the reactive coarse aggregate although the fine aggregates exhibit
reactive components in the Montigny viaduct concrete. You can find the
details on this study* in Proceedings of the 33th Int. conference on cement microscopy.
*
O. Copuroglu, G. Einarsson, "Montigny viaduct revisited: Microstructure
of an ASR damaged concrete from 1959", Proceedings of the 33th Int.
conference on cement microscopy, San Francisco, California, U.S.A, April
17-20, 2011
Recently a new researcher joined PAT-ASR team. Dr Marc Ottelé started in September 2011 as a post-doc. He will be working on the experimental part of our project. You can find more information about him here (only in Dutch). A warm Welcome to Marc.
The first meeting of IS2C (www.is2c.nl), project domain that we are involved, is held in Woerden, May 19th. PAT-ASR team was present in this event and presented a poster.
Google introduced an interesting graphics tool to present keywords search in literature. According to Official google blog "datasets backing the Ngram Viewer, produced by Matthew Gray and intern Yuan K. Shen, freely downloadable so that scholars will be able to create replicable experiments in the style of traditional scientific discovery".
And, I was instantly curious to see results for our topic. Here is a snapshot from the website or you can follow this link: Ngram Results.
It is true that reliability for this figure is dependent on available online dataset used, and limited to keyword matches, nevertheless gives a quick general idea on ASR.
In the recent years, alkali silica reaction (ASR) has been regarded as one of the critical aspects for durable concrete design. Common practice is to avoid the reactive aggregate and to use low-alkali cement, which is seemingly an easy solution. It is often too risky for an engineering office to use one particular accelerated ASR test result and design for a service life of decades. Or, as often encountered, it is important to estimate the remaining service life of a structure showing ASR cracks.
In The Netherlands, the first reference an engineer would consult for an ASR-proof structural design is CUR Recommendation No. 89 - a decision tree on the assessment of ASR risk. The parameters involved are cement type, alkali content, aggregate type and results of accelerated tests. The tool eventually suggests either to continue with the design or to modify the concrete composition. By definition it is a decision tree. Therefore it lacks a precise recommendation on the modification method and its possible consequences i.e. effect of limestone filler or other mineral additives. Furthermore CUR has produced Recommendation No. 102, which deals with inspection and evaluation of concrete structures with ASR. This is a beneficial tool to examine a structure showing symptoms of ASR damage and decide if the structural safety is still guaranteed. However the propagation of the ASR mechanism and the consequences for the structure is not part of the evaluation with CUR recommendation 102.
Therefore the aim of PATASR is to combine the tasks of above-mentioned recommendations in a single interactive tool where it is possible to include alternative materials, environmental profiles and structural parameters in the design process of ASR-proof concrete.
PATASR project attempts to develop a unique comprehensive integrated tool for engineers for modelling possible ASR development in new concrete structures as well as evaluating the remaining durability of existing structures. The outcome provides a full-scale technical report as well as financial implications of the desired concrete design. The software will also provide an option, a database to keep track of ASR related characteristics of concrete materials, structural properties and environmental profiles which enables transfer of knowledge to the future projects.
Leader of the project, Dr. O. Copuroglu is assistant professor in the section of Materials and Environment, Faculty of Civil Engineering and Geosciences, Delft University of Technology. His research field is the microstructure of cement-based materials, durability aspects, self healing and materials characterization. Dr. Copuroglu has published over 40 journal and conference papers mainly on durability of concrete, including ASR.
Dr. ir. E. Schlangen is an associate professor in the section of Materials and Environment / Microlab. His research interest involves fracture mechanics, early age behaviour of concrete, numerical modelling, chemomechanics and self healing. Dr. Schlangen is the developer of the world-wide and renowned Delft-Lattice model.
Dr. ir. M.A.N. Hendriks is an assistant professor in the Section of Structural Mechanics, Faculty of Civil Engineering and Geosciences, Delft University of Technology. His research field is computational modelling of structures and has over 20 years of experience in finite element modelling.
Currently two PhD researchers are appointed for this project.
Guðbjartur Jón Einarsson - Ph.D. Project I – Experimental Study.
Spent 5 years doing carpentry, before getting a Bachelor’s degree in civil engineering from the University of Reykjavik, Iceland. And after two years of working in a concrete testing and research lab in Iceland, came to Delft for a Master’s degree also in civil engineering, upon completion of which he joined the PATASR team in April, 2010.
Main goals are:
-Determination of vital parameters.
-Organizing lab-based accelerated and real-time experimental parameter study.
-Organizing national/international round robin tests.
-Gathering information on the national/international ASR experience.
-Analysis of test results and integration in the PATASR tool.
Got his Bachelor’s and Master of Science Degree in Civil engineering from Middle East Technical University, Turkey. After working in the industry for several years and participating in a 2 year research project in University of Reading, UK, joined the PATASR team in April, 2010.
Main goals are:
-Setup model to simulate effect of tested parameters in experimental program. Feedback loops with article of the experimental program.
-Setup template of PATASR.
-Run examples with PATASR and compare with examples from practice.
3-Aim of this Blog?
The idea came up to keep a diary of the progress in the project. We also believe that using a blog will create an opportunity for effective brainstorming and international collaboration. We are hoping this blog will help to create a register of interesting experiences, memories throughout these 4 years, as well as publicising research results as soon as possible with the hope of getting comments and criticism from people in the field of ASR research.
