On October 2nd to October 4th I had the pleasure of attending a Symposium on UHPFRC (I expect that if you are reading this blog you are familiar with the acronym) held in Montpellier, France. And I do mean “pleasure” – leaving damp and chilly Denmark in the autumn for sunny South of France was very nice. The weather and the sights of Montpellier may have had something to do with it, but the attendance was quite good with 300 participants (plus 100 students) and 108 contributions with 20 countries represented.
My main excuse for attending was networking – and also my boss always expects me to sell a few projects. He should know by now that we have others in the company that are much better suited for this – and a conference where two thirds of the other participants represent the “competition” is perhaps not the best venue for landing fat contracts. The reason for using quotation marks for “competition” is that we only compete against other UHPC producers for very few projects – we mostly compete against steel or conventional concrete – so a conference like this can be used to discuss common challenges and interests.
I should let you know, that this post will be divided into two parts – my presentation at the symposium and how this was received and my impressions from the conference, so if you are not up to reading my full post, please skip to the part that you are most interested in – now you have been warned :).
The title page of my presentation is shown below:
The presentation reflected on the fact that a number of the presentations at the conference dealt with guidelines that are being developed in a number of countries (Spain, Germany, Canada, the US) and have already been introduced in other countries (Switzerland, Czech Republic, Australia, Japan, France). In France the guidelines have been implemented as a national annex to the European Standards.
At the moment the French standards are the most comprehensive and well-developed guidelines – but as the guidelines are based primarily on the experience of French engineers they are biased a bit towards UHPFRC that either rely solely on fibre reinforcement or that include prestressing. The standards, however, also cover UHPFRC with conventional reinforcement – the type that is used exclusively by Hi-Con.
My presentation – and the accompanying paper – touched upon our puzzlement that a type of UHPFRC that has been used for more than 70,000 tons of structural elements over the years did not comply with the French standards (although it does comply with most of the other guidelines that are being developed). The failure to comply is based solely on the requirement of the standard, that the minimum characteristic strength measured on cubes should be 165 MPa for a UHPFRC to be suitable for structural applications. In our case we test from our regular production, which gives us a relatively high standard deviation as opposed to just testing for one specific project. This means that while our mean strength is 165 MPa, our characteristic strength is only 151 MPa.
If compressive strength was very important in our design we could improve on this (heat curing, improved grading, other aggregates), but as discussed in another post on our blog (link) other parametres such as ductility, durability and stiffness are much more important. Even if we doubled our compressive strength, our design would look pretty much the same as long as we use conventional reinforcement. This means that increasing our compressive strength just to comply with requirements of a standard would make the concrete more expensive without gaining any advantage – and thus reduce our ability to compete against steel and conventional concrete (which is what we do for 99% of our projects).
I think my presentation was well received. Jacques Resplendino, chairman of the organizing committee of the conference, commented after the presentation that compressive strength was indeed less important when conventional reinforcement was used, and ductility and durability were more important parametres. Francois Toutlemonde, chairman of the scientific committee, mentioned in his own presentation of the French codes, that there were still some adjustments to be made in the standards, especially regarding concretes in the “border zone”. Both of these French gentlemen are prominently involved in the French standard so I am choosing to take this as a positive sign that our way of thinking – that for UHPFRC with conventional reinforcement there should be less emphasis on compressive strength – is at least acknowledged. Others mentioned in the presentations of their projects that calculated compressive stresses were actually quite low – and Vic Perry, chairman of the Canadian task group drafting Materials and Methods for UHPC, mentioned that if CRC failed to meet the Canadian specifications, at least it would not be due to compressive strength.
In Denmark there are no efforts under way with regard to developing guidelines and we have no influence on how other countries decide to do this, but at least there was an understanding that UHPFRC are many things – and part of being “Ultra High Performance” means that the concrete is tailored specifically for certain applications. Ideally, the specifications should reflect this, so that they are not unnecessarily restrictive, leading to increased cost and less flexibility.
La Mantilla – balustrades in white BSI from Eiffage.
I was amazed at how many different applications were presented and how many countries were using on their own versions of UHPC. I participated in my first conference on UHPC (back then it was called HSC – High Strength Concrete) at Berkeley in 1990 and at that early string of conferences the vast majority of participants were related to universities and most of the presentations dealt with research projects (Stavanger 1987 (HSC), Berkeley – 1990 (HSC), Lillehammer – 1993 (HSC), Paris – 1996 (HSC/HPC), Sherbrooke – 1998 (HPC/RPC), Hawaii – 1997 (HSC) and Orlando – 2000 (HPC).
In this second string of conferences applications have featured much more prominently. The most important ones (off the top of my head) are probably the HiperMat conferences held at Kassel in 2004, 2008, 2012 and 2016, the French conferences held in Marseille in 2009 and 2013 and in Montpellier in 2017, the US conference in 2016 in Des Moines (the second conference will be held in Albany in 2019) and possibly the upcoming conference in Fuzhou in 2018.
After following the relatively slow implementation of UHPC in Europe and the US it is very interesting to see how quickly things develop in other countries. In Europe things started out with the first applications in the early nineties – then a long time of very gradual development and now momentum is starting to build. In North America it took a very long time for the first applications, but now things are moving rapidly – especially with applications for bridge deck renovations and in-situ cast UHPC joints for bridges (close to 200 bridges). In China, Korea, Malaysia and the Middle East (and to a certain extent the Czech Republic) the idea seems to have been to start getting practical experience as quickly as possible, and it Malaysia for instance this has resulted in close to 100 bridges in UHPC being built in a relatively short time span. The majority of architectural applications are located in Europe and the Middle East.
Apart from the number of presentations on guidelines and standards, the presentations on applications was the most significant part of the conference (at least to me). Tuesday afternoon of the conference included a technical visit to some of these places and I have included a few pictures from the trip.
As mentioned, at the first conferences most of the participants were researchers. While researchers can be quite interesting people, I have appreciated the increasing diversity among the participants. We are seeing more contractors, engineers and architects and I can only encourage this. I hope that more will participate at future conferences – and ask the nasty questions (but what does it cost????) that we also need. As long as technical visits are included it will be easier to attract a more diverse audience – and as we see more and more applications we should also be able to place the conferences close to interesting projects.
The new TGV station in Montpellier – the roof covering is produced in Ductal from Lafarge.
If you have comments – regarding the point of my presentation at the conference, whether I missed the most important features of the conference (there were dual sessions so I can always claim to have been in the other session 🙂 ) or anything else, please leave a note in the comment section and I will get back to you.
Bendt Kjær Aarup
Group Material Development Manager
Read about Bendt’s 30 years of experience with CRC right here
7 thoughts on “First impressions from a UHPC conference in Montpellier, France”
It was great to meet you in Montpellier!
As mentioned earlier, this blog is great and nicely presesents your work with CRC.
Could you select a different shape of the compression test specimen which is more favorable to the mean value 😉 ?
If so, next you should be able to reduce the standard deviation by a stricter control of the production.
Thanks to Svatopluk and Dan for their comments. Svatopluk – I am glad you appreciate the blog and please feel free to comment based on your experience with some very spectacular projects. I enjoy hearing about the very different projects that are carried out with Ductal – and seeing things from a different perspective as it is very seldom you use conventional reinforcement.
Dan – we have actually changed from using cylinders to using cubes in an attempt to reduce the standard deviation on our results. This has helped, as the cubes are much less sensitive to the preparation. In Denmark we cast the cylinders with a top and store them in a horisontal position, which means there is usually no preparation of the ends (as you know). In other countries some preparation of the ends is often used such as capping or grinding, which reduces the sensitivity to the casting process of the test specimens. So switching to cubes has actually increased our characteristic strength – also when we convert the values to cylinders. It is true that we could reduce the standard deviation by a stricter control of the production – which we would do if necessary. At the moment we allow some variation of water/binder ratio depending on the specific elements we are casting and depending on the temperature in our mix and during production (usually between 0.155 and 0.165).
Tough one – if your best achievable mean is smaller than the characteristic strength, of course a reduced the standard deviation is indifferent. So you can either change the mix design, change the codes or elect to do nothing 🙂 If you are reluctant to change the mix design, let’s hope the codes adapt.