Concrete Truths

But a new study is under way into monitoring technology, which should help predict the design life of concrete structures more accurately and manage their maintenance better. For this work, CIRIA is working in partnership with Imperial College’s professor Nick Buenfeld.

The project will assess the validity of existing “intelligent” corrosion and damage monitoring technologies, drawing on practices in other industries. It will assess existing life prediction models, comparing predictions against laboratory data and historical materials/structure performance.

At the end, two guides will be produced: Intelligent Monitoring of the Deterioration of Concrete Structures and Models for Predicting the Life of Concrete Structures.

To learn more about the project, CM contacted CIRIA consultant Alan Gilbertson to quiz him on why this project is important.

Out there in the real world, how often do concrete structures begin deteriorating before their predicted design life is over? What are a few high-profile examples?

Historically, many concrete structures have started to deteriorate visibly after only a few years and many have given their owners a great deal of trouble and cost them huge sums; there have even been collapses. The concept of design life is in fact meaningless once a building is in use as most building owners assume that their buildings will last indefinitely. Therefore, the real issue is whether an owner and his advisers can manage a building into the future.

Examples:

• Pipers Row car-park – collapsed due to degradation of concrete
• Midlands Link flyovers – major rebuilding of supports due to severe rebar corrosion.
• Devon and Exeter Hospital – demolished due to severe cracking (alkali-silica reaction)

How would an outside observer rate our existing life-prediction models? Do we get it right enough?

Models that exist for monitoring with online data transmission will be evaluated as part of this project and work on this has now started. For most structures, designers do not use life-prediction models; they design to codes that are meant to give acceptable out-turn results. UK codes are currently unclear about how long structures might last; many structures have required extensive modification and repair to remain in use.

When concrete structures prove less durable than predicted, who is to blame, builders or designers?

Different problems arise from different reasons and there is no pool of knowledge which would enable you to take an overall view on who is “to blame”. The reasons for problems occurring are in fact often complex and involve several parties - plus the fact that the basic science is not always fully understood. This situation is likely to continue as long as we are trying new materials or using older materials in new situations. Note that concrete as a material is infinitely variable, with no two loads being identical.

What is the current frontier in terms of building concrete structures in extreme environments? How and when might we be able to push it further?

Concrete as a material is infinitly variable with no two loads being identical

Alan Gilbertson, CINIA

The use of concrete in extreme environments such as tunnels is a young science; we are still trying new ideas out in each new project. We will continue to do this in response to experience in use (particularly where there are problems) and as our understanding of the science improves.

In the term “Intelligent Monitoring of Concrete Structures”, what is the intelligent bit? Why is it called that?

By “intelligent” monitoring we mean monitoring using devices which give real-time information which is handled electronically to inform us what is going on and, ideally, alerts us to situations where an intervention should be considered. The degree of “intelligence” varies but it will always be an improvement on the “regular inspection” approach in which interventions necessarily occur only when there is sufficient damage for it to be noticed.

Can you Give examples of current use of real-time remote monitoring devices, and how much they are being used?

Many owners are shy of publicity but we can give some information on this:

• London Underground is developing expertise in monitoring the performance of tunnel linings
• Prestressing wire breaks are being monitored on the Great Manmade River Project in Libya by continuous monitoring of acoustic emissions
• Corrosion monitoring devices are routinely fitted when cathodic protection systems are applied to reinforced concrete structures.

What other industries might we learn from? What do they do?

Industries that we can learn from include those which are also involved in monitoring: environmental monitoring, water quality monitoring (for chemical sensing), nuclear facility monitoring and the aerospace industry (in-flight monitoring). Relevant technologies include: wireless communications, fibre optics and chemical sensing.

This study is taking 30 months. Clearly it’s important. What’s at stake? What is the underlying goal?

The overall picture in this area of endeavour is not easy to ascertain and the length of this project reflects the need to find information, extract it, understand it and interpret it. The goal is to provide recommendations on the way forward so that follow-on work can be focused on building on what works and plugging knowledge gaps which hold us back.

Can contractors in the UK assist in any way with this study?

Several UK companies involved in monitoring and repair are already involved in the project as members of the steering group: they are Capsis, Concrete Repairs, Colebrand, Fosroc, Sandberg and STATS. Skanska is also involved; their particular interest is in monitoring the behaviour of foundations – particularly piles – so that they can be re-used in the future, with confidence. Other contractors are welcome to contribute experience into the project.