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The project to build the Queensferry Crossing has a dedicated, on-site testing laboratory. Here, Jim Woods, FCBC Deputy Laboratory Manager, explains the importance of the work carried out by the laboratory team.
Q: What’s the purpose of the FCBC lab?
A Essentially, the work we do is to ensure that the materials employed in the permanent works – whether excavated on-site and then re-cycled or delivered from off-site – are suitable for the specific purpose they are intended for.
Q: What sort of materials are we talking about?
A: Well, for a start, there’s soil. For example, thousands of tonnes of soil are being removed during the connecting road excavations currently under way from Echline to Dundas on the south side. Most of it is intended for re-use somewhere else on the site – to form embankments, say, or noise reduction bunds within the permanent roadworks. However, before it can be recycled in this way, we test it to make sure it is fit for purpose. Too much or too little moisture and the soil will not compact properly.
Q: Concrete is a major feature on any road and bridge project. Do you also test concrete?
A: We certainly do. We test the concrete being produced by the FCBC batching plant situated in Rosyth docks. Currently, we are using underwater concrete in and around the caissons and cofferdams. This type of concrete will be used to create the concrete plugs which connect the bedrock to the structural concrete in the tower and pier foundations. Other grades of concrete are being used in the reinforced concrete elements of the various pier foundations on dry land as well as on new bridges in the Ferrytoll area and the new Queensferry Junction on the south side. In due course, different grades of concrete will be produced to form the reinforced foundations for the bridge’s three towers, the towers themselves, the piers carrying the road viaducts to and from the bridge and, eventually, the road surface foundations.
Q: How do you go about testing concrete?
A: We are testing for “workability”. That is, how fluid is the concrete and how suitable is it for the task it is being used for. We make up small cubes from fresh concrete and carry out strength tests by crushing them. The cubes are left to harden or “cure” in water for 28 days before being crushed to determine their compressive strength – as measured in Newtons per millimetre squared. The lab is accredited to UKAS (UK Accreditation Service) which obliges us to record all results for regulatory inspection. The underwater concrete for the foundations is being tested every 50 cubic metres. The amount of concrete for this operation will total in the region of 33,000 cubic metres, so you can see that a lot of testing is involved!
Q: Do you use specialist equipment?
A: The most specialist equipment we use is in the measuring and recording of the data produced in the tests we carry out every day. Later on in the project, we will be employing a Falling Weight Deflectometer which will assess the strength of the final, black-topped road surfaces being used on the bridge, the viaducts and the approach roads. This machine is one of very few in the country and is “leading edge” in its capabilities, so we are looking forward to using it.
Q: What gives you most satisfaction?
A: I suppose it’s knowing that what we do enables our colleagues out there on the construction site to get it right first time, every time. We help ensure that the project can proceed on time without any delays being caused by inferior materials being used.