Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | SEPTEMBER 2015 | 27 W ith ever demanding safety and environmental concerns, as well as the water industry's drive towards total expenditure (Totex), correct storing and handling of liquids prompts all kinds of important questions. Metal, GRP, membrane or concrete? And if it's the latter, then should it be precast - away from the construction site - or cast in-situ? What are the pros and cons of different tank materials? Metal (steel) tanks will always be a cheaper option, but depending on the requirements of your application, they are not really permanent structures, which therefore may fail to meet the requirements set out by Ofwat for Totex. With concrete, standard longevity is still considered by many as up to 60 years, but more and more companies are designing and building walls, tanks and structures for a 100 year design life. Metal also cannot be used for underground storage, whereas high quality concrete will provide excellent load bearing for stormwater tanks. As the anaerobic digestion (AD) market continues to gain momentum in the UK we have started to see membrane tank covers in operation, as well as concrete and glass-fused- to-steel tanks. Membranes offer cost savings, but it is a matter of choice in an area where safety is critical as to whether you feel comfortable with site personnel peeling back lids, or are happier with a far more solid structure. Meanwhile, GRP can be cheaper for certain applications as it is lighter, although it can be limited on span, and will therefore only be able to sustain restricted loadings. What is the advantage of precast concrete compared to cast in-situ? Even on the most practical level, where space is invariably restricted on site, nobody wants materials taking up room when they're not needed. Having your concrete panels delivered, ready for commencement, ticks all the boxes for minimising time and cost, with speed of construction greatly accelerated. At the 800,000m 3 Doe Park Reservoir in Yorkshire, for example, we reduced the upgrade of a wave wall from 12 months to just six by minimising the amount of steel fixing required on site. Precast concrete also provided another benefit by (instead of traditional masonry) having its exposed external faces finished with masonry-effect formliner to blend in with the local environment. Alone, this more sustainable and aesthetically-pleasing option saved £70,000. How green is precast concrete? Precast is extremely sustainable, made of natural raw materials (stones, gravels, sand, cement), available almost everywhere and in an enormous quantity. Compared with other construction materials, precast concrete minimises the whole life cycle impact on the environment and can be re-used or recycled almost entirely. STEPHEN CASEY PRojEcT EnginEER WhiTES concRETE Precast and Practical Precast concrete tanks answer many current industry needs, offering longevity and sustainability while minimising on-site construction time In the know Getting to grips with… concrete tanks

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