Last year was a time of recovery for the construction industry and as we enter 2014, things are looking brighter still. But with increased economic activity, new challenges have come to the fore in the shape of challenging project timescales and strict sustainability requirements. Designers and specifiers want affordable materials that are readily available and have a good environmental profile. And as a result, demand for lightweight secondary aggregate (LWA) has been growing steadily over the past year according to the UK’s largest producer, Lytag.
Lytag’s LWA is made from fly-ash, the waste generated by coal-fired power stations, and takes the form of low-density pebble-shaped pellets with a honeycomb internal structure. Besides concrete, the material is also in demand as a horticultural drainage medium and is widely used in green roofs. “Contractors and engineers are making use of [LWA’s] sustainability credentials and the reduced dead-load it offers when used in structural concrete,” explains Gareth Moores, managing director of Lytag. Lytag can produce a structural material 35% lighter than concrete made with traditional-weight aggregate, says Moores, and this can have significant knock-on benefits in terms of cost, time and resources. “Lower weight reduces the scope of piling and foundation works and requires lighter structural reinforcement with consequent savings in materials costs and project timescales,” he says. As a secondary material, Lytag also has a positive impact on BREEAM environmental assessment ratings.
Encouraged by the increase in demand for its product, Lytag has recently opened a new plant on the site of Drax Power Station in North Yorkshire. The new plant increases the availability of Lytag to projects across the UK with the option to deliver to site more simply and quickly than was previously possible. Drax itself is an ideal location for a new plant, despite its conversion to co-generation (see feature, page 32 in the March issue of The Construction index magazine) because there are large quantities of fly ash already stockpiled at the power station. Moores says these stockpiles alone are enough to keep the plant producing for several years. A typical recent project using Lytag LWA is 6 Bevis Marks, a new commercial development in the City of London. This new 16-storey building is built on the site of a previous seven-storey 1980s office block and is claimed to be some 80% more energy efficient than the one it replaces. The design has been awarded a BREEAM ‘Excellent’ rating. One of the key requirements for this project was that the design should re-use as much of the existing materials and structure as possible. The building – now substantially complete - was therefore constructed using over 50% of the original structure, including re-use of the original piling. Consulting engineer Waterman Structures needed to ensure that any new superstructure was within the structural capacity of the existing piles; hence the mass of the new 16-storey building needed to be kept to a minimum. The structural frame of the new building is therefore of a lightweight steel design and the floors were designed as composite ‘holorib’ slabs with a layer of ready-mixed concrete laid on top. To keep the weight down, Waterman Structures used Lytag LWA in the concrete mix instead of traditional quarried stone aggregate. This resulted in a 20% reduction in the weight of the floors - roughly 1,800kg/m3 compared with around 2,400 kg/m3 for a traditional mix. In total, some 2,872m3 of Lytag LWA was used in the floor structures.
“Given the inherent sustainability of Lytag LWA, we not only helped to realise a more sustainable design but also delivered the added benefits of diverting a material from landfill and reducing reliance on quarried aggregates,” declares Moores. He believes that while construction teams strive to ensure projects are completed on time, to budget, and according to strict sustainability criteria, the demand for alternative materials will continue to grow. “With sustainable, lightweight aggregate now more readily available in the UK, engineers and contractors can take full advantage of the benefits it offers,” he says
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