Precast concrete, already widely recognised for its fast construction and buildability benefits, is now winning the sustainability arguments as well.
As with in situ concrete, precast concrete has a wide range of benefits that makes it well suited to sustainable construction compared with other materials: high thermal efficiency and fabric energy storage (FES); fire resistance; sound insulation; minimum vibration; long life; use of recycled raw materials, including industry by-product streams; local sourcing and transport.
FABRIC ENERGY STORAGE Of these benefits, FES is increasingly embraced by forwardthinking clients and designers. Here, concrete stores and releases heat to stabilise the internal temperature of a structure, thereby reducing the need for heating and air conditioning. Increasingly, the potential of precast concrete's FES is being realised for new construction. Developers report capital costs reduced by 5-20 per cent due to the reduction or removal of air conditioning and suspended ceilings. Users report reduced operational costs.
There are two types of FES: passive and active. With passive FES, exposed soffits use natural or assisted ventilation together with night-time purging to cool the building space.
Active FES has controllable systems of air ducted through plenums or floors. Tests show that they emit 50 per cent less CO 2 than air conditioning. Furthermore, the limited fabric energy storage of lightweight frame structures offers just 6-10W/m 2 of cooling compared with 15-20W/m 2 for passive concrete FES and 25-35W/m 2 and beyond for active concrete FES.
The use of FES significantly increases a building's sustainability. The CO 2 emission level from the lifetime operation of a building is far higher than that of the embodied CO 2 of its construction materials. Indeed, over 50 per cent of the UK's carbon emissions results from the operational use of buildings. So reducing a building's operational heating and air conditioning requirements reduces its real environmental impact. Over its full life cycle, a lightweight framed building will result in higher CO 2 emissions than a heavyweight framed building. The buildings designed using FES also appear to be free of sick building syndrome.
CONSTRUCTION IMPACTS The other inherent benefits of fire resistance, sound insulation, minimum vibration and long life mean that precast concrete reduces the need for additional protective coatings, preservative treatments and vibration-damper systems. All of this significantly reduces the environmental impact of precast concrete. As does the fact that precast concrete is UK sourced. There is growing concern over the 'air miles' CO 2 impact of transportation. Timber and the iron ore for steel often travel many thousands of miles.
Sustainability benefits are not restricted to frames. Precast paving can also actively improve the environment by reducing the level of pollution caused by nitrogen oxides (NOx). Developed by Mitsubishi in Japan, precast paving treated with titanium dioxide has been shown to significantly lower pollution by absorbing NOx.
Cement additives based on titanium dioxide also provide a concrete finish that is self-cleaning. The material reacts with sunlight and rain to clean off airborne spores and pollution.
It has been successfully used by Richard Meier for the Dives in Misericordia white concrete church in Rome.
MORE FROM LESS The precast industry is making significant progress towards placing sustainability high up the construction agenda. It has implemented a 'more from less' programme to examine the sustainability issues for the precast sector and how best to tackle those issues.
To this end, the sector has established sustainability and health and safety committees to provide a pan-industry approach to sustainability; a Concrete Targets Award scheme to improve health and safety; and Best Practice Awards to recognise and promote excellence among the membership of British Precast in the areas of innovation, health and safety and the environment.
The 2005 awards, sponsored by The Concrete Centre, were given to a range of simple and cost-effective solutions that reduced water consumption, eliminated a hazardous waste stream previously sent to landfill, implemented energy-saving programmes and overall waste-reduction programmes. Details of all the 2005 award entries and winners can be found at www. britishprecast. org In addition, British Precast is working on a four-year research project with Loughborough University to develop a sector-wide approach to sustainability. The Sector Sustainability Strategy project will:
identify the economic, social and environmental impacts, both good and bad, of the precast sector;
establish the precast industry's awareness of the opportunities and threats related to sustainable development; and establish objectives, targets and indicators for future improvement.
The project is currently examining the industry's sustainability priorities, and the action it needs to take. Further details can be found on www. sustainableprecast. com British Precast has been working with the British Cement Association on a joint approach to the sustainability of cement and concrete. The role of cement in improving the sustainability profile of precast concrete is important. Furthermore, precast manufacturers are reporting a significant move towards recycled aggregates and industrial by-products.
So in addition to the inherent benefits of precast concrete that offer the potential to significantly reduce the environmental impact of a building's operation, the industry is actively seeking ways to reduce the energy and materials used to manufacture the product. This, together with improved health and safety, increased manufacture and construction efficiency, and the development and implementation of an industry-agreed sustainability strategy, means that precast concrete is able to provide a construction solution that truly offers 'more from less'.