Designers at the Building Research Establishment of Hertfordshire in the UK have carried the notion of environment consciousness right down to the foundations of buildings. Crushed concrete is being used in the construction of the Energy Efficient Office of the Future in Hertfordshire. The remains of the demolition of a 12-storey bank in London is being used in the concrete for foundations, floor slabs and structural columns. Ground blast furnace slag, a byproduct of the iron industry is also being used with concrete. These materials can replace about 50 per cent of the portland cement in the two different mixes.