Concrete is a familiar, simple material: an engineer from 1911 would recognise what is produced today from sand, stone, water, cement. Every layman knows what concrete is, but nobody likes it – a negative perception that needs changing, as concrete plays an important role in modern life:
•Construction is the biggest industrial employer in Europe, producing more than 10% of GDP and employing over 15 million workers, with twice as many indirectly dependent on it;
•The role of construction in economic life is reflected by the fact that it is used by almost every government as an engine for economic recovery – government-sponsored construction projects have been used in this way since at least Roosevelt’s New Deal for the USA in the 1930s;
•Concrete is the most widely used construction material in both developed Western economies and developing countries alike. In fact, it is the most widely used material of any kind, after water. It is difficult to imagine any construction project that does not include concrete – high speed rail, the Olympic Stadium, the Channel Tunnel, the Øresund Bridge would all be impossible without concrete.
Concrete is produced in three ways: ready-mixed and fresh, for sale to contractors; precast elements in factories; and on site, by contractors themselves. Ready-mixed concrete represents over half of production, providing work for about 100,000 people in Europe, in spite of recent declines. More than one-third of these are employed by SMEs.
The concrete industry accepts without reservation the need for sustainability in construction, and has managed its businesses in this light for many years. Moreover, concrete has intrinsic sustainability benefits that should be recognised, such as:
•Its life cycle is extremely long, often more than 100 years, and its thermal mass makes buildings cooler in summer and warmer in winter, reducing energy needed for heating and cooling;
•The industry is a net user of waste: it uses 20 times more waste than it sends to landfill;
•At the end of its life in a structure, concrete is re-used – it is recycled into pavement and road construction, and into new concrete. In the UK, almost 100% of ‘hard’ construction waste is re-used;
•Most of the constituents of concrete need little carbon for production, and concrete actually absorbs CO2 by carbonation, particularly when it is crushed after demolition;
•The raw materials necessary for concrete are widely available, and will continue to be so for future generations.
The European Raw Materials Initiative
Two of the three objectives of the European Raw Materials Initiative concern sustainable raw materials from European sources, and recycling. For simple economic reasons, concrete must use local materials, making it a local industry that uses local aggregates. Transport distances for concrete are usually less than 15km. However, recycling must be looked at closely. Most concrete from demolition is already recycled, and insistence on the use of recycled materials in concrete may not make sense in terms of sustainability if long transport distances are required.
Even in wet Britain, water is an increasingly scarce and important resource. Water is essential for fresh concrete (about 17% by volume), and in most plants, no water is now wasted: there is no discharge to water courses, rainwater is collected, and water for washing trucks and plants is recycled. Moreover, the use of chemical admixtures (in most ready-mixed concrete) reduces water consumption by 10% or more.
Cement is the essential ‘glue’ in concrete, and the main contributor to its carbon footprint. However, we should bear in mind that concrete and cement are necessary to modern life, and we should be aware of the huge strides made by the cement industry to reduce its carbon footprint by the use of fuels such as municipal waste, solvents, old tyres and even sewage.
The concrete industry accepts its responsibilities, and uses increasing amounts of ‘waste’ in cement. This includes fly ash from coal-fired power stations, and slag from iron production. The UK leads Europe in using these materials at the concrete mixer, with an estimated 30% of cement in ready-mixed concrete from fly ash or slag.