Looking At Concrete In A New Light
Concrete may have been viewed in a poor light in the past, but Steve Crompton, UK technical director with CEMEX, argues that recent developments mean the material has a vital role to play in the future development of more sustainable communities
Concrete has traditionally endured a poor reputation as a fundamental building material owing to perceptions concerning its reliance on virgin raw materials and the energy consumption and emissions associated with its production process. Based on recent developments, however, it can be argued that concrete should instead be viewed as a sustainable, strong, long-lasting, versatile and economically important construction material that has a vital part to play in the UK’s development of more sustainable communities.
Concrete is the most widely used construction material in the world. It is all around us; from offices to schools, roads to railways and dams to homes. Its powerful economic sway sees over 40,000 people directly employed in its UK manufacture, and it supports a construction industry employing 7% of the UK population. However, when it comes to considering its sustainable credentials, which will ensure that the current rate of development is balanced against the resource requirements of future generations, it is important to look at concrete from several angles: its environmental and lifecycle aspects; its economic impact; and its contribution to society in general.
There is clear evidence that improvements in environmental performance are under way to minimize the impact of concrete production. These changes include actively reducing the emissions associated with the concrete manufacturing process, and reducing the reliance on virgin raw materials by increasing the use of by-products in concrete. Add in better management of waste, the use of more recycled aggregates and alternative fuels, as well as the thermal mass of concrete, which, in the face of climate change, can help keep future housing cooler in summer than lightweight houses, while also saving heating fuel in winter, it is clear that concrete has a fundamental part to play in helping to deliver the energy-efficient buildings of the future.
While the total construction industry impact accounts for 10% of total UK CO2 emissions, concrete is responsible for just 2.6% of this. Compared to the 26% generated by transport, this is a relatively small amount, especially considering its importance as a basic construction material. Concrete also comes out favourably when compared with structural steel, where the amount of CO2 generated per tonne is approximately 10 times greater than that of reinforced concrete.
The use of waste products from other industries, such as ground blast-furnace slag or fly-ash, either as a mixer addition or incorporated in factory-blended cements, significantly reduces the overall greenhouse gas emissions, and means that this essential building material is making, and will continue to make, a significant contribution to the Government’s UK Climate Change Programme to drive down CO2 emissions by 60% by 2050.
In addition to actively consuming waste products from other industries and processes, the concrete industry is working towards improving production plants and compliance with international standards, such as ISO 14001, to prevent pollution and ensure continual improvement through the implementation of environmental management systems (EMS). The use of recycled water at production plants is also on the increase and is increasingly commonplace.
It is not only the environmental aspects of concrete that should be assessed as sustainable and positive; its overall lifecycle must also be considered.
Like other building materials, concrete has a life span. When compared with other commonly used construction materials it is by far the most durable, with a typical design life of at least 60 years. Essentially, it has three phases of life. Its creation, its use in buildings and structures, and its reuse through recycling once the building comes to the end of its life.
It is far more likely that a modern concrete building will be deemed obsolete due to no further perceived usage, than the concrete fabric of the structure having failed due to age. With this in mind, and with cost-efficiency and sustainability now to the fore, the reuse of concrete buildings is ever more commonplace. The material offers flexibility and seemingly redundant concrete structures can be worked on, redesigned and rebuilt with new, up-to-date specifications. If demolished, however, the resulting aggregate can also be used for a number of applications as a ready-made and important recycled material.
Contrary to popular belief, not all rubble ends up in landfill after a building is demolished. Up to 95% of a building’s components can be recycled, including the most heavily reinforced concrete.
Indeed, recycled concrete aggregate (RCA) has proven performance characteristics and is being used in the ongoing production of new concrete – thus completing its life circle. New European Standards have cleared the way for greater use of recycled concrete aggregates in the manufacturing process, supporting UK Government targets of increasingly meeting construction demand with material from secondary and recycled sources.
The use of RCA is becoming more established and under BS 8500-2:2006 such materials are permitted in a wide range of mixes.
Introducing RCA into concrete can have an effect on strength leading to a requirement to increase cement contents, as shown in figure 1. However, up to around 25% replacement of the coarse fraction of the aggregate is possible before there is any significant effect on strength. Where the replacement level is low, ie less than 10% of the coarse aggregate fraction, the impact on both the fresh and hardened properties of the concrete is minimal.
From an economic point of view, concrete and its sustainable credentials are well matched. To improve their sustainability credentials, products should be consumed as near to the place of production as possible. For ready-mixed concrete in the UK, the average distance travelled from the manufacturing plant to the point of use is less than six miles. The UK’s self-sufficiency in providing the core materials required for concrete production means that inbound raw material transport and import levels are kept to a minimum. More often than not, the concrete industry uses locally sourced materials for local construction projects, thereby minimizing transport-related impacts. Compare this with timber, which imports over 98% of the total volume used in UK construction.
With increased pressure on conserving fossil fuels, such as coal, for future generations, rising energy costs and changes to the climate, concrete can contribute positively by offsetting the heating up of buildings (especially in summer). Concrete’s high thermal mass can help absorb the heat generated by people, computers, lighting and electrical equipment, and keep internal temperatures lower.
The thermal mass in concrete walls and floors stores energy from the sun and the building’s own heating system, and releases this at night, thereby sustaining warmer overnight temperatures and reducing the need for heating.
Finally, from an economic standpoint, as a self-sufficient producer of this material and a UK net exporter of concrete and component materials, concrete more than holds its own against other important materials.
Contribution to society
Concrete offers many virtues to society as a whole. It produces natural light when used in exposed areas within a structure, reducing the need for artificial lighting. It is naturally inorganic and inert, and does not need treatment with additional toxic chemicals. It has inbuilt fire resistance and offers secure characteristics due to its strength and robustness, and will last for a minimum of 60 years with little or no maintenance.
There is no process of natural decay, which bodes well for future predicted environmental changes, and as a material for buildings it is well regarded by designers and the public alike, who, according to research, view masonry-built houses as having the longest life expectancy of all construction options.
Sustainability is no longer an issue of choice but must be considered at the heart of the ongoing development of society. Assessing the sustainable credentials of products is a complex business and must take into consideration their combined environmental, economic and social impact and performance.
As illustrated here, concrete is a fundamental building material whose combined environmental, economic and social performance is strong. It does, therefore, have a critical role to play in delivering more sustainable communities, by reducing emissions and providing long-lasting and secure, as well as cost- and energy-efficient, buildings for the future.
Britain’s cement and concrete industries can be proud of the essential role they have played in creating the country’s built environment and there can be no doubt that they have a lot more to contribute in the future.