Fly ash has long been a mainstay in the construction industry. But is it threatened by the closure of some coal-fired power stations? Robert Carroll thinks not
The construction industry is finally showing signs of growth which can be felt right through the sector, from the producers and suppliers of construction materials to the specifiers, contractors and construction managers. As a result, at the grassroots of the industry, demand for resources is picking up and order books are beginning to fill.
According to a recent Mineral Product Association (MPA) report, sales of minerals and aggregates in particular are on the rise. The sale of aggregates increased by 6% during 2013 and concrete sales were up by 11%. As the organisation I work for, the UK Quality Ash Association, represents businesses who produce and use fly ash as a secondary material, I welcome this news.
Fly ash is a by-product of the combustion process used at coal-fired power stations and is produced in large quantities on a daily basis in the UK. As such it’s an easily accessible, low carbon secondary resource that is widely available at a number of locations. Fly ash is a very fine and consistent material which can be used in a huge variety of UK building materials – including concrete, bricks, blocks and even engineering fill. It is well known as a key constituent in modern sustainable construction, helping to meet environmental targets and reduce the embodied carbon of our building stock.
In recent years, however, some in the industry have become concerned about the impact that the closure of coal-fired power stations could have on the supply of fly ash – not least the adverse effect that the resulting pressure to use more primary aggregates will have on the environment. The UKQAA, however, does not share these concerns.
Coal has been a core part of the energy mix for many generations and, as it still generates over a third of the UK’s energy need, will remain so for many years to come. As a result the UK already has significant stockpiles of fly ash – up to 50m tonnes in long-term storage – which are added to every day. These stocks alone are enough to supply demand for the foreseeable future, even without any additional production.
And although EU emission regulations will make it harder for some of the older coal-fired power stations to continue operating, much investment is planned for new carbon saving technologies like carbon capture and storage (CCS). Proposed schemes such as the White Rose Project at Drax will allow more traditional forms of energy generation to continue. They will be significantly cleaner and more efficient, and so will provide high quality fly ash as a result.
In the intermediate period, co-combustion (co-firing of coal and biomass) is established in the UK. Cheaper than CCS technology, co-combustion lowers carbon emissions from power stations by reducing the amount of coal burned. Controlled co-combustion of coal and biomass is allowed in EN 450, the European standard specifying fly ash for concrete. The fly ash produced retains the same benefits as “pure coal ash” and is permitted for a wide variety of uses, including as a cementitious material within concrete.
All this is encouraging. It shows that despite the changing landscape of energy generation in the UK, coal-fired power stations will still have an important role to play for many years to come, and fly ash will continue to be a valuable low-carbon construction material. As new technologies develop and are adopted, fly ash will become a cleaner raw material, with an important place in the future of sustainable construction in the UK. So whether it’s concrete, grout or as a fine filler, fly ash will retain its place in construction and remains a valuable component of a resurging minerals and aggregates market.
Dr Robert Carroll is technical director of the UK Quality Ash Association (UKQAA). For more information, visit its website.