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As fly ash supplies dwindle what should the construction industry do?

29 May 2018
The march towards cleaner and more sustainable energy has impacted supplies of 'fly ash' to the construction industry. Nigel Cooke from the UK Quality Ash Association (UKQAA) proposes some alternatives.
As fly ash supplies dwindle what should the construction industry do?
Pulverised fuel ash (PFA) is the fine ash produced during the combustion process used at coal-fired power stations.

When finely ground coal is burned the fine ash is carried out with the flue gas and it is sometimes referred to as 'fly ash'. The ash passes through electrostatic precipitators that remove these fine particles from the gas stream where it is stored in silos or hoppers.

It has played a major role in many construction products and construction applications for the past 50 years.

However, all coal fired power is expected to cease by 2025 and securing sources of PFA throughout the year is already becoming harder resulting in the need for imports and extraction from temporary stock piles. 

PFA is collected from the silos and can either be sold dry for use in concrete and applications such as aerated concrete blocks or wetted (called conditioning) for applications such as fill, grouts, etc.  Any excess ash has traditionally been mixed  with large quantities of water and pumped to lagoons or conditioned and sent to landfill. Both lagoon and landfill ash can be recovered  and sold for fill, grouting and other applications.

What impact will dwindling supply have?

Securing future supply and safeguarding existing assets is now becoming urgent and it is with this in mind that ICE members views on UKQAA’s proposal below are welcome.

Many ICE members may be aware of the pozzolanic benefits of using PFA in concrete, which enhances chemical resistance and durability as well as producing more pumpable mixes. However, ICE members might be less aware that some 1.5m tonnes a year of PFA is used in the manufacture of aerated concrete blocks and grouts for mine filling and ground stabilisation.

Blast furnace slag can be substituted for PFA in concrete though prices of slag are increasing and sourcing is becoming more difficult with some slag being imported from as far away as China. Sand can replace PFA in the manufacture of aerated concrete blocks and for grouting though the performance of sand in such applications is not as good as PFA. Moreover, sand is also becoming a scarce commodity.

UKQAA’s proposed solution

It is estimated that there are well in excess of 50m tonnes of PFA currently deposited in landfill sites in the UK and managed as a waste.  UKQAA is seeking to redefine such deposits as future 'pozzolanic reserves' that could be adopted under future minerals plans. This would then allow the UK construction industry to secure such reserves as a 'national asset' for future extraction for use in cementitious and non-cementitious applications.  

UKQAA recognises that a considerable amount of work is required to align all the various stakeholders to redefine PFA landfill deposits as pozzolanic reserves. As a consequence UKQAA welcomes informed views and comment from ICE members to either address or include in our proposal document.

Further information and submitting your views

ICE members are encouraged to submit their views  or contact Nigel Cooke at UKQAA:

[email protected]