UKQAA Biostore Seminar, 5 September 2006, London. Lindon K. A. Sear, BSc, PhD, FICT Technical Director. The UKQAA is

Transcription

1 UKQAA Biostore Seminar, 5 September 2006, London Lindon K. A. Sear, BSc, PhD, FICT Technical Director The UKQAA is A non profit making trade association: Wholly funded by the members who are; > EON UK (formerly Powergen) > RWE Innogy - National Ash. > ScotAsh Ltd. > CEMEX - Rugby. > Scottish & Southern Energy. > EDF Energy. > International Power. > Hargreaves CCP (Drax Power Ltd). > British Energy. > Uskmouth Power Ltd

2 There are 18 coal fired power stations in the UK; Ash from a power station

3 The products produced are: Pulverised fuel ash (PFA) > or fly ash, as it is known in many countries and in concrete Dry material mainly for use in concrete. > Transported in cement tankers Conditioned material for use mainly for fill and grouting applications > Water is added to produce an earth dry material that can be transported in sheeted tipping vehicles. Readily available in large quantities Lagoon ash also for use for fill and grouting applications > Material is mixed with copious amounts of water and sluiced to lagoons The products covered: Furnace bottom ash (FBA). All wet bottom furnaces in UK, > so thoroughly washed > Mainly used as a lightweight aggregate in block manufacture. Cenospheres Float on lagoons as lighter than water > Many uses as a filler - lightweight, thermally stable, nonconducting, etc. > Due to changes in ash disposal quantity of cenospheres available now very small!

4 Fly ash is widely used in concrete Fly ash can be used in many ways in concrete. The following are the main approaches; As a cement - BS EN197 and BS EN14216 > Factory made blends of Portland cement and fly ash As a filler aggregate > BS EN12620 Aggregates for concrete > BS EN Lightweight aggregates for concrete As an Type II addition - BS EN450:2005 > March 2005 harmonized version published > Mixer blended fly ash for concrete in two forms in the same document PFA - typical oxides... Major oxide proportions, % by weight Fe2O3 Al2O3 SiO 2 CaO % by weight

5 PFA in concretes PFA is a pozzolana This means a material that reacts with lime to form silicate hydrates - these hydrates give concrete strength and durability. Pozzolanas were used by the Romans to build many buildings, for example the Pantheon. Classified/processed PFA reduces the water content of a concrete - reducing permeability. PFA improves the sulphate resistance and reduces the risk of alkali silica reaction It reduces the heat of hydration compared to Portland Cement PFA is supplied to BS3892 Part 1 and EN450 The Pantheon was built with fly ash... but from a volcano

6 Hydration of PFA PFA reacts with the lime produced by the hydration of cement to give more hydration products - reducing the voids and lowering the permeability. Strength gain properties of pfa When cured at 20C PFA concrete gains more strength after 28 days compared to PC (CEM I) concrete.

7 Insitu strength performance in thick sections... BS EN450-1: fly ash in concrete Construction projects BS 3892 Part 1 fly ash (now BS EN450-1: Category S) has been used in many important projects in the UK, from the Thames barrier to Canary Wharf...

8 Applications for fly ash from self compacting concrete to wind farms Applications for fly ash to Heathrow Terminal 5 to sewage treatment plants

9 Applications for fly ash to the Channel Tunnel Rail Link. Where has BS EN450 Category N fly ash been used? East Midlands Airport - 35,000 m 3 of lean mix made with 30% BS EN450 fly 1,000 m 3 per day.

10 PFA for grouting mines and caverns... PFA grouts can be used to fill old mine workings. Grouting is used to prevent settlement and make sites suitable for construction. In the West Midlands area in excess of 5,000,000 tonnes of pfa has been used to stabilise old workings. 1,100,000 tonnes currently being used to fill the Northwich Salt Mines. Filling Dudley caverns

11 Small grouting contracts Small grouting contracts

12 PFA as a fill on Selby by-pass A42, Kegworth Link PFA in use as a bridge infill Pfa as a fill material...

13 Chadderston, Derby PFA can be landscaped with a little top soil - It must never be left exposed! Pfa for landscaping... Reinforced Engineering Fill Reinforced earth fill at Wolverhampton s low level station where a bridge was removed.

14 Why use fly ash in Biostore? The pozzolanic reaction produces; A matrix with low permeability; Continuing strength with time; > In the presence of water and when lime is available Chemically stable hydration product > In an alkaline environment Fly ash is readily available It is a cost effective material Higher carbon ashes should be beneficial in absorbing any leachates Barriers to the use of PFA The classification the PFA/fly ash that it is a waste! A long and complex story The Environment Agency and SEPA believe PFA is a waste The UKQAA/Power Industry believe that fresh PFA is NOT a waste! Discussions have been ongoing for years EU Thematic Strategy may resolve; > PFA/fly ash would be classified as a by-product > WRAP style protocols may be part of a solution Issues should be clear by spring 2007?

15 Proportions of Sold Material by Application - Jan to Dec 2004 Fill and ground remediation 14% Misc. including Lytag 4% Gypsum sold 19% Biostore Biostore in in 2010? 2010? FBA utilisation 14% Aerated blocks 16% Cenospheres 0% Grouting 6% Cement raw material 6% Non-aerated concrete blocks and precast 9% Concrete Addition 11% Blended Cement 1% The environmental factors in cementitious systems Using PFA reduces the Portland Cement required for a given 28 days: This reduces overall CO 2 and other greenhouse gas emissions Every tonne of Portland Cement made produces ~960kg of CO 2 Enhanced durability: The concrete lasts longer lessening overall environmental impact Reduced leaching potential: PFA produces low permeability concrete - that leaches less, is more durable, etc so will last longer!

16 Emissions to the environment: CIA/DETR project showed that using 30% PFA for equal 28 day strength in a concrete mix that: Greenhouse gas emissions are reduced by 17% Acidification reduced by 15%. Winter smog reduced by 15%. Eutrophication reduced by 13%. Primary energy requirements reduced by 14%. Reduced impacts using additions: Current savings due to the use of cementitious additions (PFA and GGBS) Primary aggregate consumption in cement manufacture reduced by 12%. 1,200,000 tonnes of CO 2 emission saved million megawatt hours of energy saved. 6,000 tonnes of SO 4 equivalent saved. Overall reduction of environmental impact 9% due to utilising PFA. These figures are increasing every day that passes As more cement companies, concrete producers, road makers, etc see the environmental benefits of PFA/fly ash

17 Benefits of PFA to the environment Overall reductions of CO 2 emissions savings are; For PFA/fly ash + Flue Gas Desulfurisation Gypsum + FBA production > ~625,000 tonnes of CO 2 saved annually Utilisation rate for power station products (2004); FBA 100% Gypsum 100% PFA/fly ash 58.6% For more information about PFA or the UKQAA contact us... Dr Lindon K. A. Sear UKQAA Regent House Bath Avenue Wolverhampton West Midlands WV1 4EG or visit our WEB site Tel: Fax: LKASear@UKQAA.org.uk