Introduction The use of Pulverised Fuel Ash (PFA), also known as fly ash, as anaddition to concrete results in environmental benefits includingconserving primary aggregates, saving water and reducing carbonemissions, while at the same time delivering enhancedperformance benefits, including long – term strength gain anddurability of the finished structures.

DescriptionPulverised Fuel Ash or “fly” ash is the fine ash produced in thefurnaces of coal-fired power stations.The ash is a by-product fromthe combustion of pulverised coal at very high temperatures andpressures.

The ash is a mineral rich substance that cools and solidifies intorounded glassy particles in the flue gases, which are carriedupwards and captured by electrostatic precipitators.

The PFA particles are mostly extremely fine, glassy spheres thatare similar to cement in appearance. BS EN 450 is a harmonisedEuropean Standard for fly ash that replaced the former BritishStandard BS 3892: Part 1 in January 2007.

Quality AssuranceScotAsh products are manufactured under a Quality ManagementSystem (QMS) that complies with the requirements of BS ENISO: 9001.

The QMS is registered with and audited by BSI. Our BS EN 450 fly ash product carries the CE mark.

BS EN 450 fly ash (PFA) is used in projects where strengthand durability is fundamentallyimportant, such as the dam atthe Glendoe hydro-electricscheme at Loch Ness

UniclassL621

CI/SfBYq2BS EN 450 Fly Ash

Sustainable solutions for construction specialists

June 2008

The packaging team at ScotAsh

From left, Leslie WWT plant, Fraserburgh ship lift and Loch Ness, site of the Glendoe hydro-electric project, all have used ScotAsh BS EN 450 fly ash

BS EN 450 Fly Ash

NOTES: 1 The declared mean value is 15%, the upper and lower limit should be +/- 10% from thedeclared Mean 2 There is no upper or lower limit the results should not vary by +/- 200 kg/m3 fromthe declared value. ScotAsh declared value is 2150 kg/m3

Fresh Concrete Properties

SpecificationThree categories of fly ash are permittedunder BS EN 450:! Category A: LOI not more than 5.0%! Category B: LOI 2.0% to 7.0% and! Category C: LOI 4.0 to 9.0%

ScotAsh does not produce Category Cfly ash, which is not permitted in UKconcrete, as the LOI upper limit under BS 8500 is 7.0%.

There are two categories for fineness:! Category N: not more than 40%retained on the 45 microns sieve and alimit of + 10% on the supplier’s declaredmean value permitted! Category S: not more than 12%retained on the 45 microns sieve

ScotAsh produces Category N fly ashonly.The table (right) outlines the mainrequirements of the standard and thetypical values for ScotAsh material.

SelectionBS EN 450 Fly Ash is specially selected atScottishPower’s Longannet Power Station.

‘Real Time’ Carbon analysers monitorthe Loss-on-ignition of the PFA as it iscarried out in the flue gases to ensure thatm a t e ri a l of not more than 5% carbon isselected for sale.

The ‘fly ash’ particles resemble cement inappearance and are very similar chemically,containing the same basic oxides indiffering proportions andmineralogy.

Moreover they demonstratepozzolanic properties inconcrete, i.e. the ‘fly ash’ hasthe ability to react with the limereleased by hydrating Portlandcement to producecementitioushydrates. BS EN450, when usedcorrectly, offersmany benefits toboth the placingand finishing ofconcrete andconcreteproducts.

The physical characteristics of PFA offerseveral key advantages when it is used inconcrete.

The spherical, ultrafine particles result inimproved rheology, reduced bleeding andhelp to reduce the water requirement,making the concrete more thixotropic.

The concrete mix will appear drier thanordinary Portland cement concrete and careshould be taken during mixing to guardagainst excess water use.

Concretes containing PFA have greaterpumpability and often it is possible to pumpmixes directly without altering the fineaggregate proportion.

Bleeding of concrete can be aproblem with conventional mixes, oftendue to the lack of suitably gradedsands.

When PFA is used the higher finematerial content and reduced waterdemand results in a more cohesivemix that is less prone to segregationand bleeding.

Electrostatic separation enables us tocontrol the carbon content of the ash

Loss of Ignition (%)

Fineness on 45mm (%)

Sulfuric anhydride as SO3 (%)

Particle Density (kg/m3)2

Soundness (mm)

Chlorides (%)

Reactive Calcium Oxide (%)

Activity Index (%) 28 Day

Activity Index (%) 90 Day

2.1-4.0

12.5-18.0

0.22-0.69

2090-2120

0.5

<0.010

1.26-3.9

78-82

92-95

5.0

75

85

5.0

25.0 1

3.0

10.0

0.10

10.0

Property

TypicalScotAshresults

BS EN 450 re q u i re m e n t s

Lowerlimit

Upperlimit

_

ApplicationsPulverised Fuel Ash (PFA), or ‘fly ash’ as itis known, has both pozzolanic and physicalproperties that enhance the performanceof concrete.The reaction between thefree lime from the hydrating Portlandcement and the fly ash improves thestrength, durability, chloride and sulfateresistance of concrete.

The advantages of using fly ash inconcrete can be summarised as follows:! Improves long term strengthperformance and durability ! Reduces permeability, which reducesshrinkage, creep and gives greaterresistance to chloride ingress and sulfateattack ! Minimises the risk of alkali silica reaction ! Reduces the temperature rise in thicksections ! Makes more cohesive concrete that hasreduced rate of bleeding, is easier tocompact, gives better pumping propertiesand improves the finish of the struckconcrete

Utilising the properties of fly ash makesit particularly advantageous for thefollowing applications:

! For use with alkali-reactive aggregate ! Mass concrete sections ! Effluent treatment plants ! Marine environment ! Pumped concrete ! High quality finishes ! Sulfate-bearing environments ! Chloride-bearing environments ! Water retaining structures ! Self compacting concrete !Concrete products & precast operations

It also gives satisfactory results:! For air entrained concrete! For thin sections! For cold weather

However, it can be used only with carein high early strength applications unlesshydration is accelerated by increasing thetemperature.

For general purpose applications,concrete containing between 25% and

40% BS EN 450 is most suitable.Theexact proportion of PFA used in the mixfor optimum results will depend on otherfactors such as:! Cement content! Placing method! Strength requirements! Durability requirements

Where long term durability is anessential requirement, a minimum PFAcontent of at least 30% by weight of thecementitious content is often specified.

Mix DesignConcrete can be mixed simply byreplacing a proportion of the Portlandcement with the same amount of PFA,although this may lead to a slightreduction in the early strength.

Alternatively, the mix can be designed toachieve a specific strength at a particulartime. ScotAsh is happy to provide adviceon the mix design to any customer onrequest. Normal admixtures can be usedin concrete containing PFA, though somemanufacturers offer admixtures that aredesigned specifically to work with the finerparticle size of PFA.

BS EN 450 Fly Ash

Leslie WWT works (above and below) under construction in Fife

The information in this datasheet is accurate at the time of printing. ScotAsh Ltdreserve the right to amend details as part of their product development programme

Hardened Concrete PropertiesStrength DevelopmentThe typical strength development of concrete containing PFA isillustrated (top), where both mixes have been designed for equal28-day strength.

There is a marginal decrease in early strength development upto seven days, which can be exacerbated in cold we a t h e r. After 28d ay s , the PFA concrete continues to increase in strength due to thep o z zolanic properties of PFA .

E x t e rnal factors affecting strength gain includes ambientt e m p e ra t u r e, which is illustrated (centre).

Heat of HydrationOne of the main uses for concretes containing PFA is the controlof the heat of hydration. Reductions in heat generated can be inthe order of 20-30% (illustrated below, right).

Drying ShrinkageIt has been demonstrated that the use of PFA in concrete canreduce shrinkage by up to 80%.

CreepCreep is significantly less than Portland cement concretes as PFAconcrete continues to gain strength with time.

DurabilityThe durability performance of PFA based concretes matches orexceeds that of plain Portland cement concrete.

Generally, concretes containing PFA show significantly improveddurability characteristics when used correctly.

In addition, they are resistant to chemical attack, including:! Sulfate Resistance (including Thaumasite Sulfate Attack):Concretes containing PFA are allowed in all classes of sulfateconditions, apart from DC-4m! Chloride Ingress: Correct use of PFA in concrete can reducechloride ingress by up to 90%! Alkali-silica Reaction: PFA in concrete reduces the risk of ASRwhere aggregates cannot be classified as non-reactive. Seeguidelines issued by the Concrete Society and BRE or contactScotAsh for details The resistance of PFA based concretes tosulfate attack and chloride ingress make it particularly suitable foruse in marine environments.

Colour and FinishGenerally concretes containing PFA tend to be slightly darkerthan Portland cement concretes, although PFA concretes can becolour treated.

If concretes containing differing amounts of PFA are to be usedin adjacent sections, or alongside concrete containing onlyPortland cement, consideration should be given to the aestheticsas there may be visible differences in colour. It is widely

acknowledged that concretes containing PFA provide anaesthetically superior finish to conventional PC concretes.

Health & SafetyPFA is not considered to be hazardous to health, but it should behandled in accordance with good occupational hygiene and safetypractices. High concentrations of dust may cause irritation.

It is recommended that Personal Protective Equipmentincluding eye protection, hand and skin protection and dust masksare worn when handling this product. For further informationsee the Health and Safety information sheet for PFA.

To contact ScotAsh please telephone, fax or visit our we b s i t e

ScotAsh Limited, Longannet Power Station, K i n c a rd i n e, FK10 4AA, S c o t l a n d

T F W01259 730110 01259 731055 www.scotash.com

BS EN 450 Fly Ash