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Technology Digest 1
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Use of
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450
in structural concrete
Concrete Society Technology D igest 1
Ref CS 133
ISBN 0 946691
82 7
0
Concrete Technology Unit, University of Dundee,
2002
Further copies of this publication, information about o ther Concrete Society publications and mem bership of The
Concrete Society may be obtained from:
The Concrete Society, Century House, Telford Avenue, Crowthorne, B erkshire RG4.5 6YS, UK
Tel: +44(0) 1344-466007, Fax: +44(0) 1344-466008, Email: consoc@ concrete.org.uk
All rights reserved. Except as permitted under current legislation no part of this work may be p hotocopied, stored
in a retrieval system, published, performed in public, adapted, broadcast, transmitted, recorded
or
reproduced in
any form
or
by any means, without the prior permission of the copyright owner. Enquiries should be addressed
to The Con crete Society.
The recomm endations contained herein are intended only as
a
general guide and, before being used in connection
with any report or specification, they should be reviewed with regard to the full circumstances of such use.
Although every care has been taken in the preparation of this report, no liability for negligence or otherwise can
be accepted by T he Concrete Society, the mem bers of its working parties, its servants or agents.
Concrete Society publications are subject to revision from time to time and readers should ensure that they are
in possession of the latest version.
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Technology Digest 1
USE
OF FLY ASH
TO BS
EN
450 IN
STRUCTURAL CONCRETE
Ravindra K. Dhir
Michael
J.
McCarthy
Kevin
A.
Paine
Concrete Technology Unit, University
of
Dundee
ENVIRONMENT
TRANSPORT
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2
Use
ofjly
ash to BS EN
450
in structural concrete
FOREWORD
This Techno logy Digest has been prepared as part of a technology transfer programme
undertaken at the Concrete Technology Unit (CTU) of the University of Dundee unde r
the Partners in Technology Programme
of
the Department of the Environment,
Transport and the Regions. It has been w ritten by the staffof the CTU.
The project was guided by a steering comm ittee representing the University and all
contributing partners.
STEERING COMMITTEE
University of Dundee
Professor
R K
Dhir, OBE (Chairman)
Dr M J M cCarthy
Dr K A Paine
Departmentof The E nvironment, Transport and the Regions
Dr
S B
Desai, OBE
Industrial Partners
Mr W Armstrong ScotAsh Ltd
Mr C Bennett ScotAsh Ltd
Mr P B rennan
Mr
R
Coombs
Professor T A H arrison
Mr
P
Livesey
Mr F McCarthy
TXU Europe Power Ltd (formerly Eastern Generation Ltd)
National Power plc
Quarry
Products Association
Castle Cement Ltd
Electricity Supply Board, R epublic of Ireland
The S teering Committee
is
grate hl to Dr L
K
A Sear and
Dr
G
R
Woolley for their
comm ents and contributions.
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Use ofjly ash to BS
EN
450 in structura l concrete
3
CONTENTS
1
Introduction
2
B S E N 4 5 0
3 Properties of concrete with BS EN 450
fly
ash
3.1
Fresh concrete properties
3.2
Strength development and a chieving equal strength
3.3 Engineering properties
3.4 Durability
4
Method s for using
BS
EN 450
fly
ash
4.1
Equivalent cement method
4.2 K-value method
4.3
Equivalent concrete performance method
4.4
Treatment with respect to ASR
5
Concrete production
5.1
Storage, handling and use
5.2
Effect of
*10%
fineness variation on strength
5.3
Loss-on-ignition
6
Case studies
6.1 Ratcliffe cooling tower strengthen ing
6.2 High Marnham substation
7
Availability
References
Appendix: Taking accoun t of
fly
ash characteristics in mix d esign
page 5
5
6
6
6
6
7
9
9
9
10
11
11
11
12
12
13
13
14
15
17
19
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ash
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450 in
structural concrete
5
1 INTRODUCTION
The European standard BS EN
450 ly ashfor concrete- efinitions requirements and
quality
control
['I
covers a broader range of fly ashes as a cementitious comp onent for
use in concrete than previous UK standards. This Technology Digest brings together
current knowledge of the properties on fly ash to BS EN 450, and offers technical
guidance on how the m aterial should be used in concrete. Factors relating to concrete
production are also covered, and two case studies show how fly ash to BS EN 450 has
been used successfully.
2 BSEN450
The scope of BS EN
450
is fly ash produced by the co mbustion of hard coal, i.e. what
is known as pulverized-fuel ash (PFA) in the UK. Fly ashes produced from burning
other materials are not, at present, w ithin its scope.
The requiremen ts for fly ash to conform to
BS
EN 450 are shown in Table 1.
It should be noted that fly ashes conforming to BS
3892:
Part 1 I fall within the sco pe
of BS EN 450. The m ain difference between these standards
is
in the allowed range of
fineness (measured as percentage retained on a
45
pm sieve). BS
3892:
Part 1 allows fly
ashes of fineness up to only 12.0%, but this has been extended in BS EN 450 to 40 .
To control variability BS EN 450 does not allow the fineness to vary by more than
10 from the declared mean.
The perm itted loss-on-ignition (LOI) for fly ash also differs. BS
3892:
Part
1
has an
upper limit of
7.0
while BS EN
450
is based on an auto-controlled value. The standard
specifies
5.0
as the norm but permits values up to 7.0 on a national basis. The British
Standards Institution have proposed the use of the higher value in the UK. Due to
Table 1. Requirements
o r j l y
ash given in BS EN
450 [ and BS 3892: Part
Property BS EN 450 BS 3892: Part 1
Fineness, maximum
(
retained on 45pm) 40 12.0
Fineness variation
10.0% on mean
value
Loss-on-ignition
( 30)
Particle
density (kg/m3)
Chemical composition:
SO,, maximum ( )
Free CaO, maximum
Yo)
Total CaO, maximum ( )
Chloride,
maximum ( )
Moisture content, maximum ( )
Water requirement,
maximum
( )
Activity
index, minimum
( )
(ii')
Soundness (mm)
5.0 (7.0 on national basis)
auto-controlled
7.0 maximum
150on
mean value
5 2000
3
2
10
(sub-bituminous ashes) 10
0.1 0.1
0.5
95
80
(28
days)
10 0)
10
1.0
or
2.5"'
ii)
75
(28 days),
85
(90
days)
Notes: (i) Soundness
test
required only if free CaO exceeds I .
(ii) Fly ash to be stored and transported dry.
(iii) BS EN 450 uses 25 fly ash content by mass est cam ed out on equal water content basis,
whereas
BS 3892
uses
30
fly ash content by mass, est carried
out
on equal flow basis.
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Useofjly ash to
BS E N 4.50
in structural concrete
seasona l variations in LO I, the auto-control value in BS EN
450
will be mo re difficult
to ach ieve than the absolute value in
BS
3892: Part 1.
Other differences from BS 3892: Part 1 are that BS EN 450 requires soundn ess to be
measured only w here the free calcium oxide lim it is not satisfied, and the activity index
(referre d to in
BS
3892
as the ‘strength factor’) should be determ ined on an equal water
content basis. Additionally, BS EN 450 has no water requirement. It should be noted that
with some coarser fly ashes, water reductions for equal workability might not occur.
BS EN 450 is being revised into a ‘harmonised’ form. This means it can be used as the
basis for CE marking. During this process, the activity index is being reviewed, and
considerationgiven to including fly ashes produced by co-combustion of coa l with other
fuels.
3 PROPERTIES OF CONCRETE WITH
BS
EN
450
FLY
-ASH
3.1 Fresh concrete properties
There are many reports on the physical and chemical influences of fly ash on the
properties of fresh and hydrating concrete. In general, fly ash inclusion in concrete
reduces water dem and, improves workability and reduces bleeding and se gregation. The
benefits associated with these effects enable water con tents to be lower and concrete to
be designed w ith reduced w ater/(cement
+
fly ash) ratios for equal workability [31.
Since
BS
EN 450 allows a wide range of fineness to be used, there is a p ossibility that
the beneficial effects of improved w orkability with finer fly ashes w ill reduce as the
coarseness of the fly ash component increases. Investigations into the relationship
between slump and fly ash properties at equal water contents have indicated a strong
correlation with fly ash fineness
41.
However, it has been shown that coarse fly ash
(fineness>30 ) can be used effectively n conjunction with water-reducingadmixtures
to achieve equivalent workability and strength to that of finer fly ash concrete[’]. This
need to include water-reducing admixtures may influence the econo mics of co ncrete
production.
3.2
Strength development and achieving equal strength
Test results have shown that use of coarser fly ashes leads to a reduction in com-
pressive strength for equal watedcement ratio. This effect (shown in F igure
1)
increases
with dec reasing water/(cement
+
fly ash) ratio. Gen erally, a
5
increase in
45
pm sieve
retention will lead to a strength reduction of between 0.4 and 1.5 N / m 2 or typical
cement + fly ash contents.
It has been show n that concretes of equal strength can be p roduced from fly ashes with
finenesses over the full range permitted in BS EN 450. Strength may be controlled by
adjusting the water/(cement
+
fly ash) ratio, changing the relative proportions of
constituent materials or co mbina tions of these.
Use of fly ashes with LOI up to 8.0 has been shown to have only a minor influence on
strength16] nd use of fly ash conform ing to the L OI requirem ents in BS EN 450 should
present no problem s with regard to strength.
3.3
Engineering properties
The effect of using fly ashes of differing fineness on the elastic modulus, creep
coefficient and ultimate shrinkage of co ncrete are compared in T able 2. In general, these
follow the expected behaviour in terms of the effect of the design strength on each
property. However, there are no significant effects of fly ash fineness on any of these
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Use offly ash to BS EN 45 0 in structural concrete
3.4.2 Carbonation
The effect
of
different fineness and
LOI
of fly ash on carbonation rates appears to have
little influence for equal strength concrete. In stud ies 9-111 he m aximum difference in
depth of carbonation between concrete specimens containing different qualities of fly
ash has been found to be well within experimental variab ility. For practical purposes it
can be assumed that fly ash fineness and LOI have no influence on carbonation rates.
All fly ashes conforming to
BS
EN
450
are therefore suitable for exposure to
environm ents in which carbonation may occur.
Table
3. Comparison of aspects of durabilily for concrete containingfly ashes of digering
finenessLn1.
ly ash
content
=
30% by mass of cement +fly
ash.
Design strength
Fly ash
fineness
(N/mm2) 3.5 -.35.0
Durability property
Chloride diffusion (cm*/s
x
10-9)
i)
35
9.4 10.2
50 4.9 4.3
60 1.2
1.5
Carbonation depth
(mm) ( i i )
25 31.0 32.0
35 17.0 17.5
25 41 45
Sulfate resistance, expansion ( x io- iii) 35 28 28
50
0 0
35
51
48
Freeze-thaw durability factor ( ) (iv) 50 72 65
35 v i 0 98 97
Abrasion (mm) (* vi)
35 1.10 0.92
50
0.79
0.8
.
Notes: (i) Two compartment cell. (ii) 4.0% enriched CO,, 20°C, 55
RH 30
weeks). (iii) 6.0g/I MgSO,
1 84 days exposure). (iv) ASTM C666, Procedure A
[ I z 1 ,
(v) Modified BCA method [ I 3 ] (vi) Cured for
seven days wrapped
in
polythene , then air at 20 C,
55 RH
o 28 days. (vii) Air-entrained concrete.
3.4.3 Sulfate resistance
The use o f fly ash in concrete gives adequate resistance to the ettringite form o f su lfate
attack, which is generally considered to reflect the reduction in quantity of reactive
material present and the enhancement in the concrete microstructure
[I4].
Although
different levels of sulfate resistance may be obtained by using fly ash from different
s o~ r c e s [ ' ' ~ ,his is believed to be related to com positional rather than physica l effects of
fly ash['61.
Short-term tests have shown that fly ash concretes of similar strength have comparab le
resistance to sulfate attack, with concretes of strength greater than
50
N/mmz showing
little expansion[']. N ote that, where using fly ash as a com ponent of ce ment o r in com-
bination with a CEM I cem ent for sulfate resistance, BS 8500 I7] the complementary
UK
standard to
BS
EN
206-1 I R 1 ,
recommends a minimum fly ash content of
25%
by mass.
At present no guidance can be given on the use of
BS
EN
450
fly ashes to resist the
thaumasite form of sulfate attack.
3.4.4 Freeze-thaw resistance
The rate of deterioration
of
concrete under freeze-thaw conditions decreases with an
increase in concrete strength. For equal concrete grade there appears to be no influence
of fly ash fineness or LOI on the a bility of concrete specimens to resist freeze-thaw
attack
[6*'o,'91.
Although adequate performance in freeze-thawconditions can be achieved
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450
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9
by increasing the comp ressive strength, the 'mo st 'efficient m eans o f enhancin g
performance is through the u se o f air-entraining admixtures (AEA ).
Irrespective of the fly ash fineness, the do sage of AEA required to obta in the necessary
air content is approximately the same. However, for fly ash with high LOI, greater
dosages of AE A m ay be required than for fly ashes with low LOI. U sers of fly ash
should therefore pay particular attention to any variability in L OI and the sub sequent air
content and concrete strength to ensure that concrete freeze-thaw resistance is main-
tained (see Section
5.3).
3.4.5
Abrasion
resistance
There is evidence
[91 to
suggest that, when concrete is properly cured there is a minor
impro vemen t in the abrasion resistance when using fine ash
(3.5
and
13.5
retained
on a 45 pm sieve) over that obtained using c oarser ash (35 retained).
4
METHOD USING
BS
EN
458
FLY
ASH
4.1 Equivalent cement met
The introduction of the equivalent cement method in BS 3892: Part 1 in 1993 has
resulted in
it
becoming the most widely used method in the UK for controlling the
incorporation of fly ash into concrete, and it is used by suppliers to dem onstrate that a
Portland cemendfly ash combination from a defined source has the properties and
proportions required by a cement conforming to the equivalent cement standard. The
basis of the method is that any cemenvfly ash combination that conforms to the equiva-
lent cement stand ard will give adequate performance.
The procedure given in BS
3892:
Part
1 :
199712]
s included in BS
8500
I7]
the comple-
mentary British Standard
to
BS EN
206-
1
Ix1.
It should be noted that testing is carried
out at equal water contents so the rheological improvements brought about by the
inclusion o f fly ash are not recognised. The procedure is applicable to fly ashes con-
forming
to
BS
3892:
Part
1
and BS EN
450
with an LOI not greater than
7 .
Work has
demonstrated [* that the method is applicable
to
fly ashes conforming to BS EN 450, and
its use is recommended.
The equivalence procedure determines the range o f proportions over which the require-
ments of the ceme nt standard are satisfied. The producer is able
to
use any proportion
within this range, thus giving flex ibility
to
optimise the mix design, but proportions of
fly ash shall not exceed
55
of the combination. How ever, the applicable range varies
with the properties of the fly ash and cement.
4.2
K-value method
The k-value approach to using fly ash in concrete was proposed by Smith
[211,
and
assumes that fly ash is 'k' times as effective as an equal m ass of cement in the
developm ent of strength, engineering properties and durability resistance. T he 'effective
cement content' to be used in the calculation of minimum 'cement' content and maxi-
mum water/'cem ent' ratio is therefore calculated as
(c +
kf), where
c
is the actual
cement content an df is the fly ash content.
Any type of cemen t can be used, but the k-value concept is not applied when fly ash is
part of the cement. In this case, the fly ash is, in effect, taken as having a k-value of 1
.O
(equivalent cemen t method Section 4.1)
k-values can be calculated for many aspects of performance but it is usual to use them
for strength. Values of k for streng th between 0.1 and 0.8 [ ' I . 20-231 have been reported,
depending on fly ash fineness, LOI and content in the mix. Users of the k-value
approach usually limit the maximum quantity of fly ash that can be counted as
cementitious and restrict the amount by which the cement content can be reduced. A
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Use ofj ly ash to
BS
EN 450 in structura1 concrete
value of k
= 0.4
is given in BS EN 206-1 [ I for use with
BS
EN
450
fly ash up to a
maximum fly ash content of 25%, when used in combination with CEM 1-42.5 N
cement. (It is assumed that fly ash above this level acts as filler.) A value of 0.2 is
permitted for use with C EM 1-32.5 N cement.
The k-value method is simple to use, but
it
is questionable whether a single k-value of
0.4 is applicable to the full range of fly ashes permitted by
BS
EN 450. The achievement
of sufficient strength to give adequa te performance is therefore uncertain. A hr ther
problem is that k-values based on strength are not necessarily appropriate to many
aspects of durab ility performance, where the relative effectiveness of fly ash co mpared
with cement may be considerably different.
It has also been shown that where the minimum cement content controls the mix design,
the k-value m ethod leads to a significantly higher cement + fly ash content[241han that
obtained using o ther methods. This has significant implications for the co st of con crete
designed using the k-value approach.
Guidance on the methods for measuring the k-value and the problems associated with
this method will be given in a CEN report[251.
4.3 ance
metho
The equivalent concrete performance m ethod,
as
originally conceived, was intended to
permit m ix designs that incorporate non-standard materials, with the aim of produ cing
optimum performance from locally available materials, such as fly ash. The con crete is
specified by performance, usually in terms of d urability, and all concretes that mee t
these requirem ents, irrespective of constituents, are considered equivalent. There is no
requirement to ma tch the performance of a reference concrete. The shortcoming in this
approach is the lack of standardised durability tests on concrete. Therefore, any
performance tests have to be agreed on a project-by-project basis.
As a way forward, an alternative method of app lying the eq uivalent concrete perfor-
mance concep t for fly ash co ncrete is given in
BS
EN 206-1 [ I. This method permits
amendments to the requirements for minimum cement content and maximum
wa terkem ent ratio, if it can be proven that a conc rete made with a pa rticular fly ash and
cement has equivalentperformance to a reference concrete meeting the requirements for
the relevant exposu re condition. The equivalent performance sho uld be judged with
respect to the particular specification for which the concrete is intended, especially
environm ental actions and durability.
The reference concrete against which the fly ash concrete
is
assessed shou ld contain
cement to BS EN 197-11261and have constituents corresponding to the co mbination of
fly ash and cement.
BS EN 206-1 recom mends the following limits on the range of fly ashlcem ent com-
positions:
(i) the total amount of fly ash should be within the limits in BS EN 197-1 for
permitted types of cement
(ii) the sum of cem ent and fly ash should be at least equal to the minimum cement
content in
BS
EN 206-1
(iii) the water/(cement + fly ash) ratio should be no greater than the maximum
waterkem ent ratio in BS EN 206-1.
Tests have shown that equal performance for chloride ingress, abrasion resistance,.
freeze-thaw resistance and ca rbonation can be achieved when the above restrictions are
applied and the fly ash co ncrete has equal 28-day com pressive strength to the reference
concrete. The refore, for BS EN 206- 1 exposure classes XO, XC , XD and XF, no further
durability testing is necessary provided the concrete durability requirements contain a
requirement for compressive strength. This makes the equivalent concrete performance
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Use o jly ash to BS
EN
450 in structural concrete 11
i J
method easy to apply, as long as the effect of fly ash on strength is known, and reliable,
because the strength is checked.
The fineness of fly ash can affect the performance o f concrete and BS EN 450 permits
a greater range than BS
3892:
Part
1.
Because of this, there is a need for a concrete m ix
design method that can take in to account the variations in fineness. Such a mix design
method has been develop ed[61 n which equal strength is achieved for different fly ash
concretes by sim ple adjustmen t to the free water/(cement + fly ash) ratio. T his may be
attained by:
(i) maintaining the existing cement
+
fly ash content and adjusting the fr ee water
content
(ii) maintaining the existing free water content and adjus ting the cemen t + fly ash
content or
(iii) adjusting both the free water and cemen t + fly ash contents.
4.4 Treatment
with
respect
to
ASR
BRE Digest
330 271
offers guidance on minimising the risk of damaging alkali-silica
reaction (ASR) in new construction using different cementitious materials. T his requires
fly ash to conform to
BS
3892: Part 1
,
nd
so
does not cover the w ider range o f fly ash
fineness allowed by BS EN
450.
However, there is nothing in current European
standards or published data to support this restriction. Where the fly ashkement
comb ination is manufactured by inter-grinding the con stituents, the fineness limit is not
required s long as all other properties satisfy BS 3892: Part 1.
Digest 330 states that definitive guidance on fly ash to BS EN 450 cannot be given
because of lack of technical data. Where fly ash is used for purposes other than to
modify the risk of
ASR,
Digest
330
states that
it
should be treated in a man ner similar
to a BS 3892: Part 1 fly ash as if it were a com ponent of a com bination, for the purpose
of its contributions to the recommended maximum combination content, and to mix
alkali contents. Th us the use of BS EN 450 ly ash should be restricted to concrete not
at risk from deterioration due to
ASR,
either from its intended use or the use of non-
reactive aggregates, until data are available to confirm performance levels. However,
when ch ecking a con crete for its resistance
to ASR,
all BS EN
450
ly ashes should be
treated as being equally effective as those conforming to BS
3892:
Part
1.
A research
programme
is
in progress at the University of Dundee to confirm this aspect
of
performance.
5.1 Storage,
handUing and M S ~
Fly ash can be supplied in four forms:
Dry
This
is
how fly ash is supplied for most cement, concrete and specialist grout
applications.
Dry
ash is handled in a similar manner to Portland cement and oth er fine
powders. Storage is in sealed silos with the associated filtration and desiccation
equipment, o r in bags.
Conditioned
Water can be added to fly ash to facilitate compaction and handling. T he amount o f
water added isdetermine d by the end use. Conditioned fly ash is widely used in aerated
concrete blocks, grout and specialist fill applications.
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Use
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ash
to
BS
EN 450
in structural concrete
13
6
CASE STUDIES
Fly ash conforming to BS EN 450 has had little use in the UK and most work has
involved fly ash to BS 3892: Part 1 , with a tightly controlled fineness. Projects that have
used coarser fly ash were mostly completed before the introduction of BS
3892:
Part
in 1982 or carried out within th e electricity generating industry using ‘run of station’ fly
ash.
6.1 Ratclif fe cooling
tower
strengthening
Because of structural problems occurring in some cooling towers at power stations
belonging to the Cen tral Electricity G enerating Board in the late
1980s,
a strengthening
programm e was initiated. This involved add ing a man tle of concrete to the outside of
the existing shells. Woolley and Cabrera reported this work in 1991 2 ’ ] Data is available
for the work at Ratcliffe power station, Nottingham, between August 1989 and February
1990.
The concrete had a
28-day
characteristic strength of
30
N/mm2 but to enable early
stripping of the formwork, strength o f at least 7 N/mm2 at 24 hours was required. T he
mix design was developed from a plain concrete mix with the fly ash added a s a direct
substitution o f the cement and representing 35 of the cement + fly ash content. The
amoun t of sand was slightly reduced to achieve constant yield.
The mean fineness of the fly ash was 3 1.0 ,varying between 14.4 and 42.9 . This
is outside the variability permitted by BS EN
450 (*to )
but is tending towards the
finer end of the range.
The mean 28-day cube strength was 49.5 N/mm 2 with a standard deviation
of
3.6 N/mm2. This standard deviation is low despite the fly ash being m ore variable than
permitted by BS EN
450.
The plot o f strength against fly ash fineness in Figure
2
show s the scatter of results. A
trend can be seen tow ards lower strength concrete with increasing coarseness o f the fly
ash. From the diagram it
is
estimated that the concrete strength at 28 days varies by
about
4
N/mm2 over a
20
fineness range for the fly ash.
Major defect limit
- 6
0
10
1
20
30
40
FINENESS (
retained On.45 pm sieve)
Maior .defect
limit
k
50 60
Figure
2 .
Scatter of strength results with l y ash fineness for Ratcliffe cooling tower strength-
ening project. The major defect limits relate to the conformity criteria of f
5% in
BS EN
450.
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Use ofjly ash to BS EN 450 in structural concrete
The mean
LOI
recorded over the same seven-month period w as
4.4 ,
which gives an
upper limit of
6.1
based on the statistical factors in
BS
EN
450.
Two results were
above
7.0 ,
but below
9.0 .
This means that the fly ash supplied to the contrac t would
not meet the requirements of
BS
EN
450
unless, as proposed for the
UK,
the
7.0
imit
was adopted.
6mz MiqDh
~~Ormnh~oOn
MbSaSl~iOGU
High Marnham power station, near Newark in Nottinghamshire, was constructed
between 1956 and 1962; the 275 kV substation associated with the power station was
constructed in 1957-58. The substation bases were cast in PC concrete, except for a
limited number of control areas which contained fly ash. Unusually for the time, the
work was well-documented
[291
and the concrete was examined
25
years later and the
results published [301
The m aterials used were ordinary Portland cemen t and Trent Valley aggregates with a
maximum size of
38
mm . The fly ash was 'run of station' ash
from
North W ilford power
station in Nottingham. T he properties o f the cement and fly ash are shown in Table
5.
Table 5. Mean values fo r OPC an dfl y ash properties used in High
Marnham project.
~~~~ ~
Property
QPC
Fly ash
SiO, ( )
A1,0, ( )
Fe203
CaO ( )
20.8 46.7
7.2 27.8
3.3
9.5
61.7
.,
7.1
MgO ( )
2.3 3.8
Na,O ( )
0.9
0.9
K,O
( )
0.5 0.6
so,
( )
1.7 1.24
Loss-on-ignition( )
1.6 2.5
Specific surface area [Blaine] cm2/g) 2250 3260
Fineness( retained on 90
pm
sieve) 4.6 12.3
Soundness (mm)
3.1
Particle densitv (g/cm31 2.03
Th e cement was relatively coarse and had a high alkali content. Th e specific surface at
2250
cm 2/g was at the low er limit for Portland cement of the time, and would now be
considered as a controlled fineness cement. The alkali content was
1.22
sodium
equivalent (Na,O), which would be considered a high-alkali cemen t according to BRE
Digest
330[*'].
.
The fly ash was unusual in its chemistry: the calcium, magnesium and sulfate levels
were higher than are typically found, although they w ere within the lim its set in
BS
EN
450;
the alkalis were low
(1.26
sodium equivalent).
The specific surface value indicates that the fly ash was finer than the cement, the
opposite to what was sug gested by the
90
pm sieve retention. The fineness of fly ash is
currently expressed as the percentage retained on a
45
pm sieve, but a mean retention
on a 90 pm sieve of 12.3 s equivalent to a retention of around 25 on a 45 pm sieve.
This is above th e limit in BS 3892: Part 1 , but within the limits of BS EN 450. There are
no data for the variability in fineness of the fly ash, nor any indication of its control.
Details of the mixes are shown in Table 6. The mix design was based on Road N ote 4 [3'1,
with
a
minimum 28-day compressive strength of 2 N/mm 2. Road N ote 4 requires the
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Use ofj ly ash to BS EN 450 in structural concrete 15
minimum strength to be
60
of the mean,
so
the target mean strength was
35
Nlmm2.
The fly ash was added as a direct replacement of cement to represent 20% of the cement
+
fly ash content by mass. Beca use the density of fly ash
is
lower than that of cement,
the volum e of fines increases. However, n o correction was applied, nor was any adjust-
ment made to the water content, and hence a more workable mix was accepted .
Table
6
Concrete
mix
design used at High Marnham.
M aterial DroDertv Con trol mix Flv ash mix
Cement (kg/m3) 280
220
Fly ash (kg/m3)
Fine aggregate (kg/m3)
600 595
55
Coarse aggregate (kg/m3)
1390 1375
Water (kg/m3)
145 145
Waterlcement ratio
0.52 0.52
Nominal slump (mm) 25
40
The strengths are summarised in Table
7.
The compressive strength, expressed as
equivalent cube strength , used a facto r of 1.15 for all cores, whether they w ere obtained
from horizontal or vertical drilling. Th is would give conserv ative results overall.
The streng ths of the plain and fly ash con crete are similar after 25 years, although the
fly ash concrete had a marginally greater strength gain from on e year to 25 years.
The plain concrete was slightly more porous than the fly ash concrete, and had more
pores of 5 pm and above in diameter.
There wa s no evidence of carbonation o f the fly ash concrete, even close to the surface,
whereas carbo nation was observed up to 15 mm depth in the plain concrete. All bases
were set in the ground with upper surface s exposed
to
the atmosphere.
Although the alkali content of the concrete was high, no evidence of alkali-silica
reaction (ASR) was found[291.
This case study indicates that even with a simplistic mix design, durab le concrete could
be m ade using a relatively coarse fly ash.
Table 7. Summary of 2.5-year strengths at High Marnham[3n1.
Mean equivalent cube Indirect tensile
compressive strength strength
(N/mm2)
(N/mm2)
Control mix
66.5 4.10
Fly ash mix
69.0 4.20
7 AVAl lABlLlTY
The annua l UK production of coal fly ash is around 7 million tonnes, which is produced
by 18 coal-fired power stations. The geographical distribution of stations enables fly ash
to be supplied to all major cities and industrial centres.
Fly ash
is
produced
24
hours each day, throughout the year, with production varying
only with electricity demand. Most stations have the capability
to
offer stockpiled
conditioned fly ash or lagoon ash
to
the market alongside dry ash, ensuring adequate
supply throughout the year.
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Use ofj ly
ash
to BS EN 450
in
structural concrete
For a num ber of reasons there has been a move away from coal-fired generation of
electricity since privatisation of the industry. However, it is now accepted that there
is
a role for coal as a fuel in electricity generation for the foreseeable future, due to the
need to maintain a balanced approach to energy supplies.
There is an increasing emphasis placed by G overnment and the m arket on sustainable
developmen ts and waste minimisation. These objectives are met by the utilisation of
industrial by-products, like fly ash and reclaimedrecycled materials, which are of
particular benefit where there
is
a proven track record
of
use in the construction
industry.
Further information about availability of fly ash can be obtained from:
United Kingdom Q uality Ash A ssociation (UKQAA)
Regent House, Bath Avenue,
Wolverhampton, West Midlands WV1 4EG
Tel: +44 (0)1902 576586, Fax:
+44
(0)1902 576596
[email protected];www.ukqaa.org.uk
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Use
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EN 450
in structural concrete
17
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
BRITISH STANDA RDS INSTITUTION, BS EN 450: 1995, Fly ash fo r con-
crete. Definitions requiremen ts and quality control. 20pp.
BRITISH STA NDARD S INSTITUTION, BS 3892: Part 1: 1997,Pulverized-jiuel
ash. Specijication o r pulverized-fuel ash o r use with Portland cement. 22pp.
ELL IS, M.S.,
Compositional characterisation of
UK
PFA fo r use in concrete
University of Dundee Internal Report, 1984.
DHIR, R.K., HUBBAR D, F.H., MUN DAY , J.G.L. and JONES , M.R. Charac-
teristics of low -lime fly ashes significant to their use in concrete, Fly ash silica
firme and naturalpozzolans in
concrete. V.M. M alhotra (Ed.) American Concrete
Institute S P 91-33, 1986, pp.693-721.
CRIPW ELL, B. Research and developm ent: a review of PFA in the literature,
Concrete
Vol. 26, No. 3, MayIJune 1992, pp.21-26.
DHIR, R.K., M cCAR THY , M.J. and MAG EE, B.J. Impact of BS EN 450 PFA
on con crete construction in the UK, Construction and Building Materials Vol.
BRITISH STAN DAR DS INSTITUTION. BS 1881: Part 121: 1983. Testing
concrete. Method fo r determination of static m odulus in compression. 8pp.
THO MA S, M.D.A. Marine performance of PFA concrete,
Magazine
of
Concrete
Research Vol. 43, No . 156, 1991 , pp.171-185.
DHIR, R.K., McCA RTH Y, M.J. and M AGE E, B.J. Use of PFA to EN 450 in
structural concrete
Report CTU I 196, Concrete T echnology Unit, U niversity of
Dundee, 1996.
LEW AND OW SKI, R. Effect of different fly ash quan tities and qualities on the
properties of concrete, Betonwerk und Fertigteil-Technik Vol. 49, 1983. Part 1
:
No 1, January, pp.11-15; Part 2: No. 2, February , pp.105-111; Part 3:
No.
3,
March, pp.152-158.
SCHIESS L, P. and HAR DTL, R. Eflc ienc y offry ash in concrete: Evaluation of
ibac test results
Document N42, Institut E r Bauforschung, RWTH , Aachen.
1991.
12, NO. 1, 1998 , pp.59-74.
AMER ICAN SOCIETY FOR TESTING AND M ATERIALS. ASTM C666-97.
Standard test method fo r resistance of concrete to ra pid fiee zing and thawing.
Philadelphia. 6pp.
LAWRENCE, C.D., Sulphate attack on concrete, Magazine of Concrete
Research Vol. 42, No . 153, 1990 , pp.249-264.
DHIR, R.K., HEW LETT , P.C. and CHA N, Y.N. Near surface characteristics of
concrete: abrasion resistance.
Materials and Structures.
Vol. 24, No, 140, 1991.
MEH TA, P.K., E ffect of fly ash co mpo sition on sulfate resistance of cement,
Journal of the American Concrete Institute Proceedings Vol. 83, No. 6, 1986,
pp.994-1000.
TIKA LSK Y, P.J. and CAR RASQ UILLO , R.L. Influence of fly ash on the sulfate
resistance of concrete,
ACZM aterials Journal
Vol. 89, No. 1, 1992 , pp.69-75.
BRITISH STANDA RDS INSTITUTION, BS 8500, Concrete. Complementary
British Standard to BS EN
206-1. Part 1: 2001.
Method of specihing and
guidance fo r the specijier.
50pp. Part 2: 2002.
Specification fo r constituent
materials and concrete. 38pp.
pp. 12 1-128.
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18
Use
offly
ash to BS EN 450 in structura1 concrete
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
BRITISH STANDARDS INSTITUTION, BS EN 206- 1 2000,
Concrete. Speci-
fication performance p roduction and conformity.
74pp.
DHIR, R.K., McCARTHY, M.J. and PAINE, K.A. Technology transfer pro-
gramme
for
the use
of
PFA to EN
450
in structural concrete: Freezehhaw
resistance using CEN /TC
51
test method
Document No. EN 450/2 2, Concrete
Techno logy Unit, University of Dundee. 199 9.
DHIR, R.K., McCARTHY, M.J. and PAINE, K.A. Technology transfer
programme fo r the use of PFA to EN 450 in structural concrete Report No.
CTU/ 1400, Concrete Technology Unit, University of Dund ee. 2000.
SMITH, I.A. The design of fly ash concrete,
Proceedings of the Institution
of
Civil Engineers
Vol. 36, 1967 , pp.769-790.
WESCHE, K., SCHUBERT, P. and W EBER, J.W. Strength and durability of
concrete with coal fly-ash as an additive,
Betonwerk und Fertigteil-Technik
INTRON, Institute for Material and Environmental Research BV,
Fly ash as
addition to concrete CUR Report 144, AA Balkema Publishers, 19 92,9 9pp.
HARRISON, T.A. The effect of the k-value for fly ash on concrete mix pro-
portions, Proceedings of XIth European Ready Mixed C oncrete Congress June
1995, Istanbul. Turkey Ready Mixed . Concrete Association, Istanbul.
pp.409-4 18.
CEN, K-value orp ow der coalfly ash CEN Draft Committee Document, 1998.
BRITISH STANDARDS INSTITUTION, BS EN 197- 1 2000,
Cement. Compo-
sition speci3cations and conformity criteria
for
common cem ents.
5Opp.
BUILDING RESEARCH ESTABLISHMENT, BRE Digest 330: Part 2,
Alkali-
silica reaction in concrete: Detailed guidance o r new con struction
1999.
WO OLLEY , G.R. and CABRE RA, J.G. Early-age in-situ strength developm ent
of fly ash concrete in thin shells,
Blended cements in construction
ed. Swamy,
R.N., Elsevier Applied Sc ience , Barking , 1991 . pp. 166-1 78.
HOWELL, L.H.
Report o f pulverised fuel ash as a partial replacement o r
cement in normal works concrete
Central Electricity Generating Board, East
Midlands Division, 1958, I, 36 and
11,
37.
CABRERA, J.G. and WOOLLEY, G.R. A study of twenty-five year old
pulverised fuel ash concrete used in foundation structures,
Proceedings of
Institution of C ivil Engineer s
Part
2
Vol. 7 9, March 1985, pp.149-165.
ROAD RESEARCH LABORATORY, Design of concrete mixes HMSO,
London, 1950, Road Note 4,2 nd edition.
BUILDING RESEARCH ESTABLISHMENT. Design
of
normal concrete mixes.
BRE Report 33 1. Garston, 1997.
Vol. 50, NO. 6, 1984 . pp.367-374.
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Use ofjly ash to BS
EN
450
in
structural concrete
19
APPENDIX
Taking account of f ly ash characterist ics in mix design
Tests [see Section 4.31 have shown that a simple approach to applying the equivalent
concrete performance method with respect to chloride ingress, abrasion, freeze-thaw
resistance and carbonation is the achievement of equal 28-day compressive strength to
a su itable reference concrete. Thus, for
EN
206- 1 exposure classes XO, XC, XD and XF,
no hr th er durability testing is necessary provided the concrete durability requirements
include a m inimum cube strength.
Research on the effects of fly ash fineness [see Section 3.23 has dem onstrated that fly
ash with properties across the range of
BS
EN
450 requirem ents may influence concrete
cube strength.
A
method developed at the University of D un de eh ak es into account the
effects of fly ash characteristics on cube strength by simp le adjustment to the free
water/(cement
+
fly ash) ratio. T his a straightforward approach which is e asy to apply
in practice; the method is descr ibed below.
The adjustment in the w ater/(cement
+
fly ash) ratio to account for variations in fly ash
fineness over a range of typical concrete strengths is shown in Figu re
A-
1 for a fly ash
content of 30% by mass. The required adjustm ent in the water/(cement
+
fly ash) ratio
increases with cube strength, because of the increasingly significant effect of fly ash
fineness on cube strength as the cemen t
+
fly ash content increases[ .
The following two examples show the selection of w ater/(cement
+
fly ash) ratio for
two
fly ashes, fly ash
A
with fineness
5
(retained on 45pm sieve) and fly ash
B
with
fineness 35%.
70
60
50
40
30
20
10
0
10
I I
15 20 25
30
35 40 45
50
55 60 65
28-day
cube
strength, Nlrnrn'
-
-
w/(c+9
ratio cu
with fineness
of 5%
(45 pm sieve retention)
0.30 0.35
0.40
0.45
0.50 0.55
0 60 0.65 0.70 0 75
w/(c+f) ratio
Figure
A-1. Relationship between watedcement + fl y ash ratio (w/(c+fl)
and 28-day cube strength or jl y ash conforming with BS EN 450.
FIy ash content: 30% by mass.
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Use ofjly
ash
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450
in structural concrete
Examples
Requirement to m eet the exposure XC 1 for carbonation using
30
fly ash as cement
comp onent by mass (i.e. minimum streng th 25 N/mm2,maximum w/c
=
0.65, minimum
cement = 260 kg/m3), where a reference C25 PC concrete with a target strength o f
35
N/m m2 has been show n to perform adequately.
Fly
ash
A
Fly ash fineness “h etained on 45pm sieve) 5 (1)
Figure A-l(a ). Water/(cement
+
fly ash) ratio
0.49 (2)
Variation of fineness from 5 [(1)
- 5 ] /5
0 (3)
ratio per
5%
fineness variation 5.2
x
1 0 - ~ (4)
Target cube streng th of reference concrete 35 N/mm2
Figure A-l(b). Correction to water/(cement
+
fly ash)
Water/(cement
+
fly ash) ratio
(2)
-
(3)
x
(4)]
Therefore, assuming water content = 165 l/m3with a plasticizer in the mix, possible m ix
proportions are given in Table A-1. The aggregate proportions are calculated using
normal mix design methods, e.g. BRE Design of normal concrete mixes [321, in which
aggregate proportions are calculated by estimating) he wet density of concrete, and
proportioning the percentage o f fine aggregate to the required slump.
Table A-1
0.49
Design w/(c+f) Concrete mix proportions
(kg/m3)
strength Free PC Fly ash Aggregate
(N/mmz) water Fine
lOmm
20mm
35.0 0.49 165
235
100
j
680 405
810
Fly ash B
Fly ash fineness
(
retained o n 45pm sieve)
I ’
35 (1)
Figure A-l(a). Water/(cement
+
fly ash) ratio 0.49 (2)
Variation of fineness from
5 [(1)-5115 6 (3)
ratio per
5%
fineness variation
5.2
x
10-3
(4)
Target cube streng th of reference concrete
35 N/mm2
Figure A- 1 b). Correction to water/(cement + fly ash)
Water/(cement
+
fly ash) ratio
(2) - (3)
x
(4)]
Correspo nding mix proportions for fly ash B would be a s given in Table A-2. Aggregate
proportion s have minor adjustmen ts to maintain yield.
Note that the use of the coarser fly ash
B
requires a w/(c+f) ratio
0.03
lower than that
for the finer fly ash A. For the same free water content, this means an increase of 25
kg/m3 in the total cemen t
+
fly\ash content. Alternatively, the lower w /(c+f) ratio co uld
have been achieved by reducing the water content, or altering both the water content and
cement + fly ash content.
Table A-2
0.46
Design w/(c+f) Concrete mix proportions (kgjm’)
strength Free PC Fly ash Aggregate
(N/mm2)
water Fine lOmm 20mm
35.0 0.46 165 250 110 680 395 790
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The Concrete Society Technology Digest
C . E W D ~ V M W B r n r n r n ~ ” W1
Ravindra K. Dhir Michael J McCarthy Kevin
A.
Paine
Concrete Technology Unit University
of
Dundee
The European standard BS EN 450 Fly ash for concrete - definitions, requirements
and quality control covers a broader range of fly ashes as a cementitious component
for use in concrete than previous UK standards. This Technology Digest brings
together current knowledge of the properties on fly ash to BS EN 450, and offers
technical guidance on how the material should be used in concrete. Factors relating
to concrete production are also covered, and two case studies show how fly ash to
BS EN 450 has been used successfully.
This Technology Digest has been prepared as part of a technology transfer
programme undertaken at the Concrete Technology Unit of the University of Dundee
under the Partners in Technology Programme of the Department of the Environment,
Transport and the Regions.
The project was guided by a steering committee representing the University and all
contributing partners.
Order Ref: CS 133
ISBN
0
946691 82 7
The Concrete Society
Century House, Telford Avenue
Crowthorne, Berkshire RG45 6YS, UK
Tel: +44(0)1344 466007,
F a :
+44(0)1344 466008
www.concrete.org.uk
sed copy:
chris.elsom@severnt
rent.co.uk, Severn Trent Water Ltd, 09/09/2009, Uncontrolled
Copy, ®The Concrete