Modern Cements and How to Specify Them

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Modern Cements and How to Specify Them
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Background

• Until recently the term cement was almost
  synonymous in the UK with BS 12 Portland cement
• The publication of the harmonised European
  Standard for common cements in 2000 (BS EN 197-1)
  has introduced a wider range of structural
  cements for potential use in the UK
• This presentation examines what is meant by
  cement today and how to specify it

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Terminology Cement

• In BS EN 197-1, cement is defined as
• A hydraulic binder, i.e. a finely ground
  inorganic material which, when mixed with water,
  forms a paste which sets and hardens by means of
  hydraulic reactions and processes and which,
  after hardening, retains its strength and
  stability even under water.
• Factory produced EN 197 cements are given the
  designation CEM

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Terminology Additions

• Pozzolanic or latent hydraulic materials, such as
  pulverized-fuel ash (pfa) or ground granulated
  blastfurnace slag (ggbs) are Type II additions
• When additions are mixed with Portland cement at
  the concrete batching plant, they form a
  combination not a blended cement
• In British Standards, mixer combinations are
  given the designation C not CEM

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Key Cement Standards

• BS EN 197-12000 (Inc. Amendment No.12004)
• Composition, specifications and conformity
  criteria for common cements
• BS EN 197-42004
• Composition, specifications and conformity
  criteria for low early strength blastfurnace
  cements
• BS EN 196-series
• Methods of testing cement

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Cements

• Cements are factory produced materials primarily
  conforming to BS EN 197-1 or BS EN 197-4
• Some cements, such as Sulfate-resisting Portland
  cement (SRPC) are however, still covered by
  residual British Standards
• There is a wide range of cements ranging from
  simple Portland cement to Composite cements
  containing up to three major constituents
• Cements may be produced by inter-grinding or
  blending the constituents at the cement works
• Cements can be CE marked against BS EN 197
  standards using BS EN 197-2 Conformity evaluation

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Types of BS EN 197-1 Cement
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HOW ARE CEMENTS DESIGNATED
Example CEM II/A-LL 42,5 N
CEM II Portland composite cement
A-LL A signifies low proportion of second
constituent (6-20 in this case) L or LL
signifies limestone as the second main
constituent (LL signifies high purity limestone)
42,5 N Cement strength class 42,5 Normal
strength development
Portland-limestone cement
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PORTLAND CEMENT
Portland cement is CEM I NOT Ordinary Portland
cement, OPC or PC BUT CEM I
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Cement Strength Classes (I)

• There are three cement strength classes, based on
  the minimum 28 day mortar prism strength
• 32,5
• 42,5
• 52,5
• Each class can be subdivided based on early
  strength development
• L Low early strength
• N Normal strength development
• R High early strength

Note Use of comma rather than decimal point
Example class 42,5R
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Cement Strength Classes (II)
These classes apply to all CEM cements
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Cement Strength Classes (III)
These low early strength classes apply only to BS
EN 197- 4 CEM III cements
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Low Heat Cements

• BS EN 197-1 2000 (inc. Amendment 12004) now
  covers some low heat cements
• Low Heat is defined as a characteristic heat of
  hydration not exceeding 270 J/g (measured at 7
  days (EN 196-8) or 41 hrs (EN 196-9))
• Low heat cements carry an LH suffix ie

Example CEM III/B 32,5N - LH
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Other Specified Cement Properties (Class 42,5N)
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Common CEM II Cements
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Common CEM II Cements
Available in UK
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CEM III Cements
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CEM IV Cements
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CEM V Cements
Example Composite cement with18-30 ggbs (S) and
18-30 siliceous fly ash (V) plus clinker would
be designated as CEM V/A (S-V) 32,5N
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Minor Additional Constituent (I)

• BS EN 197-1 allows for the inclusion of up to 5
  by mass of a minor additional constituent (or
  mac) in all types of cement
• A mac is defined as specially selected
  inorganic natural mineral materials, inorganic
  mineral materials derived from the clinker
  production process or specified cement
  constituents unless they are already included
  as main constituents in the cement
• Materials typically used as a mac include
• Finely ground limestone
• Fly Ash
• Cement kiln dust (CKD)

Example A fly ash mac should not be used in a
Portland- fly ash cement (CEM II/B-V)
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Minor Additional Constituent (II)

• Cement containing a mac has to meet the same
  performance criteria as the same cement type and
  class without a mac
• Setting time
• Strength
• Soundness/Chemical requirements
• In specification terms a CEM cement with a mac
  is considered to be identical to the same CEM
  cement without a mac

A CEM I Portland cement with 5 mac is still a
Portland cement and will perform in the same way
as a similar cement without a mac !
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Other Cements

• Sulfate-resisting Portland cement still covered
  by residual British Standard BS 4027
• Low early strength blastfurnace cements covered
  by British Standard BS 1462002 (to be withdrawn
  Jan 2006)
• High-alumina cement still covered by residual
  British Standard BS 915

These standards will eventually be replaced by
new European Standards, but progress on a
standard for sulfate-resisting cement is slow
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BS EN 206-1 and BS 8500

• BS 5328 Concrete has been superseded and
  withdrawn
• EN 206-1 is the European Standard for concrete
  (UK version is BS EN 206-1)
• BS 8500 is the complementary British Standard to
  BS EN 206-1 and describes how to apply the
  principles of the European Standard in the UK
• Note BSI have also published Standards for
  fresh concrete (BIM 2002), which combines BS EN
  206-1 and BS 8500 and adds a commentary

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Concrete Specification to BS 8500

• BS 8500 gives guidance on the choice of
  appropriate cement types for different exposure
  classes
• For a given combination of exposure class and
  cover depth, BS 8500 places limitations on
• Permitted cement types
• Minimum concrete strength class
• Maximum water/cement ratio
• Minimum cement content
• These limiting values may be different for
  different types of CEM cement
• This reflects the different relative (durability)
  performance of different cement types

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Permitted Cements

• BS 8500 permits the general use of all BS-EN
  197-1 and BS EN 197-4 cements in concrete
• However, the use of Composite cement (CEM V) is
  restricted to situations where it is specified or
  when its use is accepted by the specifier
• Cements conforming to certain residual British
  Standards are also permitted
• BS 4027 Sulfate-resisting Portland cement
• BS1462002 Blastfurnace cements
• BS 6610 Pozzolanic cements

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Minimum Cement Content

• When specifying concrete to BS EN 206-1/BS 8500,
  the specified minimum cement content applies to
  the cement, be it CEM I, CEM II, CEM III, CEM
  IV or CEM V
• For a non CEM I cement, this does NOT mean the
  amount of the Portland cement clinker in the
  cement

The limiting values in BS 8500 take account of
the composition of the cement. There is no
technical justification for additional increases
in cement content for non CEM I cements
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Water/Cement Ratio

• The specified maximum water/cement ratio is the
  ratio of free water to CEM cement
• This is a major factor influencing concrete
  strength
• This does NOT mean the ratio of free water to the
  amount of Portland cement clinker in the CEM
  cement

The limiting values in BS 8500 take account of
the composition of the cement. There is no
technical justification for additional reductions
in water/cement ratio for non CEM I cements
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Footnote
Analysis of hardened concrete

• If there is a dispute about whether the cement
  that was specified was actually used, then
• a combination of chemical analysis and microscopy
  (optical and/or analytical) should be able to
  determine the identity of the major constituents
  but determining the proportions is much more
  difficult
• If there is a dispute about the cement content of
  the concrete then
• routine chemical analysis determines soluble
  silica, lime and insoluble content
• relationships between these vary between cement
  type and any addition used
• the simplest, most accurate, case is where only a
  CEM I cement has been used
• in other cases, the determination of cement
  content, and addition content, is subject to
  more assumptions and therefore less accuracy

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For further information

• Visit BCAs website at
• www.cementindustry.co.uk