developments in european and national concrete...

Developments in European andNational Concrete Standards- Service Life Aspects

John Matthews, BRE Centre for Concrete Construction

Durability by Intent Workshop, BRE, 19 February 2002

Current British StandardsBS 5328: ConcretePart 1: 1997 Guide to specifying concretePart 2: 1997 Methods for specifying concrete mixesPart 3: 1990 Procedures to be used in producing and

transporting concretePart 4: 1990 Procedures to be used in sampling, testing

and assessing compliance of concrete

BS 8110: The structural use of concretePart 1: 1997 Code of practice for design and construction

Service Life & Concrete Standards

“The degree of exposure anticipated for the concrete duringits service life together with other relevant factors relatingto mix composition, workmanship and design should beconsidered.” (BS 8110: 1985)

“A durable concrete is one that performs satisfactorily in theworking environment during its anticipated service life.The materials and mix proportions specified and usedshould be such as to maintain its integrity and, ifapplicable, to protect embedded metal from corrosion.”(BS 5328:1990 onwards)

European Standard for Concrete

BS EN 206-1: 2000 Concrete - Part 1:Specification, performance, production and

conformity

Approved by CEN on 12 May 2000Published by BSI and came into effect on15 February 2001


BS EN 206-1: 2000 Concrete - Part 1:Specification, performance, production and

conformity

not a harmonised standard as referred toin the Construction Products DirectiveCE marking not possiblebut national provisions permitted

Complementary British Standardto BS EN 206-1

BS 8500 : 2002Part 1: Method of specifying and guidance for

the specifierPart 2: Specification for constituent materials

and concrete

Publication by BSI imminent

Future of concrete standards

The joint package of BS EN 206-1 and BS 8500will co-exist with BS 5328 until 1 December2003 when BS 5328 will be withdrawn.

Exposure Classes in CP 110 & BS 8110

CP 110: 1972Four (Mild, Moderate, Severe, Subject to De-icing salt)

BS 8110: 1985Five (Mild, Moderate, Severe, Very Severe, Extreme)

BS 8110: 1997Six (Mild, Moderate, Severe, Very Severe, Most Severe,

Abrasive)

Plus five classes for sulfate attack from BRE Digests


BS EN 206-1: 2000 contains eighteen differentexposure classes for concreteBased upon environmental action:- ClassesX0 - No risk of corrosion or attack 1XC - Carbonation-induced corrosion 4XS - Chloride-induced corrosion (sea water) 3XD - Chloride-induced corrosion (not sea water) 3XF - Freeze-thaw attack 4XA -Chemical attack 3


Requirements for concrete related to exposure class:-

Limiting values for concrete composition and establishedconcrete properties (i.e. strength)EN 206-1 gives only recommended valuesRequirements given in national provisionsCover will be specified in EN 1992-1 for X0, XC, XD and XSexposure classes (variation permitted in National Annex)


“The provisions valid in the place of use of the concreteshould include requirements under the assumption of anintended working life of at least 50 years under theanticipated maintenance conditions.”

Requirements may also be derived from performance-relateddesign methods for durability, based on local experience,data from performance tests or use of proven predictivemodels.


Potential problem for UK engineers :-

EN 1992-1 will give a single value for minimum cover foreach relevant exposure class (X0, XC, XD, XS) assuminga 50 year service life

No allowance for “trade-off ” between concrete qualityand cover to reinforcement


but the minimum cover values in the final draft EN 1992-1“are subject to a National Annex which takes account ofEN 206 and a possible complementary NationalStandard.”

The UK National Annex will refer to BS 8500

BS 8500 - Complementary BS to EN 206-1

Exposure classes adapted to UK conditionsGives concrete requirements relevant to the UKfor each exposure classGives a range of permitted concrete qualitiesallowing for trade-off with coverGives values of cover as a minimum value plus atolerance ∆ to accommodate fixing precision(BS 8110 gives cover as nominal cover)


Recommended limiting values for compositionand properties of concrete for XC and XFexposure classes are considered suitable for anintended working life of “at least 50 years” andalso for “at least 100 years”


More onerous values are given for 100 year life inXC 3-4 where carbonation-induced corrosion is arealistic prospect.

Moisture conditions in XC 3-4 are defined as‘moderate humidity or cyclic wet and dry’.

BS 8500 - Complementary BS to EN 206-1Where chloride-induced corrosion is relevant (XD andXS), recommended limiting values for composition andproperties of concrete are given only for an intendedworking life of at least 50 years

The spread of data from research and from surveys ofstructures indicates that precise recommendationscannot be given for 100 year service life in chlorideenvironments


However, “as a first estimate” for working lives ofat least 100 years in XD and XS exposure classes,it is suggested that the minimum coversrecommended for a working life of at least 50years be increased by 15mm (EN 1992-1 willrecommend 10mm)

Guidance for durable structures forlong service lives

If reliable guidance is to be given for durablestructures for long service lives, i.e. 100 years ormore, especially in chloride-bearingenvironments, there is an essential need for long-term performance data from research and/orstudies of existing structures.

Such data is needed both to enable prescriptivespecification of concrete and to validate servicelife models.

BS 8500 - Complementary BS to EN 206-1Requirements for XC classes for intended working

life of at least 50 yearsExposureclass XC1 XC2 XC3-4

Nom inalcover 15 + ∆ 25 + ∆ 35 + ∆ 30 + ∆ 25 + ∆ 20 + ∆

Minim umstrengthclass

C20/25 C25/30 C25/30 C28/35 C32/40 C40/50

Max w /cratio 0.70 0.65 0.65 0.60 0.55 0.45

Min cemcontent See Table A.18

Cem ents All in TableA.17 All in Table A.17 except IVB

BS 8500 - Complementary BS to EN 206-1Requirements for XC classes for intended working

life of at least 100 yearsExposureclass XC1 XC2 XC3-4

Nominalcover 15 + ∆ 25 + ∆ 45 + ∆ 40 + ∆ 35 + ∆ 30 + ∆

Minim umstrengthclass

C20/25 C25/30 C28/35 C32/40 C35/45 C40/50

Max w/cratio 0.70 0.65 0.60 0.55 0.50 0.45

Min cemcontent See Table A.18

Cem ents All in TableA.17 All in Table A.17 except IVB

BS 8500 - Complementary BS to EN 206-1Requirements for XD3 class for intended working

life of at least 50 years

Exposureclass XD3Nominalcover 50+∆ 45+∆ 40+∆Minstrengthclass

C35/45 C28/35 C25/30 C40/50 C32/40 C28/35 C45/55 C35/45 C32/40

Max w/cratio 0.45 0.50 0.40 0.45 0.35 0.40Mincementcontent

As in Table A.18 plus 20 kg/m3

Cements Group4

Group5

Group6

Group4

Group5

Group6

Group4

Group5

Group6

BS 8500 - Complementary BS to EN 206-1Requirements for chemical attack exposure classes (XA)

differ from EN 206-1Follow BRE Special Digest SD1 (“Concrete in AggressiveGround”)Ground conditions classified according to:-

sulfatemagnesiumpotential sulfate from oxidation of sulfidestype of ground (natural or brownfield)groundwater mobilitygroundwater pH

to give Aggressive Chemical Environment for Concrete(ACEC) Class


ACEC Class is then considered together with StructuralPerformance Level and concrete section thickness togive the Design Chemical Class (which is specified tothe concrete producer) and the number of AdditionalProtective Measures

BS 8500 - Complementary BS to EN 206-1Table A.3: Guidance on the selection of the

Structural Performance LevelStructuralPerformance Level

Typical attributes

Low• Short service life structures <30 years• Unreinforced concrete• Non-critical structural details• Temporary structures• Long service life structures, but with

associated low stress levels e.g. housefoundations (unreinforced).

Normal • Intermediate service life (30-100 years)• Not falling in either high or low category

High• Long service life structures >100 years

e.g. transport structure foundations• Vulnerable critical details e.g. slender

structural elements, hinges, joints, etc• Structures retaining hazardous materials

SummaryUntil now, British Standards for concrete have not relatedconcrete quality or cover to the required life of thestructure

EN 206-1 requires that national concrete provisionsshould include requirements based on the assumption ofa working life of at least 50 years

Similarly, Eurocode 2 will give values for concrete coverapplicable to a service life of 50 years although thesemay be varied in a National Annex

SummaryBS 8500 recognises the need for guidance on service lifeby recommending concrete compositions and propertiesfor working lives of:-

“at least 50 years” and “at least 100 years” forcarbonation and freeze-thaw environments

“at least 50 years” in chloride environments

SummaryBS 8500 introduces from BRE SD1 the concept ofStructural Performance Level with respect to concretein aggressive ground conditions

More data are needed from both research and in-servicestructures to enable guidance for long service lives inchloride environments

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