maintenance and repair of transport infrastructure

TECHNICAL GUIDEDur

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Copyright © LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, I. P. Divisão de Divulgação Científica e TécnicaAV DO BRASIL 101 • 1700-066 LISBOAe-e: livraria@lnec.ptwww.lnec.ptPublisher: LNEC

Collection: Manuals

Series: MN 13

1st. edition: 2012

Printing: 100 copies

Descriptors: Transport infrastructures / Steel structure / Reinforced concrete structure / / Maintenance of structures / Repair of structures / Durability of structures / / Structural testing / Guide / Europe

Descritores: Infraestruturas de transportes / Estrutura metálica / Estrutura de betão armado / / Conservação de estruturas / Reparação de estruturas / Durabilidade de estruturas / / Ensaio de estruturas / Guia / Europa

CDU 624.05[012.4]9:625(026)(4) 624.05[014]9:625(026)(4)

ISBN 978-972-49-2237-9 (paperback)

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CONCRETE STRUCTURESPART IV

durability factors and requirementsVOL 1

Sudarshan Srinivasan

António S. Silva

Sreejith V. Nanukuttan

Manuela SaltaDurati

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AuthorsSudarshan SrinivasanResearch assistant, Queen’s University Belfast

António Santos SilvaResearch officer, LNEC

Sreejith V. NanukuttanLecture in Civil Eng., Queen’s University Belfast

Maria Manuela SaltaPrincipal researcher and head of Metallic Materials Division, LNEC

Other contributionsKarim Ait-MokhtarProfessor, University of La Rochelle

Quirino TomásDuratinet research fellow, LNEC

ReviewerArlindo GonçalvesPrincipal researcher and Director of Materials Department, LNEC

Final revision by Editorial Commission memberMuhammed BasheerProfessor and director of research, Queen’s University Belfast

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PREFACE

This is Part IV, Volume 1 of the DURATINET Technical Guide - Maintenance and Repair of Transport Infrastructure, which contains guidelines on durability factors and requirements in concrete structures.

The content of this volume was prepared and reviewed within DURATINET working group WG A3 – Maintenance and repair of concrete structures.

The aim of WG A3 was to harmonize the needs of maintenance and repair of concrete structures and identify knowledge gaps in the partner countries. Within this WG, technical guidelines were developed relating to durability factors (both environment and material related), deterioration processes (damage mechanisms and defects), testing techniques for inspection, repair methods for concrete structures. All these subjects are considered in the four volumes of Part IV of the DURATINET Technical Guide.

WG A3 – Maintenance and Repair of Concrete Structures

WG Leader: Sree V. Nanukuttan Queen’s University Belfast, UK

Partners active membersCountry Institution Members

Portugal LNEC

Manuela Salta, Paula Rodrigues, António S. Silva, Elsa V. Pereira, Quirino Tomás

EP Afonso Póvoa, Luis Freire Teixeira Duarte Rita Moura

France

IFSTTAR Xavier Dérobert, Géraldine Villain, Odile Abraham, Laurent Gaillet

University of Bordeaux

Denys Breysse, Zoubir-Mehdi Sbartaï

University of Nantes Marta Choinska, Stephanie Bonnet University of La Rochelle

Karim Ait-Mokhtar, Ouali Amiri

Ireland NRA Albert Daly

UK Queen’s University Belfast

Muhammed Basheer, David Cleland, Sree V. Nanukuttan, Sudarshan Srinivasan

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DURATINET project approved by the Atlantic Area Programme and co-financed by ERDF

CONTRACT Nº: 2008-1/049

PROJECT TITLE: Durable Transport Infrastructure in the Atlantic

Area Network

ACRONYM: DURATINET

LEADER: Manuela Salta

Laboratório Nacional de Engenharia Civil (LNEC)

Materials Department

Portugal

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GENERAL INDEX

Part IV Concrete Structures

Vol. 1 Durability factors

Overview of European standards for concrete structures design

National standards or guidelines to complement EN 206-1

Comparison of the national requirements in complement to EN 206-1

Examples of projects with performance limits for concrete durability

Vol. 2 Deterioration

Physical / mechanical deterioration processes

Chemical deterioration processes

Biological and organic deterioration process

Classification of defects and deterioration symptoms

Vol. 3 Testing techniques

Visual Examination

Crack Index

Non-destructive testing techniques (NDT)

Destructive testing techniques (DT)

Consideration on testing selection

Vol. 4 Repair methods

Concrete surface preparation prior to repair

Methods for protection and repair of reinforced concrete

Selection of the repair methods

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CONTENTS

Part IV - Concrete Structures: Vol. 1

1  General considerations ................................................................................. 1 

2  Overview of European standards for concrete structures design ................ 5 

2.1  Classification of the exposure environments ........................................ 7 

2.2  Durability requirements for concrete ..................................................... 9 

2.2.1  Prescriptive method for concrete properties specification ............. 10 

2.2.2  Performance-related concrete design methods ............................ 12 

2.2.3  Concrete cover depth specification ............................................... 13 

3  National standards or guidelines to complement EN 206-1 ....................... 17 

3.1  United Kingdom .................................................................................. 17 

3.1.1  Defining the exposure classes ....................................................... 17 

3.1.2  Select the concrete strength and cover ......................................... 17 

3.1.3  Selecting the intended working life, e.g., service life ..................... 17 

3.1.4  Cement types and minimum cement content ................................ 18 

3.1.5  Complementary requirements for constituent materials ................ 18 

3.1.6  Air content ...................................................................................... 18 

3.1.7  Freeze/thaw aggregates ................................................................ 18 

3.1.8  Aggressive ground ......................................................................... 19 

3.1.9  Consistence ................................................................................... 19 

3.1.10  Chloride Class ........................................................................... 19 

3.1.11  Conformity ................................................................................. 19 

3.2  Ireland ................................................................................................. 21 

3.3  Portugal .............................................................................................. 24 

3.3.1  Prescriptive specification of concrete ............................................ 24 

3.3.2  Equivalent concrete performance concept .................................... 27 

3.3.3  Specification of concrete based on the performance - related design methods with respect to durability ................................................... 28 

3.4  France ................................................................................................. 29 

3.5  Spain ................................................................................................... 30 

4  Comparison of the national requirements in complement to EN 206-1 ...... 31 

4.1  National standards or regulations ....................................................... 31 

4.2  Exposure classes ................................................................................ 32 

4.3  Methods for minimising risk of damage by AAR ................................. 32 

4.4  Limiting values for concrete mixes ..................................................... 33 

5  Examples of projects with performance limits for concrete durability ......... 36 

6  Conclusions ................................................................................................ 42 

7  References ................................................................................................. 44 

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1 General considerations

Numerous examples of premature deterioration of reinforced concrete structures particularly in marine environments have highlighted the need to consider durability requirements while designing concrete structures. It is now widely accepted that the concept of designing concrete based mainly on strength does not take into account the time-evolution of performance of the structure or the change in environmental/structural loading.

The standard EN 206-1:2000 [1] was introduced as an attempt to quantify the durability requirements for concrete structures exposed to different environments. This standard helps designers to specify or prescribe minimum requirements for a concrete mix so that the structure will achieve a service life of 50 or 100 years. Although this can be considered as a step in the right direction, the “prescriptive” or “deemed to satisfy” approach does not guarantee a service life of 50 or 100 years. Service life of a concrete structure will depend mainly on the quality of concrete and the deterioration mechanisms that are associated with various exposure environments. The factors that can influence deterioration of concrete structures are presented in Fig. 1.

Fig. 1. Main factors that can influence the deterioration of concrete structures. [2]

MaterialsDesign and

workmanshipEnvironmental Physical actions Maintenance

Sources ofdeterioration

Potentialcauses of

deterioration

Quality ofmix design

Aggregatecharacteristics/

reactivity

Inadequatewater/cement

ratio

Cement type andadditionsselection

Additives andcontaminants

Poordetailing

Insufficientcover to

reinforcement

Poordrainage

Inadequatedesign for

creep

Poor vibrationand

compactation

Bleeding andsegregation

Poorconstruction

joints

Problematicfinishes

Inadequaterepairs

CO2 and acidgases action

Sea water and marine atmosphere

Chemicalattack

Biologicalgrowth

Thermalactions

Fire action

Inadequatedesign for

loads

Impact

Vibration

Settlement

Seismic

Change of use increased floor

loadings

Wind

Abrasion

Nonmaintenance

Inadequaterepair

methods

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The deterioration of concrete structures may arise due to a number of reasons as shown in Fig. 1, including:

poor design, specification, detailing or execution during construction;

poor planning or implementation of maintenance operations;

lack of funds for routine maintenance and lack of understanding of the roles and responsibilities;

environmental loads and other actions on the structure;

ageing process;

increased or varying loads.

In practice, it can be considered that the level of durability achieved in concrete structures depends on a combination of adequate design, materials selection and execution. The sensitivity of the design concept, the structural system, the shape of members and structural/architectural detailing are all significant design parameters for durability.

The compatibility of materials, the construction method, the quality of workmanship, levels of control and quality assurance are also other significant parameters for achieving durability. Workmanship and maintenance strategies are also vitally important in achieving durable structures. Tables 1-3 depict some of the common causes which results in premature deterioration of concrete structures.

Table 1. Concrete deterioration caused by inadequate or wrong design.

Causes of the problem Results Poor reinforcement details, for example congested or inadequate cover to environment action, and voids around the steel reinforcement

Cracking, poor compaction, insufficient reinforcement or inadequate reinforcement distribution

Poor detailing of fixings, window frames, handrails, supports, and expansion joints defects

Water penetration, localized cracking and balcony

Long, slender components Excessive deformation and cracking

Inadequate design for creep Deflection due to strain under continued stress

Decorative finishes, such as acid etching, bush hammering, and fluting

Varying depth of cover around the steel and localised corrosion

Poor drainage Water ponding and localised corrosion/degradation

Incorrect concrete grade for purpose Concrete with too low or too high strength for the application

Concrete mixes with high drying shrinkage Possible cracking Concrete mixes that are highly permeable to chloride ions

Chloride induced reinforcement corrosion

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Table 2. Concrete deterioration caused by the lack of workmanship or quality control.

Causes of the problem Results Inadequate mixing proportions facing casting conditions

Inhomogeneous concrete, localised weakness and reinforcement corrosion

Inadequate water/cement ratio Variable strength, inadequate durability, increased drying shrinkage, excessive permeability

Inadequate compaction/vibration Honeycombing, voids, excessively permeable concrete, localised reinforcement corrosion

Scattering or inadequate cover depths of reinforcements

Localised reinforcement corrosion, penetration of damaging substances

Poor curing techniques Shrinkage cracks, increased permeability Premature stripping of formwork Cracking and deformation Control of maximum temperature during setting and hardening

Possible thermal cracks and Delayed Ettringite Formation (DEF)

Table 3. Concrete deterioration caused by inadequate concrete specifications by the user.

Causes of the problem Results

Low cement content Inadequate concrete strength and low performance to environmental actions.

High cement content Inadequate workability, shrinkage and cracking

High water cement ratio Inadequate concrete strength and increased permeability to gases and chloride

Calcium aluminate cement Loss of concrete strength especially in wet environment

Finely-ground cements or binders Concrete shrinkage

Reactive aggregates Expansive reactions (AAR) and loss of concrete strength and stiffness

Contaminated aggregates Steel corrosion initiation

Poorly shaped and badly graded aggregates

Poor workability, requiring extra water or vibration and leading to segregation and bleeding

Considering that the quality of concrete is a function of the concrete mix design, e.g., material properties, placement and workmanship, one can start to understand the limitations of the “prescriptive” or “deemed to satisfy” approach which concentrates solely on the concrete mix design. An improvement to the current practice would be to specify the expected performance further to the “prescriptive” requirements (hereafter termed as prescriptive specifications). However, specifying performance would require at the least a thorough understanding of the concrete behaviour in different environments and of testing techniques to assess the performance. Fig. 2 shows four different approaches for achieving durability, with the current and simplest approaches given to the right. The complexity of the suggested approaches increase as the practice moves from “deemed to satisfy” on the right to "partial factor based" or

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"probabilistic design" approach on the left. The main advantage of the latter approaches is that they are capable of taking into account the expected extreme scenarios during the life of a structure as design factors, for example expected low and high temperatures acting on the structure. The probabilistic approach would be capable of going one step further by taking into account the daily/yearly variations in the factor itself, e.g., daily temperature fluctuations as a design factor. In any case, it is expected that the complex design approaches would allow users to select concrete mixes which will perform in an environment to which they are designed. Nonetheless, even the simplest of the design approach can be successful if all the factors influencing deterioration of a structure is taken into account during the design process. The focus of this volume is to introduce durability based design by reviewing the current specifications and codes of practice across Europe. An emerging concept of performance based specification is also introduced as a means of addressing the shortcomings of the existing specification method as per 206-1:2000 [1].

Fig. 2. Different levels of durability based design approach. [3]

The focus of this volume is to introduce durability based design by reviewing the European standards and codes of practice for concrete structures design. An emerging concept of performance based specification is also introduced as a means of addressing the shortcomings of the existing specification method and the National Documents of Application or the national standards with requirements to compliment the EN 206-1:2000 [1] where it is only informative. A comparison of the National requirements for concrete durability is also done for the countries involved in DURATINET. Examples of performance based specifications for concrete durability used on recent projects in the UK, Ireland, Portugal, France and in other European countries and in the world are also presented.

Less complex More Complex

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2 Overview of European standards for concrete structures design

In order to achieve the required service life, adequate measures need to be taken during the design phase to protect each structural element against the relevant environmental actions. The requirements for durability need to be considered during the following phases of a concrete structure: structural design, concrete design, construction details, execution/workmanship, quality control, inspection, verifications and when special measures are introduced namely to avoid corrosion.

Last ten years at the level of CEN the standards for concrete structures have been reviewed and significant improvements were made. Due to this evolution, the design, specification and execution of concrete structures are supported by the three main standards: EN 1992-1-1:2004 [4] for design of concrete structures, EN 206-1:2000 [1] for concrete specifications and EN 13670:2009 [5] for execution of concrete structures. The flowchart presented in Fig. 3, shows the role of the three main standards and all other subsidiary standards in concrete production.

Fig. 3. European standards for concrete structures. [1]

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The main three standards for concrete design cover the following subjects:

EN 1992-1-1:2004 [4] establishes the principles and rules for design of concrete structures and, in particular, specifies the durability considerations regarding minimum cover for reinforcement.

EN 206-1:2000 [1] deals with concrete requirements and specification and it is applicable for cast in situ concrete, precast and structural precast concrete products for buildings and civil engineering structures.

EN 13670:2009 [5] establishes the requirements for the execution (workmanship) of concrete structures designed according EN 1992-1-1:2004 [4].

The EN 206-1:2000 [1] standard, specifies requirements for:

the constituent materials of concrete;

the properties of fresh and hardened concrete and their verification;

the limitations for concrete mix design;

the specification of concrete;

the delivery of fresh concrete;

the production control procedures;

the conformity criteria and evaluation of conformity.

The EN 206-1:2000 [1] standard outlines methods for selecting an appropriate concrete mix based on the requirements for fresh and hardened concrete properties, such as workability/consistency, density, compressive strength, expected durability/service life and protection of embedded steel against corrosion. The Standard also outlines guidelines for conformity and quality control during the production process and execution/workmanship.

Where not detailed in the specification, the producer shall select types and classes of constituent materials from those with established suitability for the specified environmental conditions. The EN 206-1:2000 [1] presents the prescriptive limiting values for concrete composition to withstand the environmental actions for the different exposure classes and taking into account the intended working life of 50 years for the concrete structure. However, this Standard also gives the possibility that the requirements may be derived from performance-related design methods. The rules for this approach must be fixed in the national normative annex prepared by each country.

Several clauses of EN 206-1:2000 [1], namely those related with the design of concrete mixes and the exposure classes are concerned with the design of concrete and it seems more appropriate to be included in the Eurocode for concrete design. Furthermore, the durability related requirements established in EN 13369:2004 [6] are slightly different from those defined in EN 206-1:2000 [1].

Nowadays it is recognised by different countries that it is necessary to re-analyse the methodology defined in the Standards indicated in Fig. 3, for durability based service life design of concrete structures. For that a new working group at European level was created - JWG TC250/SC2 in association

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with the following technical committees, TC104/SC1, CEN TC229 and ISO TC71/SC3, to:

review the durability parameters in current Standards in light of the on-going work in TC 104/SC1 on equivalent durability;

consider various methods for predicting or designing service life based on fib MC and ISO, work with a view to incorporate these methods as an annex to Eurocode 2;

review all clauses of Standards related to durability to ensure their correctness/appropriateness;

review all clauses of Standards to ensure that they are placed in the right Standards, based on user requirements.

The following sections review the durability requirements for concrete design based on EN 206-1:2000 [1].

2.1 Classification of the exposure environments The methodology followed in EN 206-1:2000 [1] is to classify the micro and macro environment surrounding a concrete structure into various exposure classes. Table 4 shows the exposure classes and the guidance for identifying exposure classes. The concrete may be subjected to one or more of the exposure classes and the environmental loading to which it is subjected may thus need to be expressed as a combination of the exposure classes. In this case the requirements should satisfy that of the most exigent of the exposure classes. The limiting values for aggressive chemicals from natural soil and ground water for different exposure classes are also specified in EN 206-1:2000 [1] as shown in the Table 5.

Table 4. Exposure classes related to environmental conditions in accordance with EN 206-1. [4]

Class designation

Description of the environment Informative examples where exposure classes may occur

1 No risk of corrosion or attack

X0

For concrete without reinforcement or embedded metal: all exposures except where there is freeze/thaw, abrasion or chemical attack. For concrete with reinforcement or embedded metal: very dry

Concrete inside buildings with very low air humidity

2 Corrosion induced by carbonation

XC1 Dry or permanently wet

Concrete inside buildings with low air humidity Concrete permanently submerged in water

XC2 Wet, rarely dry Concrete surfaces subject to long-term water contact Many foundations

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Table 4 (cont.). Exposure classes related to environmental conditions in accordance with EN 206-1. [4]

Class designation

Description of the environment Informative examples where exposure classes may occur

XC3 Moderate humidity Concrete inside buildings with moderate or high air humidity External concrete sheltered from rain

XC4 Cyclic wet and dry Concrete surfaces subject to water contact, not within exposure class XC2

3 Corrosion induced by chlorides

XD1 Moderate humidity Concrete surfaces exposed to airborne chlorides

XD2 Wet, rarely dry Swimming pools Concrete components exposed to industrial waters containing chlorides

XD3 Cyclic wet and dry

Parts of bridges exposed to spray containing chlorides Pavements Car park slabs

4 Corrosion induced by chlorides from sea water

XS1 Exposed to airborne salt but not in direct contact with sea water

Structures near to or on the coast

XS2 Permanently submerged Parts of marines structures

XS3 Tidal, splash and spry zones 5 Freeze/thaw attack

XF1 Moderate water saturation, without de-icing agent

Vertical concrete surfaces exposed to rain and freezing

XF2 Moderate water saturation, with de-icing agent

Vertical concrete surfaces of road structures exposed to freezing and airborne de-icing salts

XF3 High water saturation, without de-icing agents

Horizontal concrete surfaces exposed to rain and freezing

XF4 High water saturation, with de-icing agents or sea water

Road and bridge decks exposed to de-icing agents Concrete surfaces exposed to direct spray containing de-icing agents and freezing Splash zone of marine structures exposed to freezing

6 Chemical attack

XA1 Slightly aggressive chemical environment according to EN 206-1, Table 2

Natural soils and ground water XA2 Moderately aggressive chemical environment according to EN 206-1, Table 2

XA3 Highly aggressive chemical environment according to EN 206-1, Table 2

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Table 5. Limiting values for exposure classes for chemical attack from natural soil and ground water in accordance with EN 206-1. [1]

The aggressive chemical environments classified below are based on natural soil and ground water at water/soil temperatures between 5 C and 25 C and a water velocity sufficiently slow to approximate to static conditions. The most onerous value for any single chemical characteristic determines the class. Where two or more aggressive characteristics lead to the same class, the environment shall be classified into the next higher class (unless a special study for this specific case proves that it is not necessary).

Chemical characteristic

Reference test method

XA1 XA2 XA3

GROUND WATER

SO42- mg/L EN 196-2

≥ 200 and ≤ 600

> 600 and ≤ 3000

> 3000 and ≤ 6000

pH ISO 4316 ≤ 6.5 and ≥ 5.5

< 5.5 and ≥ 4.5

< 4.5 and ≥ 4.0

CO2 mg/L aggressive

prEN 13577 ≥ 15 and ≤ 40

> 40 and ≤ 100

> 100 up to saturation

NH4+ mg/L

ISO 7150-1 or ISO 7150-2

≥ 15 and ≤ 30

> 30 and ≤ 60

> 60 and ≤ 100

Mg2+ mg/L ISO 7980 ≥ 300 and ≤ 1000

> 1000 and ≤ 3000

> 3000 up to saturation

SOIL SO4

2- mg/kg (1) total

EN 196-2 (2) ≥ 2000 and ≤ 3000 (3)

> 3000 (3) and ≤ 12000

> 12000 and ≥ 24000

Acidity ml/kg DIN 4030-2 > 200

Baumann Gully Not encountered in practice

(1) Clay soils with permeability below 10-5 m/s may be moved into a lower class. (2) The test method prescribes the extraction of SO4

2- by hydrochloric acid; alternatively, water extraction may be used, if experience is available in the place of use of the concrete. (3) The 3000 mg/kg limit is reduced to 2000 mg/kg, where there is a risk of accumulation of sulfate ions in the concrete due to drying and wetting cycles or capillary suction.

2.2 Durability requirements for concrete According to EN 206-1:2000 [1], specifications for designing concrete which will be exposed to various environmental actions are based on "deem-to-satisfy" approach, such as maximum water/cement ratio, minimum cement content, minimum cover depth, etc. and the assumption is that if these rules are met, the structure will achieve a service life of 50 years.

Furthermore, EN 206-1:2000 [1] also defines the basic requirements for constituent materials and concrete compositions. The amounts of harmful ingredients which can be present in the constituent materials are restricted in view of the durability of the overall structure. For example, if aggregates contain varieties of silica susceptible to attack by alkalis (such as Na2O and K2O present in the concrete) and the concrete is exposed to humid conditions, actions need to be taken to prevent the occurrence of alkali-silica reaction. The Standard also limits the initial chloride content of concrete; the maximum permissible values based on the use of concrete are given in Table 6. It is understood that each country may adopt its own limiting values for the maximum permissible chloride content.

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Although the prescriptive approach may work well for certain durability mechanisms, such as alkali-silica reaction, sulfate attack or abrasion, a robust performance-based approach is necessary for other more complex mechanisms to guarantee the service life. Both approaches are introduced in the following sections.

Table 6. Maximum chloride content of concrete.

Concrete use Chloride

content class Maximum Cl- content by mass of cement

Not containing steel reinforcement or other embedded steel metal with the exception of

corrosion resisting lifting devices Cl 1.0 1.0 %

Containing steel reinforcement or other embedded metal

Cl 0.20 0.20 % Cl 0.40 0.40 %

Containing prestressing steel reinforcement

Cl 0.10 0.10 % Cl 0.20 0.20 %

a For a specific concrete use, the class to be applied depends upon the provisions valid in the place of the use of concrete b where type II additions are used and are taken into account for the cement content, the chloride content is expressed as the percentage chloride ion as the mass of cement plus total mass of additions that are taken into account.

2.2.1 Prescriptive method for concrete properties specification

The prescriptive method of specification of concrete to resist environmental actions is given in terms of established concrete properties and limiting values (or tolerance).

The requirements for each exposure class are presented in terms of:

permitted types and classes of constituent materials;

maximum water/cement ratio;

minimum cement content;

minimum concrete compressive strength class (optional);

minimum air-content of the concrete (if relevant).

As the limiting values only target the material properties of concrete, in order to ensure good workmanship or adequate quality control during placement and throughout the service life, further requirements are also specified, namely,

the concrete is properly placed, compacted and cured e.g. in accordance with EN 13670:2009 [5] or other relevant standards;

the concrete has the minimum cover to reinforcement in accordance with the relevant design standard requirement for the specific environmental condition, e.g. EN 1992-1-1:2004 [4];

the appropriate exposure class was selected;

the anticipated maintenance is enforced.

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Furthermore, EN 206-1:2000 [1] Annex F presents recommendations for prescribing limiting values for a concrete structure with a service life of 50 years (Tables 7 to 10). The recommendations are provided for CEM I cement conforming to EN 197-1:2000 [7] and having a cement strength class of 32.5 and aggregate with maximum nominal upper size in the range of 20 mm to 32 mm. The Standard recommends that the limiting values for the maximum water/cement ratio and the minimum cement content must be applied in all cases, but concrete strength may be specified separately if required. For shorter or longer working life than 50 years, less onerous or more severe requirements may be necessary, respectively.

Table 7. Minimum concrete requirements for corrosion induced by carbonation.

Corrosion induced by carbonation No risk of

corrosion or attack XC1 XC2 XC3 XC4

Maximum w/c ratio - 0.65 0.60 0.55 0.50 Minimum Strength

Class C12/15 C20/25 C25/30 C30/37 C30/37

Minimum cement content (kg/m3)

- 260 280 280 300

Table 8. Minimum concrete requirements for corrosion induced by chloride.

Corrosion induced by Chloride No risk of

corrosion or attack

Sea water Chlorides other than

from sea water

Exposure class XS1 XS2 XS3 XD1 XD2 XD3

Maximum w/c - 0.50 0.45 0.45 0.55 0.55 0.45

Minimum Strength Class

C12/15 C30/ 37

C35/ 45

C35/ 45

C30/ 37

C30/ 37

C35 /45

Minimum cement content (kg/m3)

- 300 320 340 300 300 320

Table 9. Minimum concrete requirements for chemical attack.

Chemical Attack XA1 XA2 XA3

Maximum w/c ratio 0.55 0.50 0.45 Minimum Strength Class C30/37 C30/37 C35/40

Minimum cement content (kg/m3) 300 320 360 Other requirements - Sulfate resistant cement

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Table 10. Minimum concrete requirements for freeze/thaw attack.

Freeze/thaw attack XF1 XF2 XF3 XF4

Maximum w/c ratio 0.55 0.55 0.50 0.45 Minimum Strength

Class C30/37 C25/30 C30/37 C30/37

Minimum cement content (kg/m3)

300 300 320 340

Minimum air content - 4.0a 4.0a 4.0a

Other requirements Aggregate in accordance with EN 12620 with sufficient

freeze/thaw resistance a Where the concrete is not air entrained the performance of the concrete should be tested according to a appropriate test method in comparison with a concrete for which freeze/thaw resistance for a relevant exposure class is proven

2.2.2 Performance-related concrete design methods

The EN 206-1:2000 [1] also indicates that concrete may be specified in terms of performance-related parameters such as the resistance to environmental actions, e.g. scaling of concrete in a freeze/thaw test. Annex J of the Standard provides some guidance on the use of an alternative performance-related design method for ensuring durability. The application of this alternative method may depend on several factors, including the knowledge and facilities to assess the expected performance, availability of predictive models and knowledge and skills to interpret the data. Based on the availability of resources, European countries could develop their own methodologies for the application of the performance-related concrete design methods.

The performance-related method should consider each relevant deterioration mechanism, the working life of the element or structure and the criteria which define the end of this working life quantitatively. Such a method can be based on satisfactory experience with local practices in local environments, on data from an established performance test method for the relevant mechanism, or on the use of proven predictive models.

This approach can be considered to be appropriate where:

a working life significantly differing from 50 years is required according the type and relevance of structure, Table 11;

the structure is "special" requiring a lower probability of failure;

the environmental actions are particularly aggressive, or are well defined;

standards of workmanship are expected to be high;

a management and maintenance strategy is to be introduced, perhaps with planned upgrading;

significant populations of similar structures or elements, are to be built;

new or different materials are to be used.

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The methods that may be used include:

The refinement of the prescriptive method, considering the minimum requirements, based on long-term experience of local materials and practices and on detailed knowledge of the local environment.

Methods based on approved and proven tests that are representative of actual conditions and have approved performance criteria. The implementation of these methods require large experience permitting to assume that certain test results will be indicative of adequate performance to the specific environmental action simulated in the test.

Methods based on analytical models that have been calibrated against test data representative of actual conditions in practice.

In applying these methods, it is important to define in advance, at least the following:

the type of structure and its form;

the local environmental and local micro-climate conditions;

the level of execution;

the required working life or service life;

the concrete composition and the constituent materials should be closely defined to enable the level of performance to be maintained.

Table 11. Indicative design working life for structures. [8]

Design working life category

Indicative design working life (years)

Examples

1 10 Temporary structures 1

2 10 to 25 Replaceable structural parts, e.g. gantry girders bearings

3 15 to 30 Agricultural and similar structures

4 50 Building structures and other common structures

5 100 Monumental builds structures, bridges, and other civil engineering structures

1 Structures or parts of structures that can be dismantled with a view to being re-used should not be considered as temporary

2.2.3 Concrete cover depth specification

Concrete cover is probably the greatest single factor that can influence the premature corrosion of reinforcement and the performance of the structure can be highly sensitive to defects in cover. Consequently, measures taken to control and ensure a suitable cover can be more beneficial than any other preventative measure. Fig. 4 demonstrates how cover depth can influence the service life, which is ascertained by the advance of carbonation front and chloride ions towards the reinforcement [9].

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Fig. 4. Influence of cover to reinforcement on carbonation and chloride penetration.

The EN 1992-1-1:2004 [4] establishes the following principles and rules in relation to reinforcement cover:

the cover is the distance between surface of the reinforcement (including links and stirrups) closest to the nearest concrete surface (regardless it is horizontal, vertical or inclined);

the nominal cover, cnom, (to be specified on the drawings) is defined as the sum of a minimum cover, cmin, plus an allowance for deviation ∆cdev.

cnom= cmin + ∆cdev (1)

∆cdev = 10 mm, in the EN 13670:2009 [5] but could be less if specific quality control is implemented or in particular type of elements. The nominal cover shall be guaranteed in the execution by the use of spacers separating the reinforcement from the formwork. The minimum concrete cover, cmin, is the greater of a set of values never less than 10 mm, given by:

cmin = max{cmin,b; cmin,dur; ∆cdur,y - ∆cdur,st - ∆cdur, add; 10 mm} (2)

Where:

cmin,b -minimum cover due to bond requirement

cmin,dur - minimum cover due to environmental conditions

∆cdur,y - additive safety element

∆cdur,st - reduction of minimum cover for use of stainless steel

∆cdur, add - reduction of minimum cover for use of additional protection

In general, the cmin intended to ensure the following:

Safe transmission of steel-concrete bond forces. For such, the corresponding minimum cover, cmin,b shall not be less than the bar diameter or, in the case of bundled bars, the equivalent diameter

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Φn = Φ√n ≤ 55 mm, n being the number of bars limited to n ≤ 4 for compressed bars and in joints and n ≤ 3 in the other cases (exceptions to this rule are the bars placed one over the other).The value of cmin,b, shall be increased by 5 mm if the aggregate has a maximum size larger than 32 mm. In the case of pre-tensioned and post-tensioned concrete, EN 1992-1-1:2004 [4] provides a few recommendations.

Suitable fire resistance (according EN 1992-1-2:2004).

Steel protection against corrosion.

The minimum cover required, cmin,dur, for reinforced concrete based on the exposure class is presented in Table 12. The corresponding values for pre-stressed concrete (both pre-tensioned and post-tensioned) are given in Table 13.

Table 12. Minimum reinforced concrete cover (mm) in EN 1992-1-1 [4], cmin,dur.

Structural class

Environmental exposure class

X0 XC1 XC2/3 XC4 XD1/ XS1

XD2/ XS2

XD3/ XS3

1 10 10 10 15 20 25 30 2 10 10 15 20 25 30 35 3 10 10 20 25 30 35 40 4 10 15 25 30 35 40 45 5 15 20 30 35 40 45 50 6 20 25 35 40 45 50 55

Table 13. Minimum prestressed concrete cover (mm) in EN 1992-1-1 [4], cmin,dur.

Structural class

Environmental exposure class

X0 XC1 XC2/3 XC4 XD1/ XS1

XD2/ XS2

XD3/ XS3

1 10 15 20 25 30 35 40 2 10 15 25 30 35 40 45 3 10 20 30 35 40 45 50 4 10 25 35 40 45 50 55 5 15 30 40 45 50 55 60 6 20 35 45 50 55 60 65

The recommended structural class for a design working life of 50 years is S4 for the indicative concrete strengths given in EN 206-1:2000 [1]. In a similar manner, once a structural class is chosen for reinforced or prestressed concrete elements, the corresponding cover values for each exposure class, cmin,dur, can be determined in accordance with EN 1992-1-1:2004 [4]. The structural class can be reduced in the following situations:

when using, as replacement for current steel, stainless steel;

if the strength class of the concrete used, in each exposure class, is higher than the strength classes indicated;

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if the surface of the concrete in contact with the aggressive agent is coated in compliance with the requirements established;

if the steel bars, ready to be placed in formworks, are previously covered with epoxy resins, by fulfilling the requirements defined;

if the structural concrete part is laminar (of the type slab or wall);

the recommended modifications on the structural class are given in Table 14 for different situations.

Table 14. Recommended structural classification according to EN 1992-1-1. [4]

Structural Class

Criterion

Exposure Class according to EN 206-1

X0 XC1 XC2/ XC3

XC4 XD1 XD2/ XS1

XD3/ XS2/ XS3

Design working life

of 100 years

Increase class by

2

Increase class by

2

Increase class by

2

Increase class by

2

Increase class by

2

Increase class by

2

Increase class by

2

Strength Class

≥ C30/C37 reduce

class by 1

≥ C30/C37 reduce

class by 1

≥ C35/C45 reduce

class by 1

≥ C40/C50 reduce

class by 1

≥ C40/C50 reduce

class by 1

≥ C40/C50 reduce

class by 1

≥ C45/C55 reduce

class by 1

Member with slab geometry

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Special quality

control of concrete

production ensured

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

Reduce class by

1

1. The strength class and w/c ratio are considered to be related values. A special composition (type of cement, w/c value, fine fillers) with the intent to produce low permeability concrete may be considered.

2. The limit may be reduced by one strength class if air entrainment of more than 4 % is applied. Dur

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3 National standards or guidelines to complement EN 206-1

3.1 United Kingdom Anyone wishing to specify concrete to BS EN 206-1:2000 [10] in the UK can use BS 8500-1:2006 [11] and BS 8500-2:2006 [12] alongside Eurocode 2 [4].

BS 8500-1:2006 [11] is the complementary British Standard to BS EN 206-1:2000 [10]. BS 8500-2:2006 [12] contains specifications for materials and procedures that are outside of European standardisation but within national experience. This Standard supplements the requirements in BS EN 206-1:2000 [10].

The guidelines given in BS 8500:2006 [11],[12] for durability are based on the latest research and therefore recommended strength, cover, cement content and water/cement ratio for similar exposure conditions may vary compared to guidance given in previous Standards, such as BS 8110-1:1997 [13]. The following sections will review the features of BS 8500:2006 [11],[12] Standards.

3.1.1 Defining the exposure classes

BS 8500:2006 [11],[12] exposure classes are related to the deterioration processes of carbonation, ingress of chlorides, chemical attack from aggressive ground and freeze/thaw similar to those specified in EN 206-1:2000 [1] (see Table 4).

3.1.2 Select the concrete strength and cover

Further to the exposure classes, a recommended/minimum strength class and cover to reinforcement (cnom) are selected to satisfy common exposure conditions for the chosen working life (50 or 100 years typically). BS 8500:2006 [11],[12] uses compressive strength class to define concrete strengths; the notation used gives the cylinder strength as well as the cube strength.

Furthermore, the durability guidance given in BS 8500:2006 [11],[12] is based on the assumption that the minimum cover for durability is achieved. An allowance should be made in the design for deviations from the minimum cover (Δcdev). This should be added to the minimum cover to obtain the nominal cover. Eurocode 2 [4] recommends that Δcdev is taken as 10 mm, unless the fabrication is subjected to a quality assurance system where it is permitted to reduce Δcdev to 5 mm. It is recommended that these values are adopted when using BS 8500:2006 [11],[12]. The nominal cover and permitted deviation should be clearly stated on the drawings.

3.1.3 Selecting the intended working life, e.g., service life

The recommendations in BS 8500 [11],[12] are for an intended working life of at least 50 years for most exposure classes and 50 and 100 years only for

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carbonation XC classes. For each of the exposure classes, the Standard specifies nominal cover, minimum strength class, maximum water-binder ratio (w/b), minimum cement (binder) content and allowable cement types. Table 15 presents BS 8500:2006 [11],[12] guidelines for chloride resistance and Table 16 summarises the guidelines for carbonation resistance.

3.1.4 Cement types and minimum cement content

There are six groups of cement combinations specified in BS 8500:2006 [11],[12]

depending on the exposure classes and they are presented in Table A.17 of BS 8500-1:2006 [11] . Minimum cement content can also be selected from BS 8500-1:2006 [11] (Table A.18 of BS 8500-1:2006) [11] based on w/b and the maximum aggregate size. It should be noted that the strength, water/cement ratio and minimum cement content may vary depending on the cement type used. In the UK, all cement/combinations are available (except SRPC), although in most concrete production plants either ground granulated blast furnace slag (ggbs) or fly-ash (pfa) is available; not both. When using a designated concrete, it is not necessary to specify the types of cement/combinations.

3.1.5 Complementary requirements for constituent materials

BS 8500-2:2006 [12] specifies the complementary requirements to EN 206-1:2000 [1] specification for concrete constituent materials. This section is useful where the types and classes of constituent materials have not been specified and the concrete producer is required to select the materials based on the designation given in this section. The notations, conforming standard and designation for different types of cement and their combinations, are specified in this section. Section 4.3 of BS 8500-2:2006 [12] emphasises on specifications for aggregates to be used in different types of concrete. In addition to specifications and conformity standards on normal, heavy and light aggregates described in EN 206-1:2000 [1], section 4.3 of BS 8500-2:2006 [12] describes guidelines for use of recycled concrete aggregates (RCA). It is important to note that for exposure classes X0, XC1, XC2, XC3, XC4, XF1 and DC1 the recycled concrete aggregates are limited to use for a maximum strength class of C40/50.

3.1.6 Air content

Where air entrainment is required for exposure classes XF3 and XF4 the minimum air content by volume of 5.5 %, 4.5 %, 3.5 % and 3.0 % should be specified for 10, 14, 20 and 32/40 mm maximum aggregate size respectively. Further details are given in Table A.14 of BS 8500-1:2006 [11].

3.1.7 Freeze/thaw aggregates

For exposure conditions XF3 and XF4 freeze/thaw resisting aggregates should be specified. The producer is then obliged to conform to the requirements given in BS 8500-2:2006 [12].

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3.1.8 Aggressive ground

Where plain or reinforced concrete is in contact with the ground, further checks are required to ensure durability. An aggressive chemical environment for concrete class (ACEC class) should be assessed for the site. BRE Special Digest 15 gives guidance on the assessment of the ACEC class and this is normally carried out as part of the interpretive reporting for a ground investigation. Knowing the ACEC class and the thickness of the section, a design chemical class (DC class) can be obtained from Table A.4 in BS 8500-1:2006 [11].

For designated concretes, an appropriate foundation concrete (FND designation) can be selected using Table A11 in the code; the cover should be determined from Table A9 in the code for the applicable exposure classes. A FND concrete has the minimum strength class of C25/30; therefore, where a higher strength is required, a designed concrete should be specified. Moreover, fully designed concrete in UK need not be designed for freeze-thaw resistance. Therefore, the specifications for designed concrete method do not take into account conditions where chlorides are present in the soil or freeze-thaw resistance is required.

3.1.9 Consistence

The term workability has been replaced by the term consistence and a series of consistence classes has been introduced. Table A16 in BS 8500-1:2006 [11] gives the slump and flow classes for different applications of concrete based on the type of concrete compaction adopted.

3.1.10 Chloride Class

Concrete that is to be prestressed or heat cured should normally be specified as chloride class Cl 0.10. Reinforced concrete should be specified as class Cl 0.40 except for concrete made with cement conforming to BS 4027:1996 (SRPC) [14], which should be specified as class Cl 0.20.

3.1.11 Conformity

Under BS 8500:2006 [11],[12], the concrete producer is now required to follow a formal procedure called conformity to verify that the concrete is in accordance with the specification. It is, therefore, recommended that the concrete supplier should have third party certification. Where this is not adopted, the specifier is advised to adopt adequate identity testing to ensure the concrete is as specified.

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Table 15. Current BS 8500:2006 [11],[12] guidelines for chloride resistance. B

S 8

500:

2006

, Val

ues

Minimum cover (mm)

25+ Δc

30+ Δc

35+ Δc

40+ Δc

45+ Δc

50+ Δc

Cement Type

Exposure Class

XS1

C45/50E

0.35F 380

C35/40E 0.45 360

C32/40E 0.50 340

C32/40E

0.50 340

C32/40E

0.50 340

CEM I, II/A, II/B-S, SRPC

C40/50E

0.35F

380

C32/40E 0.45 360

C28/35 0.50 340

C25/30 0.55 320

C25/30 0.55 320

II/B-V, III/A

C32/40E

0.40 380

C25/30 0.50 340

C25/30 0.50 340

C25/30 0.55 320

C25/30 0.55 320

III/B

C32/40E

0.40 380

C28/3 0.50 340

C25/30 0.50 340

C25/30 0.55 320

C25/30 0.55 320

IVB-V

XS2

C40/50E

0.40 380

C32/40E 0.50 340

C28/35 0.55 320

C28/35 0.55 320

C28/35 0.55 320

CEM I, II/A, II/B-S, SRPC

C35/45E

0.40 380

C28/35 0.50 340

C25/30 0.55 320

C25/30 0.55 320

C25/30 0.55 320

II/B-V, III/A

C32/40E

0.40 380

C25/30 0.50 340

C20/25 0.55 320

C20/25 0.55 320

C20/25 0.55 320

III/B, IVB-V

XS3

C45/55E

0.35F 380

C40/50E 0.40 380

CEM I, II/A, II/B-S, SRPC

C35/45E

0.40 380

C32/40E 0.45 360

C28/35 0.50 340

II/B-V, III/A

C32/40E

0.40 380

C28/35 0.45 360

C25/30 0.50 340

III/B, IVB-V

XD1 C40/50

0.45 360

C32/40 0.55 320

C28/35 0.60 300

C28/35 0.60 300

C28/35 0.60 300

C28/35 0.60 300

All cements

XD2

C40/50E

0.40 380

C32/40E 0.50 340

C28/35 0.55 320

C28/35 0.55 320

C28/35 0.55 320

CEM I, II/A, II/B-S, SRPC

C35/45E

0.40 380

C28/35 0.50 340

C25/30 0.55 320

C25/30 0.55 320

C25/30 0.55 320

II/B-V, III/A

C32/40E

0.40 380

C25/30 0.50 340

C20/25 0.55 320

C20/25 0.55 320

C20/25 0.55 320

III/B, IVB-V

XD3

C45/55E

0.35F 380

C40/50E 0.40 380

C35/45E 0.45 360

CEM I, II/A, II/B-S, SRPC

C35/45E

0.40 380

C32/40E

0.45 360

C28/35 0.50 340

II/B-V, III/A

C32/40E

0.40 380

C28/35 0.45 360

C25/30 0.50 340

III/B, IVB-V

E If the concrete is specified as being air entrained in accordance with the XF2 or XF4 recommendations in Table A.8, the minimum compressive strength class for corrosion induced by chlorides may be reduced to C28/35. F In some parts of the UK it is not possible to produce a practical concrete with a maximum w/c ratio of 0.35.

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Table 16. Current BS 8500:2006 [11],[12] guidelines for carbonation resistance.

BS

850

0:20

06, V

alue

s

Minimum cover (mm)

15+ Δc

20+ Δc

25+ Δc

30+ Δc

35+ Δc

40+ Δc

45+ Δc

Cement Type

Exposure Class

XC1 C20/25

0.70 240

C20/25 0.70 240

All

cements

XC2 - - C25/30

0.65 260

C25/30 0.65 260

All

cements

XC3 - C40/50

0.45 340

C30/37 0.55 300

C28/35 0.60 280

C25/30 0.65 260

All

cements, not IVB-V

XC4 - - C40/50

0.45 340

C30/37 0.55 300

C28/35 0.60 280

C25/30 0.65 260

IVB-V

3.2 Ireland In December 2003, the Irish Standard for Concrete IS 326:1995 Part 2 [15] was replaced by the new European Standard IS EN 206-1:2002 [16]. The Irish version IS EN 206-1:2002 [16] comprises the core text of the European standard EN 206-1:2000 [1], along with the Irish National Annex, currently in circulation for comments.

Ireland, compared to other countries in Europe, has substantially more resources per capita of the constituent materials which go into the manufacture of concrete. For this reason concrete is produced on a local basis and generally delivered within a radius of 30 miles.

IS EN 206-1:2002 [16] is the only national Irish standard for concrete specification and production since December 2003. Concrete producers are in the process of adapting their quality and production control systems to become fully compliant with the requirements within it. Designers and users are required to specify concrete in accordance with the requirements of IS EN 206-1:2002 [16], to ensure uniformity and clarity in the full construction process. Structural design will continue to be guided by the existing design standards (IS 326/BS 8110 etc.) and some disparities may occur in the interim period. Table 17 shows the current Irish guidelines for the carbonation exposure classes outlined in EN 206-1:2000 [1] for a 50-year design life. As shown, the Irish National annex guidelines do not give limits for covers < 20 mm, compared with BS 8500:2006 [11],[12], which give limits for all covers. For exposure class XC1, the Irish guidelines appear to be more conservative where a higher concrete grade, lower w/c ratio and a higher minimum cement content is used compared with those used in BS 8500:2006 [11],[12]. This appears to be a general trend throughout.

The Irish guidelines make use of ‘trade-offs’ allowed in EN 206-1:2000 [1] which can be seen in exposure class XC2 for example. As may be observed, the guidelines in bold are the recommended values to be used for this exposure class using a cover of 25 mm+Δc. However, recognising that by decreasing the

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cover (to 20+Δc), the recommendation is to increase the concrete grade (to C32/40), decrease w/c ratio (to 0.50) and increase the minimum cement content (to 340 kg/m3). Alternatively, by increasing the cover (to 30 mm+Δc), the concrete grade may be decreased (to C25/30), the w/c ratio may be increased (to 0.65) and the minimum cement grade may be decreased (to 280 kg/m3).

For exposure class XC3, all cement types except IVB-V are recommended while for XC4, only cement type IVB-V is recommended. Cement Type CEM IVB-V is a pozzolanic type cement with an allowable clinker content of 45-64 %, a siliceous fly-ash content of 36-55 % and a minor constituent’s allowance of 0-5 % (EN 197-1:2000 [7], Table A.4).

As discussed above, the main protection for reinforcement to carbonation attack is by the cover concrete. For exposure classes XC1 and XC2, it is assumed that nominal cover would be suitable for both classes. For Ireland and UK, exposure classes XC3 and XC4 are most relevant. In comparing the exposures classes in

Table 16 and Table 17, XC1, XC2, XC3 and XC4 would correspond to mild, moderate, moderate and severs respectively. The BS 8110-1:1997 [13] guidelines are conservative, compared with both the Irish and BS 8500:2006 [11],[12] guidelines, particularly in terms of the concrete grade. For example, for exposure class XC2 (or moderate exposure) for a cover of 30 mm, the concrete grade suggested by BS 8110 is C40 concrete, compared to C28 and C25 for the Irish and BS 8500:2006 [11],[12] guidelines respectively. However, there is relatively little difference between the maximum w/c ratio and minimum cement contents. Table 15 and Table 18 give the specifications for the chloride exposures in BS 8500:2006 [11],[12] and IS EN 206-1:2002 [16].

Table 17. Draft Irish guidelines for carbonation resistance (for information only).

Iris

h N

atio

nal A

nnex

Val

ues

Minimum cover (mm)

20+Δc 25+Δc 30+Δc 35+Δc 40+Δc Cement

Type

Exposure Class

XC1 C25/30

0.65 280

All

cements

XC2 C32/40

0.50 340

C28/35 0.60 300

C25/30 0.65 280

All

cements

XC3 C35/45

0.50 360

C30/37 0.55 320

C28/35 0.60 300

C25/30 0.65 280

All cements

XC4 C40/50

0.45 400

C35/45 0.50 360

C30/37 0.55 320

C28/35 0.60 300

C25/30 0.65 280

All cements

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Table 18. Draft Irish guidelines for chloride resistance (for information only). Ir

ish

Nat

iona

l Ann

ex V

alue

s

Minimum cover (mm)

25+ Δc

30+ Δc

35+ Δc

40+ Δc

45+ Δc

50+ Δc

Cement Type

Exposure Class

XS1

C40/50

0.45 400

C35/45 0.50 360

C30/37 0.55 320

CEMI,

CEM II/A-L, LL, V

C35/45

0.45 400

C32/40 0.50 360

C28/35 0.55 320

CEM III/A, CEM II/B-

V

C32/40

0.45 400

C28/35 0.50 360

C28/35 0.55 320

CEM III/B

XS2

C45/55

0.40 420

C40/50 0.45 400

C35/45 0.50 360

C32/40 0.50 340

CEM I,

CEM II/A-L, LL, V

C40/50

0.40 420

C35/45 0.45 400

C32/40 0.50 360

C30/37 0.50 340

CEM III/A, CEM II/B-

V

C35/45

0.40 420

C32/40 0.45 400

C30/37 0.50 360

C28/35 0.50 340

CEM III/B

XS3

C50/60

0.40 440

C45/55 0.40 420

C40/50 0.45 400

C35/45 0.50 350

CEM I, CEM II/A-L, LL, V

C45/55

0.40 440

C40/50 0.40 420

C35/45 0.45 400

C32/40 0.50 360

CEM III/A, CEM II/B-

V

C40/50

0.40 440

C35/45 0.40 420

C32/40 0.45 400

C28/35 0.50 360

CEM III/B

XD1

C40/50 0.45 400

C35/45 0.50 360

C30/37 0.55 320

C28/35 0.60 300

CEM I,

CEM II/A-L, LL, V

C35/45 0.45 400

C32/40 0.50 360

C28/35 0.55 320

C25/30 0.60 300

CEM III/A, CEM II/B-

V C35/45

0.45 400

C30/37 0.50 360

C25/30 0.55 320

C25/30 0.60 300

CEM III/B

XD2

C45/55

0.40 420

C40/50 0.45 400

C35/45 0.50 360

C30/37 0.55 320

CEM I,

CEM II/A-L, LL, V

C40/50

0.40 420

C35/45 0.45 400

C32/40 0.50 360

C28/35 0.55 320

CEM III/A, CEM II/B-

V

C35/45

0.40 420

C32/40 0.45 400

C28/35 0.50 360

C25/30 0.55 420

CEM III/B

XD3

C50/60

0.40 440

C45/55 0.40 420

C40/50 0.45 400

C35/45 0.50 360

CEM I, CEM II/A-L, LL, V

C45/55

0.40 440

C40/50 0.40 420

C35/45 0.45 400

C32/40 0.50 360

CEM III/A, CEM II/B-

V

C40/50

0.40 440

C40/45 0.40 420

C32/40 0.45 400

C28/35 0.50 360

CEM III/B

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3.3 Portugal In Portugal the European standard NP EN 206-1:2005 [17] has been implemented since 2005 and it contains a national annex (National Document of Application) with Portuguese requirements to compliment the EN standard in the several aspects where EN standard is only informative. Included in the national annex are three main specifications prepared by LNEC: LNEC E 461:2004 [18], LNEC E 464:2005 [19] and LNEC E 465:2005 [20].

The Portuguese annex included in NP EN 206-1:2005 [17] considers the same environmental actions as in the EN 206-1:2000 [1], except the classes XF3 and XF4 of the freeze/thaw attack, as they are not applicable to Portugal. For example, in the national annex, document LNEC E 461:2004 [18] guidelines are provided for a methodology to classify the reactivity of aggregates in concrete. The methodology takes into consideration preventive measures for alkali-silica reaction in concrete structures based on different levels of risk and different humidity levels in the environment. If none of these measures are applicable, it recommends the evaluation of the susceptibility of aggregates or compositions of concrete to the alkali-silica reaction, using mortar and concrete expansion tests in accordance with ASTM C 1260-01, RILEM AAR-3 or AAR-4. A similar methodology is established for the internal sulfate attack (ISA), for which it recommends a concrete expansion test to be carried out to confirm the possibility of ISA.

LNEC E 464:2005 [19] defines the suitability of cement types as concrete constituents with informative examples of exposure classes of Table 1 of EN 206-1:2000 [1]. The document also deals with prescriptions on concrete composition and strength classes for a design working life of 50 and 100 years and some other common prescriptions on cements and mixes in combination with the exposure classes. The general framework on the guarantee of the design working life is introduced through performance-related design methods taking into consideration the durability specifications given in EN 206-1:2000 [1]. This specification also establishes the suitability of the equivalent performance concept, the properties to be determined and gives an example with results and analysis

LNEC E 465:2005 [20] specification highlights the main principles and application rules related to the durability of reinforced concrete stated in the EN 1990:2002 [8]. The general methodology of a durability design is mentioned. The minimum reliability indexes for each of 3 reliability classes and the serviceability limit state that corresponds to the crack initiation due to the corrosion of the steel were also described in this document.

The specification of concrete for enhanced durability requirements are provided by three different methods, which includes the prescriptive method, the equivalent concrete performance concept approach and the performance- related design methods.

3.3.1 Prescriptive specification of concrete

LNEC E 464:2005 [19] provides guidelines for prescriptive specification for concrete to sustain various exposure conditions mentioned in EN 206-1:2000 [1].

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25

The prescriptions for maximum water-cement ratio, minimum cement content and minimum strength class are provided in Table 19 and Table 20 for exposure conditions leading to reinforcement corrosion and Table 21 and Table 22 for freeze/thaw and chemical attack respectively. For the exposure classes XC and XS, the minimum values for the nominal cover which shall be defined in the design and implemented on site by the concrete user are also indicated in Table 19 and Table 20.

Table 19. Limits for the composition and the compressive strength class of the concrete under the action of carbon dioxide, for a design working life of 50 years. [19]

Type of cement

CEM I (Reference); CEM II/A(1) CEM II/B(1); CEM III/A(2); CEM IV(2);

CEM V/A(2) Exposure

class XC1 XC2 XC3 XC4 XC1 XC2 XC3 XC4

Minimum nominal

cover (mm) 25 35 35 40 25 35 35 40

Maximum water/

cement ratio 0.65 0.65 0.60 0.60 0.65 0.65 0.55 0.55

Minimum cement

content, C (kg/m3)

240 240 280 280 260 260 300 300

Minimum strength

class

C25/ 30

LC25/ 28

C25/ 30

LC25/ 28

C30/ 37

LC30/ 33

C30/ 37

LC30/ 33

C25/ 30

LC25/ 28

C25/ 30

LC25/ 28

C30/ 37

LC30/ 33

C30/ 37

LC30/ 33

(1) Not applicable to cements II/A-T and II/A-W and to cements II/B-T and II/B-W, respectively. (2) Not applicable to cements with a Portland clinker percentage less than 50 %, by mass.

Table 20. Limits for the composition and the compressive strength class of the concrete under the action of chlorides, for a design working life of 50 years. [19]

Type of cement CEM IV/A (Reference); CEM IV/B; CEM III/A; CEM III/B; CEM V; CEM

II/B(1); CEM II/A-D CEM I; CEM II/A(1)

Exposure class XS1/ XD1

XS2/ XD2

XS3/ XD3

XS1/ XD1

XS2/ XD2

XS3/ XD3

Minimum nominal cover

(mm) 45 50 55 45 50 55

Maximum water/cement

ratio 0.55 0.55 0.45 0.45 0.45 0.40

Minimum cement content,

C (kg/m3) 320 320 340 360 360 380

Minimum strength class

C30/37 LC30/33

C30/37 LC30/33

C35/45 LC35/38

C40/50 LC40/44

C40/50 LC40/44

C50/60 LC50/55

(1) Not applicable to cements II-T, II-W, II/B-L and II/B-LL.

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Table 21. Limits for the composition and the compressive strength class of the concrete under the action of freeze/thaw, for a design working life of 50 years. [19]

Type of cement CEM I (Reference); CEM II/A (1) CEM II/B(1); CEM III/A; CEM IV; CEM

V/A Exposure class XF1 XF2 XF1 XF2

Maximum water/cement

ratio 0.60 0.55 0.55 0.50

Minimum cement

content, C (kg/m3)

280 280 300 300

Minimum strength class

C30/37 LC30/33

C30/37 LC30/33

C30/37 LC30/33

C30/37 LC30/33

Minimum air content (%)

____ 4.0 ____ 4.0 (1) Not applicable to cements II/A-T and II/A-W and to cements II/B-T and II/B-W, respectively. (2) Not applicable to cements with a Portland clinker percentage less than 50 %, by mass.

Table 22. Limits of the composition and the compressive strength class of concrete under a chemical attack, for a design working life of 50 years. [19]

Type of cement CEM IV/A (Reference); CEM IV/B; CEM III/A; CEM III/B; CEM V; CEM

II/B(1); CEM II/A-D CEM I; CEM II/A(1)

Exposure class XA1 XA2(2) XA3(2) XA1 XA2(2) XA3(2) Maximum

water/cement ratio

0.55 0.50 0.45 0.50 0.45 0.45

Minimum cement content,

C (kg/m3) 320 340 360 340 360 380

Minimum strength class

C30/37 LC30/33

C35/45 LC35/38

C35/45 LC35/38

C35/45 LC35/38

C40/50 LC40/44

C40/50 LC40/44

(1) Not applicable to cements II-T, II-W, II/B-L and II/B-LL. (2) When the aggressiveness results from the presence of sulfates, the cements shall fulfill the requirements mentioned in clause 5.3, namely in Table 10, the requirements established in this table 9 for CEM IV being applied.

For the design working life of 100 years, the requirements mentioned in Table 19 to Table 22 shall contain the following alterations:

in reinforced and pre-stressed concrete subject to the action of carbon dioxide or of chlorides, Table 19 and Table 20, the nominal cover is increased by 10 mm, with the requirements applicable to concrete being maintained.

in concrete subject to freeze-thaw action or to chemical attack, Table 21 and Table 22, the maximum water/cement ratio is decreased by 0.05, the minimum cement content is increased by 20 kg/m3 and the compressive strength class of concrete is increased by two classes.

In the case of environmental exposure with the risk of reinforcement corrosion, the prescriptions established in Table 19 and Table 20 do not make it possible

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to consider the influence of cover different from that defined, other concrete mixes or designs of working life different from 50 and 100 years. Furthermore, in class XS1, it is not possible to take into account the decrease in the aggressive action with distance from the coast line and, in class XS2, the influence of the increase in the aggressive action with depth. Therefore, to accommodate them, two general frameworks must be followed:

3.3.2 Equivalent concrete performance concept

According to equivalent concrete performance concept, a reference mix has to be prepared fulfilling the limit requirements of composition and mechanical strength defined in Table 19 to 22, depending on the exposure class of the equivalence study and with the reference cement indicated for that class. The resultant reference concrete samples are tested according to the test methods indicated in Table 23 and the results are compared with the test mix, e.g., with the formulation of which the performance has to be assessed.

Table 23. Properties, methods and test specimens.

Exposure class

Properties to be determined

Test methods Number and type of

specimens (mm)

XC1 XC2 XC3 XC4

Accelerated carbonation

LNEC E 391 1 specimen

150 x 150 x 600

Oxygen permeability LNEC E 392 3 specimens

150 h= 50

Compressive strength

NP EN 12390-3

3 specimens of 150 x 150 x 150

XS1/XD1 XS2/XD2 XS3/XD3

Chloride diffusion coefficient

LNEC E 463 2 specimens

100 h= 50

Capillary absorption LNEC E 393 3 specimens

150 h= 50

Compressive strength

NP EN 12390-3

3 specimens of 150 x 150 x 150

The materials to be used in the reference and test mixes shall have their suitability defined as concrete constituent materials and shall be supplied by the concrete manufacturer. Particularly, the aggregates and the corresponding fractions shall be the same in the reference mixes as in the test mixes.

The results obtained on the reference mix are then compared with the corresponding values of the test mix and conclusions are drawn about the equivalence of performance of the two mixes as regards penetration resistance to carbon dioxide or to chlorides in the concrete.

The relations presented in Table 24 should be observed between each test mix and the corresponding reference mix.

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Table 24. Properties to be observed between the concrete mix in study and the reference mix.

Properties to be determined Relation

Accelerated carbonation depth (ACD) 1.3

Capillary absorption (CA) 1.3

Oxygen permeability (K) 2.0

Chloride diffusion coefficient (D) 2.0

Compressive strength (fc) ,

,1.1

Conclusions can also be drawn about the equivalence of specific binder and the w/c ratio used in the test mix, as regards the corresponding pair of values used for the reference concrete. When defining the cover, the recommendations given in Table 12 and Table 13 shall be strictly followed.

3.3.3 Specification of concrete based on the performance - related design methods with respect to durability

This Specification presents a methodology to implement the tasks and responsibilities of the concrete specifier established in the EN 206-1:2000 [1], regarding the definition, in the design of reinforced or prestressed concrete works, of concrete performance requirements related with the resistance to the reinforcement corrosion. It also defines the acceptance criteria to be adopted in the control of those requirements. The models of concrete performance on which the methodology is based have two parameters which define the resistance to penetration of the aggressive agent and to corrosion.

The model generally accepted for the evolution with time of the deterioration of reinforced or pre-stressed concrete by steel corrosion considers the working life divided into two periods – initiation and corrosion propagation as showned in Fig. 5.

Fig. 5. Tutti model of reinforced concrete deterioration under the

environmental action XC or XS. [21]

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The initiation period corresponds to the time necessary for either the carbon dioxide or the chlorides to penetrate in the cover concrete through the system of open pores and to create steel depassivation conditions. The period of propagation is initiated with depassivation and ends when a certain Durability Limit State is reached, as a result of electrochemical reactions in the concrete pore solution which produce reinforcement corrosion (or corrosion of the metal embedded in the concrete). Therefore, the steel corrosion and the reinforced concrete deterioration only occur during the propagation period. Nevertheless, as the mechanisms involved in each period are different, from a physical and chemical point of view, detailed models are created to predict the initiation period and the propagation period, with performance properties which consider those mechanisms. These differences are also considered in the modelling of environmental actions. A Serviceability Limit State is chosen, in which the maximum admissible deterioration for reinforcement corrosion is very limited. Therefore, the criterion used is the one consisting of estimating minimum values for the propagation period and of characterising the concrete using the properties related with the initiation period. The concrete directly involved in the penetration resistance is the cover concrete of the reinforcement. In the Specification E 465:2005 [20], only the minimum cover is considered (Table 12 and Table 13), which are the highest of the values, with the minimum of 10 mm, which make it possible to ensure the transmission of steel-concrete bond forces, the fire resistance and the protection against corrosion.

LNEC E 465:2005 [20] applies the probabilistic method presented in the RILEM Report 14 (1996) to the Tutti's model of the deterioration of the reinforced concrete. Besides, it establishes the performance models for the initiation period under carbonation and chlorides and a model for the propagation period which permits to estimate the minimum deterministic propagation periods satisfying the serviceability limit state. Examples are presented for each exposure class, each values of the performance properties of these models, as function of the minimum covers for durability, the reliability classes of concrete structures and the design working life.

3.4 France In France the present standard on concrete specification, performance, production and conformity has been defined and discussed in French version of European standard NF EN 206-1:2004 [22] and the first edition of this standard was adopted by French standards institute - AFNOR in February 2002. The present second edition NF EN 206-1:2004 replaces the previously approved standards NF EN 206-1:2002 dated February 2002, NF P 18-010 dated December 1985 and experimental standard XF P 18-305 dated August 1996. The French standard NF EN 206-1:2004 exactly reproduces the European standard EN 206-1:2000 [1] with addition of National Annex (NA), which defines the clauses to be respected in France. The recommendations in French NA are included in the main text of EN 206-1:2000 [1] and the texts are differentiated by a double frame with a grey background. The amendments made to EN 206-1:2000 [1]

have been adapted by French standard as NF EN 206-1/A1:2005 [23] in April

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2005 and NF EN 206-1/A2:2005 [24] in October 2005. The amendments in NF EN 206-1/A1:2005 describe modifications of specifications relating to consistence classes, requirements for hardened concrete, concretes with specified properties, conformity control criteria and batching requirements. The amendments in NF EN 206-1/A2:2005 detail the requirements relating to exposure classes according to the actions due to concrete environment and consistence.

3.5 Spain In Spain the National Technical Specification: EHE-08 - Instructions for structural concrete defined the requirements for structural concrete. This specification was approved by the Spanish Government by the law 1247/2008 published on 18 July 2008. This technical specification contains the requirements concerning structural and fire safety and also the protection to environment conditions which must be fulfilled by new constructions and the maintenance of existent structures.

As it concerns the prescriptive requirements for protection to environmental conditions, several classes of exposure are defined adopting a slight different classification than that used in EN 206-1:2000 [1]. Mainly, three groups of classes are defined: for corrosion, chemical attack and erosion.

Currently, an initiative to prepare a national guideline to include the requirements and concepts contained in the European standards EN 206-1:2000 [1] and also the EN 1992-1-1:2004 [4] are being prepared in Spain.

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4 Comparison of the national requirements in complement to EN 206-1

This section presents a summary of the regulations, standards and other documents which form the basis of local practice developed to complement the EN 206-1:2000 [1] standard by the five countries involved in the DURATINET project with particular attention to the aspects more related with the concrete durability for the intended service life.

This comparison uses information given by the project partners and Technical Report prepared by the CEN/TC 104/SC1 [25], which has the main objective to provide a picture of how EN 206-1:2000 [1] is being applied in practice and to identify additional national requirements or needs for simplification.

4.1 National standards or regulations The countries have developed in complement to EN 206-1 [1] national standards or regulations which form the local practice and the national requirements and methodologies. Table 25 summarises the national documents in the five countries.

Table 25. National standards or regulations.

Country Location of national requirements France One standard National annex included in the NF EN 206 Ireland National Annex; published with IS EN 206-1 as a single document.

Portugal

The Portuguese requirements are in the National Annex to NP EN 206-1 and to NP EN 13670-1 and in the following National Civil Engineering Laboratory (LNEC) specifications, referenced in the NA of NP EN 206-1. LNEC E 461:2007: Methodology for avoiding internal expansive reactions LNEC E 464:2005: Prescriptive methodology for a 50 and 100 years design working life under the environmental exposures. LNEC E 465:2005: Methodology for estimating the concrete performance properties allowing to comply with the design working life of the reinforced or prestressed concrete structures under the environmental exposures XC and XS.

Spain Spain has not adopted yet EN 206-1 [1]

United Kingdom

BS 8500: Concrete - Complementary British Standard to BS EN 206-1 - Part 1: Method of specifying and guidance for the specifier. - Part 2: Specification for constituent materials and concrete.

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4.2 Exposure classes In the classification of exposure classes, the European countries have found the need to simplify the system and have grouped classes. The major reasons for grouping exposure classes are: to simplify the system for local needs, in some local environments two classes co-exist at same time; the concrete specification is the same for different classes and it is difficult for engineers to distinguish some classes for other. Table 26 presents the classes grouped in the countries. Some countries have not grouped the exposure classes, but have the same quality of concrete for several exposure classes. If they are following EN 1992-1-1:2004 [4], this may lead to different minimum cover depths to reinforcement.

Table 26. Grouped exposure classes in each country.

Country Grouped exposure classes

France (XC1, XC2)

(XC3 XC4, XD1, XF1) (XS1, XS2)

Ireland None Portugal (XS, XD)

United Kingdom

(XC3, XC4) In 2006 revision of BS 8500-1, the recommendations for resisting the XD and XS exposures are adequate for resisting the associated XC exposure

4.3 Methods for minimising risk of damage by AAR EN 206-1:2000 [1] leaves provisions to resist alkali-aggregate reaction (AAR) to national rules. Each country developed their own methods to avoid or minimise the damage by AAR. Table 27 summarises the national standard or specifications with the requirements to reduce the risk of AAR in concrete. Table 28 is a summary of the methods used to minimise the concrete damage by AAR and for classification of reactivity of aggregates. Table 29 lists the methods used in the different countries to evaluate the resistance of concrete to AAR.

Table 27. National recommendations and standards for reduce the risk of AAR.

Country Location of national requirements

France Guidelines: Recommendations for the prevention of damage by the alkali-aggregate reaction, LCPC, 1994.

Ireland Alkali-Silica Reaction in Concrete, published by The Institution of Engineers of Ireland and The Irish Concrete Society, 2003. (IEI/ICS ASR Report).

Portugal LNEC E 461:2004: Methodology for avoiding internal expansive reactions. United

Kingdom BS 8500-2 (see Table 1). More detailed guidance is provided in BRE Digest 330: Alkali-silica reaction in concrete.

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Table 28. Methods to minimise damage by AAR and classification of aggregates reactivity.

Country

Methods

Aggregates reactivity Use of type II additions

Maximum alkali

content

Performance method

France No

Yes; value depends upon cement type and aggregate reactivity.

Yes on the annex G of the French Guidelines.

Yes, FD P 18-542: (Criteria for the classification of aggregates) + XP P 18-594 (Performance tests, petrographic analysis, chemical tests).

Ireland Yes

Yes; value varies with aggregate reactivity.

Yes; Testing, History of use, for moisture control.

Yes; IEI/ICS ASR Report

Portugal

Yes, using silica fume, fly ash or slag in defined contents for reactive class II and III (LNEC E 461:2004).

Yes; value varies with aggregate reactivity.

Yes, in the Specification LNEC E 461, for reactive classes II and III.

Yes, given in LNEC E 461:2004: Methodology for avoiding internal expansive reactions.

United Kingdom

Yes for normal reactivity aggregates.

Yes for normal and high reactivity aggregates.

Yes for highly reactive aggregates.

Yes, given in BRE Digest 330: Alkali-silica reaction in concrete.

Table 29. Performance methods used to evaluate concrete resistance to AAR.

Country Performance method

France NF P 18-454: (Performance test on concrete) and NF P 18-456 (Criteria to assess the reactivity of the concrete tested in accordance with NF P 18-454).

Ireland Reference made to test methods described in IEI/ICS ASR Report. These may assist in making judgments but are not regarded as necessarily definitive.

Portugal ASTM C 1260-1 for evaluating the reactivity of aggregates class II or III or of a reactive mixture of aggregates and RILEM AAR-3 and AAR-4 for evaluating the reactivity of the aggregates or concrete composition.

United Kingdom

Uses BS 812-123 test and expansion at 2 years to determine the alkali content to give 0.08 % expansion. The limit for concrete using this aggregate is then set at 1.50 kg/m3 Na2O less than the determined alkali content. Described in Testing protocol for greywacke aggregates.

4.4 Limiting values for concrete mixes EN 206-1:2000 [1] recommends limiting values for CEM I concrete with each of the exposure classes, but in reality limiting values for durability are given in the national requirements. As an example, Fig. 6 and Fig. 7 show the national

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requirements/recommendations for maximum w/c ratio, minimum cement content and minimum compressive strength class in exposure classes XC4 and XS3 respectively in the four countries considered for the comparison for an intended working life of 50 years. The data show that there is no agreed relationship between compressive strength class, maximum w/c ratio and minimum cement content. In few cases for a given exposure class, the use of some blended cements is linked to a higher/lower cement content and a lower/higher water-cement ratio, as shown in Fig. 6 and Fig. 7.

Fig. 6. Comparison of National Provisions to EN 206-1 for the exposure Class XC4.

0

50

100

150

200

250

300

350

400

EN

20

6-1

FR IR PT

UK

Minimum cement content (kg/m3)

minmin

maxmax

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

EN

20

6-1

FR IR PT

UK

Maximum W/C ratio

min

min

maxmax

0

10

20

30

40

50

60

EN

20

6-1

FR IR PT

PT

UK

Minimum compressive strength class for cubes (MPa)

min

maxDurati

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Fig. 7. Comparison of National Provisions to EN 206-1 for the exposure Class XS3.

310

320

330

340

350

360

370

380

390

400

EN

20

6-1

FR IR PT

UK

Minimum cement content (kg/m3)

max max

min min

0

0,1

0,2

0,3

0,4

0,5

0,6

EN

206

-1 FR IR PT

UK

Maximum W/C ratio

min

min

max

max

0

10

20

30

40

50

60

70

EN

20

6-1

FR IR PT

UK

Minimum compressive strength class for cubes (MPa)

min

min

max

max

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5 Examples of projects with performance limits for concrete durability

This section will present examples of performance based specifications for concrete durability used on recent projects in the UK, Ireland, Portugal, France and in other European countries and in the world. The amount of literature in this area is relatively scarce, which further highlights the needs for research into this area.

Table 30 give examples of performance requirements for these projects including tunnels, viaducts, bridges and marine structures.

Projects such as the Oresund-link Tunnel between Denmark and Sweden (Fig. 8) have also specified the gas permeability, chloride diffusion coefficient and the electrical properties of the concrete as performance requirements. Also, the Confederation Bridge in Canada (Fig. 9) and the Rion-Antirion Bridge in Greece (Fig. 10) specified performance criteria for the concrete in terms of the electrical properties.

Fig. 8. Left: Oresund bridge. Right: Esquematic of the connection between Denmark and Sweden – Bridge and tunnel.

Fig. 9. Confederation Bridge in Canada.

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Fig. 10. Rion-Antirion Bridge in Greece.

Table 31 outlines the tests used to assess the performance and the limit values established for some of the projects listed in Table 30.

What has also been demonstrated by the examples of performance limits is the need for one test to assess if the concrete has satisfied the guidelines set. A RILEM committee TC 189 [26] has been set up to do just this with contributions by the various tests to assess their viability.

The RILEM Technical Committee TC 189 [26] reported a review of common tests that measured various concrete durability transport properties, namely gas and liquid permeability, capillary absorption of water and chloride ion ingress. Using a selection of frequently used methods for these properties suitable for laboratory and on-site testing, an evaluation of the suitability and range of applicability was made, along with proposing improvements and correlating the measured transport parameters for durability characteristics. The transport coefficients investigated are being used as criterion for concrete durability at an early age (during pre-testing of concrete mixes) and routine testing in production control, as well as on material coefficients for numerical modelling. The Cembureau method is used for measuring the gas permeability as it was found to be very reliable, easy to handle and produced good repeatability. The bore methods were found to frequently fail due to leakage. In terms of capillary absorption, the modified Fagerlund test was recommended as again it was found to be easy to conduct and the results showed very little scatter. However, despite the three tests used, a recommendation to measure the chloride ion diffusion could not be made.

In Ireland, examples of performance specifications are few but recent inclusion of ggbs in specifications by the National Roads Authority is considered as a step to improve the durability and the life expectancy of bridges. Performance criteria for a harbour project near Dublin are shown in Table 32, where, for the various cements types used, the ranges of acceptable diffusion rates are indicated. Other examples of this type of performance criteria are found in projects including bridges, marine projects, basement structures, multi-storey car-parks and water and wastewater plants.

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Table 30. Examples of engineering projects with performance based criteria for durability. [27]

Structure Channel

Tunnel (UK-France)

Vasco da Gama Bridge

(Fig. 11) (Portugal)

Medway Viaduct (Fig. 12)

(UK)

Millau Bridge (Fig. 13) (France)

Extension of

Condamine Port floating

dyke (France)

Construction Period

1987-1992 1995-1998 1998-2001 2002-2004 1999-2002

Specified service life

120 years 120 years 100 years 120 years 100 years

Concrete Type B45 & B55 B40, B45 and

B50 C40 to C60 B60 B54, B65

Type of Binder CEM I PM (additions permitted)

PM (seawater)

cement containing

FA

CEM I + slag or

CEM I + FA

CEM I 52.5 N PM ES CP2 – no additions

CEM I PM (seawater) + FA + SF

Max w/c ratio 0.32 0.33 to 0.42 0.45 – 0.50 Max. 0.45 Weff/c 0.335

0.35

Min. Cement (kg/m3)

400 for 425 requested

400 - 420 -

Min. Cement and additions

(kg/m3) - - 325 to 350 - 425

Aggregates NR NR - Class A, NR Class A, NR

Water porosity - - - 11-13 (piers) < 12 (B54) < 10 (B65)

Water Permeability

(m/s) < 10-13 - - - -

Gas Permeability

(m2) -

< 10-17 (at 28 days)

- <10-17

(at 90 days)

< 10-16 - 10-17 (28 days 80 ºC drying)

Apparent Chloride Diffusion

Coeff.(m2/s)

- < 10-12

(at 28 days) < 10-12

<10-12 (at 90 days)

< 5 x 10-12

(B54) < 1 x 10-12

(B65) Oxygen Diffusion

Coeff.(m2/s) - - < 5 x 10-8 - -

Quantity of electricity

(coulombs) -

< 1500 at 28 days

< 1000 at 90 days

- -

100-1000 (B65)

1000-2000 (B54)

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Fig. 11. Vasco da Gama bridge in Lisbon, Portugal.

Fig. 12. Medway Viaduct in UK.

Fig. 13. Millau Bridge in France.

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Table 31. Description of tests used to assess the performance and the limits of parameters measured. [27]

Project Property Specified durability

property Description of

tests Results

Channel Tunnel

Water permeability

(m/sec) < 10-13

Water permeability tests

measuring the depth of ingress of

water

0.6 – 0.7 x 10-13 m/s at 50 days

1.4 x 10-13 m/s at 8 months

Vasco da Gama Bridge

Gas Permeability

(m2)

< 10-17 at 28 days

Cembureau method

0.7 – 0.3 x 10-17 m2

between 28 and 90 days

≤ 0.01 x 10-17 m2

at 18 months

Vasco da Gama Bridge

Apparent Chloride Diffusion

Coeff. (m2/sec)

< 10-12 at 28 days

Migration test in non-steady state

conditions

1.0 – 4.0 x 10-12 m2/s

between 28 and 90 days

0.2 – 0.8 x 10-12 m2/s

at 18 months

Quantity of electricity

(coulombs)

<1500 at 28 days

< 1000 at 90 days

AASHTO test (ASTM Standard

C1202.

Extension of Condamine Port floating

dyke

Water porosity < 12 (B54) < 10 (B65)

Mercury Intrusion (water porosity). AFPC-AFREM

procedure (mercury porosity)

8.8 – 9.4

5.8 – 5.6

Gas Permeability

(m2)

< 10-16 - 10-17 (28 days 80 ºC

drying)

AFPC-AFREM Test procedure

5.54 x 10-19 – 1.25 x 10-18

Apparent Chloride Diffusion

Coeff.(m2/sec)

< 5 x 10-12 (B54) < 1 x 10-12 (B65)

Non-steady state (Tang Method)

Quantity of electricity

(coulombs)

100-1000 (B65) 1000 - 2000 (B54)

AASHTO test (ASTM Standard

C1202) 377 - 401

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Table 32. Specified diffusion limits for various concrete types in a harbour project in Ireland. Similar limits are used for other projects such as bridges, basements, car-parks and water and waste-water plants.

Cement Type Diffusion Coefficient (m2/s)

CEM I 7 - 18 x 10-12

CEM II/A 7 - 17 x 10-12

CEM II/B 5 - 10 x 10-12

CEM III/A 2 - 5 x 10-12

CEM III/B 0.9 - 3.5 x 10-12

In terms of the air and water permeability, the Autoclam apparatus (developed by Queen's University Belfast) provided a quick and simple non-destructive test that can be easily set-up on any concrete element on site where results can be obtained for each property after 15 minutes. They have shown to give good repeatability and the results had little scatter.

For chloride ion diffusion the PERMIT apparatus (developed by Queen's University Belfast) is a non-destructive test which is easily conducted on site with good repeatability. The comparative testing carried out by the RILEM Technical Committee TC 189 [26] was unable to recommend a suitable test to measure the chloride ion diffusion.

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6 Conclusions

This volume has presented a review of the new concrete code EN 206-1:2000 [1] along with a complementary specification to achieve these recommendations, namely BS 8500:2006 [11] [12] in the UK, Irish National annex to IS EN 206:2002 [16] in Ireland and the Portuguese national annex to NP EN 206-1:2005 [17] which include the three specification LNEC E461:2004 [18], LNEC E464:2005 [19] and E 465:2005 [20] in Portugal. These standards may prove easier for clients/specifiers to use than EN 206-1:2000 [1] and, particularly in the Irish code, give recommendations or ‘trade-offs’ between cover depth and cement quantities and the use of cement replacement products like ggbs and pfa.

It is now widely accepted that the concept of designing concrete based mainly on strength does not take into account the time-evolution of performance of the structure or the change in environmental/structural loading.

The durability of concrete structures depends on a combination of adequate design, materials selection and execution. The sensitivity of the design concept, the structural system, the shape of members and structural/architectural detailing are all significant design parameters. The compatibility of materials, the construction method, the quality of workmanship, levels of control and quality assurance are also significant parameters for achieving durability. Workmanship and maintenance strategies are also vitally important in achieving durable structures.

Actually the design, specification and execution of concrete structures are supported by the three main standards: EN 1992-1-1:2004 [4] for design of concrete structures, EN 206-1:2000 [1] specification, performance, production and conformity of concrete and EN 13670:2009 [5] for execution of concrete structures.

EN 206-1:2000 [1] was introduced as an attempt to quantify the durability requirements for concrete structures exposed to different environments. Service life of a concrete structure will depend mainly on the quality of concrete and the deterioration mechanisms that are associated with various exposure environments. The methodology followed in EN 206-1:2000 [1] classify the micro and macro environment surrounding a concrete structure into various exposure classes.

The EN 206-1:2000 [1] also indicates that concrete may be specified in terms of performance-related parameters such as the resistance to environmental actions, e.g. scaling of concrete in a freeze/thaw test.

Considering that the quality of concrete is a function of the concrete mix design e.g., material properties, placement and workmanship, one can start to understand the limitations of the “prescriptive” or “deemed to satisfy” approach which concentrates solely on the concrete mix design.

An improvement to the current practice would be to specify the expected performance further to the “prescriptive” requirements (hereafter termed as prescriptive specifications). However, specifying performance would require at the least a thorough understanding of the concrete behaviour in different environments and test methods to assess the performance.

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Through this approach, the recommendations in EN 206-1:2000 [1] will be met as they must satisfy the following requirements:

long-term experience of local materials and practices and on detailed knowledge of the local environment;

approved and proven tests that are representative of actual conditions and have approved performance criteria;

analytical models that have been calibrated against test data representative of actual conditions in practice. The concrete composition and the constituent materials should be closely defined to enable the level of performance to be maintained.

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7 References

[1] EN 206-1:2000/A2:2005, Concrete-Part 1: Specification performance, production and conformity.

[2] MACDONALD, S. The investigation and repair of historic concrete. [Parramatta, Australia]: NSW Heritage Office, 2003.

[3] FIB. Model code for service life design - Bulletin 34. Lausanne: FIB, 2006. ISBN 13: 978-2-88394-074-1.

[4] EN 1992-1-1:2004/AC:2010, Eurocode 2: Design of concrete structures-Part 1-1: General rules and rules for buildings.

[5] EN 13670:2009, Execution of concrete structures.

[6] EN 13369:2004/AC:2007, Common rules for precast concrete products.

[7] EN 197-1:2000, Cement - Part 1: Composition, specifications and conformity criteria for common cements.

[8] EN 1990:2002/A1:2005/AC: 2010, Eurocode - Basis of structural design.

[9] THE CONCRETE SOCIETY. Technical report 31: Permeability testing of site concrete - A review of methods and experience. London: Concrete Society, 1988.

[10] BS EN 206-1: 2000, Concrete. Specification, performance, production and conformity.

[11] BS 8500-1:2006, Concrete. Complementary British Standard to BS EN 206-1. Part 1- Method of specifying and guidance for the specifier.

[12] 8500-2:2006, Concrete. Complementary British Standard to BS EN 206-1. Part 2 - Specification for constituent materials and concrete.

[13] BS 8110-1:1997, Structural use of concrete. Code of practice for design and construction.

[14] BS 4027: 1996, Specification for sulfate-resisting Portland cement.

[15] IS 326-2-1: 1995, Concrete - part 2-1: guide to specifying concrete.

[16] IS EN 206-1: 2002: Concrete - Part 1: Specification, performance, production and conformity (Consisting of I.S. EN 206-1:2002 and the Irish National Annex).

[17] NP EN 206-1:2005/A1:2006, Concrete. Specification, performance, production and conformity (Portuguese National Annex).

[18] LNEC E 461:2004, Concrete. Methodologies for avoiding internal expansive reactions.

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[19] LNEC E 464:2005, Concrete. Prescriptive methodology for a design working life of 50 years and of 100 years under environmental actions.

[20] LNEC E 465:2005, Concrete. Methodology for estimating the concrete performance properties allowing to comply with the design working life of reinforced and prestressed concrete structures under the environmental exposure XC e XS.

[21] TUTTI, K. Corrosion of steel in concrete. Swedish cement and concrete. Stockholm: CBI, 1982.

[22] NF EN 206-1: 2004, Concrete. Part 1: Specification, performance, production and conformity (French National Annex).

[23] NF EN 206-1/A1:2005, Concrete. Part 1: Specification, performance, production and conformity, Amendment A1 (French National Annex).

[24] NF EN 206-1/A2:2005: Concrete. Part 1: Specification, performance, production and conformity, Amendment A2 (French National Annex).

[25] CEN. Technical Report. Survey of national requirements used in conjunction with EN 206-1:2000. 2007.

[26] TORRENT, R. and F. LUCO, eds. Report of RILEM Technical Committee TC-189-NEC: Non-Destructive evaluation of the penetrability and thickness of cover concrete. RILEM Report 40.

[27] BAROGHEL-BOUNY, V. et al. Concrete design for a given structure service life – durability management with regards to reinforcement corrosion and alkali–silica reaction. State-of-the-art and guide for the implementation of a predictive performance approach based upon durability indicators. Scientific and technical documents of AFGC. Paris: AFGC, issue in French 2004 and issue in English 2007.

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