15 september 2009 - university of colorado...

15 September 2009

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Specialist Engineering, Materialsand Environmental Consultants

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MANAGEMENT OF AARAFFECTED STRUCTURES :

ANALYSIS, PERFORMANCE ANDPREDICTION

Coyne and Bellier, Paris,Tuesday 15 September 2009

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WHAT IS AAR ?

Dr Ian SimsDirector, RSK STATS Limited, UK

www.stats.co.uk

Dr Ian SimsDr Ian SimsDirector, RSK STATS Limited, UK

www.stats.co.uk

A member of the RSK Group plcA member of the RSK Group plc4


Val de laMare Dam,Jersey

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What is AAR?What is RILEM?AAR and its controlling factorsDiagnosis & prognosisPrevention & testingRILEM guidance & application to dams

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RILEM TC 219-ACSAlkali-Aggregate Reactions inConcrete andStructures

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RILEM

Founded in 1947 and based in ParisAcronym of French wordsThe International Union of Testing andResearch Laboratories for Materials andStructuresTechnical CommitteesMaterials and StructuresReports

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RILEM & AARTC 106TC 106 - 1988 to 2000Accelerated for AAR potential of aggregatesTC 191-ARPTC 191-ARP - 2000 to 2006Added diagnosis & specificationTC 219-ACSTC 219-ACS - started work in 2006Added performance testing, appraisal &modellingChairman: Dr Philip Nixon

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RILEM & AARTC 106TC 106 - 1988 to 2000Accelerated for AAR potential of aggregatesTC 191-ARPTC 191-ARP - 2000 to 2006Added diagnosis & specificationTC 219-ACSTC 219-ACS - started work in 2006Added performance testing, appraisal &modellingChairman: Dr Philip Nixon

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RILEM TC 191-ARP & TC 219-ACSTC 191-ARP: … to develop integratedassessment, specification & diagnosisprocedures for AAR ...Built on the earlier work of RILEM TC 106International Specification requested 20001st draft at 12th ICAAR in Beijing in 2004TC 191-ARP Completed work in 2006Further development by current TC 219-ACS2nd draft at 13th ICAAR in Trondheim 2008

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Why International Specification?Globalisation - engineers work internationallyGrowth of regional/international StandardsPrinciples of AAR are well established andapply globally without deference to politicalboundariesIncreasing plethora of incompatible testsComplexity of different approachesRILEM proposals accepted by ICAARs

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Alkali-Aggregate Reactivity

Alkali-Silica Reactivity - ASRcommonest, worldwide examplesAlkali-Silicate Reactivityvariety of ASR, described in CanadaAlkali-Carbonate Reactivity - ACRrare, examples in Canada & ChinaCombined ASR & ACR possible‘ACR’ might not exist!

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Alkali-Silica Reactivity

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Alkali-Silica ReactionA simplification - in concrete:Potentially reactive silica in aggregate+ Alkali hydroxides from cement= Alkali-silica gel+ Further water absorbed by the gel= Swelling, expansion & damage

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ASR with Greywacke

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ASR with Greywacke

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ASR needs all the following:Sufficient alkalis:mainly from the cementCritical amount of reactive aggregate:might be small % of total - ‘pessimum’Sufficient moisture:includes all external & >75% RH

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Other FactorsDamaging ASR also needs:

Calcium hydroxide:low-calcium gel is less- or non-expansiveSwelling type of gel product:lithium can modify the gel characteristicsLimited facility for gel accommodation:porous concrete or aggregate less affectedEffects of temperature - internal & externalEffects of scale and long service life?

Damaging ASR also needs:Calcium hydroxide:low-calcium gel is less- or non-expansiveSwelling type of gel product:lithium can modify the gel characteristicsLimited facility for gel accommodation:porous concrete or aggregate less affectedEffects of temperature - internal & externalEffects of scale and long service life?

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Reassurance & Risks

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Reassurance & RisksCracking is superficialCracking is superficial

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Reaction and Cracking

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Reaction and Cracking

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Reassurance & RisksCracking is superficialPerformance less impaired than appearsCracking is superficialPerformance less impaired than appears

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Restraint of Expansion

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Reassurance & RisksCracking is superficialPerformance less impaired than appearsCracking is superficialPerformance less impaired than appears

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Minimising the risk of ASR in new work:Concrete Society TR30 (latest 1999)& BRE Digest 330Eliminate one or more of the 3 factors:- Limit alkali content - preferred in UK- Use non- or less reactive aggregate- Exclude moisture

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UK Specification - Digest 330

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UK Specification - CS TR30

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InternationalRILEM: tests, diagnosis, specificationICOLD: updating bulletinNational guidanceHow special are dams?

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Diagnosis & PrognosisNot appraisal of affected structuresSite inspection + petrography & analysisAAR usually identifiableNot necessarily expansive!Other causes of damage less obvious?Combinations of causes?Testing or monitoring for prognosis

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Site AssessmentDamage or deteriorationDamage or deterioration

ASR in theBritishIsles

Val de laMare Dam,Jersey

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Site Assessment

Displacement

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Site AssessmentDamage or deteriorationDamage or deterioration

Maentwrog Dam - ASR caused by greywacke42


Site AssessmentDamage or deterioration & gel depositsDamage or deterioration & gel deposits

MaentwrogDam -

long-termASR and

watermigration

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Site AssessmentDamage or deterioration & no gel depositsDamage or deterioration & no gel deposits

Bridge in New Brunswick, Canada - argillite aggregate44


Concrete PetrographySampling

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Concrete Petrography

Sampling

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Concrete PetrographyTechniquesTechniques

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Gathering the evidence -thin-section microscopy

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Concrete PetrographyDamage or deteriorationDamage or deterioration

Reaction site under microscope in thin-section52


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Gel deposits - infilling void54



Gel deposits - in peripheral crack

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Concrete PetrographyA directobservationtechnique!

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Gel detected using uranyl acetate

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Alkali-Reactivity - CarbonatesCarbonate aggregatesAlkali-carbonate reaction – ACRCanada & especially now ChinaACR usually occurs much sooner than ASRBoth ACR & ASR in same material?ASR masquerading as ACR in some cases?RILEM developed assessment methodsDoes ACR really exist?

Carbonate aggregatesAlkali-carbonate reaction – ACRCanada & especially now ChinaACR usually occurs much sooner than ASRBoth ACR & ASR in same material?ASR masquerading as ACR in some cases?RILEM developed assessment methodsDoes ACR really exist?

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Pavement in Cornwall, Ontario, Canada60



Reactive Carbonate Texture

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Non-expansive ACR, Libya62


Diagnosis - Caution!Do not jump to conclusionsNot all concrete expansion is AARDelayed ettringite formation (DEF)?Combinations of evidenceOther sulfate reactionsOther causes of cracking & damage

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Delayed Ettringite Formation

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Case Study

Concrete silos in Saudi ArabiaCracking and detachment of coverAlleged ‘alkali-carbonate reaction’Actually thermal crackingNon-expansive carbonate reactionImportance of careful investigation

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PrognosisIf AAR has been establishedWill reaction continue & damage get worse?Monitoring?Modelling increasingly practicableDirect testing of concrete samples?Indicative - but caution required!

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BCA Core Test Arrangement

Demec gauge measuringstuds

End point measuringstuds on adhesive

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Core Test Results

Demec Studs

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 50 100 150 200 250 300 350 400

Elapsed time (Days)

Expa

nsio

n (M

icro

stra

in) C1

C3C4C6C9C11C12C14

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ASR needs all the following:Sufficient alkalis:mainly from the cementCritical amount of reactive aggregate:might be small % of total - ‘pessimum’Sufficient moisture:includes all external & >75% RH

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RILEM ProceduresAAR-0 : the key - outline & criteriaAAR-1 : petrographical examinationAAR-2 : accelerated mortar-bar testAAR-3 : 38oC concrete prism testAAR-4.1 : 60oC accelerated concrete prismAAR-5 : carbonate aggregate assessmentAAR-6.1 : diagnosis & prognosisAAR-7.1 & 7.2 : specifications - ASR & ACRAAR-8 : releasable alkalis

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RILEM International SpecificationAAR-7.1 – Alkali-silica reactions(ASR)Principles: Damaging ASR needs simultaneous occurrence of:

A sufficiently alkaline pore solutionA critical amount of reactive silicaA sufficient supply of water

Specification based on ensuring absence of at least oneAllow for interactions other environmental actions:

Freezing/thawingDe-icing saltsMarine atmosphere

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AAR-7.2 - Carbonate aggregatesGenerally not susceptible to AAR but

vulnerable in some circumstances:Contains finely divided SiO2

ASR and AAR-7.1 measures appropriate.Dolomitic carbonate rocks.

Mechanism still controversialOptions for control are limitedPrimarily identification & avoidance ofpotentially susceptible aggregatesPerhaps use of very high levels of ggbs?

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AAR-7 International SpecificationOverall Structure:

Two basic stages:Determine necessary Level of PrecautionIdentify any preventative or PrecautionaryMeasures appropriate to that Level ofPrecaution

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Determining the Level ofPrecaution

The level of precaution will depend on:

The consequences of damage- structural needs and service life

The likelihood of damage - the environment to which the concrete isexposed

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S1Low risk

N on-load-bearing e lem ents inside bu ild ings Tem porary or short life structures Sm all num bers of easily rep laceable elem ents M ost low rise dom estic structures

S2N orm al risk

M ost build ings and civ il eng ineering structures P recast elem ents w here costs o f replacem ent h igh

S3H igh risk

Long service life or h igh ly critica l structures w here deteriora tionunacceptab le e.g.

N uclear insta lla tions D am s Tunnels Exceptionally im portant bridges and viaducts S tructures retaining hazardous m aterials C ritica l elem ents very d ifficult to inspect or repa ir S tructures where loss of function is unacceptab le

Categorisation of structural risk

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S1Low risk

N on-load-bearing e lem ents inside bu ild ings Tem porary or short life structures Sm all num bers of easily rep laceable elem ents M ost low rise dom estic structures

S2N orm al risk

M ost build ings and civ il eng ineering structures P recast elem ents w here costs o f replacem ent h igh

S3H igh risk

Long service life or h igh ly critica l structures w here deteriora tionunacceptab le e.g.

N uclear insta lla tions D am s Tunnels Exceptionally im portant bridges and viaducts S tructures retaining hazardous m aterials C ritica l elem ents very d ifficult to inspect or repa ir S tructures w here loss of function is unacceptable

Categorisation of structural risk

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Likelihood of damage:Characterising the Environment

Three levels of environmental categorisation are proposed:E1 protected from external moistureE2 exposed to external moistureE3 exposed to external moisture and additionally to

aggravating factorse.g. freezing /thawing, de-icing salts, marine environment,prolonged elevated temperatures

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Level of Precaution

Structural and environmental categories are combined to givethree levels of precaution:

P1: No special precautions against ASRP2: Normal level of precaution against ASRP3: Special level of precautionP4: Extraordinary level of precaution

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Level of PrecautionEnvironment E1 E2 E3

Structural risk

S1 P1 P1 P1

S2 P1 P2 P3

S3 P2* P4 P4

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Structural risk

S1 P1 P1 P1

S2 P1 P2 P3

S3 P2* P4 P4

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Structural risk

S1 P1 P1 P1

S2 P1 P2 P3

S3 P2* P4 P4

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Structural risk

S1 P1 P1 P1

S2 P1 P2 P3

S3 P2* P4 P4

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Structural risk

S1 P1 P1 P1

S2 P1 P2 P3

S3 P2* P4 P4

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Level of PrecautionStructural and environmental categories are

combined to give three levels of precaution:


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Level of PrecautionStructural and environmental categories are

combined to give three levels of precaution:


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Precautionary MeasuresP1 – No special precautionsP2 – Normal level of precaution:One of 4 Precautionary Measures:M1, M2, M3, M4

P3 - Special level of precaution:P2 + design to resist aggravating factors

P4 – Extraordinary level of precautionCombined application of two or more measures

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Precautionary MeasuresP1 – No special precautionsP2 – Normal level of precaution:One of 4 Precautionary Measures:M1, M2, M3, M4



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Precautionary Measures

M1 - Controlling alkali contentM2 - Non-reactive aggregate combinationM3 - Preventing moisture accessM4 - Ensuring non-expansive gel

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Precautionary Measure M1Controlling the alkali content of the concrete- cement & other constituents- thesholds vary with aggregate reactivity- low, medium (>4.0kg/m3) or high(<4.0kg/m3)Use of low alkali cementInclusion of sufficient gbfs, fly ash (pfa),silica fume, metakaolin or other pozzolana

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Precautionary MeasuresCan they work with dams?


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M1 - Controlling alkali contentM2 - Non-reactive aggregate combinationM3 - Preventing moisture accessM4 - Ensuring non-expansive gelM2 & M3 might be impracticable

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M1 - Controlling alkali contentM2 - Non-reactive aggregate combinationM3 - Preventing moisture accessM4 - Ensuring non-expansive gelM4 might be too expensive, even if thelithium dosage can be determined

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Precautionary Measures - Problem?P1 – No special precautionsP2 – Normal level of precaution:One of 4 Precautionary Measures:M1, M2, M3, M4



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Precautionary MeasuresProposed Solutions


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Precautionary Measure M1Controlling the alkali content of the concrete- cement type & contentUse of low alkali cementInclusion of sufficient gbfs, fly ash (pfa),silica fume, metakaolin or other pozzolana

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Precautionary Measure M1Controlling the alkali content of theconcrete- cement type & contentUse of low alkali cementInclusion of sufficient gbfs, fly ash (pfa),silica fume, metakaolin or other pozzolanaTwo separate M1 items for P4 level?

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Precautionary Measure M1Controlling the alkali content of theconcrete- cement type & contentUse of low alkali cementInclusion of sufficient gbfs, fly ash (pfa),silica fume, metakaolin or other pozzolanaTwo separate M1 items for P4 level?Plus design issues - fibre reinforcement?

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AAR-7.2 - Carbonate Aggregates

Key issue – identifying potentiallysusceptible aggregates

History of use is good guide whereapplicable

If no local knowledge RILEM methods canbe used

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Identifying potentially deleteriouscarbonate rocksPetrographical examination (AAR-1).If possible carbonate reactivity (impureand/or dolomitic limestone:Use RILEM AAR-5 procedure:(rapid preliminary screening test forcarbonate aggregates): combined AAR-2 &new AAR-5AAR-5 is similar to AAR-2 but uses 4/8mminstead of 0/2mm aggregate grading

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Possible outcomes of AAR-2/AAR-5AAR-2 > criteria in AAR-0AAR-5 < AAR-2 by at least 0.01%- potential for ASR reaction: apply Part 1 measures

AAR-2 > criteria in AAR-0AAR-5 > AAR-2- potential for carbonate reaction: apply MC1 or MC2

AAR-2 < criteria in AAR-0AAR-5 < AAR-2 by at least 0.01%- no special precautions

AAR-2 < criteria in AAR-0AAR-5 > AAR-2- potential for carbonate reaction: apply MC1 or MC2

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Precautionary Measures forPotentially Reactive CarbonateRocksTentative RILEM suggestionsMC1: Identification & rejection of susceptibleaggregateMC2: Use of very high replacement levels ofblastfurnace slag in cementPerformance testing needed for MC2

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Performance TestingParticular objective of RILEM TC 219-ACSProbably based upon AAR-4.1 (AAR-4.2)60oC accelerated concrete prism testApplicable to actual or proposed concretemixesApplicable on a project-specific basisValidating method against field performance

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Prevention SummaryAAR-7.1 & 7.2 proposed by RILEMLevel of Precaution - structure & environmentPrecautionary Measures for each LevelDams likely to be P4P4 needs 2 Measures + any further protectionSpecial proposals included for damsTentative guidance for reactive carbonateAAR-4.2 performance test being developed

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RILEM methods overall guideAAR-0

Integrated assessment procedureDraft published in Materials & Structures, August-September

2003

Under continual review -TC now prepared updated version,

including annex for assessing carbonate aggregates

To be published in Materials & Structuresor as part of a RILEM Report

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Petrographic methodPublished in Materials & Structures,

August-September 2003

Possibly to be re-published as part of a RILEM Report

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Opal Vein in Limestone

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Gel-Pat Testing for Opal

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Strained Quartz

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Reactive Carbonate Texture

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Aggregate Assessment to AAR-1

Interpretation & classification:

- unlikely to be alkali-reactive - Class I

- potentially alkali-reactive - Class II sub-divided for silica, carbonate or silica & carbonate

- very likely to be alkali-reactive - Class III

Pictorial atlas in preparation

Interpretation & classification:

- unlikely to be alkali-reactive - Class I

- potentially alkali-reactive - Class II sub-divided for silica, carbonate or silica & carbonate

- very likely to be alkali-reactive - Class III

Pictorial atlas in preparation

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Accelerated mortar bar test - AMBTDraft published as TC 106-2 in Materials and Structures, June

2000

TC completed a revised edition,based largely on PARTNER recommendations

To be published in Materials & Structures,or as part of a RILEM Report

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Inter-laboratory trial ofaccelerated mortar bar test (AAR-2)

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IND

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Aggregate combinations from 10 countries

Exp

ansi

on (%

) @ 1

4 da

ys ExpansiveAnomalous (possibly a porous flint content)Non-expansive

Expansive

Non expansive

Potentially expansive

Field experience:

--Tentative criteria

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38°C Concrete prism test - CPTDraft Published as TC 106-3 in Materials and Structures, June

2000

TC completed a revised edition,based largely on PARTNER recommendations


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Inter-laboratory trial of 38°Cconcrete prism test method (AAR-3)

Figure 2: Concrete prim test trials

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I 3B B3 B4 B2 B1

ZA 1 IS1

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Aggregate combinations from 10 countries(B suffix indicates enhanced alkali content in test)

Exp

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yea

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Expansive

Anomalous (aggregate type needs enhanced alkali content in test)

Non-expansive

Expansive

Non expansive

Possibly expansive

--Tentative criteria

Field experience:

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60°C Accelerated concrete prism testInternational trial completed

TC currently finalising AAR-4.1(accelerated aggregate test)


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Inter-laboratory trial of 60°C accelerated concrete prism test (AAR-4.1)

Expansion after 20 weeks

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Expa

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Non-reactive aggregate Reactive aggregate

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Expansion after 20 weeks

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Participant

Expa

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R1Non- reactive

R2Ref. reactive

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Tentative Recommended Criteria:

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Combination non-reactive: 0.03% or lessCombination non-reactive: 0.03% or less

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Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%

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Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%Initial decision no sooner than 15 weeks

Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%Initial decision no sooner than 15 weeks

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Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%Initial decision no sooner than 15 weeksFinal decision usually at 20 weeks

Combination non-reactive: 0.03% or lessCriterion might be relaxed to 0.04%Initial decision no sooner than 15 weeksFinal decision usually at 20 weeks

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Rapid Preliminary Screening Testfor Carbonate Aggregates

Draft Published in Materials and Structures, October 2005

Comparison:AAR-2 (0/2mm favouring ASR) &AAR-5 (4/8mm favouring ACR)

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Aggregate test - releasable alkalis

Draft procedure under review by TCbased on extraction using alkaline solutions

International trial being arranged

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AAR-0Integrated Aggregate Assessment

Phase 1 - Initial characterisation andclassification using AAR-1Phase 2 - Rapid screening tests using AAR-2and AAR-5Phase 3 - Concrete expansion tests usingAAR-3 and/or AAR-4.1

Phase 1 - Initial characterisation andclassification using AAR-1Phase 2 - Rapid screening tests using AAR-2and AAR-5Phase 3 - Concrete expansion tests usingAAR-3 and/or AAR-4.1

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AAR-1 Petrographical Examination Carried Out?

Yes No

Class I Class II or III

No further action required

Silica IIS (IIIS) Silica & Carbonate IISC (IIISC) Carbonate IIC (IIIC)

Rapid Screening Test? Rapid Screening Test?

YesYes No

Both AAR-2 and AAR-5 Concrete Microbar Test

AAR-2 Ultra-accelerated Mortar Bar Test

Non-reactive

Reactive or Potentially Reactive

Non-reactive


AAR-4 Ultra-accelerated (60ºC) Concrete Prism Test

Either And/or

ASR and/or Carbonate Reactivity

ASR only

Petr og raph y R

apid Sc reeni ng Te stsC

o ncret e E xpa ns ion Te sting

No

AAR-3 Conventional (38ºC) Concrete Prism Test 152




Yes No




Rapid Screening Test? Rapid Screening Test?

YesYes No



Non-reactive


Non-reactive



Either And/or


ASR only

Pet rog ra phy Rap id Scr ee nin g T es ts

Co ncre te Ex pan sio n Tes tin g

No

AAR-3 Conventional (38ºC) Concrete Prism Test

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Yes No




Rapid Screening Test ? Rapid Screening Test ?

YesYes No



Non-reactive


Non-reactive



Either And/or


ASR only

Petro graphy R ap id Scre eni ng T es ts

Con cre te E xpansi on T estin g

No

AAR-3 Conventional (38ºC) Concrete Prism Test154


Resumé - What is AAR?What is RILEM?AAR and its controlling factorsDiagnosis & prognosisPrevention & testingRILEM guidance & application to dams

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Key IssuesRILEM TCs seeking international solutionsImproved understanding of ASR & factorsACR might not exist as a separate reactionGood petrography central to diagnosisRILEM TCs developed agreed proceduresSeparate specifications for ASR & ACRTentative added proposals for dams

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The EndThe End

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Thank you for your attention

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Materials Consultancy

RSK STATS Limited18 Frogmore Road, Hemel Hempstead,Hertfordshire, HP3 9RT, United Kingdom

Tel: +44 (0)1442 416674Fax: +44 (0)1442 437550Contact: Dr Ian Sims

e-mail: [email protected]

RSK STATS Limited18 Frogmore Road, Hemel Hempstead,Hertfordshire, HP3 9RT, United Kingdom

Tel: +44 (0)1442 416674Fax: +44 (0)1442 437550Contact: Dr Ian Sims

e-mail: [email protected]

15 september 2009 - university of colorado...

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