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Advancing Concrete for Bridges andAdvancing Concrete for Bridges and Infrastructure:Petrography (TR71) and other testing methods

7 July 2011

7 July 20111 Petrography (TR71) and other testing methods - Jeremy Ingham

AgendaAgenda

• What is petrography?p g p y

• What’s involved – the techniques of petrography?q p g p y

• What can and can’t be achieved by petrography?What can and can t be achieved by petrography?

• Key publicationsKey publications


What is Petrography?What is Petrography?

• from the Greek petra meaning rock and• from the Greek petra meaning rock and graphus meaning writing or record

l i l t h i d ti b k 150• geological technique dating back 150 years• 40 year history of industrial concrete

petrography


The Role of Petrography in Assessment ofConcrete Bridges

• New construction – may be required in case of cube strength non-compliance or if concrete quality is in doubtq y

• Existing structures – can be useful as part of condition survey inspections e.g. to Design Manual for Roads and Bridges to Design Manual for Roads and Bridges BD 63/07 ‘Inspection of Highway Structures’ and BA 35/90 ‘Inspection

d R i f C t Hi h and Repair of Concrete Highway Structures’

• Used in Principal Inspections (every 6 p p ( yyears) and Special Inspections (as required)


Standards and Competencies for Concrete Petrography

• Concrete petrography is unlike most laboratory tests as it requires particularly highly qualified operators and expensive microscopical equipmentp q p

• The Applied Petrography Group of the Geological Society maintains a list of competent petrographic test houses –www appliedpetrographygroup comwww.appliedpetrographygroup.com

• Currently no BS or EN Standard• ASTM C856 ‘Standard Practice for the Petrographic Examination g p

of Hardened Concrete’ – long standing and widely accepted• APG SR2 – The Applied Petrography Group has a code of practice

for the petrographic examination of concretefor the petrographic examination of concrete


AgendaAgenda






What’s Involved – the techniques of qPetrography?• Inspection design considerations• Inspection design considerations• Sampling• Specimen preparation• Visual examination & low power microscopyy• Polarised light (high power) microscopy• Fluorescent light microscopy• Fluorescent light microscopy• Scanning electron microscopy


Inspection Design ConsiderationsInspection Design Considerations

• Involve the petrographer in the inspection design, to ensure correct sample number/type scheduled to achieve the investigation objective

• Plan a ceiling budget based on likely number of samples for visual g g y pexamination (typically £50-80 per sample) and microscopical examination (typically £200-300 per sample), and then add a contingency sum

• Allow sufficient turnaround time for petrography in the inspection programme (typically 3 weeks)programme (typically 3 weeks)

• Review the petrography test programme and budget with the petrographer once the samples have been obtained petrographer once the samples have been obtained


SamplingSampling

• Petrography requires intact concrete samples – ideally 70-100mm diameter core samples, depth at least 150mm or to centre of element

• Cores should be double wrapped and labelled at siteM st al a s consider the str ct ral • Must always consider the structural impact of core sampling and avoid cutting reinforcement


Specimen PreparationSpecimen Preparation

• Thin sections • Finely ground slices• Highly polished specimens


Visual Examination & Low Power MicroscopyVisual Examination & Low Power Microscopy

• Examination of sample ‘as-received’• Unaided eye• Low power binocular microscope (up to x100)


Polarised Light (High Power) MicroscopyPolarised Light (High Power) Microscopy

• Polarised light examination of thin sections (up to x600)


Fluorescent Light MicroscopyFluorescent Light Microscopy

• Concrete impregnated with resin containing fluorescent dye• Microscopical examination in UV light• Highlights porosity & cracks


Scanning Electron MicroscopyScanning Electron Microscopy

• Electron images of highly polished specimens

• Micro-chemical analysis using X-ray microanalysis system


AgendaAgenda






What can and can’t be achieved by yPetrography?• Concrete Composition & Quality• Concrete Composition & Quality• Concrete Condition


Concrete Composition: AggregateConcrete Composition: Aggregate

• Aggregate type• Aggregate grading• Distribution (check for segregation)

U di i bl tit t• Undisirable constituents• ASR potential classification


Concrete Composition: Cement TypeConcrete Composition: Cement Type

• The main phases within Portland cements are readily observed through the microscope

• Confident determination of cement type - OPC/SRPC/White• Definitive identification of high alumina cement concrete • Definitive identification of high-alumina cement concrete

(HACC)


Concrete Composition: Mineral AdditionsConcrete Composition: Mineral Additions

• Presence of pfa or ggbsp gg• Quantity of pfa or ggbs• Difficult to detect Microsilica

and Metakaolin


Concrete Composition: Chemical AdmixturesConcrete Composition: Chemical Admixtures

• Can’t see plasticisers etc using microscopes• Effects of admixtures are sometimes seen through microscope (e.g.

entrained air voids)• Infrared spectroscopy can be used to determine admixtures typep py yp• Difficult to quantify admixtures even by infrared spectroscopy


Concrete Composition: Cement ContentConcrete Composition: Cement Content

• Mix proportions determined by point counting concrete slices• Point counting offers comparable/improved accuracy over

BS1881:Part 124 chemical analysis method


Concrete Composition: Water/Cement RatioConcrete Composition: Water/Cement Ratio

• Can be determined by fluorescence microscopy• Image analysis software has been developed• Argueably more accurate than physico-chemical method in

BS 1881: Part 124BS 1881: Part 124


Concrete Composition: Air VoidsConcrete Composition: Air Voids

• Visual examination for entrapped air voidspp• Manual bubble counting for detailed analysis (BS EN

480-11 or ASTM C457)• Automated option - ‘Rapidair’ machine


Concrete Composition: StrengthConcrete Composition: Strength

• Concrete composition data gained from petrography can be used to estimate strength using Feret’s formula

• Core strength tests more accurate than petrographic strength estimate

• Petrography often used to determine cause of low strength following cube strength failures in new build


What can and can’t be achieved by yPetrography?• Concrete Composition & Quality• Concrete Composition & Quality• Concrete Condition


Concrete Condition: CarbonationConcrete Condition: Carbonation

• Phenolphthalein indicator solution can underestimate carbonation depth

• Petrography is the definitive • Petrography is the definitive method for carbonation depth determination


Concrete Condition: Chloride Ion IngressConcrete Condition: Chloride Ion Ingress

• Chloride content requires chemical analysis to BS q y1881: Pt 124

• Corrosion features (cracks, rust deposits) can be examined


Concrete Condition: CrackingConcrete Condition: Cracking

• Determining the cause of cracking by observation of crack morphology, understanding concrete composition and by eliminating possible causes


Concrete Condition: WeatheringConcrete Condition: Weathering

• Leaching actionsLeaching actions• Frost attack

S lt t lli ti• Salt crystallization


Concrete Condition: Sulfate AttackConcrete Condition: Sulfate Attack

• Sulfate from the groundwater causes formation of expansive ettringite with associated weakening

• Petrography definitive diagnostic tool for sulfate attack• Sulfate content requires chemical analysis to BS 1881: Pt124• Sulfate content requires chemical analysis to BS 1881: Pt124


Concrete Condition: Thaumasite Form of Sulfate Attack (TSA)

• Confident diagnosis of TSA• Determining the depth of damage


Concrete Condition: Delayed Ettringite FormationConcrete Condition: Delayed Ettringite Formation

• Delayed Ettringite Formation (DEF) – expansive reaction where concrete curing temperature exceeds 65°C

• Crack patterns often mistaken for ASR• Has characteristic microscopical featuresp


Concrete Condition: Alkali-Aggregate ReactionsConcrete Condition: Alkali Aggregate Reactions

• Definitive diagnosis of alkali-silica i (ASR) b di reaction (ASR) by direct

observation of reactions sites and gel deposits

• Alkali content measurement requires chemical analysis to BS 1881: Pt124


Concrete Condition: Multiple Deleterious Reactions• Evidence for several different deterioration mechanisms my be found

together making diagnosis difficult.• ASR/DEF combination relatively common, also TSA, leaching,

seawater attack and acid attack have all been found in co-existence with ASR

• Petrography is crucial to understanding relative significance of the various mechanisms


Concrete Condition: Fire Damage AssessmentConcrete Condition: Fire Damage Assessment

• Petrography provides the most accurate fire damage depth (300°C thermal contour)


Concrete Condition: Assessment of RepairsConcrete Condition: Assessment of Repairs

• Assessing the quality of concrete repairsg q y p• Determining the causes of repair failure


AgendaAgenda






Key PublicationsKey Publications

Concrete Society – www.concrete.org.uk

TR71 – Concrete Petrography: Ani t d t id f thintroductory guide for thenon-specialist

TR32 – Analysis ofHardened ConcreteHardened Concrete


Key PublicationsKey Publications

St John, Poole & Sims -Concrete Petrography:A handbook of Investigative Techniques

Ingham –Geomaterials Under the Microscope


Thank youThank you

Q ti ?Questions?


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