8. corrosion assessment

www.utm.my innovative ● entrepreneurial ● global 1

MAB 1033

Structural Assessment and Repair

Professor Dr. Mohammad bin Ismail

8. Corrosion Assessment


Learning Outcome

At the end of the course students should be able

to understand:

• important to carry proper inspection on

reinforced concrete structure


References

1. Testing of Concrete in Structures, 4th. edition,

J.H Bungey, S.G. Millard & M.G. Grantham, Taylor & Francis, 2006


GUIDANCE FROM STANDARDS, ETC

● BS

● ASTM

● ISO

● FIP

● RILEM

● ACI

● etc


TEST METHOD AVAILABLE

Property under

investigation

Test Equipment Type

Corrosion of

reinforcement

Half-cell, resistivity, LPR,

cover depth, carbonation,

chloride concentration

Concrete quality,

durability and

deterioration

Surface hardness, UPV,

Permeability, absorption,

petrographic, sulphate,

expansion, cement

type/content, abrasion

Concrete strength Core, pull-out, pull-off,

penetration resistance

Integrity and

performance

Reinforcement location,

strain or crack

measurement, load test

Table: Principal test method


TEST PROGRAMME PLANNING

● Consider most appropriate test

● Extent or number of test

● Test location

– General sequential approach: a properly structured programme is essential, with interpretation as an ongoing activity, whatever the cause or nature of an investigation


Stages of test programme


Typical stages of test programme

● STAGE 1: (Planning)

establish aims and information required→documentation survey→preliminary site visit→agree interpretation criteria→systematic visual inspection, initial test selection & costing


Typical stages of test programme (cont.)

● STAGE 2: Non-destructive testing

comparative survey→calibrated assessment→

● STAGE 3: Further Testing

localised investigation (cores, break-out, etc)→load testing

www.utm.my innovative ● entrepreneurial ● global 11MAB 1033 Structural Assessment and

Repair11


DOCUMENTATION AND STANDARDS


Reasons for Structural Testing

● To determine strength.

● To carry out a comparative quality survey – condition survey.

● To examine localised integrity.

● To assess potential durability.

● To identify causes & extent of deterioration

Deterioration Factors.doc


Repair14

● Large structures have a routine schedule every structure is inspected every 5 to 12 years– Proper follow-up can be taken before damage is too

large

– Change ownership

– Insurance companies

– Structures damage due to accident

● Damage due to corrosion of reinforcement– Preliminary survey

– Detailed survey


Basis of Structural Investigation

● Quality control procedure.

● Assessing non-compliance of specimens.

● Uncertainties in quality of workmanship.

● Monitoring strength development.

● Assessing load carrying capacity for upgrading or change of loading.

● Suspected or observed deterioration or distress.

● Regular maintenance inspection.

● Determining cause of failure or defects.


Scope of Assessment *

● Strength Assessment – assessment of concrete strength;

● Durability Assessment – identifying nature & extent of observed or suspected deterioration including reinforcement corrosion;

● Integrity Assessment – determination of localised integrity or generalised assessment of behaviour of whole structure.

www.utm.my innovative ● entrepreneurial ● global 17MAB 1033 17

Classification of Cracks

www.utm.my innovative ● entrepreneurial ● global 18MAB 1033 18

Classification of Cracks


Repair19


Some typical type of cracksa. Corrosion of rebarb. plastic shrinkagec. sulphate attackd. alkali /aggregate reaction

Visual inspection not confined to the surface, also include examination of bearing, expansion joints, drainage channels, post-tensioning ducts and etc.


ASR

Shrinkage

Crazing

Corrosion

Freeze & Thaw

Thermal


Repair22MRR2 2004


Repair23


Repair24


Repair25


Repair26

Example of integrated methodology of inspection for assessing corrosion of reinforcement

Preliminary analysis of the

structure (type, history,

environmental data)

For planning subsequent

inspection and interpretation of

measurement

Visual inspection

For confining areas where

corrosion is likely (honeycombs,

voids, etc.) and where corrosion

is already evident (cracking

spalling, delamination)

Identification of

corroding area

Potential mapping

For confining areas where

corrosion cannot be observed

from the surface of concrete


Repair27

Polarization resistance or concrete

resistivity measurement (areas

with low potential)

Potential mapping

For evaluating the

corrosion rate in the areas

where it is more likely

Chemical analyses of concrete

(carbonation, chloride penetration)

For evaluating the causes

of corrosion and the rate

of penetration of the

depassivating front

Inspection of rebars (visual or by

means of other methods) in the

areas of corrosion

For evaluating the damage

already occurred to the

reinforcement

Evaluation

of residual

life of the

structure


Repair28

VISUAL INSPECTION


VISUAL Inspection

● Visual Inspection

– 1st. Step in any investigation

– Special attention given to presence of cracks, concrete spalling, wet areas, signs of water run-off or rust staining

– Crack

– Corrosion of reinforcement – rust staining, cracking parallel to reinforcement and spalling parts of the cover

● Results and its interpretation confirmed by testing

– Cover measurement is good to start with


– provide valuable information. – Visual features may be related to workmanship,

structural serviceability and material deterioration. Able to differentiate between various types of cracking. * segregation/ bleeding – concrete mix* honeycombing – low standard of construction workmanship* deflection/ flexural cracking – lack of structural adequacy* material deterioration – surface cracking and spalling* reinforcement corrosion – inadequate cover, high chloride concentration

Visual Inspection:


Repair31

Equipment

● Main equipment – human eye and brain, aided with a note book, pro forma, camera, binoculars and computer

● It is normal to record date, time and weather conditions when doing the survey, also noting visual observations such as water or salt run down and damp areas


Repair32

Limitations

Main limitation is the skill of the operative. Some defects can be mistaken for others

When corrosion is suspected, it must be understood that rust staining can come from iron bearing aggregates rather than from corroding reinforcement

Different types of cracking can be attributed to different causes

Visual surveys must be followed up by testing to confirm the source and cause of deterioration


Repair33

COVER Measurement

● New Structures

– Adequate cover as specified or identify area of future corrosion risk

● Old Structures

– When corrosion is observed. Low cover allow corrosion agents (chloride and carbonation) and fuels (moisture and oxygen) access.


Repair34


Repair35

Property measured

● A cover survey requires the location of the rebars to be measured in three dimensions

● If construction drawings are not available then it may be necessary to measure the rebar diameter as well as its location


Repair36

Equipment

● Magnetic covermeter –logging capabilities and digital output

● Deep cover and closed spaced rebar affected the readings

● Standard: BS 1881, Part 204


Repair37


Cover Thickness


Important ! Cover Thickness


Repair40

Limitations

● Main problems– Congestion of rebar giving misleading

information

– Iron bearing aggregates – influence magnetic field

– Different steels have different magnetic properties

– Always excavate and expose one or more bars for calibration


Repair41

Electrochemical Technique


Repair42

Types of information obtainable from different electrochemical technique

Corrosion

Penetration

DepthPotential

Mapping and

MacroCells

Linear

Polarization

and

concrete

Resistivity.

Initiation Propagation

Time

Service Life of the Structure.


Repair43

Half Cell Potential Measurement

The term anode and cathode come from electrochemistry which is the study of the chemistry of electrical cells. The cell is composed of two half cells, copper in copper sulphate and zinc in zinc sulphate. In each half cell the metal is dissolving and ions are precipitating

M Mn+ + ne-

Copper is more resistant to this reaction than zinc so when we connect the two solutions by a semi-permeable membrane and connect the two metals with a wire, zinc goes into solution, and the copper sulphate solution plates out (is deposited) on the copper electrode

The voltage of any half cell can be recorded against a standard hydrogen electrode (half cell). Table below gives the standard half cell potentials that are of interest to us as we evaluate corrosion problem. Half cell potentials are a function of concentration as well as the metal and the solution.


Repair44

A current will flow in a cell made up of a single metal in two different concentrations of the same solution. We can consider the corrosion of steel in concrete as a concentration cell. We can measure the corrosion risk in that cell by introducing an external half cell.

By placing a half cell on the concrete surface and connecting it via a volt meter to the steel, we have a similar circuit to our Daniel cell

The electrical potential difference will be a function of the iron in its pore water environment. If we move the cell along the steel we will see different potentials because the iron is in different environments


MAB 1033 Structural Assessment and Repair

45

Half cells potentials

Zn Zn2+ + 2e-

Fe Fe2+ + 2e-

Cu Cu2+ + 2e-

-0.76 V

-0.44 V

+0.34 V

Potential mapping is widely recognised and standardised non- destructive

method for assessing the corrosion state of rebars in concrete structures

Potential mapping provided very useful ND means to locate areas of

corrosion for monitoring and condition assessment as well as in determining the

effectiveness of repair work


Repair46

● By convention connect the +ve terminal of the voltmeter to the steel and the –ve terminal to the half cell

● Very –ve potentials can be found in saturated condition where there is no oxygen to form passive layer

● This the weakness of potential measurement. They measure the thermodynamics of the corrosion, not the rate of corrosion

● Half cell potential measurement gives an indication of the corrosion risk of the steel linked by comparisons to the probability of corrosion


Repair47

Schematic representation of the measurement of potential of steel reinforcement


Repair48

Equipment

● Standard half cell with Silver/silver chloride or mercury/mercury oxide electrode are recommended. In laboratory saturated calomel electrode usually used

● Copper/copper sulphate electrode are also used

● It is important to record the equipment used because different half cell have different offsets


Repair49

● A high impedance digital voltmeter is used to collect the data

● Other options are to use a logging voltmeter or logger attached to voltmeter


Repair50

Procedure

1. Decide on area of measurement

2. Use cover meter to locate the steel and bar spacing

3. Make electrical connection to the steel

4. Check the steel is electrically continuous

5. Mark out a grid, typically 0.2-0.5 m2

6. Check and calibrate the half cell and voltmeter

7. Wet the whole area to ensure good electrical contact

8. Take and record the reading

9. Examine for anomalies, check for most –ve for sign or causes of corrosion


Repair51

Examples of Half Cell Potential maps


Repair52

Interpretation

● In atmospherically expose reinforced concrete the potential of passive steel is between +50 and –200mV vs CSE

● The best way to interpret data is to expose areas of rebar which show the most –ve, intermediate and least –ve to correlate corrosion condition reading

ASTM C876-91

Measured Potential E

(mV vs CSE)

Probability of Corrosion

E > -200

-200 > E > -350

E < -350

< 10% - low

Intermediate

> 90% - High risk


Repair53

Correlation between potential and state of corrosion of reinforcement


Repair54

Resistivity Measurement

● Electrical resistivity have a bearing on the corrosion rate of the concrete as an ionic current must pass from the anodes to the cathodes for corrosion to occur

● Four-probe (Wenner) resistivity meter frequently used for measurement of concrete resistivity

● Current is applied between two outer probes and potential difference measured across the two inner probes

● For a semi-infinite, homogeneous materials the resistivity is = 2aV/I


Repair55

● Resistivity is an indication of the amount of moisture in the pores, and size and tortuosity of the pore system

● Resistivity is strongly affected by concrete quality (cement content, w/c ratio, curing and additives used


Repair56

Wenner Technique to determine electrical resistivity


Repair57

Wenner Technique to determine electrical resistivity


Repair58

Equipment

● Four probe system needs a probe spacing larger than the maximum aggregate size to avoid mesuring the resistivity of the aggregate

● If it is not possible to avoid the influence of reinforcing steel then readings should be taken at right angles to the steel rather than along the length of it to avoid short circuit


Repair59

Minimising the effect of the steel on four-probe resistivity measurement


Repair60

Interpretation (resistivity)

Concrete Resistivity (k.cm) Corrosion Rate

>20 k cm

10 – 20

5 – 10

< 5 k cm

Low corrosion rate

Low to moderate

High corrosion rate

Very high corrosion rate


Repair61

Chloride Determination


Repair62


Repair63

Chloride Determination

● Chloride can be present as cast-in chlorides or transported into concrete from the environment.

● Once chloride ions reached the steel surface the passive layer is progressively destroyed and corrosion commences.

● Therefore chloride depth profile should be determined.

● Chlorides are usually measured by dissolving powder samples in acid


Repair64

0

1

2

3

4

5

1 2 3 4 5 6

5

10

15

16 24 36 48

% CaCl2 by weight of cement Age (hours)

Tim

e A

fter

Mix

ing (

hours

)

Com

pre

ssiv

e S

trength

(M

pa)

(a

)

(b)

8

Typical effects of calcium chloride admixture on (a) setting times, and (b) early strength of

concrete.

2% CaCl2

Control

Final Set

Initial Set


Repair65

● The samples are taken from drillings or from crushed cores

● It is preferable to collect a series of drillings at different depths so that a chloride profile can be produced. Alternatively

● A core can be cut into slices and the slices crushed

● Chloride testing will show

– Whether chlorides concentration high enough to cause corrosion

– Whether chlorides were cast in or diffused in later


Repair66

● Chloride contents can be measured in laboratory as well as in the field

● In the laboratory

– Powdered samples are usually digested in acid and then titrated to find the in the conventional wet chemicalmethod

● In the field

– Quantab strips: modest accuray

– specific ion electrode: highly accurate

● Any field technique should be checked against laboratory analysis of duplicate samples


Repair67

● The results of the above methods are referred to as the total or acid soluble chloride contents

● There are also methods for measuring the free chloride or water soluble chlorides (AASHTO T260)

– This refer to the fact that it is the chloride dissolved in the pore water that contributes to the corrosion process


Repair68

Property to be Measured

● The most accurate and reproducible tests are the acid soluble chloride tests that effectively measure total chlorides.

● Pore water extraction and water soluble chloride measurements are less reproducible and less accurate

● The chloride threshold values are based on total chloride levels


Repair69

Equipment

● The collection of chloride samples should be done incrementally from the surface either by taking drillings or secions from cores

● Measurements of chloride content are made at suitable increments, typically 2 to 5 mm

● For improved statistical accuracy when taking drillings, multiple adjacent drilling are made and the depth increments from each drilling are mixed

● Sample sizes required for analysis vary from 10-50g


Repair70

● Several ways of measuring the chlorides

– Field measurement of acid soluble chloride• chloride specific ion electrode (Herald et al., 1992)

• Conventional titration (BS 1881, Part 124)

• Potentiometric titration method

–

– Water soluble chloride – ASTM D1411, 1982, and AASHTO T260, 1984

●


Repair71

Interpretation

● There is a well known “chloride threshold” for corrosion given in terms of the chloride/hydroxyl ratio

● when the chloride concentration exceeds 0.6 of the hydroxyl concentration passive layer will break down

● This approximates to a concentration of 0.2-0.4% chloride by weight of cement or 0.05% chloride by weight of concrete


Repair72

Carbonation

● The term carbonation refers to the penetration of atmospheric carbon dioxide into the concrete matrix.

● Since dissolution of carbon dioxide in water give rise to a weak (carbonic) acid, continuous diffusion of this gas into the concrete will result in the progressive neutralization and subsequent acidification of the pore water.

● Other acidic gases such as sulphur dioxide would produce similar effect in locations where the discharge of industrial gases into the air is allowable practice.


Repair73

Equipment

● Carbonation of concrete is associated with loss of alkalinity of the pore solution

● Carbonation depth is easily measured by exposing freshconcrete and spraying it with phenolphthalein– This can be done either by breaking away a fresh surface or by

coring and splitting the core in the laboratory

– A phenolphthalein will remain colourless where concrete is carbonated and will turn pink where concrete is still alkaline

● The best indicator solution for maximum contrast of the pink colouration is a solution of phenolphthalein in alcohol and water, usually 1g indicator in 100 ml of alcohol/water (50:50) mix or more alcohol to water


Repair74

Limitations

● Phenolphthalein changes colour at pH 9

● The passive layer breaks down at pH 10-11

● Some aggregates can confuse phenolphthalein readings. Some concrete mixes are dark in colour and seeing the colour change can be difficult

● Carbonation by ground water does not always produce the clear carbonation front induced by atmospheric CO2 ingress


Repair75

www.utm.my innovative ● entrepreneurial ● global 76MAB 1033 Structural Assessment

and Repair

76

Petrographic Test

● To determine content and types in concrete mix, microstructure, quality, durability and degradation

● Visual


Flood


Tall Building


Flood


Tsunami


Water Leakage


Corrosion of

reinforcement


Earthquake – Collapse Flyover


Safety


Vice-Chancellor Zaini [email protected]://www.utm.my/vc

ADVANTAGE WORKING WITH UTM

www.utm.my innovative ● entrepreneurial ● global 87Pengelih Johor Sept 2012

Knowledge acquired shared with students, particularly

Malaysian (JKR staff included)

Enhance lecturer experience


Repair88

Good experienced team (friendly Lecturers)


Good experienced team (and Technicians)


Reliable equipments

www.utm.my innovative ● entrepreneurial ● global 9191Full Scale Testing

Good

laboratories

facilities


Negotiable costs

www.utm.my innovative ● entrepreneurial ● global 94Stadium Larkin 2010

Stadium larkin, 2010


Tg. Pengelih, 2012


Stesyen KeretapiTanjung pagar,

Singapura


Majlis Perbandaran Melaka

www.utm.my innovative ● entrepreneurial ● global 100Majlis Perbandaran Melaka


ACPI, Gelang patah , Johor

www.utm.my innovative ● entrepreneurial ● global 102102MPJBT, Skudai, Johor


Rumah

kedai,

Senai,

Johor


Maktab Perguruan, Sabah


Rebranding Key Amal Indicators (KAI)

Tangible KAIs● Publications● Research● PG programs● Education ● Intellectual property● RU-compliance etc

Intangible KAIs● Teamwork, ukhuwah● Knowledge culture● Integrity, passion● Entrepreneurship● Taqwa, amal soleh etc

World classuniversity

CultureBarakahSynergy

Jannah


mutiara hadith

Daripada Abu Musa r.a., meriwayatkan bahawa baginda Rasulullah s.a.w. bersabda: Perumpamaan ilmu dan hidayah yang dengannya aku diutus oleh Allah SWT adalahseumpama satu hujan lebat yang menimpa bumi. (Bumi terbahagi kepada tiga tanah) ● Pertama ialah tanah baik, lembut dan menyerap air yang kerananya tanah menjadi subur,

menumbuhkan tumbuh-tumbuhan yang banyak. ● Kedua ialah tanah yang keras tidak menyerap air tetapi dapat mengumpulkan air bagi

keperluan manusia, binatang ternak dan tanam-tanaman yang lain. ● Ketiga ialah tanah yang keras yang tidak menyerap dan tidak dapat mengumpulkan air dan

tidak menumbuhkan tanam-tanaman. (Begitulah dengan manusia yang terbahagi kepada tiga golongan):● Mereka yang diberi faham agama dan mendapat hidayah. Dengan hidayah itu mereka

mengenaliku, mendapat manfaat dengan ilmu yang diberikan Allah SWT kepadaku. Mereka belajar dan mengajarkan kepada orang lain.

● (Golongan kedua) ialah yang tidak mengambil manfaat bagi dirinya tetapi orang lain dapatmanfaat darinya.

● (Golongan ketiga) ialah orang yang tidak peduli dirinya dan tidak mendapat hidayah Allah SWT apa yang diturunkan melalui aku.

(Hadis Riwayat Bukhari).


SUMMARY

● Don’t keep quiet (diam)

● Good Manners

● Follow Schedule of work

● Time management

● Do not avoid Meeting

● Follow development


The only way you do great work is to love what you do!

Stay hungry!Stay foolish!

Steve Jobs (2005)

8. corrosion assessment

Documents