8. Corrosion Assessment
Transcript of 8. Corrosion Assessment
www.utm.my innovative ● entrepreneurial ● global 1
MAB 1033
Structural Assessment and Repair
Professor Dr. Mohammad bin Ismail
8. Corrosion Assessment
www.utm.my innovative ● entrepreneurial ● global 2
Learning Outcome
At the end of the course students should be able
to understand:
• important to carry proper inspection on
reinforced concrete structure
www.utm.my innovative ● entrepreneurial ● global 3
References
1. Testing of Concrete in Structures, 4th. edition,
J.H Bungey, S.G. Millard & M.G. Grantham, Taylor & Francis, 2006
www.utm.my innovative ● entrepreneurial ● global 5
GUIDANCE FROM STANDARDS, ETC
● BS
● ASTM
● ISO
● FIP
● RILEM
● ACI
● etc
www.utm.my innovative ● entrepreneurial ● global 6
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
www.utm.my innovative ● entrepreneurial ● global 7
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
www.utm.my innovative ● entrepreneurial ● global 9
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
www.utm.my innovative ● entrepreneurial ● global 10
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 1313
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
www.utm.my innovative ● entrepreneurial ● global 14MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 1515
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.
www.utm.my innovative ● entrepreneurial ● global 1616
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 20
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.
www.utm.my innovative ● entrepreneurial ● global 21
ASR
Shrinkage
Crazing
Corrosion
Freeze & Thaw
Thermal
www.utm.my innovative ● entrepreneurial ● global 22MAB 1033 Structural Assessment and
Repair22MRR2 2004
www.utm.my innovative ● entrepreneurial ● global 26MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 27MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 28MAB 1033 Structural Assessment and
Repair28
VISUAL INSPECTION
www.utm.my innovative ● entrepreneurial ● global 2929
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
www.utm.my innovative ● entrepreneurial ● global 30
– 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:
www.utm.my innovative ● entrepreneurial ● global 31MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 32MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 33MAB 1033 Structural Assessment and
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.
www.utm.my innovative ● entrepreneurial ● global 35MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 36MAB 1033 Structural Assessment and
Repair36
Equipment
● Magnetic covermeter –logging capabilities and digital output
● Deep cover and closed spaced rebar affected the readings
● Standard: BS 1881, Part 204
www.utm.my innovative ● entrepreneurial ● global 40MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 41MAB 1033 Structural Assessment and
Repair41
Electrochemical Technique
www.utm.my innovative ● entrepreneurial ● global 42MAB 1033 Structural Assessment and
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.
www.utm.my innovative ● entrepreneurial ● global 43MAB 1033 Structural Assessment and
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.
www.utm.my innovative ● entrepreneurial ● global 44MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 45
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
www.utm.my innovative ● entrepreneurial ● global 46MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 47MAB 1033 Structural Assessment and
Repair47
Schematic representation of the measurement of potential of steel reinforcement
www.utm.my innovative ● entrepreneurial ● global 48MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 49MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 50MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 51MAB 1033 Structural Assessment and
Repair51
Examples of Half Cell Potential maps
www.utm.my innovative ● entrepreneurial ● global 52MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 53MAB 1033 Structural Assessment and
Repair53
Correlation between potential and state of corrosion of reinforcement
www.utm.my innovative ● entrepreneurial ● global 54MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 55MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 56MAB 1033 Structural Assessment and
Repair56
Wenner Technique to determine electrical resistivity
www.utm.my innovative ● entrepreneurial ● global 57MAB 1033 Structural Assessment and
Repair57
Wenner Technique to determine electrical resistivity
www.utm.my innovative ● entrepreneurial ● global 58MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 59MAB 1033 Structural Assessment and
Repair59
Minimising the effect of the steel on four-probe resistivity measurement
www.utm.my innovative ● entrepreneurial ● global 60MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 61MAB 1033 Structural Assessment and
Repair61
Chloride Determination
www.utm.my innovative ● entrepreneurial ● global 63MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 64MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 65MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 66MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 67MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 68MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 69MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 70MAB 1033 Structural Assessment and
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
●
www.utm.my innovative ● entrepreneurial ● global 71MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 72MAB 1033 Structural Assessment and
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.
www.utm.my innovative ● entrepreneurial ● global 73MAB 1033 Structural Assessment and
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
www.utm.my innovative ● entrepreneurial ● global 74MAB 1033 Structural Assessment and
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
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
www.utm.my innovative ● entrepreneurial ● global 86
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
www.utm.my innovative ● entrepreneurial ● global 88MAB 1033 Structural Assessment and
Repair88
Good experienced team (friendly Lecturers)
www.utm.my innovative ● entrepreneurial ● global 9191Full Scale Testing
Good
laboratories
facilities
www.utm.my innovative ● entrepreneurial ● global 105
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
www.utm.my innovative ● entrepreneurial ● global 106
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).
www.utm.my innovative ● entrepreneurial ● global 107
SUMMARY
● Don’t keep quiet (diam)
● Good Manners
● Follow Schedule of work
● Time management
● Do not avoid Meeting
● Follow development