identifying and managing deterioration of concrete structures in
TRANSCRIPT
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Identifying and Managing Deterioration of Concrete Structures in the UKProfessor Peter RoberyTechnical Director for Asset Management and Engineering
In situ monitoring and assessment of concrete structures
A ‘UK‐China Science Bridge’ event
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Today
• Concrete is a sophisticated construction product
• No longer the standard 1 : 2 : 4 of the 1960s
• Key properties can be modified to suit requirements:
• Workability options, ranging from sprayed high-build concrete, to self-compacting concrete that flows “like water”,
• Resistance to explosive spalling, for improved fire resistance, particularly in tunnels,
• Ultra-high strength and high elastic modulus concrete, necessary for our tallest towers,
• Enhanced durability concrete, enabling lasting structures to be designed for exposure in the most hostile of environments.
• But old concrete was not that bad…
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Historic Concrete Structures
Some recent ones not so well…
1897
1933
Some older concrete buildings have lasted well
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Historic Concrete Structures
Some older concrete structures have lasted well in seawater:
1944
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Historic Concrete Structures
Some older concrete structures have lasted well in seawater:
19/6/2010
Some recent ones not so well…
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Historic Concrete Structures
Some 1960s bridges have lasted well:
• Byker Viaduct
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Historic Concrete Structures
Some 1960s bridges have lasted well:
19/6/2010
Some recent ones not so well…
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• Beetham Tower
• Landmark £150 million development in Manchester city centre
• At 171m tall, it is the tallest building in Manchester, has the UK's highest living space and is the tallest concrete tower in the UK
• Includes a five star, 285 bedroom Hotel from levels 5-23, a 'destination sky bar' on the 24th floor and apartments up to floor 50.
• At floor 24 the building dramatically juts out 4m from the floors below with a cantilever
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• Beetham Tower
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• Docklands Light Railway
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• Burj Dubai +800m
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• self-compacting concrete in the foundation pile cap, protected against corrosion by Cathodic Protection, and 100MPa compressive strength, 48GPa modulus structural concrete for the tower
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Celebrating Concrete Excellence
• Constructing the 21st Century
• Quality construction, with hundreds of trained “former fishermen” for labour
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What’s the next frontier…?
• Hong Kong to Macau…?
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• Sustainability means re-using assets:
• Marine Crescent in Folkestone
• Early unreinforced concrete building built in 1870
• Following renovation, is set to celebrate its 200th anniversary!
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• Marine Crescent measures up to 2007:
• Acoustic performance of 57dB between partition walls, attained naturally by the concrete mass
• Lower energy bills, through the Victorian concrete's thermal capacity, keeping apartments cool in summer and warm in winter
• The conversion of concrete basements into one-bed apartments gives optimum land-use
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• Sustainability means re-using assets:
• Park Hill, Sheffield
• First post-war slum clearance scheme of an entire community in Britain, built between 1957 and 1961
• 1998 Park Hill was listed as Grade II*
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• March 2006 Urban Splash submitted outline planning permission for:
• New doctor’s surgery and nursery facilities
• Retail and leisure facilities
• High quality public and private spaces
• Around 580 flats for sale on the open market
• Flats for rent and low cost home ownership
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• Sustainability means re-using assets:
• Trebor Mint Building, Katherine Road, London
• Architects converted London's disused Trebor factory into 65 live/work units
• The 1930s factory's concrete structure was in good condition and was adapted to support two extra floors of a lighter weight, set back from the parapet
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Concrete Re-born
• Sustainability means re-using assets:
• Hoover Building (West London)
• Built 1932
• ‘30s Art Deco style (for Hoover vacuum cleaners)
• Ceased trading in 1982 & left derelict
• Significant carbonation & spalling
• Refurbished by realkalisation
• Surface protection system
• Re-opened as a supermarket
• Thank you Tesco!
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deteriorating Concrete
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Failing Concrete
• Repairs fail again
• Why did the concrete fail in the first place?
• How durable is reinforced concrete?
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Failing Concrete – history’s lesson
• Weavers Mill
• Built in 1897
• Earliest example of Hennebique ferro-concrete framed building
• Virtually no carbonation (in the 1970s)
• High cement content (500kg/m3)
• High quality construction
• Demolished (for a supermarket)
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Carbonating environment
• Importance of cover
• Effect of age (cover and carbonation)
• 1950-70s = slender structures, therefore low cover
• Designed for low strength, with low resistance to carbonation
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
TimeT0 T1 T3protective
system failuree.g. water-proof
membrane, joint, etc.
chlorideingress
activecorrosion
T2arrival of
chloride ions at bar & onset of
corrosion
Cor
rosi
on
onset ofdelamination
structureunsafe
failurecorrosion &
delamination
NOW
T3
Deterioration Modelling
• Age
• Cover
• Carbonation
• Chloride ingress
• Onset of corrosion
• Propagation:
• Non-linear
• Model future chloride ingress
• Consider changes to environment
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling
• Age
• Cover
• Carbonation
• Chloride ingress
• Onset of corrosion
• Propagation:
• Non-linear
• Model future chloride ingress
• Consider changes to environment
Cl %
by
wei
ght o
f cem
ent
ConcreteQualityHighMedLow
Corrosion Risk
DRY<50% RH
high resistivitylow risk
DAMP85% RH
alternate wet/dryhigh risk
SATURATED100% RH
lack of oxygenlow risk
Ris
k of
Cor
rosi
on
Carbonated
Uncarbonated
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
05
1015202530354045
0 20 40 60 80
50%95%
Carbonation Modelling
Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Carbonation survey:• measure depth of carbonation• assess design parameter• predict future carbonation rates
19/6/20100
10
20
30
40
50
60
tcDX ..2=
?
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Carbonation Modelling
0
10
20
30
40
50
0 20 40 60 80Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Depth of Cover
0%1020304050607080901
010
2030
4050
Rate of carbonation Dc:• cement content, cement type, w/c ratio (strength grade)• compaction, curing• humidity, wet/dry cycles, [CO2]
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01
02
03
04
05
06
0
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling - Activation
0
10
20
30
40
50
0 20 40 60 80Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Depth of Cover
0%1020304050607080901
010
2030
4050
60
3% active at 10 years30% active at 20 years
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling - Corrosion
0
10
20
30
40
50
0 20 40 60 80Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Depth of Cover
0%1020304050607080901
010
2030
4050
60
0% corroding at 10 years3% corroding at 20 years30% corroding at 30 years
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Carbonating environment
• We know why concrete carbonates
• Design for durability, not for strength
• Check the materials are of the intended quality
• Educate the workforce not to cut corners
• Use appropriate site supervision of works
• Accept that reinforced concrete may need surface protection
• Cement is inherently a highly durable material, its steel that is the problem !
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Failing Concrete – history’s lesson
• Phoenix Units (in seawater since 1944)
• 150 structures, 61m long, 18m wide, 18m tall
• Towed to Normandy Beach
• 1980s testing - hardly any damage:
• Coarse-ground cement (600-700kg/m3)
• Impervious matrix
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride environment
• Importance of cement content and type:
• Sulfate resisting (low C3A) vs chloride resisting (high C3A)
• Cement replacements (Fly ash, GGBS, SF)
• Importance of cover:
• Concrete-in-the-Oceans project
• Traditional cover depths are an ineffective barrier
• High cover depths increase cracking and breach protection
• Importance of absorption:
• Chloride ingress models absorption, permeability and diffusion
• Does “Fick’s 2nd Law” have any relevance at all?
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride ion ingress
• Chloride ingress prediction
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
−=
teffsnx
DxerfCC
.21
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride ion ingress
• Chloride ingress prediction
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
−=
teffsnx
DxerfCC
.21 ?
Absorption
Surface levelIncreasing with time
Pressure
Diffusion
Cracks
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride ion ingress
• Chloride ingress prediction – do we know enough to predict performance
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
19/6/2010
15 year survey
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride ion ingress
• Chloride ingress prediction – do we know enough to predict performance
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
19/6/2010
30 years?
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Today, have we got it right ?
• BS EN 206 Exposure classes (plus BS8500 for UK).
• In BS 5328, simple system using relative terms, e.g. mild, moderate etc.
• Exposure classification in BS EN 206-1 is based upon deterioration process, e.g. corrosion due to carbonation
• X0: No risk of corrosion or attack
• XC: Corrosion induced by carbonation
• XD: Corrosion induced by chlorides other than from sea water
• XS: Corrosion induced by chlorides from sea water
• XF: Freeze-thaw attack
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Today, have we got it right ?
• EN 206 Exposure classes
• Scope covers:
• normal ranges of exposure
• normal service lives (50 years, 100 years)
• Excludes:
• “hostile” exposure
• Extra protection may be needed
• Routine Maintenance still needed
• Major repairs should not be required
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Today, have we got it right ?
19/6/2010
• Traditional codified approach:– Table of cover depths linked to exposure definitions– Little recognition of modern concrete technology– Based on temperate / northern climates– “Deemed-to-satisfy” philosophy, little scientific basis– Assumes consistent good quality workmanship– Inadequate for long lives or severe exposure
• Durability modelling approach:– Inputs include:
• Exposure severity• Climatic conditions• Concrete mix parameters• Extra protection options
– Outputs include:• Extent (%) of corrosion
vs age (years)
Durability Design
Extreme Environment
Poor Workmanship
CODES
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Today, have we got it right ?
• We need to assess the severity of the chloride environment:
• bridge decks, car parks, coastal structures
• We know concrete isn’t maintenance free
• understand the mechanisms & how to repair the damage
• Need higher cementitious contents, low water contents, special chloride-resisting concrete
• Cement replacement materials (GGBS/PFA/SF)
• Waterproofing additives
• Sometimes the concrete needs extra help:
• Cathodic protection, applied at construction (cathodic prevention)
• Surface protection systems
• Corrosion inhibitors
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Looking after Older Assets
Asset Management
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Managing Assets
Asset Creation
• planning, designing and supervising the construction of new infrastructure, e.g.
• Highways, bridges, tunnels, drainage
• Rail and airports
• Water and sewage networks
• Coastal developments
• Ports, harbours, marinas
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Managing Assets
Asset Management
• planning, engineering and performing the operation of infrastructure
• Highways, bridges, tunnels, drainage
• Rail and airports
• Water and sewage networks
• Coastal developments
• Ports, harbours, marinas
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Why Asset Management ?
• Increasing worldwide focus on effective operation and maintenance of existing infrastructure
• Driven by:
• Greater user demand
• Overstretched budgets
• Ongoing deterioration of assets
• Greater accountability on investment decisions
• Increasing public expectations
• Availability of new technology
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What is Asset Management ?
Regulated Industries embrace Asset Management:
• Water, Rail, Power
Public Sector obliged to use Asset Management:
• UK Government Driver – Whole of Government Accounts:
• Value all Government Assets
• Predict future costs necessary to maintain value
Unregulated private sector:
• Resistance to spend money on “maintenance”
• UK driver – corporate governance
Gives demonstrable Return on Investment
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What is Asset Management ?
BSI’s PAS 55 defines Asset Management as:
“A framework and support tools to facilitate systematic, consistent, and evidence-based decision-making for the
management, operation, preservation and enhancement of physical asset portfolios, providing the required level of
service most cost-effectively”
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What is Asset Management ?
Or in plain English…
Asset management is about a public entity or private business knowing:
• what assets it owns• how it expects its assets to perform• what condition its assets are in• how its assets should best be looked after• when assets need to be repaired or replaced• what assets will cost over their planned life• what may need to be done differently in the future to manage
its assets better• how all of this will impact on the most cost effective provision
of service to its customers
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What is Asset Management ?
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Life-Cycle Cost Modelling
• Life-cycle cost modelling
• Data collection
• Database
• Financial modelling
• Benefits
– Manipulate data
– Run scenarios to create and then justify budgets
– Scalable
– Large capacity
– Very consistent
– Adaptable
– Data sources
– Common platform for all experts to add value
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Occurs because of:
• Poor Buildability
• Poor Selection of Materials
• Poor Workmanship
• Knowledge Gap (outside the scope of Codes)
• Changes in properties of materials
• Addition of deleterious materials
• Deleterious reactions
• Environmental aggressiveness
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Common Causes of DeteriorationDefects in Concrete Reinforcement Corrosion
Mechanical
Chemical
Physical
Carbonation
Stray currents
CorrosiveContaminants
•Abrasion•Impact•Overload•Movement (e.g. settlement)•Explosion•Vibration
•Alkali-aggregate reaction•Aggressive agents (e.g.:
sulfates, salts, soft water)•Biological action
•Freeze / thaw•Thermal effects•Salt crystallization•Shrinkage•Erosion•Wear
•Cement content & type•w/c ratio•Curing •Rainfall•Temperature / humidity
•At mixing:•Chloride salts
•From external environment:•Sea water•Road salt•Other contaminants
Fire
After EN1504-9
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Wrong approach to the care of assets:
• Gravity warnings
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Wrong approach to the care of assets:
• Gravity warnings
Ouch!
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Wrong approach to the care of assets:
• Gravity warnings
• Lack of investment in testing/monitoring
Just the one, then?
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Wrong approach to the deterioration of assets:
• Gravity warnings
• Lack of investment in testing/monitoring
• Savings this year
• Winners in the long term are:
• Lawyers
• Experts
• The one that got it least wrong….
£££££
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Premature Deterioration
Occurs because of:
• Poor Buildability
• Poor Selection of Materials
• Poor Workmanship
• Knowledge Gap (outside the scope of Codes)
• Changes in properties of materials
• Addition of deleterious materials
• Deleterious reactions
• Environmental aggressiveness
• Deterioration affects the value of the asset on the balance sheet
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
What is Asset Valuation
Need for reliable, timely & relevant information on public finances for:
• Economic monitoring
• Control of public spending
Financial information that:
• Reflects actual investment & outcomes
• Provides a balance between maintenance & depreciation
• Provides a budget that is less easy to cut
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Ass
et V
alue
0
100%
ExpectedLife
Acquired without a
full survey
Assumed value
Linear Asset Depreciation based on Book Value
Life of the Asset
Now
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Ass
et V
alue
0
100%
ExpectedLife
Acquired without a
full surveyProblems
Discovered
ImpairedLife
Assumed value
Linear Asset Depreciation based on Book Value, with Impairment
Life of the Asset
Now
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Ass
et V
alue
0
100%
ExpectedLife
Acquired without a
full surveyProblems
Discovered
ImpairedLife
True Depreciation
Assumed value
Actual value
Linear Asset Depreciation based on Book Value, with Impairment
Life of the Asset
Now
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Ass
et V
alue
0
100%
ExpectedLife
Acquired without a
full surveyProblems
Discovered
ImpairedLife
Impairment: Shortened life
delivers a substantial “hit” to the accounts
True Depreciation
Assumed value
Actual value
Linear Asset Depreciation based on Book Value, with Impairment
Life of the Asset
Now
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Depreciation:
Standard Saloon
Year 1- 46%
Year 2 - 38%
Year 3 - 31%
Year 4 - 26%
Or a Porsche…
Year 1 - 10%
So, what does that mean?
0
20
40
60
80
100
0 1 2 3 4
SaloonPorsche
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Impairment…
Sudden, unforeseen change
Current Performance << Potential Performance
Required Performance >> Current Performance
Need a Plan to restore the value…
So, what does that mean?
0
20
40
60
80
100
0 1 2 3 4
Porsche
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
So, what does that mean?
Impairment:
Bridge Strike
Inspection Reports
• sudden identification of hidden damage
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
So, what does that mean?
ASR TSA NaCl-19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Ass
et V
alue
0
100%
ExpectedLife
Acquired without a
full surveyProblems
Discovered
ImpairedLife
Impairment: Shortened life
delivers a substantial “hit” to the accounts
True Depreciation
Assumed value
Actual value
Linear Asset Depreciation based on Book Value, with Impairment
Life of the Asset
Now
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
100%Engineered Asset to Offset Impairment, based on Book Value
Ass
et V
alue
0 ServiceLife
Deterioration begins Problems
Investigated &Repaired
ImpairedLife
Assumed value
Actual value
Life of the Asset
Now
Cost to repair deterioration?
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
100%Engineered Asset to Offset Impairment, based on Book Value
Ass
et V
alue
0 ServiceLife
Deterioration begins Problems
Investigated &Repaired
ImpairedLife
Assumed value
Actual value
Life of the Asset
Now ExtendedLife
Cost to repair deterioration?
Extended life increases value
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
100%Engineered Asset to Offset Impairment, based on Book Value
Ass
et V
alue
0 ServiceLife
Deterioration begins
ImpairedLife
Assumed value
Actual value
ExtendedLife
Engineered value
Life of the Asset
Now
ProblemsInvestigated &
Repaired
Extended life increases value
Repairs can be self-financing
due to revaluation
New depreciation
profile
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Best Practice in Extending Asset Life
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Towards a new Standard
• CEN Member States – 28 Countries
• Committee Reference CEN TC104/SC8
• Started in 1990
• Evolved from the Construction Products Directive
• CE marked products for the protection and repair of concrete structures
1997Dec 2008
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Towards a new Standard
What does it mean, and how can I use it?
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Construction Products Directive
• Intended to remove barriers to trade for products sold in Europe
• Establishes harmonised product standards & technical approvals
• Removes conflicting national standards
• Compliance with specifications demonstrated by the CE mark on a product
• Mandatory for many public procurers because of the European Public Purchasing Directives:
• Client specifications have been amended
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504
• Establishes for products & systems:
• Methodology of repair
• Minimum product performance levels
• Product identification tests
• Unified test methods across CEN member states
• Guidance on site application
• “Date of Withdrawal” 31 December 2008:
• Conflicting national standards will be withdrawn
• Conflicting EOTA testing to be discontinued
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
CE Marking
• Basis for placing products on the market across Europe
• Presumed to conform with existing regulators:
• UK: building control, trading standards
• Requires third party certification of factory production control in most cases
• CE marked products meet the applicable standard
• CE marked products can be used for the intended purpose:
• shown on the document which includes the CE mark
• CE marked products can be applied with confidence for the intended use
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504
Part TitlePart 1 General Scope and DefinitionsPart 2 Surface protection systemsPart 3 Structural and non structural repairPart 4 Structural bondingPart 5 Concrete injectionPart 6 Grouting to anchor reinforcement or to fill external voidsPart 7 Reinforcement corrosion prevention
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504
Part TitlePart 1 General Scope and DefinitionsPart 2 Surface protection systemsPart 3 Structural and non structural repairPart 4 Structural bondingPart 5 Concrete injectionPart 6 Grouting to anchor reinforcement or to fill external voidsPart 7 Reinforcement corrosion preventionPart 8 Quality control and evaluation of conformityPart 9 General principles for the use of products and systemsPart 10 Application of products & systems and quality control of the
works
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504-9 ContentSection No Section Title
Foreword, Introduction
1 Scope
2 Normative references3 Definitions4 Minimum requirements before protection and repair5 Protection and repair within a structure management strategy6 Basis for the choice of protection and repair principles & methods7 Properties of products and systems required for compliance with
the principles of protection and repair8 Maintenance following completion of protection and repair9 Health, safety and the environment
10 Competence of personnelAnnex A
(Informative)Guidance and background information on the standard text
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504-9
Step 4Choose Repair Principle(s)
Section 6Step 5Choose Method(s)
Section 6Step 6Choose Materials
Sections 7, 9 & 10Step 7Specify ongoing requirements
Section 8
Step 1Assess damage
Section 4
Step 2Management StrategyOptions
Section 5Step 3Factors affecting Management Strategy
Section 5
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment – corrosion detection
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment – half-cell
19/6/2010
V High impedance voltmeterAg-AgCl2 half-cell on sponge contactPositive bar connection (screwed)
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment – half-cell
19/6/2010
Exposure Zone
Atmospheric
Splash
Tidal
Submerged
Atmospheric zone:+100 mV > Ecorr > -350 mV
At the boundary between the splash and atmospheric zones:-300 mV > Ecorr > -550 mV
At a depth of several metres in the submerged zone:-800 mV > Ecorr > -810 mV.
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment - radar
19/6/2010
Tendons
Reinforcement
Spacing
Dep
th“N
oise
”
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment - radiography
19/6/2010
Plate
Shadows - Density Related
Source
Transmission
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment
19/6/2010
Empty duct, corrosion present on 7-wire strand
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment - petrography
• Samples taken from cores or lump samples
• Impregnated in resin and reduced to 30 microns thickness or polished
• Samples examined using petrological microscope in transmitted or reflected light
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment - petrography
• Aggregate type, grading, shape and condition
• Nature of cement paste (pc, pfa, ggbs etc)
• Volumetric proportions of constituents
• Nature and degree of paste hydration
• Aggregate bond
• Porosity of cement paste
• Air entrainment
• Presence of deleterious materials
• Depth of carbonation
• Cracks, voids and inclusions
• Evidence of sulfate attack, frost damage, ASR
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Damage Assessment - monitoring
19/6/2010
• Embedded half-cells• Resistivity probes• Corrosion probes• Linear Polarisation• Precipitation detectors• Internal RH probes• Temperature sensors• Impact/deflection
sensors• Crack movement• Tilt/lean sensors• Video-surveillance• Reported to mobile
devices
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Principle Part Examples of Methods based on the Principles1. Protection
against ingress
222
5
1.1 Hydrophobic impregnation1.2 Impregnation1.3 Coating (including crack-bridging)1.4 Surface bandaging of cracks1.5 Filling Cracks1.6 Transferring cracks into joints1.7 Erecting external panels1.8 Applying membranes
4. Structural Strengthening
6
43,455
4.1 Adding or replacing embedded or external reinforcing bars
4.2 Adding reinforcement anchored in pre-formed or drilled holes
4.3 Bonding plate reinforcement4.4 Adding mortar or concrete4.5 Injecting cracks, voids or interstices4.6 Filling cracks, voids or interstices4.7 Prestressing - (post tensioning)
19/6/2010
BS EN 1504-9
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
BS EN 1504-9
Principle Part Examples of Methods based on the Principles7. Preserving or
Restoring Passivity
33
7.1 Increasing cover with additional mortar or concrete7.2 Replacing contaminated or carbonated concrete7.3 Electrochemical realkalization of carbonated concrete
(see CEN/TS 14038-1 - Electrochemical realkalization and chloride extraction treatments for reinforced concrete – Part 1: Realkalization)
7.4 Realkalization of carbonated concrete by diffusion7.5 Electrochemical chloride extraction
10.Cathodic Protection
10.1Applying an electrical potential(see EN 12696: 2000, “Cathodic protection of steel in concrete”)
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Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Product Specifications (pts 2-7)
• Product conformity standard
• Minimum performance requirements to agreed, unified test methods
• All intended uses
• Certain intended uses
• Identification methods in the event of a dispute
• Additional tests developed for “special applications”
• Verify no release of dangerous substances
• Verify safe reaction to fire
• marked products
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Surface Protection
19/6/2010
CO2
CO2
H2O
H2O
H2O
Coating Concrete
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Cathodic Protection
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Some Research Issues
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Inspection problems – Half-joints
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Inspection problems – tendon ducts
19/6/2010
Tendon Duct & Multi-wire Stressing Strands
Trapped AirPocket
Profiled Tendon Duct
Leakage path
Grout
Duct Venting Pipes
Gap in Duct
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
05
1015202530354045
0 20 40 60 80
50%95%
Carbonation Modelling
Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Carbonation survey:• measure depth of carbonation• assess design parameter• predict future carbonation rates
19/6/20100
10
20
30
40
50
60
tcDX ..2=
?
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling – corrosion initiation/rate
0
10
20
30
40
50
0 20 40 60 80Age since Casting
Dep
th o
f Car
bona
tion
(mm
)
Depth of Cover
0%1020304050607080901
010
2030
4050
60
0% corroding at 10 years3% corroding at 20 years30% corroding at 30 years
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling – chloride ingress
• Chloride ingress prediction
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
−=
teffsnx
DxerfCC
.21 ?
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Chloride ion ingress
• Chloride ingress prediction – do we know enough to predict performance
Typical modelling of chloride ion penetration into concrete, based on Fick’s Law
19/6/2010
30 years?
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling - Uncertainties
We can:
• Indicate if corrosion can take place
• Measure corrosion rates on the bar
• Indicate whether corrosion is present on the bar
We cannot (yet) examine concrete surfaces in the field and:
• Reliably predict time to activation
• Reliably predict section loss & volumes of rust on bar:
• Low oxygen state & expansive state
• Reliably predict time from activation to spalling
• If we cannot predict it – we cannot design for it!
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Deterioration Modelling - Uncertainties
How do we currently design for EXTREME exposure?
• Assess environment, life, exposure are outside codes/standards
• e.g. Hong Kong – Macau Crossing
• Examine best concrete diffusion resistance performance achievable
• Assess local cements, materials
• Give reinforced concrete some extra assistance:
Options:
• Surface protection systems
• Corrosion-resisting additives/admixtures
• Impressed Current Corrosion Prevention
19/6/2010
Identifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Conclusions
Identifying and Managing Deterioration of Concrete Structures – Professor Peter RoberyIdentifying and Managing Deterioration of Concrete Structures – Professor Peter Robery
Conclusions
• Concrete is an excellent investment vehicle:
• It could be eve better, with a little more testing and evaluation
• Signs of deterioration must be acted upon, preferably monitored:
• Waiting for gravity is not good enough
• Need better predictability of the performance of older assets
• Develop improved models for performance monitoring
• Need effective options to extend the life of assets:
• Use EN1504 to provide increased value on the balance sheet
• Educate asset owners and other clients about the importance of “whole life value” decisions
• Whole Life Value will not be Lowest Initial Price!
19/6/2010