Post on 16-Dec-2015
Table of contents
M. McKenzie Guidelines on the selection of innovative techniques for the rehabilitation of concrete highway structures 3A. Žnidarič Optimised assessment of bridges 31E. Denarié Ultra High Performance Fibre Reinforced Concretes (UHPFRC)
for rehabilitation – 1. Motivation and Background 69M. Richardson Guidance on use of surface-applied corrosion inhibitors
Context and Framework of Guidance 97A. Žnidarič Optimised assessment of bridges
Case study 1 - Medno bridge - Soft Load Testing 135A. O’Connor Optimised assessment of bridges
Case study 2 – Danish examples 149JC. Putallaz Ultra High Performance Fibre Reinforced Composites (UHPFRC)
for rehabilitation - 2. Case study – first application 165M. Richardson Guidance on use of surface-applied corrosion inhibitors
Workshop on detailed guidance and Case Studies 197E. Brühwiler Advances in rehabilitation of highway structures Discussion, Summary and Perspectives 233
Guidelines on the selection of innovative techniques for the rehabilitation of concrete highway structuresMalcolm McKenzieTRL Ltd, UK
Development Team
• Richard Woodward, TRL Ltd• Team:
Ales Žnidarič ZAG Mark Richardson UCD Emmanuel Denarié EPFL Tomasz Wierzbicki IBDIM Alan O’Connor TCD Professor Joan Casas UPC Ciaran McNally UCD Malcolm McKenzie TRL Bill McMahon TRL
Overview
• Guidelines and innovation• Deteriorating concrete structures• Selecting the ‘best’ rehabilitation option
for a structure• Special procedures for innovative
techniques• Ranking projects when budgets are
limited
GUIDELINES NOT RULES
Guidelines and innovation
• Innovation is an essential part of engineering development
• Materials and techniques are always being improved
• There are acknowledged problems with existing rehabilitation techniques
• Cautious approach aimed at controlling risks and developing experience
• Yesterday’s innovation is today’s tradition
Concrete bridge deterioration
Some deterioration mechanisms
• Reinforcement corrosion• Alkali silica reaction• Freeze/thaw effects• Sulfate attack• Cracking (settlement, thermal)• Overloading• Impact damage
Identification of problem
• Cause• Extent• Importance
based on
• Inspection• Structural Assessment
MAINTENANCE OPTIONS
• Do nothing• Monitor further deterioration
• Carry out remedial treatment• Carry out strengthening
• Replace element or structure
Procedure
Is option innovative
Identify need
Select & rank rehabilitation option
Control risks
Y
Apply TechniqueN
OptionsAvailable
Innovative techniques: additional risk
Lack of a long established track record
Uncertainties in:• Conditions under which they will be effective• Side effects• Long term durability• Implications for future maintenance• Monitoring effectiveness
Balance conflicting Issues
Technical aspects need to be considered along with other relevant factors to meet the needs of current and future customers.
COST TIME ENVIRONMENT
Wallet
Cost of repairs
Running costsImpact on local
economy
Cost of delays
Affordability
Renewal costs
Watch
Time of works User delays
When Life of repair
World
User delays
Raw materials
Energy usage
Transport of materials
Noise
Pollution
Aesthetics
• Rigorous
• Engineering Judgement
Decision making - WWW
Rigorous approach
• Methodology
Convert everything to financial value
Minimise cost over life of structure
• Problems
Conversion to money
Lack of data
Not practicable
Engineering Judgement
• Advantages
Simple to use
Allows engineer to take all factors into consideration
• Problems
Subjective
Decisions could vary
Structured Engineering Judgement
• Formalise the decision making process• Justification of decisions at each stage
• Best option for a structure• Rank individual projects
• Independent review eg via a Workshop
Decision criteria
• Define objectives of the rehabilitation• Define factors to be considered
• Define decision criteria Basis of comparison eg whole life cost Relative importance of each factor Subjective or numerical approach
Select rehabilitation options
• Identify potential options
• Implications of using an innovative technique
• Assessment of options in relation to decision criteria
taking account of any additional actions resulting from innovative procedure
• Recommend option(s)
Assessing innovative techniques
• Desk study of structure and environmental conditions relevant to technique
• Laboratory testing• Feasibility trials
• Cost/time implications
Select technique - 1
Example: Reinforcement corrosion
• Early Stages• Few visible defects• Low levels of chloride• Half-cell potentials mainly passive• Low corrosion currents
• Preventative maintenance• Slow down chloride ingress eg surface
treatment• Corrosion inhibitors to prevent corrosion?
Select technique - 2
Example Reinforced concrete
• Visible defects• Higher chloride levels• More negative half cell potentials• Higher corrosion currents
• Concrete repairs• Electrochemical techniques• Corrosion inhibitors to reduce corrosion
rates??
Prioritise competing projects
• Risk associated with not carrying out maintenance
• What is the consequence of this occurring? Safety Functionality Sustainability Environment
• What is the likelihood of this occurring?
Prioritisation – Scoring
• This comprises three parts:
• Risks averted• Added value• Timing
All ranked on a numerical basis
Procedure
Is option innovative
Identify need
Select & rank rehabilitation option
Control risks
Y
Apply TechniqueN
OptionsAvailable
InspectionAssessment
Innovativetechniques
Decision
User
Experience
Guidelines and innovation
• It is wise to be cautious in the use of innovative techniques
• It is foolish to be over-cautious
• Engineers need to take controlled risks to grow confidence in new techniques
• Today’s innovation is tomorrow’s tradition
THANK YOU FOR
YOUR ATTENTION
Optimised assessment of bridges
Aleš ŽnidaričSlovenian National Building and Civil Engineering Institute
Contents
• General about bridge assessment• Load testing• Traffic loading
Static Dynamic
• Conclusions
Why optimised assessment?
Design vs. assessment
• new bridges are designed conservatively: uncertainty about
increased loading inexpensive to add
capacity
• assessment should be less conservative: expensive to strengthen/replace or post a bridge capacity and loading can be
measured/monitored
Design vs. Assessment
New bridges: high uncertainties:
• conservative capacity • design loading
schemes• design methods
high safety factors unnecessary:
• costly rehabilitation• load limits
Existing bridges: better defined inputs:
• realistic capacity• realistic loading• assessment methods
lower safety factors savings:
• cheaper rehabilitation• posting of bridges
Why optimised assessment?
• to select optimal rehabilitation measures: do nothing protect repair strengthen replace
Assessment of existing bridges
Important factors : condition, level of
damage structural safety:
• carrying capacity• loading (dead, traffic,
dynamic loading)• reliability of data
serviceability (clearances, traffic, obsoleteness)
service life, importance
1. What is the carrying capacity?• age, condition,
drawings…2. What is the real
behaviour?• influence lines• load distributions
3. What is the real loading?• in a country, type of
road, on specific bridge• dynamic amplification5-level assessment
Condition assessment
• Objectives: Detect possible deterioration processes Indication of the condition of:
• structure • its elements • highway structure stock
Ranking the structures Optimisation of budget allocation
Condition assessment
Influencing factors affecting deterioration: Design stage:
• Detailing• Durability• Materials
Construction stage Loadings Maintenance
Condition assessment
D19. Report on assessment of structures in selected countries: condition rating:
• Cumulative• Highest value
4 factors:1. Type of damage and its affect
on the safety, serviceability and/or durability2. Maximum intensity3. Influence of the affected structural member on safety,
serviceability and durability of the whole structure or its component
4. Extent and expected propagation
Condition assessment
Handbook of damages: http://defects.zag.si/ 10 types of damages descriptions:
• affected bridge component• influencing factor: design,
material, construction, overloading, environment and maintenance
• specific influencing factor• additional data or
explanations• photos
Living application
Safety assessment
• to verify that a structure has adequate capacity to safely carry or resist specific loading levels:
R>S
Load testing Live load assessment (static and dynamic)
• How to relate condition and capacity?
R
kSk
RS
Load testing
on bridges that seem to carry out normal traffic satisfactorily, but fail to pass the assessment calculation
the available model of the bridge does not perfectly match with the real bridge itself
to supplement and check the assumptions and simplifications made in the theoretical assessment
To optimise bridge assessment by finding reserves in load carrying capacity
Load testing
benefits: less severe
rehabilitation measures less traffic delays tremendous savings
drawbacks: very costly danger of damaging the
structure
• best candidates: difficult structural modelling lack of documentation
(drawings, calculations,…) when savings are greater than the cost of load test
Load testing
• Types of load test: proof diagnostic soft
Soft load testing - advantages
• the lowest level of load application• uses bridge WIM to provide:
“normal” traffic data information about structural behaviour of the bridge:
• influence lines• statistical load distribution• impact factors from normal traffic.
• “quick&cheap”: no need for pre-weighed vehicles no need to close the traffic
• no risk of overloading and damaging of the structure
BWIM shema
Strain measurementsStrain measurementsStrain measurementsStrain measurements
Axle detectionAxle detectionAxle detectionAxle detection
Soft load testing
• Theoretical vs. measured influence line
Soft load testing – limitations
• not intended to predict the ultimate state behaviour
• validity of bridge assessment is often short-term and depends on the level of safety
• if higher traffic loading is expected, measurements should be extended or replaced by a normal diagnostic load test
• the soft load testing procedure has only been tested and used on bridges shorter than 40 m
• requires an experienced engineer who can realistically evaluate situation
Traffic load modelling
• calibrated notional load models (loading schemes) for: design assessment (rating loading schemes)
• site specific modelling based on traffic data: Monte Carlo simulation simplified models (convolution)
0%
5%
10%
0 10 20 30 40 50 60
GVW (Tonnes)
Fre
qu
en
cy
0%
5%
10%
0 10 20 30 40 50 60
GVW (Tonnes)
Fre
qu
en
cy
0%
5%
10%
0 10 20 30 40 50 60
GVW (Tonnes)F
req
ue
ncy
0%
5%
10%
0 10 20 30 40 50 60
GVW (Tonnes)
Fre
qu
en
cy
Truck histograms from Europe
Truck histograms from Europe
There is an urgent need for effective overload enforcement – better compliance with legal limits will greatly reduce traffic loading on bridges.
Comparison of sites in NL and SI
0,00,10,20,30,40,50,60,70,80,91,0
10 20 30 40
Bridge Length (m)
Ch
ara
cte
risti
c M
om
en
t
NL - Site 1 NL - Site 2NL - Site 3 SI - Site 1SI - Site 2 SI - Site 3
Dynamic Amplification Factor
• problem: combining the extremes of dead load and dynamic effects => very high DAF
• options: codes – conservative modelling – time-consuming and difficult
due to many unknowns measurements – promising, but only
possible since recent development of bridge WIM systems
Dynamic Amplification Factor
Case Study Calculating dynamic amplification for 1000-year extreme loading event: Mura River Bridge, Slovenia 2 lanes, opposing directions extensive Monte Carlo static
load simulation – 10 years identified 100 max-per-
month static loading events
Dynamic Amplification Factor
Case Study• FE model of
bridge and 5-axle articulated vehicles
• Calibrated by site measurement
• Considered edge beam• Found total effect for each
max-per-month event
Dynamic Amplification Factor
Case Study• Max-per-month
Data of static vs. total • Fit to bivariate
extreme value distribution
• Extrapolated the trend to the 1000-year situation
• Dynamics was very small – less than 6%
Dynamic Amplification Factor
SAMARIS experiment: 31-m long span to assess influence
of pavement unevenness
to evaluate DAF for 1000’s of vehicles
upgraded SiWIM system
Dynamic Amplification Factor
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
0 1 2 3 4 5 6
Str
ain
(V
)
Static
Dynamic
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
0 0,5 1 1,5 2 2,5 3
Str
ain
(V
)
Static
Dynamic
Dynamic Amplification Factor
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
0 0,5 1 1,5 2 2,5 3
Str
ain
(V
)
Static
Dynamic
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
0 1 2 3 4 5 6 7 8 9
Str
ain
(V
)
Static
Dynamic
Dynamic Amplification Factor
• Before resurfacing
0,91,01,11,21,31,41,51,61,71,81,92,02,1
0 4 8 12 16 20 24 28 32
Strain (V)
DA
F
One vehicle - Lane 2
One vehicle - Lane 1
MP with a light vehicile
MP of heavy vehicles
Slovene Bridge design code
Sem
i-tr
aile
r 40 t
ons
Dynamic Amplification Factor
• After resurfacing
0,91,01,11,21,31,41,51,61,71,81,92,02,1
0 4 8 12 16 20 24 28 32
Strain (V)
DA
F
One vehicle - Lane 1
One vehicle - Lane 2
MP with a light vehicile
MP of heavy vehicles
Slovene bridge design code
Sem
i-tra
iler
40 t
ons
Dynamic Amplification Factor
Average value Coefficient of variation
100%
102%
104%
106%
108%
110%
112%
0 5 10 15 20 25
Before resurfacing
Af ter resurfacing
0%
2%
4%
6%
8%
10%
12%
0 5 10 15 20 25
Before resurfacing
Af ter resurfacing
Conclusions (1/2)
• Design conservatively, assess optimally• Proper assessment (with monitoring) can:
prove that many existing bridges are safe in their current condition for their current loading: factors from Eurocodes are too high for
assessment of existing bridges• traffic patterns in EU, EEA and CEC are different• carrying capacity is higher than expected
justify optimal rehabilitation measures save a lot of money
Conclusions (2/2)
• soft load testing is proposed as a simpler way of defining real bridge behaviour
• dynamic amplification factors for the extreme load cases are considerably lower than specified in the design codes
• additional topics in the D30: factors required for efficient bridge inspection specifications for diagnostic load test several case studies
Acknowledgment
WP 15 team: ZAG Ljubljana: Igor Lavrič, Jan Kalin UCD Dublin: Prof. Eugene O’Brien, Colin
Caprani, Gavin OConnell, Abraham Getachew
TCD Dublin (now Rambøll): Alan O’Connor UPC Barcelona: Prof. Joan Casas IBDiM Warsaw: Tomasz Wierzbicki
Ultra High Performance Fibre Reinforced Concretes (UHPFRC) for rehabilitation – 1. Motivation and Background
Emmanuel DenariéLaboratory for Maintenance and Safety of Structures Laboratory for Maintenance and Safety of Structures (MCS)(MCS)
OUTLINE
1. Introduction2. UHPFRC materials3. What is proposed?4. Why?5. Validation6. Conclusions7. Acknowledgements
1. Introduction
Road networks = variety of structures, with a variety of sizes, geometries, local conditions, and …common weak zones
Exposures to environmental loads
Most severe = contact with liquid water - XD2, XD3, XA2,3
Reinforced concrete cannot withstand it for a long time !
2. UHPFRC materials
•Ultra compact cementitious matrix•Multilevel fibrous reinforcement•Outstanding mechanical and protective
properties
CEMTECmultiscale® developed by Rossi et al. (2002)
“Selfcompacting” “Ductile as steel”
UHPFRC composition
• Silica fume - SF/C = 0.26 (mass)• Superplasticizer – SP/C = 1 % (mass, dry extract)• Water/Binder = 0.125 to 0.140• Cement: 1051 to 1434 kg/m3
MicrosilicaCement
CEM I 52.5Fine sand
Dmax=0.5 mm
Matrix
UHPFRC composition
• Steel wool + 10 mm/0.2 mm straight fibres • Total dosage 468 - 706 kg/m3 (6 to 9 % Vol.)
Fibrous reinforcement
MicrofibresSteel wool
MacrofibresL=10 mm, D=0.2 mm
CEMTECmultiscale® developed by Rossi et al. (2002)
Fractured surface of UHPFRC with pulled-out steel fibres
10 mm
3. What is proposed ?
Long-lasting, targeted « hardening » of critical zones subjected to severe mechanical and environmental loads
« Apply an everlasting winter coat on bridges »« Apply an everlasting winter coat on bridges »
Concept of application
Cast in place waterproof UHPFRC overlay No thermal treatment, moist curing 8 days
Pavement applied without waterproofing membrane
« An everlasting wintercoat for bridges »« An everlasting wintercoat for bridges »
Concept of application
Combine UHPFRC and rebars to reinforce structures
« An everlasting wintercoat for bridges »« An everlasting wintercoat for bridges »
3. Why ?
• Rehabilitation works are becoming the dominant activity in road construction
Consider impact on a network and society !• Rehabilitations are too often short lived !• Increase load carrying capacity without
increasing deadweight• Limit duration and number of interventions
during service life simplify and shorten !
Combine materials in efficient structures !
4. Validation
• Method of concrete replacementStudy composite UHPFRC-concrete construction
• Consider local conditionsApplication on inclined substrates
• « New material »Test on a wide range of scales of time and
dimensionsProvide guidelines for design and use
• Validate use with existing facilities and tools
Replacement of existing concrete
Successful « Structural rehabilitations » are a major challenge
Major issues:
Processing
Monolithic behaviour
Protective function
Mechanical performance
Durability
Restrained shrinkage
Silfwerbrand (1997)
Stress = stiffness × free strain × degree of restraint
Stiffness: f(Emod, creep/relaxation) material property,Free strain: material property
Degree of restraint: structural property
Typical values: -New layer on bridge deck slab: 0.4 to 0.6
-New layer on stiff beams: 0.6 to 0.8
-New kerb cast on bridge deck: 0.75
-Full restraint: 1.00
Study structural configurations with various degrees of restraint
Summary of R & D worksOngoing studies at MCS-EPFL since 1999.
• Early age and long term behaviour of composite members with UHPFRC
• Composite structural members with UHPFRC, with various geometries: beams, slabs, walls
• Fatigue of composite members with UHPFRC• Tensile behaviour of UHPFRC• Effect of damage on permeability of UHPFRC• Time-dependent behaviour of UHPFRC (creep,
shrinkage)• Combination of UHPFRC with reinforcement bars• Rheological behaviour at fresh state• Numerical modelling and design tools
Range of studies
Creep, shrinkage, permeability
Structural response
Res
ista
nce
Uniaxial tensile response – strain hardening
Modulus of elasticity 30 % higher than normal concretes Tensile strength of matrix 3 to 4 x higher than normal concrete Finely distributed multiple cracking during hardening phase Similarity with yielding of metals (Luders strips)
CEMTECmultiscale®
Mechanical propertiesDenarié et al. (2006)
UHPFRC NC
Compressive strength
[MPa]
160-250 ~ 40
E modulus[GPa]
48-60 ~ 35
Tensile strength
[MPa]
9-20 ~ 3
Strain hardening
[%] 0.05 - 0.2 0
First crack strength
[MPa]
7-16 ~ 3
NC: Normal Concrete
General overview
Structural response
540
150 240 150
f1 f3f2
30
hU
f5f4
30
F F
60 60 60 60120 120
15
ODS U ODS L
3.4
2,5
200
f6 f7UHPFRC
RC
20 20
+
Flexural tests on composite beams with UHPFRC, Habel (2004)
Effect of new UHPFRC layer thickness (hu) Effect of combination of UHPFRC with rebars
Flexural tests on composite beams with UHPFRC, Habel (2004) UHPFRC alone = significant stiffening UHPFRC + rebars = stiffening + increase of load carrying capacity
Structural response
NL: 10 cm
NL: 5 cm
New layer: UHPFRC New layer: UHPFRC + rebars
Analytical modelling
Composite UHPFRC-Concrete structures = multi-layer systems Tensile behaviour of UHPFRC can be taken into consideration Take eigenstresses into consideration for design !
Tensile response of UHPFRC
Habel (2004)
Compression - UHPFRCTension – UHPFRC
UHPFRC
Reinforced
Concrete
Main results of R & D works - 1
• UHPFRC and concrete behave monolithically in composite members, up tp ULS, Habel (2004).
• Interface roughness of 5 mm with wavelength 15 mm is sufficient for monolithic behaviour, Wuest et al. (2005), Herwig et al. (2005)
• UHPFRC exhibit moderate shrinkage (0.6 ‰ after 3 month), and significant viscoelasticity, (creep coeff ~ 0.8) Habel (2004), Kamen et al. (2005), AFGC (2002).
Main results of R & D works - 2
• Under full restraint (worst case), eigenstresses under shrinkage remain moderate (~ 50 % of tensile strength), Kamen et al. (2005)
• Eigenstresses decrease the apparent tensile strength of UHPFRC in composite members, Habel (2004), Clevi (2005), Sadouki et al. (2005) consider for design
• Anisotropic orientation of fibres, function of application consider impact on properties
Main results of R & D works - 3
• Very low transport properties for liquids (sorptivity) and gases, Charron et al. (2004).
• Up to equivalent crack openings of 0.1 mm (strain of 0.1 %) permeability remains very low, Charron et al. (2004), and behaviour under fatigue loading is controlled, Herwig (2005).
• Self-healing capacity for microcracks• Promissing combination of UHPFRC with rebars,
for reinforcement of structures, with no increase of dead weight, Brühwiler et al. (2005), Habel (2004), Wuest et al. (2005).
Geometries of application
P: UHPFRC hu= 15 to 30 mm = Protection
PR: UHPFRC + replacement of corroded rebars (hu~ 50 mm) = Reinforcement
R: UHPFRC + additional rebars (hu>=50 mm) = Reinforcement
Habel et al. (2004)
Recommandation: UHPFRC
Apply UHPFRC where it is worth it! For zones of severe exposure classes (XD2,3, evt. XA2,3)! To improve existing or new structures!
7. Conclusions
«Targeted local hardening» of highway structures, in most critical zones, by using UHPFRC.
Simplification of the construction process. Reduction of the dead loads
(superstructure and pavement). Increase of the performance of existing and
new structures (protection and reinforcement).
Dramatic decrease of the number and severity of interventions during service life.
Concept has been technically validated on a wide range of scales and duration
Acknowledgements
• UHPFRC team of MCS-EPFL: Prof. Eugen Brühwiler, John Wuest, Aicha Kamen, Andrin Herwig, Dr. Katrin Habel*, Prof. J.P. Charron*, Roland Gysler, Sylvain Demierre,
* Former collaborators of MCS-EPFL
• Partners in Project SAMARIS
Dr. P. Rossi Dr. R. Woodward
Guidance on use of surface-applied corrosion inhibitorsContext and Framework of GuidanceMark RichardsonUniversity College Dublin
Work Package Team
UCD M. Richardson (Team Leader),C. McNally, T. A. Soylev.E. Grimes
ZAG A. Legat
TRL M. McKenzie
Sika P. Mulligan, B. Marazzani, M. Donadio
Cardiff University B. Lark
C-Probe Systems Limited /Structural Healthcare Associates G. Jones
Outline
Background– Methodology, Concept, Motivation
Objectives of SACI in a Maintenance Strategy– Reactive and Proactive Context
Primary Factors Influencing Effectiveness
Framework of Guidance for Specifiers of SACI
Background to SACI
• Methodology
• Concept
• Motivation
Methodology
SACI are applied to mature concrete surfaces where they are absorbed.
Penetrate through the cover concrete by capillary action and diffusion.
Form a protective layer on the reinforcement.
Concept
Before: uncontrolled corrosion activity (existing or future)
After: delay in onset and/or control of corrosion rate
Evans DiagramEvans Diagram
Potential (E)Potential (E)
anodic reactionanodic reaction
cathodic reactioncathodic reaction
Current (I)Current (I)
Potential (E)Potential (E)
E E corrcorr
I I corrcorr
Current (I)Current (I)
After inhibitor applicationAfter inhibitor application
Potential (E)Potential (E)
Current (I)Current (I)
After inhibitor applicationAfter inhibitor application
Potential (E)Potential (E)
E E corrcorr
I I corrcorr
Current (I)Current (I)
Motivation
Benefit of SACI compared to ‘traditional’ repair optionReduce disruption to road users during rehabilitation of structure by time and access efficiency
Sustainability aspect in preventative maintenanceArrest deterioration before it becomes significant and costly to repair
Objectives of SACI in Maintenance Strategy
• Objectives related to overall maintenance strategy
• Specifically consider objectives in ‘Reactive’ and ‘Proactive’ strategies
Reactive Maintenance Strategy
• Inhibitor may be used to reduce (or at least prevent an increase) in the rate of corrosion, thus extending residual service life, unless extent of corrosion is too advanced.
Time
Service life extension
With inhibitor
Without inhibitor
Limit
Deterioration Level
• However in a more general context note that:
Repair occurs when deterioration is apparent and possibly significant
Residual capacity of existing structure may be significantly diminished at time of intervention
Proactive Maintenance Strategy
• Inhibitor may be used to delay the onset of depassivation and thereafter positively influence the rate of corrosion, thus extending residual service life.
Time
Service life extension
With inhibitor
Without inhibitor
Limit
Deterioration Level
• Also in a more general context note that: Measures for performance monitoring of the
structure could be included at time of repair.
Inhibitor may be subsequently reapplied (e.g. a decade later) if performance monitoring indicates it is warranted, before deterioration becomes significant.
Parameter
Time
Resistance Rp,
Corrosion rate, µm/yr
Inhibitor applied
Inhibitor re-applied
Primary Factors Influencing Effectiveness
Effectiveness is influenced by:
Ability of surface to ‘take up’ the inhibitor Ability of inhibitor to penetrate the cover
concrete Ability of inhibitor to form a layer on the
reinforcement Ability of inhibitor to sustain the protective
layer
Appropriateness of SACI
Appropriateness of SACI therefore depends on the following primary factors: Degree of saturation of concrete Permeability characteristics of concrete Corroded state of reinforcement at time of
repair Chloride levels
Degree of saturation of concrete
• State of surface at time of application (initial take-up)
• Surface condition immediately after application (wash out)
• Influence on permeability
Permeability characteristics of concrete
• Ease with which inhibitor may penetrate depends on intrinsic permeability characteristics and degree of saturation
• Permeability also influences ease which other contaminants may enter post-repair (additional protection from suitable coating may be required)
Corroded state of reinforcement
• Inhibitor must form mono-molecular layer on reinforcement
• Ease of formation depends on surface state at time of repair
• Clean or lightly corroded – optimal state
• Heavily corroded – outside inhibitor’s effectiveness window
Chloride levels
• Critical consideration is the relative inhibitor to chloride concentration
• Inhibitor must form a mono-molecular protective layer and displace chloride ions from the reinforcement
• Competitive surface adsorption reaction between inhibitors and chloride ions
• Inhibitors most effective if applied before significant build up of chloride concentration
Framework of Guidance for Specifiers
• Specifiers evaluating or developing a repair strategy based on surface applied corrosion inhibitors are encouraged to view it in the context of a structured approach to deciding on an optimum repair strategy.
• Such a structured approach is presented in SAMARIS Report D31.
Context for Guidance: SAMARIS D31
Determine condition
Rank maintenance option
(Value Management)
Control risks
Apply technique
Select maintenance option
(Value Engineering)Options available
No
Yes
Innovative?
Objectives of maintenance
Identify need
Determine
Rank option
Control risks
Apply technique
Select optionOptions
N
Y
Innov?
Objectives
IdentifySAM
ARIS D
31 G
uida
nce
SAMARIS
D25
a G
uida
nce
Framework of Guidance: D25a
Reference: SAMARIS Report D25a
Summary Flowchart
Yes
Apply technique
No
Initial desk study assessment
Inhibitor potentially
appropriate?
Control of risk to specifier’s
satisfaction?
Re-examine alternative ranked
options
No
Yes
• Overview of guidance flowchart
• Overview of guidance flowchart
Conduct preview and analyse results
No
YesControl of risk to
specifier’s satisfaction?
Define performance criteria for preview
Finalise proposed rehabilitation strategy
• Overview of guidance flowchart
If resources permit conduct post repair monitoring as part of a proactive maintenance strategy and reapply technique if required during residual service life
Control of risk to specifier’s
satisfaction?
Apply technique
Finalise proposed rehabilitation strategy
Re-examine alternative
ranked options
Yes
No
Summary
• Initial Assessment:
• Consider findings, • Balance constraints (funding, time,
urgency, traffic disruption etc.) against control of risk to specifier’s satisfaction,
• Decide: • Go? No go? Go to preview study?
Summary
• Preview Study Assessment (if used): • Consider findings, • Modify proposed strategy if necessary (e.g.
inhibitor + coating rather than inhibitor only),
• Balance constraints (funding, time, urgency, traffic disruption etc.) against control of risk to specifier’s satisfaction,
• Decide: Go? No go?
• Post-repair monitoring• If ‘Go’ consider also follow up monitoring
as part of a proactive maintenance strategy
Further Information
• Follow up presentation • (Guidance on use of surface-applied
corrosion inhibitors: Detailed Guidance and Case Studies)
• SAMARIS Report D25a
Optimised assessment of bridges Case study 1 - Medno bridgeSoft Load TestingAleš ŽnidaričSlovenian National Building and Civil Engineering Institute
Assessment of existing bridges
Important factors: condition, level of
damage structural safety:
• carrying capacity• loading (dead, traffic,
dynamic loading)• reliability of data
serviceability (clearances, traffic, obsoleteness)
service life, importance
1. What is the carrying capacity?• age, condition,
drawings…2. What is the real
behaviour?• influence lines• load distributions
3. What is the real loading?• in a country, type of
road, on specific bridge• dynamic amplification5-level (step-by-step) assessment
Safety assessment
• to verify that a structure has adequate capacity to safely carry or resist specific loading levels:
R>S
Rating factor:
R
kSk
RS
nGd
GGR
RF
Case study – Medno bridge
Structure from 1937: no drawings refurbished in 1997 in very good condition 11.95 m long span total width 8.5 m 5 RC beams 1.35 m apart cross beams above
abutments, at ¼, ½ and ¾ of the span
unknown fixity of supports located on a road with 1150
heavy vehicles ADT posted to 30 tonnes GVW
Carrying capacity
• Assumed characteristics of concrete:
fc = 20 MPa
no information about steel reinforcement: 8 bars from profometer test likely 25 or 28 mm,
assumed 822 mm bars of 240/360 MPa steel
RM = 867.4 kNm
Soft load testing
• to check the assumptions made in the model• bridge WIM used to provide:
normal traffic data (not in this case) information about structural behaviour:
• influence lines• statistical load distribution• impact factors from normal traffic (not in this
case) only 1 pre-weighed vehicle for BWIM
calibration the bridge need not be closed to traffic
BWIM shema
Strain measurementsStrain measurementsStrain measurementsStrain measurements
Axle detectionAxle detectionAxle detectionAxle detection
Soft Load Testing
Soft load testingSimply supportedSimply supportedRF RF << 1.0<< 1.0
Soft Load Testing
Soft load testingSimply supportedSimply supportedRF RF << << 1.01.0
MeasuredMeasuredRF RF >>>> 1 1.0.0
Message:Message:Check, how Check, how bridges really bridges really behave.behave.
Soft Load Testing
Load distribution: normally guestimation bridge WIM evaluates it statistically
± 0
Regular inspection
R factor
Service life
Resistance
Normal Limited
Design
Testing Estimate
= 0.85
Severe
Minor
Bad Good
Redundancy No
Detailed inspection
Yes
No
c = 3.5
c = 2.5
VR = 10% VR = 15% VR = 20% - 0.1
+ 0.1
> 0.95
+ 0.05
0.95
- 0.15
+ 0
- 0.2
No
Average
Yes
No
No Yes
BR×e
R×C×VR
Maintenance
Yes
START
Deterioration
Selection of capacity reduction factor
Capacity reduction factor:
Φ = BR × e -.βc.V
SI procedure accounts for: condition of the structure reliability of data redundancy of structure method of calculation
Medno bridge:Φ = 0.86
Selection of safety factors
Dimensions taken on site:
Safety factor for traffic loading:
WIMEstimated
Estimated
Traffic loading
Rating loading schemes
Lateral loaddistribution
Measured
Q 1.4
Q 1.6
Q Q + 0.2
Q Q - 0.2
Q Q + 0.1
Q Q + 0.1
Estimated
Impact factor
Measured
Service life Limited
Q Q - 0.2
Normal
Yes
Q Q + 0.2
>1000 trucks/day
No
Q = 1.6
G = 1.2
Q = 1.7Q = 1.9
Structural safety of Medno bridge
Calibrated structural model:1. Loading scheme with 2 4-axle rigid 38-ton
trucks, one in each lane:
1.03
28.16.2349.1
7.2352.14.86786.0
nGd
GGR
RF
2. Loading scheme with 81-ton 8-axle vehicle in one lane and rigid 38-ton truck in the other:
1.08
00.15.2469.1
7.2352.14.86786.0
nGd
GGR
RF
Room for further optimisation of analysis
Conclusions
• on Medno bridge soft load testing proved beneficial
• 2004 assessments for special transports for the Slovene Road Administration: 13 posted bridges assessed 11 proved safe even for a
165-tonnes special vehicle with 12 axles
for the rest missing data on carrying capacity
on shorter bridges normal traffic worse than special transports
Optimised assessment of bridges Case study 2 – Danish examplesAlan O’ConnorRambøll
Problem:
1) Lack of load carrying capacity or exceedance of structural/performance limit state due to
– weak bridges– deteriorated/(ing) bridges– Increasing loads
2) Low budgets for strengthening
and/or rehabilitation where required
Idea: 1) Demonstration of higher capacity through Probabilistic safety assessments incorporating better calculation/response models
Principal Motivation:
Cost saving through Budget Optimisation
Problem, idea and motivation
The general approach:
Assessments based upon deterministic
codes for both (a) New bridges and (b) Existing bridges
Generalisation
• Partial safety factor format
• Deterministic Load specification
• Many types of bridges
BenefitEfficient and easy to use
DrawbackCostly in case of lack of capacity may result in unnecessary repair/rehabilitation
Safety approaches for assessment of existing bridges
Concept:
• Not necessarily have to fulfill the requirements of a general code rather the Overall requirement for the safety level must be satisfied on a individual basis
Purpose:
• Cut strengthening or rehabilitation costs without compromising safety level
Method: Probabilistic-based assessment
Site specific modelling of specific conditions/structure:
• Traffic load
• Capacities
• Response Models
Bridge specific “code” is obtained
The individual approach
Decision Process
Yes
Yes
No
No
No
Yes
Assessment from traditional evaluation OK ?
Implement traditional strengthening project
Yes
Assessment from traditional evaluation OK ?
Implement traditional strengthening project
Refinedassessment beneficial?
No
Refined strengthening project
Traditional decision process
New decision process considering refined assessment
Refinedassessment OK ?
Case Studies
Practical experience: The Danish Road Directorate has saved more than $50 million USD Bridge Deterministic Analysis Probability-based as-
sessment Cost Saving
Mio. $US Vilsund Max W = 40 t Max W = 100 t 4 Skovdiget Lifetime ~ 0 years Lifetime > 15 years 15.0 Storstroem Lifetime ~ 0 years Lifetime > 10 years 20.0 Klovtofte Max W = 50 t Max W = 100 t 2 407-0028 Max W = 60 t Max W = 150 t 1.5 30-0124 Max W = 45 t Max W = 100 t 0.5 Nørresø Max W = 50 t Max W = 100 t 0.3 Rødbyhavn Max W = 70 t Max W = 100 t 0.5 Åkalve Bro Max W = 80 t Max W = 100 t 1.0 Nystedvej Bro Max W = 80 t Max W = 100 t 2.0 Avdebo Bro Max W = 80 t Max W = 100 t 2.0
Case Studies - Savings
Savings > $ 4 mio.Savings > $ 4 mio.
Savings > $ 15 ml.Savings > $ 15 ml.
Savings > $ 20 ml.Savings > $ 20 ml.
Savings > $ 0.5 ml.Savings > $ 0.5 ml.
Savings > $ 2 ml.Savings > $ 2 ml.
Case Studies - Savings
Savings > $ 0.Savings > $ 0.33 ml. ml.
Savings > $ 0.5 ml.Savings > $ 0.5 ml.
Savings > $ 1.Savings > $ 1.00 ml. ml. Savings > $ 2.0 ml.Savings > $ 2.0 ml. Savings > $ Savings > $ 22.0 ml..0 ml.
Probability based Maintenance Management
0. Fact-finding 1. Formulation of problem 2. Safety requirements 3. Deterministic models for failure 4. Probability-based safety-model for critical failure modes. 5. Stochastic variables 6. Safety of the non-deteriorated bridge 7. Safety of deteriorated bridge 8. Analysis of repair and rehabilitation options 9. Requirements for the visual appearance of the bridge 10. Cost-optimal management plan using decision analysis to determine optimal rehabilitation options
SAFETY
MANAGEMENT
Practical 10-phase procedure
WestBridge
EastBridge
Post tensioned concrete box-girder bridges12 spans, 220 m longCarries a 4-lane highway
Skovdiget Bridges: Location / OverviewSAVING €20ml.
History
West Bridge East bridge
1965-1967 Construction Construction
1978 Majorrehabilitation
1978-1999 Inspection 4 times Principal Inspectiona year. Load testing every 5 years.every 5 years. Normal M & R
procedure.
Bridge in bad Bridge in good condition. condition.
1998-2000 Implementation ofprobabilistic-based management plan.
Design, Deterioration & Assessment
Poor workmanship during construction: un-injected or poorly injected post-
tensioned cable ducts insufficient and poor drainage area around gulley poorly made
bad waterproofing
Fast Slow Service Emergency Bicycle lane &
lane lane lane lane footway
Gulley
Main girder 3
Main girder 4
Deterministic analysis of bridge & failure modes Main girders, moment and shear failure Shear failure of transverse girders (above
columns) Transverse ribs between main girders 3 and 4 East and west cantilever wing
Identifying areas with most severe deteriorationIdentifying critical combinations
Modelling of stochastic variablesModelling of strengths
concrete, reinforcement steel, cables
Modelling of loads total traffic load dynamic amplification factors transverse distribution of vehicles
Model uncertaintiesPrediction of the deterioration
Calculation of safety allowing for deterioration
Development of the safety index
Maintenance Management OptionsTraffic, repair and information options:Traffic options - Weight restrictions Repair/strengthening - or replacement - options - Minor / major repair - or - strengthening - Preventive actions - ReplacementImprovement of Information level- Inspections to update estimate of current
deterioration - Test loading- Determine actual weight the bridge- Monitoring system- More advanced analysis and response models- Extended routine and special inspections
A Safety-based management plan is established and implemented for Skovdiget WestExtended lifetime > 15 years & Cost savings > €20 millionThe Danish Road Directorate is now using the methodology for other bridgesThe safety level is not compromised
A rational methodology is implemented for practical application
Probabilistic-based assessment of bridges cuts strengthening or rehabilitation costs. The cost savings can be significant
www.vd.dk
Conclusions
• Reliability based assessment of bridges and Probability Based Maintenance Management cuts strengthening or rehabilitation costs
• The safety level is not compromised• A well established
methodology is implemented for practical application
• The cost saving can be millions of € per year
Ultra High Performance Fibre Reinforced Composites (UHPFRC) for rehabilitation - 2. Case study – first applicationJean-Christophe Putallaz SRCE/VSEmmanuel Denarié – MCS/EPFLMCS/EPFL
OUTLINE
1. Rehabilitation strategy2. First application3. Conclusions4. Acknowledgements
Rehabilitation strategy
• Limit costs (construction and life-cycle)• Decrease number and duration of interventions• Provide sufficient durability …… Promote STRATEGY APromote STRATEGY A
2. First application
Creep, shrinkage, permeability
Site application 1 - 2004Structural response
Res
ista
nce
First application
Rehabilitation and widening of the Bridge over river La Morge - Switzerland
Execution: October – November 2004
GEOGRAPHICAL LOCATION
Swiss alps, Valley nearby Sion, 480 m above s.l Secondary road with sustained traffic Heavy salt spraying in winter
Prior to rehabilitation
Downstream kerb Upstream kerb
No waterproofing membrane,Kerbs severely damaged by chloride induced corrosion
Concept of the intervention
Span 10 m No waterproofing membrane
Protective function provided by UHPFRC
Widening of the bridge
Prefabricated UHPFRC kerb downstream
Thin UHPFRC overlay (3 cm) applied on deck
UHPFRC rehab. kerb usptream
Span 10 m
Construction joint for UHPFRC
Prefabricated downstream kerb
Prefabricated kerb in UHPFRC - joint
UHPFRC materials
• Cement CEM I 52.5 (low C3A)• Fine quarz sand (Dmax < 0.5 mm)• Silica fume - SF/C = 0.26• Superplasticizer = 1 % dry extract • Steel wool + 10/0.2 mm steel fibres• Total fibres = 9 % Vol. or 706 kg/m3)
Basis: CEMTECmultiscale® - Rossi et al. (2002)
No thermal curing Protection with plastic sheet + 8 days moist curing
UHPFRC materials
Recipe
Cement[kg/m3]
W/B[--]
W/C[--]
Application
CM22 1410 0.131
0.165
RehabilitationUpstream kerb
CM23 1434 0.125
0.155
Downstream kerb + overlays CM 23: tolerates slope up to 2.5 %
Both recipes are selfcompacting Slump flow ~ 400 mm
Preparation of the UHPFRC
• Concrete plant mixer with 500 to 750 litres capacity • 300 litres UHPFRC pro batch• 3 batches = 900 litres in 45 minutes• 900 litres pro truck - 635 kg steel fibres per truck !
Application on ½ road downstream – october 22, 2004
On the site
Processing of the UHPFRC
The thixotropic, selfcompacting UHPFRC, is handled using simple tools (Photo A. Herzog)
In-situ air permeability testing
Air permeability tests after Torrent et al. (1995)
Extremely low kT values measured on bridge
Comparative uniaxial tensile behaviour
Denarié et al. (2006)
Uniaxial tensile tests on UHPFRC
Test results on 5 specimens, at 28 days
fct = 13.5 MPa (mean)
hardening = 1.5 ‰ (mean)
Denarié et al. (2006)
Cost analysisComparison of three alternatives
A. Executed project with UHPFRC and no waterproofing membrane
B. Similar case with rehabilitation mortar and waterproofing membrane
C. Similar case with cheaper (- 30 %) UHPFRC and no waterproofing membrane
Case Relative construction costs
A 112 %
B 100 %
C 107 %
Realized
The bridge, after first winter
Detail of UHPFRC, after first winter
View of the surface of the prefabricated kerb with UHPFRC, with superficial corrosion of steel fibres tips near to the surface.
UHPFRC cast on site
Prefabricated
Conclusions of first application
UHPFRC CEMTECmultiscale® was easy to produce and cast on site with standard equipments.
Quality of the UHPFRC was verified in-situ and in the laboratory. Excellent properties were achieved.
Waterproofing membrane not necessary with UHPFRC.
Bituminous layer can be applied after 8 days on UHPFRC, instead of several weeks for normal concrete.
Superficial corrosion of steel fibres on UHPFRC skin, is linked to processing.
Although a purely superficial concern, has to be mitigated by adapted processing techniques.
Owner’s point of view
« The main advantages of this technique are:
Shortening of duration of works, quicker reopening of traffic lanes, and longer durability.
Significant savings in terms of reduced traffic disturbances and associated indirect costs.
Reduction of rehabilitation layer thickness and capacity to reinforce without increasing deadweight.
Prevent costly reinforcement of main parts of the structure.
Application by local contractors, with standard equipments. »SRCE - DTEE CANTON DU VALAIS
7. Conclusions
«Targeted local hardening» of highway structures, in most critical zones, by using UHPFRC.
Simplification of the construction process. Reduction of the dead loads (superstructure and
pavement). Increase of the performance of existing and new
structures (protection and reinforcement). Dramatic decrease of the number and severity
of interventions during service life. Concept has successfully demonstrated its
technical maturity and economical feasibility in a first full scale application.
What is the future ?
Creep, shrinkage, permeability
Site application 2 - 2007
Site application 1 - 2004Structural response
Res
ista
nce
Why not you ?
Partners of the project
Owner:Owner: Département des Travaux Publics du canton du Valais, Sion, Suisse, Département des Travaux Publics du canton du Valais, Sion, Suisse, Service des routes et Cours d'eau, Section du Valais central/Sion, Switzerland.Service des routes et Cours d'eau, Section du Valais central/Sion, Switzerland.
Concept and supervision:Concept and supervision: Laboratory for Maintenance and Safety of Structures, Laboratory for Maintenance and Safety of Structures, Ecole Polytechnique Fédérale de Lausanne (EPFL), SwitzerlandEcole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Advice for the UHPFRC recipes and processing:Advice for the UHPFRC recipes and processing: Dr. P. Rossi, Laboratoire Dr. P. Rossi, Laboratoire Central des Ponts et Chaussées (LCPC), Paris, France.Central des Ponts et Chaussées (LCPC), Paris, France.
Execution plans and local direction of works:Execution plans and local direction of works: PRA ingénieurs conseil SA, rue PRA ingénieurs conseil SA, rue de la Majorie 9, CH-1950 Sion, Switzerland, de la Majorie 9, CH-1950 Sion, Switzerland,
Production of UHPFRC, realisation of prefabricated UHPFRC kerb and Production of UHPFRC, realisation of prefabricated UHPFRC kerb and reinforced concrete beam:reinforced concrete beam: Proz Frères SA, matériaux de construction, CH-1908 Proz Frères SA, matériaux de construction, CH-1908 Riddes, Switzerland, Riddes, Switzerland,
Contractor:Contractor: Evéquoz SA, rue des Peupliers 16, CH-1964 Conthey, Switzerland, Evéquoz SA, rue des Peupliers 16, CH-1964 Conthey, Switzerland,
Acknowledgements
UHPFRC team of MCS-EPFL: Prof. Eugen Brühwiler, John Wuest, Aicha Kamen, Andrin Herwig, Dr. Katrin Habel*, Prof. J.P. Charron*, Roland Gysler, Sylvain Demierre, *Former collaborators of MCS-EPFL
Partners in Project SAMARIS
Dr. P. Rossi Dr. R. Woodward
Service des Routes et Cours d’Eau – DTEE SRCE – Canton du Valais
Guidance on use of surface-applied corrosion inhibitorsWorkshop on detailed guidance andCase StudiesM. RichardsonUCD
Outline
• Initial Assessment
• Preview Study option
• Post-repair Monitoring option
• Case Study: Assessment and Monitoring – Kingsway Bridge
• Case Study: Post-repair monitoring – Fleet Flood Span Bridge
Initial Assessment
Yes
Apply technique
No
Initial desk study assessment
Inhibitor potentially appropriate
?
Control of risk to specifier’s satisfaction?
Re-examine alternative
ranked options
No
Yes
Summary of Guidance - 1
Issues in Initial Assessment
• Extremes of in-service environmental conditions
• Degree of saturation of concrete• Chloride levels• Permeability and carbonation• Corroded state of reinforcement at
time of repair• Ecological constraints
Issues in Initial Assessment
• Extremes of in-service environmental conditions
• Degree of saturation of concrete• Chloride levels• Permeability characteristics of concrete• Corroded state of reinforcement at
time of repair• Ecological constraints
Issues in Initial Assessment
• Extremes of in-service environmental conditions
• Degree of saturation of concrete• Chloride levels• Permeability characteristics of concrete• Corroded state of reinforcement at
time of repair• Ecological constraints
Extremes of environmental conditions
Environment
IndicativeTemperature
Potential Consequence
Sustained lowtemperatures
≤ -5oC Alteration in the physical nature of the inhibitor, with implications for its mobility in concrete.Temperature limit of –5°C is only applicable for the storage condition.Application to be carried out above +5°C.
Frequent hightemperatures
≥ 40oC Potential loss of volatile material to the atmosphere.Coating the concrete surface may be an option to reduce evaporation loss.
Degree of saturation of concrete
Moisture State
Indicative Example
Possible Consequence
Permanentlysaturated
Elements ofhighwaystructures predominantly below the waterlevel of a lake
Inhibitor take up by absorption would be low.Subsequent penetration would not be assisted by capillary action.
Note: corrosion would be low in these areas if oxygen access is equally restricted.
Frequent and regular wettingcycles
Elements ofcoastal highwaystructures withinthe tidal zone
Potential washout of inhibitor immediately after application.Inadequate concentration at the reinforcement.
Chloride levels
Chloride State
Indicative Free Chloride Ion at
Level at Reinforcement
Possible Consequence
Low ≤ 0.5 % Chloride ion
by mass of cement
Corrosion inhibitor potentially viable as a preventive maintenance strategy before any significant active corrosion takes place.
Moderate
≤ 1 % Chloride ion
by mass of cement
Corrosion inhibitor may be effective if a satisfactory inhibitor to chloride ion concentration ratio is achieved – much depends on existing degree of corrosion.Protective measures to prevent further chloride build up are recommended in chloride-rich environments.
continued …
Chloride levelscontinued …
Chloride State
Indicative Free Chloride Ion at
Level at Reinforcement
Possible Consequence
High 1 – 2 % Chloride ion by mass of cement
Corrosion inhibitor dosage level may have to be increased beyond typical manufacturer’s recommendation and additional protective measures required.May take the technique beyond its recommended effectiveness window, introducing higher risk.
Very high
> 2 % Chloride ion by mass of
cement
Corrosion inhibitor unlikely to be a successful component of the repair strategy.
Permeability and carbonation
Carbonation
State
ConcretePermeability
Possible Consequence
Cover fullycarbonated
Moderate Inhibitor potentially effective.
High Inhibitor potentially effective initially but reservoir may not be retained in concrete reducing effectiveness over time.May need additional measures such as a suitable coating.
Corroded state of reinforcement
continued …
Existing Corrosion Rate
Indicative Corrosion Rate
over a sustained
period
Possible Consequence
Low to Moderate
< 0.5 µA/cm2
< 5 μm/year
Best scenario possible with inhibitor used as part of a proactive preventive maintenance strategy.
Moderate to High
0.5 – 1.0 μA/cm2
5 - 10 μm/year
State of reinforcement is potentially suitable for consideration of corrosion inhibitor treatment.
Corroded state of reinforcementcontinued …
Existing Corrosion Rate
Indicative Corrosion Rate
over a sustained
period
Possible Consequence
High 1.0 - 10 μA/cm2
10 - 100 μm/year
State of reinforcement will depend on corrosion rate lies - effectiveness of the inhibitor correspondingly influenced.Higher risk at higher corrosion rate.Corrosion monitoring recommended in case of higher corrosion rates.
Very High > 10 μA/cm2
> 100 μm/year
Reinforcement may be heavily corroded - corrosion inhibitor is unlikely to be a successful component of the repair strategy.
Ecological constraints
Local environmental or health and safety constraints?
Example: work near drinking water supply source
Preview Study option
Conduct preview and analyse results
No
YesControl of risk to
specifier’s satisfaction?
Define performance criteria for preview
Finalise proposed rehabilitation strategy
Summary of Guidance - 2
Preview Study – Indicative Criteria
Objective Indicative Performance Criteria
Defer the initial time to depassivation
< 5 μm/year loss of steel (or < 0.5 µA/cm2)
Reduce the rate of corrosion
65% reduction from pre-treated levels over a defined time period or ……………
< 5 μm/year loss of steel (or < 0.5 µA/cm2)
Retard incipient action (ring anode)
No increase in loss of steel prefer …………Decrease to < 5 μm/year loss of steel (or < 0.5 µA/cm2)
Post-repair monitoring option
If resources permit conduct post repair monitoring as part of a proactive maintenance strategy and reapply technique if required during residual service life
Control of risk to specifier’s satisfaction?
Apply technique
Finalise proposed rehabilitation strategy
Re-examine alternative
ranked options
Yes
No
Summary of Guidance - 3
If resources permit conduct post repair monitoring as part of a proactive maintenance strategy and reapply technique if required during residual service life
Control of risk to specifier’s satisfaction?
Apply technique
Finalise proposed rehabilitation strategy
Re-examine alternative
ranked options
Yes
No
Summary of Guidance - 3
If resources permit conduct post repair monitoring as part of a proactive maintenance strategy and reapply technique if required during residual service life
Case Study of assessment and monitoring
Kingsway Bridge
Case Study 1
Kingsway Bridge, Warrington, U.K.
Acknowledgement: Warrington Borough Council
• Reinforced concrete• multi-span arch, • 1932
• Main spans, 2 x 26.21m• Reinforced concrete arches• Thickness: 450mm (arch)
1300mm (springings), • Sagging and hogging
bending moments• Drainage route along top
curved surface of arch• Subject to chloride run-off
Environmental conditions Not significant
Degree of saturation Not significant
Chloride levels Typically 0.3% Max. 0.6 –
1.2%
Carbonation 2mm
State of reinforcement Light surface rust
Some pitting
Ecological constraints Over water
Findings from Initial Assessment
• Threat from chloride-induced corrosion.• Chloride-entrained rain and deicing salts
passing through deck and accumulating at crown of arch and later behind springings.
• Surface applied corrosion inhibitors identified as a candidate strategy for rehabilitation.
• Agreement from Warrington Borough Council to allow further investigation including a form of ‘preview’ study of corrosion inhibitors within SAMARIS
• Areas selected:Crown of ArchUnder Arch
• Corrosion inhibitor applied after base measurements
• Monitoring locations established
Corrosion Rates: Crown Arch
0
5
10
15
20
25
30
35
40
6/24
/04
11/3
/04
1/23
/05
2/6/
05
2/20
/05
3/6/
05
3/20
/05
4/3/
05
5/8/
05
5/22
/05
6/5/
05
6/19
/05
9/11
/05
9/25
/05
10/9
/05
10/2
3/05
11/6
/05
11/2
0/05
12/4
/05
12/1
8/05
1/1/
06
C1RC2RC3RC4R
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
C3R Control
C1R Waterproofing
C4R Inhibitor only
C2R Inhibitor plus
waterproofing
Corrrosion Rates: Under Arch
0
4
8
12
16
20
24
6/24
/04
11/3
/04
1/23
/05
2/6/
05
2/20
/05
3/6/
05
3/20
/05
4/3/
05
5/8/
05
5/22
/05
6/5/
05
6/19
/05
9/11
/05
9/25
/05
10/9
/05
10/2
3/05
11/6
/05
11/2
0/05
12/4
/05
12/1
8/05
1/1/
06
F1RF2RF3RF4RF5RF6RX1RX2RX3R
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)Corrosion Rate Values
Case Study: Post-repair monitoring – Fleet Flood Span Bridge
Case Study 2
Concrete repair and corrosion inhibitor treatment to trestles and abutments.
Monitored previously from 2000 to 2002, reactivated 2005.
Fleet Flood Span Bridge
Trestle 1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
4
8
12
16
20
24
28
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
1
2
3
4
5
6
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
2
4
6
8
10
12
14
16
18
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
Trestle 2
0
0.5
1
1.5
2
2.5
3
3.5
4
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
3.6
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
3.6
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
North Abutment
1
2
3
4
5
6
7
8
9
10
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
5
10
15
20
25
30
35
40
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(um
/yr)
Corrosion Rate Values
0
10
20
30
40
50
60
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
South Abutment
0
1
2
3
4
5
6
7
8
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
0
5
10
15
20
25
30
35
40
45
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values0
1
2
3
4
5
6
7
2/14
/00
3/10
/00
3/14
/00
3/16
/00
7/5/
00
11/1
6/00
2/13
/01
4/24
/01
5/21
/02
11/1
6/05
Test Date
Co
rro
sio
n R
ate
(u
m/y
r)
Corrosion Rate Values
Summary
• Inhibitor effectiveness is very influenced by the state of the reinforcement at time of treatment and the hostility of the chloride environment.
• This inter-relationship makes it difficult to specify precise limits on the effectiveness window but qualitative guidance is proposed.
• Optimal use of inhibitors may be as part of a proactive maintenance strategy and the earlier they are applied the better.
• The use of corrosion monitoring is invaluable in managing such repair strategies
Further Information
• SAMARIS Report D21• Field Studies
• SAMARIS Report D25a• Guidance on use of surface-applied
corrosion inhibitors
Advances in rehabilitation of highway structuresDiscussion, Summary and PerspectivesProf. Eugen BrühwilerMCS/EPFL
… improving the performance !
• apply advanced structural assessment to limit interventions
• improve the structure (not just repair it)• reduce the duration of interventions • reduce life-cycle costs (without increasing the
cost of intervention)
Achieving improved performance …through:• education motivation• applications demonstration• guidelines regulation