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7th Australian Small Bridges Conference
Extending the Life, Serviceability & Durability of the Sylvania Waters Concrete Bridges
Ian Godson Managing Director
Infracorr Consulting Pty Ltd
Infracorr Consulting
• Specialist Consultants in the Repair and Preservation of Infrastructure
• Investigation & Condition Reporting
• Design & Specification of Repair Systems
• Tender Assistance
• Supervision of Repairs
• Commissioning & Ongoing Monitoring
• Design for Durability (New Structures)
Sylvania Waters Estate BridgesBuilt in the late 1960’s, these structures are located in the Sylvania Waters estate in Sutherland Shire of NSW, approximately 15 km from Sydney Airport.
The six bridges generally conform to the following arrangement:
• Single span road bridges
• 3 to 8 m long; 12 to 15 m wide
• Precast driven sea-wall panels forming abutments
• In-situ capping beams
• In-situ reinforced concrete deck slab
Visual Condition of the BridgesThe bridges were in a poor visual condition including Cracking, Delamination & Spalling
• Soffits
• Mostly Sound
• Localized Delamination & Spalling
• Capping Beams
• Significant Cracking & Rust Stains
• Delaminated & Spalling Areas
• Failed Previous Patch Repairs
• Precast Seawall Panels
• Mainly Sound
• Some cracking
• Spalling Sections on some Panels
Investigation of Concrete Distress
• Delamination/ Spalling
• Carbonation depth
• Chloride concentration with depth
• Cover depth (the time fuse)
• Half cell potential (equipotential)
• Corrosion rate
• Concrete resistivity
• Electrical continuity
Stages of Reinforcement Corrosion in Concrete
initiation phase timepropagation phase
amo
un
t of co
rrosio
n
2
3
4
collapse
1
crackingdepassivation
spalling of cover
initiation phase timepropagation phase
amo
un
t of co
rrosio
n
2
3
4
collapse
1
crackingdepassivation
spalling of cover
CorromapCorrosion Rate & Half Cell Potential
70 mm
PSIONWork About
Reinforcement
Guard ring
Counterelectrode
Ag/AgClReferenceelectrode
EQUIPMENT
Belgrave Esp BridgeCapping Beams• Significant cracking & rust at base• Failed Previous Patch repairs• Half Cell- ACTIVE Corrosion 90%• Chloride 0.54% Cl wt Concrete (10 Times Critical of 0.05%)• Corrosion Rate –VERY FAST (17mA/m2) Spall within 5 yearsSoffit• Sound most areas (Spalling 5% area)• Half Cell – Majority Passive• Only 10% Active Corrosion here, but average 50%• Chlorides 0.03%- NON Critical to 0.2% Critical• Corrosion Rate- Slow Passive; Fast in localized areas
Equipotential Map (mV vs CuCuSO4) of Belgrave Esplanade Bridge - North West Beam
NE← →SW
Resistance Map (kOhm) of Belgrave Esplanade Bridge - North West Beam
NE← →SW
Equipotential Map (mV vs CuCuSO4) of Belgrave Esplanade Bridge – Soffit adjacent North West beam.
NE← →SW
Resistance Map (kOhm) of Belgrave Esplanade Bridge - Soffit adjacent North West beam.
NE← →SW
Richmond Ave BridgeCapping Beams• Significant cracking & rust staining• Half Cell- ACTIVE Corrosion 100%• Chloride 0.23% Cl wt Concrete (5 Times Critical of 0.05%)• Corrosion Rate –VERY FAST –Spalling within 5 years
Soffit (Precast)• Sound • Half Cell –Passive• Chlorides 0.02%- NON Critical• Corrosion Rate- Slow Passive
Equipotential Map (mV vs CuCuSO4) of Richmond Avenue Bridge - South West Beam
SE← →NW
Resistance Map (kOhm) of Richmond Avenue Bridge - South West Beam
SE← →NW
Equipotential Map (mV vs CuCuSO4) of Richmond
Avenue Bridge – Soffit Beam near SE side
SW← →NE
Resistance Map (kOhm) of Richmond Avenue
Bridge – Soffit Beam near SE side
SW← →NE
Seawall Panels• Typical Panel Half Cell indicates active corrosion- Caution with wet
elements as results deceiving
• Corrosion Rate Moderate to Fast – Spalling in 5-10 years
• Chloride levels Very High (0.3% Cl/wt concrete) 8 x Critical
• Panels corroding in top 1m but at slower rate than capping due to high moisture levels
Bridge Condition SummaryBRIDGE SPAN/
WIDTH
(m)
Seawall Panels Capping Beam Slab Soffit
%
Spalling
%
Corroding
%
Spalling
%
Corroding
%
Spalling
%
Corroding
1 Bogan Ave 3.0/13.0 5 60 40 100 40 80
2 Richmond
Ave
4.0/12.0 4 70 20 100 5 10
3 Warrego
Ave
4.5/14.5 5 50 40 100 5 60
4 Belgrave
Esp
8.0/12.5 10 70 50 100 5 80
5 Bellinger Pl 3.5/14.0 5 55 20 75 10 40
6 Tuross Ave 3.5/14.0 10 60 30 100 15 40
Repair Options
• Preventative Coatings (Silane Impregnations)
• Patch Repairs
• Impressed Current Cathodic Protection (ICCP)
• Hybrid CP
The Sutherland Shire Council required a life extension of 30 years for the bridges. Options considered for the repairs included:
Patch Repair (PNG 1992)
Patch repairs • Remove concrete 30mm behind bars• Clean & repair reinforcement• Replace mortar (pour, spray or hand
place)
Structurally InvasivePoor Durability Don’t address corroding areas in sound
concrete
Impressed Current Cathodic ProtectionUses a small, permanent DC current to virtually stop the corrosion process
Morell Bridge – Melbourne 1995Earth filled bridge built 1890’s
•12 No. soil anodes
•Manual control system
•Institute of Engineers Award
Soil anodes
VicRoads Deep Creek BridgeTooradin, Gippsland Highway
• ICCP Internal Anodes (central)
• Remote Monitoring
• Cardinia Creek Bridge Similar design
Hybrid CP System
• Hybrid CP System
• Anode made of Zinc Alloy
• Installed in 30mm dia holes
• Hole filled with special mortar
• Connected with Ti wire to small junction box
Hybrid • System is powered for 1 to 2
weeks
• 6V to 12 V DC power (small T/R)
• Cables & Power Supplies then removed
• Anodes connected to rebar in JB
• Anodes maintain protection-galvanic (around 1-2mA/m2)
Galvanic Currents-5
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160
Cu
rre
nt
in m
A/m
2 s
tee
l
Time (Hrs)
LIP Galvanic Phase Current Logging - Pile GCurrent per sqm steel
Lower
Upper
Anode Life Calculation• Anode Life Calculation included impressed current &
Galvanic current
• Used average Galvanic Current after 1 month (ie no seasonal effects considered)
• Anode Life in Tidal Zone considerably less than upper zone (REDESIGN LOWER ZONE ANODE ARRANGEMENT?)
Zone Life
(average)
(years)
Range
(Years)
Min Life
Pile Years
Upper 50.3 20.3 - 97.5 L 20.3
Lower 30.4 14.8 – 52.9 A 14.8
Queensland Box Culvert• Precast Box Culvert Conveyor Tunnel
• Significant spalling (Chloride)
• Half Cell Mapping
• Hybrid Anodes to actively corroding zones
Main Roads Queensland
• Cairns Box Culverts with significant Spalling• Corromap Half Cell Survey• Hybrid Anodes to actively corroding areas• Silane coatings in sound concrete areas
Princes Wharf . Repair Project Nov 2013-Mar 2014 • Continuity Established in Hydro Holes
• Hybrid Anodes Installed (low voltage )
• Corroded Strand Cut Out
• Concrete Repair (no strand replacement)
• Carbon Fibre Laminates to Beam Soffit
Sylvania Waters BridgesRepair System Selection• Time related repair costs were evaluated (30 years)
• Repeated Patch repairs most economical initially, but most costly over 30 years
• ICCP Relatively costly install, with high annual monitoring & maintenance costs
• Hybrid CP
• Reduced installation costs compared to ICCP
• Reduced Monitoring & Maintenance compared to ICCP
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
$K
Years
Sylvania Waters BridgesForecast Cost vs Repair Type over 30 years
Patch Repair ICCP Hybrid CP
Hybrid CP DesignHybrid CP designed to protect:
• Pile Wall (Top metre)
• Capping Beams entire length
• Soffit Slabs ( Selected locations actively corroding)
Hybrid CP Design• Typical design for Capping Beams & Top of Pile Walls
• Capping Beam, 2 anodes high at 350mm spacing
• Pile wall, 9 anodes at 300mm spacing
• 1 Junction Box
Repair Phase
• Tender to Licensed Hybrid CP contractors
• Awarded February 2014 (Marine & Civil)
• 2 Bridges at a time
• Access by hung platforms
• QA by Infracorr
Installation Hybrid CP• Concrete Removal by Small Jackhammers
• Capping Beam large scale rebar repair
• Anode holes drilled with percussive drills
Repair & Installation
• Some sections of Capping Beams severely deteriorated
• Anode Installation prior to final gunite mortar application
• Soffit spalling breakout required in some areas
• Bulk of soffit anodes installed into sound concrete
Hybrid CP Based Repair• Repair works from March–November 2014
• 2 Bridges at a time (around 3 months each bridge)
• Junction Box only visible sign of CP installation
Finished view of a completed bridge
Junction Box is only visible Hybrid CP component.
Sylvania Waters Bridges Repair• Hybrid CP Based repair selected
• Most economical option over 30 years
• 30 Year design life (likely 50 plus)
• All Seawall panels, capping beams & selected soffits protected
Sylvania Waters BridgesConclusion• Always Investigate to determine extent of corrosion, Not just extent of
spalling• Get in early to maximize prevention options (Coatings)• Consider the lifetime required for the structure repairs• Choose repair options based on most economical treatment for LIFE
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