WILL YOU STILL NEED ME.. WHEN I’M SIXTY-FOUR? A STORY OF AGEING BRIDGES Dean Ferguson, General Manager, Infracorr Consulting Ian Godson, Director and Principal Engineer, Infracorr Consulting Scott Gleason, Materials Engineer, Infracorr Consulting INFRACORR COMPANY OVERVIEW Investigation and Condition Assessment Commissioning Design and and Ongoing Specification of Monitoring Repair Systems Infracorr Consulting Pty Ltd Construction Quality Durability Assurance Design Specialist Consultants in the Repair and Preservation of Infrastructure 2 BENEFITS OF EARLY INVESTIGATION OF REINFORCED CONCRETE STRUCTURES Level 1 & 2 bridge inspections provide only visual defects & cannot detect the early stages of reinforcement corrosion. Technical investigations provide: • Prediction of time to corrosion • Early detection of active corrosion • Ingress depth of contaminants (Carbonation & Chloride) • Early detection of ASR (Alkali, Aggregate Reaction) Early detection enables preventative strategies to be adopted providing significant savings 3 TYPICAL CONCRETE INVESTIGATION • Delamination survey • Chloride, carbonation, cement content • Resistivity testing • Electrical Continuity • Half cell potential mapping • Corrosion rate (time to spalling 4 EARLY INTERVENTION HOPKINS RIVER BRIDGE – OVERVIEW • 160 metre long coastal bridge • Prestressed trough beams, precast piles, insitu headstocks • Age 18 years • Visual Condition – Excellent Prestressed beams ~1.2m 5 above high water level HOPKINS RIVER BRIDGE One day investigation to prestressed beams found: • 30mm designed cover to ligatures (40mm to strand) • Critical chloride to depth of 25 to 28mm • No active corrosion, low corrosion rates (passive) • Predicted corrosion of ligatures and strand in 2-5 years 6 Prestressed trough beams had 30mm cover PRESTRESSED BEAMS IN MARINE CONDITIONS Prestressed “I” beams incorporating high strength strands • Strands corrode & pit quickly once critical chloride levels reached • Rapid brittle failure of strands & beams • Patch repair not possible due to stress & brittle strands • Strands cannot be welded or repaired • Can utilize CP with difficultly (Hydrogen embrittlement, lack of continuity) HOPKINS RIVER BRIDGE SOLUTION • Immediate treatment with chloride barrier coatings (silane) • Predicted delay in chloride activated corrosion, 35 – 40 years • Project budget $120,000 • If delayed ~5 years, CP based repair ~$2 million 8 MID–STAGE INTERVENTION TRAFALGAR PARK FOOTBRIDGE – OVERVIEW • Footbridge at Nelson. South Island New Zealand • Constructed 1996 (22 years old) • 63m single span, arch bridge • 2 Reinforced concrete arches, connected by 6 cross beams • Supported by reinforced concrete pile caps 9 TRAFALGAR PARK FOOTBRIDGE Chloride instigated corrosion in tidal splash areas including: • Lower arches • Pile caps • Lower two cross tie beams 10 TRAFALGAR PARK FOOTBRIDGE SOLUTION 50 Year Life extension design Targeted Galvanic anodes utilizing Hybrid CP • Pile Caps, lower arches & cross beams Coatings to atmospheric structure to prevent chloride ingress Hybrid CP anodes to tidal splash elements 11 LATE–STAGE INTERVENTION MORELL BRIDGE – OVERVIEW Arch bridge over the Yarra River in Melbourne • Constructed 1896 (Heritage listed) • First reinforced concrete bridge in Victoria • Built by Sir John Monash’s company (Monash & Anderson) • 99 metres long (3 x 33m spans) • 0.5m thick arches • Earth fill bridge (sandy clay) 12 MORELL BRIDGE Condition in 1994 • Spalling to ~10% of soffits • Carbonation past lowest matt of steel • Significant chloride levels • Active corrosion to 100% lower rebar 13 MORELL BRIDGE SOLUTION (1995) • CP through soil anode passes current through soil to lower rebar • Surface based concrete repair • 12 No. impressed current soil anodes • Surface protective coatings • Manual control system • Institute of Engineers Award Soil anodes Soil anodes installed through footpath 14 MORELL BRIDGE SOLUTION • Original repair in 1995 • Damage to cabling in 2017 during landscaping works • Damage repaired and anodes upgraded in 2017 for 30 year + life 15 CURRENT BRIDGE INSPECTION PRACTICES Level 1 and 2 Inspections • Visual only and only identify visible deterioration which impacts on the serviceability of the bridge Level 3 Inspections • Have the capacity to include the type of assessment needed, but are typically only triggered when a Level 1 or 2 Inspection identifies a need. Preliminary bridge inspections are typically undertaken by personnel with experience in bridge structural requirements, but rarely by those with materials durability experience 16 PROPOSED BEST PRACTICE APPROACH Early Stage Preliminary Durability Assessments • Validate design assumptions and allow identification of unexpected deterioration • Preliminary screening of deterioration mechanisms to enable predictive modelling • This design validation can be performed ~10 years after construction (or later) • Base future technical investigation schedule on initial modelling. Preventative Maintenance Approach • Plan to undertake preventative maintenance to greatly reduce the life cycle costs (eg application of coatings) 17 COMPARISON OF REMEDIAL OPTIONS Technique Overview When to Use Relative Cost Coatings Preventative Maintenance. Low. Used to protect a concrete element by preventing Prior to initiation of reinforcement Costs are often associated with providing ingress of aggressive environmental species which corrosion safe access for application. cause deterioration. Cannot stop the deterioration process once reinforcement corrosion initiates. Concrete Repair Mid or late stage. Medium. Effective way of repairing deteriorating concrete. Although high when repeated repairs are However, all contaminated concrete must be required. completely removed. Electrochemical Treatment Mid or late stage. Medium to High. CP options include galvanic CP, ICCP and hybrid CP. Different CP options would be Initial costs for a full CP system can be high, Other electrochemical treatments including chloride selected depending on the while local, targeted application of galvanic extraction and realkalisation can be used. structure and asset owner or hybrid systems can be undertaken requirements as well as the extent economically. of deterioration. Other Structural Repair Late stage. High. Other forms of structural repair, including pile Once structural capacity has or will In addition, these forms of repair can encasement or member replacement (recasting) can be compromised due to require closure of the structure during the be used to reinstate structural capacity. deterioration. works. 18 TAKE AWAY Early Investigation • Many structures in marine environments have critical Chloride to reinforcement by age 10-15 years leading to significant corrosion and spalling by age 25-30 • Early investigation allows preventative strategies to be adopted • Significant reductions in repair works • Considerable cost savings • Reduced disruption & structural weakening Remedial Techniques • Preventative Coatings (Silanes, co-polymer etc) • Cathodic Protection • Many forms of CP (Impressed, Hybrid, Galvanic, water & soil etc) • Combination Systems (eg CP with localized repair & preventative coatings) 19 OPERATING THROUGHOUT AUSTRALASIA.