Transcript Wexford Bridge Group 17.ppt

Wexford Bridge
Chloride Ingress
Group 17
The Bridge
• Originally Constructed in 1959
• Seven Spanned Prestressed Concrete
Balance Bridge
• Spanned 383m
What Went Wrong?
• Excessive Chloride Ions in Concrete
• Serious Corrosion in Steel Reinforcement
and Prestress Anchors
• Damage was Irreparable
The Mechanism of Chloride Ingress
• It Is a Two-Phase Process
• Phase One : The Chloride Is Transported
Into The Concrete
• Phase Two : The Corrosion Process
The Transport Process
• Due To Ion Transport Within Concrete
• Water Diffuses Quicker Than Chloride
• Causing a Slow Accumulation Of Chloride
Ions
The Corrosion Process
• The Chloride Destroyed The Passivity of
The Steel Causing It To Corrode
• This Is Called ‘Pitting Corrosion’
• Causes Significant Mechanical Stress In
The Steel
The Solution
• NO SOLUTION!
• Unfortunately Wexford Bridge Had To Be
Demolished
• Replaced By New Bridge In 1997
• Continuous Steel Girder Deck With a Composite
Concrete Slab
How To Prevent Chloride Ingress In
Your Bridge
• Use a Hydrophobic Surface Treatment
• Introduce Pozzolanic Binders Capable Of
Immobilizing Free Chlorides
• Don’t Build In Wexford
The Replacement Bridge
• Continuous Steel Girder Deck With a
Composite Concrete Slab
• Corrosion Inhibitors Were Added
• Steel Was Painted To a 20 Year Marine
Specification
The New Bridge