“Remediation of Half Joint Structures:

Stangmore East & West Bridges”

COLAS Papers Competition 2011

By Robert Devenney

Overview

•General Arrangement of a Half Joint Structure

•Amey’s Brief

•Scope of Special Inspection Works

•Refurbishment works

•Conclusions

•Questions

Robert Devenney

What is a Half Joint Bridge?

Durability Concerns

Prestressed Beam Prestressed Beam

Crosshead Beam

Bearing Bearing

A lot of water is trapped behind the

bearings leaving a high concentration of

chlorides above the crosshead beam rib

Chlorides make their way through weak areas

such as areas with cracks, poor compaction and

low cover

Some water makes its

way along the

crosshead beam nib and

down the half-joint to the

crosshead beam soffit

Water containing chlorides leaks from the road

through failed bridge deck joints and down through

the half-joint

Durability Concerns

What happens if durability is ignored?

How is Amey Involved?

•Joint venture contract

•Worth £250 million

•Design and Build

•Maintenance/Operation period

DBFO Package 2 Chart

Overseeing Organisation

Public Sector

Contract Area

A1

A4 M1

Standards and Policies relating to

Half Joint Structures

•Historic Design

•Moratorium (DfT)

•BA and BD 57

•IAN 53/04

•DEM 71/04

Special InspectionScope of Special Inspection:

1.Visual Inspection

2.Dust Sampling for chloride analysis

3.Half-cell survey

4.Resistivity readings

Visual Inspection

The visual inspection observed:

•Water Leakage with leachate

•Reinforcement corrosion

•Cracking with rust staining

•Spalling and delamination

Hatched area shows defective concrete

observed during the Visual Inspection

Dust Sampling

•Two dust samples at three locations on

each crosshead

•High chloride contents (BA35/90)

Half-cell / Resistivity

•High negative potentials

•Low Resistivity readings

Refurbishment Work

•Replace deck joints

•Concrete Repair

•Cathodic Protection

Deck Joints

Existing APJ replaced with Buried Joints

Concrete Repair

Hydro demolitionGuniting

Cathodic Protection

Discrete Anodes

Conclusion

•Safety Critical Factors

•Primary Source Permitting chloride

ingress

•Primary economical factors

References•Amey Consulting, “Further Special Inspection of

Stangmore East and West bridges” 2011

•http://www.laganconstruction.com/ - Accessed 01/02/2011

•“Commission of Inquiry into the collapse of a portion of the

de la Concorde Overpass” 2007

•Stangmore East Bridge Maintenance Manual

•Stangmore West Bridge Maintenance Manual

•BA and BD 57 (www.standardsforhighways.com.uk) and

IAN 53/04

•BRE Information Paper IP 21/86

•BA 35/90 (www.standardsforhighways.co.uk )

•ASTM C876-80

•BS1881:Part 201:1986

Questions

Fe Fe2+ + 2e -

Fe2+ + 2Cl- FeCl2

2Fe(OH)2 + 1/2O2Fe2O3 + 2H2O

1/2O2 + H2O + 2e - 2OH-

FeCl2 + 2OH- Fe(OH)2 + 2Cl-

2OH-

Fe3O4

γFe2O3

Fe3O4

γFe2O3

Anode

2e -

Cathode

Corrosion Cell in Concrete