Wellington Arch, Hyde park, London
Steel Pillar Insert, Gloucester Cathedral
Barton Seagrave Orangery
Downside Abbey Rose Window
St. Aldelm's Church, Somerset
St. Catherine's Church, Batheaston
The corrosion of embedded metalwork is becoming an increasing problem in our historic buildings and monuments. Even if the rate of corrosion is relatively low, in the long term it results in the fracturing of the surrounding stones and in severe cases the loss of structural integrity. This is due to the incredible expansion forces created by corrosion; the volume ratio between iron and rust can be as high as 1:7.
Architects have, in the past, attempted to remove as much of the original iron fittings as possible and replace them with more corrosion resistant materials. The conservation policy now followed in the UK for heritage buildings is that of ‘minimum intervention’ with the intention of retaining as much of the original structure as possible.
Cathodic protection (CP) is a non-destructive method of controlling the corrosion of iron and steel embedded in stone, masonry or brick. It is the application of a small negative charge to the embedded metalwork, and is being used increasingly to control corrosion within historic buildings. In recent years, Rowan Technologies have used CP to protect concrete from steel reinforcement corrosion.
There are two types of CP system:
Sacrificial Anode Cathodic Protection (SACP): SACP systems use a sacrificial anode (a large piece of zinc or magnesium buried in the ground) which corrodes preferentially to the embedded metalwork. The sacrificial anode is placed in close proximity to the corroding metalwork and is electrically connected to it. As the sacrificial anode corrodes, it generates a current that passes through the building material to provide protection to the embedded metalwork.
Impressed Current Cathodic Protection (ICCP): ICCP systems require an external power supply, normally using mains powered electronics to provide the DC current to the iron or steel to be protected.
One of CP’s main advantages is that it provides corrosion control without changing the immediate physical environment; there may still be now, or in the future, damp stone, masonry or concrete adjacent to the metal which would previously have allowed corrosion to continue. Cathodic protection provides the electrochemical conditions to control this corrosion process.
The application of cathodic protection to historic structures is now becoming widely accepted as the process is fully reversible, cost effective and is in accordance with modern day conservation principles.
Rowan Technologies are experts in the application of cathodic protection to historic buildings and monuments, and have installations in many well-known and listed structures.
Further Reading
Installed Cathodic Protection Systems
(PDF File 5.4 MBytes)
Cathodic Protection of Iron and Steel, Recent Applications to Heritage Buildings
D.M.Farrell, K Davies, I. McCaig, Building Conservation Directory 2001.
(PDF File 2.6 MBytes)
D.M.Farrell, K.Davies, APT Symposium, New York 2004.
(PDF File 2.9 MBytes)
Cathodic Protection of Tie Bars and Ring Beams in Church Towers
C. Hunt and D.M Farrell, May 2010
(PDF File 2.1 MBytes)
