Civil Engineering Reference
In-Depth Information
• Acoustic emission
• Acceleration/vibration.
The main techniques for corrosion or concrete parameter monitoring are:
• Concrete resistivity
• Reference electrode potential
• Corrosion rate
• Linear polarisation resistance
• Galvanic current
• Relative humidity probes
• Temperature probes.
The reasons for carrying out monitoring are:
•
Early warning of significant deterioration (limit state being reached)
•
Input into planned maintenance
•
Monitoring the effectiveness of repairs or protective measures being
installed
•
Development of a whole-life deterioration and costing model for a
structure or group of structures.
7.1 Regular surveys to monitor corrosion
This has been done on motorway bridges in the UK where corrosion caused
by de-icing salt leakage through expansion joints onto substructures is an
acknowledged problem. A major cost is access on each survey as well as
the manpower. The progress in chloride ingress and reference electrode
potentials can be monitored along with a delamination survey.
Broomfield (2000) carried out regular surveys using linear polarisation
resistance (LPR) on some reinforced concrete support pillars which had
calcium chloride cast in as a set accelerator. These had been repaired with
vapour phase corrosion inhibitors applied. Measurements from 1995 to 1999
showed the increase in the corrosion rate in treated and untreated control
areas, with the corrosion rate peaking at around 0.5 to 1.0 μA/cm
2
(equivalent
to a metal loss of 5 to 10 μm per year) with cracking seen approximately one
year later. This demonstrated that the inhibitor applied was insufficient to deal
with the chloride content of the structures. It also showed that a factor of two
difference in corrosion rate between the treated and untreated areas made no
significant difference to the rate and extent of cracking.
7.2 Permanent corrosion monitoring systems
A number of the techniques described in
Chapter 1
are suitable for
embedding in concrete for permanent monitoring. The main requirements
