On 5 March, SANRAL project managers, Edwin Kruger and Ravi Ronny held a seminar on the concrete Repair and protection titled “the good, the bad and the ugly concrete structures.”
Normal design life is 50 or a100 years for a bridge. If a bridge is built for a mine that only has a life of 10 years then durability is not considered a high priority- only coast- and that is a mistake.
Environment is influenced by what is left behind even when a project has served its purpose. Engineers have an ethical duty towards society.
Causes of defects
- Bad initial design and detailing
- Bad construction
- Lack of attention to durability of concrete materials used at time of design and construction
- Accidental damage – over-height vehicles
- Extreme weather or natural events like earthquakes
SANRAL uses a standard tender document for tenders for diagnostic tests depending on the extent of repairs required. Testing could also include for concrete strengths and cover tests.
Rehabilitation
SANRAL developed standard specifications for repair of structures as series 12000 that relates to concrete repairs and is comprehensively detailed. Performance specifications are now the norm for SANRAL in which contractors have to supply performance guarantees.
Concrete protection
Very old concrete showing signs of distress, carbonated or chlorinated concrete needs protection. Coating with a silane penetrant coating and not barrier coatings generally improve this. Barrier concrete must breathe as they provide protection and aesthetics, often have maintenance problems in the long term if not properly fixed.
Lessons Learnt
- Use far less barrier coatings in the future for carbonated concrete
- Use of silanes/ siloxanes instead of barrier coatings in certain applications
- Drawings must be complete before project handover to contractor. Lead times to allow for testing needs to be increased.
- Get guarantees early in contract. If necessary, withhold payment.
- Limited extended life before further repairs to 15 years is now requested to avoid “Rolls Royce” solutions. Client must accept the risk.
Conclusion
- Our defects-based BMS has proved effective in prioritization
- Performance guarantees for products results in a more positive approach
- Emphasis now on durability and not strength only
- The cost of associated items such as traffic accommodation and access contributes a large percentage of repair costs
- Hopefully less future maintenance on newly built structures
- Having performance criteria for asset preservation built into strategic objectives ensures that bridges do get repaired
- Aesthetics is important to the public
Hopefully there will less of this:
And more of these:
To quote from Dr. Konrad Lorenz, the eight deadly sins of a civilized man states that “the beauty of nature and the beauty of the man-made cultural environment are apparently both necessary to maintain man’s mental and physical health.”