The Client's Perspective Edwin Kruger Presented by: Bridge Network - PowerPoint PPT Presentation

The Client's Perspective Edwin Kruger Presented by: Bridge Network Manager SANRAL

The Dilemma Clients Face – a bit of background • The fact remains that durability problems generally take years to manifest. Then the severity of the perceived failure may vary greatly. • It is generally accepted that the design life for structures such as bridges is between 50 and 100 years. However one must look critically what this means. The reasons to replace or rehabilitate of structures when they reach design life varies greatly. Sometimes way before design life is reached some rehabilitation or maintenance will be required. • 1. Become obsolete • 2. Deteriorate too potential collapse or collapse due to lack of maintenance • 3. Not all failures of concrete structures can be attributed o lack of durability.

We are all fascinated by the dramatic but the world soon moves on. Genoa Bridge Opened on 4 September 1967 – Designed by Riccardo Morandi

Dramatic collapses do sometimes and the blame game starts. Here durability of concrete and Collapsed 14 August 2018 after just under 61 years (43 people died) long term properties played itself out to catastrophic results. Many factors contributed including: 1 Design 2 Concrete deterioration 3 Steel corrosion 4 Lack redundancy 5 Lack of timely maintenance and retrofitting 6 No single factor normally leads to collapses especially of they occur after a considerable period of time.

ON BBC News Yesterday – One year since collapse

Another collapse – N3 Geldenhuis Pedestrian Bridge Collapsed early morning on 9 August 2017 (Public Holiday) Closed whole of N3 N3 Opened again at Midnight Cause?? Nothing to do with durability. Not all collapses due to durability. Virtually no carbonation. Cover adequate and strengths 60MPa

Cause of Geldenhuis Pedestrian Bridge Collapse A coil of steel coming of a transporter hitting pier at about 92km/hr. 18 ton. Freak accident with low probability of reoccurrence.

PE Bridges 2004 (Burman Drive)

Demolished deck but piers were retained Piers subjected to impressed current chloride extraction and barrier coated. New deck and repaired piers. We probably need to go back and check chlorides Bridge is abut 75m from shore break. On one bridge used Stainless steel rebar for the repair of pier. Chloride attack is much more serious than pure carbonation.

Why emphasis on durability? Koelenberg Culvert Chlorides everwhere! Carbonation? Combination!

Some structures built since durability specification introduced OLIFANTS RIVER BRIDGE How long will this last? 100 plus year I hope.

Mount Edgecombe Interchange! Full durability Specification.

All starts with specifications • You only get what you specify and nothing more. Sometimes less • The tradition worldwide was to specify strength but the move towards durability testing is accelerating. • Incorrect assumption is Higher Strength = Higher Durability. This perception still exists today • SANRAL has experience of using “Durability Concrete” or “W Concrete” for the past 12 years. • The most critical parameter to check is cover to rebar yet this is the most neglected area of research. It seems so obvious yet 95% of problems are due to reduced cover. If your specification does not allow you to check cover after the fact then the problem of lack of cover will continue. • Penalties and guidance on what to accept and what not to accept is needed • Good mix design for both durability and strength is the basics. Note durability first and then strength! Even low strength concrete can have good durability properties.

What was said in 2007. What has changed?

SANRAL AND COTO SPECIFICATIONS • Draft COTO specifications to be published soon. Workshopped thoroughly over a period of 3 years.

SANRAL AND COTO SPECIFICATIONS W becomes D Concrete Experience has now shown that specifying durability concrete does not add to the price

Mtentu Bridge – Concrete quality is paramount to ensure long term durability?

The future generations wellbeing are in our hands Must not become Clients, Consultants and Contractors need to look long term to leave a positive legacy

THANK YOU Questions?