Concrete Durability 

Design for durability is a critical part of the design of many concrete structures. Section 3 of the New Zealand Concrete Structures Standard – NZS 3101: 2006 covers the basic requirements for designs which meet the requirements of the Building Code, but this Standard does not cover severe or unusual corrosive conditions.

Golden Bay Cement can offer specialist assistance to customers, or specifiers using GBC cement, or Microsilica 600, who wish to understand the effects of the environment on their structure and develop alternative solutions for a more economical durability design.

The common durability issues facing the New Zealand construction industry are:

• Chloride ion attack, in marine environments or due to wind-blown salt
• Carbonation due to atmospheric carbon dioxide
• Chemical attack – typically from sulfates and sulfides
• Abrasion
• Freeze-thaw resistance in cool-stores and blast freezers.

Golden Bay Cement can assist with economical solutions for these applications.

For optimum durability in marine environments, GBC recommends the use of Self-compacting concrete containing a triple-blend cementitious binder consisting of Golden Bay’s GP or HE Cement, Huntly Fly Ash and Microsilica 600. This mix has extremely low sorptivity (essential for long-term durability of concrete in the splash zone); low chloride ion permeability and high electrical resistivity.

To understand the mechanisms involved in Marine Durability:

1. Concrete Sorptivity determines the thickness of cover concrete where the rapid absorption of salt water will hold chlorides in contact with the structure.
2. Chloride Ion Permeability determines how long chloride ions, held in that surface layer will take to penetrate to the level of the reinforcing steel, and reach the critical level required to initiate bar corrosion.
3. Electrical Resistivity of the hardened concrete determines how long the propagation phase of the corrosion mechanism will take to cause structurally significant effects.

Golden Bay Cement has access to durability modeling software which can calculate the design life of marine structures. GBC can also provide specialist durability planning advice for major projects and undertake durability testing. 

Making use of specialist durability knowledge through GBC can provide a competitive advantage, as demonstrated on a recent major bridge project.

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