Corrosion of steel reinforcement in concrete is the most common problem affecting the durability of reinforced concrete structures. With much of NZs infrastructure located close to the coastline, protection against marine environments is a paramount consideration for the construction industry.
Concrete offers physical and chemical protection to the reinforcing steel. Steel reinforcement in concrete is protected against corrosion by passivation of the surface due to the high alkalinity of concrete. Chloride resistance depends on:
To limit the level of chloride within the concrete and the reinforced or prestressed structure, NZS3101:2006 restricts acid soluble chloride of any reinforced concrete exposed to moisture or chloride to 0.8 kg/m3.
In most cases, excessive amounts of chloride in concrete originate from external sources. This means the transfer of chlorides into concrete occurs through various mechanisms that depend on exposure.
A Chloride diffusion coefficient is a measure of the resistance of concrete to chloride diffusion. The diffusion coefficient and concrete cover combine to measure the overall resistance of concrete to chloride ingress.
They also enable the prediction of service life, being the most direct means of specifying chloride penetration resistance. The most common test method utilised is NordTest Build 443.
Diffusion coefficients from a short-term exposure period (28 or 56 days) are a practical specification used for major infrastructure projects – especially when there is adequate lead time for the concrete mix design to be developed and tested.
Diffusion coefficients are good indicators of longer-term chloride resistance.
The most aggressive exposure classifications C and B2 are based on chloride ingress in the exposure conditions:
NZS 3101:2006 has used prescriptive requirements in the durability section, detailing Cement Binder Type, Minimum Binder Content, Maximum Water/Cement Ratio, Concrete Grade, Minimum Concrete Cover and the Minimum Curing Period.
Golden Bay Cement products are durable solutions to combating marine environments.