Factors Influencing Reinforced Concrete Durability Design in New Zealand’s Marine Environment

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Title: Factors Influencing Reinforced Concrete Durability Design in New Zealand’s Marine Environment

Author(s): D. H. Chisolm

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 797-822

Keywords: Absorption; blended cements; chlorides; compressive strength; diffusion; durability; exposure; marine atmospheres; permeability.

Date: 7/1/1997

Abstract:
Changes to the New Zealand concrete design standard incorporate requirements for durability, based on a minimum design life of 50 years for structural elements as required under the New Zealand Building Code. Many New Zealand cities are near the coastline. and concrete quality and reinforcement covers are designed to control chloride induced reinforcing steel corrosion. Four exposure classifications in the Standard require increasing protection from chlorides based on increasing exposure to a marine environment. The paper outlines how these exposure classifications were established. The concrete structures standard specifies minimum concrete strength and reinforcement cover based on the use of normal portland cement concretes for each classification. The enhanced durability performance of some blended cement concretes is recognized along with the role of concrete coatings, and alternative combinations are permitted provided the designer establishes equivalent performance. A BRANZ research program is targetted towards developing an assessment methodology in the laboratory for evaluating the durability performance of blended cement concretes against normal portland cement concretes. The first stage of a laboratory program evaluating the performance of normal Portland, slag, silica fume and flyash cement blend concretes is reported. Evaluation methods used included absorption, rapid chloride ion penetration, chloride diffusion and chloride ponding. Further research using site surveys of concrete structures in the near coastal zones is planned.