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Durability Design for Concrete Immersed in Seawater or Brine.

Paper Number: 15
Author/s: F.Papworth
Organisation: BCRC, Perth, Australia


It is well recognised that concrete fully immersed in seawater does not typically suffer from damage induced by reinforcement corrosion during 100 year design lives. Hence, Australian Codes have much lower prescriptive requirements for immersed concrete than for concrete in the splash zone. Up until recently the high performance of immersed concrete was considered to be due to oxygen starvation of the cathode limiting the corrosion rate. However Andrade has shown that corrosion occurs even when there is no oxygen available if the steel is not passivated. This casts doubt on the oxygen availability theory.

In a recent study on corrosion of cracked piles in high chloride groundwater the residual life of the piles as assessed based on chloride ingress to cause corrosion activation using the chloride ingress model in fib Model Code 2020. The assessment included:
a)The activation level of reinforcement in saturated concrete
b) The surface chloride levels expected
c)The self-healing period of cracks of different widths
d) The diffusion coefficient of cracked and self-healed cracked concrete
e)The aging coefficient for immersed concrete

The paper provides a review of Andrade’s research, and that of others, to give background to the expected deterioration process in immersed situation. It explains the process of calculating a residual design life. The analysis was not taken to be precise but rather to give an indication as to whether there was any cause for concern.