Reinforced Concrete in the Marine Environment

If you require further details, please feel free to contact CIA NSW [email protected]  or call 02 9955 1744.  





 

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When

Wednesday, 21 April 2021
6:00 PM - 9:00 PM

Where

Kirribilli Club
11 Harbourview Crescent , Lavender Bay NSW 2060

Overview

This seminar will address key questions to further our understanding of reinforcement corrosion in marine concrete structures. Professor Rob Melcher of The University of Newcastle will examine why we see evidence from actual concrete structures indicating no corrosion loss after 75-85 years in tidal and splash zone conditions. Should we consider whether we need to reappraise conventional ideas associated with ‘chloride-induced’ reinforcement corrosion. It seems existing theory and models don’t predict the onset of chloride-induced reinforcement corrosion very well, particularly when compared with observations for actual concrete structures and practical experience.
 
Warren Green of Vinsi Partners will outline recent field experiences in relation to long-life marine concrete structures. He will explore the reasons why “active corrosion/pit propagation” doesn’t necessarily progress despite there being sufficient chloride at the reinforcement surface. Warren will examine several mechanisms that explain this effect to increase understanding of how to achieve long-life durable structures in chloride environments.
 
Jason Chandler from Boral will discuss various chloride durability test methods together with their limitations and the ongoing research in this area. Boral has embarked on a multi-year program of trials with both conventional and improved cementitious materials and some of their recent findings will be discussed.

Prices

CIA Members $88.00 CIA Retired Members $44.00 CIA Student Members $22.00 Non Members $110.00

Presenters

Professor Robert Melchers
Professor of Civil Engineering - University of Newcastle

Warren Green
Principal Corrosion Engineer - Vinsi Partners

Jason Chandler
National Technical Development Manager - Boral

Topics

Professor Robert Melchers, Professor of Civil Engineering, The University of Newcastle 
Changing our understanding of reinforcement corrosion in marine concrete structures

Existing theory and models do not predict the onset of chloride-induced reinforcement corrosion very well, particularly when compared with observations for actual concrete structures and practical experience. Although high concentrations of chlorides in the concrete next to the reinforcement may initiate some reinforcement corrosion. The severity of corrosion is much related to the size and volume of air voids next to the reinforcement bars. In low permeability concretes corrosion then declines to a relatively low rate. For high quality, well-compacted, very low permeability concretes the early corrosion tends to be negligible and to show only very low or negligible rates of long term corrosion. For such concretes, serious corrosion does not commence until there is extensive loss of concrete calcium hydroxide through leaching to the environment. This is accelerated by the presence of chlorides. Evidence from actual concrete structures support these observations with some showing essentially no corrosion loss even after 75-85 years in tidal and splash zone conditions, usually considered the most aggressive exposures. These various observations and  the related inferences require a re-appraisal of conventional ideas and concepts associated with ‘chloride-induced’ reinforcement corrosion. 


Warren Green, Principal Corrosion Engineer, Vinsi Partners [Newcastle]
Long Life Marine Concrete Structures - Some Recent Field Experiences

Reinforced concrete structures in marine and saline environments can be very durable and may not necessarily suffer significant chloride-induced corrosion of steel reinforcement even when well beyond their design lives. Condition surveys of several reinforced concrete marine structures and coastal bridges up to 100+ years of age have identified chloride levels at reinforcement depth of up to 0.6% by weight concrete (~4% by weight cement) but with no significant reinforcement corrosion propagation occurring (or duly diagnosed as occurring). The reasons for this are contemplated via deliberations on corrosion mechanistic considerations including exploration as to why “active corrosion/pit propagation” does not necessarily progress despite what should be sufficient chloride at the reinforcement surface to result in propagation. It is surmised that several mechanisms may explain this effect including cement chloride binding and adsorption, the presence of a sound portlandite rich layer around reinforcement and the “active corrosion model” and “metastable pitting and pit growth mechanistic considerations”. An understanding of these mechanisms and models results in long-life durable structures in chloride environments with minimal maintenance expenditure (including not having to waste monies on electrochemical treatment technologies) as well as improved assurance of chloride durability in the design of new structures.

Jason Chandler, National Technical Development Manager, Boral
Durability of Concrete in Marine Environments
Concrete durability in marine environments is a complex topic.  By slowing down the rate of chloride ingress in a concrete, the concentration of chlorides at reinforcement depth can be reduced to delay chloride induced corrosion of reinforcing steel and extend the service life of a concrete structure.  However, the commonly used method of including supplementary cementitious materials in the concrete, can lead to an increased carbonation and reduction of pH in the concrete surrounding the reinforcement.  As pH levels of concrete drop, the corrosion of steel is accelerated. Test methods exist to approximate the rates of chloride ingress as well as carbonation but the accelerated nature of the methods themselves may give false security or concern.  Actual test results for a range of different concrete will be presented and discussed, and alterations to test methods proposed.
 
 

Program

5.30pm     Registrations Open
6.00pm     Welcome, Introduction and Presentations
7.45pm     Question Time & Panel Discussion
8.15pm     Networking. Drinks and Light Refreshments.
9.00pm     Close
 

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