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Concrete In Australia : December 2014
Concrete in Australia Vol 40 No 4 33 Australian durability requirements with international requirements. Hence Z7/02 provides different exposure classes for each type of exposure and applies them to concrete in all structure types. The ISO 16204 exposure classes are adopted where possible but the ISO format for exposure classes is adopted in all cases. Different projects will have different design life and reliability requirements and this also needs to be factored into the durability design. In some cases the different Australian Standards may have incorporated these aspects into the exposure classifications and this may account for why the exposures classes are different in different Australian Standards. However, it is possible to allow for different life and reliability requirements for individual elements rather than forcing every project of a certain type to adopt the same life and reliability level. For example, some elements of a marine structure may be highly critical and require a high reliability associated with an ultimate limit state (e.g. reliability around 4) while others may have virtually no failure consequence should they deteriorate and have a much lower reliability requirements (e.g . as low as 0.5). The same structure may only be required for 20 years or 100 years. Further details on design life and reliability can be found in CIA’s Z7/01 – Durability Planning. The base for the European classification was the fib Model Code 2010 and EN201 as these have had extensive recent discussion from participants from all over the world. Where a departure from these documents is used in Z7/02 the reason for the departure is given. The principal reason for departures is that in Australia a broader range of exposures in some exposure types has been recognised. The exposure classes discussed in Z7/02 are the criteria against which deemed to comply provisions in Z7/03 are defined. Hence Z7/02 can be considered a commentary on the exposures used in Z7/03. Whilst exposure and the access of moisture has an influence on deterioration associated with items such as Alkali Silica Reaction, Delayed Ettringite Formation, Shrinkage and other materials related aspects the control is more related to materials design and hence specific exposure classes have not been developed for them. Exposure classes include: • XC – atmospheric carbonation inducing • XS – seawater exposure • XD – chlorides other than seawater • XA – aggressive chemicals in ground exposure • XF – freeze thaw • XG – exposure to liquids, vapours and gases • XM – water migration • XX – metals in the cover zone • XR – abrasion • XI – moisture and ASR • XH – temperature and delayed ettringite formation. A common criticism of the first version was that there was no guide to how the exposure classes in Z7/02 related to exposure classes in Australian Standards. Appendices have now been added that describe this. 4.0 Z7/03 DURABILITY – DEEMED TO COMPLY REQUIREMENTS At the commencement of the task groups it was agreed that deemed to comply requirements would be prepared after the other Z7 recommended practices so that it could be based on them. Hence at the time of going to press attention is only just refocussing on Z7/03. The group, chaired by Frank Papworth, set the following as the approach to be followed: • Provide requirements for each exposure class (e.g. chloride, sulphate, acid, atmospheric gases). • Requirements linked to cement systems including GP cement, fly ash, slag and silica fume). • Provide guidance for galvanised and stainless steel reinforcement, prestressing and steel fibres. • Give recommendations for effect of coatings on other durability requirements. • Define significance of curing methods on other durability requirements. • Provide advice based on minimum cover. • Incorporate reliability as a factor in determining durability requirements. Figure 1: Reliability based on full probability analysis for a coastal structure using a 0.45 w/c ratio and 45 mm minimum cover. Using GP Cement Using Fly Ash 31-37 - Papworth.indd 33 31-37 - Papworth.indd 33 21/10/14 12:29 PM 21/10/14 12:29 PM