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This report presents an overview of performance based testing methodology for concrete durability and work currently underway jointly at Queens University Belfast and Heriot Watt University, Edinburgh, to undertake this research under a EPSRC funded project (EP/G02152X/1).
EN206-1 superseded BS 5328 on 1st December 2003 and allows designers and producers to use a wide range of cements and aggregate types for a variety of exposure conditions. In this new standard, the durability of concrete is specified in terms of the constituent materials of concrete, properties of fresh and hardened concrete, limitations for concrete composition, specification of concrete, delivery of fresh concrete, production control procedures, conformity criteria and evaluation of conformity and verification of these properties. Within this, six basic forms of exposure is also specified, namely XO (no risk of corrosion), XC (Corrosion induced by carbonation), XF (Freeze / thaw attack), XS (Corrosion induced by chlorides from seawater), XD (Corrosion induced by chlorides other than from seawater) and XA (Chemical attack).
According to EN206-1, the performance method adopted should be based on satisfactory experience with local practices in local environments from data obtained from an established performance test method for the relevant mechanism, or using appropriate proven predictive models. Therefore, the methods that may be used include those methods based on:-
· long-term experience of local materials and practices and on detailed knowledge of the local environment.
· approved and proven tests that are representative of actual conditions and have approved performance criteria.
· analytical models that have been calibrated against test data representative of actual conditions in practice. The concrete composition and the constituent materials should be closely defined to enable the level of performance to be maintained.
In order to determine the best methods for assessing concrete durability for performance, it is important to review those methods which have been developed and used in Queens University Belfast and Heriot Watt University to test for permeability, diffusion and absorption as well as electrical methods used to assess if the performance criteria have been achieved in structures using non-destructive testing methods.
Prior to specifying durability performance testing methods, a review of previous projects where limits on permeability, diffusion, electrical resistivity etc, are presented along with the various durability tests used to assess these limits. The examples given are from a number of projects in the UK, Ireland and Europe of varying complexity and size. Due to the relatively small number of such examples in the UK and Ireland, the need for the research presented here is further justified.
The proposed experimental work for the EPSRC project is presented which includes a breakdown of the concrete samples, tests and details of a new marine exposure site on the Northwest coast of Ireland.
Based on the findings of this experimental work and the numerical calibration using the ClinConc model, development of a methodology for testing the concrete durability to assess the performance limits set will be determined. Through this work, the performance methods adopted will satisfy the EN206-1 guidelines above.
Holmes, N., Basheer, P., Nanukuttan, S., Basheer, L.: Performance-based Testing Methodology for Concret Durability. RILEM TC-PSC Meeting, Toulouse, France, June 5th, 2009.