Concrete Standards update

Concrete, Aug 2006 by Harrison, Tom

Surprising as it may seem, the European concrete Standard EN 206-1(1) was published six years ago. In November 2005 it was adopted for a further five years on the understanding that by 2010 there would be a full review. At this review a number of important and difficult issues need to be addressed and it will take time to reach a consensus.

Consequently, the European Concrete Committee, CEN TCl 04/SC1, has already set up a coordinating committee and instigated a number of preliminary steps including:

* a survey of national provisions used with EN 206-1 (this will be published as a CEN Report in 2006)

* standardisation of five test methods for self-compacting concrete

* standardisation of performance tests for concrete (chloride resistance and carbonation resistance)

* developing a specification for self-compacting concrete.

Key areas for attention

While the whole of EN 206-1 needs reviewing, it is already established that the key areas that need addressing are:

a) self-compacting concrete

b) durability

c) use of additions including the use of ground-granulated blastfurnace slag

d) conformity (to conform to Guidance Paper M(2) and Product Standards and Conformity Assessment Guideline131)

e) Essential Requirement 3: Hygiene, health and the environment.

The coordinating committee will consider if there is a realistic chance of making further progress on these topics by 2010. In my view the answer will be 'yes' to a), c) and d) and 'no' to b) and e).

At present, EN 206-1 leaves durability to national provisions, although it does provide some 'recommended' values for CEMI cement concrete. The survey of national provisions has also shown that, for a given exposure class, the requirements for the concrete are not the same (see Table 1 ). This is not surprising as, for example, cyclic wet and dry is not the same in Spain, the Netherlands and Finland. There are technically justifiable differences in requirements and so trying to agree a common set of concrete requirements for the EN 206-1(1) exposure classes is doomed to failure.

While the European Commission wants CEN Technical Committees to address Essential Requirement 3 in a more comprehensive way, it is unlikely that the procedures on how this should be done will be agreed by 2010. After years of testing in the Netherlands and elsewhere, there is no evidence that concrete leaches significant amounts of regulated, dangerous substances into the environment, but getting concrete onto an 'accepted without testing list' will be a long and difficult process. More progress was being made with concrete in contact with drinking water, but it has been realised recently that there was no legal basis for the concept being worked on and setting this up (or abandoning the European Acceptance Scheme) will take some time to resolve.

Revisions

BS 8500(4) is in its final stages of a revision; public comment has been taken into account and it is expected that the revised BS 8500 will be published before the end of 2006. BS 8500(4) will be aligned with the recommendation in BRE SD1(5) for concrete to resist aggressive ground, and the provisions to resist chloride attack have been refined and extended. There are several other changes that reflect experience of use of the 2002 version and the net result is a Standard that is simpler to use.

prEN 13791 : Assessment ofin-situ compressive strength in structures and precast concrete elements is out for a combined comment/vote. If the vote is positive, BSI will revise BS 6089(6) and turn it into a complementary Standard.

Reviews

All the European concrete test methods are undergoing a five-year review and many will have minor changes. There are some issues still to be resolved, including the proposal to have different classes of compressive test machines. Having sorted out the problems of test machines in the 1960s, the UK is very reluctant to accept a lowering of standards. A possible solution is to have classes and a national choice on what class is permitted.

Concluding remarks

In a new development, CEN has started work on standardising performancerelated tests for corrosion of reinforcement. This is linked to the fib model code on service life design (durability design)'71. This model code lays the philosophy for the most fundamental change to the way in which durability is specified since water/cement ratio. In the future, this will be the way to specify concrete, but it is 10-15 years away from realisation.

References:

1. EUROPEAN COMMITTEE FOR STANDARDISATION. EN 206-1 : Concrete - Part 1: Specification, performance, production and conformity. 2000.

2. EUROPEAN COMMISSION. Conformity assessment under the CPD-Initial type-testing end factory production control, Guidance Paper M, April 2005.

3. EUROPEAN COMMITTEE FOR STANDARDISATION. BT N 6287: Product standards and conformity assessment guideline. 2000.

4. BRITISH STANDARDS INSTITUTION. BS 8500: Concrete. Complementary British Standard to BS EN 206-1. Method of specifying and guidance tor the specifier, 2002.

5. BUILDING RESEARCH ESTABLISHMENT. Special Digest 1: Concrete In aggressive ground. Watford, 2005.