The Building Research Establishment (BRE) has recently revised Special Digest 1 “Concrete in aggressive ground”. This new edition (SD1: 2005), funded by The Concrete Centre, was published as a single volume in June, following the completion of a four year research programme on combating the thaumasite form of sulphate attack (TSA) . There are two key changes to the procedure for assessing the ground;
1. The limits of the design sulphate classes based upon 2:1 water/soil extract tests on soil have been reduced to bring sulphate classifications based on 2:1 water/soil extract tests and on groundwater into parity. This will result in some sites being rated as more aggressive to concrete than hitherto.
2. High magnesium levels are no longer taken into account for natural ground.
There are five key changes to the procedure for the specification of concrete;
1. The recommended maximum water/cement ratios and the minimum cement contents have been revised.
2. A new classification for cements and blended cements has been introduced to harmonise with European standards.
3. The recommended concrete quality now caters for the inherent possibility of exposure to an external source of the carbonate required for TSA.
4. The number of additional protective measures to be applied at higher sulphate levels has been reduced, in general by two.
5. The use of the concept ‘intended working life’ replaces that of ‘structural performance level’ to harmonise with European standards.
BRE has told FPS that the take up of its revised SD1 would likely be slow as it has received no funding to mount a promotional campaign. It is relevant to note that currently some of the on-line information services are still offering just the SD1:2003 version, some 6 months after publication of the latest edition. Also, even if professionals do know of the existence of SD1:2005, they may not feel obliged to use it at the moment as the current edition of BS 8500 Concrete refers to SD1:2003. BS 8500 will unlikely to be updated before the latter part of 2006.
It is often not clear which version of SD1 has been used to classify the ground and the concrete.
The members of the Federation of Piling Specialists (FPS) are supplied with numerous site investigation reports and Engineer’s Particular Specifications every working day. Currently it is often not clear in these which version of SD1 has been used to classify the ground and the concrete. It is the exception when clear reference is made to say SD1: 2005.
FPS requests that in future all site investigation reports and Particular Specifications make clear reference to SD1: 2005. Our Clients can then be confident that piling concrete is provided in accordance with the latest requirements by eliminating the potential for misunderstanding to enter into the specification process.
Grout is a different material to concrete and SD1:2005 is only applicable for concrete.
In addition, FPS also requests that where the foundation solution may comprise minipiles, ground anchors, soil nails, grouting, base or shaft grouted piles, permanent sleeves to piles, or cross-hole sonic logging of piles, i.e. any case where grout is likely to be used either in lieu of, or in addition to, concrete, that reference is not made to SD1: 2005 for these options. This is due to the fact that grout is a different material to concrete and SD1: 2005 is only applicable for concrete.
Technical Development Manager Stent Foundations Ltd
Chair Technical Committee
Federation of Piling Specialists