Special Digest Third editionConcrete in aggressive groundBRE Construction Division BRE is committed to pro. Download Citation on ResearchGate | BRE report – Concrete in aggressive grounds: An introduction to BRE Special Digest 1 | The codes and standards for. The introduction of the edition of BRE Special DIgest 1 (SP1) provides the guidance on concrete in sulfate-bearing ground. The range of exposure.
|Published (Last):||24 March 2006|
|PDF File Size:||1.38 Mb|
|ePub File Size:||8.55 Mb|
|Price:||Free* [*Free Regsitration Required]|
Because of the rarity of chemical attack attributed to ammonium ions, assessment of ammonium concentration is not specifically included in the scheme presented in this document for assessment of ground aggressive to concrete, or for guidance on specification of chemically resistant concrete.
Table D2 Concrete qualities to resist chemical attack for the general use of in-situ concrete: Oxidisable sulfides OS This is the amount of sulfate that may result from the oxidation of pyrite or similar sulfides in the ground — most likely due to ground disturbance. For all sites, the engineer should consider concrfte impact of a proposed development on the ground and surface water regimes.
Part A Accordingly a new version of Digest was issued in January which drew attention to the risk of TSA in concretes containing internal calcium carbonate and promised further guidance based on ongoing research.
Chemical agents aggressive to concrete that are found only rarely eg ammonium salts should be investigated if their presence is suspected; for example, from past use of the site. Assessing the aggressive chemical environment incorporating March amendment No longer brw but cited in Building Confrete guidance.
Also, the possible damaging effect of high levels of aggressive carbon dioxide are catered for in Part F in the design of specific precast concrete products such as pipeline systems.
Camberley, The Concrete Society, The new limits bring sulfate classification based on 2: This reaction product also has a greater solid volume than the original constituents and in some cases can contribute to degradation bfe the concrete. A salt particularly implicated in this latter mechanism is sodium sulfate which, when subjected to alternate wetting and drying, may itself alternate between anhydrous thenardite Na2SO4 and hydrous mirabilite Na2SO4.
It is calculated as the sum of sulfates already present in the ground, plus those that may result from oxidation of pyrite or similar minerals Section C5. Assessing the aggressive chemical environment C5. In some regions underlain by halite-bearing Mercia Mudstone, it may come from natural brine seepages.
Concrete in Aggressive Ground:3rd edition
The category of a site or individual site location should be provisionally established by desk study Section C4. Note that new limiting values are introduced in SD1: Design guides for common applications incorporating March amendment No longer current but cited in Building Regulations guidance.
The concept of this measure is to consider routes by which aggressive groundwater can reach below-ground concrete and, where necessary, to modify the drainage of the site to minimise contact between the groundwater and concrete. The principal changes as compared with SD1: Design guides for specific precast products.
BRE Group: News
If only one type of sample groundwater or soil was tested, the class determined for this type may be taken as the Design Sulfate Class for the location.
However, in much of the UK there is sufficient calcium carbonate available in the ground eventually to neutralise any sulfuric acid by forming calcium sulfate gypsum.
Appendix C2 on page 36 gives guidance on a more comprehensive site investigation that may be needed for a case of sulfate attack on concrete. The first will provide data on a possible source of external carbonates that can fuel TSA in the absence of carbonate aggregates, while the inclusion of all three will enable an ion balance check to be made to provide an assurance that the principal constituents of the groundwater have been accurately determined.
Want access to British Standards? A list of sponsors and members of the steering group who ber on its preparation is shown on page vi. Care is needed during construction to avoid temporary or permanent situations that increase risks. Intended working life This is the period of time during which the performance of the concrete in the structure concretee be kept at a level compatible with the fulfilment of the performance requirements of the structure, provided it is properly maintained BS EN Assessing the aggressive chemical environment C3 Presence and mobility of groundwater The rate of chemical attack of concrete depends on the concentration of the aggressive ions and the ease with which they can be replenished at the reaction surface in the concrete.
These products are manufactured under rigorous quality control to ensure appropriate mix composition and achieve relatively low concrete permeability.
Ammonium salts are reported to act as cation-exchange compounds, transforming the insoluble calcium in the hardened cement paste into readily soluble calcium salts that are subsequently leached away. In contrast, BS guidance for concrete has integrated the provisions for resistance to chemical attack into the numerous other requirements for practical concrete specification; for example, strength class and consistence, resistance to alkali—silica reaction and chloride content in respect of corrosion of reinforcing steel.
Disturbed ground This is, initially, natural ground that is substantially disturbed; for example, by cutting and filling to terrace a site, or by excavation and backfilling, so that air can enter and oxidise any pyrite contained therein. The recommendations here should lead to a more accurate assessment of aggressive ground conditions and to an appropriate specification for the concrete to be used.
Additionally, this part identifies some of the more rarely occurring forms of chemical attack caused by high levels of chemical species such as ammonium ions, and organics such as phenols. In this case the recommended APM may often be achieved by redesigning the construction so that the concrete remains surrounded spwcial impermeable ground that forms a barrier to movement of concete groundwater; for example, using a dugest foundation or trenchfill foundation for a structure rather than a spread footing constructed in an open excavation.
However, the levels of chloride found in the ground are generally chemically innocuous; indeed, they may be beneficial since there is considerable evidence, from seawater studies, that the presence of chloride generally reduces sulfate attack. The digwst phenomenon accounts for the formation of solution features karst in limestone strata.
Surface protection is needed to prevent ingress of rainfall and for safety of personnel. Notes a Where the hydraulic gradient across a concrete element is greater than 5, one step in DC Class or one APM over and above the number indicated in this table should be applied except where the original provisions included APM3.
Diversion pipes or culverts around dams retaining moorland waters containing high concentrations of aggressive carbon dioxide can be subject to erosion, as can poorly compacted concrete or permeable concrete products eg some aggregate concrete blocks used in foundations. These stem from a further study of occurrences aggreseive sulfate attack in concrete structures, and recent field and laboratory research Section A3.
Composition, specifications and conformity criteria Draft for public comment 49 Part E Specifying surface-carbonated precast concrete for general use in the ground E1 Introduction This part applies to the general use in the ground of precast concrete that has assured surface carbonation.
For soil, the sulfate analysis, expressed as SO4, should be on a 2: A relatively new finding is, however, that a pH greater than 10 such as occurs by mixing cement or dogest with soil also accelerates pyrite oxidation .
These are locations where the ground contains pyrite which, if disturbed, may oxidise to sulfates Section C5.
Key outcomes in respect of the mechanism of TSA and concrete specification have been: Some geotechnical problems associated with pyrite bearing mudrocks.
Concrete in Aggressive Ground:3rd edition – PDF Free Download
The permitted relaxations are applied in Table E1 on page 51 which here replaces Table D1. If no desk study has been carried out, it should be assumed that pyrite may be present in the ground and the site testing procedures given in Sections C5.
In early summer to mid-autumn, when groundwater levels are generally low, these simple field tests may fail to detect seasonally adverse mobile groundwater conditions. The rate and extent of oxidation will depend on the type of pyrite and the local environmental difest.