2.1 Concrete and its reinforcement
Appendix 2.1-A
Table 1 - General purpose concrete mixes - minimum concrete specification (non-hazardous conditions)
| Use | BS 8500 and BS EN 206-1 | ||
|---|---|---|---|
| Ready-mixed concrete (Designated mix) | Site-mixed concrete (Standardised Prescribed mix) | Slump class | |
Substructure and ground floors
| GEN1 | ST2 | S3 |
| GEN1 | ST2 | S3/S41 |
| GEN1 GEN2 | ST2 ST3 | S2 S2 |
| GEN3 | ST4 | S2 |
| RC35 | ST52 | S2 |
Superstructure
| RC30 RC35 RC40 | 3 4 - | S2 S2 S2 |
In-situ external concrete
| PAV1 GEN1 | ST55 ST1 | S2 S1 |
Notes
- Slump class S3 should be used for strip foundation concrete and Slump class S4 should be used for trench fill foundation concrete.
- ST5 mix for house and garage floors may only be used in conjunction with Chapter 5.2 'Suspended ground floors'. In all other cases the designated mix should be used.
- In this situation an ST4 mix may be used but only for small quantities of concrete. In all other cases the appropriate designated mix should be used.
- In this situation an ST5 mix may be used but only for small quantities of concrete. In all other cases the appropriate designated mix should be used.
- Not suitable in areas of severe exposure to frost attack (see Chapter 6.1 Appendix B).
Tables 2a, 2b and 2c - Site-mixed concrete for Standardised Prescribed Mixes
Table 2a - Mix proportions by weight
This table applies to cement strength class 32.5 and 20mm maximum aggregate size. Where cement strength class 42.5 or higher is used the cement weight should be decreased by 10%.
| Standardised Prescribed Mix | Slump Class (see Table 2c) | Cement (kg) | Fine aggregate (kg) | Coarse aggregate (kg) |
|---|---|---|---|---|
| ST1 | S1 | 230 | 770 | 1155 |
| ST2 | S2 | 265 | 760 | 1135 |
| ST2 | S3 | 285 | 735 | 1105 |
| ST2 | S4 | 300 | 815 | 990 |
| ST3 | S2 | 295 | 745 | 1120 |
| ST4 | S2 | 330 | 735* | 1100 |
| ST5 | S2 | 375 | 720* | 1080 |
Table 2b - Mix proportions by volume
This table applies to 20mm maximum aggregate size
| Cement strength class | Standardised Prescribed Mix | Slump Class (see Table 2c) | Number of (25 kg) bags of cement | Fine aggregate (litres) | Coarse aggregate (litres) |
|---|---|---|---|---|---|
| 32.5 | ST1 | S1 | 1 | 60 | 85 |
| ST2 | S2 | 1 | 50 | 75 | |
| ST2 | S3 | 1 | 45 | 70 | |
| ST2 | S4 | 1 | 50 | 60 | |
| ST3 | S2 | 1 | 45 | 65 | |
| 42.5 or higher | ST1 | S1 | 1 | 65 | 95 |
| ST2 | S2 | 1 | 55 | 80 | |
| ST2 | S3 | 1 | 50 | 75 | |
| ST2 | S4 | 1 | 55 | 65 | |
| ST3 | S2 | 1 | 50 | 75 |
Table 2c - Slump classes
| Slump class | Slump in mm |
|---|---|
| S1 | 10 to 40 |
| S2 | 50 to 90 |
| S3 | 100 to 150 |
| S4 | 160 to 210 |
Notes
* Fine aggregate grading to be grades CP or MP only of BS EN 12620.
Table 3 - Exposure conditions
| Environment | Exposure conditions |
|---|---|
| Mild | Concrete surfaces completely protected against weather or aggressive conditions |
| Moderate | Exposed concrete surfaces but sheltered from severe rain or freezing wind whilst wet Concrete surfaces continuously under non-aggresive water Concrete in contact with non-aggressive soil (AC-1 and AC-1s classes) Concrete subject to condensation |
| Severe | Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing or severe condensation |
| Very severe | Concrete surfaces exposed to sea water spray, or de-icing salts (directly or indirectly) Concrete surfaces exposed to corrosive fumes or severe freezing conditions whilst wet |
| Most severe | Concrete surfaces frequently exposed to sea water spray or de-icing salts (directly or indirectly) Concrete in sea water tidal zone down to 1m below lowest water |
Notes
This table is based on Table 3.2 of BS 8110-1. For very severe and most severe exposure conditions follow guidance in relevant documents explained in Design clause 2.1-D4.
Tables 4a and 4b - Buried concrete in aggressive ground
Tables 4a and 4b are based on extracts from BS 8500-1 & 2 and BRE Special Digest 1. They cover the lower range of chemical aggressiveness. For concrete exposed to more aggressive conditions, specialist advice should be sought. For the purposes of Chapter 2.1 the following terminology is used. Other related terms, which might be encountered in specialist reports, are described in BRE Special Digest 1.
Table 4a - Aggressive Chemical Environment for Concrete (ACEC) site classification(1)
This table applies to concrete exposed to ground with a pH value greater than 2.5
| Sulfate and magnesium | Natural soil | Brownfield(3) | ACEC Class for site | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Design Sulfate Class for site | 2:1 Water/soil extract | Groundwater | Total Potential Sulfate(2) | Static water | Mobile water | Static water | Mobile water | |||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| SO4 | Mg | SO4 | Mg | SO4 | pH | pH | pH(4) | pH(4) | ||
| g/l | g/l | g/l | g/l | % | ||||||
| DS-1 | <1.2 | All Mg values | <0.4 | All Mg values | <0.24 | All pH values | All pH values | AC-1s | ||
| >5.5 | >6.5 | AC-1 | ||||||||
| ≤5.5 | 5.5-6.5 | AC-2z | ||||||||
| 4.5-5.5 | AC-3z | |||||||||
| <4.5 | AC-4z | |||||||||
| DS-2 | 1.2-2.3 | All Mg values | 0.4-1.4 | All Mg values | 0.24-0.6 | >3.5 | >5.5 | AC-1s | ||
| >5.5 | >6.5 | AC-2 | ||||||||
| ≤3.5 | ≤5.5 | AC-2s | ||||||||
| ≤5.5 | 5.5-6.5 | AC-3z | ||||||||
| 4.5-5.5 | AC-4z | |||||||||
| <4.5 | AC-5z | |||||||||
Notes
- For concrete quality and APM for ACEC Classes above AC-2z follow specialist advice. For the full list of ACEC Classes refer to Table A.2 of BS 8500-1 or BRE Special Digest Part 1 Table 2.
- Applies only to sites where concrete will be exposed to sulfate ions (SO4) which may result from the oxidation of sulphides such as pyrite, following ground disturbance.
- 'Brownfield' is defined as sites which may contain chemical residues remaining from previous industrial use or from imported wastes.
- An additional account is taken of hydrochloric and nitric acids by adjustment to sulfate content.
Explanation of suffix symbols to ACEC Class number
- Suffix s indicates that, as the water has been classified as Static, no Additional Protective Measures are generally necessary.
- Concrete placed in ACEC Classes which include the suffix z have primarily to resist acid conditions and may be made with cements from any of the Groups in Table 3 of Part 2 of BRE Special Digest 1.
This table is based on Table 2 of Part 1 of BRE Special Digest 1.
Table 4b - Design guide for concrete elements in the ground
| Concrete element | ACEC Class(1) | Designated mix |
|---|---|---|
| Strip or trenchfill foundation, raft foundation, pile(3) and ground beams | AC-1, AC1s | As Table 1 |
| AC-2, AC2s | FND2(2) | |
| AC-2z | FND2z(2) |
Notes
- For all other ACEC Classes refer to BS 8500-1 Table A.4 or follow specialist advice.
- Portland limestone cement may only be used if the Design Sulfate Class (see Table 4a) of the site does not exceed DS-1.
- Applies to cast-in-situ piles only and for other types of pile refer to BRE Special Digest 1 or follow specialist advice.
Glossary of terms
Aggressive Chemical Environment for Concrete Classification (ACEC Class) - A new system for the classification of aggressive ground conditions that are derived from Design Sulfate Class. It takes into account the site (natural or brownfield) and the mobility and pH of groundwater. Brownfield, 'Mobile' water and low pH (acidic) conditions, may have adverse effects on buried concrete and hence result in a more severe ACEC Class.
Additional Protective Measures (APM) - These are defined as the extra measures that could be taken to protect concrete where the basic concrete specification might not give adequate resistance to chemical attack.
Design Chemical Class (DC Class) - This defines the qualities of concrete that are required to resist chemical attack. The DC Class is derived from the ACEC Class of the ground and other factors including the type of concrete element and its required structural performance.
Design Sulfate Class (DS Class) - It is a site classification based on the determined sulfate (including Potential sulfate) contents of the ground and/or groundwater. It is also dependent of the type of site, presence or absence of magnesium ions, pyrite and for pH less than 5.5 chloride and nitrate ions. Five levels of classification are given that are equivalent to those given in BRE Digest 363 (now superseded).
Enhanced concrete quality - An incremental step in concrete quality that could be used as an Additional Protective Measure (APM). Each increment in concrete quality is counted as an extra APM.
Mobile groundwater - Sites where water is free to flow into an excavation to give a standing water level are affected by mobile ground water. The threshold ground permeability is greater than 10-6 m/s (i.e. 86 mm/day).
Static groundwater - The sites where the free flow of water is confined due to either permanently dry condition or the soil is relatively impermeable, of permeability less than 10-6 m/s.
Total Potential Sulfate (TPS) - The total potential sulfate content is the result of the combination of sulfates already present in the ground and that which may be added due to the oxidation of pyrite in the ground.
