Type 1 unbound mixture shall be made from crushed rock, crushed slag, crushed concrete, recycled aggregate or well burnt non-plastic shale.
The composition of all Recycled aggregate (RA) and Recycled concrete aggregate (RCA) used in unbound mixtures shall have been tested in accordance with Clause 710 of the Manual of Contract Documents for Highway Works: Volume 1 (MCHW1). Clause 710 requires that the composition be determined in accordance with BS EN 933-11. Recycled aggregate (RA) and Recycled concrete aggregate (RCA) used in unbound mixtures in accordance with Clause 803 (MCHW1) shall comply with the composition requirements of Table 8/3 of the 800 Series, reproduced below.
Clause 710 requires that recycled aggregates are produced in accordance with the ‘Quality Protocol for the production of aggregates from inert waste’ and the ‘Producers’ compliance checklist’ published by the Waste & Resources Action Programme (WRAP). The results of all quality control checks carried out by the Contractor shall be complied in accordance with the procedure set down in the above document and with those in Clause 710. These shall be delivered promptly to the client on request. For further information refer to the WRAP quality protocols for the production of aggregates from inert waste and the WRAP quality protocol checklists and guidance notes for producers, specifiers and purchasers of sustainable aggregates.
The operation of a Factory Production Control system for the production of unbound mixtures is required by BS EN 13285.
Burnt colliery spoil and spent oil shale are required to be non-plastic.
Volume 7, Section 1, Chapter 2 (HD 35/04) in the Highway’s Agency’s Manual of Contract Documents for Highway Works notes that to 15% by mass of Incinerator bottom ash can be a component of Unbound mixtures for subbases, although more can be used following additional testing.
Volume 7, Section 1, Chapter 2 (HD 35/04) in the Highway’s Agency’s Manual of Contract Documents for Highway Works notes that Recycled glass can be used in Unbound mixtures for subbases, although it is not specifically named in Series 800 of the MCHW1.
The recycled and secondary aggregates listed have a specific or a general provision for use within the Manual of Contract Documents for Highway Works, and may be used as long as these materials meet the required properties for aggregates given above.
The Structural Design of Heavy Duty Pavements for Ports and other Industries suggests the use of Type 1 or Type 2 unbound subbase material, as defined in MCHW1, Series 800.
Table 8/3 - 800 Series:
|Unbound Mixture||Type 1||Type 2||Type 4 (asphalt arisings)|
|Component Identified by Clause 710||Maximum Permitted Content (% by mass)|
|Asphalt (Class Ra)||50||50||0|
|Glass (Class Rg)||25|
|Other materials (Class X), including wood, plastic and metal||1|
The categories used to express the requirements of the mixture are given below:
Unbound mixture (BS EN 13285)
Type 1 Unbound subbase mixture
Mixture requirement category
- Designation (see Note 1)
- Maximum fines category (UF)
(i.e. < 9% by mass passing the 0.063 mm sieve)
- Oversize category (OC)
(i.e. 75 to 99% by mass passing D)
Grading requirement category
- Overall grading (G)
The aggregate grading shall be within the limits below:
Sieve size (mm)
Percentage by mass passing the sieve size shown
Overall grading range
Supplier declared value grading range
Tolerance on the supplier declared value
75 - 99
43 - 81
54 – 72
23 - 66
33 – 52
12 - 53
21 – 38
6 - 42
14 – 27
3 - 32
9 – 20
0 - 9
Additional requirements for individual batches from a Factory Production Control (FPC) system are given below:
Grading of individual batches - differences in values passing selected sieves
Retained sieve size (mm)
Passing sieve size (mm)
Percentage by mass passing the sieve size shown
Not less than
Not more than
1. Aggregate sizes are expressed as d/D or lower limiting sieve size/upper limiting sieve size.
2. Annex B of BS EN 13285 contains an explanation of supplier declared grading values.
Aggregates shall comply with the requirements listed in Clause 801 and Table 8/2 of the 800 Series of the Specification for Highway Works. There are volume stability requirements for blastfurnace and steel slag.
Subject to any tolerances given in MCHW table 7/1, material shall not be frost susceptible if used within 450 mm of the designed final surface of a road or paved central reserve area, or 350 mm if the Mean Annual Frost Index (MAFI) of the site is less than 50. Material shall be classified as non frost susceptible if the mean heave is 15 mm or less, when tested in accordance with BS 812-124:2009.
General requirements for sulfur compounds of materials deposited within 500 mm, or other distances described in Appendix 7/1 of the MCHW, of concrete, cement bound materials, other cementitious materials, stabilised capping or metallic structural elements forming part of the Permanent Works are given in Clause 801.2 and 801.3 of the 800 Series of the Specification for Highway Works (Series 800). The requirements above shall not apply to metallic items protected by concrete and ancillary metallic items such as the tops of chambers and gullies. Further details are given in the Notes for Guidance for the Specification for Highway Works, NG800 Series (Series NG800) and in TRL 447.
No further restrictions on chemical properties are specified. However, in certain circumstances, the Environment Agency in England and Wales, (or their equivalent in Scotland and Northern Ireland) will require that the construction activities will not lead to contamination of ground or surface waters due to leaching or spillages. For this reason you are advised to discuss, as a matter of routine, your intended application with the relevant regulatory authority.
Under the Construction Products Regulations, CE marking will be mandatory for aggregates from July 2013. This includes aggregates from primary, recycled and secondary sources.
Maintained by TRL Limited from October 2009.
revised: 24 Jan 2011
The information set out above is only concerned with the technical aspects of construction and is of a general nature only and not intended to be relied upon in specific cases.
It is derived from currently available UK Standards and Specifications applicable at the time of writing. Reference should be made to the relevant Standards and Specifications applicable at the time of writing and you should seek and rely upon expert professional advice on specific issues.
The information does not take account of environmental issues which you should discuss as a matter of routine with the regulatory authorities (the Environment Agency in England and Wales, the Scottish Environment Protection Agency in Scotland and the Department of the Environment in Northern Ireland).
Consequently, the information is provided only on the condition that WRAP and their sub-contractors will not be liable for any loss, expense or damage arising from your use or application of such information. See clause 3 of our Terms and conditions.