BS 434-2:2006 pdf download

BS 434-2:2006 pdf download.Bitumen roademulsions – Part 2: Code of practice for the use of cationic bitumen emulsions on roadsand other paved areas.
7 Surface dressing of carriageways
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7.1 General
Surface (tressing is a process which comprises the application of chippings and binder. It is critically dependent on correct design and execution by experienced personnel (see Foreword). Surface dressing is one of the most economic and efficient surfacing systems for waterproofing a pavement. One or more thick films of binder should be sprayed onto the surface upon which chipphigs, in various sizes or combinations of sizes, should be spread and rolled.
The following guidance should be followed when determining the most suitable type of surface dressing for use in a l)ar(icular application.
Single dressing — Single layer of rhipping.s on a single film of hinder. The simplest. fonn of dressing and best suited to lightly trafficked roads.
Racked-in surface dressing — A single (hick film of binder plus two layers of chippings spread upon it. The first. layer of chippings should be the larger and spread at approximately 90% shoulder to shoulder (in accordance with uS 598-108 orBS EN 12272.1)coveragc. The second smaller chipping layer should be spread to slight excess in order to lock the larger chippings into place.
Double dressing — Two films of binder plus two layers of chippi.ngs. The first film of hinder should be sprayed. Theii the larger chipping should be spread followed in order by the second film of binder and the second, smaller, chipping. This is the most robust of the standard types of dressing and is less sensitive to variations in the substrate compared to single and racked-ui dressings.
Sandwich dressing — Similar to a double dressing but the first film of binder is omitted. The larger chippings should be spread on the existing surface then a film of binder should be sprayed onto them and then the smaller chippings should be spread. This dressing is sometimes used where there is extensive fatting of the existing surface, or where there are wide variations in hardness transversely across a site. it is possible to combine double and sandwich dressing by using an initial spray in the areas that have not fatted if they are very nigose (for example outside the wheel tracks) and then continuing over the whole with the remainder of the sandwich process. Similarly it is also possible to combine single and sandwich dressings by using the first layer of larger chippings in, for example the wheel tracks and applying a single dressing over the whole.
Inverted double dressing — Used to be called pad-coat. An initial dressing of small chippings on a film of binder followed immediately or subsequently by a further single dressing of larger chippings. It is useful in some circumstances where the existing surface is very variable, particularly in hardness.
7.2 Design and preparation
Road Note 39 121 published by the TRL gives detailed guidance on the selection and design of surface dressing suitable for conditions in the United Kingdom. It also gives some guidance on the preparation of roads for surface dressing, however more detailed guidance on the practical aspects of the preparation of roads and the installation of surface dressing is given in the Code of Practice for surface dressing 171 available from the Road Surface Dressing Association.