BRITISH STANDARD BITUMINOUS MIXTURES, THAT CAN BE LAID THINLY

CONTENTS

NOTES FOR LAYING BITUMINOUS MIXTURES THINLY
PROPRIETARY MATERIALS ( "THIN SURFACINGS")
TABLE OF BRITISH STANDARD MIXTURES THAT CAN BE LAID THINLY
THE APPROPRIATE BRITISH STANDARDS
LAYER THICKNESS

NOTES FOR LAYING BITUMINOUS MIXTURES THINLY

Three of the materials I include in the table are actually ''Preferred mixes''.
''Preferred mixes'' have been introduced into BS 4987 to encourage rationalisation of coated macadam compositions, and the British Standard quotes :-
''Mixtures suitable for most uses can be selected from this reduced range and purchasers are encouraged to adopt their use wherever possible''.

It is important that all bituminous mixtures laid thinly have good tack coats applied to the existing surface prior to laying to ensure bonding of the thin layer to the existing road.
This means a complete wetting of the existing surface with a K1-40 emulsion, to produce a complete coating of bitumen once the emulsion has ''broken''.

BS 594 states 0.35 to 0.55 litres/metre².

A black wiggly line disappearing into the distance, or a mist spray so thin you can see through it, are not to be regarded as a tack coat.

The materials shown in the table can be regarded as practically impervious, especially if the correct rate of spread of tack coat is applied completely sealing the existing surface.
The exceptions to the above statement are the 6mm. medium textured wearing course and the 10mm. open graded wearing course.
These will allow passage of water through the material matrix to a greater or lesser degree depending upon their grading.
This may or may not be a problem but should be considered.

I have quoted the normally used binders for the materials mentioned in the table, for stiffer materials and increased stability the viscosity of the binder in the mix can be increased accordingly.

For less stiff materials, and increased workability at lower laying temperatures reduce the viscosity of the binder, but be aware this will reduce the stability of the material in use.

A good example of the use of a less stiff binder are the Medium Temperature Asphalts, which are in fact High Stone Content Asphalts, (HSCA), with a 100pen or 200pen bitumen according to the traffic conditions of the site.

The 6mm. macadams with 200/100pen binders when machine laid are cost effective alternatives to slurry macadam where site conditions permit, i.e. if you can lay the increased thickness that you will obtain with a 6mm. macadam you will achieve a thicker layer to the road pavement for your money.

Bituminous mixtures laid thinly cool very quickly on laying, ensure compaction takes place while the material is still hot.
The stiffer mixture can ''drag'' when laid, especially if the material is to the bottom end of the laying temperatures, and the paving machine is going too fast for the material workability.
Instruct/request the supervisor to decrease the paver speed if dragging is occurring.

PROPRIETARY MATERIALS ( "THIN SURFACINGS")

There are an increasing number of proprietary materials coming on to the highways maintenance scene, and they are being very forcefully marketed.
Most of these products are excellent materials when you choose the correct material for the job in hand.

But

They are expensive compared to a similar British Standard material.

They are not always as comprehensively specified as a British Standard material, so you may not know what you are actually buying.

Exaggerated claims are being made for some of these materials especially in view of the fact they are relatively recent introductions to the U.K. market.
The similarity between proprietary and British Standard materials is sometimes remarkable, a B.S. material in many instances can comply with the proprietary specification.

Recently I received ''sales'' literature for a new proprietary material from one of the very large bituminous material suppliers, sold under a single particular brand name.
The company offered any size grading I should require coupled with any viscosity of binder I needed all under the same product name.
This practice is known as a "Thin Wearing Course System", and you still need to know which mixture in the "system" is most suitable for your surfacing need.

Why not just find a material suitable for a particular site from B.S. 4987 or B.S. 594 ( you will find far more guidance in which material to choose ) and have funds left in your budget to help surface another site.

IMPORTANT:- From the 1st. of January 2008 the materials descriptions used in this comparison will no longer apply to the bituminous mixtures referred to in the table. ( For further information click ------> HERE )
This does not mean these bituminous mixtures will not be available, but it does mean that you must be aware of the new description, and more importantly that you have defined/specified the "target composition" of the bituminous mixture description that you want to receive when you purchase that particular mixture.
I fear there could well be a substantial amount of confusion in the whole (supply and use ) of the bituminous mixture industry, with the purchaser/user experiencing the greater difficulty.
At this time the "table" will remain as it is, with descriptions that actually meant particular/specified bituminous mixtures.
It is up to you the specify and purchase similar bituminous mixtures to those shown below if you believe they are suitable for a particular use, on a particular site.
It may not be possible to create such a table with new material descriptions, because each general material description could cover many variations of an actual bituminous mixture composition/recipe.

TABLE OF BRITISH STANDARD MIXTURES THAT CAN BE LAID THINLY

THE APPROPRIATE BRITISH STANDARDS

BS 594:Hot Rolled Asphalt for Roads and other Paved Areas :-
Part 1:Specification for constituent materials and asphalt mixtures
Part 2:Specification for the transport, laying and compaction of rolled asphalt

BS 4987: Coated Macadam for Roads and other Paved Areas :-
Part 1:Specification for constituent materials and mixtures
Part 2:Specification for transport, laying and compaction

and the new specifications that will be introduced on 1st. January 2008

BS EN 13108-1  : 2006:Bituminous mixtures. Material specifications. Asphalt Concrete
BS EN 13108-2  : 2006:Bituminous mixtures. Material specifications. Asphalt Concrete for very thin layers
BS EN 13108-3  : 2006:Bituminous mixtures. Material specifications. Soft asphalt
BS EN 13108-4  : 2006:Bituminous mixtures. Material specifications. Hot rolled asphalt
BS EN 13108-5  : 2006:Bituminous mixtures. Material specifications. Stone mastic asphalt
BS EN 13108-6  : 2006:Bituminous mixtures. Material specifications. Mastic asphalt
BS EN 13108-7  : 2006:Bituminous mixtures. Material specifications. Porous asphalt
BS EN 13108-8  : 2005:Bituminous mixtures. Material specifications. Reclaimed asphalt
BS EN 13108-20 : 2006:Bituminous mixtures. Material specifications. Type testing
BS EN 13108-21 : 2006:Bituminous mixtures. Material specifications. Factory production control

P.D. 6691:2007:Guidance on the use of BS EN 13108 Bituminous mixtures. Materials specifications,

BS 594987:2007:Asphalts for roads and other paved areas - 
Specifications for transport, laying and compaction and type testing protocols,

The above British Standards are comprehensive WORKING DOCUMENTS and if you have any involvement in the specifying, supervision, or purchasing of bituminous materials you MUST have access to these specifications, the information they contain is excellent.
In fact many of the more reputable proprietary materials even defered to Part 2 of either BS 594 or BS 4987 for transport laying and compaction.

The "NEW" bituminous material industry really does not like people being aware that they exist, they would much rather sell you a proprietary material at an enhanced price that has a lot less onerous specification.
But it is not beyond the bounds of possibility the the "industry" will introduce a range of proprietary, "branded" mixtures the were the well used "preferred mixtures" of BS 4987 and BS 594, but at proprietary prices.

If you can still obtain copies of BS 4987 and BS 594 I would advise it, and use the mixtures contained in them as reference mixtures, their days are numbered as a specifying option, but the information they contain will always be useful.

You should also be aware that the "NEW" proprietary bituminous mixtures, (and that is all they are, mixtures of bitumen and aggregate in varying formulations ) are being marketed as "Systems" so one proprietary name will apply to a number of distinctly different materials.

So if you do choose the proprietary material path be very sure you know what you are buying.

For more information on "Thin Surfacings" press -----------> HERE

LAYER THICKNESS

The thickness of layer for the various aggregate sizes in the table above are based upon, but modified from a little personal experience, figures stated in tables in BS 4987:Part 2, and are such that the material will have a fairly dense nature when laid, in line with procedures that have been standard practice until recently.

These nominal aggregate size, layer thickness combinations, have been recommended because dense layers of bituminous materials will better prevent the ingress of water into the road matrix and also reduce the rate at which bitumen oxidisation occurs, both being conditions that will reduce the life of the road pavement.

However with the recent introduction of proprietary Thin Surfacings, with a predominantly open graded/ single sized aggregate content, there is now a body of thought to lay mixtures in thinner layers to provide a high surface texture.

This means that depending on the nature and thickness of the mixture it is likely that the material layer will be porous in nature and will not provide a physical barrier to the ingress of water into the road pavement, and rate of oxidation of the bitumen will be increased.
This in turn will mean a reduced life compared with Hot Rolled Asphalt Wearing Course, or other dense bituminous mixtures used for the wearing course layer of a road pavement.

For further information on laying thin bituminous surface courses, press ----------------------------> HERE

For a table comparing the various thin asphalt / bituminous surfacing materials that are available
Press ---------------------->HERE

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