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The Idiots' Guide to Highways
SURFACES, A CLOSE STUDY
I regard these images as typical examples of how I believe the named bituminous mixtures should appear, other engineers /suppliers may have a different view on how a particular mixture should appear.
A badly designed, poorly manufactured, or poorly laid material is just that and should not cloud your judgement on the merits of a correctly designed, manufactured and laid bituminous mixture.
Selecting an appropriate bituminous mixture, or suitable surface applied treatment, that has incorrect aggregate, composition or bitumen properties is a different matter, to put it bluntly, you have selected the wrong material for the site!
YOU MUST BE AWARE THAT
ULTIMATELY YOUR VEHICLE TYRES WILL BE "RIDING" UPON "STRIPPED BARE" AGGREGATE,
PRESENTED TO THE ROAD SURFACE IN A WIDE VARIETY OF FORMS, MOST OF THEM BEING
ABLE TO BE CLASSIFIED INTO BROAD DESCRIPTIONS ACCORDING TO HOW THE AGGREGATE IS
BEING "HELD", e.g.'s :-
Hot Rolled Asphalt, Bitumen Macadam /Asphalt Concrete, Stone Mastic Asphalt, Surface Dressing, Slurry Macadam
IT FOLLOWS THAT THE CHOICE OF AGGREGATE (PSV and AAV), AND THE FORM OF THE SURFACE TEXTURE THAT THE AGGREGATE PRESENTS TO THE VEHICLE TYRES IS EXTREMELY IMPORTANT, AND SHOULD BE APPROPRIATE TO THE SITE AND TRAFFIC CONDITIONS.
IT IS UP TO YOU THE ENGINEER / ENGINEERING TECHNICIAN TO UNDERSTAND THE VARIOUS BITUMINOUS MIXTURES, AND THEIR PROPERTIES, OR BE ABLE TO CONSULT AN INDEPENDENT MATERIALS ENGINEER / ROAD PAVEMENT ENGINEER FOR ADVICE.
|55%/14mm. NEWLY LAID - HOT ROLLED ASPHALT WEARING COURSE||14mm. CLOSE GRADED MACADAM (CGM)|
|55%/10mm. ESTABLISHED - HOT ROLLED ASPHALT WEARING COURSE||10mm. NEWLY LAID OPEN GRADED MACADAM|
|10mm. STONE MASTIC ASPHALT, (SMA)||10mm. OPEN GRADED MACADAM - AFTER TRAFFICKING|
|14mm. STONE MASTIC ASPHALT||30%/14mm. HOT ROLLED ASPHALT WEARING COURSE AND 14mm. PRECOATED CHIPPINGS|
|10mm. SURFACE DRESSING||35%/14mm. "DESIGN" HRA WEARING COURSE AND 20mm. HIGH P.S.V. PRECOATED CHIPPINGS|
|10mm. CLOSE GRADED (DENSE) MACADAM|
|IMAGES OF A TYPE OF PROPRIETARY "THIN SURFACING" ( 20mm. ASPHALTIC CONCRETE / PERVIOUS MACADAM)|
|IMPORTANT - Further information on the Introduction of the new BS EN 13108 Family of Bituminous Mixtures - Replacing BS 594 and BS 4987|
55%/10mm. ESTABLISHED - HOT ROLLED ASPHALT WEARING COURSE,
( OFTEN REFERRED TO AS HIGH STONE CONTENT ASPHALT, HSCA
Below is a 55%/10mm. High Stone Content Asphalt (HSCA) after approximately 5 years trafficking, you are able to see the sand bitumen matrix that is typical of a hot rolled asphalt, as this matrix is worn away the texture will increase.
STONE MASTIC ASPHALT, (SMA)
STONE MASTIC ASPHALT
Below is a magnification of the picture
A good surface dressing on a structurally sound road surface will create good macro-texture, and coupled with a high polished stone value (PSV) aggregate will provide a road surface with a high skid resistance in a cost effective manner.
CLOSE GRADED (DENSE) MACADAM AFTER APPROXIMATELY THREE MONTHS
|Below is a magnification of the the 10mm. CGM image above, to better observe the considerable texture that is present on this type of material. Even though it will not show a deep texture depth when tested by the sand patch test it is still likely to have a texture depth above 0.8mm (sand patch). This amount of texture is quoted in many reports as being quite adequate for unstressed locations, remember skid resistance is not solely related to texture depth.|
CLOSE GRADED MACADAM (CGM)
10mm. NEWLY LAID OPEN
GRADED MACADAM - AFTER TRAFFICKING
HOT ROLLED ASPHALT (HRA) WEARING COURSE AND 14mm. PRECOATED
35%/14mm. "DESIGN" HOT ROLLED ASPHALT (HRA) WEARING COURSE AND 20mm. HIGH
POLISHED STONE VALUE (PSV) PRECOATED CHIPPINGS
OF A TYPE OF PROPRIETARY "THIN SURFACING" ( 20mm. ASPHALTIC
CONCRETE / PERVIOUS MACADAM)
The above image shows the nature of the failure that this type of "open" material experiences over time, i.e. the fretting out of the aggregate particles.
The above are an extremely small representation of surface courses (wearing courses), of the many generic bituminous mixtures that are available from,
BS 594:Hot Rolled Asphalt for Roads and other Paved Areas :-
Part 1:Specification for constituent materials and asphalt mixtures
BS 4987: Coated Macadam for Roads and other Paved Areas :-
Part 1:Specification for constituent materials and mixtures
Note : The specifying of various types of bituminous mixtures by reference to the above standards has been superseded by the various parts of BS EN 13108 : Bituminous Mixtures - Materials Specifications, from 1st. January 2008.
It is possible that BS 594 and BS 4987 may still be available from BSI for some time after this date, as it may well be that existing contracts that contain reference to these standards will need to run their term.
I have also included images of proprietary, Thin Surfacing, bituminous mixtures.
Accessing the pages containing lists of some of the British Standard specified materials will indicate the diversity of options you have to choose from, although in truth it is possible to satisfy nearly all of your requirements from a number of "highlighted" materials in the full specification that have the title "preferred mixtures".
If you have any involvement in the specifying, purchasing and laying of bituminous materials I suggest that you retain copies of BS 594 and BS 4987 for reference purposes.
The above links will provide you with a summary of the history of the development of BS 594 and BS 4987, and the mixtures that were available.
Only compare good bituminous mixtures with other good bituminous mixtures, you will learn little from comparing a badly, designed, manufactured and laid product with a well, designed, manufactured and laid product that is of a different type.
You may wish to change your type of bituminous mixture to suit the engineering needs of the site, i.e. durability, ride quality, noise generation, traffic management at the time of laying, and not least the amount of money you have available.
If need be, obtain advice from your Materials Engineer / Road Pavement Engineer, do not specify a bituminous mixture, especially a proprietary material that you do not know what are its design (mixture) requirements and its engineering properties.
information on the Introduction of the new BS EN 13108 Family of Bituminous
Replacing BS 594 and BS 4987
IMPORTANT:- From the 1st. of January 2008 the material/s descriptions used above, and taken from BS 4987 or
BS 594, will no longer apply to the bituminous mixtures referred to in the text above.
( For further information and guidance 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 mixture composition" of the bituminous mixture description that you want to receive, when you purchase that particular mixture.
The new material descriptions will cover many possible "target mixture descriptions" for that particular description.
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 text above, and throughout the website, will still refer to BS 594 and BS 4987 bituminous mixture descriptions, that actually meant particular/defined/specified bituminous mixtures.
It is up to you to specify and purchase similar bituminous mixtures to those referred to above if you believe they are suitable for a particular use, on a particular site.
It may not be possible provide similar text as above in the future because each general material description could cover many variations of an actual bituminous mixture composition/recipe, providing significantly different engineering properties.
The new specifications that were introduced on 1st. January 2008, include,
BS EN 13108-1 : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete
(This standard largely replaces BS 4987, for specifying Target Mixture Compositions for "macadam" bituminous mixtures. )
BS EN 13108-2 : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete for very thin layers
(This standard can be used to provide Target Mixture Compositions for the finer "macadam" mixtures.)
BS EN 13108-3 : 2006:Bituminous mixtures. Material specifications - Soft asphalt
BS EN 13108-4 : 2006:Bituminous mixtures. Material specifications - Hot rolled asphalt
(This standard replaces BS 594 for providing appropriate Target Mixture Compositions.)
BS EN 13108-5 : 2006:Bituminous mixtures. Material specifications - Stone mastic asphalt
(This standard can be used to provide appropriate Target Mixture Compositions for SMA.)
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. 6691:2010:(supersedes 2007 edition) Guidance on the use of BS EN 13108 Bituminous mixtures - Materials specifications,
BS 594987:2010 (supersedes 2007 edition) Asphalts for roads and other paved areas -
Specifications for transport, laying and compaction and type testing protocols,
You will also need to be aware of the new documents,
Interim Advice Note 101/07 - A revised copy of the 900 Series, of the Manual of Contract Documents for Highway Works
Interim Advice Note 102/7 - The introduction of BS EN standards for bituminous mixtures - Site supervision aspects
The changes in the nature of specifying bituminous materials is major, and you do need to be aware of the changes if you are in any way responsible for specifying and using bituminous mixtures in highway works.
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