ANALYSIS OF A BITUMINOUS MACADAM (14MM. CLOSE GRADED BITUMINOUS MACADAM)

INTRODUCTION TO UNDERSTANDING A BITUMINOUS MIXTURE

The principles that apply to a 14mm. Close Graded Macadam will be very similar, if not the same for ALL coated macadams, i.e. surface courses (wearing courses), binder courses (basecourses) and base (roadbase).

It is important to note that this bituminous mixture is now referred to as Asphaltic Concrete (AC).
The specifications/"recipes" that defined these mixtures in the now superseded,
BS 4987:Coated macadam for roads and other paved areas - Part 1:Specification for constituent materials and for mixtures
can, for practical purposes, be replicated by the correct use of BS EN 13108-1   : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete,
or  P.D. 6691:2010 (supersedes 2007 edition) : Guidance on the use of BS EN 13108 Bituminous mixtures -  Materials specifications.
So the materials that you receive on site, if you have specified them correctly, should be the same, given the allowable tolerances within the specification.

ALL bituminous materials are basically a mixture of aggregate (coarse and fine) and bitumen (of various grades), the properties and uses of these mixtures will depend upon the proportions (recipe) of the mixture, i.e. the "design".
ALL mixtures, even British Standards, were designed once upon a time for the use intended, and even modern "designed" mixtures require a "recipe" at the plant for the "designed" mixtures to be manufactured in a consistent manner.
So I find it difficult to understand the argument that proprietary bituminous mixtures cannot be sampled, and tested for compliance, in the normal way to ensure they have been manufactured as intended.
Any enhanced performance from binder modifiers can be tested for in a different manner. 
However it is becoming increasingly cost effective to test for binder additives by various forms of gas chromatography, so even this could be tested for in the laboratory, and not in dangerous positions on site with the high cost of traffic management. 

A 14MM. SAMPLE OF THE REQUIRED WEIGHT FOR THE ACTUAL TEST AFTER RIFFLING / QUARTERING

BS 4987 : COATED MACADAM FOR ROADS AND OTHER PAVED AREAS

ALL information relating to this bituminous mixture can be found in the British Standard, BS 4987.
I have repeatedly said, and I will go on saying, if your work (in the U.K) involves you in specifying, purchasing or laying bitumen coated macadams you must have access to these documents, purchasing copies for you technical library is strongly to be advised. 

Please be aware that a new edition of, 

BS 4987:Coated macadam for roads and other paved areas,  
Part 1:Specification for constituent materials and for mixtures, 
and 
Part 2:Specification for transport, laying and compaction, 

was published in 2003, 

However there has been a more recent edition of BS 4987:Part 1, published in 2005
BS 4987 : Part 1 : 2005 : Coated macadam (asphalt concrete) for roads and other paved areas - 
Part 1 : Specification for constituent materials and for mixtures

ADDITIONAL BITUMINOUS MIXTURE SPECIFICATIONS

There are additional specifications for other bituminous mixtures, e.g.,
BS 594 : Hot rolled asphalt for roads and other paved areas, 
and the various parts of recently introduced, 
BS EN 13108 : Bituminous Mixtures. Material Specification
Contained in the above specification are parts that will eventually (unlikely for several years) replace BS 4987 and 
BS 594, BS EN 13108 contains, Part 5 : Stone mastic asphalt, that can already be specified.


More information on the development of BS 4987 over the past few years is obtained by pressing HERE  
I am pleased to say the actual mixtures specified are much the same, it is just the terms that are used to specify them that have changed, but be aware of the "small print" that can allow significant changes with some mixtures.
It is also necessary, in my opinion, to exercise a little care in specifying base (roadbase) and binder course (basecourse) in the latest editions because you may inadvertently specify a "drier" design mixture, when you actually wanted a recipe mixture because it is likely to have a higher binder content and provide increased durability in lower trafficked situations.
An indication of the bituminous mixtures included in BS 4987 can also be found on the linked page, provided above.

The following information is obtained from BS 4987, similar information (and much more) can be obtained for a whole range of bituminous mixtures for use in highways maintenance and construction.

TYPICAL SPECIFICATION ("RECIPE") FOR FOR A 14MM. CLOSE GRADED MACADAM

APPEARANCE OF A 14MM. CLOSE GRADED MACADAM  AFTER REMOVAL OF BINDER AND SIEVING

GRAPHICAL DISPLAY OF GRADING (PROPORTIONS) OF A TYPICAL SAMPLE

NOTE the proportions of the aggregate particles shown above after washing with solvent and sieve analysis.   The figures above are actual percentages of a total of 100%, figures in British Standards and shown on grading sheets (as below) are percentages passing a particular sieve size.

Not a particularly good image, but for the small file size the image is sufficient for what I wish to demonstrate.  That is that the grading envelope (shown in green) is produced by plotting the figures in the British Standard, and the actual plot (shown in red) is of the analysis (grading) of this particular sample. You will note that the sample is out of specification in that it had too much material (aggregate particles) passing  the 10mm. sieve retained on the 6.3mm. sieve.  It had no aggregate retained on the 14mm sieve, but this is permitted, i.e. 100% is allowed to pass the 14mm. sieve. But between 70% & 90% is required to pass the 10mm. sieve, no more, in fact 95% of the sample passed the 10mm. sieve. This is not a serious failure providing the binder content is within the higher range of the specification, and sufficient to coat all the smaller aggregate particles. However it is not what was specified and therefore will not comply with the requirements of the contract document, and it needs to be brought to the attention of the contractor and through him the supplier. If this is an isolated case "reasonable" parties should be able to work this situation out, if a supplier repeatedly supplies out of specification material a more serious course of action should be implemented. However it should be noted from this specification that mixtures can be quite different in appearance according to where they lie within a particular grading range (specification) and still be regarded as 14mm. CGM, and the principal is similar with all other mixtures.

CORE OF A TYPICAL 10MM. CLOSE GRADED BITUMINOUS MACADAM

Unfortunately I do not have a picture in my library of a core of a 14mm. closed graded surface course (wearing course), so this picture of a 10mm. material will have to be presented.  The structure of aggregate interlock will be almost the same, but the range in aggregate particles from largest to smallest will not be so great in a 10mm. material. The image serves the purpose of showing how load bearing strength in coated macadam is predominantly due to aggregate interlock, with the binder acting, as the name indicates, as a binding agent holding the aggregate particles in position. The bitumen will also act as a waterproofing agent where the aggregate grading of the bituminous mixture is of the "dense" type.

14mm. CLOSE GRADED MACADAM (CGM) SURFACE APPEARANCE Below is a photograph of a typical 14mm. Close Graded Macadam after approximately two years trafficking. With this image a click on it will link to a larger file size picture to show more detail. This surface tends to have less depth of macro texture and increased micro texture, this is from the well graded nature of the mixture and the higher content of finer aggregate material, macro texture will increase over the life of the material as the fines are removed by trafficking. With a generic (BS 4987) CGM there is not a significant amount of bitumen build-up on the surface aggregate, and it is quickly removed by traffic.

Introduction of the new BS EN 13108 Family of Bituminous Mixtures, 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 will be introduced on 1st. January 2008

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 particular 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,

[ Top of Page ]