HOT ROLLED ASPHALT AND ASPHALT CONCRETE (BITUMEN MACADAM),
INFORMATION PRESENTED AS INDIVIDUAL TOPICS

INTRODUCTION

This page is related to the bituminous mixtures, hot rolled asphalt and bitumen macadam, now referred to as asphalt concrete.
The information is presented in small individual paragraphs so you can take a topic at a time, but they are are all mixed up , so learn how to use the "find/search" facility in most web browsers to locate what you are looking for, and hopefully you will gain even more knowledge than you were seeking, good luck.
However you must be aware that major changes have been introduced (from 1st. January 2008) relating to the way in which  bituminous mixtures are specified, this is the introduction of the BS EN 13108 family of standards for the specification of bituminous mixtures. 
Hot Rolled Asphalts and Asphalt Concrete (Bitumen Macadam), are included in this family of standards.
They are listed below for reference,

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

Basically BS EN 13108-1 has replaced BS 4987:Part 1, with perhaps BS EN 13108-2 being used to replace the 
BS 4987:Part 1 for specification of the smaller nominal size mixtures.

BS EN 13108-4 has replaced BS 594:Part 1 for mixture specification of hot rolled asphalts.

BS 594987:Asphalt for roads and other paved areas - Specification for transport, laying and compaction and type testing protocols, is a combined standard replacing BS 4987:Part 2 and BS 594:Part 2.

The published document, PD 6691:Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications,
has been produced, as the title suggests, to offer guidance on the specification of bituminous mixtures to the 
BS EN 13108 family of standards.

However, in my opinion, to obtain bituminous mixtures equivalent to the proven mixtures that you have a history of using it is likely that you will need to make reference to BS EN 13108-20 and BS EN 13108-21, as well as the particular standard for the bituminous mixture you wish to specify.

You will note that BS EN 13108 includes a standard for Stone Mastic Asphalt (SMA), i.e. BS EN 13108-5.

Rather than repeat myself on the progress and nature of these changes may I suggest you study the,
Summer 2007 Newsletter to get up to date.

At this time it is my advice is that you do not throw away your BS 594's and your BS 4987's for a while, if ever. 
This is because  they contain information on good designs and working practice that you may well need when converting your current "well tried" mixtures to an equivalent new BS EN 13108 specification.
The notes below still make reference to BS 594 and BS 4987, but this will be for information purposes only, you will not be able to use these standards for specification purposes. 
The information/guidance included by reference to superseded BS 594 & BS 4987 I regard as still useful.
But the properties and qualities you are familiar with in BS594 and BS 4987 can be obtained by the correct use of the BS EN 13108 family of bituminous mixtures, even if the process is not user friendly.
The amount of cross referencing and introduction of new test methods for fundamental engineering characteristics is  causing me concern, and in these limited notes it is only possible to give a hint of the knowledge that is required to specify bituminous mixtures under the new BS EN 13108 family of specifications.
With a few exceptions  you will still be specifying empirical / "recipe" mixtures as, at this time, as there is insufficient data available for the of specifying bituminous mixtures to "fundamental" procedures.  
In my opinion you MUST get independent advice from an experienced Materials /Road Pavement Engineer on these matters if you are not familiar with the specifying of bituminous mixtures that will be suitable for the sites you intend to surface.
Ii is my belief that in regard to local authority highway networks, it would be advisable to produce a small number of defined specifications that could be referred to for the majority of road surfacing situations.
These defined bituminous mixture specifications being for base, binder course and surface course applications. 
These proven bituminous mixtures are already known by local highway engineers and technicians, but what they may need is assistance in converting existing specifications, pre 1st. January 2008 , to comparable specifications using the BS EN 13108 family of specifications.
The use of the BS EN 13108 family of standards for the specification of bituminous mixtures allows you to still specify generic bituminous mixtures that you are able to employ, in my opinion, to fill all your bituminous surfacing needs on local authority highway networks. 

HOT ROLLED ASPHALT, THE BASICS

HOT ROLLED ASPHALT refers to asphalt that is manufactured by the mixing of fine aggregate (usually sand, may be rock fines), a filler (limestone) and a stiff bitumen, (e.g. 50 pen. for HOT ROLLED ASPHALT WEARING COURSE).
Single size aggregate of the appropriate size and percentage is included to produce a range of HRA materials.
The range of HRA materials and the manner in which they are produced and was, until 31st. December 2007, covered in BS 594 Parts 1 and 2, but from the 1st. of January 2008 is now specified in/from,
BS EN 13108 - Bituminous mixtures - Material specifications - Part 4:Hot Rolled Asphalt

The load carrying/spreading ability of an ASPHALT is a result of the stiffness of the stiff binder, sand, filler matrix.
This is true of the smaller aggregate wearing courses but is less significant with larger aggregate basecourses, and higher stone content wearing courses, where mechanical interlock of the aggregate particles also occurs, also distributing load through the material.

HOT ROLLED ASPHALT WEARING COURSE

HRA WEARING COURSE usually refers to 14mm.30%HRA, laid 40mm. thick, with a layer of 20mm. precoated chippings of a high PSV aggregate spread onto the HRA surface and rolled into it.
This was the most common form of high quality road surfacing material, used mainly for trunk and principal roads, or roads that have a high traffic load or have screwing/turning/breaking from HGV's.

However the only surfacing materials you can now use on motorways and trunk roads, in England, are proprietary "Thin Surfacings".
See :- HD 36/99 : Table 2.2E (England) : Permitted Pavement Surfacing Materials for New and Maintenance Construction.
Issued in February 1999.

As a result of this fairly recent "design guide" there may still be references to HRA wearing course in relation to motorway or trunk road work that I have not yet had time to amend, please be aware of this when you are using the guide.

DESIGN ASPHALT (or RECIPE ASPHALT meeting DESIGN ASPHALT criteria) is still the chosen option on many "A" and "B" roads throughout the country, especially in highly stressed locations, e.g. tight turning points for heavy good vehicles.

HRA wearing course is hard wearing, impervious and with an application of the correct high PSV pre-coated chippings it has excellent skid resistance properties.
BS 594:Parts 1 and 2 (now BS EN 13108 Part 4) cover the constituent materials and the types of mixes.
The transport, laying and compaction of this material, is now covered by,
BS 594987:2007 - Asphalt for roads and other paved areas - Specification for transport, laying and compaction and type testing protocols
 If you are specifying or working with bituminous materials you must have these standards to hand.

PRECOATS FOR HOT ROLLED ASPHALT WEARING COURSE

PRECOATS is the term normally applied to the bitumen coated chippings applied to a 14mm. 30%HRA wearing course to give the running surface both texture and a surface aggregate that has a high PSV., these two properties combine to give a good anti skid surface.
Coated chippings shall now conform to, BS EN 13108-4:2006 - Annex C and PD 6691:2007 - Annex C,
which supersedes BS 594:Part 1, Section 4 that formerly covered the specifying of PRECOATS.

BS 594 did include the following,
a] Grading of the chippings,20mm.and 14mm.nominal size.
b] Flakiness(less than 25%)
c] Binder coating (1.5% +/- 0.3%)
d] Temperature and method of coating chippings
e] HOT SAND TEST for assessing chipping coating quality, i.e. a test to determine whether the binder has been carbonised on coating because of too hot a coating temperature.
Carbonised BINDER is inert and will not melt and bond the chipping to the HRA wearing course.
See the various parts of BS 598 for tests that may still be relevant to assess the above properties.

RUBBERIZED ASPHALT

This is a HOT ROLLED ASPHALT that has been modified by the addition of rubber.
The rubber is added normally in the form of latex at the time of mixing, and it is usual to add 4% to 5% weight of ACTUAL rubber to the mix, latex is only 70% rubber, so you add more latex to achieve the required amount of rubber.
The 4% is a percentage of the binder content and NOT a percentage of the total mix.
Also, the 4% is in addition to the normal binder content and not as a replacement of part of it.
Rubber in asphalt is destroyed by overheating at the time of mixing and prolonged storage at a high temperature, ROAD NOTE 36 PROVIDES FULL DETAILS ON THE FORMULATION, MIXING, STORAGE AND USE OF RUBBERIZED ASPHALT.
Correctly formulated, mixed and laid rubberized asphalt is much more able to resist cracking AND WHEEL TRACK DEFORMATION, and is particularly suitable for laying over old concrete pavements.
Rubber can of course be included in binder course (basecourse) and base (roadbase).

DESIGN HOT ROLLED ASPHALT

The procedure testing of DESIGN ASPHALT was fully covered in :-
BS 598:Part 107, Sampling and examination of bituminous mixtures for roads and other paved areas. Method of test for the composition of design wearing course asphalt.
But from the 1st. of January 2008 this specification has been superseded by, BS EN 13108 : Part 4.
(At this time I am assuming the principles of designing a hot rolled asphalt remain as previously described in BS 594, because as yet I have not studied the appropriate part/s of BS EN 13108-4.) 
The grading specification of DESIGN ASPHALT is the same as that for a RECIPE ASPHALT, what MAY be different is the sand source and the binder percentage.
In the design process many mixes are made using the same constituents and proportions BUT with a range of BINDER contents.
All these mixes are tested for their STABILITY using the MARSHALL TEST APPARATUS, and a graph is drawn of stability against binder content, the binder content at the maximum stability is noted.
A similar exercise is also undertaken for the properties of "maximum mix density" and "maximum aggregate density".
The 3 optimum binder contents are averaged and a factor of .7% added to produce the DESIGN BINDER CONTENT this figure is adjusted to produce the TARGET BINDER CONTENT.

ASPHALT STABILITY - RUTTING RESISTANCE

STABILITY when used in the "broad" context of HRA is used to convey its resistance to deformation, and in particular when applied to DESIGN ASPHALT.
STABILITY meant the maximum resistance to deformation in newtons of a moulded specimen that was made and tested in accordance with the requirements of BS 598:Part 107. (i.e. "THE MARSHALL TEST")
It was necessary to know the STABILITY, determined in this manner, because there was laid down in :-
BS 594:Part 1:Anex B:Table B.1, STABILITY values for certain traffic categories.
In truth it is the ability of an asphalt to comply to the STABILITY and FLOW criteria of a standard such as BS 594 that permitted the bituminous mixture to be referred to as DESIGN ASPHALT rather than the actual "design" procedure.
And many RECIPE ASPHALTS will comply with DESIGN ASPHALT criteria quoted in the table above because it is not sensible/cost efficient for the supplier to use two different sands in his production process.

ASPHALT FLOW - RUTTING - WHEELTRACKING

FLOW is just what it suggests, i.e. the ability of the substance to move under load / traffic.
BUT from a HIGHWAYS MAINTENANCE point of view we MUST use the term FLOW in a specific manner, such as it was defined in BS 594 : Part 1
That is :- FLOW is the deformation of the moulded specimen in millimetres at the point of maximum resistance when made and tested in accordance with the requirements of BS 598 : Part 107, i.e. the "MARSHALL" test.
Choosing HRA wearing course with low FLOW values will help prevent RUTTING and WHEEL TRACKING.
The usual maximum FLOW value for DESIGN ASPHALT is 5mm. for STABILITY values up to 8kn., above 8kn. 7mm. is permissible. This was stated in BS 594:Part 1:Table 11

There was in Table 11 of BS EN 13108-4 a range of wheel tracking rates appropriate to a range of road classifications, and it being the engineers responsibility to specify the appropriate wheel tracking rate.

Reference to criteria for "Resistance to permanent deformation" can also be found in, 
PD 6691-Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications,
Table C.3 - Limiting wheel-tracking recommendations for site classifications, although it is stated that experience in the new test method still needs to be built up.

RECIPE HOT ROLLED ASPHALT

RECIPE ASPHALT is the term applied to HRA SURFACE COURSE (WEARING COURSE) as formerly described in :-
BS  594, Section 3.3, the percentage, or "recipe", of all ingredients is given including the binder percentage.
The composition of various HRA wearing course were given in BS 594:Table 6.
However the term RECIPE is increasingly used to cover all types of HRA mixes in BS 594 with the exception of the specifically named DESIGN mixes, this is because more and more authorities are specifying DESIGN criteria for these other mixes.
This only adds to the confusion, because many RECIPE mixes meet the engineering criteria specified for DESIGN mixes.

AND WE MUST GET THE IDEA OUT OF OUR HEADS THAT "DESIGN" AND "RECIPE"
H.R.A.'s ARE ENTIRELY DIFFERENT, THEY ARE NOT !!!

THEY CAN BE ONE AND THE SAME THING, AND QUITE OFTEN ARE, BECAUSE IT IS MORE EFFICIENT FOR A SUPPLIER TO PRODUCE ONE HRA  SURFACE COURSE (WEARING COURSE), WITH ONE SOURCE OF GOOD ASPHALT SAND, THAT COMPLIES WITH THE SPECIFICATION FOR BOTH "DESIGN" AND "RECIPE".

MIXING TEMPERATURES - ASPHALT - MACADAM

The term MIXING TEMPERATURE was no longer referred to in either BS 4987 or BS 594.
Instead we had the term MAXIMUM TEMPERATURE AT ANY STAGE, and these temperatures for the various materials were quoted in tables in the British Standards.
This creates the interesting point that we had to use this temperature, (as it is  the only figure specified), as both maximum MIXING TEMPERATURE and maximum DELIVERY TEMPERATURE.
So if the DELIVERY TEMPERATURE is too high you know the MIXING TEMPERATURE was also too high.
N.B. Be aware that the maximum mixing temp. for 30%/14mm. with 50pen. bitumen has returned to 190 deg. Centigrade with the most recent BS 594, but check the current standard as this temperature is argued about.

ROLLING TEMPERATURES - ASPHALT - MACADAM - COMPACTION

Stated rolling temperatures can be a little confusing because in BS 4987:Part 2,(macadams) two rolling temperatures are given in separate tables.
There is a "minimum rolling temperature" given in TABLE 3 and there is a "minimum temperature immediately prior to rolling" in TABLE 4.
The "minimum temperature immediately prior to rolling" is the temperature I have quoted in BITUMINOUS TEMPERATURE TABLE.
The first definition i.e. "minimum rolling temperature" is usually understood to mean the temperature by which rolling is substantially complete.
With HRA mixtures there was just one rolling temperature quoted i.e. the "minimum rolling temperature", these were in TABLE 1 of BS 594:Part 2,
The BS's quoted above should be available to all staff involved with bituminous materials.

Currently minimum rolling temperatures can be found in,
BS 594987:2007 - Asphalt for roads and other paved areas - Specification for transport, laying and compaction and type testing protocols

ASPHALT - MACADAM - LAYING TEMPERATURES

Laying temperatures in general (including cement bound material) are covered in the DOT Specification for Highway Works, Clause 703, Cold Weather Working, of the 700 Series, Road Pavements-General.
WIND CHILL information is provided in DTP DESIGN MANUAL HD 27/94.
Laying temperatures appropriate to "Recipe" H.R.A. were stated in B.S.594:Part 2:1992 Specification for the transport, laying and compaction of rolled asphalt.
See para 6.1 in this edition, it states you can lay at minus 3 degrees in CALM weather.
Laying temperatures appropriate to COATED MACADAM are stated in B.S.4987: Part 2 : Specification for transport, laying and compaction. Para 5.2
You MUST consult the current documents for accurate advice, but criteria common to both BS 594 & BS 4987 were:-
1) laying shall cease at 0 deg.C on a falling thermometer, when NOT calm.
2) laying may begin at -1 deg.C on a rising thermometer.

Minimum rolling temperatures for hot rolled asphalt and asphalt concrete can currently be found in, 
BS 594987:2007 - Asphalt for roads and other paved areas - Specification for transport, laying and compaction and type testing protocols

TAKING TEMPERATURES - MACADAM - ASPHALT

The detail of how to take the temperatures of hot material, the type of thermometer to be used and the calibration of the thermometer is all to be found in the following standard.
BS 598:1990:Sampling and examination of bituminous mixtures for roads and other paved areas:
Part 109, Methods for the assessment of the compaction performance, and recommended procedures for the measurement of the temperature of bituminous materials
Basically the British Standard "recommends the use of a 300mm. long probe and an electronic thermometer accurate to +/- 2 degrees with the probe inserted at least 250mm. into the material, 500mm. from the edge of the lorry body, moving the probe frequently only then recording the final temperature.

WIND CHILL FACTOR - LAYING ASPHALT AND BITUMINOUS MACADAM

It is extremely important to take into account the WIND CHILL FACTOR when laying hot bituminous materials, especially when laid in thin layers.
Notably HRA WEARING COURSE when applying PRECOATS, and in particular with "dry" HRA DESIGN WEARING COURSE.
The minimum air temperatures laid down in specifications allowing the laying of bituminous materials do not take account of wind speed.
The rate at which a "hot material" looses heat is greatly increased with increase in wind speed.
Graphs are available in the "700" series in the March 1998 DOT Specification for Highway Works.
This is a VERY VERY real problem, and if you do not take account of it in your site management the quality of work will suffer.
A good practice to adopt in windy conditions when laying HRA and precoats is,
ALL MATERIAL THAT IS TO BE LAID, TO BE ON SITE BEFORE YOU START LAYING, HAVE THE CHIPPER CLOSE BEHIND THE PAVER, AND THE ROLLER CLOSE BEHIND CHIPPER

A hot material laid at an actual air temperature of plus 7 degrees centigrade and a wind speed of25 m.p.h. will loose heat at a rate equal to a still air temperature of minus 5 degrees.

DELIVERY TEMPERATURES - BITUMINOUS ASPHALT & MACADAM

This is the temperature of the material when it arrives on site, and temperatures should be taken within 30 minutes of arrival.
This is no problem if material is being used quickly, but if there is a delay in tipping lorries their load temperatures should be taken on arrival.
BS 598:PART 109, described the full procedure for taking temperatures.

PERVIOUS MACADAM - POROUS ASPHALT - OPEN GRADED - SPRAY REDUCTION

As the name suggests this material is "designed" to allow the passage of water through its matrix.
I use the term "designed" loosely, because basically this material is an OPEN GRADED MACADAM with a suitable high viscosity, stiff, binder/bitumen.
The principal in using a stiff binder, combined with the mechanical interlock of the macadam grading, is to prevent the deformation of the material so keeping the water pathways open.
This material is desirable in as much as it reduces the hazard from reduced visibility caused by spray considerably, it is also a quieter running surface compared to HRA wearing course, at least in its early life.
The decrease in spray is brought about by the water being dispersed through the pathways in the open nature of the material, and not thrown up as spray by the vehicles wheels.
The longevity of this material is not yet proven, problems with the blocking of water pathways with detritus have occurred, as have frost problems with trapped water.
Also it cannot be disputed that oxidation of the bitumen will be increased in the matrix of the layer, and there will be hydraulic scouring as water is forced through the interconnecting voids.
This material is specified in BS 4987:PART 1, CLAUSE 8.1, AND CLAUSE 8.2.

ROAD NOTE 36 - RUBBERIZED ASPHALT - RRL/TRL PUBLICATION

This is the Specification for the manufacture and use of rubberized bituminous road materials and binders, access to a copy is a MUST if you are specifying / using rubberized asphalt.

FINE COLD ASPHALT - FOOTWAY SURFACING AND OVERLAYS - 3MM. SIZE, FINE GRADED WEARING COURSE

This was/is a fine wearing course material particularly used for footways, but it has undergone a name change to :-
MACADAM, 3MM. FINE GRADED WEARING COURSE.
This is a very good material for footway surfacing, overlaying and patching.
Choose the correct viscosity binder, a 300 or 200pen. STRAIGHT RUN bitumen, lay it at the correct temperatures,
AND ROLL IT AS SOON AS YOU HAVE IT RAKED TO THE REQUIRED LEVEL!
Observe the minimum rolling temperatures, do not allow large areas of material to be laid, going cold, before you start rolling it, or you will not obtain the required compaction and the life of the surfacing will be reduced substantially.

SLURRY MACADAM - MICRO ASPHALT

This product is becoming increasingly popular, mainly because of its ease and speed of laying. 
Although it is a good material used in the right situation, it is relatively expensive compared to a conventional British Standard material, e.g. a 20/30mm. overlay of a 6mm. wearing course macadam or 10mm/55% HRA wearing course.
Although I do not like using proprietary names in this database, it is difficult not to do so in this case because all SLURRY MACADAM is supplied under proprietary trade names, the most well known being RALUMAC, and the word RALUMAC is being used to describe the process, just as SHELLGRIP is used to describe calcined bauxite / epoxy binder high friction / anti-skid surfacing.
SLURRY MACADAM adds very little if any strength, depending on thickness, to a road pavement.
It should, really, only be considered as a surface treatment, and may best be considered as a "safer" alternative to surface dressing in "sensitive" urban areas with regard to stripping of aggregate.
Although SLURRY MACADAM will usually shed some aggregate soon after laying and it can look a little untidy until it settles down.
SLURRY MACADAM / MICRO ASPHALT can considerably extend the life of a sound surface course that is starting to undergo surface fretting, as can surface dressing.

COLD WEATHER WORKING - LAYING BITUMINOUS MATERIAL - ASPHALT - BITUMEN
MACADAM

This topic was covered in BS 594:Part 2,(hot rolled asphalt), BS 4987:Part 2, (coated macadams).
Be aware the specification criteria is different for "RECIPE" and "DESIGN" asphalt, because DESIGN ASPHALT is usually a stiffer material.
DESIGN ASPHALT was used on trunk roads/motorways and information on this material can still be found in the DfT. Specification for Highway Works, Volume 1, Series 700 and 900.
It is very important that you pay attention to the WIND CHILL FACTOR when laying bituminous materials, especially if you are laying thin layers.
Minimum recommended ROLLING TEMPERATURES and maximum DELIVERY TEMPERATURES
can be found on this web site for some bituminous materials, but it is far easier if you still have copies of BS 4987 AND BS 594, or a current copy of BS EN 594987
With proprietary materials you have to look to the recommendations made by the supplier.

RATE OF SPREAD OF PRECOATS FOR HOT ROLLED ASPHALT

The correct rate of spread of precoated chippings is required so that we may achieve the correct surface TEXTURE of the wearing course, and no more.
Unfortunately some wearing courses have been over-chipped to make absolutely sure that they achieve the TEXTURE DEPTH specification, and this is to the detriment of the road surface.
This has lead to chipping loss and poor quality wearing course surfaces.
The ideal rate of spread is "shoulder to shoulder" cover with no chippings on top of chippings, this is unrealistic, so 70% of the "shoulder to shoulder" rate is aimed for.
If you need a figure to work with, for 20mm. PRECOATS, use 14kg./sq.metre, and be prepared to adjust it a little on site.
Use a CHIPPING TRAY to check the rate.
Remember good TEXTURE is important on high speed roads, but is less important on low speed roads.
The PSV of the PRECOATS is the more significant factor in SKID RESISTANCE at lower speeds.

ORDERING MATERIAL - ASPHALT - COATED MACADAM

It is VERY, VERY, VERY IMPORTANT to order the correct material for the particular site.
It is no use at all to blame the material for being "no good" if you ordered it incorrectly, OR, did not specify it correctly to your chosen supplier, this applies to all materials, but in particular BITUMINOUS MIXTURES/MATERIALS.
Included in this guide are descriptions of all the common HOT ROLLED ASPHALT and ASPHALT CONCRETE (BITUMINOUS MACADAM) materials, and included in the information within this website are the appropriate specification references, QUOTE IT when ordering that material.
Also quote the particular VISCOSITY you require.
It has to be noted that since 1st. of January 2008, and the introduction of the BS EN 13108 family of standards for specifying bituminous mixtures it has become increasingly difficult for the "general" highway engineer or technician to be confident in specifying/ordering the correct bituminous mixture appropriate to the site that they are responsible for surfacing.

WHY DID IT FAIL ? - ASPHALT - BITUMEN MACADAM - SPECIFYING

It's truth time, did you specify the material correctly, you cannot blame the material if you decided to use a material that was not suitable for the particular job in hand, or to use it in unsuitable weather conditions.
There is plenty of information within this guide to help you specify materials correctly.
BUT do not forget to call upon the advice and knowledge of your peers and colleagues, (this does not always help!).
Here is a list of items to consider:-
1] weight of traffic using road
2] thickness of layer, i.e. maximum stone size
3] viscosity of binder
4] hand laid or machine laid
5] ambient laying temperature, etc.,etc.,etc.,

HOT ROLLED ASPHALT BASE (ROADBASE) - BINDER COURSE (BASECOURSE)

Interestingly there is now no difference between HOT ROLLED ASPHALT BASE (ROADBASE) and HOT ROLLED ASPHALT BINDER COURSE (BASECOURSE) with regard to the constituent specification of the two materials. 
These specifications were detailed in BS 594:Part 1:Table 2.
It is really just a case of which pavement layer the material is included in as to whether it is called HOT ROLLED ASPHALT BASE (ROADBASE) or HOT ROLLED ASPHALT BINDER COURSE (BASECOURSE).
But generally the larger stone sizes laid in thicker layers are used as BASE (ROADBASE).

BS 598:PART 107 - DESIGN HOT ROLLED ASPHALT

The full title was :-
BS 598 : Sampling and examination of bituminous mixtures for roads and other paved areas
: Part 107 : Method of test for the composition of design wearing course asphalt.

DESIGN BINDER CONTENT - ASPHALT

The DESIGN BINDER CONTENT is the binder content of an asphalt mix that was produced in accordance with 
BS 598:Part 107 i.e. the binder content that will give you the highest stability figure for the sand, aggregate and filler you have used, and also provide you with a FLOW figure within specified limits.
The DESIGN BINDER CONTENT can be the TARGET BINDER CONTENT, but this is not necessarily so.
The TARGET BINDER CONTENT can be increased to allow for such properties as WORKABILITY and DURABILITY.
It is necessary to check that the TARGET BINDER CONTENT will still meet the appropriate specified limits for FLOW and STABILITY that were stated in,
BS 594:Part 1 for a particular traffic category.
For a more complete explanation read BS 594:PART 1:1992, para 3.2.4.

BINDER CONTENT CORRECTION - ASPHALT - MACADAM

The correction of found BINDER and FILLER amounts was fully covered in :-
BS 598 : PART 102, Clause 6.
These corrections applied to, HRA materials and DENSE coated macadam roadbases and basecourses.
14MM.and 10MM. CLOSE GRADED MACADAMS were included in the above clause to have their binder results corrected according to fines content of the sample, but this is NOT the case now, there has been an amendment excluding them from this clause.
Why we correct is to allow for the vagaries of sampling, if a sample has been taken incorrectly and because of this has a high fines content it will follow there will be a higher than expected FOUND BINDER CONTENT and FOUND FILLER CONTENT.
This is because a sample with a high fines content has far more surface area of aggregate coated with BINDER, and on analysis this will give the high binder content.
So we make these binder adjustments to correct back to a mid specification aggregate grading.

One of the significant changes with regard to specifying and testing of bituminous mixtures introduced with the BS EN 13108 family of standards is that there is now no adjustment made to to test results to allow for the vagaries of sampling.
"As found" results of analysis are now quoted in test results, although it is possible some materials laboratory and test houses may still supply "adjusted figures" if they are requested, but these adjusted figures will be for information purposes only.

NOTTINGHAM ASPHALT TESTER - NAT - ELASTIC STIFFNESS

This apparatus is capable of performing the INDIRECT TENSILE TEST to measure ELASTIC STIFFNESS, and the REPEATED LOAD AXIAL CREEP TEST to determine resistance to deformation, i.e. CREEP STIFFNESS.

PEN - PENETRATION - BITUMEN VISCOSITY

PEN is a shortening of the word PENETRATION, the term is used in stating the grades of viscous / stiff BITUMEN.
E.g. 50PEN. BITUMEN is used in HOT ROLLED ASPHALT WEARING COURSE.
What it actually means is that in the penetration test for the BITUMEN the needle penetrated 50 tenths of a milimetre into the BITUMEN sample at standard conditions.

BITUMEN PERMITTIVITY - WEATHERING

It is thought that BITUMEN with a high PERMITTIVITY value will weather to a higher degree allowing the maintenance of higher texture depths in HOT ROLLED ASPHALT WEARING COURSES.

TRRL REPORT LR 370 : Full-scale road experiments using rubberized surfacing materials

This report relates to full scale RUBBERIZED BITUMINOUS MATERIAL trials (including HRA) conducted on various sites throughout the country.
This report includes two Leicestershire sites, the A6 Lockington and the A426 Dunton Basset.
The material was laid over roads of concrete bay construction to help prevent reflective cracking from the joints between bays.

TRRL REPORT LR 308 : Resistance to cracking of rubberized asphalt : Full-scale experiment on Trunk Road A6 in Leicestershire.

This report is a case study of a full scale experiment, the length of road chosen for the experiment was of concrete bay construction, and a BINDER (BASECOURSE) and SURFACE COURSE (WEARING COURSE) were laid, 4% and 5% of rubber by weight was added to the 50PEN. BITUMEN in the form of rubber latex.
The latex itself being 68% dry rubber, it is very interesting to note the BINDER percentage of the WEARING COURSE was also increased by 1% giving quite a rich mix.
The report declared the trial a success, especially the sections with a 75mm. binder course (basecourse) and 50mm. wearing course.
This road did not suffer abnormal rutting and I suggest anybody considering adding rubber to "dry" DESIGN ASPHALT read this report.

MARSHALL TEST APPARATUS - DESIGN HOT ROLLED ASPHALT

This apparatus is used in the design of HOT ROLLED ASPHALT where asphalts of a known high stability are required, such as airport runways.

HOT ROLLED ASPHALT JOINTS - WEARING COURSE

This topic was fully specified in BS 594 : PART 2 : Para 6:6, but is now included in BS 594987.
And again I stress BS 594 was a "working" document and I suggest that access to these superseded documents may still provide very useful information.
To summarise the method most widely used is to cut back the exposed joint to a VERTICAL face of not less than the specified thickness, i.e. usually 40mm., discarding ALL loosened material, and painting the vertical face COMPLETELY with hot 50/70 pen. bitumen.
You will be told many "tales" of why other less bothersome methods work just as well.
All I would like to say is that after 20 years I know this method works.
You only have to look at all the opening/fretting joints on HOT ROLLED ASPHALT SURFACE COURSES (WEARING COURSES) to know that this subject is one that needs to have attention focused on it.

DESIGN ASPHALT BINDER CONTENT - HOT ROLLED ASPHALT SURFACE COURSE (WEARING COURSE)

A minimum TARGET BINDER CONTENT for DESIGN HOT ROLLED ASPHALT WEARING COURSE is important, to ensure that you retain the properties of WORKABILITY and DURABILITY in the asphalt, as well as STABILITY.
Accepting a DESIGN ASPHALT with too low a BINDER content can result in poor WORKABILITY and poor DURABILITY, so STABILITY is not the only mix property you need to consider.
Minimum TARGET BINDER CONTENTS should be set for each DESIGN wearing course material.

HOT ROLLED ASPHALT SURFACE COURSE (WEARING COURSE) - PRECOAT LOSS - FAILURE

PRECOATS are lost in two ways.
1) They are lost into the HRA mat at the time of application and rolling,
2) They are lost from the mat due to poor bonding and embeddment.

However there are a number of reasons for both these types of chipping loss!

Reasons for PRECOATS lost into the mat:-
[1] Material too hot, if temperature is within specification delay
rolling.
[2] HRA mat too thick, regulate prior to wearing course to achievecorrect nominal thickness.
[3] Unstable material, WET SAND (usually after heavy rain), or bad mix proportions.

Reasons for PRECOATS lost FROM the mat:-
[1] Material too cold, PRECOAT binder coating is not melted to create bonding, check ALL temperatures
[2] HRA mat too thin, check thickness.
[3] Over chipping, chips on chips, check rate of spread.
[4] Delay in first pass of roller.
[5] PRECOAT bitumen coating too thin OR burnt/carbonised so no bonding of chips to asphalt.

WET SAND IN HOT ROLLED ASPHALT - RIDE QUALITY FAILURE - LOSS OF PRECOATED CHIPPINGS

This is a phenomena which DOES occur whatever suppliers claim !
It is a rare happening, but when it does happen it is usually after a period of heavy or continuous rain that has saturated the sand stockpiles.
The time for the sand spent in the drier will not have been increased to remove the extra water, OR production pressure does not allow for the increasing of drying time.
The water is not of course water but steam trapped around the sand particles, this produces instability in the asphalt.
It will show itself in the lorry body by being absolutely flat with usually free bitumen on the surface, and if stood on, (on top of the sheet), in extreme cases you will be able to make the asphalt move like a liquid.
Because of its instable nature it is difficult to control the "bed" of the Blaw Knox making it difficult to lay to levels, also PRECOATS applied to the surface may disappear into it.

HOT ROLLED ASPHALT LAYER THICKNESS

Nominal LAYER THICKNESS values were included in BS 594.
In order to achieve required thickness of bituminous layers it is necessary to know about LAYER TOLERANCES that are specified in the DfT. Specification for Highway Works.
The "manipulation" of these tolerances on individual construction layers can lead to significant reductions in overall pavement thickness.
This can have a profound effect on a ROAD PAVEMENT that has a relatively thin bituminous layer e.g. a typical 60mm. BINDER COURSE (BASECOURSE) and 40mm. WEARING COURSE construction.
Check it out!

ASPHALT - MACADAM - LAYER THICKNESS - ROAD PAVEMENT DESIGN

The thickness of bituminous materials, (or indeed any other road making material), will be decided upon as a result of a ROAD PAVEMENT DESIGN based on TRRL REPORT 1132, or even ROAD NOTE 29, if it is not a heavily trafficked road.
This is especially applicable to the BASE (ROADBASE) layer with both MACADAM and ASPHALT, as the BASE (ROADBASE) layer is the main load distributing layer of the ROAD PAVEMENT.

POROUS ASPHALT WEARING COURSE

The name POROUS ASPHALT is technically misleading this material is not an ASPHALT in its make up and characteristics, as UK road engineers traditionally understand the term, POROUS ASPHALT is a STIFF open graded macadam.
It was specified in,
BS 4987: Coated macadams for roads and other paved areas,
Clauses :-
2.8.1 MACADAM, 10MM. SIZE POROUS ASPHALT SURFACE COURSE (WEARING COURSE)
2.8.2 MACADAM, 20MM. SIZE POROUS ASPHALT SURFACE COURSE (WEARING COURSE)
BS 4987:1993 is now issued and PERVIOUS WEARING COURSE is now called POROUS ASPHALT SURFACE COURSE (WEARING COURSE), this is a change from BS 4987:1985

Porous asphalt is now specified in accordance with,
BS EN 13108-7   : 2006:Bituminous mixtures. Material specifications. Porous asphalt

POROUS ASPHALT will reduce spray during wet weather, it will also reduce road noise.
This has to be balanced against increased costs and a considerably reduced life compared to a conventional 30%/14mm. H.R.A. asphalt surface course (wearing course), with an applied PRECOAT layer.

MEDIUM TEMPERATURE ASPHALT - MTA

This term can be a bit ambiguous but the most common use of the term MEDIUM TEMPERATURE ASPHALT is to describe materials graded similarly to HIGH STONE CONTENT ASPHALT but with a less viscous binder, e.g. a 100pen or 200pen. replacing a 70pen or 50pen..
This means the material can be less hot, and still have the same workability.
The theory behind this is that the higher stone content will replace the stability in the mix lost through the reduction in stiffness of the bitumen binder.
It is NOT usual to put a less stiff BINDER into a normal 14mm./30% HRA WEARING COURSE that includes PRECOATS except where a BINDER modifying agent is included, e.g. EVA in a 70pen. BITUMEN, the EVA increases asphalt stiffness at ambient temperatures.
MEDIUM TEMPERATURE ASPHALT is gaining favour in high quality HAND LAY PATCHING, and is being used, on occasions, to patch areas of proprietary Thin Surfacing when Utility work takes place.

TRRL RESEARCH REPORT 323 - POROUS ASPHALT

This report is a comprehensive study on trials conducted on POROUS ASPHALT with differing binders and additives, as well as associated trial areas of HOT ROLLED ASPHALT for comparison purposes.
The trials taking place on the A38 Burton Bypass in November/December 1987.
This report is recommended reading for anybody considering using POROUS ASPHALT, and seeking information on various modified bitumens included in the trial.
The Shell bitumen MULTIPHALTE was included as a binder in the HOT ROLLED ASPHALT trial lengths.

TRRL RESEARCH REPORT 122 : The effect of EVA modified bitumens on rolled asphalts containing different fine aggregates

This report covers trials documenting the effect of EVA modified bitumens on hot rolled asphalts containing different fine aggregates.
WELL WORTH READING, if you want some basic information on EVA in HRA, especially HRA wearing courses.

TRRL TECHNICAL REPORT 303 - ASPHALT SUBSTITUTION

This report presents road trials that have been carried out to assess the potential for using bituminous materials to replace thicker layers of granular materials in road construction.
It was shown that providing the foundation was strong enough to support construction traffic with negligible deformation and ASPHALT SUBSTITUTION was worth considering.
It is important to stress the subgrade/laying surface MUST be able to take construction traffic. 
Conventional design with a granular sub-base layer will be able to cope much better with the vagaries of English weather and the softening of subgrades.

HOT ROLLED ASPHALT ROADBASE MATERIALS

There are three available HOT ROLLED ASPHALT BASE (ROADBASE) MATERIALS, information on these materials is to, be found in the web site under the following headings:-
ASPHALT 60/20 BINDER COURSE/BASE (BASECOURSE/ROADBASE)
ASPHALT 60/28 BINDER COURSE/BASE (BASECOURSE/ROADBASE)
ASPHALT 60/40 BINDER COURSE/BASE (BASECOURSE/ROADBASE)
Make sure you choose the correct stone size for the job in hand, this does not always mean slavishly following the recommended stone sizes in the specification.
Any doubt in your mind, and it is safer to choose smaller than larger.

HIGH STONE CONTENT ASPHALT - HSCA - MEDIUM TEMPERATURE ASPHALT

HSCA is short for HIGH STONE CONTENT ASPHALT.
This is NOT a new material, if you knew how to specify what you wanted from BS 594, it has been around for at least 25 years, and used in many areas of the UK.
It is a good material used on  suitable sites.
There are two HSCA's which were specified in BS 594 as design asphalts :-

14mm./55%, (Table 3,Col.3/5)
10mm./55%, (Table 3,Col.3/4), both with a 50pen. or 70pen. binder.

They are good stable materials, but do not have a high surface texture, so include a coarse aggregate that has a suitable polished stone value for the nature, speed and traffic conditions of the site.
While on the subject there is another term now being used, that is MEDIUM TEMPERATURE ASPHALT.
These mixes are HSCA gradings but with a less viscous binder, e.g. a 100pen. or a 200pen.
Again not new materials if you new the specification, but a new name.
The ASPHALT BINDER COURSE (BASECOURSE), 55/10 and 55/14 should also be considered as HSCA's with higher binder contents.

TRL RESEARCH REPORT 298 : CRUSHED ROCK FINES IN HOT ROLLED ASPHALT

This is a study of trials carried out on the A303 near Mere in Wiltshire.
Trial plots with wearing course mixes incorporating crushed rock fines, different penetration binders and amounts of binder were laid and tested over a period of six years, the results are tabulated and discussed in this report.

GOOD BOOKS ON ASPHALT / MACADAM COMPACTION

These include:-
1) BS 4987:Part 2
2) BS 594:Part 2
3) BS 598:Part 104
4) BS 598:Part 109

These BS's contained excellent information regarding the compaction of bituminous materials, and although now superseded hopefully they will still be available to all those supervising the laying of bituminous materials, and needing guidance.
Current specifying information can be found in,
BS 594987:Asphalt for roads and other paved areas - Specification for transport, laying and compaction and type testing protocols
There are a number good books/booklets produced on compaction by the manufacturers of compaction equipment, e.g. "Bomag".

ASPHALT RATES OF SPREAD - COVERAGE

The rate of spread of each particular ASPHALT material will be found in the subject entry appropriate to that material in the list of asphalt concrete mixtures (bitumen macadams) and hot rolled asphalts.

e.g. the rate of spread of ASPHALT 14MM/30% WEARING COURSE will be found under that material heading.


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