|[ Top ]||Hot Rolled Asphalt and Bitumen Macadam|
The Idiots' Guide to Highways Maintenance
Copyright © 2000/15, C.J.Summers
BITUMEN VISCOSITIES FOR BITUMINOUS MATERIALS
|UPDATE OF SPECIFICATION FOR PAVING GRADE BITUMENS||A DEFINITION OF VISCOSITY|
|BITUMINOUS MATERIAL VISCOSITY TABLE||BITUMEN DENSITY|
|BITUMEN VISCOSITY||FLUXED BITUMEN|
|THE RANGE OF BITUMINOUS MATERIALS AVAILABLE||CUTBACK BITUMEN|
|A BIT ABOUT BITUMEN||
BS 2000 - STANDARDS
FOR THE TESTING OF BITUMEN
AND BITUMINOUS PRODUCTS
IN PLANT BLENDING/FLUXING OF PENETRATION GRADE BITUMENS
NEW! AND SIGNIFICANT CHANGE TO GRADES OF BITUMEN
"LOW ENERGY ASPHALT"
NEW! (and the title in inverted commas will be explained)
|FREE TECHNICAL INFORMATION|
SPECIFICATION FOR PAVING GRADE BITUMENS
The bitumen grades included in the table below are as stated in,
BS 3690 : 1989 : Bitumens for building and civil engineering : Part 1, Specification for bitumens for road purposes.
The figures in brackets are those relating to BS 3690
From 1st January 2002,
BS EN 12591 : 2000 : Bitumen and bituminous binders - Specifications for paving grade bitumens,
will be replacing BS 3690, so you should obtain a copy of BS EN 12591 as soon as possible if you do not already have a copy.
The figures in red are the "new" viscosity grades quoted in BS EN 12591.
The changes in relation to how the penetration grades of bitumen are specified are not great, however the way the softer grades of bitumen will be specified in relation to current practice could lead to some confusion.
So, if you are involved in specifying the more workable, hand-lay type of bituminous materials some serious homework on the subject will be necessary, and I have not included the new softer grades in this table to avoid confusion.
From 30th. September 2009,
BS EN 12591 : 2009 : Bitumen and bituminous binders - Specifications for paving grade bitumens,
has superseded BS EN 12591:2000 which is withdrawn.
This European Standard provides a framework for specifying a range of properties and relevant test methods for bitumens, which are suitable for use in the construction and maintenance of roads, airfields and other paved areas, together with requirements for evaluation of conformity.
In my opinion this is a working document which any office regularly ordering bituminous mixture material should contain a copy.
BS EN 12591 : 2009 also contains informative guidance on the selection of appropriate "standard" grades of bitumen, i.e. Table NA.1 and Table NA.2
It also provides details relevant to preparing a declaration of conformity which enables the manufacturer to affix a CE marking.
BITUMINOUS MATERIAL VISCOSITY TABLE
( using the widely available range of "normal" straight run bitumens, but you MUST be aware of in plant blending with flux oil, more below )
NOTE : Since the specification BS EN 12591 : Bitumen and bituminous binders - Specifications for paving grade bitumens was introduced bitumen viscosities are stated as a range rather than a central target figure with a permissible tolerance, e.g. 50pen. should now really be referred to as 40/60pen.
Machine-lay material, needs to be hotter
when mixed, and for high temperatures
to be retained up to and including laying,
difficult to lay by hand, and requires heavier compaction but will produce higher stability
Needs less heat in mixing,
and retains some workability when cool, but finished surfaces can be "lively"
and slow to harden.
Easy to work by hand, but prone to deformation
the less viscous, the more "lively" it is.
40/60 (50) PEN :- 30/35% HRA surface course and SMA surface course on trunk roads, principal roads, and other roads carrying heavy traffic, i.e. lots of HGV's.
HRA binder course (basecourse) and base (roadbase), also some of the modern bitumen macadam "heavy duty" binder course (basecourse) and base (roadbase).
Dense bitumen macadam (asphalt concrete) binder course (basecourse) and base (roadbase), and similar hot rolled asphalt mixtures under the surface course mixtures already described.
100/150 (125 ) PEN :- Surface course mixtures on less heavily trafficked roads but still with significant traffic, also dense bitumen macadam (asphalt concrete) binder course (basecourse) and base (roadbase) under macadam surface course (wearing course).
160/220 (190) PEN :- Surface course bituminous mixtures on less heavily trafficked highways, or where there is slight movement in road pavement to allow for settlement without cracking.
Usually the "base" bitumen in surface dressing binders, it is a good compromise between fatting up and being brittle.
250/330 (290) PEN :- Binders suitable for hand-lay work according to :-
(1) Working temp., i.e. summer or winter, hot or cold.
(2) How quickly material can be laid, i.e. 2 hours work or all day working.
(3) How warm can material be kept, i.e. stockpile on road or in insulated "hot-box".
The more factors against laying choose a more workable binder,
remembering a workable binder at the time of laying can give problems later through lack of stiffness, especially during hot summer weather.
Change from penetration grade bitumens
Very workable "sticky" binder for use in
temporary patches, pothole repairs, etc
# It is worth pointing out that this method of specifying cutback bitumen is still referred to in recent Shell Bitumen Handbooks, whereas if you look in the final editions of BS 4987, before they were superseded, and the new BS EN standards, cutback and deferred set bituminous mixtures are "specified" in an entirely different way, so consult BS EN 12591.
Personally I prefer the Shell approach, as a materials technician I believe it gives me greater control over specifying the bituminous mixture I require for a particular type of work, as well as the specifying process being far simpler.
None standard "Depot Stock", and "Bucket" materials
There are binders which have been further "cut-back" (i.e. extra volatile light oil such as kerosene, creosote is no longer permitted, has been added to the binder) for use in mixing material intended for depot stock, this material
can be used cold over a period of days, quite often used for emergency patching of a temporary nature, this material is prone to "plucking out" and binder stripping by carriageway water.
In emergency situations where the amount of material is not great it may be preferable, and even more cost effective, to use a specialist "tubbed" material with a very volatile cutback used in quite a stiff penetration grade binder.
The volatiles (usually white spirit) evaporate rapidly leaving quite a durable material if workmanship in preparation of the pothole has been good.
The row of "stars" *********** in the table above Indicates the point where the way of stating the viscosity (i.e. degree of stiffness) of bitumen from a penetration based laboratory test (PEN. tenths of a millimetre), to time based laboratory "flow" test (SECS., seconds of time), from a Standard Tar Viscometer, even though we are now testing bitumen.
A 300PEN. bitumen will be such that a standard needle having a 100g. load on it will penetrate a standard sample cup of bitumen 300 tenths of a millimetre, at 25 degrees centigrade in 5 seconds.
With a 200SECS. cut-back bitumen, it is so called because it will take 200 seconds for 50 ccs. of bitumen to run through a standard hole at 40 degrees centigrade.
Be Careful The smaller the number with penetration (PEN.) grade bitumens the stiffer the material i.e. 50PEN. is stiffer than 100PEN. bitumen.
The stiffer bitumens resist penetration giving a low number.
The smaller the number with "time" (SECS.) grade cut-back bitumens the more lively it will be, i.e. 100SECS. bitumen will be more lively than 200SECS bitumen.
The stiffer bitumens take longer to flow through the standard orifice giving a high number.
THE RANGE OF BITUMINOUS MATERIALS AVAILABLE
A full range of bituminous materials incorporating the above binder grades can be found in :-
BS 594:2003 Hot rolled asphalt for roads and other paved areas : Part 1 : Specification for constituent materials and asphalt mixtures.
BS 4987:2003,Coated macadam for roads and other paved areas : Part 1 : Specification for constituent materials and for mixtures.
However these standards have now been superseded, so for good, easy to understand, specifications that are practically the same specifications, "recipes", as in BS 594 and BS 4987
refer to the appendices of,
British Standard, PD 6691:2010:Guidance on the use of BS EN 13108 Bituminous mixtures - Materials specifications,
Asphaltic Concrete / Bitumen Macadam "One Page Guide"
Hot Rolled Asphalt "One Page Guide"
for simple guidance on bituminous mixtures and their common viscosities.
BUT, HAVING EXPLAINED ALL THE ABOVE I WOULD NOT RECOMMEND CUTBACK MATERIALS UNLESS ABSOLUTELY NECESSARY
BITUMINOUS MIXTURES WITH A "300"PEN. STRAIGHT RUN BITUMEN, KEPT HOT BY "HOT-BOX" OR THERMAL BLANKET,
I BELIEVE, IS THE BEST COMPROMISE FOR SMALL HAND-LAY WORK
A BIT ABOUT BITUMEN
Bitumen is a viscous liquid consisting mainly of hydrocarbons of complex molecular structure.
It is a product derived from the refining of crude oil.
Only a few sources of crude oil are capable of producing good quality bitumen compared with the many oil producing areas in the world.
The British Standard covering bitumens used in road construction and maintenance was :-
B.S.3690:1989:Bitumens for building and civil engineering :
Part 1, Specification for bitumens for road purposes.
But from 1st. January 2002 is,
BS EN 12591 : 2000 : Bitumen and bituminous binders - Specifications for paving grade bitumens,
The above specifications cover the composition and properties of bitumens used in producing materials for road making including cutback bitumen and bitumen emulsions for surface dressing.
It is its thermoplastic nature, (stiff when cold liquid when hot), that makes bitumen so useful.
Bitumen is manufactured in different viscosities, and the appropriate viscosity should be chosen for the particular material, site conditions, and traffic.
A DEFINITION OF VISCOSITY
VISCOSITY can be defined as, "the property of a fluid which enables it to resist flow".
So the more VISCOUS a BINDER is the more it will resist flow and conversely the less VISCOUS a BINDER is, the less it will resist flow.
VISCOSITY can also be a numerical measure of the above property,
E.g. "what is the VISCOSITY of a conventional hot rolled asphalt wearing course binder ?
Answer, it is 50pen."
The density of bitumen is approx. 1 tonne per cubic metre at 20 deg.C., i.e. about the same as water, but bitumen expands when it is hot as with most materials, so if you are purchasing in litres be sure you know at what temperature the litres are being measured.
1 tonne of cutback bitumen or bitumen emulsion used in surface dressing if sprayed at 1mm. thickness will give 1000 sq.metres,
i.e. 1kg. of bitumen gives a 1mm. covering over 1 sq.metre.
Remember K1-70 bitumen emulsion commonly used for surface dressing is only 67% bitumen, the remainder being water.
FLUXED BITUMEN refers to a BITUMEN that was a stiff PENETRATION GRADE but has had its VISCOSITY reduced, i.e. made less viscous, by the addition of a NON VOLATILE oil.
So that we now have a BITUMEN of lower viscosity i.e. lower stiffness.
I repeat, the oil used to FLUX the stiff BITUMEN is NON VOLATILE, it will not evaporate, you have produced a less viscous, less stiff BITUMEN, "more runny", a very un-technical term but I hope it conveys the meaning.
A FLUXED BITUMEN will NOT revert to its original VISCOSITY but remain at the new VISCOSITY you have created by the addition of the FLUX OIL.
A FLUXED BITUMEN is different from a CUTBACK BITUMEN for the above reasons.
A FLUXED BITUMEN will be formulated to remain a penetration grade bitumen, but a softer / less stiff grade suitable for the material and conditions where it is to be used.
A CUTBACK BITUMEN is a BITUMEN that has been blended with a VOLATILE oil, most likely to be kerosene but others are used, so that when the volatiles have evaporated, with time, the BITUMEN will eventually revert to its original VISCOSITY.
Time being the critical factor, it may take many months or even years before the cutback mixture regains the viscosity of the bitumen that was cutback.
Whilst the material remains in the softer condition it will be susceptible to damage from overloading of the material layer.
Information on the former use of creosote as a cutback oil, and reaction to testing for tar.
BS 2000 - STANDARDS FOR THE TESTING OF BITUMEN AND BITUMINOUS PRODUCTS
BS 2000 : British Standard Methods of test for Petroleum and its products.
This standard and its various parts have identical equivalents with the Institute of Petroleum, (IP).
BS 2000 has many parts.
2000:Part 72 - Viscosity of cutback bitumen
This standard sets out the procedure for determining the viscosity of cutback bitumen using the Standard Tar Viscometer,
This British Standard is identical with IP 72/86(92).
Although this piece of apparatus is called the Standard Tar Viscometer
it is more commonly used for testing the viscosity of Cutback Bitumen these days,
(there's not a lot of TAR about).
The Standard Tar Viscometer measures viscosity in time, i.e. seconds.
E.g. the common viscosity for Cutback Bitumen for Surface Dressing is 100secs..
This is the time it takes for 50cc's of the BINDER under test,
held at 40 degrees centigrade in a standard cup to run through a standard orifice,
(hole), in the bottom of the cup.
2000:Part 49 - Penetration of bitumen and bituminous materials
This is the standard that covers the testing of penetration grade bitumens
using the needle method, this British Standard is identical with IP 49/86(89)
The "Penetration Test" is the popular name for this commonly performed test.
It is not difficult to reclaim binder from samples taken from the road to perform this test,
to check whether the correct bitumen grade has been used in the supplied material,
or to determine whether the bitumen has been hardened by overheating in storage or mixing,
or held at too high a temperature for too long a period.
This testing of reclaimed bitumen may be more relevant since the introduction of in plant blending of penetration grade bitumens, see the item below.
BS 2000 : British Standard Methods of test for Petroleum and its
Part 58:Softening point of bitumen.
This British Standard is identical with IP 58/86(89)
The "Ring and Ball Test" is the popular name for this commonly performed test.
This is because this simple test employs a piece of standard apparatus that consists of 2 standard rings and balls,
so perhaps it should be called the "rings and balls test".
It is not difficult to reclaim binder from samples taken from the road to perform this test, to check whether the correct bitumen grade has been used in the supplied material, or to determine whether the bitumen has been hardened by overheating in storage or mixing, or held at too high a temperature for too long a period.
This testing of reclaimed bitumen may be more relevant since the introduction of in plant blending of penetration grade bitumens, see the item below.
BLENDING/FLUXING OF PENETRATION GRADE BITUMENS
NEW! AND A SIGNIFICANT CHANGE TO GRADES OF BITUMEN
In my recent internet browsing on highways related matters I found that,
BS EN 12591:2009:Specifications for paving grade bitumens, has recently been published to supersede BS EN 12591:2000 which has been withdrawn.
A "Guidance Brochure", describing the changes and additions to the 2000 edition is available on the RBA (Refined Bitumen Association) website.
Once on the RBA website follow the toolbars for "Bitumen" and then "Testing and Standards", and the document is available to download as a .pdf file.
(While there you may also like to download the guidance document relating to polymer modified bitumens.)
On reading this note you will find mention to the fact that there is now included in BS EN 12591:2009 a table, Table NA 1, that provides guidance on the use of paving grade bitumens from 20/30 pen. to 160/220pen. "for use in the construction and maintenance of roads and airfields in the UK".
Table NA 2 gives guidance on softer, less viscous, bitumens.
My interpretation of these "informative" tables is that they are a common sense suggestion that you specify a penetration grade bitumen from the "normal/standard" range of available penetration grade bitumens.
It following that you do not use cutback bitumen in bituminous mixtures if it can be avoided.
However, I feel that I still have to mention the recent introduction of in-plant blending of penetration grade bitumens, this procedure being introduced in the final years of BS 594 and BS 4987, and has followed into the new European specifications for bituminous mixtures.
My reading on this subject suggests that this can be a blending of a stiffer grade bitumen with less viscous bitumen to produce an intermediate grade of bitumen, or of more concern, the use of a suitable flux oil to modify a highly viscous bitumen down to a much less viscous grade of bitumen.
I find the introduction of this practice a little concerning, as since this time I have noticed examples of highly rutted HRA surface course patching, which clearly should not be occurring.
I will not go into the reasons for the in plant blending of penetration grade bitumens being approved for general use, but suffice to say it reduces cost to the production facility, and it is likely that it was "industry" representation on the Standards Committees (European or British) that brought this significant change about.
As it is my opinion that this process for producing specific grades of bitumen would not be a preferred option of Highways Engineers
In my opinion a 125pen. (100pen) bitumen is an acceptable, pragmatic, compromise bitumen for a HRA surface course, in a patch, in difficult hand laying conditions, in cold winter weather. It will give the gang a much better opportunity of laying and compacting a successful surface course to any hand laid patch.
However this material, containing a 125pen straight run bitumen will not rut to the degree that I have observed on some occasions recently.
Perhaps trying to "blend" a small quantity of bitumen in a small tonnage of material is going beyond the capabilities of some plants, or some operators, I do not know. My observation of heavily rutted HRA surface course patching has increased since the permitted introduction of in plant blending of penetration grade bitumens, it may be a coincidence but I think not.
(NOTE : I preferred the former 100pen. grade because a 125pen. at the high end of its permitted tolerance is very close to the viscosity of a 190pen. at the low end of its permitted tolerance, and you would not really recommend a 190pen. grade bitumen for HRA patching, well I would not. When the patch is machine laid I see no real reason to to use any other grade than a 50pen., but hand laying of a patch is likely to save cost.)
Of course, the bottom line is that the penetration/viscosity of the bitumen in the mixture shall be that which is specified whether the source has been a tank holding a straight run bitumen of the grade required, or if the bitumen in the mixture is a result of blending two other components to produce a bitumen of the specified viscosity.
The only way you will know what the actual viscosity of the bitumen in the supplied bituminous mixture is, is by taking a sample of the laid material, have a materials laboratory recover the binder and then perform a penetration test on the recovered binder. A very expensive procedure if traffic control is needed to obtain the sample, although it could be taken when the necessary remedial work takes place, the actual laboratory work probably being the smallest part of the cost.
It is my fear, that in reality, the arrival at the correct penetration grade bitumen in the bituminous mixture through blending may not always be achieved.
So, I had hoped to see some further reference to in-plant bending of bitumen in BS EN 12591:2009:Specifications for paving grade bitumens, but I was disappointed.
There is a very brief reference to "loading through an in-line blender" and "a procedure for checking the performance of the blender", but in my opinion it is brief and not specific.
I am further "troubled" by the comment at the beginning of the document that states, "This European Standard does not directly address 'cohesion, adhesion and setting ability'", this is more fully detailed in the "Introduction" to the specification.
There is a significant reference to blending of bitumen in,
NHSS (National Highway Sector Schemes for Quality Management in Highway Works) 15 : The Supply of Paving Bitumens.
The information relevant to bitumen blending can be found in, Section 8.2.4 - Monitoring and Measurement of Product
This document refers to blending of bitumens prior to introduction into the mixing plant, usually at the bitumen production/supplier facility, but I suppose could occur at the bituminous mixture production plant if a large amount of blending was deemed necessary.
NHSS (National Highway Sector Schemes for Quality Management in Highway Works) 14 : Quality Management in Highway Works,
Does include an item on "Binder Blending Protocol".
This is found under item, "7. Product Realisation" sub paragraph "7.1 In-Plant Blending of Bitumen".
I am not going to spell it all out, the information is there for you to read in the relevant documents if you are concerned with this process, and need reassurance that it is being carried out correctly and that it is being appropriately monitored as described in NHSS 14.
I believe, an independent audit, once a year, is required to show that suitable monitoring is being performed on the in-plant blending of bitumen.
It is up to you to ensure that this process is taking place, probably by the inclusion of a brief but appropriate clause in any contract document that exists between you and your bituminous mixture supplier.
All NHSS documents can be downloaded from the publications section, when you find it, of the UKAS website.
This depth of knowledge, in an ideal world, should not be part of the purchasers responsibility, you should be receiving the materials that you have specified.
Note what I have just said, if you do not know what material you require that is not the responsibility of the Supplier, talk to your Materials Engineer for guidance.
The good old standby that a product should be "fit for purpose" only applies when you have correctly specified the product, and you have not received what you specified.
But knowing more than you strictly need to know I have always found to be useful and beneficial, and helps prevent problems arising. I believe it is a far better policy to prevent a problem than letting it happen and then trying to apportion blame.
"LOW ENERGY ASPHALT"
It is necessary to place this information here, on the "viscosity page", because the various technologies and associated processes linked with the production of low energy asphalt will significantly change the physical attributes (mixing and compaction temperatures) associated with the the initial viscosity of the penetration grade bitumen used in the first part of the mixing process.
British Standard information on mixing and compaction temperatures related to the bitumen viscosity of the bituminous mixture will not apply to low energy asphalt, you will have to look elsewhere for the appropriate guidance, and each particular low energy asphalt production technology will have different guidance. It could become confusing.
I have to point out that the use of the words
"low energy asphalt" are used to describe any asphalt (asphalt concrete/bitumen
macadam, stone mastic asphalt or the various hot rolled asphalt bituminous
mixtures) that employs a bitumen additive and/or production process, or a
combination of both, to reduce the amount of energy consumed in its production
compared to hot mix production.
It is necessary to be careful with the use of terminology because the term "low energy asphalt" is used as a registered description of the production process developed by Lea-Co of France, so when you see a low energy bituminous mixture described as Low Energy Asphalt ® this material has been produced from a production plant that has been licensed to produce a low energy asphalt as described in the Lea-Co registered process.
There are many other low energy asphalt technologies in the course of development and you will find relevant information on them by using the key words "low energy asphalt" in a Google search, and I leave you to do your own research on the processes and additives available.
I will however use the Low Energy Asphalt ® as my example of this technology because this company offers the most information on the process, which is accessible from their website, and this technology seems to be the most promoted in the UK at this time.
I will continue under the basis that it is generally in order to describe "asphalts" as low energy asphalts meaning that they have a method of production that will reduce the amount of energy (heat) that is needed in their production.
But I repeat it would seem that the only Low Energy Asphalt ® that you can buy under that product description is that which you purchase from a company that has a license from Lea-Co for a particular production plant.
I would urge all engineers and engineering technicians, and contractors to visit the website www.lea-co.com/en. as the French company LEA provide a great deal of information on the process that they have developed on their website, and you will learn much from it.
This process being the use of a foaming additive added to the hot/preheated coarse aggregate and hot bitumen fed into the mixer before the fine aggregate at ambient temperature, and which has not been dried, so it is wet to a variable degree, is added to the already hot components.
The addition of the wet fine aggregate causes the hot bitumen containing the additive, which is now coating the larger aggregate particles, to foam and the bitumen foam then coats the fine aggregate.
So the saving in energy is achieved by not heating/drying the fine aggregate, and the lower temperature of these mixtures is the result of the lowering of the initial temperature caused by the addition of the cold, wet fines.
I am very much a traditionalist, and "hot mix" preferring engineer, this is because because of the simplicity and clarity in achieving the "recipe" of the designed bituminous mixture by weighing into the mix aggregates that are dry and therefore have a precise weight, achieving a bituminous mixture with precise properties.
It has always been my intention to "save carbon" by recommending hot mix hot rolled asphalts and bitumen macadams that will give very long life before needing replacing or overlaying, or receiving an appropriate surface treatment to prolong its life.
I have to add I did not realise that I was "saving carbon" at the time I was just looking to earn my salary by recommending mixtures and layer thickness that provided the best value for the money available in the budget.
With this philosophy you will save energy/carbon by not having to repeatedly replace materials that have not had durability as a significant factor in their production and promotion.
It is not currently possible to accurately compare the long term carbon saving of using conventional "hot mix" long life traditional British Standard bituminous mixtures against recently introduced low energy asphalt mixtures, there just has not been sufficient passage of time to fully evaluate the "low energy" bituminous mixtures.
Lauding the findings from recent trials, and they have been trials, with all the associated attention and supervision, as an indication of the long term success of these materials in general use may be premature.
I could draw attention to a number of "new" materials and processes that have been introduced over the past twenty years that were initially introduced as going to revolutionise the highways maintenance surfacing industry and save lots of money in the process, but I will not.
Suffice it to say there were a lot of disappointed "people" and a lot of money needed to be found to rectify the shortcomings (failures) of these much hyped materials and processes.
As I understand it, at 24-11-2011, the Highways Agency has not approved any low energy asphalt bituminous mixture material as an option as a base, binder course or surface course material on motorways and trunk roads in the UK.
It may be that they are looking for such bituminous mixtures to come through the HAPAS approval route, or they could just be being extra cautious after previous experience with "new" and "innovative" materials.
However, I truly believe there is a place for this technology amongst the many materials and processes employed in the highways maintenance industry, but it must be used appropriately and not hyped out of the situations where it will be satisfactory.
There must also be considerable control and monitoring equipment placed in the production plant to ensure the appropriate total free moisture in each particular bituminous mixture is accurately controlled and maintained.
Over the last 15/20 years I have observed perfectly good "materials" and "materials processes", with good histories, brought over from Germany and France only to become totally different "materials" and "material processes", and yet still be marketed on the sound background of the original materials.
I am not going to be specific on the "materials" and "materials processes", but anybody who has had a serious involvement with bituminous mixtures for highways maintenance will know what I am referring to, and I am not going to "spoon feed" the "suits" who claim to know about bituminous mixtures.
This particular low energy asphalt production system appears to have serious energy saving potential with regard to particular bituminous mixtures used in particular applications.
The trials that I have seen mentioned all seem to be 32mm. asphalt concrete (bitumen macadam) base, i.e. a "macadam" mixture that will have most of its load carrying ability (resistance to deformation) in the mechanical interlock of the aggregate particles.
It will also have a relatively low amount of the smaller "fines" compared to many bituminous mixtures, especially surface course bituminous mixtures.
I can certainly see the potential of this process as a means of safely incorporating asphalt planings containing a tar binder element, as from what I have read the poly aromatic hydrocarbons contained in tar are unlikely to be "released" at temperatures under 140°C, and this process can produce materials at 100°C.
My caution with this process is that the control of the water percentage in the mixture is critical.
Too little moisture/water and you will not have adequate foaming of the already added hot bitumen to coat all the "fine" and "wet" material added to the hot coarse aggregate, binder, and foaming additive.
Too much water and and you are going to have a very "soggy" material that may be prone to stripping, especially in wet weather, when it may happen quite quickly.
This process very much reminds me of practical concrete design, in that to obtain a correct water cement ratio you need an accurate assessment of the moisture in the sand stock pile before you know how much "free" water to add to the total mix to obtain the correct strength of concrete for the particular amount of cement in that mix.
So in my opinion it is going to need some careful monitoring of the "cold" and "wet" fine material or reclaimed asphalt planings (RAP) to produce a consistent LEA bituminous mixture, and I am wondering if many plants will have this degree of expertise, and plant control, and indeed covered and drained areas that will keep the fines and/or RAP at a stable moisture content in all UK climatic conditions.
There are many aspects of this technology that I would like to know more about, perhaps we interested engineers could see a more technically complete article/paper in one of "engineering journals".
I am sure there are many more highway engineers, other than myself, who would enjoy reading it, but please no more "pubic relations" promotions, they only impress the "suits".
Perhaps I could start the ball rolling with the question, how do these moisture containing bituminous mixtures cope with periods of storage in hot storage bins, is there any migration of moisture, or indeed evaporation of the moisture from the stored material?
Also related to storage, are there any problems with transporting these bituminous mixtures, are they stable in the lorry body, and again is the length of time in the lorry body in any way detrimental?
These are quite ordinary, but important, practical questions that hauliers and laying contractors are likely to want answering. If there are not any problems then lets have that confirmed.
Please view the Lea-Co website, pretty much all the information you need relating to this particular production process is there if you study all of the website.
But just to state the obvious the energy saving is made by not drying/heating the fine/RAP element of the mixture, these are coated by the foaming process.
The workability of the low energy asphalt mixtures containing penetration grade bitumen would appear to depend on the 0.5% moisture in the mixture to provide "lubrication" as the temperatures are too low to provide the workability purely in relation to the viscosity of the bitumen.
My concerns are that if the producer gets the moisture content significantly wrong you are going to have problems with laying, as well as what it looks like after compaction.
On occasion I have seen high fine content conventional bituminous mixtures that have been laid with moisture in them, when dryers have malfunctioned, and they were "interesting" to say the least when rolled/compacted, with the binder migrating to the surface.
They were also very interesting to transport, i.e. they are not stable in the lorry body and move around as if they were a very viscous liquid, the drivers were not happy.
( I have stood on top of sheeted loads, and watched them "move", I do have the experience, one of the few benefits of being old, and having being practically involved in highways materials most of your life, not just in a laboratory.)
Do not take my word for any of this, ask your own questions of your Materials Engineer, and the people who want to sell you these materials, not to the salesmen or the public relations people but ask the production manager at whichever plant it is being supplied from, if "they" will let you talk to him.
If the information that you require it is regarded as "commercially sensitive" because it is a branded/proprietary product and he will not tell you anything then I would be concerned.
Again, I am not saying do not use these various low energy asphalt technologies, I am saying use them appropriately, on appropriate sites, and use them with knowledge.
Note, free technical information
The major bitumen suppliers such as Shell, B.P., Nynas, Lanfina, etc. are usually very good at sending you technical information on their products and bitumen in general.
The websites of these companies also provide much information on bitumen and bitumen related topics, (some websites are more rewarding than others).
This is because you usually receive their products indirectly, i.e. from the supplier of your bituminous materials, surfacing contractor, surface dressing contractor, etc..
Bitumen producers do like you to know of their products so that you can specify them in particular if you so choose to do.
Pictures here have been produced from "The Shell Bitumen Handbook", because it actually states in this book that extracts may be reproduced provided the source is acknowledged, I believe this is because they want you to know about bitumen, and its properties and uses.
The book is a must for your technical library, it now costs £40:00, but it is excellent value if you read it and consult it, and do not just leave it sitting on the shelf.
If you wish to browse a small but excellent preview of the information included in the "Shell" handbook, press, -------------> HERE
I can also recommend that you try and obtain back copies of "Network" the "Nynas Digest of Bitumen", they contain a lot of technical information on bitumen and bitumen products. Unfortunately the publication has been discontinued, but if copies still remain in your technical libraries they are well worth reading
Just exercise a little caution when reading documents that are free from suppliers, they are going to be a little biased to their point of view, but it does not stop them being well worth reading, just try and separate the "marketeering" from the technical.
You ought to know a little bit about the interaction between the bitumen producer/supplier, the producer/manufacturer of bituminous mixtures and other bituminous products, and the contractor/layer of materials containing bitumen,
if you think you do, press --------> HERE
I try to refer to as few
commercial sites as possible in compiling my site, but when a site offers
particularly useful information about a subject I make an exception.
For further information on bitumen in the many forms it is used in road construction and maintenance,
press --------------------------------------> HERE
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