BITUMEN VISCOSITIES FOR BITUMINOUS MATERIALS

CONTENTS

UPDATE OF SPECIFICATION FOR PAVING GRADE BITUMENS
BITUMINOUS MATERIAL VISCOSITY TABLE
BITUMEN VISCOSITY
THE RANGE OF BITUMINOUS MATERIALS AVAILABLE
A BIT ABOUT BITUMEN
A DEFINITION OF VISCOSITY
BITUMEN DENSITY
FLUXED BITUMEN
CUTBACK 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
FREE TECHNICAL INFORMATION

UPDATE OF 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has superseded BS EN 12591:2000 which is withdrawn.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

NOTE
# It is worth pointing out that this method of specifying cutback bitumen is still referred to in the most recent Shell Bitumen Handbook. Whereas if you look in the recent BS 4987, cutback and deferred set bituminous mixtures are "specified" in an entirely different way. 
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.

None standard "Depot Stock", and "Bucket" materials

There are binders which have been further "cut-back" (i.e. extra volatile light oil such as creosote 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 test (SECS., seconds of time).

BITUMEN VISCOSITY

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.

and

BS 4987:2003,Coated macadam for roads and other paved areas,
Part 1 : Specification for constituent materials and for mixtures.

WARNING !
BUT, HAVING EXPLAINED ALL THE ABOVE I WOULD NOT RECOMMEND CUTBACK MATERIALS UNLESS ABSOLUTELY NECESSARY
BITUMINOUS MIXTURES WITH A 300PEN. STRAIGHT RUN BITUMEN, KEPT HOT BY "HOT-BOX" OR THERMAL BLANKET, I BELIEVE, IS THE BEST COMPROMISE FOR 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."

BITUMEN DENSITY

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

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.

CUTBACK BITUMEN

A CUTBACK BITUMEN is a BITUMEN that has been blended with a VOLATILE oil, 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.

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.

BS 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.

BS 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 products. 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.

IN PLANT 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.

However,
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.

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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