Bitumen viscosity, hot rolled asphalt, bitumen macadam, asphalt thin surfacing, stone mastic asphalt, highway maintenance

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.

BITUMINOUS MATERIAL VISCOSITY TABLE

STIFFNESS

STIFF
Machine-lay material,
difficult to lay by hand,
and requires heavier
compaction but will
produce higher stability

LIVELY
Easy to work by hand, but prone to deformation and pick-up the less viscous (more lively) it is.

BITUMEN GRADE

50PEN, REMAINS

125PEN (100PEN)

190PEN (200PEN)

290PEN (300PEN)
-
(450PEN)

******************

#(200SECS)

#(100SECS)

#(50SECS)

APPLICATION

30/35% HRA. Trunk roads, principal roads, and other roads carrying heavy traffic.
HRA basecourses and roadbases, also some of the modern bitumen macadam "heavy duty" basecourses and roadbases.

Dense bitumen macadam basecourses and roadbases under 30% HRA. Also heavy duty macadam wearing courses.

Dense macadam basecourses and roadbases under macadam wearing courses, for use in less heavily trafficked areas. Also wearing courses in less heavily trafficked areas, 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.

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.

Very workable "sticky" binder for use in temporary patches, pothole repairs, etc

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 untechnical 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 wil 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.

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".

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