bituminous material and pavement design

LEEDS METROPOLITAN UNIVERSITY FACULTY OF ARTS, ENVIRONMENT & TECHNOLOGY Highway Engineering A

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMINOUS MATERIAL

Native asphalts, have been utilised since 3500 B.C. in buildings and road construction. Their main uses have been as an adhesive, waterproofing agents and mortars. Native asphalts occur when petroleum rises to the earths crust and the volatile oil evaporates, leaving pools or lakes. The best known of these is the Trinidad Lake deposits, which were used extensively for road-making in the UK in the 50s and 60s. In 1869 the first flexible pavement was built in London using tar mixed with aggregate, which became known as Tar Macadam after its inventor. Tar is produced during the carbonisation of coal in the production of coke. Two types are produced depending on the temperature of the process. High temperature tars are produced during the manufacture of coke for the iron and steel industry (about 1000C) and low temperature tars are produced during the production of smokeless fuel (about 700C). Tars are categorised by their viscosity using the standard tar viscometer.Tars are more temperature susceptible than bitumen and mixes using tar will be softer at higher temperatures and stiffer at lower temperatures than mixes using equivalent bitumen grades. A major advantage of tar is that it is less susceptible to softening by oil based products such as diesel or petrol and can thus be used successfully on service areas, lorry parks and airfield taxiways where fuel spillage would cause damage to bitumen based products.With the invention of the automobile the petroleum industry developed, a bi-product of which was bitumen. This material generally replaced native asphalt and tar as the material of choice for flexible pavement construction.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering APETROLEUM BITUMEN

Petroleum bitumen is a hydrocarbon binder which is characterised by being:Black or very dark brownStickyThermoplasticIt has good adhesion, waterproofing and weatherproofing properties, which means that it finds extensive uses in construction generally and in the manufacture of paving mixes specifically. A key property of bitumen is its viscosity. Viscosity is the resistance to flow and the viscosity of binders decreases as the temperature increases.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering APETROLEUM BITUMEN

Petroleum bitumen is obtained during the separation of crude oil by fractional distillation. The resulting bitumen is modified during production to give a range of properties for use in construction.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering APENETRATION GRADE BITUMEN

Penetration grade bitumens are relatively stiff and are graded by their penetration as determined by the penetration test. This test involves a standard load (100g) being applied for a standard time (5secs) to a needle which penetrates a bitumen sample at a standard temperature (25oC).

The penetration is measured in tenths of a millimetre and the smaller the penetration figure, the stiffer the bitumen. Thus, 25 pen bitumen is stiffer and more viscous than a 50 pen bitumen. Penetration grade bitumen can be modified by the use of additives such as polymers which can, for example, increase adhesion or stiffness of the bitumen.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering APENETRATION GRADE BITUMEN

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACUTBACK BITUMENCutback bitumens are penetration grade bitumens which are blended with lower viscosity oils thus making the bitumen less viscous. Bituminous mixtures containing cutback bitumens can be used at lower temperatures and are more workable over longer periods of time.

Curing of cutback bitumen occurs when the cutting agent evaporates, leaving the bitumen behind. By changing the cutting agent, the rate of curing can be altered. This is illustrated in the following table.

Rate of CuringCutting AgentSlowDiesel or CreosoteMediumKeroseneFastGasoleneLEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACUTBACK BITUMEN

The viscosity of cutback bitumen is measured using the standard tar viscometer where, under standard temperature conditions, the time is measured in seconds for 50ml of bitumen to flow through a standard orifice. A cutback bitumen of 200 secs viscosity is stiffer than one with a viscosity of 100 secs.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN EMULSIONS

An alternative to the use of cutback bitumen is to use penetration grade bitumen in the form of an emulsion. All emulsions are dispersions of one liquid into another. The particles within a dispersed liquid are extremely small, mostly only a few microns in diameter, and are prevented from joining together by the presence of a third substance known as the emulsifier. Bitumen emulsions are normally of the oil-in-water type in which the oil or bitumen phase constitutes between 30% and 80% by mass. These bitumen emulsions are generally fluid when used either cold or at relatively low temperatures. After application, the water is lost and a continuous film of bitumen is deposited on the pavement or stone. This action is known as breaking or setting.

Petroleum bitumen is obtained during the separation of crude oil by fractional distillation. The resulting bitumen is modified during production to give a range of properties for use in construction. A flow chart of the refining process is shown below.Petroleum bitumen is obtained during the separation of crude oil by fractional distillation. The resulting bitumen is modified during production to give a range of properties for use in construction. A flow chart of the refining process is shown below.Petroleum bitumen is obtained during the separation of crude oil by fractional distillation. The resulting bitumen is modified during production to give a range of properties for use in construction. A flow chart of the refining process is shown below.LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN EMULSIONS

Emulsifiers concentrate at the surface of the bitumen particles as their molecules have two parts, one of which is attracted to water, the other to bitumen. These emulsifiers carry an electrical charge.

If the charge is +ve, the emulsifier is cationic and the resulting emulsion is anionic, since it results in electro-positively charged bitumen particles.

If the charge is -ve, the emulsion is cationic, with negatively charged bitumen particles.

Since the stone surface can also carry an electrical charge, the type of emulsifier used can have a significant effect on the behaviour of the emulsion in contact with stone.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN MIXES Typical Cross Section

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN MIXES

Bituminous mixtures are generally employed in the base, binder course and surface course. These layers are a carefully proportioned mixture of aggregate, bitumen and mineral filler, which is mixed together at temperature and laid on the road in its hot state. The requirements of a bituminous mixture are:Stiffness - to ensure that loads are spread through the pavement construction to the underlying sub-base and sub-gradeFatigue resistance - to prevent cracks occurringStability - to resist the deformation caused by the loadsDurability - to resist the effects of the weatherWorkability - to ensure that the material can be laid and compacted correctly.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN MIX BATCHING PLANT

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ABITUMEN MIXES

In the UK, two basic bituminous mixtures are used, these being:coated macadamrolled asphaltBoth macadams and asphalts are produced in a variety of forms depending on where the material will be used within the pavement construction and the predicted traffic load. As a very general statement, rolled asphalts are used mainly as surface courses and macadams are used for the lower layers, especially the base. There are many variations to this general statement and it will not always hold true, especially in very heavily trafficked situations.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACOATED MACADAM

BS 4987 Specification for Coated Macadam for Roads and other Paved Areas.Binder courses and base materials are usually dense Macadams consisting of a continuously graded aggregate mixed with binder. The strength of the mix is derived partly from the interlock of the aggregate particles and partly from the adhesion of the binder. These dense Macadams will typically use a 100 pen binder.BS 4987 contains specifications for a range of coated macadams for pavement and footway construction. Details of delivery temperatures, rolling temperatures and requirements for the laid material are also included.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering AROLLED ASPHALT

BS 594 Specification for Rolled Asphalt for Roads and other Paved Areas.This material is a dense mixture of aggregate, sand, filler and binder. It is a gap graded material, typically containing 30% of a coarse aggregate which is held in a mortar of sand, filler and binder. The strength is derived from the mortar and is highly influenced by the sand, which comprises a major part of the mortar. Rolled asphalt will normally contain 50 pen bitumen.Rolled asphalt for surface courses are categorised into Recipe Mixes and Design Mixes. The Design Mixes are based on a laboratory mix design process and take into account the binder requirements of the aggregates being used. This generally leads to more stable and economical mixes and Design Mixes are now used extensively for heavily trafficked rolled asphalt wearing courses.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACONSTRUCTION

Spreading of bituminous mixtures is generally undertaken using a paving machine. This consists of a tractor unit and a screed unit. The tractor unit may be pneumatic tyred or crawler track mounted. It supports a hopper into which the truck dumps the mix and against which the truck wheels bear as the paver pushes the truck along. The mix is transferred from the hopper by a slat conveyor through control gates onto the pavement where it is distributed by screw conveyors over the full width in front of the screed. The screed unit comprises:Levelling arms, hinge connected to the tractor unit at one end and rigidly connected to the screed at the other end.A screed plate with provision for heating.A vibrating device (some use tamping devices).Controls for adjusting thickness, camber and width.The screed unit has a floating action as it slides along being supported by the freshly placed mix. The thickness of the spread mix is changed by adjusting the tilt of the screed plate.




Initial rolling should be started as soon after laying as is possible and is carried out using steel wheeled rollers only. Vibratory rollers are usually operated in the static mode for initial passes. On deep lift work, pneumatic tyred rollers may be used.

Secondary rolling should follow immediately behind initial rolling. Vibrating steel rollers, static steel rollers or pneumatic tyred rollers (with tyre pressures between 500kN/m2 and 600kN/m2) should be employed.

Final rolling is usually undertaken using a pneumatic tyred roller with tyre pressures of between 600kN/m2 and 700kN/m2. This eliminates the roller marks and produces an even finish. The final rolling must be completed whilst the mix retains some heat.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACONSTRUCTIONTwin Drummed Steel Wheeled Vibrating Roller

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACONSTRUCTIONPneumatic Tyred Roller

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ACONSTRUCTIONTemperature ControlTemperature control is essential for proper mix workability during spreading and compaction. For normal bituminous mixes the following temperatures should apply.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering AFLEXIBLE PAVEMENT DESIGNTypical Cross Sections

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering AFLEXIBLE PAVEMENT DESIGN

The major contributor to the strength of a pavement is the base. The binder course forms an extension to the base in terms of its strength contribution and also provides the regulating course so that a constant thickness of surface course can be laid. For flexible pavements, the thickness of these layers may be assessed using the following design methods:Design tables for example, Leeds City Council Street Design Guide.Transport and Road Research Laboratory, TRRL Laboratory Report LR1132, The Structural Design of Bituminous Roads.DoT Design Manual for Roads and Bridges, Volume 7, Pavement Design and Maintenance, HD24/94.


LR1132 and HD24/94 have quite different design philosophies, the fundamental process in each method is: Determine an initial flow of heavy goods vehicles.Determine a design life for the pavement.Determine the growth rate for heavy goods vehicles over the design life of the pavement.Determine the equivalent number of standard axles for each heavy goods vehicle.Determine a total load carried by the pavement in millions of standard axles (msa).From the CBR determine the base thickness or base/capping thickness.From the total load to be carried by the pavement determine the thickness of the bound (upper layers) of the pavement.


For the purposes of this course we will consider the approach defined by LR1132, which is often employed by Local Authorities. The method prescribed by the DoT Design Manual for Roads and Bridges, Volume 7, Pavement Design and Maintenance will be considered in Highways B.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ALEEDS CITY COUNCIL HIGHWAY DESIGN GUIDE

The Design table employed by Leeds City Council is based on street types as discussed in Lecture 1b Introduction and summarised below.


The range of acceptable surfaces to carriageways specified by Leeds City Council includes the following:Hot rolled asphalt (HRA).Hot or cold applied coloured surfacing (resin system).Standard surface course materials using a coloured binder and coloured aggregate or chippings.Standard 80mm concrete-block paving surface course.Tegula or similar approved concrete-block paving surface course.Dense bitumen macadam (DBM).


Example designs for the bound pavement layers are detailed in the table below, which shows the minimum design thickness for a variety of alternative materials for various street types. The pavement construction for any street types or roads not included in the table shall be subject to site-specific designs.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ATRANSPORT AND ROAD RESEARCH LABORATORY, LR1132

LR1132 is based on observations and measurements of full scale road experiments over a 20 year period, supplemented by structural analysis to rationalise and extend the data.

The analysis uses the elastic stiffness modulus of the various pavement and foundation layers, to calculate the strains developed within the structure. The strains are related to pavement life.

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ATRANSPORT AND ROAD RESEARCH LABORATORY, LR1132Estimation of Design Traffic

It has been shown that the total number of commercial vehicles, Tn, using the slow lane over the design life of the road can be expressed in terms of the initial daily flow, the growth rate and the proportion of vehicles using the slow lane as follows:

WhereTn = Total number of commercial vehicles using slow lane.Fo =Average annual daily flow (AADF) at opening(from traffic survey data).r =Growth rate for the road (Assume 0.02 unless more detailed information is available). n =Design life of the road.P =Proportion of commercial vehicles using the slow lane(assume P =1 for single carriageway and P = 0.970-0.385(10-4)Fm for dual or 3 lane carriageway).


In order to convert this cumulative number of commercial vehicles to equivalent standard axles, it must be multiplied by the number of equivalent number of standard axles per commercial vehicle at the mid-term of the design life. The factor is calculated from the following formula which is based on the results of dynamic weighbridge measurements carried out over a number of years. It gives an estimate of the vehicle damage factor, D, for any mid-term year t based on the 24hr AADF of commercial vehicles in that year Fm given that the base year is 1945, i.e. the year 2010 corresponds to t = 65.

WhereD =Damage factort =mid term year counted from 1945Fm =F0 (1+r)0.5n


The cumulative traffic, expressed in million standard axles (msa) used in the attached graph (Fig3) for roads with bituminous base is given from the following formula.N (msa) = Tn * D * 10-6

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ATRANSPORT AND ROAD RESEARCH LABORATORY, LR1132Design Thickness

LEEDS METROPOLITAN UNIVERSITYFACULTY OF ARTS, ENVIRONMENT & TECHNOLOGYHighway Engineering ATRANSPORT AND ROAD RESEARCH LABORATORY, LR1132Example

Design a pavement using Transport and Road Research Laboratory, LR1132, The Structural Design of Bituminous RoadsDesign Parameters Single carriagewayCBR = 4%Roadbase is Dense Bitumen Macadam (DBM)AADF at opening = 740cv/d (assumed each way)Design life = 20 yearsOpening in 2014

bituminous material and pavement design

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