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EAPA

Asphalt - meeting the performance demands of Heavy Duty Pavements.

Enrobes, satisfaire aux exigences des chaussees lourdes.

ISBN 90-801214-6-0

Asphalt, Erfullt die Anforderugen besonderer Verkehrs beanspruchungen.

European Asphalt Pavement Association P.O. Box 175, 3620 AD Breukelen, The Netherlands

©Copyright 1995, EAPA

IMPORTANT NOTICE This document has been published by the European Asphalt Pavement Association as a contribution to the debate on Europe's future road construction and maintenance. The statements it contains represent the policy of EAPA but no warranties are expressed or implied.

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CONTENTS

1. INTRODUCTION ..... ...................................................................................................... 1

1.1 General situation ............................................................................................. 1 1.2 Developments in traffic load enforcement ................................................... 2 1.3 Scope of this report ......................................................................................... 3

2. WHAT ARE "HEAVY DUTY PAVEMENTS" .................................................................. 4

2.1 Pavement loading ........................... .............................................................. 4 2.2 Temperature .................................................................................................... 4 2.3 EAPA description of HDP ............................................................................... 6 2.4 Determination of the equivalent number of standard axles ...................... 7 2.5 Conclusion ................. .................................................................................... 12

3. HEAVY DUTY ASPHALT PAVEMENTS IN PRACTICE .................................... .. ....... 13

3.1 Germany .. .................................. .. ................... .............................................. 14 3.1.1 Specific conditions ................................................................................... 14 3.1.2 Developments in traffic load enforcement .................. .. ......................... 14 3.1.3 Scope of this report ......................................................................... ........ 14 3.1.4 Typical example of Heavy Duty Asphalt Pavement ............................... 14

3.2 France ........................................................................................................... 15 3.2.1 Specific conditions .................................................................................. 15 3.2.2 Pavement design procedure ................................................................... 15 3.2.3 Mix design method .................................................................................. 15 3.2.4 Typical example of a Heavy Duty Asphalt Pavement ............................ 15

3.3 Netherlands ............. ... .................................................................................. 16 3.3.1 Specific conditions .......................................................................... ......... 16 3.3.2 Pavement design procedure ................................................................... 16 3.3.3 Mix design method ........................................................... :-...................... 16 3.3.4 Typical example of Heavy Duty Asphalt Pavement ............................... 16

3.4 United Kingdom ........................................................................................... 17 3.4.1 Specific conditions ........... .. .................................................................... 17 3.4.2 Pavement design procedure ................................................................... 17 3.4.3 Mix design method .................................................................................. 17 3.4.410 year old example of Heavy Duty Asphalt Pavement ...................... 17

. 3.5 Surfacing materials used for Heavy Duty Asphalt Pavements ................. 18

4. THE ADAPTATION OF THE EXISTING ROAD NETWORK ....................................... 19

4.1 Strengthening ofthe existing pavement .................................................... 19 4.2 Road widening .............. ... ............................................................................ 20 4.3 Increasing maintenance intervals ............................................................... 21

5. TECHNOLOGICAL TOOLS TO MATCH INCREASING DEMANDS ......................... 22

5.1 Pavement design models ............................................................................ 22 5.2 Practical directions for pavement design improvements derived from

available theory ........................................................................................... 23 5.3 New developments in theory and laboratory ............................................ 24

5.3.1 Functional approach of mixture design ................................................. 24 5.3.21mprovement of mixture characterisation ............................................. 25 5.3.31mprovement of pavement design methods ......................................... 27

5.4 A framework for developing an optimum solution ................................... 28 5.5 Conclusion .................................................................................................... 29

6. PRACTICAL EXPERIENCE WITH THE NEW TECHNOLOGY .................................... 30

6.1 Structural pavement design ........................................................................ 30 6.2 High modulus base course .......................................................................... 30 6.3 Multigrade bitumen ..................................................................................... 31 6.4 Modified bitumens ....................................................................................... 32 6.5 Porous asphalt .............................................................................................. 33 6.6 Stone Mastic Asphalt (SMA) ....................................................................... 33 6.7 Improvement of the resistance to permanent deformation of

bituminous mixes ........................................................................................ 33

7. COST EFFECTIVENESS AND CONTRACTUAL DEVELOPMENTS .......................... 35

7.1 Cost effectiveness ........................................................................................ 35 7.2 Contractual developments .......................................................................... 35

7 .2.1 The conventional construction contract ................................................ 36 7.2.2The "Design and Build" contract ............................................................ 36 7.2.3The "Functional" contract ....................................................................... 36 7 ,2.4 The "Design, Build, Finance and Operate" contract ............................. 38 7.2.5"Technical Approval" .............................................................................. 38

7.3 Contractual adaptations .............................................................................. 39 7.4 Conclusions .................................................................................................. 39

8. SUMMARY AND CONCLUSIONS ............................................................................ 40

9. ACKNOWLEDGMENTS ............................................................................................. 42

ANNEX ........................................................................................................................... 43

LITER.ATURE .............................................................................................................. .... 49

1. INTRODUCTION

1 .1. General situation

A well designed and well maintained asphalt road construction performs satisfactorily as a Heavy Duty Pavement, and also provides a comfortable and especially safe road surface.

In 1991 EAPA's "Status Report on Heavy Duty Pavements for Roads", provided general

descriptions of pavements in a number of European countries which support this state­

ment.

Since then, road authorities continue to be confronted with increasing pressures: traffic

densities are growing, users' demands are becoming more and more important, and envi­

ronmental considerations enforce greater limitations on road construction and the materi­

als used.

Traffic loads

As a result of greater prosp~rity and economic growth in Europe, the amount of traffic is

growing enormously. On average throughout Europe, traffic is estimated to be growing by

3% per year.

Improvements in transport efficiency and technical developments in the automotive indus­

try have contributed to increased axle loading as well as higher tyre pressures. Greater use

of high pressure super single tyres is expected, and total truck weights are growing.

These developments are expected to continue in the future. Pavement designers must

accept ever-increasing loads.

User demands As traffic continues to grow, traffic delays become more and more common, leading to an

increasing amount of user delay time (viz. delay costs). From several studies it has become

clear that this cost is substantial. So users require a sufficient number of easily accessible

roads with minimum delay caused by maintenance.

Road widening projects must be carried out quickly; road materials and design must pro­

vide low-maintenance constructions by offering longer life and increased durability . .. Environment Stricter environmental and occupational health legislation puts new limitations on the road

builder. These limitations relate to the selection of raw materials, to working practices, and

to the recyclability of pavement materials. In addition the capability to incorporate waste

materials from "foreign" sources (from outside the road industry) is possible.

From the past it is clear that the asphalt industry has always easily adapted its materials,

mixtures and pavement constructions to meet changing demands. By doing so, asphalt pavements have retained their ability to fulfil the requirements of both the road authority

and the road user.

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More recently, the introduction and development of porous asphalt surfacings has made a

major contribution to traffic noise reduction in addition to virtually eliminating spray for the ·road user.

EAPA expects asphalt pavements to remain as "road user-friendly" and "road authority­

friendly" as they have been in the past, and this will be achieved, even with the growth in both total traffic and axle loading.

1.2. Developments in traffic load enforcement Within the scope of this paper, traffic loading is the main factor to be taken into account

when considering Heavy Duty Pavements. Developments in the automotive industry are

thus very important.

The OECD report "Dynamic Loading of Pavements"2 states that "reflecting the growing

emphasis, world-wide, on economic productivity and transport efficiency, there is an

increasing need for the development of appropriate management policies for both vehicles

and roads and for performance standards to be applied on road systems, including pave­

ments and bridges, and to vehicles ..... Road loading and its dynamic component are the

major cause of pavement and bridge wear and depend on the number and types of vehi­

cles using the road, their features and the loads they carry as well as the characteristics of the road itself."

The increase in road wear due to traffic may, according to OECD, be counteracted by a significant increase in the use of "road-friendly" vehicles: vehicles which cause less dam­

age to the road. To reduce their effect on the road and increase vehicle productivity, an

appropriate balance between vehicle weight, and vehicle performance should be struck.

The OECD report contains recommendations to achieve this balance in practice, concen­

trating on the "road-friendliness" ofthe vehicles and the optimisation of road maintenance intervals and techniques.

These developments could well decrease the potential loading per HGV (Heavy Goods

Vehicle) passage. However, as a result of continuing traffic growth, an increase in total HGV

induced damage is expected. So pavement design and materials design still require to be

adapted to meet increasing demands .

1.3 Scope of this report This paper presents examples from several countries of materials and pavements which

have been proven to withstand the heavy loads of today, and discusses methods to

increase asphalt performance to meet future requirements.

A brief description of each section is given below.

Section 2 gives a description of "Heavy Duty Pavements". Traffic loads are assessed

very differently across Europe. Scientifically these differences can be elimi­nated by using: the equivalent number of standard axles (ESAL:'s). The nor­

mally used procedure to determine this number from the actual load distri­

bution is described.

Section 3 contains a number of examples of HOP's from current practice in Germany, France, the Netherlands and the UK. These pavements have been shown to

perform well under the most severe traffic conditions.

Section 4 discusses the adaptation of the existing motorway network to carry heavier

traffic loads as well as the specific question of road widening.

Section 5 considers some of the innovations which have already been implemented in

practice.

Section 6 discusses scientific innovations in design and construction theory of pave­

ment constructions and mixtures. Such innovations are the results of, for

instance, the Finnish ASTO-project, SHRP-USA, projects in France, the Netherlands, Australia and others. The expansion in the use ofthin surfacings

and new binder technology is also examined.

Section 7 covers subjects such as cost effectiveness, contractual relations, and environ­

mental aspects including recyclability. These subjects are not covered exten­

sively in this report as other EAPA papers on them are available.

Section 8 contains a summary and conclusions.

It is clear that heavier loading brings new challenges to the road industry- technological, operational and contractual.

The asphalt industry has shown in the past that it is able to anticipate such challenges and

respond effectively: asphalt pavements fulfil the demands of today's traffic and the indus­

try is in full swing to anticipate the challenges of tomorrow. Thus continuing the leading

role that asphalt possesses in road building in Europe! _

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2. WHAT ARE "HEAVY DUTY PAVEMENTS"?

2.1. Pavement loading Traffic loading is the primary design factor for roads. Although other design criteria such

as climate may be very relevant to pavement maintenance, this report concentrates on mechanisms directly related to heavy traffic.

Table 2.1 presents the current maximum legal axle loads, gross vehicle weights and total vehicle length in Europe3

• This table shows that significant differences in pavement load­

ing are withstood by asphalt. As far as traffic loads are concerned, potentially the most

severe pavement conditions are met in France and the Netherlands (single axle loads 130

kN, tandem axles 260 kN, triple axles up to 300 kN). Maximum damage to bridges etc. is

found in Sweden and Finland with a maximum gross weight of 560 kN. Norway and The

Netherlands also permit high bridge loading. These limits have formed the basis for the

structural design of the road network.

The values indicated are legal" maxima; it is known that in some countries legal limitations

are seen as "targets to be passed". And from paragraph 2.4.1. it will be clear that such

excessive loadings dramatically increase pavement damage: often exponentially to the 4th-1Oth power!

In December 1993 the European Commission proposed a new directive concerning axle

loading and truck weights. 4 The purpose of this proposal is to harmonise the maximum

authorised weights and dimensions for road vehicles and vehicle combinations through­

out the European Union. It is based on Directive 85/35 which for the first time introduced

harmonised sizes and weights of vehicles in the EU. The overview is given in Table 2.2. Depending on axle and tyre configurations, maximum truck weights of 36 to 44 tonnes

are being proposed and maximum non-driven axle loads of 10 to 24 tonnes (single/tan­dem/triple axles) or driven axle loading of 11.5 to 19 tonnes (single/tandem axles). The pro­

posed maxima will substantially increase the need for stronger pavements. (See also paragraph 4.1 .)

2.2 Temperature In addition to traffic loading, climate also contributes to pavement wear: partly by alte ring

the resistance to wear by traffic, and partly independent of traffic.

Higher temperatures are especially of importance for heavy duty pavements. As tempera­

tures increase, the viscosity of bituminous materials decreases, which significantly reduces

resistance to permanent deformation.

Surface temperatures in asphalt pavements of 70°C and higher have been measured in mid­

dle and southern Europe. However, traffic flow exerts a cooling effect on pavements due to

the draught and shade effects from passing vehicles. So for pavements with high traffic den­

sity the maximum temperature within surface courses could be reduced to 40 - 60°C.

Norway 16-18 50 18.5 (1) One driving axle

Sweden 10 16-20 20-24 56 24 Finland 10(1) 16-20 21-24 56(2) 22 (1) Bus driving axle 10.5t

(2) 60 tons on frozen ground for seven axle loads

Denmark 10 16-20 22-24 44 18.5 Belgium 10 16-20 22-27 44 18

12(1) (1) Driving axle 13(2) (2) Steering axle

Germany 10 11.5-20 21-24 44 18 Spain 13 14.7-21 21-24 44 18 France 13 21 24 44 18 Portugal 12 12-20 21-24 44 18.35 UK 10.5 (1) 20.3 {1) 22.5 (1) 38 · 18 {1) Lower limits may apply

Italy 12 17-20 18-24 44 18 Luxembourg 10 19-20 24-27 44 24

11.5(1) {1) Driving axle 12(2) (2) Air suspension

Netherlands 10(1) 10-20{1) 24-30 50 18 {1) Single wheel 13(2) 13-26(2) (2) Dual wheel

Austria 10 16 16 38 18 EU 10 11-20 21-24 44 USA(1) 9 16.2 18.9 36 {1) State regulations apply

*Dependent on axle spacing **Dependent on vehicle type

Table 2.1: Allowable axle loads, gross vehicle weights, and total vehicle lengths in Europe3

The length of time that high temperatures are experienced is also of importance. As a rule of thumb, rutting potentially can occur only when the temperature profile of the surface

course is over 35°C; that is, when sufficient heat has accumulated in the surface course.

The occurrence of this depends on a number of factors: the maximum ambient tempera-

ture, the period of direct heating by the sun and the local topography.

Low temperatures can also affect general road wear significantly, independent of the traf­

fic load; this is especially the case in its effect on durability.

Thermally induced cracking may be the main reason for surface damage in many

instances. Together with stripping, this mechanism may result in lack of cohesion in the

surface course, and thus in ravelling. On a larger scale, thermally induced cracks may

extend from the surface into the total pavement construction.

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DIMENSIONS MAXIMUM VALUE

length Width Height

WEIGHTS

Truck

Towed truck

Articulated bus Combination truck

Container combination

Combination truck

Air suspension and twin tyres

2 axles 3 axles 2 axles 3 axles 4 axles 3 axles 2x2 axles 2x3 axles 3x3 axles

18.75 m 2.65m 4.00m

180 kN 260 kN 180 kN 250 kN 320 kN 280 kN 360 kN 400 kN 440 kN

Table 2.2 limit values from the EU directive on vehicle weights and dimensions4

2.3. EAPA description of HDP Heavy Duty Pavements bear the highest traffic loading in a country. So, what is the "high­

est traffic loading"?

Different countries use different expressions for traffic loading, such as "number of vehi­cles", "number of commercial vehicles" or "number of heavy vehicles". However, in struc­

tural terms it is not just the number of vehicles passing which determine the traffic load,

but also the impact that each vehicle has on the pavement. As the structural impact of a light vehicle differs from the impact of a heavy vehicle, the concept of the "Equivalent num­

ber of Standard Axles" (ESAL's) has been developed: the impact of each axle of vehicles

passing is equal to the impact of an equivalent number of standard axles (where the load­

ing of the standard axle generally is 80kN, 100kN or 130kN).

Through this concept, totally different traffic. situations can be made comparable. In this

paper traffic loads are expressed in numbers of ESAL's. Paragraph 2.4 explains how to

determine the number of ESAL's from a known traffic distribution.

Traffic situation~ differ from site to site and from country to country. So the content of the

term "Heavy Duty Traffic" will be experienced differently from road authority to road

authority and from country to country. A general definition of "Heavy Duty Traffic" is there­

fore not very fruitful. However a broad indication of the magnitude of Heavy Duty Traffic in

Europe is given.

Following a survey of the traffic loadings in its member countries, EAPA's "Status Report

on Heavy Duty Pavements;', Heavy Duty Pavements were defined as:

ROADS which carry more than 1.2 x 106 standard axle loads of 100 kN per year (approx.

5000 SAL 100kN/Iane/day or 3000 - 5000 HGV/HGV-Iane/day). These pavements carrying very high traffic volumes will have 10 to 20% commercial vehicles.

CONTAINER TERMINALS, AIRFIELDS, INDUSTRIAL SITES, PARKING AREAS which

carry static loads of over approximately 1 N/mm2 etc.;

BUS LANES, STACKING LANES, CREEP LANES etc. with more than 1.2 x105 standard axle loads of 100 kN per year (approx. 500 SAL 100kN/HGV lane/day).

Note 1: The number of 100kN standard axles equals the number of 80kN standard axles divided by 2.44 and vice versa.

Note 2: The number of 130kN standard axles equals the number of 100kN standard axles divided by 2.8 and vice versa.

Note 3: Many pavements will bear loadings only slightly below the levels mentioned. Thus the conclusions of this report also apply in these situations; however it

might not be necessary to apply the most wear resistant solutions.

The current state-of-the-art approach to road construction postulates that the design crite­

ria in the structural model are the horizontal fatigue strain at the bottom of the pavement

or the compressive fatigue strain at the top of the subbase.

It is known that this model does not cover all performance criteria, see also paragraph

2.1.; it is possible that even more significant ones are neglected such as thermally induced

cracking or traffic induced fatigue cracking from the surface of the pavement. Surface rav­

elling and permanent deformation of the pavement are certainly not covered. However it is believed that this model offers the best approach available to compare the effects of dif­

ferent axle and tyre loads on pavements. In Section 4 refinements to this approach, espe­

cially in the field of permanent deformation, are discussed.

In many countries other definitions of heavy duty pavements have been used; they gener­

ally are related to numbers of HGV's. These definitions often fit those national circum­

stances well; however they make it difficult to present a comparison across Europe, so they

are not used in this paper.

2.4. Determination of the equivalent number of standard axles When using the EAPA definitions of heavy duty pavements, the traffic load must be expressed as "equivalent number of standard axles" (ESAL's). This equivalent can be cal­

culated from axle numbers and axle load distribution measurements, or it can be estimat­

ed from traffic census data.

2.4.1. Determination by calculation

Calculation models

Two specific situations can be distinguished: the determination of the equivalent number

of standard axles for structural design purposes (thickness design) and the determination

of the equivalent number of standard axles for deformation calculations.

For structural design purposes the equivalent number of standard axles can be calculated

from actual measured axle loads and numbers by the Fourth Power Law: "the damaging

effect of an axle load is the fourth power of the relative axle load compared to the standard

load".

This means for example that the damaging effect of 1 axle load passage of 100 kN is

equivalent to the damaging effect of:

- 0.4 passages of an axle load of 130 kN (one 130 kN-axle equals 2.5 100 kN-axles); - 0.6 passages of an axle load of 115 kN (general maximum EU permitted axle load); - 2.4 passages of an axle load of 80 kN; - 162 passages of an axle load of 28 kN; - 160,000 passages of an axle load of 5 kN (average private car).

NB: From this list it becomes clear that for the structural design of an asphalt pavement, in

general, only commercial vehicles are relevant!

For permanent deformation calculations another rule should be followed, e.g. as given in

the Shell Pavement Design Manual (SPDM)6• In the permanent deformation model of the

SPDM the damaging effect of a wheel passage is related to the (1/q)-power, where q is the slope of the log Sm;x-log Sb;,-curve. This means that the effects of increasing wheel loads viz.

contact pressure between tyre and pavement, develop between the fifth and the tenth

power, depending on the asphalt mixture type.

For typical values, where (1/q) = 7, the damaging effect from one application of a 100kN

axle load in terms of deformation is equivalent to the following:

- 0.2 passages of an axle load of 130 kN (one 130 kN-axle equals five 100 kN-axles); - 0.4 passages of an axle load of 115 kN (general maximum EU-axle load); - 4.8 passages of an axle load of 80 kN; - 7 400 passages of an axle load of 28 kN; - 1,300,000,000 passages of an axle load of 5 kN (average private car).

So in relation to permanent deformation the effects of low axle loads/tyre pressures can be

discounted even earlier than is the case in structural design, whereas the effects of over­

loading/higher pressures are even more marked!

In table 2.3. an example of the calculation of the equivalent number of standard axles from

a measured axle load distribution is given both for structural design and permanent defor­

mation calculations.

Adaptation of the calculation results to traffic parameters

In general only dynamic axle loads and numbers per loading class are considered. This

results in an approximation of the actual pavement loading as the damaging effects vary

according to the specific road site and the specific vehicle characteristics.

The actual wear created by HGV's is heavily dependent upon vehicle speed and axle

loading.

year

1 <20 1.2 9.6 X 10 2 20-40 16.6 6.9 X 103

3 40-60 32.6 1.1 X 105 1.3 X 104

4 60-80 27.7 3.4 X 105 1.2 X 105

5 80-100 11.8 3.9 X 105 2.9 X 105

6 100-120 7.2 5.4 X 105 2.5 X 105

7 120-140 2.5 3.7 X 105 8.2 X 105

8 140-160 0.8 2.1x105 7.0 X 105

9 160-180 0.3 1.3 X 105 6.2 X 105

10 >180 0.1 6.5 X 104 4.6 X 105

Total actual 100 2.2 X 106 3.3 X 106

' }: Conversion factor structural design: a,= (p;:Peq} 4 = (p; : 100}4• p, is class average; number of ESAL;s in class

i =a, x n,. ' }: Conversion factor permanent deformation: ad = (p;:P,ql'= (p;: 100}' (power factor depends on mix type; 7

chosen as a typical example}. p; is class average; number of ESALd's in class i = ad x n,.

Table 2.3.: Calculation of the equivalent number of 100 kN standard axles from axle distribution

So far as speed is concerned, a recent Dutch study7 has shown, using Shell's BISAR calcula­

tions, that the relative damaging effect of a wheel passage increases significantly when

traffic speed is below 10-15 km/h. In the case of permanent deformation the damage could increase by a factor of 70 compared to the damage at 50 km/h! Whereas, in the case of

fatigue, damage increases by a factor of 4, see figure 2.1.

Relative damage

100

80 Subsoil deformation

60 Asphalt fatigue cracking

Asphalt rutting

40

20

1 10 100 1000

Traffic speed, km/h

Figure 2.1: Effects of Traffic Speed on Damaging Factor7

Significant variations in pavement loading may also occur due to differences in tyre and

axle configuration, suspension systems etc. According to the OECD report2

some typical

adjustments are: * Wide single tyres vs. dual tyres: factor 1.5 to 1 0; * Unequal suspension load sharing: factor 1.5 to 3; * Moving dynamic loading vs. moving constant loading, averaged out along the road sur­

face: factor 1.1 to 1.4; *Spatially repeatable moving dynamic loading vs. moving constant loading, at the worst

locations along the road surface: factor 2 to 14.

The effects of tyre pressure on asphalt pavements have also been described in a

comprehensive Norwegian study.3

The main findings are:

*Operational tyre inflation pressures tend to be set at the maximum recommended infla­tion pressure and not adjusted to the actual wheel load. Thus, for a given tyre, inflation

pressure is largely independent of wheel or axle load. This is mainly for ease, to avoid

frequent inflation/deflation of the tyres.

*The tyre/pavement contact pressure is different from tyre inflation pressure. The contact

pressure consists of both normal and tangential (shear) components. The maximum con­

tact pressure may be in the order of 1-2 times the corresponding inflation pressure.

* Recommended inflation pressures for super single tyres (wide base tyres) do not exceed

recommended inflation pressures (of 600-1000 kPa) for ordinary dual tyres. Oper­

ationally, however, inflation pressures of super singles may exceed operational inflation

pressures of ordinary dual tyres by 50 kPa.

*Super single tyres can cause up to twice as much damage to pavements as dual tyres. *The degree of damage depends on pavement thickness and the properties of the pave­

ment materials; a typical example of the effects is given in figure 2.2.8

Ez -l.Ox10-4 -5.0xl0- 4 -l.Ox10 -3 -15x10-3

o+-----~----~~~~~~----~

50

100

31.71125 150

200

234~------~~----------------

depth,mm

Course of vertical strain with constant single tyre load (31.7kN) and variable inflation pressure.

Ez -l.Ox10- 4 -5.0x 10-4 -l.Oxl0-3 -Uxl0-3

0

50

100

150

200

depth,mm

Course of vertical strain with constant inflation pressure (800kPa I 8 bar) and variable single tyre load.

Figure 2.2: Effects of tyre inflation pressure and wheel load on vertical pavement strain8

High inflation pressures are significant in relation to rutting in the upper half of the struc­

ture whilst the effect of increasing wheel load is significant in relation to fatigue cracking at

the bottom of the asphalt layer.

The effect of a combined variation intyre configuration and tyre inflation pressure is inves­

tigated in a Dutch stud/. According to BISAR and Moebius calculations, the effects are very marked, particularly in the case of super single tyres, see figure 2.3 and table 2.4.

Damaging factor

7

6

5

4

3

2

1

0-r---.---.----.---.---~--~

OS OE 0~ OB 09 1 1.1

Tyre pressure, MPa

---+--- Super single - strain

------- Super single - rutting

____.,___ Dual tyre- strain

~ Dual tyre - rutting

Figure 2.3: Damaging factor at increasing inflation pressure (axle load 100 kN) 9

Table 2.4: Equidamaging numbers of axles and transport volumes8

2.01

0.58 1.11 3.05 6.63

0.46 0.88 1.95 3.73

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:::;:-

~ ttl ttl :::!'. ::::l

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-1 ::r ttl

~ ttl .., 0' .., 3 1).1 ::::l t"l ttl

0 ttl 3 1).1 ::::l c. "' 0 -:I: ttl 1).1 <:

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0 r::: .-+

'< ~ 1).1 <: ttl 3 ttl ::::l .-+

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From several studies10

it is known that horizontal shear stresses in the contact area tyre­

pavement can cause premature fatigue cracking in the pavement, prior to "normal" fatigue

·cracking starting at the bottom of the pavement. This effect will be greater in cases of

increased pavement loading.

The damaging effect of a passing wheel also varies according to the pavement structure.

It depends on the pavement materials used, the type of pavement construction, the sub­

soil properties, environmental conditions, the nature of the wheel load (in terms of its mag­

nitude, speed and frequency) and on the extent of previous damage9

•

2.4.2. Determination by traffic census

It is clear that there is no simple relationship between the damaging effect of individual

HGV passages and their tyre/axle configurations. However, a general relation between the

total number of HGV's and the average damaging factor has been found. Such a relation­ship will be specific to each country due to its legal limits, policing activities and other

national influences. In several Dutch studies the relation, as given in table 2.5. has been found.

11•12

•13

The HGV damaging factor multiplied by the number of HGV's provides the

number of 100 kN standard axles (ESAL's).

HGV traffic classification HGV damaging factor

Light (average < 2.5 axles per HGV)

Moderate (average 2.5-3 axles per HGV)

Heavy (average 3 axles pr HGV)

Table 2.5: HGV damaging factor related to traffic intensity11•12

•13

2.5. Conclusion

0.2-0.5

0.5-1.0

1.0-2.0

It is clear that it is a complex task to determine the precise effect of increasing pavement

loadings in individual situations unless actual measurements are taken. Further research in

this area is needed.

However, on a road network level, it is generally sufficient to estimate the effects of grow­

ing traffic in terms of increased average damage. Studies which provide information on

these effects are becoming more and more widely available. With the available top-class

theoretical tools, translation to daily practice becomes more and more common. The

empirical knowledge gained with existing pavements provides a sound base to incorpo­rate these studies in a disciplined way in actual construction and materials design.

The EAPA descriptions are generally valid for structural design comparison based on

fatigue. In the case of permanent deformation they are valid for a "normal" axle load spec­

trum and a "normal" distribution of axle and tyre configurations, tyre pressures and traf­

fic speed. In other cases the contribution of heavy traffic, axle and tyre configurations, tyre

pressures and, to a limited extent, traffic speed should also be considered as described in

paragraph 2.4.1.

3. HEAVY DUTY ASPHALT PAVEMENTS IN PRACTICE Although the major part of the European motorway network is in a very good condition,

stretches can be identified that have visibly suffered from damage due to excessive traffic. The main reason for the rutting seen on these stretches, is that they have been exposed to

heavier traffic (more axle loads, higher tyre pressures, more super singles tyres, more

dynamic loading or more overloading) than was specified in the original design.

This section considers a number of typical Heavy Duty Asphalt Pavements which are cur­

rently being used in several European countries, supporting the contention that heavy duty asphalt pavements are already performing well. However, the whole of the existing road

network requires adaptation to meet increasing traffic loads.

Road wear depends on the combination of the loads imposed by HGV's and on the resis­

tance of the pavement. The first depends predominantly on axle loads, tyre pressures, axle

and tyre configurations and driving speed. The latter on the pavement materials used, the pavement construction ch?Jracteristics and design, the bearing capacity of the subsoil and

the climate.

The following describes the situation in country/ pavement locations. Please note that this

comparison is only for information - no profound analysis has been undertaken.

A survey of national descriptions of heavy duty pavements is given in the annex to this

paper, and some specific bituminous mixtures, which have proved to be very successful in

HOP's, are discussed in Section 6.

-· Boulevard Peripherique, Paris. The slow lane of each carriageway carries 9000 HGVs per day.

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3.1. Germany 3.1.1. Specific conditions * Legal pavement loading (table 2.1 ): average; *Traffic intensity: high; * Climate(related to rutting): moderate/severe; *Contribution to wear by overloaded trucks (figure 3.1 ): moderate. * Effect of new EU legislation: severe (increase of maximum authorised loads ->

estimated increase in ESAL's by a factor of 1.5)

3.1.2. Pavement design procedure Standard catalogue RStO 1989 (empirical). Principle:

Formation level: Ev2 > 45 MN/m2; Frost protection course (250- 560 mm) to be applied; Design span: 20 years; Traffic load: number of trucks (VB) over 28 kN per day per lane. Highest traffic class SV: VB > 3200 . Traffic number corrected for lane width, number of lanes, gradient

Typical Heavy Duty Asphalt Pavement thickness: 340 mm full-depth, 300 mm bituminous+ 150 mm crushed gravel, 280 mm bituminous+ 200 mm crushed gravel.

Typical mixtures for HDAP: * Surface course: 40 mm Gussasphalt, 30-50 mm asphaltic concrete, 25-50 mm

stone-mastic asphalt. *Binder course: 80 mm asphaltic concrete,

with special requirements and reccomendations. * Roadbase: asphaltic concrete

Typical main criterion for (intermediate) maintenance: permanent deformation.

3.1.3. Mix design method Empirical; with Marshall specimen.

For specific cases: additional mechanical testing e.g. wheel tracking.

3.1.4. Typical example of a Heavy Duty Asphalt Pavement14

Highway A 5, Interchange "Frankfurter Kreuz": 152,000 vehicles/day; estimated number of trucks 10-20% -> 7,500 - 15,000 trucks/day/lane. Estimated number of 100 kN standard axles/year/lane: 2 - 4 x 106

•

Number of ESAL's over 20 years: approx. 6.0 x 107•

Typical construction: * 35-37 mm Gussasphalt 0/11 surface course; * 66 mm asphaltic concrete binder course 0/22; * 133 mm a.c. Roadbase ATS 0/32; * 150 mm Frost protection course, cement stabilised gravel: E3 > 120 MPa. * Formation level: E3 > 45 MPa.

Pavement construction: 1977. Performance as at the end of 1994: slight rutting of 7.3mm, which is far less than the 'warning' level of 10mm!

3.2. France 3.2.1. Specific conditions * Legal pavement loading (table 2.1 ): high; * Traffic intensity: high; * Climate (related to rutting): moderate/very severe; * Contribution to wear of overloaded HGV's: high. * Effect of new EU-Iegislation: positive (reduction of maximum authorised loads-> less

wear).

3.2.2. Pavement design procedure Standard catalogue; specific adjustment by Alize-model possible. Principle:

Design span 20 years; assuming traffic will increase by 7% per year. Traffic load: number of trucks over 50 kN. Highest traffic class: > 2000 trucks/lane/day. Traffic number corrected for overload, number of lanes. Formation level: E > 20- 120 MN/m2

•

Typical mixtures for a Heavy Duty Asphalt Pavement * Surface course: 20-50 mm asphaltic concrete, 25-50 mm stone-mastic asphalt,

30-50 mm porous asphalt. * Binder course (under ultra thin surface courses (approx. 20 mm) and porous

asphalt): 50 mm asphaltic concrete. * Roadbase: 280-380 mm upper/lower base course asphalt concrete 0/20-0/14;

150-250 mm High Modulus asphaltic concrete 0/20-0/14

Typical main criterion for (intermediate) maintenance: fatigue cracking.

3.2.3. Mix design method Functional: fatigue, permanent deformation, stiffness, workability, water sensitivity.

3.2.4. Typical example of a Heavy Duty Asphalt Pavement

Boulevard Peripherique, Paris:

Average daily traffic (both directions): 200,000 vehicles

One direction 100,000 vehicles, 10% HGV's of which 90% on the slow lane= 9,000 HGV's

with ESAL 130kN

Design life assumes traffic growth at 7% per year with life of 20 years= 41

Number of ESAL 100 kN for 20 years= 9,000 x 1.0 x 2.8 x 365 x 41 = 3.7 x 108

Pavement structure: Surface course: 40 mm porous asphalt · Upper roadbase: 110 mm high modulus asphalt concrete;

Lower roadbase: 110 mm high modulus asphalt concrete;

Formation level: E3 = 120 MPa.

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3.3. Netherlands 3.3.1. Specific conditions * Legal pavement loading (table 2.1 ): very high;

* Traffic intensity: high; * Climate (related to rutting): moderate;

*Contribution to wear of overloaded trucks: very high.

* Effect of new EU-Iegislation: positive (less wear).

3.3.2. Pavement design procedure. State road authority method (derived from Shell's SPDM/BISAR).

Principle:

Design span 20 years;

Traffic load : SAL,ookN.

Highest traffic class: class 4: > 6150 SAL10okN/Iane/day Traffic number corrected for lane width, number of lanes, axle & tyre configuration,

traffic growth, and Mean Average Annual Temperature.

Formation level: E3 = 100 MPa.

Typical Heavy Duty Asphalt Pavement thickness: 280 mm

Typical mixtures: *Surface course: 50 mm porous asphalt; 25-35 mm stone mastic asphalt;

40 mm asphaltic concrete;

* Binder course: 45 mm asphaltic concrete 0/22 (0/16).

* Roadbase: 185 mm asphaltic concrete 0/22

Typical main criterion for (intermediate) maintenance:

for pavements with porous asphalt surface course: ravelling.

for pavements with asphaltic concrete surface course: permanent deformation .

for pavements on weak subsoil: embankment settlement.

3.3.3. Mix design method Empirical: based on Marshall method. (NB: Mixture composition requirements have been

verified by fatigue, creep, wheel tracking and indirect tensile tests.)

3.3.4. Typical example of a Heavy Duty Asphalt Pavement ·•

State Highway A67 from Antwerp to the Ruhr area in Germany:

60,000 vehicles/direction/day, which includes 10% HGV's (6,000). Number of 100 kN standard axles per year: ESAL10okN = 6,000 x 0.93 x 1.6 x 250 = 2.2 x 106

;

over 20 years: ESAL10okN = 4.4 x 107•

Pavement structure: Surface course: 50 mm porous asphalt 0/16 mm;

Binder course: 45 mm asphaltic concrete 0/16 mm;

Roadbase: 240 mm asphaltic concrete 0/22 mm.

Formation level: E3 =:o 100 MPa.

3.4. United Kingdom 3.4.1. Specific conditions

* Legal pavement loading (table 2.1 ): low;

* Traffic intensity: high; * Climate (related to rutting): very moderate;

* Contribution to wear of overloaded HGV's: moderate.

* Effect of new EU legislation: significant (increase of wear to be expected).

3.4.2. Pavement design procedure TRL method (TRL report 1132/1984): SPDM failure criteria.

Principle:

Design span 20 years;

Traffic load : SALsokN.

Highest traffic class: 4000 HGV's/lane/day; damaging factor 3.2 -> 1.3 x 104

SALsokN/day/direction = 5.2 x 103 SAL,ookN/day/direction Granular base layer: 225 mm;

Capping layer when CBR < 5%;

Formation level: E3 > 50 MPa.

Typical Heavy Duty Asphalt Pavement thickness: 400 mm

Typical mixtures:

*Surface course: Hot Rolled Asphalt;

* Roadbase: Upper roadbase: Heavy Duty or Dense Bitumen Macadam.

Lower roadbase: Hot Rolled Asphalt.

Typical main criterion for (structural) maintenance: deformation.

3.4.3. Mix design method

Empirical:

Hot Rolled Asphalt: based on Marshall method.

Dense Bitumen Macadam: recipe.

3.4.4. 10 year old example of Heavy Duty Asphalt Pavement

Westbound carriageway of the M4, in Wiltshire, which carries 35,000 vehicles/day in each

direction of which over 12% are HGV's.

Number of 100 kN standard axles per year: (4,200 x 3.2 x 250) : 2.44 = 1.4 x 106;

over 20 years: 2.8 x 107•

Pavement structure:

Surface course: 40 mm Hot Rolled Asphalt;

Binder course: 60 mm Dense Bitumen Macadam

Roadbase: 300 mm Heavy Duty Macadam

After 10 years the road is in good condition with no significant cracking or deformation. Deflection measurements on the heavy duty macadam are at least 20% lower than on the conventional dense bitumen macadam.

Formation level: E3 = 100 MPa

3.5. Surfacing Materials Used for Heavy Duty Asphalt Pavements Section 6 covers the role of a number of materials such as Stone Mastic Asphalt, Thin

Surfacings and Porous Asphalt, along with new techniques and new binders.

United Kingdom. Heavy duty asphalt pavement in service for over ten years (M4)

..

4. THE ADAPTATION OF THE EXISTING ROAD NETWORK

In general, the good performance of the asphalt pavements described in Section 3 is due

to them being new constructions. However, many existing pavements need to be adapted

to accept increased traffic loads.

Two specific requirements can be distinguished (and both may occur together): existing

pavements have to be strengthened and/or have to be widened.

4.1. Strengthening of the existing pavement When a pavement has to meet higher traffic demands, strengthening can be achieved by

either increasing the thickness or stiffness of the road base or improving the resistance to

permanent deformation.

a. Increasing the thickness or stiffness of the roadbase

The required increase in structural strength can be calculated from the expected number

of axle passages using avai~able design methods. The overlay type and thickness depends

on the amount of traffic and the strength of the existing pavement. The latter can be esti­

mated from the existing thickness and the equivalent number of standard axles passed, or can be calculated e.g. by FWD measurement (Falling Weight Deflectometer).

Figure 2.2 shows the expected effects of increasing axle loads. As far as structural design

is concerned, the effects of increasing axle loads (right figure) are relevant: the strain at the

bottom of the pavement (which predominantly determines the resistance to fatigue crack­

ing) increases by approximately a factor of two.

As a rule of thumb, it can be stated that double the number of standard axles requires (for

HDAP constructions) 20-25 mm extra thickness.

By increasing the stiffness of the roadbase by a factor of 5, the predicted number of stan­

dard axles that the pavement will carry is increased by a factor of 5 to 10. It should be noted

that this can be applied to all asphalt layers, but the most significant contribution will be made by the road base.

b. Increasing the resistance to permanent deformation

Where resistance to permanent deformation needs to be improved, layers which do not

fulfil the requirement are removed and replaced by new mixtures designed to bear the

increased loads. In principle all deformable layers should be removed; in practice it is always a question of- how deep to go?

In figure 4.1. the theoretical development of the shear stresses (which are considered to be

most relevant for permanent deformation) in an half-infinite space is illustrated. In a pave­

ment maximum shear stresses occur at 50-80 mm below the surface in the case of mov­

ing traffic; in cases of accelerating/decelerating traffic (e.g. at intersections) these maxima

will occur over the upper 60-100 mm. Where there is insufficient resistance to permanent

deformation, the material should be renewed at least over this thickness; the resistance to

permanent deformation of the remaining material should be considered carefully.

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•

In general both the measures to strengthen the structure and to increase resistance to per­manent deformation are carried out together.

4.2. Road widening Where there is a substantial increase in vehicle numbers, existing roads may have to be

widened. This usually means that an additional lane will be built as the new inside lane, ·bearing the largest number of HGV's, and therefore the highest traffic load. (Unless the

road alignment is also changed.)

In such cases the question arises as to how to design such a widening, and how to carry

out the construction with the least disruption to traffic - especially as road-widening pro­

jects are normally a response to heavy traffic congestion.

In the Netherlands it is expected that approx. 25% of the total highway system will have to

be widened before the year 2010. New and widened constructions must be designed with

low maintenance requirements to reduce user delays.

A recent project9 found that:

* Road widening can be designed in the same way as new pavements for heavy duty traf­

fic as the design models are sufficiently reliable.

*When constructing on subsoil with a low bearing capacity, the settlement of the embankment will cause most problems and not the pavement itself. Therefore, such

embankments should be constructed to the highest quality level; no concessions in con­

struction quality should be accepted simply to shorten lane closure periods.

* As settlement cannot be prevented on weak subsoil, asphalt pavements should always

be used because of their flexible nature and ease of repair.

There are no situations where asphalt is unsuitable.

4.3. Increasing maintenance intervals The asphalt mixes used today in the Netherlands are well suited for heavy duty pavements,

both in general applications and in road widening. Improvements to further reduce main­

tenance are however necessary in two specific areas:

*The standard surface course for highways is porous asphalt. When applied on a suitable

basecourse, this mixture can provide pavements with no permanent deformation viz.

where rutting remains insignificant.

*The porous asphalt applied (conventional bitumen 80/100, 4.5% without modifiers or

drainage inhibitors, 0.5 - 1.0% hydrated lime added) lasts for approximately 10 years.

Further work is required to find ways to extend life.

* For other HDAP's (e.g. in cities), the critical factor for intermediate maintenance is per­

manent deformation of the surface course. Stone Mastic Asphalt can provide an appro­priate solution in many cases.

In France the use of modified asphaltic concrete as a wearing course (thin asphaltic con­

crete for example) increases the interval required to maintain good surface characteristics

of the pavement. The techniques used can allow the fast and efficient resurfacing of sub­

stantial lengths of road overnight, causing minimum traffic disruption.

Several possibilities are available to improve bituminous materials; however the cost ben­

efits are not yet quantifiable as direct comparisons are, so far, impossible to achieve. New

test methods are needed: uniaxial and triaxial testing might offer the required solution. The

tools required to better evaluate the materials used in HDAP's to give long term low main­

tenance for all situations are currently being assessed.

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5. TECHNOLOGICAL TOOLS TO MATCH INCREASING DEMANDS

The pavement constructions discussed in Section 3 have performed well in practice. In

general they are empirically based and time has proved their suitability.

However the fast increase of traffic loads demands faster adaptation of pavement materi­

als and constructions than in the past.

The costs of traffic hindrance do not allow for ill-considered experimentation so the risks of failure must be kept to a minimum. This requires a sound theoretical/technological basis.

In this section we discuss the available scientific tools for the design of Heavy Duty Asphalt Pavements.

5.1. Pavement design models Two principles of asphalt pavement design are used in Europe: * Empirical design, based on practical knowledge and experience using a catalogue of

standard pavement structures.

*Analytical design, based on analytical models and fundamental material properties.

The empirical approach works well with known traffic loads, construction materials and cli­

matic details. However should there be significant change in one or more of these param­

eters, then new practical experience has to be gained by trial and error within a relative

short period. These changes occur more and more frequently (increasing traffic load, recy­

cling mixtures, new binders etc.) so the mathematical approach will be taken more often.

This development is certainly supported by the recent progress of theory verification and

by the growing availability of user-friendly design programs running on more powerful

personal computers. There is a growing interest in a scientific basis for construction and mixture design by specifiers.

At present there are three main mathematical pavement design methods operative in

Europe:

* Shell Pavement Design Manual 1978 (plus Addendum 1985)

* Esso Moebius 1987 * Alize 111

In some countries road authorities have developed their own methods from one of these

models, and some of these analytical models are being used directly for specific design purposes.

The scientific principles of these three methods are generally similar: all are linear-elastic

multi-layer models assuming homogeneous materials with isotropic behaviour. The

design criteria of these models are in general:

* Fatigue cracking from the bottom of the bituminous ba.se course;

* Permanent deformation of the subsoil;

* Permanent deformation of the bituminous courses.

The methods also offer the possibility to predict the extent of rutting.

These methods are sufficiently reliable for "standard" structural construction design

(strength), especially where national materials properties and national verification data are

being incorporated. In this context "sufficiently reliable" means that at this moment the

critical factor is not the accuracy of the design model, but the knowledge of the mixture

properties and the loads applied by traffic and hence the actual stress/strain conditions in

the pavement. Thus improvement of the design method would not increase accuracy, so a

significant safety factor is required to ensure that the design meets the practical need.

The methods do not take account of the effect of horizontal stresses in the contact area

tyre-pavement which may be large enough to create fatigue cracking at the surface. This is

especially the case when the resistance to fatigue of the surface material is reduced, e.g.

due to ageing. The magnitude of these stresses can be calculated by the mathematical

models, which are ·used in the design methods (like BISAR and CRR); however this failure

criterion is often not recognised. See paragraph 5.2.

With regard to rutting, the prediction methods do not yet offer comparable accuracy. The

stress-strain conditions under a moving wheel are very complicated, as shown in section

2, and the actual mixture properties in the pavement are not static. They not only depend

on the mixture composition, but also significantly on the stress/strain situation and on the

temperature profile in depth at the specific spot in the pavement.

Although the accuracy of the methods for rut prediction is therefore limited, they never­

theless offer sufficient possibilities to develop construction and mixture improvements on

a rating scale. This allows the effects of improvements in structure or in mix to be esti­

mated in relation to the actual situation when using conventional materials. It is even more

worthwhile when improved testing devices, offering improved simulation of actual load­ing conditions, are used. See paragraph 5.3.

5.2. Practical directions for pavement design improvements derived from available theory

Operative analytical pavement design methods show in which direction improvements of

bituminous mixtures and pavements can be made to meet the increasing demands of

heavy traffic loading. These improvements should match the design criteria mentioned in

paragraph 5.1. Some indications to solutions are:

* Related to fatigue cracking from the bottom of the asphalt course:

Increase resistance to fatigue of the base mixture to reduce the consequences of strain application;

Increase resistance against cracking/crack growth to reduce the consequences of strain application;

Improve healing performance of a mixture which suffers fatigue;

Increase pavement thickness to reduce fatigue strain at the bottom of the course;

Increase stiffness of all asphalt courses to reduce fatigue strain at the bottom of the course.

* Related to permanent deformation of the subsoil:

Increase thickness of the pavement structure/subbase to reduce stresses;

Increase stiffness of the pavement materials to reduce stresses; Improve bearing capacity of the subsoil.

* Related to permanent deformation of the pavement:

Increase resistance to permanent deformation of the applied bituminous mixtures;

Increase stiffness of the pavement courses to reduce deformation stresses.

A combination of these solutions can be chosen.

Remark: The improvements mentioned are related to the mechanical properties of mix­

tures and constructions limited to operative pavement design methods. When

developing such improvements, the effects on other mechanisms and conditions

should be taken into account. (See paragraph 5.3 for an indication of criteria.)

Some of the recommendations concerning fatigue cracking are also valid for sur­face fatigue and thermal cracking.

Analytical methods are useful for maintenance; to analyse the source of pavement wear

and to select such maintenance strategies that will increase life. Surface cracking may be

due to fatigue from the bottom or from the surface of the pavement, due to reflection crack­

ing or thermal cracking. Rutting may have started in the surface course, in the intermedi­

ate course where deformation stresses are largest, or from deformation of the subsoil

when structural strength was insufficient. In the case of overlaying, the existing surface

course may become the intermediate course and suffer large deformation stresses which it was not designed to resist.

By using construction design methods to analyse the symptoms of failure and the effects

of maintenance, optimum techniques can be selected.

5.3. New developments in theory and laboratory In many countries research projects are being carried out to improve the measurement of the relevant mixture parameters to further advance analytical pavement design methods.

Some important developments are covered below.

5.3.1. Functional approach of mixture design

To date, analytical pavement design methods only take account of some mechanical fail­

ure criteria: fatigue at the bottom of the pavement and permanent deformation of subsoil

and bituminous courses. Recently however it has become the practice to incorporate other

failure criteria and other limiting conditions in the mixture design procedures in a system­atic way. e.g.:

- resistance to ravelling/stripping

- resistance to thermal cracking

- resistance to fatigue cracking in the surface course

- workability

- recyclability

\

This requirement is recognised in France, SHRP-USA, ASTO-FIN, CROW-NL and others.

Also CEN TC 227/WG 1 "Bituminous Mixtures" follows this principle of mix design.

5.3.2. Improvement of mixture characterisation

In the past, bituminous mixtures were predominantly designed by the Marshall method,

but the value of this method related to performance is limited. For example in a recent

Dutch study16 it was demonstrated that -for generally applied bituminous mixtures -the

Marshall stability had absolutely no relation, and the Marshall flow only a weak relation, to

mixture stiffness and deformation sensitivity as measured by repeated load uniaxial test­ing and indirect tensile testing. For this reason, many countries have developed additional

requirements covering, for instance, raw materials, mixture composition limits, and other

properties.

Tests have come into use which provide better functional or fundamental mixture

properties.

("Functional mixture properties" are those properties which show a direct relationship to

pavement performance; e.g. susceptibility to permanent deformation. "Fundamental mix­

ture properties" are basic physical properties e.g. visco-elastic properties, stiffness etc.

Functional properties can be fundamental properties; however this is not self-evident.)

Examples of such tests which are also being considered by CEN for European stan­

dardisation:

* Wheel tracking test. This test is operative in France and Denmark, and in other countries, like Germany and

the UK, in specific cases. The test offers an insight into the resistance to permanent deformation in a stress-strain condition which is largely comparable to those condi­

tions in the pavement. The successful application of this test method depends largely

on the quality of specimen preparation. 17 This test also has a good discrimination

power provided the test temperature equals the actual significant maximum temper­

ature in the pavement. 18 Thus the test can be considered to be a functional test method. However the test does not deliver physical parameters, nor parameters which

can be used in operative pavement design methods. So the wheel tracking test is not

a fundamental test.

* 2/3/4-point bending tests. These tests are operative in many countries, generally for special purposes. They offer

insight into resistance to fatigue and stiffness. Bending tests do offer fundamental

physical properties.

* Repeated load compression test.

Most well-known is the uniaxial repeated load creep test (dynamic creep test) which

was introduced some years ago as an improvement to the static load creep test.

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The test offers insight into the resistance of bituminous mixes to permanent defor­

mation in a fundamental way. However the relation of the stress-strain conditions in

this test with such conditions in the pavement is limited. This results in a significant

under-estimation of the contribution that internal friction in the aggregate structure

of the mixture makes to the resistance to permanent deformation. As this factor is

especially important in gap-graded mixtures, the test is best used for comparisons within a mixture type (investigating effects of changes in aggregate, binder and addi­

tive properties within a certain composition envelope).

The limits of the uniaxial compression test disappear when applying a tri-axial load­

ing condition. A device which is easily used in practice has been developed in

Australia and European developments are expected soon.

* Direct tensile test.

This test, which is operational in France, offers insight into stiffness properties in a fundamental way.

* Indirect tensile test.

The test gives insight into the performance of bituminous mixes under tensile strain

and is becoming more popular due to its ease of use. When applying a repeated load,

fatigue and stiffness behaviour can be investigated. Theoretically this is a fundamen­

tal test. However, due to the applied loading conditions, the field of applicatit1n is very

limited: at temperatures above approximately 0-5 oc (for penetration grade binders)

the stress/strain condition in the test specimen is uncontrolled and therefore the sig­

nificance of the test is doubtful (the quality of the result is no better than the Marshall

test!). In the UK the significant effect of curing has been demonstrated with this test on a TRL project where the elastic stiffness was found to increase 30% after one year19

•

Repeated load axial testing to determine resistance to permanent deformation

* Thermal stress restrained tensile test.

With this test the resistance to thermal cracking resulting from relatively fast temperature

variation can be investigated. Together with fatigue cracking at the surface, this could be

the major cause of surface cracking.

In all cases, test results are significantly influenced by the method of specimen preparation:

by the mixing procedure, the compaction method and the compaction level. Several studies show that absolute conformity, in all properties, of the laboratory specimen

with specimens from the actual road cannot be achieved. However, in practice as far as

density is concerned, several devices can prepare relevant laboratory specimens: the impact compactor (Marshall hammer), the kneading compactor (gyratory compactor), the

vibratory compactor and the roller compactor.

Where mechanical properties are involved the situation is different. In a SHRP-AAMAS­projecf0 it was found that the gyratory compacted specimen correlated best with the spec­

imen from the road; roller compacted specimens acted almost equally. Impact compaction

and vibratory compaction .did not provide representative specimens at all.

A comparable Dutch study13 came to the same conclusion, based on uniaxial repeated load

testing, resilient modulus testing and indirect tensile testing- roller compaction was not

involved. However, a (constant) shift factor between laboratory and road could not be pre­

vented.

If the test methods described in a functional pavement design procedure are used appro­

priately, it will be possible to investigate the potential contribution of mixture improve­

ments (e.g. by using new materials or compositions) to improved pavement performance.

Adaptation of bituminous pavements to the increasing demands of traffic is therefore fea­sible.

5.3.3. Improvement of pavement design methods

As knowledge of the significant mixture properties and load conditions in the pavement

grows so pavement design methods will improve. Such improvements are currently being developed, especially in scientific institutes. The increasing availability of computing

power makes it possible to manage highly complex developments, such as:

*The introduction of finite-elements calculation models.

With this type of analytical model the effects of mixture inhomogeneity and anisotrophy

can be handled more easily. The effect of cracks and other irregularities can be incorpo­rated. This is of special interest in overlay design as the strength of the existing pavement

can be integrated in a more realistic way.

*The introduction of visco-elastic calculation models.

Current methods assume linear-elastic mixture beliaviour. However bituminous materi­

als display visco-elastic plasticity, so the introduction of a visco-elastic mixture model will

certainly improve the pavement design model.

*The introduction of probabilistic design.

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*The operative methods assume constant mixture properties, constant pavement loading,

constant pavement thicknesses and relatively constant climate. However in practice

these, and other, parameters show significant variation. By incorporating probabilistic

principles into the design methods the effects of these variations, and their interrelated

effects on mixture properties, will improve the design accuracy.

5.4. A framework for developing an optimum solution It has been found that the implementation of new technology requires a new approach to

mix design/type testing. In general the existing methods are based on empirical knowl­

edge: requirements are embedded in a total system of construction design, contracting, job execution, quality control and road maintenance. When changing one element, the

effects on the total system must be considered.

A new system of mix design should fulfil a number of essential requirements to permit a smooth implementation of new technology into existing ones. Such essential require­

ments are:

The mix design/type testing procedures should be functionally based In this way is it possible to develop an optimum solution for the relevant parameters in

every situation (related to traffic, climate and maintenance strategy) without predefined

constraints.

Surface texture and related properties - Hydraulic conductivity (porous asphalt) - Noise suppression (e.g. porous asphalt)

Mechanical properties - Resistance to fatigue (incl. healing) - Resistance to crack propagation . - Resistance to permanent deformation -Stiffness

Durability properties - Resistance to stripping - Resistance to temperature cracking - Resistance to wear - Resistance to ageing

Workability properties - Compatibility - Segregation sensitivity (coarse aggregate/binder drainage)

Table 5.1 EN-Standards for test methods to measure these technical properties are now being developed

The technical terms ruling the mix performance should be described in a fundamental way (as far as is practical, possible and necessary)

In this context "fundamental" means that the relevant technical parameter is described in

such a way that the performance of the pavement related to this parameter can be accu­rately predicted.

Different solutions for each situation will therefore be comparable.

A list of relevant requirements and their translation into technical terms has been devel­oped by CEN TC 227M/G1 "Road Materials- Bituminous Mixtures".

5.5. Conclusion It is clear that whilst conventional empirical test methods and construction design proce­

dures have been found adequate for conditions to date, given the increasing traffic demands of the future new methodsshould be considered necessary . Fortunately these

methods are available, or are being developed, to meet this need. However, it should be

remembered that whilst "a· good cookery-book is a pre-requisite, the proof of the pudding is in the eating!"

The structural properties of asphalt materials develop continuously over the life of the

pavement. So practical performance verification will always be essential to identify the most beneficial solutions.

Spain. Full-scale wheel-tracking testing facility, CEDEX, Madrid

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6. PRACTICAL EXPERIENCE WITH THE NEW TECHNOLOGY

Developments all over the world show that modern asphalt technology is already used in practice to the benefit of the road community. Some examples follow of the general

implementation of this technology which is becoming daily practice!

6.1. Structural pavement design The ALIZE design model and design criteria have been included in French standard proce­

dures for construction and bituminous mixtures design since 1985. Its use allows contrac­

tors to submit alternative bids when fatigue, stiffness, rutting, workability and durability

tests have been carried out.

In the Netherlands the BISAR design model is used for the State Road Design Manual.

Standardised bituminous mixtures are verified according to the BISAR design criteria by relevant test methods.

In other countries such design ·models are being used for the design of special construc­

tions or materials. The bituminous mixture design procedures used at Schiphol Airport21

are typical. A bituminous pavement for a pier extension, capable of taking the loading of

several heavy aircraft, had to be designed. The selection of the most appropriate mixture

composition (from standard bitumen to polymer modified mixtures) was based on func­

tional criteria such as resistance to cracking, resistance to permanent deformation and

workability. Furthermore, there was a stringent requirement to minimise environmental

disturbance during manufacture and laying. The pavement, constructed in 1993, is per­

forming well in service.

Surfacing 100mm

210mm 265mm 255mm

305mm 370mm

Dense Bitumen Macadam 15 pen Dense Bitumen Macadam (DBM) Heavy Duty Macadam (HDM) (DBM15)

20 yrs 40 yrs 20 yrs 40 yrs 20 y rs 40 yrs 20 yrs = 120 x 1 0' ESALao,N 40 yrs = 300 x 1 0' ESAL80,"

Higher stiffness asphalts have the benefit of longer structural life with the potential for reducing the thickness of the base. The table above shows the depth of the asphalt base for DBM {3000 MPa), HDM {4500 MPa) and DBM15 {8000 MPa) determined analytically for a 20-year and 40-year structural life, using the SPDM-PC". The results clearly show that to achieve a 40-year structural <;;life the conventional DBM would have to be 19% thicker. However the 40-year HDM would still be marginally thinner than the 20-year DBM, while the 40-year DBM15 would be 18% thinner than the 20-year DBM, and over 30% thinner than a DBM with a compara­ble design life. This offers significant savings in material and possibly earthworks costs.

Figure 6.1 Base thickness of alternative asphalts, determined analytically using the SPDM­PC22 for design lives of 20 and 40 years

6.2. High Modulus base course One ofthe significant failure criteria for analytical pavement design models is fatigue crack­

ing from the bottom of the pavement; so increase in the resistance to fatigue cracking of

the bituminous material applied there would be of interest. This benefit can be obtained by

increasing the binder content. However, merely increasing the binder content would

reduce the resistance to permanent deformation, which could introduce premature rutting.

A solution has been developed in France using the analytical design models and tests men­

t ioned earlier. A bituminous material with a balanced combination of increased resistance

to permanent deformation and resistance to fatigue, nowadays widely applied and known

as "En robe avec Module Eleve", (High Modulus Base Course) has been developed. This material gives increased resistance to permanent deformation by its increased stiffness,

and increased resistance to fatigue cracking by its increased binder content.

6.3. Multigrade bitumen Increasing the stiffness of the bitumen improves the resistance to permanent deformation of a bituminous mixture. However, harder, stiffer bitumens have a greater susceptibility to

thermal cracking. One solution is the use of polymer modified binders, but their use is gen­erally only cost-effective in demanding applications.

Cumulative strain, lQ-6

10 000

8 00

0 2 000

Bitumen stiffness, Pa

109

108

107

106

105

104

~sk of cracking

4 000 Time, s

6 000

Risk • of rutting

....... 50/70

~ Multigrade

...._SBS

-o-10/20

8 000

G) 70/100

@ 35/50

@ 35/50MG

@ 10/20

103 ~----~----~--~~--~-----r----~ -40 -20 0 20 40 60 80

Temperature, °C

Figure 6.2 The effect of a multigrade bitumen

'+-0

A new development is multigrade bitumen. This type of bitumen has the dual benefit of

slightly lower stiffness than the equivalent conventional penetration grade at low ambient

temperatures (<0°C) and higher viscosity at high service temperatures, 50°C to 70°C.

Thus it confers substantially improved resistance to rutting at high asphalt temperatures

whilst reducing the liability to cracking at low temperatures. This type of bitumen requires slightly higher mixing and compaction temperatures than the equivalent penetration

grade. Figure 6.2 shows the effect of such a binder, compared to "normal" penetration­

grade binders and a (medium content) SBS modified binder23• Full scale road trials have

confirmed the improved rut resistance and as a result these binders are gaining in popu­larity in Canada and Australia, as well as in Europe.

Although the effect of the stiff conventional binder is not reached, the deformation in the

uniaxial repeated load test of the mixture with the multigrade bitumen is comparable to

that of the mixture with a medium content SBS modified binder.

6.4. Modified bitumens· Bitumen can be modified using a range of additives, e g SBS, EVA, SBR, EPDM, APP,

polyethylene, etc. The addition of polymers significantly improves various bitumen prop­

erties, e.g. elasticity, cohesion, stiffness and adhesive properties. The result is a substantial

improvement in the performance of the asphalt. This is demonstrated in figure 6.3 which

shows that resistance to permanent deformation (wheel tracking test) improves by a fac­

tor of 3- 10 compared with conventional bitumen! Also in other tests substantial improve­

ments are found, (table 6.2). According to this last table, the repeated load creep test shows

improvements by a factor of 16 to 100! (The difference between the tests might be the result of differences in modifications or effects of the specific test conditions.)

Total rut depth, %

5 -4

! 3

I 2

lr ... ... 1

~ 0 I I I I I I I I I I I I

0 2 4 6 8 10 12 14 16 18 20 22 24 Time, h

---- 80/100 -o- EVAI

--+- EVA3 - Lin. SBS

Figure 6.3: Rutting in the wheel tracking test at 45°C24

These benefits have been reported in many papers. However, modification of bitumen with

polymers requires a sound understanding of the interrelationship of the bitumen and the

polymer. Inappropriate bitumen/polymer blends may not result in improved performance of the asphalt25

'26

•

6.5. Porous Asphalt This material exhibits high resistance to permanent deformation. When applied on a sound

base layer, porous asphalt provides pavement constructions which show no (significant)

ru tting. Systematic measurements on early test sections in the Netherlands prove this statement, see table 6.1, and porous asphalt laid later continues to do so.

Table 6.1: Rut depth in porou~ asphalt test sections, Zeist (Nl), Highway A 12, 1500 - 2000 com­mercial vehicles/day/lane, [mm]. (Maximum acceptable level: 18 mm.)

6.6. Stone Mastic Asphalt (SMA) Stone Mastic Asphalt is a mix which combines a high stability with excellent durability. The

high stability is obtained through a strong aggregate structure built by the coarse aggre­

gate particles; the good durability comes from the high binder content, which is applied as

a mastic, filling the voids in the aggregate structure and giving a void content of 2- 4%. To

prevent binder drainage, caused by the binder content in relation to the surface of the aggregate, a binder drainage inhibitor is added.

SMA has shown its advantages of good resistance to permanent deformation and dura­

bility for HOP's for many years, especially in Germany.

For HOP's i.t is vital to use good quality aggregate (particle shape) and binder with a suffi­

ciently high viscosity at higher service temperatures. Dutch experience has shown plastic

deformation when too soft a binder was used (pen 80/100 with crushed river gravel).

In France a number of special materials have been derived from standard SMA by using

special binders or additives. They are known as "Enrobe en couches tres mince"(BBM, BBUM).

It must be emphasised that when SMA is applied in very thin layers that it will only per­

form satisfactorily when the bearing capacity (the resistance to permanent deformation) of

the bound and unbound base and binder courses are sufficiently high.

6.7. Improvement of the resistance to permanent deformation of bitumi-0

nous m1xes Recently tools to measure the resistance to permanent deformation of bituminous mix­

tures in a fundamental way have become available for day to day research. Such devices

are the uniaxial creep test and the triaxial creep test.

A comparative study of permanent deformation carried out with the repeated load uniaxi­

al creep test 27

shows that substantial benefits are achievable with, small changes to mix­

ture composition, see table 6.2.

N, = number of loadings to break 'N, = deformation at N, loadings

Relative

1.00 1 .47 1.55 0.73 0.67 {-) 1.78 1.40

0.50 0.74 {-)

1.00 {-) 1.21 2.10 1.31 {-) 1.03 {-)

9.7 100 1.00 1.00 0.69 {-) 0.61 0.70 0.52 {-) 0.77 0.81

E1QOO =deformation at 1000 loadings <i = slope linear part of deformation curve

Table 6.2: Results of Repeated Load Creep Tests27

Test conditions: * Load 2000N (=0.6 MPa) * No load 1.8 sec. *Test specimen: laboratory preparation,

height= 63 mm, 0 100 mm.

* Loading time 0.2 sec *Temperature 40 oc * Number of specimens per variant: 3

The slope of the creep curve could be considered to be most significant. Analysing this

parameter shows that simply using a one grade stiffer binder improves the resistance to

permanent deformation of surface and binder course material by a factor of 2; modified

binder increases this factor to 16 (AC) or 100 (SMA)!

For base course materials a one grade stiffer binder improves resistance to permanent

deformation ofthe mix by a factor of 14- 20! (Modified binder has not been tested in this

case).

A limitation of the uniaxial test is the lack of lateral support: in the road, confining stresses

are generated in the upper part of the pavement over the neutral line.

Triaxial testing provides an answer to this shortcoming. More devices to carry out this test

in a practical way have become available.

7. COST EFFECTIVENESS AND CONTRACTUAL DEVELOPMENTS

7.1 . Cost effectiveness Cost models should incorporate whole-life costing to provide the optimum solution for the entire community. The need for this approach is clear, for instance a German study28 has

shown that the ongoing effects of changes in axle and tyre configurations and inflation

pressures would require a tremendous increase in funds to maintain the German federal t ruck network (by 100% in 10 years for pavements and 400% for bridges). However when,

in addition to the costs for the individual road authority, the costs and benefits for the road

user are taken into account, any increase in permissible axle load results in an overall ben­

efit (that means a benefit-cost ratio of over 1.0). The most profitable solution for the nation­

al economy in general would to be an increase in gross weight, without increasing axle

load, or even better, decreasing axle load. From this point of view the road industry and

road authorities can justify increased expenditure on pavements with greater durability

and structural strength.

The whole life costing benefits of asphalt as a construction material on motorways have been

demonstrated by Prof. Schmuck in a comparative study in four European countries29• In this

study, based on historical data, asphalt was compared with concrete slabs and reinforced

concrete. The UK is currently undertaking trials of a whole-life cost model for pavements

which have demonstrated how competitive asphalt designs are. In his pape~0 Bowskill high­

lighted the opportunities this work offered for the new asphalt products under development.

A recent study in the UK by the TRL which takes into account assumed future maintenance

strategies, and a longer design period, also demonstrates the benefits of asphalt as a sound

construction material from both an engineering and economic point of view.

Other benefits of asphalt as a cost effective construction material follow from the full recy­

clability of the product, and from the environmental benefits which may be achieved such as noise reduction when certain types of porous asphalt or stone mastic asphalt are

employed. These latter benefits can be further extended by the use of modified binders.

7.2 Contractual developments Improvements in the construction of Heavy Duty Asphalt Pavements can be found not only

in technology, but also in the field of the contractual relations between contractor and road

authority. In the chain from road planning to operational use the following stages can be identified:

Alignment Structural construction design

Construction execution

Pavement materials design/production

Road manage­ment

In Europe there are several systems of division of responsibility between client and con­

tractor. It is necessary to have the correct balance between risk and reward, and for this to

occur an armoury of contract types is required.

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The line of the road is generally the responsibility of the road authority as political and envi­

ronmental considerations might be involved.

In cases where the road authority is not a public authority, the alignment design would be checked by a public body.

7.2.1. The conventional construction contract Traditionally the client specifies the required construction and materials in detail. However

this approach results in a conservative attitude to road management as constructions and materials with a proven record are preferred.

This approach may be adequate when the operational environment only changes gradu­

ally so that necessary adaptations can be incorporated in time. But R&D will be minimal

and guarantee requirements will not necessarily be very significant. In the case of Heavy

Duty Pavements a faster rate of adaptation is necessary.

To allow the road contracting industry to meet the challenges of the near future, the con­

ventional contractual relation needs to be adapted to fulfil specific requirements.

Under the conventional contract the pavement construction design continues to be carried

out by the road authority. Generally this includes sub-base design, pavement thickness

design, and the choice of asphalt mixture type and of mixture properties to meet a speci­

fied traffic class/climatic range. A high level of detail is usual in the tender documents.

The task of the road contractor is to build the road structure as specified by the road author­ity. It is only rarely that techniques or materials outside the tender specifications are per­

mitted.

The road authority checks the quality of the delivered work, both during execution and by

testing afterwards. Asphalt mix design, both for new roads and for maintenance, is done

by the asphalt mix producers who tend to be private companies. Asphalt mix production

and contracting may be done by the same company or separate companies.

7.2.2. The "Design and Build" contract Design and Build contracts, where the contractor has the responsibility for initial investi­

gation and design, are becoming more popular. However, there are difficulties, as the low­

est tender price remains the main decision criterion and the results of R&D are eventually

made known to the client.

7.2.3. The "Functional" contract In this type of contract the road authority's involvement is reduced to the definition of the

required function. This includes the preferred alignment, surface requirements related to

safety, noise, comfort (rideability); traffic loading, maintenance constraints (such as avail­

ability to the road user), and climatic conditions.

The road authority has the responsibility to deliver a certain level of service to the public,

at the lowest (social) cost, and translates these service levels into technical terms such as

skid resistance, longitudinal and transverse evenness, visibility parameters, etc.

The contractor then designs, builds and maintains the road under stringent guarantee

clauses ensuring specified maintenance free periods.

When allowing the contractor to translate from the service level to the technical or from the

technical term to the specific work to be executed, the required level of quality must be

specified very accurately. To achieve this, a standard description is used in most countries. Most road authorities monitor their road system and check the service level at the required

stages in this way.

For the client to receive optimum security and the contractor the optimum freedom to offer

solutions, the following steps are essential:

a) The requirements should be functionally based and the technical terms should be

described in a fundamental way- as covered in Section 5.

b) Models should be available to compare options in an objective way covering:

Materials;

Constructions;

Maintenance techniques;

Costs.

Cost models should contain whole life costs, including reconstruction, users costs, delay

costs and other social and environmental costs.

Traditionally, the road authority only compares the initial costs (the job execution costs). In a few cases maintenance costs are considered, however decisions based on whole life

costs (including rehabilitation/reconstruction costs and users costs) are still rare.

It is possible to incorporate the cost of lane rental for future maintenance in these models.

These models make it possible for the road authority to compare the offers received and

therefore should be made part of a standardised tendering system. They should also give

companies the incentive to invest in research and development.

c) An objective system of performance warranty is required.

In deciding between the different proposals the road authority must be confident that the

pavement will perform as stated. This means that some form of performance guarantee should be contained in the contract conditions, which in turn demands that the contractor

will have to accept the increased risk inherent in this.

The type of quality assurance method described in EN 29001/2, or its equivalent, gives the

road authority the confidence that a contractors management system will ensure that both

design and construction are done to an adequate and consistent standard. This could be

extended to cover a warranty for "fault free availability of the road", a concept that is

included in some Scottish contracts.

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d) Payment for performance.

The traditional relationship between Road Authority and Contractor is based on payment

for a construction. Newer proposed relationships are based increasingly on 'payment for performance' and the contractor is seen more as a service provider than a builder. This

type of functional contract is becoming more common. In Sweden more than 20 projects

with a combined value of over US $200 million were started in 1994.

In Norway under the umbrella of "Incentive Contracts" a system is in place whereby the

resistance of the road surface to studded tyres over a predefined time period is specified

in the contract, and the contractor is subject to bonus or penalty payments according to the

actual performance of the road in service. If the surface remains usable after this period a

bonus is paid, if it requires maintenance or resurfacing a penalty is incurred which might

also include the cost of the additional maintenance.

In Scotland, the Design, Build and Commission contract is a variant ofthe functional con­

tract. The road builder takes orf all the responsibility for design and construction of the road

to agreed standards, and furthermore accepts all the risks that may occur during con­

struction until the road is "fault-free and available to traffic".

Clearly there are other factors that have to be assessed for these types of contract to oper­

ate; the basic constraints may change during the period of the contract, and the financial

stability of the contractor needs to be sufficient to accept whatever future liabilities may be

incurred.

7.2.4. The "Design, Build, Finance and Operate" contract These contracts give responsibility to the contractor for every phase of the road's initial

design and construction. In addition to which the contractor has to provide or source the

funds to pay for these activities, and operate the road in a way that is covered in the con­

tract provisions. They often allocate a substantial element of payment for 'fault free avail­

ability of the road'. The proper incentives can be incorporated for quality, giving the client

.greater assurance when permitting alternatives which are proposed by tenderers. For

these contracts to progress further, it is important that the tenderer is confident of an ·ade­

quate return for the risks accepted!!

In the U.K. the early signs are that the tenderer's perception of risk over a 30 year conces­

sion period (plus a residual life of 10 years) is somewhat different to the Department of

Transport's. However, it is undoubtedly the Government's view that DBFO will be a major force in road procurement.

This type of contract may involve ownership, as in the French, Italian and Austrian tol l

motorway systems, but not necessarily .

7.2.5. "Technical Approval" With any type of contract the introduction of innovative solutions may require ETA

(European Technical Approval) for special products, to be provided by EOTA (European

Organisation for Technical Approvals). Under this system new products can more easily

be introduced to clients. On a national level the French Avis Technique has the same objec­

ive. However a long guarantee period is often required by the client.

7.3. Contractual adaptations In the future, EU legislation will have greater impact on the product, and on the contractu­al relationship between buyer and producer.

The Construction Product Directive will make the use of CE marking mandatory on all con­

struction products including bituminous materials. This may result in the introduction of certification systems which will influence the relation between client and producer because

it could require an "independent third party" to verify that the product complies with tech­

nical requirements. Also the Public Procurement Directive influences the contractual rela­

t ion, as European Harmonised Standards are mandatory in such contracts.

7 .4. Conclusions New contract forms and new relationships between client and contractor may not only

assist in the implementatior:1 of suitable and innovative solutions; they are also likely to

bring about a new view of funding roads, via private finance rather than public, and of buy­

ing roads on a performance and durability basis.

In the Netherlands, legal pavement loading is very high (up to 50 tonnes gross weight).

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8. SUMMARY AND CONCLUSIONS

As the world economy grows, so the need for transport increases.

The road infrastructure is still the main form of transport; and it is becoming more and

more important. Congestion and delay due to a lack of road capacity, (or indeed the lack of

an appropriate road at all linking centres of activity), or lane closure for maintenance activ­

ities create high economic costs that extend far beyond the actual infrastructure costs. This provides the reason for a comprehensive view of road management: whole life costs,

maintenance need implications and actual traffic loads must be considered in order to

obtain the best results in terms of optimum social benefit. The goal should be the devel­

opment of durable pavements, which carry the expected future traffic loads without pre­

mature failure or maintenance, within reasonable time, and for the lowest social costs. In terms of whole life cost it might be beneficial to adopt solutions with a longer lifetime.

In this paper it has been demonstrated that such structural solutions in asphalt can easily

be achieved by increasing the .strength of the total construction, eventually in combination

with modified mix characteristics. This should be done in combination with good surface

management to ensure timely maintenance to guarantee the surface characteristics.

Society requires the active involvement of every branch of industry to give due weight to

environmental, health and safety concerns. The road industry, laying its products so visi­

bly "in the street", is no exception.

It is clear that asphalt will continue to provide the most "road user friendly" and "road

authority friendly" pavements: it provides a safe, skid resistant, comfortable and quiet rid­ing surface for all types of road, requiring low maintenance. And it does all this cost-effec­

tively!! This is unlikely to change in the future as asphalt can meet even the most severe

conditions. The technologies are already available to help develop solutions for likely

future conditions.

When considering the cost of strengthening the existing total road network it might be

advisable to limit maximum tyre pressures.

Current empirically-based construction and mix design methods are used satisfactorily

throughout Europe. These methods have been developed by the close co-operation of

road authorities with contractors/asphalt mix producers. Where new materials are being

introduced, or new production techniques (including recycling) are being developed, or

where the conventional relation between road authority and contractor is changing, the

need for performance based specifications in the contracts becomes apparent. In this

paper it has been shown that the technological tools are already available, and used, to

incorporate these developments in the most profitable way.

Improvements in constructing Heavy Duty Asphalt Pavements are not only found in tech­

nology, but also by changes in the contractual relationship between contractor and road

authority. This stimulates the required Research and Development to support further

improvements.

New asphalt technology requires a higher level of knowledge from the mix designer, as

mix design becomes more integrated into construction design. This, together with greater

emphasis in quality (as shown by the increasing use of quality management systems according to EN 29000/ISO 9000) provides a sound base for the development of future

asphalt mixes. This paper has described an approach within which such developments are

expected to bring benefits to all!

Asphalt pavements have always demonstrated their ability to provide optimum pavement

solutions for virtually all road needs. We are delighted to report that this will continue to

be true in the future!

Germany. Increase in heavy goods traffic throughout Europe has demonstrated the need for a comprehensive view of road management.

9. ACKNOWLEDGEMENTS

This paper has been prepared by the EAPA Technical Committee and EAPA would like to thank the following members for their contributions:

Mr. J.P. Michaut, Societe Colas S.A., France Mr. T. Lahtinen, Lemminkainen oy, Finland Mr. J. O'Brien, CRH pic, Ireland Mr. J.P.J. van der Heide, VBW-Asfalt, Netherlands Mr. P.M. Noss, AEF/AIL, Norway

Mr. C.A. Loveday, Tarmac Quarry Products Ltd., United Kingdom

Mr. J.A. Corr, R.J. Maxwell Ltd, United Kingdom Dr.-lng. H. Els, DAV e.V., Germany Mr. L. Druschner, ISV llseder Mischwerke GmbH, Germany Mr. J. Pippich, llbau, Austria Mr. P.O. Jonsson, Skanska Ent~eprenad AB Farsta, Sweden Dr. G. Bodnar, HAPA, Hungary

Mr. H. Gormsen, Superfos Construction a/s, Denmark Mr. T.M.R. Bou9a, Pavia, Portugal Dr. G. Battiato, RO.DE.CO. S.r.l., Italy Mr. J.M. Membrillo, Elsamex s.a., Spain

Special thanks need to be extended to Jos van der Heide for his major contribution to the writing and research for this report. Input from David Whiteoak and Jeremy Wood from Shell Bitumen, and Max von Devivere of EAPA has also been valuable in its preparation. The publication of this paper was made possible with a financial grant from Shell Bitumen in the UK.

Annex

Table I: National Descriptions of Heavy Duty Pavements

A.1: National Definitions HDP

Bauklasse SV: Lorries over 28 kN: > 3200/day/lane

Classe de Traffic >TO: lorries over 50 kN: > 2000/day/lane

Lorries over 30 kN: > 3000/day/lane

Traffic class 4: > 6100 SAL,ookN/day/lane (appr. 4700 trucks/day/lane

A.2. Maximum values of loadings

(> 1.2 X 10")

> 0.08 X 10"

> 2.0 X 10"

> 1.0x 10"

>1.5x10"

Country Max. legal train weight (kN) Max. axle load Max. tyre pressure (kN) (Practice) (N/mm2

) (Practice)

E.U.

A

D

DK

F

NL

UK

500

430

no limit (540)

A.3. HOP-constructions for highways

115

AC =Asphaltic Concrete PMB = Polymer Modified Binder

••

PA = Porous Asphalt VMA =Voids in the Mineral Aggregate GA = Gu~asphalt VFB =Voids (VMA) Filled with Binder HRA = Hot Rolled Asphalt Binder: % per 100% aggregate SMA = Stone Mastic Asphalt GB = Grave Bitume DBM = Dense Bitumen Macadam HDM = High Density Macadam

(0.85)

1.1

0.9

1.0-1.2

A: Austria

I

Construction Bituminous materials

Regular design; Standardised constructions RVS * 230 mm asphalt * 200 mm unbound type 1 * 300 mm unbound type 2

Formation Level: Eva > 35 MN/m2

D: Germany

* Surface course:

40 - 50 mm AC 16 40 mm PA 35-45 mm SMA - mm GuBasphalt

* Binder course: 80 - 120 mm Ac 22-32/PMB

* Base course: AC 22-32

Construction Bituminous materials

Regular design: Standard constructions RStO * 260 - 340 mm asphalt * 0 - 500 mm (un)bound aggregatlt * 250 - 550 mm Frostschutzschicht

Formation Level: Ev2 = 45 MN/m2

DK: Denmark

* Surface course: 35-40 mm GA 25-50 mm SMA 30-50 mm AC

* Binder course 70 - 100 mm AC 0/22 40- 85 mm AC 0/16

* Base course - AC 0/22 - 0/16

Construction Bituminous materials

Regular design: Individual design traffic load, frost susceptibility and subsoil bearing capacity.

Typical example HDP: * 290 mm asphalt (full depth)

NL: The Netherlands

* Surface course: based on

40 mm HRA 40 mm SMA

* Binder course: 1) AC( type 1 l for HRA AC( type 2) for SMA

* Base course: AC

Construction design Bituminous materials

Regular: Design charts (administration/DWW); Individual design based on traffic load. Note: full-depth design; equivalency factors for subbase materials.

Typical example HDP: * 280 mm asphalt * 250 mm (un)bound aggregate

Subbase: Eva = 100 MPa.

Special: individual design (Bisar/Moebius).

* Surface course: 50 mm PA

(incidentally: 40 mm AC)

* Binder course: 45 mm AC0/22 40 mm AC0/16

(with PA sometimes no binder)

* Base course: - AC 0/22

F: France

Construction design Bituminous materials

Regular: Design charts (administrations) Depending on bearing capacity formation level: a. Evz = 20 MPa: 460 mm asphalt; b. Evz = 50 MPa: 400 mm asphalt; c. Evz = 120 MPa: 360 mm asphalt. ·

When applying High Modulus asphalt: a. Ev2 = 20 MPa: 330 mm asphalt; b. Ev2 = 50 MPa: 280 mm asphalt; c. Evz = 120 MPa: 230 mm asphalt.

* Surface course:

80 mm AC 0/10 or 0/14 30-50 mm PA

*Binder course: (only with PA and ultra-thin AC - 20 mm) 50 mm AC

* Base course:

280-380 mm upper and lower base course AC 0/20 or 0/14 (Grave-bitume) 150-250 mm High Modulus AC 0/20 or

~~======================~========~==:.! · W14

Special: Scetauroute Thickness depends on bearing capacity of the subsoil.

a.·

b. Evz = 50 MPa: 370 mm asphalt c, Evz = 120 MPa: 330 mm asphalt

*Surface course: 70 mm AC 0/10 or 0/14

* Binder course (only with PA and ultra-thin AC):

50 mm AC

* Base course: Ev2 = 50 MPA: 300 mm AC (GB Ameliore) Ev2 = 120 MPa: 260 mm AC (GB Ameliore)

1} The first part of this table is for National Roads and the second part is for Motorways from Scetaroute. The dif­ferent thicknesses used are due to differences in the design life, 20 years for the former and 15 years for the latter, and differences in the rate of increase in traffic used, 7% and 4% respectively.

1: Ita ly

Construction design Bituminous materials

Regular: Individual design based on traffic load.

Typical example HOP: * 150 • 300 mm asphalt * 200 • 300 mm lean concrete * 200 • 300 mm unbound aggregate

Subbase; Evz > 35 MPa.

UK: United Kingdom

* Surface course: 40-50 mm PA 30-50 mm AC

* Binder course: 40-100 mm AC

* Base course: 70-150 mm AC 0/22

Construction design Bituminous materals.

Regular: Individual design based on design tables LR 1132 CCBR-principle)

Typical example HOP: *400 mm asphalt *225 mm subbase

*Surface course: 50 mm HRA

* Upper road base: 250 mm Heavy Duty Macadam

* Lo\(Ver road base: 125 mm HRA

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Summary

Asphalt Ev2 = 50 MPa EV2 = 120MPa

(Un)bound 0-500 agregates

Others FSS1

Formation >35 >45 Level: EV2, MN/m2

Materials Surface AC, PA, GA,

SMA SMA,AC

Binder/ AC AC Base

1 ): FSS: Frostschutzschicht 2): with High-Modulus Base 3): with GB Ameliore

400 28()2) 370')

>20- > 120

HRA, AC,PA SMA

AC AC')

4): for Binder Course only under PA and AC-Uitra Thin

360 230') 3303

)

Table II: Comparison of bituminous materials 1. Surface course

a. Asphaltic concrete

Indication Design Marshall Marshall method Marshall:

stability tracking Flow Quotient

Voids VFB 3-5

Grading >2mm 50-60 55-65 < 63pm 5-8 5-8

<2mm:Ratio crushed/ >1:1 >1:1 uncrushed

Binder -Type 865 865

Content (per 5.9-7.2 100%agg)

'): 100% crushed recommended.

200-300 250

> 35

AC,PA

AC

Gyratory Marshall Duriez Wheel-tracking Fatigue >9000 Stiffness 2-4

>2500

4-8 4-8

50-60

100% 100%

40/50 or 80/100 60/70 5.5-6.2

225

Marshall

> 7500 2-4 > 3000

2-6 <82%

60 7

3:1

80/100

6.0-6.4

b. Stone Mastic Asphalt

Parameter A D DK F NL

Indications 0/118 l 0/11 0/10 0/11

Design Recipe+ Recipe+ Gyratory, Recipe+ Duriez etc.

Voids 2-4 1.5-4 4-8 4.0 VMA >16 VFB 78-93

oC.

Grading 2)

>2mm 70-80 70-82 70-77,5 <63pm 6,5-10 4 9

<2mm: I crushed/ 1:1 100% >1:1 uncrushed

Binder: -Type B65 B60 80-100

·Content 6.5-7.5') 5.5-6.5 3) 7.0

per 100% aggregate) .

I I

1): > 6.8 recommended

2) : For surface course, only crushed aggregate is used and "rapport de concassage" (aggregate that has been crushed several times) is added, of a value of 1 to 4. For SMA this value is greater than, or equal to, 2.

3): For heavily trafficked pavements a modified binder is generally used.

c. Other types for surface courses

Type GuBasphalt Porous asphalt Hot Rolled

1 Parameter I D D F NL DK UK

Indication 0/11S 0/11 0/10 0/16 . 10. 18 HRA

Mix Design Indentation Recipe+ Gyratory, Recipe+ Marshall: Recipe + Marshall 1-3.5mm/30 voids: Duriez etc. voids: Stability stabilitY min 18-24o/o >·20% (>8000) ( > 8000)

Flow 5-7 Quotient>.; 1300

0' Voids 1-4 I

I VFB 80-93 -

Grading >2mm 45-55 80-90 70-90 85 25-50 30 <63um 15-25 3-4.5 4-6 4.5 6-12 8-12

<2mm: ratio crushed/uncrushed > 1:2 100% 100% 100%

crushed crushed crushed .,.._

Binder l Modified -Type B45 865/880 80/100 B60 40/60

-Content 6.5-8.0 1 5-5.5 4.5-5 1 4.5 6.5-7.5 0,,

'

1): < 0.09mm not< 63 ~m. ' ): 100% crushed recommended .

Marshall stab.> 7000

flow 2-4 Quotient > 3000

45/60

4.6-5.4

Voids< 7 VFB < 72

72 5

45/60

4.2-5.0

fl)

1: 3. Base course QJ

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Country A D OK F I NL UK

Indication AC 0/22 AC 0/22, Ac: GAB AC: GB0/20 AC 0/32 AC 0/22 DBM AC 0/32 AC 0/32 s 0/16 0/14 HOM

TypeCS AC Module eleve

i GB Ameliore

Design Marshall Marshall -Gyratory Marshall Recipe method -Duriez BS 4987

-Wheel tracking Marshall: -Fatigue

Stability >8000 > 7000 -Stiffness > 4000 >6000 Flow 1.5-5 1-4 2-4 1.5-3 Quotient GB: < 10o/o; > 1000 >3000

ME: < 4% 1) 2)

Voids 5-10 3-7 4-8 <7

VFB 60-80 50-68

Grading >2mm 60-80 60-75 60-8 57 BS 4987 <63pm 2.5-8 3-9 6

<2mm: >90% ratio crushed/ crushed uncrushed

Binder -Type 865/880 860 GB: 40/50 80/100 45/60 HOM: 50

ME: special; DBM: 100 ..Content > 3.6 GB: 3.6-4.7% 4.5 (per 100% ME: 5.8-6.6% aggregate

'): ME: Asphaltic concrete with high stiffness modulus. ' ):The values of 4% and 10% relate to ratios given by the wheel tracking test.

literature

1. "Heavy Duty Pavements; Status Report by the Technical Committee of the European

Asphalt Pavement Association"

EAPA Breukel~n 1991.

2. "Dynamic Loading of Pavements"

Report prepared by an OECD Scientific Group, Paris 1992.

3. "Effects of Tyre Pressures on Flexible Pavement Structures- A Literature Survey."

Directorate of Public Roads- Norwegian Road Research Laboratory Publication no. 62,

Oslo 1992.

4. "Laying Down Maximum Authorised Weights and Dimensions for Road Vehicles over

3.5 Tonnes- Circulating within the Community."

Commission of the European Communities, Proposed Council Directive, COM(93) 679 Final- SYN 486, Brussels, December 1993.

5. EC Council Directive 85/3 on "Weights, Dimensions and certain Technical

Characteristics of certain Road Vehicles".

6. "Shell Pavement Design Manual"

Shell International Petroleum Company, London 1978.

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Nabit/Road and Hydraulic Engineering Division of Rijkswaterstaat/VBW-Asfalt, Breukelen 1994.

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Sixth International Conference on the Structural Design of Asphalt Pavements,

Ann Arbor 1987.

9. "Asfalt en het Verbreden van Wegen" (Asphalt and Road Widening) (in Dutch).

Nabit/VBW-Asfalt, Breukelen 1992.

10. Gerritsen, A. H.; Van Gurp, C.A.P.M.; Vander Heide, J.P.J.; Molenaar, A.A.A.; Pronk,

A. C.: "Prediction and Prevention of Surface Cracking in Asphaltic Pavements".

Sixth International Conference on Structural Design of Asphalt Pavements,

Ann Arbor 1987.

11. De Wilde, J.G.S: "Dynamische Aslasten van (Zwaar) Verkeer op Plattelandswegen"

(Dynamic Axle Loadings of (Heavy) Traffic on Rural Roads) (In Dutch)

CROW-Publication 82, Part 1. CROW Ede, 1994.

.... 0 <ll

"'0 c ~

E Ql 0 Ql 1.1 c ~

E ... .;: ... Ql

Q. Ql

..c l-Oll c ·~ Ql

~ ....: ~ ..c c. <ll

<C

12. Stet, M.J.A.; van Harskamp, S.B.; Gerritse, E.: "Dynamische Aslastmetingen op

Provinciale Wegen in Noord-Brabant" (Dynamic Axle Load Measurements on

Provincial Roads in Noord-Brabant) (in Dutch).

CROW-Publication 82, Part 1. CROW Ede, 1994.

13. Henny, R.J.: "Aslastmetingen in TELNET" (Axle Load Measurements in TELNET) (in Dutch)

CROW-Publication 82 Part 1; CROW Ede, 1994.

14.Arand, W; "DAV Investigation on Heavy Trafficked Roads",

proceedings Asphaltstrassen Tagung 1995, Hildesheim (in German).

15. Eisenmann, J.: "Beanspruchung von bituminbsen Strassendecken unter besonderen Berucksichtigung des Zustandes Sommer" (Pavement lmposure in Specific Summer Conditions) (in German).

Strasse und Autobahn 5, 1979.

16. Hopman, P.C.: "Asfalt Mengsels en hun Ontwerp- Dee Ill" (Asphalt Mixtures and their Design - Part II) (in Dutch).

Report of the CROW-Working Group "Asfalttechnologie"; CROW Ede, 1992.

17. Ahrand, W; "Asphaltstrassen fur Schwerverkehr nach neuesten Erkentnisse" (New

Developments in Asphalt Roads for Heavy Duty Pavements) (in German); Strasse und

Autobahn 11/94.

18. Brosseaud, Y.: "Franco-English Comparative Study on Rutting Behaviour Determined by Laboratory Testing"

LCPC Nantes, 1994 (preliminary) .

19. Nunn, M.E. and Smith,T; "Evaluation of a Performance Specification in Road Construction"; TRL project report 55, 1994.

20. Von Quintus, H.L.; Scherocman, J.A.; Hughes, C.S.; Kennedy, T.W.: "Procedural

Manual for Mixture Design and AAMAS, Volume 1"

Brent Rauhut Engineering, Austin Texas 1990 .

21. Molenaar, A.A.A.; Don, W.M.W.; Mul, N.; Nata raj, N.: "Ontwerp van Polymeer

Gemodificeerde Asfaltmengsels voor de Luchthaven Schiphol" (Design of Polymer

Modified Asphalt Mixtures for Schiphol Airport) (in Dutch).

Proceedings "Wegbouwkundige Werkdagen 1994", CROW Publication 82-11, Ede 1994 .

22. Valkering, C. P.; Sapel, F. D. R.; Lijzenga, J.; "Shell Pavement Design Method on a

Personal Computer". Shell International Petroleum Company, London 1992.

23. Brossaud, Y.; Simoncelli, J.P.; Garoff, C.: "Investigation of Rutting of Asphalt Surface

Layers: Influence of Binder and of Configuration of Axle Loading"

Papers Transportation Research Board Meeting 1994.

24. "De invloed van het type polymeer op de weerstand tegen permanente vervorming"

(The Influence of the Type of Polymer on the Resistance to Permanent Deformation) (in Dutch).

Esso Belgium, Antwerp 1994.

25. Halfmann U. and Schuster F.O.; "Forschungsprogramm Strassenwesen in der

Bundesrepublik Deutschland" (German Road Research and Development Programme)

(in German); European Asphalt Magazine 4/94.

26.Anonymous; "Les techniques de modification des enrobes a chaud et leur applications" (Modifying Techniques for Hot Mix Asphalt and their Application) (in French);

Revue Generale des Routes et Aerodromes HS 1/92.

27. "Onderzoek naar de kruipeigenschappen van een aantal asfaltmengselvarianten"

(Investigation into the Creep Characteristics of a Number of Bituminous Mixture Alternatives) (in Dutch) . VBW-Asfalt, Breukelen 1993.

28. Von Becker, P.J.: "Impacts on the Roads and their Effects on Road Construction and

Road preservation Costs"

Proceedings Third International Symposium on Heavy Vehicle Weights and Dimensions. University of Cambridge, 1992.

29. Schmuck, A.; "Wirtschaftlichkeitsvergleich fuer unterschiedliche Bauweisen"

(Cost Effectiveness of Several Construction Methods) (in German) Proceedings

Eurasphalt 1992, The Hague, 1992.

30. Bowskill, G; verbal presentation on joint research at TRL by the Highways Agency

(UK Dept. of Transport), BACMI, and RBA, at ACMA Seminar November 1994.

" ... heavy duty asphalt pavements are already performing well."

EAPA. European Asphalt Pavement Association, P.O. Box 175, 3620 AD Breukelen, The Netherlands