TR 538Approved 2002-10

Published by Nordtest Phone: + 358 9 455 4600 Fax: + 358 9 455 4272Tekniikantie 12 E-mail: nordtest@nordtest.org Internet: www.nordtest.orgFIN02150 EspooFinland

SUPERPAVE TEST METHODS FOR ASPHALT

Leif BaklkkRandi SkoglundBjrn KalmanPetri Peltonen

Procedure for DSR testing

NT TECHN REPORT 538 Approved 2002-10

Authors: Leif Baklkk1 NORDTEST project number: 1535-01 Randi Skoglund1 Bjrn Kalman2 Petri Peltonen3

Institution: 1) SINTEF, Norway, 2) VTI, Sweden, 3) VTT, Finland

Title (English): -

Title (Original): Superpave test methods for asphalt - Procedure for DSR testing Abstract:

Between 1987 and 1993 in the U.S.A., the Strategic Highway Research Program (SHRP) surveyed all aspects of the physical tests currently carried out on bitumen, and it was shown that new performance-based methods, such as Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) and Pressure Ageing Vessel (PAV), are needed. The new bitumen specification developed in the SHRP was called the Superpave specification. The researchers showed that the normal physical tests, such as penetration or viscosity, did not give enough information concerning the behaviour of the road bitumens in actual road conditions. The purpose of the new methods (DSR, BBR and PAV) was to provide information on how the bitumens actually behave in practice. In the new Superpave binder specification, the most significant advancement on the European CEN standard specification was probably the move from empirical testing to advanced functional testing, where a bitumen can be characterized at a controlled rate and temperature in order to obtain the engineering properties of the binder. The new specification facilitates the purchase of superior quality bitumen. Consequently, the chosen bitumen performs adequately and does not cause pavement failure. The progress and suitability of the new testing methods, for European conditions, have been evaluated since the beginning of 2001 in the evaluation group organized by the CEN TC 336 working group WG1 for bitumens. From this evaluation, it was clear that the DSR and BBR methods in particular could also be adapted to European standards. At present, the Nordic countries are not quite as prepared as they should be for carrying out the Superpave tests. This is due to the recently adopted EN bitumen norm specification, which was based only on traditional test methods. The laboratories in the Nordic countries will probably adapt to the new methods and equipment when the CEN working group gains more experience with the new methods. Descriptions of the new methods DSR, BBR, DTT (Direct Tension Test) and PAV are included in this report. Because the DSR method was determined to be the main method for measuring the deformation characteristics of road surfaces in the future, this test has been evaluated in more detail. The description of the DSR method is structured as follows: scope and field of application, basic rheological background, device calibration, measurement by deformation or fatigue criteria, choosing the test temperature, making the specimens, and finally analyzing the performance grade (PG grade) of bitumen based on the Superpave specification. The test procedure used to measure the DSR values of the original bitumen and the PAV and RTFOT test-aged bitumens is presented. Some precision estimates are also shown. Suggestions for future work include a continuation of the evaluation of the methods within the CEN European evaluation group. Precision estimates of the DSR method must be backed up by results from similar/comparable studies. The new DSR method seems best suited to the testing of conventional bitumens. It has been difficult to operate DSR with polymer-modified bitumens (PmB). These testing problems with the PmB thus need further investigation. The details of the BBR and PAV tests should also be examined by a separate Nordtest research team in the future. Technical Group: Expert Group Building Materials and Construction

ISSN: 0283-7234 Language: English Pages: 39

Class (UDC): 625.85 Key words: Pavement, bitumen, asphalt, DSR, BBR, DTT, PAV, testing, methods

Publication code: Distributed by: NORDTEST Tekniikantie 12 FIN-02150 ESPOO Finland

Report Internet address: http://www.nordtest.org/register/techn/tlibrary/tec538.pdf

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PREFACE

Project

Nordtest project 1535-01 Funktionella testmetoder fr bituminsa bindemedel

Report title

SUPERPAVE TEST METHODS FOR ASPHALT Procedure for DSR testing Method proposal

Main procedure for DSR test. No final proposal.

Nordic project group

Asphalt experts from the Nordic asphalt testing laboratories participated in the project. The contri-butions of the following institutes and members to this Nordtest study are gratefully acknowledged.

Table 1 Experts of the project group.

Institute Member

SINTEF Civil and Environmental Engineering, Trondheim, Norway

Mr Leif Baklkk

SINTEF Civil and Environmental Engineering Mrs Randi Skoglund

SINTEF Civil and Environmental Engineering Mr Joralf Aurstad

VTI Swedish National Road and Transport Research Institute, Linkping, Sweden

Mr Bjrn Kalman (Secretary of project group)

VTT Building and Transport, Espoo, Finland Mr Petri Peltonen (Leader of project)

Furthermore, the project group express grateful thanks to the national laboratory personnel and na-tional members of the CEN bitumen working group in each country for their invaluable help with the project. This project was financed by Nordtest. The support of Nordtest is hereby gratefully ac-knowledged.

Espoo 18th of September, 2002

Petri Peltonen

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1 INTRODUCTION This Nordtest project involves the evaluation of the new functional test methods for bituminous binders, focussing on the testing procedure of the DSR (Dynamic Shear Rheometer) /1/. The aim was to review the present readiness of the laboratories in the Nordic countries to carry out the new functional procedures. Because the DSR method offers a good indication of rut formation of the road pavements in warm weather, the working group emphasized the importance of this method for the future. Consequently, the aim of the study was to provide more detailed information on the pro-cedure for the rather difficult DSR method, especially since this method has been carried out by SINTEF in Norway. This study will thus help the laboratories to qualify the importance of the method and to carry out the first measurements. The functional Superpave testing methods were originally developed during 19871993 in the U.S.A., as part of a large research programme named the Strategic Highway Research Program (SHRP). A description of the DSR method is published in the American AASHTO standard Desig-nation TP5-97: Standard Test Method for Determining the Rheological Properties of Asphalt Bind-ers Using a Dynamic Shear Rheometer (DSR) /1/. The grades of bituminous binders for asphaltic roads are tested by means of new functional testing procedures /2/, using the following equipment: - Dynamic Shear Rheometer (DSR). The purpose of this test is to determine the properties of bi-

tumen at high and intermediate temperatures. - Bending Beam Rheometer (BBR). This method determines the low-temperature properties. - Direct Tension Test (DTT). This method also determines the low-temperature properties. - Rolling Thin Film Oven Test (RTFOT). This method simulates the binder hardening during

mixing with the aggregate. - Pressure Ageing Vessel (PAV). This method accelerates long-term binder ageing. The current status of these Superpave methods in the Nordic countries, and their evaluation at the European level, have been shown in this report. The remarks made by the CEN TC 336 Working Group WG1: Bitumens concerning the utilisation of the functional methods for the European stan-dardization purpose have been noted.

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CONTENTS ABSTRACT...........................................................................................................................1 PREFACE..............................................................................................................................3 1. INTRODUCTION..............................................................................................................4 2. PRESENT STAGE OF PERFORMANCE-BASED TEST METHODS..............................6

2.1 Bitumen classification systems by physical test methods.......................................6 2.2 Purpose of new performance-based binder specification........................................7 2.3 Present evaluation of performance-based testing in Europe ...................................7 2.4 Progress in evaluation of high- and low-temperature and ageing properties of bitumen.................................................................................................................7 2.5 Preparation for performance-based testing in Nordic countries..............................8

3. PRESENTATION OF PERFORMANCE-BASED TEST METHODS ...............................8 3.1 Aim and background of performance-based testing ...............................................8 3.2 Descriptive Link between DSR, BBR, DTT and PAV ...........................................9 3.3 Description of the DSR test method ....................................................................10

3.3.1 Scope and field of application...............................................................10 3.3.2 Terminology, symbols and specific terms of the DSR test.....................12

4. PERFORMING THE DSR TEST IN THE LABORATORY ............................................13 4.1 Testing chart of DSR testing ...............................................................................13 4.2 Description of the Dynamic Shear Rheometer (DSR) ..........................................15 4.3 Calibration of the device .....................................................................................15 4.4 Temperature calibration ......................................................................................15 4.5 Calibration of the digital thermometer.................................................................15 4.6 Temperature setting ............................................................................................16 4.7 Gap setting..........................................................................................................19 4.8 Binder heating.....................................................................................................19 4.9 Making specimens ..............................................................................................19 4.10 Mounting test specimens ...................................................................................20 4.11 Test-specimen trimming....................................................................................20

5. MEASUREMENT BY THE DSR TEST..........................................................................22 5.1 Chart to measure the performance grade (PG) of bitumen ...................................22 5.2 Testing of the original binder ..............................................................................23 5.3 Testing of bitumen after the RTFOT ageing test..................................................23 5.4 Testing of bitumen after the PAV ageing test ......................................................23 5.5 Final verification of performance grade of bitumen.............................................24 5.6 Operating with strain-control mode .....................................................................24 5.7 Operating with stress-control mode .....................................................................24 5.8 Evaluation of precision and uncertainty of DSR test............................................25 5.9 Testing report......................................................................................................26

6. CONCLUSIONS AND WORK FOR THE FUTURE .......................................................27 7. REFERENCES.................................................................................................................28 8. APPENDICES..................................................................................................................29

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2 PRESENT STAGE OF PERFORMANCE-BASED TEST METHODS 2.1 BITUMEN CLASSIFICATION SYSTEMS BY PHYSICAL TEST METHODS The present classification of bitumens within CEN harmonized European standardization /3/ is based on the following physical testing methods: - Penetration EN 1426 - Softening point EN 1427 - Viscosity EN 12595 - Breaking point EN 12593 - Rolling Thin Film Oven Test EN 12607-1 - Flash point EN 22592 - Solubility EN 12592 Historically, road bitumens have been classified either based on the penetration grading system us-ing the standard ASTM D 946 or by the viscosity grading system in the standard ASTM D 3381 (AC-grading standard in the U.S.A.). Specifications for road bitumens in Europe have been based on the hardness classification by penetration values, while in the U.S.A., the bitumens are specified based on the AC grading system /4/. From October 1987 through to March 1993, the very large Strategic Highway Research Program (SHRP) in the U.S.A. looked at all aspects of highway engineering /5/. This programme predomi-nantly focused on the development of new methods of testing and specifying asphalt binders. The result of this research effort is a new US binder specification (Appendices 13) called Superpave (Superior Performing Pavements). The key characteristics of this new binder specification are: - The use of performance-based criteria for bituminous binders and asphalt concrete - The inclusion of climatic considerations in the utilisation of bitumen Three forms of distress are recognized in the new specification: - Non-load-related low-temperature cracking of bitumen during winter - Load-related long-term fatigue cracking of bitumen - Load-related high-temperature permanent deformation of bitumen during summer

2.2 PURPOSE OF NEW PERFORMANCE-BASED BINDER SPECIFICATION The test methods used in the current European specifications are empirical in nature and are not suited for the development of rational performance-based relationships between binder and mixture properties. The primary purpose of the new specification is to facilitate the purchase of a superior quality bitumen product. Thus, for the seller, the new specification will define the product that the buyer expects. The purpose of the new specification is not only to define the product but also to en-sure that the bitumen performs adequately and does not cause pavement failure. Obviously, the in-place performance is also influenced by the aggregate, mineral fines, air void content, etc. In the new Superpave binder specification, the most significant advancement is probably the move from empirical testing to advanced functional testing, where a bitumen can be characterized at a controlled rate and temperature in order to obtain the engineering properties of the binder. The Dy-namic Shear Rheometer (DSR), BBR and DTT methods (Appendix 3) will replace the normal vis-cosity, penetration and ductility tests, respectively. The Pressure Ageing Vessel (PAV) method has

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been introduced to simulate the long-term ageing of bitumen in all climatic regimes. The so-called Superpave performance graded (PG) bitumens are designed to resist deformation during the average 7-day highest pavement temperatures in summer and the lowest measured air temperature in winter. The new classification thus determines the quality of bitumen that can resist permanent deformation in summer and low-temperature cracking in winter.

2.3 PRESENT EVALUATION OF PERFORMANCE-BASED TESTING IN EUROPE The evaluation of the new functional methods for the road pavements in Europe is organized by CEN TC 336 WG1: Bitumens. In addition, the EAPA (European Asphalt Paving Association) has, since the beginning of 2001, had a separate co-ordinator involved in the adoption of the new meth-ods for the European bitumen markets. This evaluation work of CEN and EAPA has been followed up nationally by the national members. CEN TC336, WG1 was published the evaluation progress reports in 2001. The current status of the technical Nordtest report is based on these progress re-ports. In the evaluation of the new methods, the CEN task group divided the evaluation into three parts as follows: - High-temperature properties - Low-temperature properties - Binder ageing

2.4 PROGRESS IN EVALUATION OF HIGH- AND LOW-TEMPERATURE AND AGEING PROPERTIES OF BITUMEN The first conclusions of the recommendations for standardization are shown in a progress report, issued in June 2001 as follows. The recommended EN standard methods for bitumen are as follows: - Softening point EN 1427:1999 - Dynamic viscosity by vacuum capillary EN 12596:1999 Following complementary evaluation for bitumen, the recommended methods for EN standards are as follows: - Apparent viscosity - Complex modulus (DSR) - Zero shear viscosity (ZSV) by oscillation mode - Zero shear viscosity (ZSV) by creep mode Methods to be used as quality control methods in the future are as follows: - Softening point EN 1427:1999. This method is suitable for normal bitumen and for slightly modi-fied polymer-modified bitumens - Complex modulus for normal and polymer-modified bitumens - Dynamic viscosity by vacuum capillary for normal bitumens The following low-temperature methods (Appendix 3) are evaluated: - Bending Beam Rheometer Test (BBR) - Direct Tensile Test (DTT ) The following methods will remain part of the evaluation of the short-term ageing of bitumen: - Rolling Thin Film Oven Test (RTFOT ) - The PAV test for long-term evaluation is still to be examined before standardisation.

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2.5 PREPARATION FOR PERFORMANCE-BASED TESTING IN THE NORDIC COUNTRIES In the Nordic countries, SINTEF, Norway, and the major oil companies have experience in, and all the necessary equipment for, the new performance-based test methods introduced in the SHRP. In-stitutions that have some of the equipment include VTI, Sweden, (PAV, BBR, DSR); KTH, Swe-den, (PAV, BBR, DSR); Asfalt Industrien, Denmark, (DSR, BBR); Vejteknisk Institut, Denmark (DSR, PAV); Ramboll, Denmark (PAV); Fortum, Finland (DSR, BBR), Nyns, Sweden (PAV, DSR, BBR) and Vegdirektoratet, Norway (DSR, BBR).

The level of preparedness of the different laboratories in the Nordic countries to carry out the new performance-based classification is shown in Table 1. Table 1 Readiness of the Nordic countries for Superpave Performance-based bitumen testing in 2001.

Performance-based equipment in the Nordic coun-tries in 2001

Country

DSR BBR PAV

Denmark 2 1 2 Finland 1 1 0 Norway 2 2 1 Sweden 2 2 2

The introduction of the new methods has been slow due to the recently adopted EN specification for bitumen, which is based only on the traditional test methods. More of the SHRP methods are likely to be adopted in the forthcoming revisions of this specification. The adoption can only take place if more laboratories in Europe gain experience in the new methods.

3 PRESENTATION OF PERFORMANCE-BASED TEST METHODS 3.1 AIM AND BACKGROUND OF PERFORMANCE-BASED TESTING The SHRP (Strategic Highway Research Program) introduced a new type of asphalt binder specifi-cation called Superpave. One of the aims of the new specification is to focus on the local climatic conditions at the location where the binder is to be used. Another aim is to introduce test procedures that measure fundamental material properties, i.e. properties that can be related to the function of the binder in the pavement. In contrast, traditional bitumen specifications are based on test proce-dures (e.g. needle penetration and softening point) that do not give fundamental material properties as their results, although their values ultimately depend on the fundamental properties.

Three forms of binder-related distresses in asphalt concrete were recognised in the SHRP: rutting load-related permanent deformation, traffic-induced fatigue cracking, and low-temperature crack-ing. The fundamental material properties of binders related to these failure modes where identified, and test procedures to measure these were introduced

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3.2 DESCRIPTIVE LINK BETWEEN DSR, BBR, DTT AND PAV The performance grades (PG) in the Superpave binder specification are based on two temperatures Tmax and Tmin. The maximum 7-day average pavement temperature Tmax is estimated from air, re-corded in the vicinity of the road. At this temperature, the bitumen is tested for its rutting propen-sity, using the dynamic shear rheometer (DSR). Tmin is the lowest 1-day temperature recorded at the same weather station in winter. At 10 above Tmin, the binder is tested for its tendency to crack at low temperatures, using the bending beam rheometer (BBR) and the direct tension tester (DTT). At a certain temperature between these two temperature limits, the binder is also tested for its resis-tance to fatigue cracking, using the DSR. Thus the required performance grade for a binder to be used in a specific climate is designated as PG TmaxTmin. See Appendix 3 for Methods.

The properties of a binder change rapidly at elevated temperatures, e.g. during mixing in the pug-mill and during compaction. The binders also change gradually during a service life at much lower temperatures, mostly through oxidation. The Superpave binder specification uses two types of arti-ficial ageing equipment to simulate these two ageing phases. First, the Rolling Thin Film Oven Test (RTFOT) at 163C for 85 min is used to simulate the short-term ageing of the binder. Secondly, a Pressure Ageing Vessel (PAV) operated at 90110C (the temperature depends on Tmax) and 21 atm for 20 h is used to age the binder in conditions that should simulate 10 years of ageing in the field.

As binders get older, they become more stiff and brittle. Thus rutting is a more significant problem at the beginning of the service life of a pavement, and the low-temperature cracking and fatigue failure are more serious problems towards the end of the service life of a pavement. Accordingly, the DSR test to evaluate binder resistance to rutting is conducted on original binder and on binder aged in RTFOT, while binder resistance to low-temperature cracking is tested using the BBR and the DTT on binder treated in the RTFOT and the PAV. The ability of the bitumen to resist fatigue cracking (with the DSR test for fatigue) is also tested after the binder has been treated in the RTFOT plus the PAV.

The RTFOT already constitutes part of the present European standard for the specification of road bitumen and will not be discussed further. The DSR test methods will be treated in Parts 3 and 4. A brief description of the principles and operation of the PAV, the BBR test and the DTT will be given below.

It is generally accepted that bitumen hardening in the field is mostly due to oxidation. It has also been recognised that the reactions taking place in bitumen exposed to the air at low and high tem-peratures are different. A pressurised vessel operating at medium temperatures was chosen for the Superpave specification in order to have a reasonably fast laboratory method for artificial ageing. The air pressure in the vessel should be 2070 kPa (21 atm) and the temperature should be between 90 and 110C. Fifty grams of the binder, previously aged in the RTFOT, are placed on a preheated standard TFOT steel pan and placed in the cell. When the temperature has reached its target value in the cell, the vessel is pressurised. The sample is aged for 20 h in the vessel and this should be com-parable to 810 years ageing in service.

A binder should be soft and able to quickly relax during strain at low temperatures in order to resist cracking when the temperature falls in asphalt concrete. With the BBR test, a beam of the bitumen (previously aged in the RTFOT and PAV) is mounted on two supports and subjected to a constant load on the centre. The deflection of the beam is monitored for 4 min from the dimension of the beam. The observed deflection and the creep stiffness are calculated as functions of time. The creep stiffness is inversely proportional to the deflection. The creep rate (m) is defined as the slope of a Log (stiffness) vs. Log (time) curve. The test is performed at 10 above Tmin. In the Superpave

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specification, the stiffness should not exceed 300 MPa after 60 s and the creep rate should be at least 0.30 at 60 s. The stiffness of the binder after 60 s at Tmin + 10C is comparable to the stiffness of the binder after 2 h at Tmin, if the binder is in the linear viscoelastic region. See Appendix 3.

Polymer modification of bitumen can have a considerable effect on its low-temperature cracking tendency, without greatly affecting other rheological properties. A polymer-modified bitumen could be considerably less ductile at low temperatures than a non-modified bitumen with the same stiff-ness. For this reason, the DTT has been included in the Superpave specification. In the DTT, a dog-bone-shaped specimen is loaded in tension until failure. If the stiffness measured with the BBR is between 300 and 600 MPa after 60 s at Tmin + 10C, and the creep rate is at least 0.30, the binder could still belong to the performance grade if the maximum elongation before failure (failure strain) exceeds 1 % in the DTT performed at Tmin + 10C. The logic behind this practice is that materials with failure strains of less than 1 % are brittle and are not likely to withstand temperature-induced strain and vice versa.

3.3 DESCRIPTION OF THE DSR TEST METHOD

3.3.1 Scope and field of application With the fundamental material parameters obtained with the DSR tests, good empirical correlations could be established between the rutting properties of the bitumen and its ability to withstand fa-tigue.

Before discussing the DSR tests and the correlations just mentioned, the reader is advised to read Section 3.3.2, which contains a short description of basic rheology and specific terms.

When testing bitumen with the DSR tester according to the Superpave specification (Appendices 13), the sample is sandwiched between a fixed-base plate and an oscillating spindle plate.

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Figure 1. DSR apparatus.

The stressstrain pattern is recorded. The angular frequency, which is varied in many other types of test, is fixed at 10 rad s-1 in the Superpave specification, which can be attributed to the loading time within a pavement where vehicles travel at 80 km/h. Moreover, it is specified that the test should be carried out in the linear viscoelastic region where the size of the complex modulus is independent of the strain level. This can be checked by measuring the complex modulus at several maximum shear stresses or maximum strain levels. An empirical equation reported in the test section could be used to find an optimum strain level for ordinary bitumen (see equation in Section 5.6)

When the complex modulus (size and lag phase), as a function of temperature for the original bitu-men, for bitumen treated with RTFOT, and in the intermediate pavement design temperature after treatment in the PAV test, is measured, some of the criteria that determine the performance grade can be established.

Within the SHRP, the rutting of asphalt concrete measured in wheel-tracking tests was highly corre-lated to ( )G sin of the binder. Thus, bitumens with a high complex modulus and a high degree of elasticity produced pavements with a low tendency for (binder-induced) rutting. The Superpave specification states that, at the maximum pavement design temperature, the ( )G sin value should be at least 2.2 kPa in order for RTFOT-aged bitumen to resist rutting. The limit value for original bitumen is 1.0 kPa.

Another parameter of the binder was shown to be relevant for traffic-induced fatigue cracking. It was observed that above a limit in the value of ( )G sin (the product between the complex modulus and sine of the phase lag) for the binder, there was a high tendency for fatigue cracks to occur during laboratory tests. Thus, bitumens with a low complex modulus, and exhibiting fluid-

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like characteristics (low elasticity), resulted in asphalt concrete with a low tendency for fatigue cracking. The Superpave specification states that ( )G sin for the binder should be less than 5000 kPa at intermediate pavement design temperatures after ageing in PAV.

3.3.2 Terminology, symbols and specific terms of the DSR test Some basic rheology has to be understood in order to appreciate the DSR tests. Therefore, some of the terminology used in rheology will be provided as a service to the reader.

An ideal elastic body obeys Hookes Law, which states that the applied (shear) stress, , and the resulting shear strain, , are related by a unique (elastic) modulus E

= E (1)

Shear strain (dimensionless) is defined as the displacement of a sheared surface relative to a refer-ence surface, divided by the distance between the two surfaces. Shear stress is the force exerted on the body (in the shear plane) divided by the area (unit: Pa).

For an ideal elastic body, deformation is instantaneous and time-independent. It is also totally re-coverable when the stress is removed, in contrast to a completely viscous fluid, the deformation of which is linear in time for a given stress, , and completely irrecoverable. For a Newtonian fluid, the applied (shear) stress and the resulting shear strain rate d d t is related to the viscosity, , of the fluid:

= ddt

(2)

A typical bitumen has both a viscous and elastic character below 50C, i.e. it exhibits viscoelastic behaviour. A simple model gives the strain rate for a viscoelastic material where Hookes Law and Newtons Law are linked:

dd

dd

t E t= +

1 (3)

Without any elastic component or viscous component, Newtons and Hookes Laws, respectively, are recovered.

Applying stress to a viscoelastic system will deform the system (due to its fluid-like character), but on removal of the stress, the system will partly recover (due to its elastic character). On the other hand, if the material is instead subjected to an oscillatory stress and the corresponding strain is monitored and analysed, the effect of the time dependence in a viscoelastic material could be ob-served in the lag phase between the stress and the strain. For instance, suppose a sinusoidal stress is imposed on bitumen with an angular frequency and a stress amplitude of 0 :

( ) ( ) t t= 0 sin (4) The resulting strain will also be sinusoidal, but will lag the stress by some amount of time:

( ) ( ) t t= +0 sin (5)

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where 0 is the strain amplitude. For an elastic material (at any frequency), the stress and strain maxima are in phase angle = 0 , i.e. they occur at the same time. For a viscous liquid, the strain maximum (deformation) lags the stress maximum by a phase difference of 2 . Thus, the phase angle changes reflect the time dependence of the viscoelastic properties of the material. There-fore, no single parameter can be used to characterise the stressstrain relationship in bitumen at ser-vice temperatures. The complex dynamic modulus G is resolved into two components using the complex notations G G iG = + . The real part, G , of the complex modulus describes stressstrain relationships that are in phase and is called the storage (or elastic) modulus. The imaginary component G characterises the out-of-phase component and is called the loss (or vis-cous) modulus. The absolute value of the complex modulus G is calculated from the ratio be-tween the maximum stress and the maximum strain.

G =

0

0 (6)

and the balance between the storage and loss modulus is described by the phase angle:

( )tan = G G (7)

4 PERFORMING THE DSR TEST IN THE LABORATORY 4.1 TESTING FLOW CHART OF DSR TESTING This method describes the practical way in which to perform DSR measurement according to AASHTO standard TP5-97 /1/. A flow chart of the processes involved in DSR measurement is shown in Figure 2.

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Test specimen trimming

Mounting test specimen

Temperature setting

Making specimens Gap-setting

Binder heating

Measurement

Original binderG*/sin =1,00 kPa

RTFOT-residueG*/sin = 2,20 kPa

Decrease temp.-6 oC

Increase temp.+6 oC

FAILED PASSED

Deformation criteria

PAV-residueG*sin =5000 kPa

Increase temp.+3 oC

Decrease temp.-3 oC

FAILED PASSED

Fatigue criteria

Figure 2. Flow chart for DSR-measurement.

DSR

Temperature calibrationDevice calibration

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4.2 DESCRIPTION OF A DYNAMIC SHEAR RHEOMETER (DSR) There are two general types of dynamic shear rheometers: controlled strain and controlled stress. Data obtained from the two types of rheometers are interchangeable. Controlled-strain rheometers operate by applying a sinusoidally varying strain to the test specimen and measuring the magnitude phase of the resulting stress. A controlled-stress rheometer applies a sinusoidally varying stress and measures the magnitude phase of the resulting strain.

Both controlled-strain and controlled-stress rheometers consist of three major parts: (1) the rheome-ter, (2) the controller, and (3) the computer. The rheometer normally includes a housing frame, a motor for applying the strain or stress to the specimen, a transducer for measuring the response of the specimen, and a temperature control and measurement system. The controller is simply an inter-face between the rheometer and the computer, and contains the data acquisition and signal condi-tioning hardware for the motors and transducers used in the rheometer. The rheometer is operated and programmed by the computer. Instrument-specific hardware and software are included with the computer for performing tests and analysing the resulting data /6, 7/.

4.3 CALIBRATION OF THE DEVICE There are three transducers in a typical dynamic shear rheometer (Figure 1) that must be calibrated on a regular basis: (1) the torque measurement transducer, (2) the deflection measurement trans-ducer, and (3) the platinum resistance thermometer (PRT). This calibration has to be performed by the manufacturers. The operator can check the instrument by performing measurements on a viscos-ity standard. A viscosity standard is a calibrated fluid with a particular viscosity at certain tempera-tures.

4.4 TEMPERATURE CALIBRATION The rheological properties of asphalt binders are strongly dependent on temperature. For example, a change in temperature of 1C can result in a modulus change of up to 25% for some asphalt binders /6/. The equipment may not be accurately calibrated, so a temperature calibration is needed.

4.5 CALIBRATION OF THE DIGITAL THERMOMETER The temperature within the binder specimen is significant. A dummy silicone specimen and a digi-tal thermometer could be used to predict this temperature. The calibration of the digital thermome-ter is done using ASTM thermometers (or any other certified thermometer) and a stirred water bath.

Prepare a partial immersion mercury-in-glass thermometer with an appropriate range (ASTM 90 C; 030C, ASTM 91C; 2050C). Fasten the detector to the mercury-in-glass ASTM thermometer with a rubber band or rubber O-ring. Place the ASTM thermometer with the detector into the stirred water bath, Figure 3. The heating unit is adjusted until the ASTM thermometer shows the specified temperature. When the temperature is constant within 0.1C, the temperature of the digital ther-mometer is registered. Table 3 shows an example of a calibration form. The calibration should be performed at least once a year.

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Calibrated ASTM-thermometer

63,8C

Water,64,0C

Stirringheating unit

Figure 3. Calibration of a digital thermometer /8,9/.

Table 3. Calibration of a digital thermometer.

ASTM temperature, C Thermometer Read off temperature digi-tal thermometer, C

46.0 52.0 58.0 64.0 70.0

ASTM 91C ASTM 65C ASTM 65C ASTM 65C ASTM 65C

45.7 51.7 57.8 63.8 69.9

4.6 TEMPERATURE SETTING Before testing, the DSR software has to be checked at all temperatures at which the measurements are to be performed. Figure 4 shows how you can choose testing temperatures. Note that these are the temperatures that should be obtained within the bitumen sample. The actual setting on the DSR software may therefore be somewhat different.

Calibrated ASTM-thermometer

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Test temperatures

PG Grading PG Verification

Original binder RTFO Residue PAV Residue Original binder RTFO Residue PAV Residue

Perform measurements at test temperaturesindicated by the grading designation. Appendix 2.

Confirm the hightemperature grade

of the binder.

Known binder

BinderB40B60B85

B120B180B250B370PMB

Start temp, C7064

58-6458524646

above 64

Unknown binder58C

High PG-temp5258644

Start temp16192228

Figure 4. How to choose testing temperatures in PG grading and PG verification.

18

Silicone rubber wafer

Temperature sensorInlet

Outlet

Inlet

Outlet

63,8 oC

Figure 5. Measurement of the in-sample temperature /5/.

Figure 5 illustrates how to measure the in-sample temperature and hence the setting of the DSR software test temperature. In order to maintain a constant temperature, a circulating bath unit sepa-rated from the DSR pumps water into the DSR chamber, is used. A silicone wafer containing a temperature detector calibrated to the nearest 0.1C is inserted between the plates as the dummy specimen. The setting temperature in the DSR software is adjusted until the digital thermometer shows the temperature corresponding to the correct ASTM temperature.

Table 4 shows an example of a calibrating form.

Table 4. Example of how to check the DSR software setting temperature.

DSR software, setting temperature, C

Read off temperature digi-tal thermometer, C ASTM temperature, C

52.7 58.8 64.8 70.9

51.7 57.8 63.8 69.9

52.0 58.0 64.0 70.0

19

4.7 GAP SETTING The height of the sample is adjusted by gap setting. The gap has to be set at the test temperature in order to get the correct sample height, because a change in temperature will cause different changes in the dimensions of different parts of the rheometer.

A temperature change of 12C from the temperature at which the gap was set is tolerated without a new gap setting.

Most DSR devices on the markets today have an automatically functioning gap setting.

4.8 BINDER HEATING Table 5 shows the recommended heating temperatures for different original asphalt binders /8/. RTFOT and PAV residues may need a higher temperature. Modified binders with a high polymer content need a higher temperature than modified binders with a lower polymer content. The heating time should be as short as possible.

Table 5 Recommended temperatures when heating original asphalt binders /8/.

Bitumen Temperature, C

Polymer-modified bitumen Bitumen < 100 pen Bitumen 100430 pen

150170 130150 115130

4.9 MAKING SPECIMENS Parallel plate geometry should be used for specification testing. The specific plate diameter and specimen thickness (plate gap) used depend upon the temperature and the modulus of the binder, as shown in Table 6.

Table 6 Approximate temperature and modulus ranges for geometry used in dynamic mechanical analysis of asphalt binder /9, 10/.

Geometry Typical

Temperature Range, C

Typical Modulus (G*) Range,

Pa Parallel plates, 8 mm diameter Parallel plates, 25 mm diameter

040 >40

105107

20

Specimen with a diameter of 25 mm Cut plastic film into appropriate pieces. Pour approximately 0.7 g asphalt binder onto the plastic film; this is 4050% more binder than is needed for a 25-mm diameter, 1-mm high sample.

Specimen with a diameter of 8 mm Pour the hot asphalt binder into a preheated silicone rubber mould that will form a pellet with a di-ameter approximately equal to the diameter of the spindle and a height approximately equal to 1.5 times the width of the test gap. Put the silicone rubber mould, with the asphalt binder, in the oven for approximately 2 min. Allow the silicone rubber mould to cool to room temperature (approxi-mately 30 min). Use a heated knife or spatula to remove excess binder.

4.10 MOUNTING TEST SPECIMENS The filled mould may be chilled in a freezer to facilitate remoulding of softer grades of bituminous binders. Chill the mould in the freezer for only the minimum time needed to facilitate the remould-ing of the specimen.

Specimen with a diameter of 25 mm Centre the specimen on the spindle, as shown in Figure 6a. Place the spindle with the specimen and its plastic film in a freezer for a few seconds to remove the plastic film. Heat the specimen in an oven for a few seconds to melt the surface of the specimen, and then mount it into the DSR. The specimen should have a surface such as that shown in Figure 6b. If the specimen is overheated, the surface will bulge, as shown in Figure 6c. A surface such as that shown in 6c may trap air between the sample and lower plate when the sample is mounted in the rheometer. This will lead to incorrect results.

a b c

Figure 6. Mounting test specimens with a diameter of 25 mm.

Specimen with a diameter of 8 mm Remove the specimen from the mould and centre the asphalt binder on the spindle; then mount the spindle in the DSR.

4.11 TEST SPECIMEN TRIMMING Excessive material or untrimmed material can result in considerable errors in the measurements. Both under- and overtrimming are to be avoided. After the specimen has been trimmed and the gap has been closed to the target value, there should be a slight bulging at the periphery of the sample. A concave surface at the periphery of the sample is to be avoided, as it has a significant effect on the measured value of the shear modulus. To reiterate, if trimming is not done properly, there may be considerable errors in the measurements. /10, 11/

21

Trimming the size of the test specimen is done after the spindle with the specimen has been mounted in the DSR. Move the test plates together until the gap between the plates equals the test-ing gap plus 50 m (Figure 7).

The specimen before trimmingh = gap+50 m

Figure 7. Test specimen mounted in the DSR, before trimming.

Trim the specimen by moving a heated trimming tool around the upper and lower plate perimeters while trimming the excess asphalt. The tool may be heated on a hot plate or with a flame. Figure 8 illustrates convenient trimming tools.

Figure 8. Trimming tools. When trimming is complete (Figure 9a), decrease the gap by 50 m to the desired testing gap. This will cause a slight bulging of the asphalt binder at the periphery of the test specimen (Figure 9b).

22

Asphalt binder trimmed flushwith sides of plateh = gap+ 50 m

a

Slight bulge in asphalt binderafter closing gap by 50 m

h = desired gap, m

b

Figure 9. Test specimen after trimming: a. before decreasing the gap by 50 m; b. after decreasing the gap.

Now the testing can start as soon as the specimen has been tempered for 5 min after the correct test-ing temperature has been reached.

5 MEASUREMENT BY THE DSR TEST

5.1 CHART TO MEASURE THE PERFORMANCE GRADE (PG) OF BITUMEN Figure 10 shows the deformation and fatigue criteria involved in performance grading an asphalt binder. It also indicates the temperature increment when the measurement fails or passes.

Deformation Criteria

Original binderG*/sin = 1,00 kPa

RTFOT-residueG*/sin = 2,20 kPa

Decrease temp.-6 oC

Increase temp.+6 oC

FAILED PASSED

Increase temp.+3 oC

Decrease temp.-3 oC

PAV-residueG*sin = 5000

kPa

Fatigue Criteria

FAILED PASSED

Figure 10. Test criteria in performance grading.

23

5.2 TESTING OF THE ORIGINAL BINDER When performance grading the original bitumen, choose starting temperatures as shown in Figure 4 and Table 7. Perform testing at different temperatures, increase or decrease the test temperature in 6C increments, until the deformation criterion G*/sin 1.00 kPa has both passed and failed (Fig-ure 10).

Table 7 contains suggestions for starting temperatures with different bitumens.

Table 7 Possible starting temperature in performance grading (Tmax).

Binder Starting test temperature performance grading,

C B40 B60 B85 B120 B180 B250 B370

70 64

5864 58 52 46 46

PmB above 64

If G*/sin is higher than 1.00 kPa at 58C and lower than 1.00 kPa at 64C, the starting binder grade is PG 58-. But if G*/sin is higher than 1.00 kPa at 70C and lower than 1.00 kPa at 76C, the start-ing binder grade is PG 70-.

5.3 TESTING OF BITUMEN AFTER THE RTFOT AGEING TEST Perform the DSR test on the RTFOT residue to confirm the high-temperature grade (PG 52-, PG 58-, PG 64-, etc.). Start at the temperature that determined the starting PG on the origi-nal binder and perform testing at different temperatures, increase or decrease the test temperature in 6C increments, until the deformation criterion G*/sin 2.20 kPa has both passed and failed (Fig-ure 9).

Choose the lower performance grade in cases where the measurement gives conflicting grades for the original binder and RTFOT residue.

5.4 TESTING OF BITUMEN AFTER THE PAV AGEING TEST Figure 4 and Table 8 offer suggestions for potential starting temperatures for performance grading on the PAV residue. Perform testing at different temperatures, increase or decrease the test tempera-ture at 3C increments until the fatigue criterion G*/sin 5000 kPa has both passed and failed (Figure 10).

24

Table 8 Possible starting temperatures for performance grading of the PAV residue.

High-temperature grade

Start testing temperature, C

PG 52- PG 58- PG 64- PG 70-

16 19 22 28

5.5 FINAL VERIFICATION OF THE PERFORMANCE GRADE OF BITUMEN Perform the DSR measurements at the test temperature indicated by the Performance grade asphalt binder specification (Appendices 13). For example, a PG 70-16 should meet the deformation cri-teria at 70C for both original binder and RTFOT residue, and the fatigue criteria should be met at 31C.

If the binder fails to meet the specification for the grade that it has been designated, it may be treated as a binder of unknown grade and tested accordingly.

5.6 OPERATING WITH STRAIN CONTROL MODE To select a strain value to begin with, chose an appropriate strain level from Table 9. The measure-ment has to be in the region of linear behaviour (Appendix 1). When the strain is within 20% of the target value calculated by Equation 8, the measurement is in the linear region.

= 12.0/(G*)0.29 (8)

where = shear strain in percent and G* = complex modulus in kPa

Table 9 Target Strain Values.

Strain, % Material kPa Target Level Range

Original bitumen RTFO Residue PAV Residue

1.0 G*/sin 2.2 G*/sin 5000 G* sin

12 10 1

915 812

0.81.2

5.7 OPERATING WITH STRESS CONTROL MODE To select a stress value to begin with, chose an appropriate stress level from Table 10. The meas-urement has to be in the region of linear behaviour (Appendix 1). When the stress is within 20% of the target value calculated by Equation 9, the measurement is in the linear region.

= 0.12(G*)0.71 (9)

25

where = shear stress in kPa and G* = measured complex modulus in kPa

Table 10 Target Stress Values.

Stress, kPa Material kPa Target Level Range

Original binder RTFO Residue PAV Residue

1.0 G*/sin 2.2 G*/sin 5000 G* sin

0.12 0.22 50

0.090.15 0.180.26

4060

5.8 EVALUATION OF PRECISION AND UNCERTAINTY OF THE DSR TEST The criteria for judging the acceptability of dynamic shear results obtained by this method accord-ing to /1, Appendix 3/ are given in Table 11. The figures in column 2 of Table 11 are the coeffi-cients of variation that have been found to be appropriate for the conditions of the test described in column 1.

Table 11 Precision estimates /1/.

Condition Coefficient of Variation (1s %)1

Acceptable Range of Two Test Results (d2s %)1

Single-Operator Precision: Original bitumen: G*/sin (kPa) RTFO/TFO Residue G*/sin (kPa)

PAV Residue: G*sin (kPa)

3.4 3.9 7.9

9.5 11.0 22.4

Multilaboratory Precision: Original bitumen: G*/sin (kPa) RTFO/TFO Residue G*/sin (kPa)

PAV Residue: G*sin (kPa)

10.3 11.1 19.8

29.1 31.3 56.1

1 These values represent the 1s % and d2s % limits described in ASTM

Practice C 670

The results from the Rilem Round Robin Test on Binder Rheology where as follows:

Repeatability standard deviation after RTFOT (three repetitions)

- For G* between 40 and 76C: 15% - For G* between 10 and 40C: 2025% - For the phase angle between 40 and 76C: 3% - For the phase angle between 10 and 40C: 5%

26

5.9 TESTING REPORT The test report should consist of a description of the bitumen and the rheometer, test plate diameter, testing frequency, testing amplitude or torque, and the results obtained as follows:

Sample:

Rheometer:

Date/Signature:

Table 11 Results.

Instrument settings Measured values

Temp.

Plate diam.

Freq.

Stress (Constant stress rheometer)

Strain (Constant strain rheometer)

G* kPa , , %

G*/sin kPa

G*sinkPa

27

6 CONCLUSIONS AND WORK FOR THE FUTURE CEN is working towards the new functional bitumen standards. Method descriptions of DSR, BBR and PAV are under preparation. The framework for the new bitumen specifications in CEN has not yet been completed. The Superpave standard (AASHTO MP1) is not directly suitable for the Euro-pean markets because it is specified for one asphalt pavement concrete and does not include the polymer-modified bitumen. The studies referred to in this report also showed that the DSR test is better suited for conventional bitumen than for polymer-modified bitumen.

The procedure for the new DSR test, assessed in this report, also showed that the DSR method con-tains very many difficult details that must be carefully considered in order to obtain reproducible results. Due to the rather limited usage of the DSR method in the Nordic laboratories, it was not possible to obtain the final method description for inclusion in this report, as it belongs to CEN.

The traditional methods, such as conventional capillary viscosity or softening point methods are easier to carry out. Tests by Superpave are still rather expensive and details must be clarified. More experience must also be gained from the other new tests. These tests are the BBR test for the low-temperature characteristics of bitumens, and the two types of ageing tests: the RTFOT for the short-term, and the PAV test for the long-term ageing measurements of bitumens.

The contents of the BBR and the ageing tests, such as the PAV test, were only briefly mentioned in this report. Because these tests are very important for the low-temperature Nordic countries, they should be researched in more detail by the Nordic bitumen laboratories.

28

7 REFERENCES /1/ AASHTO Designation TP5-97. Standard Test Method for Determining the Rheological Proper-ties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR).

/2 / Warren, R.S., McGennis, R.B. and Bhia, H.U. Superpave Asphalt Binder Test Methods. An il-lustrated Overview. Asphalt Institute. Federal Highway Administration Washington D.C. U.S.A. 1993. Final Report N. FHWA-SA-94-068. July 1994. 140 p.

/3 / European Standard EN 12591 Bitumen and bituminous binders Specification for paving grade bitumens. Nov. 1999. 17 pp.

/4/ Bouldin, M.G., Dongre, R.N., Rowe, G.M. and Zanzotto, L. The future of performance related binder specification. www.asphalt-technology.com 14 pp.

/5/ Read, J.M. The SHRP and Superpave binder tests and specification. Shell Bitumen UK 2000. 0120. 7 pp.

/6/ AASHTO Designation PP6-94. Standard Practice for Grading or Verifying the Performance Grade of an Asphalt Binder.

/7/ Standard Test Method of ASTM E220.

/8/ Statens vegvesen Veglaboratoriet: Laboratorieunderskelser, Hndbok 014.

/9/ Andersen, Eivind O. Ny Asfaltteknologi Utprving av SHRP-utstyr og mlemetoder for bin-demidler, SINTEF-rapport A96503 August 1996.

/10/ Strategic Highway Research Program, Binder Characterization and Evaluation, Volume 3: Physical Characterization, SHRP-A-369.

/11/ Strategic Highway Research Program, Binder Characterization and Evaluation, Volume 4: Test Methods, SHRP-A-370.

/12/ Kett, I. Asphalt Materials and Mix Design Manual. Noyes Publications, Westwood New Jersey, U.S.A. 1998. pp. 170179.

29

8 APPENDICES Appendix 1: Model pages of SINTEFs control and grading report tables of bitumen.

Appendix 2: Performance Grade Asphalt Binder Superpave Specifications.

Appendix 3: Schematic pictures of the Superpave methods /12/.

30

APPENDIX 1.1 Control of Superpave Performance Grade

Sample: Journal no:

Project no:

Standard:

Date/Signature

Control of PG PMCC Flash point, C Are the specifications met Viscosity Brookfield at 135C, Pa s Mass loss after RTFOT, %

DSR_Original DSR_RTFOT Test

Temp., oC

Plate diam., mm

G*, kPa

Phase angle , o

Strain %

G*/sin, kPa

Test Temp.

, oC

Plate diam., mm

G*, kPa

Phase angle , o

Strain %

G*/sin, kPa

DSR_PAV BBR_PAV DT_PAV Test

Temp., oC

Plate diam., mm

G*, kPa

Phase angle , o

Strain %

G*sin, kPa

Test Temp.

, oC

S(60), MPa m(60)

Test Temp.

, oC

Failure Strain

%

Failure Stress Pa

* *

* Physical Hardening, 24 h conditioning DSR Original: Tmax, G*/sin at Tmax requirement G*/sin > 1.0 kPa DSR RTFOT: Tmax, G*/sin at Tmax requirement G*/sin > 2.2 kPa DSR PAV: Tint, G*sin at Tint requirement G*sin < 5000 kPa BBR PAV: Tmin, S(60) at Tmin requirement S(60) < 300 MPa

m(60) at Tmin requirement m(60) > 0.300 DT PAV: Tmin, f at Tmin requirement f > 1.0%

31

APPENDIX 1.2 Superpave Grading

Determination of Performance Grade Sample: Journal no:

Project no:

Standard:

Date/Signature

PMCC Flash Point, C Limiting Temperature Tmax, C

Viscosity Brookfield at 135C, Pa s Limiting Temperature Tint, C

Mass Loss after RTFOT, % Limiting Temperature Tmin, C

Grading

DSR_Original DSR_RTFOT

Test

Temp., oC

Plate

Diam,

mm

G*, kPa

Phase

angle , o

Strain % G*/sin, kP

a

Test

Temp., oC

Plate

Diam,

mm

G*, kPa

Phase

angle , o

Strain % G*/sin, kP

a

DSR_PAV BBR_PAV DT_PAV

Test

Temp., oC

Plate

Diam,

mm

G*, kPa

Phase

angle , o

Strain % G*sin, kP

a

Test

Temp., oC

S(60),

MPa m(60)

Test

Temp., oC

Failure

Strain %

Failure

Stress

Pa

*

*

* Physical Hardening, 24 h conditioning

DSR Original: Tmax, Temperature at which G*/sin = 1.0 kPa DSR RTFOT: Tmax, Temperature at which G*/sin = 2.2 kPa DSR PAV: Tint, Temperature at which G*sin = 5000 kPa BBR PAV: Tmin, Temperature at which S(60) = 300 MPa

Temperature at which m(60) = 0.300

DT PAV: Tmin, Temperature at which f = 1.0%

32

Table SHR

P Performance G

raded Asphalt B

inder Specifications A

PPEN

DIX

2 (3 PAG

ES)

PG 46-

PG 52-

PG 58-

PG 64-

PERFO

RM

AN

CE G

RA

DE

34 40

46 10

16 22

28 34

40 46

16 22

28 34

40 10

16 22

28 34

40

Average 7-day M

aximum

Pavement

Design Tem

perature, C a < 46

< 52 < 58

< 64

Minim

um

Pavement

Design

Tem-

perature, C a

>-34 >-40

>-46 > -10

> -16 > -22

> -28 > -34

> -40 > -46

> -16 > -22

> -28 > -34

> -40 > -10

> -16 > -22

> -28 > -34

> -40

OR

IGIN

AL B

IND

ER

Flash Point Temp, T48: M

inimum

C 230

Viscosity, A

STM D

4402: b

Maxim

um, 3 Pas, Test Tem

p, C

135

Dynam

ic Shear, TP5: c

G*/sin , M

inimum

, 1.00 kPa

Test Temp @

10 rad/s, C

46 52

58 64

RO

LLING

THIN

FILM O

VEN

(T240) OR

THIN

FILM O

VEN

RESID

UE (T179)

Mass Loss, M

aximum

, %

1.00

Dynam

ic Shear, TP5:

G*/sin , M

inimum

, 2.20 kPa

Test Temp. @

10 rad/s, C

46 52

58 64

PRESSU

RE A

GEIN

G V

ESSEL RESID

UE (PP1)

PAV

Ageing Tem

perature, C d

90 90

100 100

Dynam

ic Shear, TP5:

G*sin , M

aximum

, 5000 kPa

Test Temp. @

10 rad/s, C

10 7

4 25

22 19

16 13

10 7

25 22

19 16

13 31

28 25

22 19

16

Physical Hardening e

Report

Creep Stiffness, TP1: f

S, Maxim

um, 300 M

Pa,

m-value, M

inimum

, 0.300

Test Temp. @

60 s, C

-24 -30

-36 0

-6 -12

-18 -24

-30 -36

-6 -12

-18 -24

-30 0

-6 -12

-18 -24

-30

33

Direct Tension, TP3: f

Failure Strain, Minim

um, 1.0%

Test Temp. @

1.0 mm

/min, C

-24 -30

-36 0

-6 -12

-18 -24

-30 -36

-6 -12

-18 -24

-30 0

-6 -12

-18 -24

-30

a. Pavem

ent temperatures are estim

ated from air tem

peratures using an algorithm contained in the SU

PERPA

VE softw

are programm

e, they may be provided by the specifying agency, or by follow

ing the procedures outlined in PPX

. b.

This requirement m

ay be waived at the discretion of the specifying agency if the supplier can show

that the asphalt binder can be adequately pumped and m

ixed at temperatures that m

eet all applicable safety

standards.

c. For quality control of unm

odified asphalt cement production, m

easurement of the viscosity of the original asphalt cem

ent may be substituted for dynam

ic shear measurem

ents of G*/sin at test tem

peratures where

the asphalt is a New

tonian fluid. Any suitable standard m

eans of viscosity measurem

ent may be used, including capillary or rotational viscom

etry (AA

SHTO

T201 or T202).

d. The PA

V ageing tem

perature is based on simulated clim

atic conditions and is one of three temperatures: 90C

, 100C or 110C

. The PAV

ageing temperature is 100C for PG

58- and above, except in desert cli-

mates, w

here it is 110 C.

e. Physical H

ardening TP1 is performed on a set of asphalt beam

s according to Section 13.1, except the conditioning time is extended to 24 h 10 m

in at 10C above the m

inimum

performance tem

perature. The

24-h stiffness and m-value are reported for inform

ation purposes only.

f. If the creep stiffness is below

300 MPa, the direct tension test is not required. If the creep stiffness is betw

een 300 and 600 MPa, the direct tension failure strain requirem

ent can be used in lieu of the creep stiff-

ness requirement. The m

-value requirement m

ust be satisfied in both cases.

Table SHR

P Performance G

raded Asphalt B

inder Specifications (continued)

PG 70-

PG 76-

PG 82-

PERFO

RM

AN

CE G

RA

DE

10 16

22 28

34 40

10 16

22 28

34 10

16 22

28 34

Average 7-day M

aximum

Pavement

Design Tem

perature, C a < 70

< 76 < 82

Minim

um

Pavement

Design

Tem-

perature, C a

> -10 > -16

> -22 > -28

> -34 > -40

> -10 > -16

> -22 > -28

> -34 > -10

> -16 > -22

> -28 > -34

OR

IGIN

AL B

IND

ER

Flash Point Temp, T48: M

inimum

C 230

Viscosity, A

STM D

4402: b

Maxim

um, 3 Pas, Test Tem

p., C

135

34 Dynam

ic Shear, TP5: c

G*/sin , M

inimum

, 1.00 kPa

Test Temp. @

10 rad/s, C

70 76

82

RO

LLING

THIN

FILM O

VEN

(T240) OR TH

IN FILM

OV

EN R

ESIDU

E (T179)

Mass Loss, M

aximum

, %

1.00

Dynam

ic Shear, TP5:

G*/sin , M

inimum

, 2.20 kPa

Test Temp. @

10 rad/s, C

70 76

82

PRESSU

RE A

GEIN

G V

ESSEL RESID

UE (PP1)

PAV

Ageing Tem

perature, C d

100 (110) 100 (110)

100 (110)

Dynam

ic Shear, TP5:

G*sin , M

aximum

, 5000 kPa

Test Temp. @

10 rad/s, C

34 31

28 25

22 19

37 34

31 28

25 40

37 34

31 28

Physical Hardening e

Report

Creep Stiffness, TP1: f

S, Maxim

um, 300 M

Pa,

m-value, M

inimum

, 0.300

Test Temp. @

60 s, C

0 6

12 18

24 30

0 6

12 18

24 0

6 12

18 24

Direct Tension, TP3: f

Failure Strain, Minim

um, 1.0%

Test Temp. @

1.0 mm

/min, C

0 6

12 18

24 30

0 6

12 18

24 0

6 12

18 24

Reference:

SHR

P H

ighway

Research

Program:

Superior Perform

ing A

sphalt Pavem

ents (SU

PERPA

VE):

The Products

of the

SHR

P A

sphalt R

esearch Program

, SH

RP-A

-410, 1994.

35

APPENDIX 3/ p.1

SCHEMATIC PRESENTATION OF SUPERPAVE TEST METHODS FOR BITUMEN

Dynamic Shear Rheometer test, DSR

The test evaluates the rheological properties of bitumen at higher temperatures, where rutting is the most serious cause of flexible pavement distress. Using conventional physical testing methods, the pavement designer would specify a stiffer binder to reduce the rutting problems of the roads. This approach could, however, accelerate cracking in low temperatures. Unlike the capillary viscome-ters, which only measure the viscosity, the DSR measures both the viscosity and the elastic proper-ties of the asphalt binders. DSR is also used to measure properties at intermediate temperature. At this temperature level, the fatigue cracking is controlled.

In the schematic diagram (Figure 1), the asphalt sample, in the DSR test, is sandwiched between two plates.

Figure 1. Schematic outline of the DSR test for bitumen.

The bottom plate is fixed. A torque is applied to the top plate so that it oscillates back and forth at a rate of 1.6 cycles per second. One cycle is completed when the top plate goes from A to B and back to A, and from A to C and back to A. The DSR measures the complex shear modulus and the phase angle. This means that the test measures the overall stiffness of bitumen, including both viscosity and elastic properties.

36

Bending Beam Rheometer test, BBR 3/p. 2

The test evaluates the rheological properties of bitumen at low temperatures. The asphalt concrete pavements develop low-temperature cracking when asphalt concrete becomes too stiff at decreased temperatures. The BBR test shown in Figure 2 is used to evaluate the low-temperature stiffness properties of bitumens.

Figure 2. Schematic outline of the BBR test.

Bitumen will be tested having been aged in the Rolling Thin Film Oven Test (RTFOT test) and in the Pressure Ageing Vessel Test (PAV test) before applying the BBR test procedure. By loading the bitumen beam with a constant load for 4 min, and continuously measuring the deflection at the cen-tre of the beam throughout the 4 min, the creep stiffness and the creep rate, m, can be measured and calculated.

Direct Tension Test, DTT test

The DTT test was developed in the SHRP programme in the U.S.A., to accommodate those par-tially polymer-modified bitumens that may be stiff at low temperatures but do not develop the ex-pected low-temperature cracking. The creep stiffness, as measured by the BBR test, is not adequate for evaluating the elastic recovery of bitumen. In the DTT test shown in Figure 3, a small dogbone-shaped specimen is loaded in tension until failure.

Rolling Thin Film Oven Test (RTFOT test)

Bitumen is aged for 75 min in the rotating bottles. The test is described in more detailed in the common ASTM Designation: ASTM D 2872. This test serves two purposes. One is to provide the aged residue bitumen that can be subjected to other physical tests. The other is to measure the level of volatile hydrocarbon loss during the mixing process and in construction operations of bitumen.

37

3/p. 3

Figure 3. Schematic outline of the DTT test.

Pressure Ageing Vessel Test (PAV test)

The PAV test is illustrated schematically in Figure 4. The test determines the long-term ageing of bitumen during the service life of the asphalt concrete.

Figure 4. Schematic outline of the PAV test.

Bitumen undergoes several ageing mechanisms while in use. Two of the most important are the loss of volatiles and the oxidation of bitumen while exposed to the sun (UV) light. The PAV test ap-proximates the ageing process of bitumen that takes place in the asphalt concrete while the pave-ment is in use, which is essentially only an oxidation process.

38

3/ p.4

Figure 5

39

Table 12 Bitumen requirements in SHRP for PG 64 - 18.

Table 12 Test of bitumen property

Ageing conditions Test results SHRP specific requirements

Flash Point Original bitumen 230C min Viscosity 135C Original bitumen 3 Pa.s max Dynamic shear, G*/sin at 64C

Original bitumen 1.00 kPa min

Mass loss RTFOT-aged bitumen residue 1.00% max Dynamic shear, G*/sin at 64C

RTFOT-aged bitumen residue 2.20 kPa min

Dynamic shear, G*/sin at 22C

PAV-aged bitumen residue 5000 kPa max

Creep Stiffness, s at 18C

PAV-aged bitumen residue 300 MPa max

m-value at 18C PAV-aged bitumen residue 0.300 min

12

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