global standardisation of test methods for asphalt...

Global standardisation of test methods for asphalt mixtures

Andrew Cooper

Content

Europe

Netherlands

France

APT and pavement design

Observations

Performance tests

Performance tests are used to relate laboratory mix design to actual field performance and can be used to –• Evaluate new materials• Understand failure• Quality assure material/Specify material• Design pavements as part of an integrated

process – using linear elastic theory

Key material properties

• Deformation resistance (rutting) • Fatigue life• Modulus/Stiffness

• Moisture susceptibility• Thermal cracking resistance• Resistance to reflection cracking

Content

Europe

Netherlands

France

Observations

Time (s)

Modulus

Low stiffness

Poor load spreading Good load spreading

Compressive stress on subgrade

High stiffness

Modulus

Roadbase design chart

1 10 100 1000

Design Life (msa)

Grade 1

Grade 3

Grade 6

Grade 9

80 msa

What worked really well with ITSM was that it was developed by academics, picked up by TRL who ran the relevant precision and ruggedness trials. All interested parties were looking for a performance test which would give a modulus value.

Then, within the UK at least, there was only one manufacturer. They started to push for accreditation very early on.

Later on the procedure was picked up by CEN with only a few modifications.

CONCLUDING REMARKS1. The ITSM test is a practical test that is suitable for inclusion in a performance based specification to test laid material in a road construction contract. The test is quick, reliable, easy to use and economic. 2. Fundamental laboratory tests are not suited to this role. The technology of the ITSM test is appropriate, that of the fundamental tests is not. However, it has been demonstrated that ITSM measurements correlate well with more fundamental laboratory tests.3. The ITSM test is being used in contractual situations in major road construction contracts in the UK. 4. The UK philosophy is to test the laid product because that is what the Client is paying for and he requires assurance that what he is getting is fit-for-purpose. A laboratory mixture design study does not give the same assurance.

5. The concept of performance measurements being carried out on laid materials for assessment and compliance is applied to all road layers in the UK. The Highways Agency and UK Industry are investing heavily in this approach. Performance based specifications are currently under development for the capping layers, sub-base, asphalt roadbase and asphalt surfacing.6. The good correlation between ITSM and the FWD demonstrates that the ITSM is a good measure of load-spreading ability.7. Criteria should be established for assessing the relative merits of test protocols which should include comparison of values, precision, cost, ease of practical application, etc so that appropriate tests can be selected for each application.

UK Wheel tracking

Wheel tracking

Test Standards. BS 598 EN 12697-22:2002

T0719-1993 AST 01:1999 NLT-173

Test Temperature: 45:C & 60:C 60:C 60:C 60:C 60:C

Load: 520 (N) 700 (N) 700 (N) 700 (N) ±20N 900 (N)Specimen Size: 200mm or

300x300x50mm200mm or 300x300x50mm

300x300x50mm

300x300mmx(35-110)mm

300x300mm

Tyre: (Diameter) 200-205mm 200-205mm 200mm 200-205mm 200mm

Tyre: (Width) 50 ±1mm 50 ±5mm 50mm 50±1mm 50mmTyre: (Thickness) 13±1mm 20 ±2mm 15mm 10-13mm 20mm

Tyre: (Hardness) 80 IRHD 80 IRHD JIS 84±4 in 20:C, 78±2 in 60:C

80±10 IRHD 80 IRHD

Distance of travel: 230 ± 10mm 230 ± 10mm 230±10mm 230±5mm 230±5mm

Running Speed: 42±0.5 pp/min 26.5 ± 1.0 RPM 42±1.0 pp/min 42±0.5 pp/min 42±0.5 pp/min

Running time: 1 Hour 10K Load Cycles 1 Hour Min 10K passes (5000 Load cycles)

2 Hour

Temperature Conditioning Time:

Sample Thickness <= 60mm - Min

Sample Thickness <=

5-24 Hour Not Specified 4 Hour

EN harmonization

Content

Europe

Netherlands

France

Observations

Netherlands

Surface Base/binder

Applied Stress

(kPa)150 – 750 50-450

Confining Stress (kPa)

150 50

Temperature (°C) 50 40

Failure limits 10,000 cyc 10,000 cyc

EN options

Netherlands

4pt Round Robin

Frequency (Hz)

0 5 10 15 20 25 30 35 40 45

* * * * * * * * *

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

Round Robin results

0 10 20 30 40 50 60

Frequency [Hz]

Beam I-50-A Beam I-50-B Beam I-100-A Beam I-100-B

Beam II-50-A Beam II-50-B Beam II-100-A Beam II-100-B

Beam III-50-A Beam III-5-A Beam-III-100-A Beam III-100-BFour point Round Robin

0 5 10 15 20 25 30 35

Frequency [Hz]

Modulu

Beam I-50 Beam I-100 Beam II-50 Beam II-100 Beam III-50 Beam III-100

Four point Round Robin

0 10 20 30 40 50 60

Frequency [Hz]

Beam III - 50 Beam III - 100 Beam II - 50 Beam II - 100

Beam I - 50 Beam I - 100

Four point Round Robin

Content

Europe

Netherlands

France

Observations

The French approach

Level 3 Stiffness(Complex modulus)

Level 2Rut resistance

Level 1Water sensitivity

& Gyratory compaction

Level 4 Fatigue

Select mixture

Adjust mixture composition

10mm EME2

1 10 100 1000

Number of Gyrations

Mean % voids

2.8% voids at 100 gyrations

In spec

Out of spec

French specification

The majority of the mixture testing conducted during SHRP by the Asphalt Institute wasconducted on this modified Texas 6showed the adjusted the modified Texas 6design for the Arizona Department of Transportation. The Arizona mix would not compact down to 4 percent air voids at the lower angle of gyrations. The SHRP researchers deduced that the 1insufficient for a mix design procedure targeting 4 percent air voids. The angle was adjusted back up and the research was completed at the higher angle.

PCG correlation

SPGC PCG

• French angle is less than SHRP angle

• French load is a little more than SHRP load

0.82°(1°)1.16°(1.25°)

Gyratory angle

1 10 100 1000

Number of gyrations

% voids 0.606°

% voids 0.848°

% voids 1.055°

100 7.1% 6.7% 5.2%

Number of gyrations

1 10 100 1000

Angle influence

DAV top angle (°) DAV bottom angle (°)

test10.769 0.8080.792 0.7980.774 0.809

test20.797 0.80.771 0.7770.755 0.754

test30.784 0.8030.77 0.785

0.751 0.789

test40.795 0.8010.77 0.782

0.744 0.7650.762621769 0.783322449

Internal angle

ILS top angle (°)

square difference

ILS bottom angle (°)

square difference

test 1 0.65 0.038581951 0.612 0.06698455test 2 0.652 0.044315238 0.626 0.101429577test 3 0.654 0.056669165 0.632 0.075285999test 4 0.656 0.030015278 0.621 0.101941828test 5 0.658 0.041553182 0.63 0.051901892

0.66 0.6335

Internal angle

The French approach

Level 3 Stiffness(Complex modulus)

Level 2Permanent deformation

Level 1Gyratory compaction

& Water sensitivity

Level 4 Fatigue

Field specimens

Adoption of French method

80 gyrations SPGC(1.16°)= 100 gyrations PCG(0.82°)for EME2

Adoption of French method

Content

Europe

Netherlands

France

Observations

Accelerated testing

Use of accelerated pavement tests (APT) for development and evaluation of performance models Pierre Hornych LCPC (IFSSTAR)

Content

Europe

Netherlands

France

Observations

Modelling

Prediction

AMPT(SPT)

Flow number

Applied Stress

(kPa)600 (85 psi)

Confining Stress (kPa)

Temperature (°C)

Failure limits20,000 cycles or

5% strain

MEPDG input levels

• Level 1. The input parameter is measured directly. This level provides the most accurate information about the input parameter. The primary Level 1 material property input for HMA is the measured dynamic modulus of the mixture that will be used in the pavement.

• Level 2. The input parameter is estimated from correlations or regression equations that are embedded in the MEPDG. For Level 2, the dynamic modulus for HMA materials is estimated from gradation, volumetric properties, and measured binder properties.

• Level 3. The input parameter is based on default values provided by the MEPDG software. For Level 3, the dynamic modulus for HMA is estimated from gradation, volumetric properties, and the binder grade.

Dynamic modulus -E*

Frequency

(Hz)0.1, 0.5, 1.0, 5, 10, 25

Temperature

15.6, 19.6, 23.6

US tests

Property Used tests

Moisture sensitivity AASHTO T 283

Permanent deformation

HamburgAPA

Fatigue cracking4 Point bendingSCB/DCT/AMPT/

Thermal cracking SCB/ITD/TSRST

Reflective cracking Texas Overlay64

Hamburg wheel tracker

Simple harmonic motion

AASHTO Designation: T 324-04“The wheel shall reciprocate over the specimen, with the position varying sinusoidally over time. The wheel shall make approximately 50 passes across the specimen per minute. The maximum speed of the wheel shall be approximately 0.305 m/s (1 ft/sec) and will be reached at the midpoint of the specimen.” 66

Scotch yoke Crank arm

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5

∙s⁻¹)

Time (s)

Chart Showing Position and Velocity ofOffset Crank and Scotch Yolk Driven Wheel Trackers vs. Time

Wheel Position - Scotch Yoke Type (mm) Wheel Velocity - Scotch Yoke Type (m/s)

Scotch yoke

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5

∙s⁻¹)

Time (s)

Chart Showing Position and Velocity ofOffset Crank and Scotch Yolk Driven Wheel Trackers vs. Time

Wheel Position - Offset Crank Type (mm) Wheel Velocity - Offset Crank Type (m/s)

Crank arm

Number of Passes x 10004 6 8 100 2

)Wheel tracking

Wheel tracking

TOL specimen prep

Time (s)0 5 10 15 20 25 30 35 40 45

eTime (s)

Cracking/fatigue

S-VECD IDT Fénix ensayo

Miro y Jimenez

Cracking/fatigue

DCT SCB

Content

Europe

Netherlands

France

Observations

AMPT development

Research

Draft Test MethodPrototype Equipment

Verification

Improve

Test MethodEquipment

Ruggedness

Critical Aspects

Round Robin Testing

Precision and Bias

Commercial Equipment

SpecificationFirst Article Equipment

Production Equipment

Provisional AASHTOTest Methods

Engineering PracticeTraining

76National Cooperative Highway Research Program Project 9-29

Observations

• The evaluation of new materials is possible with repeatable tests.

• Standardised(not homemade) tests give the possibility to set some design limits for common materials within a region.

• When tests are required it makes sense to chose tests which have been standardised elsewhere.

• There is generally a payoff between fundamental tests and specimen prep/setup.

• See how similar countries have adopted tests.

El fin

andrew@cooper.co.ukandrew.cooper@jamescoxandsons.com

Specimen test

Effect of Specimen Size on Fatigue Behaviour of Asphalt Mixture in Laboratory Fatigue tests –Ning Li PhD student Delft 79

Specimen test

Find slide showing variability

The Texas Department of Transportation

specifies the minimum number of wheel passes in the Hamburg Wheel-Track test to reach

an impression depth of 12.5 mm when tested at a temperature determined by the performance

grade of the asphalt binder. These values are >10,000 for mixes produced with PG 64-XX binder,

>15,000 for mixes produced with PG 70-XX binder, and >20,000 for mixes produced with

PG 76-XX binder.

Fatigue Testing

The only standard test method available for fatigue testing of HMA is the flexural fatigue test, AASHTO T 321. In this test a beam sample, 380 mm long by 63 mm wide by 50 mm high, is subjected to strain-controlled, repeated four-point bending. The beam samples are prepared using either a kneading or rolling wheel compaction; there are no AASHTO standards for either of these methods of laboratory compaction. Figure 6-6 shows a device for flexural fatigue testing. The number of laboratories in the United States that can fabricate and test flexural fatigue specimens is limited.

During a flexural fatigue test, the beam is damaged by the repeated flexing. This damage results in a decrease in the modulus ofthe beam. The beam is considered failed when the modulus decreases to 50% of its initial value. The number of loading cycles applied to the beam can range Evaluating the Performance of Asphalt Concrete Mixtures

77 Figure 6-6. Photograph of flexural fatigue apparatus. from 1,000 to 10,000,000 or more. The results of fatigue tests are presented in the form of S-N diagrams, which are simply plots of the applied strain and the corresponding number of cycles to failure. Figure 6-7 presents a typical S-N diagram for HMA generated from laboratory test data. The point where the fatigue life becomes indefinite is called the fatigue endurance limit. Because of its extreme importance in the structural design of perpetual pavements, research is in progress to better define the endurance limit for HMA.

Generating an S-N curve for HMA requires testing several beams at different strain levels.Due to the high variability of fatigue testing, each strain level requires testing a number of replicate specimens. Because of the high level of effort required to generate S-N curves for HMA, fatigue testing is rarely performed in practice. Instead, relationships between mixture compositional factors and fatigue life that have been developed from databases of tests on a number of mixtures are used. These relationships show that the most important mixture design factor affecting the fatigue life of HMA is the effective volumetric binder content of the mixture, VBE. By controlling VBE, the mixture design process controls the fatigue life of the mixture. As discussed previously,VBE, is controlled in the design method described in this manual by controlling both the VMA and the design air void content.

• The Superpave method, like other mix designmethods, creates several trial aggregate-asphalt binder blends, each with a different asphalt binder content. Then, by evaluating each trial blend’s performance, an optimum asphalt binder content can be selected. In order for this concept to work, the trial blends must contain a range of asphalt contents both above and below the optimum asphalt content. Therefore, the first step in sample preparation is to estimate an optimum asphaltcontent. Trial blend asphalt contents are then determined from this estimate.

• The Superpave gyratory compactor (Figure 2) was developed to improve mix design’s ability to simulate actual field compaction particle orientation with laboratory equipment (Roberts, 1996[1]).

ruttingRut Resistance Testing and HMA Mix Design

In recent years, a major effort was undertaken

to develop a rutting performance test and associated criteria that could be applied universally

to HMA mixtures throughout the United States. The resulting device is the asphalt mixture

performance tester (AMPT), previously called the simple performance test (SPT) system; because

of its anticipated high level of future support by specifying agencies, this device is one recommended

in this manual to measure rut resistance. Rut resistance can be evaluated in the AMPT using the

dynamic modulus test, the flow number test, or the flow time test.

• The repeated shear at constant height (RSCH) test performed with the Superpave shear tester

(SST).

• The high-temperature indirect tension (IDT) strength test.

• The asphalt pavement analyzer (APA).

• The Hamburg Wheel-track Test.

OT modifications

Effects of different OT displacement rates:

1007 (COV =18%)

58 (COV=34%)

y = 8E+06x2 - 363520x + 4352.7

R2 = 1

0.01 0.0125 0.015 0.0175 0.02 0.0225 0.025 0.0275

Displacement (Inches)

Type C plant-mix4.3% PG 76-22 + limestone

A thixotropic fluid is best visualised by an oar blade embedded in mud. Pressure on the oar often results in a highly viscous (more solid) thixotropic mud on the pressure side of the blade, and low viscosity (very fluid) thixotropic mud on the low pressure side of the oar blade. Flow from the high pressure side to the low pressure side of the oar blade is non-Newtonian. (i.e.: fluid velocity is not proportional to the square root of the pressure differential over the oar blade).

is the property of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become thin, less viscowhen shaken, agitated, or otherwise stressed. They then take a fixed time to return to a more viscous state. In more technica

pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a step change in shear rate. So

fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Constant shear stress can be applied by shaking or mixing. Fluids which exhibit this property are usually called rheopectic. They are much less common.

The property exhibited by certain liquids of becoming fluid when stirred or shaken and returning to the semisolid state upon standing. Or changing viscosity

Permanent deformation

Witczak Predictive model for lE*l

Original Witczak Predictive model

Empirical v Performance

The word empiric is derived from the ancient Greek for experience, ἐμπειρία.. Therefore, empirical data is information that is derived from the trials and errors of experience.

The global standardisation of test methods for asphalt mixtures

SHRP• One of the principal results from the Strategic

Highway Research Program (SHRP) was the Superpave mix design method. The Superpavemix design method was designed to replace the Hveem and Marshall methods. The volumetric analysis common to the Hveem and Marshall methods provides the basis for the Superpavemix design method. The compaction methods devices from the Hveem and Marshall procedures were replaced by a gyratory compactor.

SPT/AMPTIn 1996, work sponsored by FHWA (Contract

DTFH61-95-C-00100) began at the University of Maryland at College Park (UMCP) to identify and validate SPTs for permanent deformation, fatigue cracking, and low-temperature cracking to complement and support the Superpavevolumetricmix design method.

In 1999, this effort was transferred to Task C of NCHRP Project 9-19, “Superpave Support and Performance Models Management,”

Fatigue tests

Repeated Load• Flexural Beam• Continuum Damage• Texas OverlayFracture Energy• Indirect Tensile• Disk-Shaped Compact Tension• Semi-Circular Bend• Fenix

Dy mod specimen prep

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