Global standardisation of test methods for asphalt mixtures. Andrew Cooper

Transcription

1 Global standardisation of test methods for asphalt mixtures Andrew Cooper 1

2 Content Europe UK Netherlands France APT and pavement design US Observations 2

3 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 3

4 Key material properties Deformation resistance (rutting) Fatigue life Modulus/Stiffness Moisture susceptibility Thermal cracking resistance Resistance to reflection cracking 4

5 Content Europe UK Netherlands France APT and pavement design US Observations 5

6 UK 6

7 Modulus Time (s) 7

8 Modulus Low stiffness High stiffness Compressive stress on subgrade Poor load spreading Good load spreading 8

9 Total Asphalt Thickness (mm) Roadbase design chart msa Grade Grade 3 Grade Grade Design Life (msa) 9

10 UK 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. 10

11 UK CONCLUDING REMARKS 1. 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 11 same assurance.

12 UK 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. 12

13 UK Wheel tracking 13

14 Wheel tracking Test Standards. BS 598 EN T AST 01:1999 NLT :2002 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 200mm or 300x300x50m 300x300mmx(35-300x300mm 300x300x50mm 300x300x50mm m 110)mm Tyre: (Diameter) mm mm 200mm mm 200mm Tyre: (Width) 50 ±1mm 50 ±5mm 50mm 50±1mm 50mm Tyre: (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 ( Hour Load cycles) Temperature Sample Thickness Sample 5-24 Hour Not Specified 4 Hour

15 EN harmonization 15

16 Content Europe UK Netherlands France APT and pavement design US Observations 16

17 Netherlands Applied Stress (kpa) Confining Stress (kpa) Surface Base/binder Temperature ( C) Failure limits 10,000 cyc 10,000 cyc 17

18 EN options 18

19 Netherlands 19

20 4pt Round Robin 20

21 Modulus (Gpa) Round Robin results * * * * * * * * * * * * * * * * * * Frequency (Hz) 21

22 Stiffness modulus [GPa] 73 Beam I-50-A Beam I-50-B Beam I-100-A Beam I-100-B Four point Round Robin 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-B Frequency [Hz] 22

23 Modulus [GPa] Four point Round Robin Beam I-50 Beam I-100 Beam II-50 Beam II-100 Beam III-50 Beam III Frequency [Hz] 23

24 Modulus [GPa] Four point Round Robin 77 Beam III - 50 Beam III Beam II - 50 Beam II Beam I - 50 Beam I Frequency [Hz] 24

25 Four point Round Robin 25

26 Four point Round Robin 26

27 Four point Round Robin 27

28 Four point Round Robin 28

29 Four point Round Robin 29

30 Four point Round Robin 30

31 Four point Round Robin 31

32 Four point Round Robin 32

33 Four point Round Robin 33

34 Four point Round Robin 34

35 Four point Round Robin 35

36 36

37 Content Europe UK Netherlands France APT and pavement design US Observations 37

38 The French approach Level 4 Fatigue Level 3 Stiffness(Complex modulus) Level 2 Rut resistance Level 1 Water sensitivity & Gyratory compaction Select mixture fail fail fail fail fail Adjust mixture composition

39 Void content / % 10mm EME2 0,0 5,0 10,0 2.8% voids at 100 gyrations 15,0 20,0 Mean % voids 25,0 30, Number of Gyrations 39

40 BBAC BBAC (binder) BBAGG BBME GB 2 GB 3 EME 1 EME 2 Voids % French specification Out of spec In spec 40

41 PCG correlation 41

42 SPGC PCG French angle is less than SHRP angle French load is a little more than SHRP load 1.16 (1.25 ) 0.82 (1 ) 42

43 Gyratory angle 43

44 % Voids 0 Angle influence Number of gyrations % voids % voids % voids Number of gyrations % 6.7% 5.2%

45 Internal angle test1 test2 test3 DAV top angle ( ) DAV bottom angle ( ) test

46 Internal angle ILS top angle ( ) square difference ILS bottom angle ( ) square difference test test test test test

47 The French approach Level 4 Fatigue Level 3 Stiffness(Complex modulus) Level 2 Permanent deformation Level 1 Gyratory compaction & Water sensitivity 47

48 48

49 Field specimens 49

50 Adoption of French method 80 gyrations SPGC(1.16 ) = 100 gyrations PCG(0.82 ) for EME2 50

51 Adoption of French method 51

52 Adoption of French method 52

53 Content Europe UK Netherlands France APT and pavement design US Observations 53

54 Accelerated testing 54

55 APT Use of accelerated pavement tests (APT) for development and evaluation of performance models Pierre Hornych LCPC (IFSSTAR) 55

56 Content Europe UK Netherlands France APT and pavement design US Observations 56

57 Modelling 57

58 MEPDG 58

59 Prediction 59

60 AMPT(SPT) 60

61 Flow number Applied Stress (kpa) Confining Stress (kpa) Temperature ( C) Failure limits 600 (85 psi)? ,000 cycles or 5% strain 61

62 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 62

63 Dynamic modulus -E* Frequency (Hz) Temperature ( C) 0.1, 0.5, 1.0, 5, 10, , 19.6,

64 US tests Property Used tests Moisture sensitivity AASHTO T 283 Permanent deformation Fatigue cracking Thermal cracking Reflective cracking Hamburg APA 4 Point bending SCB/DCT/AMPT/ SCB/ITD/TSRST Texas Overlay 64

65 Hamburg wheel tracker 65

66 Simple harmonic motion Scotch yoke Crank arm AASHTO Designation: T 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 m/s (1 ft/sec) and will be reached at the midpoint of the specimen. 66

67 Wheel Position, x (mm) Wheel Velocity, v (m s ¹) 150 Scotch yoke Chart Showing Position and Velocity of Offset Crank and Scotch Yolk Driven Wheel Trackers vs. Time 0, ,3 0,2 0, ,5 1 1,5 2 2,5 3 3,5 4 4,5 Time (s) 0-0,1-0,2-0,3-0,4 Wheel Position - Scotch Yoke Type (mm) Wheel Velocity - Scotch Yoke Type (m/s) 67

68 Wheel Position, x (mm) Wheel Velocity, v (m s ¹) 150 Crank arm Chart Showing Position and Velocity of Offset Crank and Scotch Yolk Driven Wheel Trackers vs. Time 0, ,3 0,2 0, ,5 1 1,5 2 2,5 3 3,5 4 4,5 Time (s) 0-0,1-0,2-0,3-0,4 Wheel Position - Offset Crank Type (mm) Wheel Velocity - Offset Crank Type (m/s) 68

69 Rut Depth (mm) Wheel tracking Number of Passes x

70 Wheel tracking 70

71 TOL specimen prep 71

72 Deformation(in) Force TOL Time (s) Time (s) 72

73 Cracking/fatigue Miro y Jimenez S-VECD IDT Fénix ensayo 73

74 Cracking/fatigue DCT SCB 74

75 Content Europe UK Netherlands France APT and pavement design US Observations 75

76 AMPT development Research Commercial Equipment Need Draft Test Method Prototype Equipment Verification Specification First Article Equipment Ruggedness Critical Aspects Improve Test Method Equipment Production Equipment Provisional AASHTO Test Methods Round Robin Testing Precision and Bias Training Engineering Practice National Cooperative Highway Research Program Project

77 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. 77

78 El fin 78

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

80 Specimen test 80

81 Find slide showing variability 81

82 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. 82

83 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 of the 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. 83

84 84

85 The Superpave method, like other mix design methods, 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 asphalt content. 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] ). 85

86 rutting Rut 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. 86

87 OT Cycles OT modifications Effects of different OT displacement rates: (COV =18%) Type C plant-mix 4.3% PG limestone y = 8E+06x x R 2 = (COV=34%) Displacement (Inches) 87

88 The property exhibited by certain liquids of becoming fluid when stirred or shaken and returning to the semisolid state upon standing. Or changing viscosity perty of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become th d, or otherwise stressed. They then take a fixed time to return to a more viscous state. In more tec astic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress luid which takes a finite time to attain equilibrium viscosity when introduced to a step change in sh state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt ta Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Co r mixing. Fluids which exhibit this property are usually called rheopectic. They are much less comm 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). 88

89 Permanent deformation 89

90 Witczak Predictive model for le*l 90

91 Original Witczak Predictive model 91

92 Original Witczak Predictive model 92

93 93

94 94

95 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. 95

96 The global standardisation of test methods for asphalt mixtures 96

97 SHRP One of the principal results from the Strategic Highway Research Program (SHRP) was the Superpave mix design method. The Superpave mix 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 Superpave mix design method. The compaction methods devices from the Hveem and Marshall procedures were replaced by a gyratory compactor. 97

98 SPT/AMPT In 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 Superpave volumetricmix design method. In 1999, this effort was transferred to Task C of NCHRP Project 9-19, Superpave Support and Performance Models Management, 98

99 Fatigue tests Repeated Load Flexural Beam Continuum Damage Texas Overlay Fracture Energy Indirect Tensile Disk-Shaped Compact Tension Semi-Circular Bend Fenix 99

100 Dy mod specimen prep 100