Hamburg Wheel-Track Test Equipment Requirements and Improvements to AASHTO T 324 (2016) / Chapter Skim
Currently Skimming:
Pages 24-68
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 24... ...
21 4. RESULTS AND ANALYSIS This chapter presents the main findings of NCHRP Project 20-07/Task 361.
|
From page 25... ...
22 Table 2. Loading mechanism (AASHTO T 324, section 5.1)
|
From page 26... ...
23 Table 3. Impression measurement system (AASHTO T 324, section 5.3)
|
From page 27... ...
24 Table 5. Data collection and reporting Vendor A B C D Standard model Economy model Number of data points collected across specimen 11 11 5 Selectable up to 21 227 Range (± from midpoint)
|
From page 28... ...
25 There are three consequences of a non-sinusoidal wheel speed: [1] the total time of loading of the front half of the specimen is less than that of the rear half of the specimen; [2]
|
From page 29... ...
26 4.2. Findings of the Nationwide Survey A nationwide survey was conducted to collect information from state agencies on the use of HWTs.
|
From page 30... ...
27 4.2.1 Type of HWTs Used The second question in the survey related to the HWT brands used by the states. Available vendors are Troxler Electronic Laboratories, Inc.; Pavement Technology, Inc.
|
From page 31... ...
28 Figure 15 Calibration of HWT 4.2.3 Test Temperature Respondents were polled on the water bath temperature. Based on the survey responses and state specifications, California, Montana, Utah and Colorado use at least two different test temperatures based on PG, which correspond to 44°C and 56°C.
|
From page 32... ...
29 4.2.4 Mix Acceptance Criteria Mix acceptance criteria based on HWT varies among the states. The main results from the HWT are the maximum rut depth and the stripping inflection point (SIP)
|
From page 33... ...
30 4.2.5 Reporting of Test Results The method adopted to calculate the maximum rut depth varies among state agencies. Since AASHTO T-324 requires reporting the maximum depression only, seven states report the maximum rut depth only (California, Colorado, Massachusetts, Utah, Washington, and Wisconsin)
|
From page 34... ...
31 The waveform obtained for the machine from Vendor D is shown in Figure 18(d)
|
From page 35... ...
32 (a) Vendor A (b)
|
From page 36... ...
33 Table 6. Equations for the position of the wheel Vendor Mechanism Slider-crank (non-sinusoidal)
|
From page 37... ...
34 In an effort to quantify the deviations from a pure-sinusoidal waveform, a goodness-of-fit measure, RMSE (root mean square error) , was computed for all the waveforms.
|
From page 38... ...
35 Table 7. AASHTO T 324, section 5.1 parameters Vendor A-1 Vendor A-2 Vendor A-3 Vendor B Vendor C Vendor D Waveform RMSE (mm)
|
From page 39... ...
36 for the machines evaluated was 0.305 m/s (1 ft/s)
|
From page 40... ...
37 Table 8. Wheel dimensions measured from different manufacturers Vendor A-1 Vendor A-2 Vendor A-3 Vendor B Vendor C Vendor D Left Wheel Right Wheel Left Wheel Right Wheel Left Wheel Right Wheel Left Wheel Right Wheel Left Wheel Right Wheel Left Wheel Right Wheel Diameter (mm)
|
From page 41... ...
38 It is noted that AASHTO T 324 does not currently set a tolerance for the wheel dimensions and only specifies the averages. This may need to be revised, as the user has currently no indication on how much the wheel dimensions can deviate from the specified values.
|
From page 42... ...
39 noted that all vendors use pound as the unit when calibrating the wheel loads. In this case, Vendor B right wheel load was 157 lbs., which is within the load requirement.
|
From page 43... ...
40 cylindrical specimen. Details of the specimen preparation and instrumentation are also presented in Appendix D
|
From page 44... ...
41 (a) Vendor A-1 (b)
|
From page 45... ...
42 (a) Vendor B (b)
|
From page 46... ...
43 (a) Vendor A-1 (b)
|
From page 47... ...
44 (a) Vendor B (b)
|
From page 48... ...
45 4.7.2 Evaluation at 25°C Figure 29 presents the results of the temperature evaluation at 25°C. The data acquisition was turned on prior to filling the bath of the HWTs.
|
From page 49... ...
46 (a) Vendor A (b)
|
From page 50... ...
47 (a) Vendor A (b)
|
From page 51... ...
48 4.7.3 Evaluation at 70°C Figure 31presents the data gathered from the sensors in the HMA specimens after they were placed in HWT baths. The data collection system was switched on prior to immersing the specimens in the bath.
|
From page 52... ...
49 (a) Vendor A (b)
|
From page 53... ...
50 (a) Vendor A (b)
|
From page 54... ...
51 Figure 33 Temperatures at 30 and 60 minutes and after the addition of a water circulator (Vendor D)
|
From page 55... ...
52 Figure 34 Metal specimen for verifying locations of deformation readings 4.8.1 Test Results The fabricated metal specimen was used to obtain rut measurements from the HWT machines. The data obtained from the HWT machines were compared to the reference rut profile of the metal specimen.
|
From page 56... ...
53 Figure 35 Impression measurement system results from HWT machine (Vendor A) Figure 36 presents the results for the HWT machine from Vendor B
|
From page 57... ...
54 Figure 37 shows the results of the evaluation for the machine from vendor C This machine records data at 23 equally-spaced locations across the track (-110, -100, -90, -80, -70, -60, -50, 40, -30, -20, -10, 0, +10, +20, +30, +40, +50, +60, +70, +80, +90, +100, and +110 mm)
|
From page 58... ...
55 Figure 38 Impression measurement system results of HWT machine (Vendor D) In an effort to quantify the deviations of the readings from the metal profile, the root mean square error (RMSE)
|
From page 59... ...
56 Table 11. RMSE values for impression measurements of metal profile Vendor RMSE (in.)
|
From page 60... ...
57 • In vendor A's software, the user specifies the locations of the creep and strip regions. In this approach, the user chooses the "start" and "end" pass numbers for the creep and strip regions and the software draws straight lines using these points to obtain the creep and strip lines.
|
From page 61... ...
58 4.9.1 Test Materials Two mixes, which were tested using the HWT manufactured by Vendor A, were selected for analysis by the various methods. While Vendor A recorded rut data at 11 points across the wheel track, the rut data corresponding to the center reading, or Point Number 6, was used in the analysis and is presented in Figure 39.
|
From page 62... ...
59 Figure 40 Data Analysis for Mix 1 Based on Different Approaches -25 -20 -15 -10 -5 0 0 5000 10000 15000 20000 ru t d ep th (m m ) number of passes Vendor A data creep slope strip slope -25 -20 -15 -10 -5 0 0 5000 10000 15000 20000 ru t d ep th (m m )
|
From page 63... ...
60 As shown in Figure 40, for Vendor A, the creep region ranged from 2,000 to 6,000 passes and the strip region from 11,500 to 12,800 passes. Since these regions are not automatically determined by the program, the results reported could vary by the user.
|
From page 64... ...
61 Figure 41 Data Analysis for Mix 2 Based on Different Approaches Table 12 and Table 13 summarize the stripping and no-stripping data sets results from the different analysis methods. For Mix 1, substantial differences were observed in the reported SIP.
|
From page 65... ...
62 seven approaches. AASHTO T 324 also requires reporting the creep slope and the strip slope.
|
From page 66... ...
63 Table 14. Summary of Seven Programs Reporting Parameters Number Of Passes Max Impression (mm)
|
From page 67... ...
64 Since three of the four machines available on the market do not have a cooling system, it is virtually impossible to set the target temperature to 25°C, especially during summer time. It is recommended to modify the low range to 35°C (95°F)
|
From page 68... ...
65 4.11. Laboratory Experimental Plan for Validation of Proposed Changes A laboratory experimental plan was developed to validate the proposed equipment modifications and specifications proposed in this study.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.