Investigating the Relationship of As-Constructed Asphalt Pavement Air Voids to Pavement Performance (2021) / Chapter Skim
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19 C H A P T E R 2 Research Approach Objective and Scope The objective of this research was to determine the effect of in-place AV on the performance of asphalt pavements using data from the LTPP database and other appropriate sources. For clarity, the term in-place AV was defined as the as-constructed AV measured during construction.
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20 LTPP Study Study Description No. of Sections SPS 1 Strategic Study of Structural Factors for Flexible Pavements, New/Reconstructed AC pavements 149 SPS 5 AC Overlay of AC Pavement 90 SPS 8 Study of Environmental Effects in the Absence of Heavy Loads 33 SPS 9N Superpave Asphalt Binder Study (New AC Pavement Construction)
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21 Figure 2-2. Distribution of selected LTPP sections in each LTPP climate zone.
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22 Figure 2-4. Distribution of selected LTPP sections by traffic.
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23 are twice as many wheel path measurements as there are non-wheel path measurements. There is a slight shift (0.32 AV)
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24 Number of Performance Measures Figure 2-8 shows that more than two-thirds of the sections have more than eight increments of performance data collected. Figure 2-8.
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25 pavement surface performance (rutting and thermal cracking) and pavement full depth performance (fatigue cracking)
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26 Figure 2-9. Location of LTPP sections initially selected for analysis.
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27 pavement section attributes dataset to obtain the final analysis dataset for each of the four performance characteristics in this study: ride, fatigue cracking, thermal cracking, and rutting. The following parts of this chapter describe each of the aforementioned data processing steps along with summary statistics of the intermediate datasets.
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28 LTPP Section Material Attributes. Asphalt mixture consists of aggregate, asphalt binder, and AV.
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29 β’ Average binder content, BCm, computed as the mean of all asphalt layers' binder content values (π΅πΆ ) weighted by the layers' thickness used as a variable for the analysis of fatigue cracking.
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30 πΈβ = ββ / ,β (5) Where: E*
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31 Where: MrBSB = compound BSB resilient modulus of section; thl = thickness of base or sub-base layer l, with L being the total number of base or sub-base layers in the pavement section; and MrBSB,l = BSB resilient modulus of layer l. Remove or Impute Data The resulting section attribute dataset contained missing values for some of the variables.
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32 implemented using R programming language (R) "mice" (Mice: Multivariate Imputation by Chained Equations)
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33 Figure 2-11. Distribution of original values and with imputed values for selected variables.
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34 over time) , a change in both, or in no significant changes to the performance of the section.
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35 minimum and maximum values for some attributes represent extreme values that would not be considered normal and have very little influence on the analysis as 1 of 400 values. Obvious examples are 221 inches of base/subbase and 4400 ksi for asphalt mixture E*
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37 β’ Precipitation, Precyr, was captured by the total precipitation for the year obtained from the LTPP database TOTAL_ANN_PRECIP field in the CLM_VWS_PRECIP_ANNUAL table. Annual Traffic Variables.
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