Construction and Maintenance Practices for Permeable Friction Courses (2009) / Chapter Skim
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Pages 43-54
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From page 43... ...
Due to the open nature of PFC, the asphalt binder coating aggregates is susceptible to accelerated oxidative aging. Oxidative aging of the asphalt binder results in an increase in stiffness within the PFC layer which would reduce pavement thickness.
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From page 44... ...
As a result, the temperature of the PFC layer will tend to be lower than for comparable dense-graded layers. In order to investigate this hypothesis, the authors conducted experiments on newly placed and 8-year-old PFC layers to compare the temperatures of pavements with porous asphalt and dense-graded wearing layers at the surface and at depth.
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From page 45... ...
California does not consider the structural benefits of PFC when determining layer thicknesses for the structural sections even though a structural value is assigned. Rational Method of Selecting PFC Lift Thickness Within most of the United States, the thickness of PFC layers placed on the roadway has been based upon experience.
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From page 46... ...
Thickness is contained within the ho term of Equation 3. Likely the most important property required to determine the required thickness of a PFC layer is a measure of rain intensity.
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From page 47... ...
per hour. As stated previously, other information for determining a minimum PFC lift thickness includes the design cross slope (α)
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From page 48... ...
Within the example problem, the rainfall intensity at 90 percent of all rain events was identified. The pavement designer must select the cumulative percentage of rain events from which rain intensity is selected.
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From page 49... ...
Cumulative percentage of rain events versus rain intensity. Design Chart for PFC Lift Thickness Based on Cross Slope 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0 34.0 36.0 38.0 0.000 0.004 0.008 0.012 0.016 0.020 0.024 0.028 0.032 0.036 0.040 0.044 4I/K t/L Cross Slope = 2.5% Cross Slope = 2.0% Cross Slope = 3.0% Cross Slope = 3.5% Cross Slope = 4.0% Cross Slope = 1.5% Figure 27.
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From page 50... ...
There is limited evidence that thicker PFC layers that have a relatively high level of permeability can maintain permeability for a longer period of time, that is, less clogging. Sensitivity Analysis A sensitivity analysis was conducted to evaluate the developed method of determining a PFC lift thickness.
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From page 51... ...
, simply increasing the design cross slope by 0.5 percent can significantly reduce the needed thickness of PFC. The final input into the PFC layer thickness methodology is the flow path length.
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From page 52... ...
Effect of rain intensity on design lift thickness. 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 90.0 110.0 130.0 150.0 170.0 190.0 210.0 230.0 250.0 270.0 Permeability, m/day PF C La ye r Th ic kn es s, m m Rainfall Intensity, I = 0.4 inches per hour Cross Slope, = 2 percent Length, L = 3.6 m Figure 30.
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From page 53... ...
0.0 10.0 20.0 30.0 40.0 50.0 60.0 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 Length, m PF C La ye r T hi ck ne ss , m m Rainfall Intensity, I = 0.3 inches per hour Cross Slope, = 2 percent Permeability, K = 100 m/day Figure 33. Effect of flow path length on design lift thickness.
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From page 54... ...
The relatively high macrotexture of PFC wearing layers provides channels for water to be displaced when a tire passes over the pavement surface. Additionally, the design curves do not take into account any hydraulic action caused by traffic which results in water being "pushed through" the void structure of the PFC layer, which makes the design curves conservative.
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