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PaveCool Help

Asphalt Pavement Cooling Tool

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Table of Contents

Running PaveCool

Follow these steps to perform a pavement cooling simulation.

  1. Select Display Options

    Units and date/time format can be changed in the Options menu.

    Units: English (°F, mph, in.) or SI (°C, km/h, mm) units.

    Time: 12 Hour (2:30 PM) or 24 Hour (14:30)

    Date: US (6/28/2015) or ISO (2015-06-28)

  2. Enter a Project Title

    The project title may be used to identify the route number and location of the project for future reference. This title will be included in printed output and exported files.

    Return to Table of Contents

  3. Enter the Start Date/Time for Paving

    The time is used in order to determine the angle of the sun for the calculation of net solar flux. The time entered here should be the start time of the paving operation.

    Time and date format can be changed in the Options menu.

    To select the date, click the down arrow at the right of the date box. Click on the desired date. Use the left and right arrows at the top to select a different month.

    Time can be entered in AM/PM or 24 hour format. It is not necessary to type a colon (:) between the hour and minutes. For ordinary daytime hours, AM or PM need not be typed. The program assumes times from 6:00 to 11:59 are AM and 12:00 to 5:00 are PM. To enter times outside of these ranges, type AM or PM after the time (an "a" or "p" will suffice). Another alternative is to type the time in 24 hour format (values less than 1000 must include the preceding zero, as in 0915). If the time is on the hour, the minutes need not be typed (Typing "1" will result in 1:00 PM; "01" or "1a" will result in 1:00 AM).

    The default time format is AM/PM. To view the time in 24 hour format, select this option on the View menu.

    Return to Table of Contents

  4. Enter the Environmental Conditions

    Air Temperature

    This is the local, average, air temperature during paving. It may be determined from the local weather report. The air temperature is used to calculate how fast the heat will be lost to the surrounding air. The default temperature is 10 °C (50 °F).

    The following range of temperatures may be used in PaveCool:

    Units Minimum Maximum
    English -40 °F 120 °F
    SI -40 °C 49 °C

    Wind Speed

    This is an estimate of the average wind speed during paving. Wind speed has a significant effect on the cooling rate of hot-mix asphalt under most operating conditions.

    The wind speed may be predicted from the local weather report, measured at the job site, or estimated using the following criteria:

    Beaufort Scale: Specifications and Equivalent Speeds from Observers Handbook, Meteorological Office, 1982, UK.

    Force Description Specifications Wind Speed
    0 Calm Smoke rises vertically. 0 - 1 mph
    0 - 2 km/h
    1 Light Air Direction of wind shown by smoke drift, but not by wind vanes. 1 - 3 mph
    2 - 5 km/h
    2 Light Breeze Wind felt on face; leaves rustle; ordinary vanes moved by wind. 4 - 7 mph
    6 - 11 km/h
    3 Gentle Breeze Leaves and small twigs in constant motion; wind extends light flag. 8 - 12 mph
    12 - 20 km/h
    4 Moderate Breeze Wind raises dust and light paper. Small branches are moved. 13 - 18 mph
    21 - 30 km/h
    5 Fresh Breeze Small trees in leaf begin to sway; crested wavelets form on inland waters. 19 - 24 mph
    31 - 39 km/h
    6 Strong Breeze Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. 25 - 31 mph
    40 - 50 km/h
    7 Near Gale Whole trees in motion; inconvenience felt when walking into wind. 32 - 38 mph
    51 - 61 km/h
    8 Gale Wind breaks twigs off trees; generally impedes progress. 39 - 46 mph
    62 - 74 km/h

    Return to Table of Contents

    Sky Conditions

    Sky conditions affect the solar heating equation during daylight hours and the radiative cooling equation during nighttime.

    Guidelines for Selecting Sky Condition

    Icon Condition Description
    sun icon Clear & Dry Use only for low humidity and/or high altitudes.
    hazy sun icon Hazy Typical sunny day during the summer months.
    partly cloudy icon Partly Cloudy Clouds block the sun/sky 50% the time.
    mostly cloudy icon Mostly Cloudy Clouds block the sun/sky 75% of the time.
    overcast icon Overcast Clouds completely block the sun/sky.

    Latitude

    This is used along with the time and date to calculate the sun’s position in the sky at the time of paving. The degree latitude may be any value between -90 and 90 with the default at 45 degrees. Negative latitudes indicate a location in the Southern Hemisphere.

    Here are some Minnesota cities and corresponding latitudes:

    City Degrees Latitude
    Minneapolis/St Paul, MN 45
    Rochester, MN 44
    Duluth, MN 47
  5. Return to Table of Contents

  6. Enter Mix Specifications

    Mixture Type

    There are currently two types of asphalt mixtures available in PaveCool. Specifying the type automatically sets the material properties that will be used in the heat flow calculations. The materials are Fine (Dense Graded) dense HMA icon and Coarse (SMA - Stone Matrix Asphalt) coarse HMA icon.

    The gradations and thermal properties of the asphalt mixtures used in the development of PaveCool are shown in the following tables.

    Asphalt Mix Gradation

    Sieve Size Percent Passing
    U.S. mm Fine (Dense) Coarse (SMA)
    3/4 in. 19.0 100 100
    1/2 in. 12.5 100 50
    3/8 in. 9.5 76 30
    No. 4 4.75 61 25
    No. 8 2.36 48 20
    No. 16 1.18 34 12
    No. 30 0.600 14 11
    No. 50 0.300 11 9
    No. 100 0.150 7 8
    No. 200 0.075 6 7

    Thermal Properties

    Return to Table of Contents

    Asphalt Performance Grade (PG)

    The Performance Grade (PG) of the asphalt dictates the recommended start compaction temperature. The user must specify the high and low temperatures which make up the grading system.

    The following guidelines are used in PaveCool:
    PG 58 or greater => Start compaction when lift has cooled to 120 °C (248 °F)
    PG 52 or lower => Start compaction when lift has cooled to 110 °C (230 °F)

    Alternatively, if compaction guidelines are available for a specific binder, the user may enter the specified Start/Stop Temperatures in the Options menu or by clicking the Start/Stop Temperatures icon Start/Stop Temperatures icon

    Warning: These recommended temperatures may not be applicable to all situations. Judgment must be used in order to achieve a properly compacted surface.

    Note: The recommended start temperatures are based upon a limited database developed at the University of Minnesota by Rachel De Sombre and David Newcomb. They reflect compaction data collected from field projects around Minnesota.

    For more information regarding performance grading consult: “Superpave Level 1 Mix Design”, Superpave Series No. 2 (SP-2), Asphalt Institute.

    Return to Table of Contents

    Lift Thickness

    This is the final compacted lift thickness. Values may be entered in the following range:

    Minimum Maximum Default
    0.5 in. 10.0 in. 3.0 in.
    13 mm 254 mm 76 mm

    Delivery Temperature

    This is the temperature that the mix is delivered into the paver’s hopper. This can be specified and/or measured on the site. The following range may be entered:

    Minimum Maximum Default
    150 °F 350 °F 275 °F
    66 °C 177 °C 135 °C

    Caution must be used in increasing mix temperatures to gain paving time. Heating asphalt above its working temperature range may prematurely harden it, causing performance problems such as raveling or cracking. Additionally, a mix that is too cool will be difficult to compact. Consult the asphalt supplier to find out the maximum and minimum temperatures at which the material should be placed.

  7. Return to Table of Contents

  8. Enter Existing Surface Conditions

    There are currently four types of existing surface materials available in PaveCool. Specifying the type automatically sets the thermal properties that will be used in the heat flow calculations. The materials are:

    dense HMA icon Asphalt
    PCC icon Portland Cemenet Concrete (PCC)
    dense HMA icon Granular base
    dense HMA icon Subgrade soil

    Asphalt and Portland Cement Concrete (PCC)

    These materials have associated thermal properties. These values do not change significantly with temperature or moisture.

    Granular Base and Subgrade Soil

    The existing surface is made of either coarse or fine unbound materials. Sand or gravel constitutes granular base material while silt or clay constitutes subgrade soils.

    The moisture content of these materials is important since it affects the thermal properties. In PaveCool there are two moisture contents to choose from:

    Wet: moisture content > optimum
    Dry: moisture content < optimum

    The state of moisture of these materials is important since it affect the thermal properties. In PaveCool there are two states of moisture to choose from:

    Frozen: Temperature < 32 °F (0 °C)
    Unfrozen: Temperature > 32 °F (0 °C)
  9. Return to Table of Contents

  10. Calculate

    Click the Calculate button after the data has been entered.

    PaveCool determines the amount of time it will take an asphalt lift to cool to the designated stop temperature. The recommended times are given in minutes and the corresponding temperatures are plotted on the chart. The temperatures correspond to the average lift temperature.

  11. Save PaveCool File

    Click the Save button save file icon or File... Save to save a PaveCool (pc3) file. To save as a new file name, click File... Save As

    .
  12. Create Report

    Click the PDF button save PDF file icon or File... Save PDF to save a PaveCool report in PDF format.

  13. Export Data

    Clicking on this button will enable the user to export the current data. Note that this option is only available after the calculate button has been clicked. After clicking, a new dialog box will open.

    Enter the filename in the edit box. Data can be saved in Excel (xls), tab-delimited text (txt), or comma-delimited text (csv) format. Providing the extension “xls” will allow the file to be automatically opened in Excel. However, the file is just tab delimited and can be opened in any type of spreadsheet or text editor.

  14. Return to Table of Contents

Documentation

  • Thermal Properties

    Material Density
    kg/m3
    Thermal Conductivity
    W/(m*K)
    Specific Heat
    J/(kg*K)
    dense HMA icon Fine (Dense) Asphalt 2000 2.0 1000
    coarse HMA icon Coarse (SMA) Asphalt 2010 1.5 1010
    dense HMA icon Existing Asphalt 2000 1.51 1025
    PCC icon PCC (Concrete) 2000 0.92 1090
    aggregate base icon Granular Base (dry unfrozen) 2000 1.16 963
    aggregate base icon Granular Base (wet unfrozen) 2000 1.22 1172
    aggregate base icon Granular Base (dry frozen) 2000 2.00 858
    aggregate base icon Granular Base (wet frozen) 2000 3.55 963
    soil icon Soil (dry unfrozen) 1800 1.35 1172
    soil icon Soil (wet unfrozen) 1800 1.87 1591
    soil icon Soil (dry frozen) 1800 1.40 963
    soil icon Soil (wet frozen) 1800 2.38 1172

    Thermal Conductivity

    Thermal conductivity, k, is used as a proportionality constant in the heat conduction equation described by Fourier’s law. The law states that the heat flux, in a given direction, is proportional to the temperature gradient in that direction. One dimensional steady-state heat conduction is described by the following differential equation:

    qz = -k (dT/dz)

    where:
    qz = heat flux in direction z
    k = thermal conductivity
    dT/dz = change in temperature with depth

    The following equations were used to calculate the thermal conductivity of aggregate base and soil (Kersten):

    Unfrozen Base k = (0.07 log10ω + 0.4)100.01γ ω ≥ 1
    Frozen Base k = 0.076*100.013γ + 0.032*100.0146γ ω ≥ 1
    Unfrozen Soil k = (0.9 log10(ω) - 0.2)100.01γ ω ≥ 7
    Frozen Soil k = 0.01*100.022γ + 0.085*100.008γ ω ≥ 7
    where
    k = thermal conductivity, Btu*in/(ft2*h*°F)
    γ = dry unit weight, pcf
    ω = gravimetric moisture content, %

    Specific Heat

    Specific heat (or specific heat capacity) is defined here as the amount of energy (Joules) required to raise 1 kg of substance by 1 C and is used with density and thermal conductivity to determine thermal diffusivity.

    The following equations were used to calculate the thermal conductivity of aggregate base and soil (Farouki):

    CU = (0.18 + 1.0 * ω/100) * Cw

    CF = (0.18 + 0.5 * ω/100) * Cw

    where
    CU = specific heat (unfrozen)
    CF = specific heat (frozen)
    Cw = specific heat of water = 4187 J/(kg*K)

    Thermal Diffusivity

    Thermal diffusivity is a measure of heat propagation speed. It is calculated by (Chadbourn, et al):

    α = k/(ρCp)

    where:
    α = thermal diffusivity, m2/s
    k = thermal conductivity, W/(m*K)
    ρ = density, kg/m3
    Cp = specific heat, J/(kg*K)

    The following moisture contents were used to represent dry and wet conditions:

    Material ωdry ωwet
    Aggregate Base 5% 10%
    Soil 10% 20%

    Return to Mix Specifications

    Return to Existing Surface Materials

    Return to Table of Contents

  • Limitations

    This application can calculate the cooling of a hot-mix asphalt lift. It is not a replacement for good engineering judgment; rather it is a tool to give the user insight into how climate conditions will affect their ability to produce a durable, quality road surface.

    Cooling rate and compaction are only two of several factors affecting pavement quality. For further information contact your state department of transportation or your local Asphalt Pavement Association.

    Special consideration must be made for polymer modified asphalt binders. In this case, manufacturer guidelines should supersede recommendations made by this program.

    PaveCool is not to be used as a substitute for contract specifications.

  • References:

    Atkins, H.N., Highway Materials, Soils, and Concretes, Third Edition, Prentice-Hall, Columbus, Ohio, 1997.

    Chadbourn, B.A., Newcomb, D.E., Voller, V.R., De Sombre, R.A., Luoma, J.A., and Timm, D.H., “An Asphalt Paving Tool for Adverse Conditions,” Final Report MN/RC - 1998-18, Minnesota Department of Transportation, Office of Research Administration, St. Paul, MN, June 1998.

    DeSombre, R.A., Newcomb, D.E., Chadbourn, B.A. and Voller, V.R., “Parameters to Define the Laboratory Compaction Temperature Range of Hot Mix Asphalt,” Asphalt Paving Technology, Vol. 67, Association of Asphalt Paving Technologists, 1998, pp. 125-152.

    Farouki, O.T., Thermal Properties of Soils, Trans Tech Publications, 1986.

    Kersten, M.S., "Thermal Properties of Soils," Bulletin No. 28, University of Minnesota Institute of Technology Engineering Experiment Station, Vol. 52, n. 21, June 1, 1949.

    Voller, V.R., Newcomb, D.E., Chadbourn, B.A>, De Sombre, R., Timm, D. and Luoma, J.A., “A Computer Tool for Predicting for Cooling of Asphalt Pavements,” Proceedings of the Ninth International Conference on Cold Regions Engineering, Duluth, Minnesota, September 27-30, 1998, pp. 661-671.

  • Return to Table of Contents

Index

air temperature
asphalt delivery temperature
asphalt gradation
asphalt lift thickness
asphalt mixture
asphalt performance grade (PG)
base material
Beaufort Scale
calculate
date
date format
delivery temperature
display options
export data
gradation
latitude
lift thickness
mix specifcations
mixture type
paving time
PDF report
performance grade (PG)
report
save PaveCool file
save PaveCool report
sky conditions
specific heat
specifcations
temperature, air
temperature, delivery
thermal properties
thermal conductivity
thermal diffusivity
time
time format
title
units
wind speed