Cool Pavements

Urban Heat Island Mitigation Issues & Strategies—Hard Surfaces

Kamil Kaloush, Ph.D., P.E.Arizona State University

Tuesday, March 10, 2009

ASTER ThermalImaging Satellite

Mobile Transects

Laboratory Testing

31.6°C

61.8°C

40

50

60

IR Thermal Imagery

Embedded Thermocouples

UHI Evaluation Techniques

3

ASTER Satellite ImageryINTRODUCTION

Paved surfaces are 40% of the urbanized land cover in Phoenix

4

Time lapse infrared view of Chicago near Millennium Park

July 14 – 15, 2007

5:00AM

8:00AM

11:00AM

1:00PM

3:00PM

6:00PM

9:00PM

• Environmental considerations:

– air, surface, and subsurface temperatures, cloud cover, direct sun light / solar radiation, humidity level, wind velocity, and surrounding land cover.

• Physical parameters:

– material constituents, surrounding materials and anthropogenic heat sources, ground heat flux.

• Age and traffic.

Influencing Factors

Source of thermophysical properties: literature, laboratory and field tests.

Fundamental Properties

• Albedo, α

• Emissivity, ε– controls the far-infrared re-radiation from the surface back

to the sky.

• Convection Coefficient, h

• Thermal Conductivity, k

• Specific Heat, C

• Density, ρ

• Thermal Diffusivity, α,κ

• Porosity, φ

reflectedemitted

heat transfer to

air (convection)

Base material

Surface material conduction

incoming solar

radiation

(insolation)

reflectedemitted

heat transfer to

air (convection)

Base material

Surface material conduction

incoming solar

radiation

(insolation)

Location

Pavements During the Day

9December 2, 2008 9

Thin and Ultra-Thin Whitetopping PCC

Parking Areas

• Many options

– Reflective (high albedo) Pavements

• Increased operation life

• Improves thermal comfort for customers

Portland Cement Concrete

Comparing Surface Temperatures

10

Surface Chip Seals and Coatings:using reflective / light-colored chip / paints

“Gritting”:reflective chipsand aggregate

Shot-Blasting:abrading surface binder

Reflective Asphalt Pavements

Synthetic Binders:using reflective aggregates

December 2, 2008

Pervious / Porous Parking Lots

Laboratory Evaluation

Heat Transfer between Pavement and its Surroundings

Pavement

Solar Radiation,q”sol

Convection,h (To-T )

Irradiation,(To

4 –T4sky)

Ground (Natural Soil) Ground)

Air @T

Initial Condition: @t = 0s, T(0) = Tinitial

Boundary Condition: @x , T(t) Tinitial

Conduction to Deep Earth, kgrd T(t)

x

To

Tm

Ti

Tn

L

Tools - Models

- No. of Pavement Layers

- Density

- Specific Heat Capacity

- Thermal Conductivity

- Pavement Layer Thickness

- Pavement Layer Interface

Thermal Contact Resistance

- Albedo of Top Layer

- Emissivity of Top Layer

- Deep Ground Properties

- Temperature

- Depth

- Sky View Factor

- Solar View Factor

Simulation Runs

15

0

100

200

300

400

500

600

700

800

900

1000

28

32

36

40

44

48

52

56

60

64

68

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

Solar R

adiatio

n Flu

x (Wm

-2)

Tem

pe

ratu

re (o

C)

Time

(1) PPCC

(2) PPCC*

(3) PCC

(4) UTW

(5) HMA

Air Temp

Solar

16

U-haul : Permeable Pavement Evaluation

subbase

geotextile

Sub grade soil

Plastic grid and

membrane

decorative rock filler

Other ?

• Improve our understanding of how paving materials

interact with the urban climate.

• Advance the state of knowledge regarding technologies

and practices to mitigate UHI impacts.

• Address model and design practices, testing and standard

development, technological approaches, and planning and

policy considerations.

• Provide a home for TRB related activities (sessions,

workshops, reports, ..)

TRB AF000(2)

Pavement Materials and the Urban Climate

Thank You!

kaloush@asu.edu www.asuSMART.com

60,000 ft2 & NCE Home - LEED Silver