USE OF SOLAR HEAT-BLOCKING PAVEMENT TECHNOLOGYFOR MITIGATION OF URBAN HEAT
M.IWAMA, T. YOSHINAKA, S.OMOTO & N.NEMOTO
Research Institute, NIPPO Corporation, Japan
iwama_masahiko@nippo-c.jp, yoshinaka_tamotsu@nippo-c.jp
omoto_shinobu@nippo-c.jp, nemoto_nobuyuki@nippo-c.jp
ABSTRACTIn recent years, increased concern about global warming and climate change has made it
desirable for roadwork engineers to tackle environmental issues. In addition, there are also
concerns that the emerging environmental issue known as the “urban heat island”
phenomena, which significantly affects pedestrians as well as asphalt surfaces, may be
associated with paved roads in urban areas. In order to tackle this problem from a paving
perspective, solar heat-blocking pavement technology was developed to achieve thefollowing benefits: a reduction in surface temperature, and mitigation of urban heat. This
paper describes the environmental and practical effects of this technology through its
development and application, with the following conclusions being drawn from this study.
With regard to the temperature, field results show that the reduction in surface temperature
through use of the solar heat-blocking pavement is approximately 16qC. In terms ofserviceability, its application to airport taxiways reveals that this technology effectively
curtails rutting, since the rut depth is reduced to about half, compared to dense-gradedasphalt surfaces. Finally, computer simulation results indicate that solar heat-blocking
pavement is likely to be useful in mitigating the “urban heat island” effect, since
atmospheric temperatures can be decreased by 0.8qC in urban areas.
KEYWORDS
CLIMATE CHANGE; URBAN HEAT; HIGH ALBEDO; SUSTAINABILITY
1. INTRODUCTION
In recent years, the increase in temperatures during summer has become a serious
problem in Japan. In particular, as the surface of asphalt pavements may reach 60°C insummer, it is thought to be a factor in the “urban heat island phenomenon” whichsignificantly affects the thermal comfort of pedestrians. In addition, high surface
temperatures influence the performance of pavement surfaces, such as in terms of rutting,aging and fatigue [1]. Bearing in mind these problems, it can be said that a reduction insurface temperature has become an increasingly important issue, in terms of sustainability
as well as the environment.
Past studies have indicated that making surfaces lighter to reflect both visible and infrared
rays (i.e. sunlight) is the most practical way of mitigating road heat [2, 3, 4] . However, outof consideration for driver visibility, dark surfaces such as black or grey are preferable,
since drivers are used to such surfaces. In addition, taking into account onsite workability
during construction, surface treatment based on paint coatings is a practical way to handle
the issue on existing surfaces. For these reasons, a new surface treatment technology
called “solar heat-blocking pavement” is developed and applied in anticipation of reducing
surface temperatures and mitigation of urban heat [5, 6].
This paper highlights the basic concept behind the technology and addresses theenvironmental and practical effects through experiments and computer simulation.
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12. SOLAR HEAT-BLOCKING PAVEMENT
2.1. Basic concept
The basic concept behind this technology is to coat the developed material onto theexisting surface so as to enable reflection of the solar and infrared rays (see Figure 1 andFigure 2) [7]. The function of the material is based on higher reflectivity for near-infrared
rays and lower reflectivity for visible rays. In general, reflectivity of solar and infrared rays
is represented by “albedo” [8]. Higher albedo means that the pavement surface reflects
infrared rays from the surface, whereas lower albedo indicates that the pavement easily
absorbs infrared rays. Thus, a higher albedo surface is desirable to prevent heating,whereas a pavement surface with lower albedo would result in an increase in surface
temperature. Therefore, a solar reflective pigment was developed to prevent absorption of
infrared rays at the surface. Also, fine hollow ceramic particles are mixed with thematerials. The details of the particles are described in the following section.

Figure 1 – Solar Heat-blocking Pavement

Figure 2 – Concept of Solar Heat-blocking Pavement
2.2. Properties of solar reflective pigment
In order to examine the albedo characteristics, a comparison was made between threesurfaces: solar heat-blocking pavement, conventional pavement (i.e. dense-graded asphalt
pavement) and normal paint material. The test was conducted in accordance with theJapanese standard, JIS A 5759 [9]. In this case, the color for both the solar heat-blocking
pavement and the normal paint is grey, whilst that of the conventional pavement is black.
Figure 3 shows the comparison results. As shown in the figure, there are clear differences
between the solar heat-blocking pavement and conventional painting materials.
Conventional painting material has almost the same or a less reflective ratio across theentire wavelength. However, in the case of the solar heat-blocking pavement, the reflective
rate for near-infrared rays in the wavelength is much higher than others. This indicates thatthe solar heat-blocking pavement has higher albedo, despite the fact that the normal paintmaterial is the same color as the heat-blocking pavement.
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Albedo (%)

100

Visiblerays

Near infrared rays

80
60

Solar Heat-blocking Pavement (Grey)

40

Normal paint materials (Grey)

20

Straight asphalt 60/80(Black)04001000 1200 1400
1600 1800 2000
500600 800 1000
1500
2000 2200

Wavelength (nm)Figure 3 – Albedo characteristics of solar reflective pigment
2.3. Effect of fine hollow ceramic particles
As mentioned above, the solar reflective pigment itself can reflect solar radiation back into
the atmosphere. However, there is some concern that the reflected solar radiation may
heat surrounding buildings, which would not mitigate the urban heat island effect.
Therefore, it is necessary for the solar reflective pigment to have recursive reflection
properties.
The fine hollow ceramic particles enable the solar reflective pigment to have such function.
The particles have a spherical structure 5 to 150 μm in diameter (see Figure 4). By mixing
the particles with the solar reflective pigment, recursive reflection properties were expectedof the solar reflective pigment.
Gomado et al. investigated the recursive reflection property of Solar Heat-blocking
Pavement [10]. They used artificial sunlight and a specific sensor which measuresreflected near-infrared rays, and a series of experiments was conducted by changing thedirections of the sunlight and sensor. As a result, it was proved that the near-infrared rays
were reflected back in the same direction as those of sunlight. Although the effect of finehollow ceramic particles was not directly investigated, the result may explain the recursivereflection property of the ceramic particles.

Figure 4 – Fine hollow ceramic particles
3. LABORATORY EVALUATION OF SOLAR HEAT-BLOCKING PAVEMENT
In general, the performance of solar heat-blocking pavement depends on the state of thecoated layer. Therefore, it is important to evaluate the performance of the coated layer
before site application. This section describes the laboratory evaluation methods of solar
heat-blocking pavement and its results, looking at six properties: surface temperature; skid
resistance, stripping resistance, odor, weather resistance and permeability.
3.1 Laboratory lamp test
In order to investigate the reduction in temperature when using solar heat-blocking
pavement, laboratory lamp irradiation experiments were carried out, as per the Japanese
pavement performance reference [11]. The schematics and experimental results areshown in Figures 5 and 6.
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In this experiment, porous asphalt mixture is used for both the solar heat-blocking
pavement specimen and the conventional specimen. A special lamp with a similar
wavelength to sunlight was used to evaluate the performance. The detailed experimental
conditions are as follows:z Experiment temperature: 30°C (temperature control cabinet is preferable)z Lamp height: A height at which the surface temperature of the conventional specimen
reaches 60°C in about three hours, is applied for the test.
z Measurement method: Thermocouples are used to measure the surface temperature
Surface temperature䋨͠䋩

70

Lamp

Specimen

Porous asphalt

65
60
55

12.0͠

Solar Heat-blocking
Pavement

50
45
40
35

Porous asphalt

30

Solar Heat-blocking Pavement

25

Temperature
control cabinet
Figure 5 – Laboratory lamp test equipment

0

30

60

90
120
150
Elapsed time䋨min䋩

180

210

240

Figure 6 – Laboratory lamp test result

As can be seen from Figure 6, the results clearly show the difference between the two
specimens. Although the result is necessarily the same as the site temperature, laboratory
lamp tests are often used to confirm the performance of solar heat-blocking pigment
before site application to predict the on-site performance.
3.2 Skid resistance
Skid resistance is a factor affecting the serviceability of pavement. It is also closely related
to traffic accidents, especially in rainy days. Therefore, it is vital to ensure good skid
resistance after coating with a solar heat-blocking pigment. In order to confirm this effect,
the skid resistance of both coated porous asphalt and uncoated porous asphalt surfaces
are measured using a Dynamic Friction tester. Tests were conducted as per ASTM E1911[12]. The results are shown in Table 1.
Table 1 – Skid resistance result
Dynamic Test speed
Friction 40km/h(μ)
60km/hPorous asphalt

Solar Heat-blocking Pavement

0.60

0.62

0.55

0.56

From this result, it was found that the skid resistance values of the two surfaces are almost
identical. However, as described in the following sections, nonskid sand is sprayed on
immediately after the primary and secondary coating to ensure skid resistance. Therefore,
it can be said that an appropriate amount of sand needs to be sprayed on to ensure theskid resistance.
3.3 Stripping resistanceConsidering the service state, the coating layer of solar heat-blocking pavement should bestrong enough and have good bonding to the original asphalt surface. In order toinvestigate these factors, laboratory stripping resistance tests were conducted. A
schematic representation of the test equipment is shown in Figure 7.
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4Imageanalysis(b)(a)

Computer
Photo
Surface state after the test
Figure 7 – Stripping resistance test (a) Schematic of the equipment, (b) Image analysis
A test load was conducted, following laboratory stripping resistance test method for solar
heat-blocking pavement material [13].Test load was applied to the specimen by turning thetires to left and right directions. A summary of the test parameters is presented below:zzzz

Loading condition: Turning the tire to the left and right direction
Test temperature: 20°C
Test load: 686 N
Number of cycles: 650 times

After the test, a digital image of the specimen’s surface was taken with a digital camera.
Then, the stripping resistance of the solar heat-blocking layer is evaluated by computer
image analysis which can record the stripped area of the surface. The result is shown in
Table 2. Compared to the performance criteria set by one organization, the coated layer
demonstrates strong adhesion to the existing surface. However, the stripping state
depends on the original condition of the surface as well as the solar heat-blocking material.
Therefore, in practice, the stripping state needs to be evaluated in every construction job.
Table 2 – Stripping test result
Stripping area rate (%)
Performance requirement
Solar Heat-blocking Pavement

Less than 40%
9.9%Note: Stripped area rate = (stripped area/ tire contact area) u100

3.4 Odor
Solar reflective material contains Methyl Methacrylate (MMA) resin. If applying solar heatblocking material in urban areas, there are some concerns that the smell of the material
may affect people living nearby. Therefore, the emission of odors should be minimized asmuch as possible during construction.
In such case, a less odorous type of material (i.e. odor-reduced resin) can be selected as
the solar heat-blocking material rather than conventional material. In order to evaluate thiseffect before construction, odor testing is conducted in accordance with laboratory odor
measurement method [14]. The test equipment is shown in Figure 8.
Test cabinet

Odor sensor

Air flow
Specimen
Figure 8 – Odor testing equipment [14]IP446-Iwama-E.doc

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As can be seen in the above photo, solar heat-blocking material is set in the cabinet; theodor of the materials is measured using an odor sensor. The maximum value of the odor isrecorded during the measurement. The detailed test conditions are shown below:
z
z
z
z
z

Air flow: 0.14 L/s (wind velocity: 0.2 m/s)
Test duration: 20 minutes
Measurement value: Odor level
Test temperature and humidity: 20°C, 50%
Specimen mass: 1.0 g

Table 3 shows the measurement results. These results clearly show the difference
between conventional and odor-reduced materials. The odor level for the conventional
material is about four times that of the odor-reduced type. Also, the odor-reduced material
meets the requirements set by the organization. In addition, the same surface performanceas conventional material has been confirmed for the odor-reduced material. Therefore, it ispossible to construct solar heat-blocking pavement even in urban residential areas if theodor-reduced type of material is selected for the solar heat-blocking pavement.
Table 3 – Odor level of Solar Heat-blocking Material
Types of Solar Heat-blocking Pavement

Odor level

Performance requirement for urban areas

300

Odor-reduced solar heat-blocking material

217

Conventional solar heat-blocking material

889

3.5 Weather resistanceIn order to confirm the weather resistance of the solar heat-blocking pavement,
accelerated weathering tests, which simulate natural environmental conditions such as
ultraviolet rays and rain in an enclosure, were carried out for 3,000 hours in total using
cores taken from trial pavements. The tests were as per ASTM G-53 [15] and a series ofexperiments was conducted. In general, conducting an accelerated weathering test for
3,000 hours is equivalent to 12 years exposure on site. After conducting the QUV test, thesolar heat-blocking pavement specimens were examined. Test conditions were as follows:zzzz

Test duration: 400 hours/time
Temperature: 60±3°C
Rain simulation: 18 minutes/120 hours
Rainfall pressure: 1.0 kgf/m3

Table 4 shows the results of the accelerated weathering test for the specimens. The
results showed a good trend as the weather resistance ratio was approximately 94 percent
after 3,000 hours. In addition, in terms of solar radiation, the solar reflective ratio, as per
JIS A 5759 [9], was 48.1 percent. This was less damage than the initial condition recordedof 51.2 percent. Therefore, it can be said that the solar heat-blocking pavement affords
good weather resistance.
Table 4 – Weather resistance of Solar Heat-blocking Pavement
Test duration(hour)

Solar reflective
ratio (%)

Weather resistanceratio (%)

Remarks

0
3,000

51.2
48.1

93.9

Initial condition
After required exposure

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3.6 Permeability
Porous asphalt surface has been the most popular type used in Japan. Considering therecent application of porous asphalt pavement, it is likely that solar heat-blocking materials
will be applied to porous asphalt surfaces as well as conventional dense-graded surfaces.
The advantage of the porous asphalt surface is that it reduces rain spray, in addition to
cutting tire noise.
In terms of permeability, it was predicted that solar heat-blocking material would clog up
the air voids of existing porous surfaces. Therefore, on-site permeability tests were
performed to ensure the performance. The tests were conducted using a cylindrical tube
filled with 400 ml of water. Then, the time taken for the 400 ml of water to flow wasmeasured. The calculation procedure for the determination of permeability is as follows:zzz

The tests are conducted three times;
The mean time for 400 ml of water to flow should be calculated;
The permeability of the asphalt mixture is determined by calculating the volume ofwater flow per 15 seconds.

Table 5 shows the test results for both normal and coated asphalt surfaces (i.e. porous
asphalt with solar heat-blocking material). In terms of permeability, the normal porous
asphalt surface drained at 1,222 cc/15 seconds, whereas the coated porous asphalt
surface drained at 1,210 cc/15 seconds. This result suggests that the coated porous
asphalt surface is permeable enough, even though the solar heat-blocking materials cover
the existing surface. As a result, it is possible to apply solar heat-blocking material toporous asphalt surfaces since the coated surface satisfied permeability requirements.
Table 5 – Result of the permeability test
Surface type
Permeability (cc/15 s)

Normal porous asphalt
1,222

Coated porous asphalt
1,210

4. APPLICATION OF SOLAR HEAT-BLOCKING PAVEMENT
4.1 Construction method
Solar heat-blocking pavements can be constructed by applying the developed solarreflective pigment to existing surfaces. In practice, MMA resin is used as the solarreflective material. The MMA type includes a two-component resin. The coating layer isabout 1.0-mm thick and consists of three components: priming layer, secondary layer andnonskid sand (see Figure 9). Firstly, the priming layer is applied to cover the existing
surface and to attach the ceramic particles to the surface; then the nonskid sand issprayed on immediately after the primary coating to ensure skid resistance; and finally, thesecondary layer is applied as the colored surface and to sandwich the nonskid sand. After
curing for an hour, the site can be reopened to traffic. The coating work is normally
performed with a specialist spray gun as shown in Figure 10.
Second layer
Prime layer
Nonskid sands are sandwithed between two layers
Coating thickness
Approx. 1 mm

Porous Asphalt Pavement

Figure 9 – Section of Solar Heat-blocking Pavement
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7

Figure 10 – MMA-type construction

4.2 Effect of temperature reduction

Surface temperature (OC)In order to examine the effect of temperature reduction, conventional pavement (i.e.
dense-graded asphalt pavement) and solar heat-blocking pavement were compared in thefield. The traffic classification of the field is more than 250 and less than 1,000
vehicles/day for heavy traffic. Figure 11 shows the temperature of the two surfaces. It canbe seen that the maximum surface temperature of the solar heat-blocking pavement wasapproximately 42qC, whilst that of conventional pavement was around 58qC; the difference
between the two surfaces reaching about 16qC. Therefore, the result clearly shows theadvantage of the solar heat-blocking pavement in reducing the surface temperature insummer.
Conventional pavement

60

16䍽C

50
40
30

Air
Solar heat-blocking pavement

20
Kyoto, 8/11䌾8/13/2004

10

0:00

12:00

0:00

12:00

0:00

12:00

0:00

Time (hour)

Figure 11 – Effect of temperature reduction
4.3. Mitigation of rut depth
The performance of solar heat-blocking pavement was demonstrated in the field. However,considering its long-term performance and further improvements in the technology, it isnecessary to examine its durability as well as the surface temperature under severe traffic
conditions and prolonged periods. In order to investigate these effects, solar heat-blocking
pavement was applied to the taxiway of an international airport (see Figure 12). Rut depth
for the two surfaces (i.e. dense-graded pavement and solar heat-blocking pavement) was
measured during regular monitoring.
Figure 13 compares the maximum rut depth of the two pavements during the four-year
monitoring period. As can be seen from the figure, the solar heat-blocking pavement can
reduce the maximum rut depth by half, when compared to that of dense-graded pavement.
As a result, a clear difference is evident between solar heat-blocking pavement and densegraded pavement, in terms of rut depth. Therefore, it can be said that the solar heatblocking pavement is an effective means of improving rut resistance [16, 17].
Rut depth (S.H.P.)

50

Rut depth (Conventional)Max. rut depth (Conventional)

40

40

Max. rut depth (S.H.P.)

34

30

30

20

16

10

10
0 0

0
After

20

0 0

0 0

1 1

0 0

0

2 months 1 year 1.5 years 2 years 2.5 years 3 years 3.5 years 4 years 4.5 years

2006.7

2007

2008

2009

Figure 12 – Application to an airport taxiway Figure 13 – Changes in the maximum rut
depth
over
four
years
(Hayakawa et al.)
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Rut depth (mm)Max. rut depth (mm)50

4.4 Noise reduction
In the case of applying the solar heat-blocking material to the porous asphalt surface,
there are also some concerns about noise reduction. This is because the materials may
clog up the air voids in the porous asphalt surface. Therefore, tire noise measurements
were conducted on the porous asphalt surface before and after coating with thesematerials. A schematic representation of the noise measurement is shown in Figure 14.
The noise from the surface is measured using a vehicle equipped with a microphone. The
measurement was conducted at a speed of 50 km/h. Table 6 shows the results of thenoise measurements. From these results, it was found that the existing porous asphalt
surface reached 88.3 dB (A), whereas the porous surface coated by the solar heatblocking material achieved 87.9 dB (A).
Tire
Microphone
Surfacelayer
Figure 14 – Schematic of the noise measurement
Table 6 – Noise measurement result
Noise level on porous asphalt
Level (Iwama et al.)Level (Tomonaga et al.)Before coating
88.3
91
Specific Tire
After coating
87.9
90
Noise dB (A)A year after coating
91
Tomonaga et al. also conducted the same investigation and also recorded a similar result(see Table 6) [18]. As a result, it can be said that the porous asphalt pavement coated withsolar heat-blocking materials retains its original performance levels, despite the materials
being coated on top of the existing porous asphalt surface.

5. THERMAL SENSATION FOR PEDESTRIANS
5.1 Thermal sensation experienced by pedestrians
In order to investigate how solar heat-blocking pavement improves the thermal sensation,
a comparative trial was conducted on a hot summer’s day when the external temperature
ranged between 30°C and 35°C. Under these conditions, the unshaded pavement surface
temperatures were found to vary by as much as 12°C.

Figure 15 - Volunteers in photographic image Figure 16 - Volunteers in thermographic
Left: Conventional pavement
image
Right: Solar Heat-blocking Pavement(Surface temperature: Approx 38°C)
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9Figures 15 and 16 show the photographic and thermographic images of two similarly
clothed men standing on a test bed of the two surfaces. Comparing the two images, it isapparent that the surface temperatures of the two pavements were significantly different.
As shown in Figure 16, the conventional surface is colored white in the sunny areas, whichindicates a surface temperature of more than 51°C, whereas the solar heat-blocking
pavement is a reddish-orange hue, representing a surface temperature of around 46.5°C.
The effectiveness of the solar heat-blocking pavement is evident from the thermographic
image. Tomonaga et al. also conducted a similar investigation, and they also concluded
that the heat radiated from the solar heat-blocking pavement is less than that fromconventional porous asphalt pavement [18]. Therefore, it can be said that solar heatblocking pavement contributes to an improved thermal sensation, especially around thefeet.
5.2 Questionnaire for human sensation
A survey concerning human sensation was conducted. Six assessors (i.e. three males andfemales in their 20’s to 30’s, respectively) were chosen at random. Also, the assessors
checked the sensation when standing on both conventional and solar heat-blocking
pavement for three minutes, respectively (see Figure 17). The ambient air temperature
was approximately 35°C. Questions the assessors answered in the survey concerned thethermal impact around the body and feet, and how sweaty they felt. Summarized resultsfrom the questionnaire are shown in Figure 18.
For conventional pavement (i.e. dense-graded asphalt pavement), 35 percent of theassessors adjudged the surface to be “very hot”. Including those who answered “ratherhot”, almost all assessors recognized conventional pavement as hot, whereas for the solar
heat-blocking pavement, some assessors identified that surface to be “cool” or “rathercool”.

Figure 17 – Experimental state for questionnaire

9%

12%

18%
27%
Solar heat-blocking
pavement28%

䂓 Very hot䂓 Hot䂓 Rather hot䂔 Neither䂓 Rather cool
䂓 Cool35%

12%
Conventional
pavement

41%

18%

Figure 18 – Thermal sensation around feet
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62%
Solar Heat-blocking
Pavement

19%
Conventional
Pavement

Figure 19 – Comfort levels
Figure 19 presents comparisons between conventional pavement and solar heat-blocking
pavement from the questionnaire. From these results, 19 percent of the assessors judged
conventional pavement as comfortable, while 62 percent of them considered solar heatblocking pavement as comfortable.
Kinouchi et al. also investigated the impact on human thermal sensation using WBGT [8].
From their research, it was found that a high albedo pavement provides a more
comfortable feeling than lower albedo pavement. Therefore, it can be said that solar heatblocking pavement mitigates thermal sensation around the feet.

6. ENVIRONMENTAL EFFECT
6.1. Atmosphere
Although the surface temperature can be reduced by the solar heat-blocking pavement, it
is difficult to verify how the pavement contributes to the reduction in atmospherictemperature in urban areas. In order to examine the influence of surface type on
atmospheric temperature, laboratory tests were conducted. The conditions of thelaboratory tests are shown in Figure 20.
In this test, a comparison was made between conventional pavement and solar heatblocking pavement. The test was conducted by shining light as artificial sunlight onto slabtype specimens in a cabinet; both surface and atmospheric temperatures were measured
simultaneously by thermo-couples. Figure 21 illustrates the relationship between
temperature reduction and the test duration. As can be seen in the figure, the results
clearly demonstrate the advantages of the solar heat-blocking pavement in terms of both
surface temperature and atmospheric temperature. This demonstrates that the solar heatblocking pavement is likely to be useful in mitigating the “urban heat island” effect.

Temperature 䋨͠䋩2520

Difference between conventional andSolar Heat-blocking Pavements

Difference in surface temp.

15
10

Difference in atmospheric temp.

500 㪈㪑㪇㪇
1 㪉㪑㪇㪇
2 㪊㪑㪇㪇
3 㪋㪑㪇㪇
4 㪌㪑㪇㪇
5 㪍㪑㪇㪇
6 㪎㪑㪇㪇
7 㪏㪑㪇㪇
8 㪐㪑㪇㪇
9 㪈㪇㪑㪇㪇
10㪇㪑㪇㪇
Testing times 䋨hours䋩

Figure 20 – Laboratory tests on atmospherictemperatures(left: conventional, right:S.H.P.)
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Figure 21 – Environmental effects
11

6.2. Computer simulation
The effect of the solar heat-blocking pavement was shown through field experiments andapplication. However, it is difficult to verify how solar heat-blocking pavement may
contribute to the reduction of urban heat wave. In order to investigate such effect, acomputer simulation was conducted by Kinouchi et al. [19].
In this simulation, it is assumed that solar heat-blocking pavement is applied to central
Tokyo, and the albedo increases from 14% to 60%. A sunny day in summer is assumed.
The ranges of temperature change are assumed to be 366 u 366 [km] as the main domain(Kanto area) and 114 u 114 [km] as a nest domain (center of Tokyo). The temperatures ata height of 1.5 m above the ground will be calculated.
The changes in air temperature due to the use of solar heat-blocking pavement are shownin Figure 22. The result indicates that air temperatures in central Tokyo tend to decrease.
Also, the air temperature is reduced by more than 0.8°C due to the reduction in surface
temperature. Thus, this technology is highly effective at mitigating urban heat islands.

366 kmElevation (m)Nest domain:
Center of Tokyo
366 kmKanto area:Japan

Figure 22 – Changes in atmospheric temperature by use of Solar Heat-blocking Pavement
In addition, calculations of sensible heat flux in the streets were carried out in case ofincreasing the surface albedo. In this case, the following condition was assumed for thesimulation; air temperature is 35°C; wind velocity is 5 m/s; surface albedo is 0.1 and 0.5.
The schematic of the simulation model is shown in Figure 23, and the calculation results
were shown in Figures 24 and 25.

10m 10m

10m

Air temperature (z=50 m): 35°C
Wind velocity (z=50 m): 5 m/s
Surface albedo: 0.1, 0.5

Figure 23 – Computer simulation model
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As can be seen in the results, the amount of sensible heat in the streets, which heats theatmosphere, decreased due to the increased reflectivity. As a result, the reduction in air
temperature in the streets improves the urban heat environment. Therefore, it can be said
that the effect of heat reduction is greater due to retro reflection.

㪇㪅㪋
㪇㪅㪊

Surface albedo: 0.5

㪇㪅㪉
㪇㪅㪈
㪇
㪇 㪉 㪋 㪍 㪏 㪈㪇 㪈㪉 㪈㪋 㪈㪍 㪈㪏 㪉㪇 㪉㪉 㪉㪋

Sensible Heat Flax (W/m2)

Albedo of all streets

㪇㪅㪌

㪌㪇㪇

Surface albedo: 0.5

㪋㪇㪇
㪊㪇㪇
㪉㪇㪇
㪈㪇㪇
㪇

㪄㪈㪇㪇 㪇 㪉 㪋 㪍 㪏 㪈㪇 㪈㪉 㪈㪋 㪈㪍 㪈㪏 㪉㪇 㪉㪉 㪉㪋

Change in the albedo of all streets with time㩷

Figure 24 – Change in albedo of all streetswith time㪍㪇㪇Sensible heat flax from all streets㩷Figure 25 – Sensible heat flux from all streets

7. CONCLUSIONSThis paper presents the development and application of solar heat-blocking pavement to
mitigate urban heat. Based on the results of laboratory experiments, field applications andcomputer simulations, the following conclusions can be drawn:
z

z

z

z

z

With regard to the performance of solar heat-blocking pavement, the surface
temperature is reduced by approximately 16qC compared to conventional densegraded asphalt paving due to the prevention of solar radiation.
Solar heat-blocking pavement can effectively reduce rutting, as the rate (based on rut
depth) was approximately half compared to the dense-graded asphalt surface used at
an airport taxiway.
In terms of the thermal sensation for pedestrians, the results of questionnaires
demonstrate that the solar heat-blocking surface contributes to improving the thermal
sensation around their feet.
From the view of laboratory experiment, this technology would be highly effective inalleviation of “urban heat” since a comparison between conventional and solar heatblocking pavements shows advantages both in surface and laboratory atmospherictemperatures.
With respect to computer simulations, the results indicated that solar heat-blocking
pavement is likely to be useful in mitigating the “urban heat island” effect, since
atmospheric temperatures can be reduced by 0.8qC in urban areas.

Solar heat-blocking pavement has to be improved and enhanced to tackle global warming
and climate change. However, considering the long-term durability and life-cycle costs ofroads with solar heat-blocking pavement, there are still some concerns about thetechnology. Therefore, further research looking at these issues is needed to build
sustainable roads in the future.

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REFERENCES
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