Presentation Information
[O12-P75]Evaluation of the Impact of Heat-Reflective Pavement on Urban Air Temperature
*Hinata Kikuchi1 (1. Tokyo Gakugei University Senior High School)
Keywords:
Heat reflective pavement,The urban heat island phenomenon,Reflectivity
Background
In recent years, the urban heat island effect has become a serious issue, partly caused by artificial road surfaces. Heat-reflective pavement has been introduced as a countermeasure, as it reflects sunlight during the day and reduces heat release at night. However, its impact on air temperature above the pavement remains unclear, and no consensus has been reached.
Objective
The objective of this study is to advance the ongoing debate by evaluating the thermal characteristics of heat-reflective pavement and to examine pavement types that may effectively mitigate the urban heat island phenomenon.
Experiment 1: Model Experiment Method
Four pavement models were prepared: Untreated asphalt Model (1) coated with a heat-reflective paint (Miracool Co., Ltd.: Miracool Road Wα Gray; water-based acrylic resin containing special aggregates and fibers) Model (1) coated with a synthetic resin paint of the same color as in (2) Model (1) coated with a black synthetic resin paint For each model, reflected light was measured using a smartphone application.
Reflection can be classified into specular reflection, diffuse reflection, and retroreflection. It is known that incident light on heat-reflective pavement undergoes retroreflection. First, the reflectance of each model was determined.
Next, the four models were placed outdoors so that sunlight was incident vertically, and surface temperatures were measured every 5 minutes for 30 minutes using an infrared thermometer. This measurement was repeated on multiple days. Simultaneously, solar radiation energy was calculated using a simple pyranometer and a mathematical model.
Results
(Fig.15–19 and Table 2)
Only the heat-reflective pavement exhibited retroreflection. When ranking the models by the rate of surface temperature increase:
① > ④ > ③ > ②
From Fig.15 and Table 2: By material: conventional asphalt > synthetic resin paint > heat-reflective paint By color: black > cool gray Using these results, the relative reflectivity was estimated. Taking conventional asphalt as the baseline: Model ②: 2.4 times, ③: 1.3 times, ④: 1.4 times These findings were used in conjunction with Experiment 2.
Experiment 2: Outdoor Air Temperature Measurement Method
From 6:00 AM to 8:00 PM, air temperatures above conventional asphalt and heat-reflective pavement were measured hourly. Measurement heights were set at 0 cm (surface temperature), 50 cm, 100 cm, 150 cm, and 200 cm above the ground. Surface temperature was measured using an infrared thermometer, while temperatures at other heights were measured using rod thermometers.
Results and Discussion
(Fig.20 and Fig.21)
Only the heat-reflective pavement exhibited retroreflection. When ranking the models by the rate of surface temperature increase:
①>④>③>②
From Fig.15 and Table 2: By material: conventional asphalt > synthetic resin paint > heat-reflective paint By color: black > cool gray Using these results, the relative reflectivity was estimated. Taking conventional asphalt as the baseline: Model ②: 2.4 times, ③: 1.3 times, ④: 1.4 times These findings were used in conjunction with Experiment 2.
Experiment 2: Outdoor Air Temperature Measurement Method
From 6:00 AM to 8:00 PM, air temperatures above conventional asphalt and heat-reflective pavement were measured hourly. Measurement heights were set at 0cm (surface temperature), 50cm, 100cm, 150cm, and 200cm above the ground. Surface temperature was measured using an infrared thermometer, while temperatures at other heights were measured using rod thermometers.
Results and Discussion
(Fig.20 and Fig.21)
No significant difference in air temperature was observed between heat-reflective pavement and conventional asphalt pavement. Combined with the results of Experiment 1, this suggests that reflected solar radiation still contributes to heating the surrounding air.
Future Prospects
In Experiment 1, reflectance was measured using a simplified method. In future work, the method described in “Measurement of Solar Reflectance of Building Materials Based on Spectral Reflectance: Examination of Measurement Conditions” (Sakai et al., 2007) will be adopted to obtain more precise values.
Additionally, since it was not possible to strictly match reflectance between conventional asphalt and synthetic resin surfaces, comparison was limited. Establishing a method to equalize reflectance will enable more accurate comparisons.
Furthermore, as part of Experiment 1 and all of Experiment 2 were conducted outdoors, the influence of environmental factors cannot be ruled out. Future experiments will be conducted under controlled indoor conditions to improve data accuracy.
In recent years, the urban heat island effect has become a serious issue, partly caused by artificial road surfaces. Heat-reflective pavement has been introduced as a countermeasure, as it reflects sunlight during the day and reduces heat release at night. However, its impact on air temperature above the pavement remains unclear, and no consensus has been reached.
Objective
The objective of this study is to advance the ongoing debate by evaluating the thermal characteristics of heat-reflective pavement and to examine pavement types that may effectively mitigate the urban heat island phenomenon.
Experiment 1: Model Experiment Method
Four pavement models were prepared: Untreated asphalt Model (1) coated with a heat-reflective paint (Miracool Co., Ltd.: Miracool Road Wα Gray; water-based acrylic resin containing special aggregates and fibers) Model (1) coated with a synthetic resin paint of the same color as in (2) Model (1) coated with a black synthetic resin paint For each model, reflected light was measured using a smartphone application.
Reflection can be classified into specular reflection, diffuse reflection, and retroreflection. It is known that incident light on heat-reflective pavement undergoes retroreflection. First, the reflectance of each model was determined.
Next, the four models were placed outdoors so that sunlight was incident vertically, and surface temperatures were measured every 5 minutes for 30 minutes using an infrared thermometer. This measurement was repeated on multiple days. Simultaneously, solar radiation energy was calculated using a simple pyranometer and a mathematical model.
Results
(Fig.15–19 and Table 2)
Only the heat-reflective pavement exhibited retroreflection. When ranking the models by the rate of surface temperature increase:
① > ④ > ③ > ②
From Fig.15 and Table 2: By material: conventional asphalt > synthetic resin paint > heat-reflective paint By color: black > cool gray Using these results, the relative reflectivity was estimated. Taking conventional asphalt as the baseline: Model ②: 2.4 times, ③: 1.3 times, ④: 1.4 times These findings were used in conjunction with Experiment 2.
Experiment 2: Outdoor Air Temperature Measurement Method
From 6:00 AM to 8:00 PM, air temperatures above conventional asphalt and heat-reflective pavement were measured hourly. Measurement heights were set at 0 cm (surface temperature), 50 cm, 100 cm, 150 cm, and 200 cm above the ground. Surface temperature was measured using an infrared thermometer, while temperatures at other heights were measured using rod thermometers.
Results and Discussion
(Fig.20 and Fig.21)
Only the heat-reflective pavement exhibited retroreflection. When ranking the models by the rate of surface temperature increase:
①>④>③>②
From Fig.15 and Table 2: By material: conventional asphalt > synthetic resin paint > heat-reflective paint By color: black > cool gray Using these results, the relative reflectivity was estimated. Taking conventional asphalt as the baseline: Model ②: 2.4 times, ③: 1.3 times, ④: 1.4 times These findings were used in conjunction with Experiment 2.
Experiment 2: Outdoor Air Temperature Measurement Method
From 6:00 AM to 8:00 PM, air temperatures above conventional asphalt and heat-reflective pavement were measured hourly. Measurement heights were set at 0cm (surface temperature), 50cm, 100cm, 150cm, and 200cm above the ground. Surface temperature was measured using an infrared thermometer, while temperatures at other heights were measured using rod thermometers.
Results and Discussion
(Fig.20 and Fig.21)
No significant difference in air temperature was observed between heat-reflective pavement and conventional asphalt pavement. Combined with the results of Experiment 1, this suggests that reflected solar radiation still contributes to heating the surrounding air.
Future Prospects
In Experiment 1, reflectance was measured using a simplified method. In future work, the method described in “Measurement of Solar Reflectance of Building Materials Based on Spectral Reflectance: Examination of Measurement Conditions” (Sakai et al., 2007) will be adopted to obtain more precise values.
Additionally, since it was not possible to strictly match reflectance between conventional asphalt and synthetic resin surfaces, comparison was limited. Establishing a method to equalize reflectance will enable more accurate comparisons.
Furthermore, as part of Experiment 1 and all of Experiment 2 were conducted outdoors, the influence of environmental factors cannot be ruled out. Future experiments will be conducted under controlled indoor conditions to improve data accuracy.