全球暖化造成熱島效應影響，使得城市溫度逐漸加劇，瀝青混凝土土鋪面在全天陽光照射吸熱與放熱中占重要角色，並對用路人對於環境溫度感受之舒適感造成影響，若能維持原始鋪面功能與安全並降低鋪面吸收太陽光輻射溫度，可有效改善此問題。本研究使用具有反射輻射熱波長效果之材料(包含氧化鈦TiO2和氧化鋯ZrO2)加入黏結劑中作為遮熱性塗料，塗裝於瀝青混凝土鋪面表層，來降低蓄積在鋪面中溫度；同時鋪灑抗滑粒料維持行車安全性，以反射率試驗進行反射材料和不同塗層厚度與輻射熱波長之關係，並使用室內照射試驗方法評估降溫效果，進而探討遮熱性瀝青混凝土鋪面績效之抗車轍能力。研究結果顯示，反射材料中氧化鈦優於氧化鋯，且氧化鈦在添加反射材料比例10%以上與塗層厚度0.6mm時即有80%之反射率。室內照射試驗結果顯示在遮熱性材料塗層厚度在0.7mm以上時，瀝青混凝土溫度降溫變化趨於穩定，在塗層厚度0.9mm時可降溫12.6°C。遮熱性瀝青混凝土由於累積溫度下降，進而對降低交通荷重產生之車轍變形量，可有效提高鋪面績效與壽命。

SUMMARY

This study manages to decrease the heat stored in pavements with the materials reflecting radiation wavelengths. Material including TiO2 and ZrO2 are added into adhesives as heat-reflection coatings, which then painted on the surface of asphalt pavements. In order to realize the relationship between reflective materials and radiation wavelengths, reflectivity tests are performed . In addition, it is laboratory lamp test which can probe into more resistant against rutting that we take the advantage of to evaluate cooling effects of asphalt pavements. The experiment indicates that among the reflective material, TiO2 is better than ZrO2. Adding over 10% TiO2 and the coating thickness over 0.6mm could help achieve 80% reflectivity. With regard to the temperature, laboratory lamp test shows that the pavement temperature can be lowered by 12.6°C when the coating thickness is reached to 0.9mm. Due to the reducing temperature of asphalt pavement with coating heat-reflection, it can both reduce the rutting depth by traffic loading and enhance the performance and life of pavements.

Key words: heat–reflection, TiO2, reflectivity, laboratory lamp test

INTRODUCTION

In recent summers, the surface of asphalt pavements may exceed 60°C in Taiwan after a period of exposure to the burning sunlight. This phenomenon not merely affects the thermal comfort of pedestrians significantly but also influences the performance of pavement surfaces. The growing temperature of asphalt pavements may influence strength of pavement, cause permanent rut deformation and hence deteriorate the service quality of the whole pavements. Bearing in mind these problems, it’s imperative to improve the asphalt pavements to defend the high temperature and to lower the blemish of city livings causing from growing temperature. This study will use the heat-reflection coatings applied to dense-grade asphalt pavement to evaluate its effect on pavement and cooling effect for environment.
The research organization in Japan has set about the study of the cooling effect of pavement with the basic concepts are coating the heat-reflection on asphalt pavements to reflect some heat radiated from the sun, adding water-retaining material on the pavement surfaces to reduce the heat when the water evaporates, improving pavements to keep away from rutting, and consequently supply pedestrians a more comfortable pathway. From the laboratory lamp test, the pavement temperature is reduced by approximately 13°C with regard to the performance of pavements with heat-reflection coatings, and we can effectively reduce rutting, as the rut depth is approximately half of the conventional dense-graded asphalt pavements.

 
MATERIALS AND METHODS

This study measures the reflectivity of coating materials with the UV/VIS/NIR spectrophotometer, under the conditions of first, 5%, 10% and 25% mixed ratio between reflection materials and adhesives and second, 0.6mm, 0.8mm, 0.9mm, and 1mm coating thickness , to find out the proper parameters among them.
Then, the study analyses the cooling effect of pavement with coating heat-reflection materials by observing the difference of the depth 2.5cm and 5cm to measure the relativity between depth and its capacity to heat ;and finally evaluate the performance of pavement by rutting test at 60°C, 55°C and 50°C testing temperature.

RESULTS AND DISCUSSION

The results of reflection test under the conditions that coating thickness between 0.6 and 1mm have showed that the reflectivity of ZrO2 coatings will be rising in sync when the coating thickness enhances, but the reflectivity of TiO2 coatings remains on about 90% no matter how its thickness changes. In addition, if TiO2 added to the adhesives spills over 10 weight percentages, the reflectivity of TiO2 doesn’t show conspicuous variations, nearly reach to a constant value.

From the laboratory lamp test, when the coating thickness reaches over 0.7mm, pavements with heat-reflection coatings will achieve the maximum of cooling effect. Furthermore, compared with variations on resistance against rutting, we can find pavements with heat-reflection coatings are much better than conventional pavements, and could improve dynamic stability of pavement for 1.1~1.2 times.

CONCLUSION

This study presents the performance of heat-reflection coatings on dense-graded pavement. Based on the results of reflectivity test, laboratory lamp test and rutting test, the following conclusions can be described:
(1)Under the same percentage of 25 of weight and wavelength 1100nm, the reflectivity of TiO2 and ZrO2 are 90% & 70% showing a better reflective effect compared to the original 4~5% conventional asphalt pavement. In addition, TiO2 surpasses ZrO2 on the effect of reflectivity.
(2)When coating thickness reaches above 0.9mm, the reflectivity will achieve its maximum no matter TiO2 or ZrO2, and would not change in sync with its thickness.
(3)The coating thickness has remarkable effect on lower the temperature, and will achieve a stable value above 0.7mm. It is 12.6°C lower compared to dense-graded asphalt pavements at the depth of 2.5cm of asphalt pavement. And owing to the effect to reduce the temperature, it could improve dynamic stability of pavement for 1.1~1.2 times than the conventional, significantly enhancing the life of pavement.

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