本研究量測瀝青混凝土介電常數並探討影響瀝青混凝土介電性質之因素，藉介電常數值建立與密度之關係，同時發展瀝青混凝土介電常數預測密度之模型。此外，評估非破壞性密度檢測運用於鋪面施工之品質控制，使其在工程上具應用價值。實驗室介電量測使用終端開路同軸探棒（Open-Ended Coaxial Probe）量測瀝青、粒料及瀝青混凝土試體之介電性質，因介電性質為電場頻率之函數，以7GHz頻率建立孔隙率、瀝青含量、溫度、含水率與介電常數之間的關係，結果顯示孔隙率每增加1%，瀝青混凝土試體介電常數值降低0.07。在相同孔隙率範圍，瀝青含量增加，介電常數降低。若水存在於瀝青混凝土孔隙中，受水分子極化機制影響，介電常數與損失因子隨含水率的提高而增加。在密度預測模型方面，以介電混合理論模型為基礎，由瀝青混凝土各組成成分及體積分率計算介電常數值，並與瀝青混凝土整體介電常數實驗量測值比較。最後利用瀝青混凝土試體孔隙率、瀝青含量以及介電常數進行迴歸分析，建立密度預測模型，密度預測值與實驗值之相關性R2為0.94，此模型將有助於發展非破壞性瀝青混凝土密度檢測。

關鍵字：瀝青混凝土、密度、介電常數、非破壞性測量

This study describes dielectric properties of asphalt concrete and establishes the relationship between dielectric constant and density of asphalt concrete. By doing so, the dielectric model for predicting density from dielectric constant is established. Besides, this study also aims to evaluate the application of non-destructive density measurement to pavement construction and its quality control in order to increase its practical utility on construction. An open-ended coaxial probe is used for measuring the dielectric properties of bitumen, aggregate, and asphalt concrete specimens. 7GHz frequency is accessible to establish the relationship between porosity, bitumen content, temperature, moisture content, and dielectric constant. The results showed that every increase of 1 percent porosity led to a decrease in the value of dielectric constant to 0.07. Moreover, in the same porosity, the dielectric constant decreases with the increase of bitumen content for asphalt concrete specimens. If water exists in the pores of the asphalt concrete, water molecules would be affected by the polarization mechanism, and therefore dielectric constant and loss factor raise with the increase of moisture content. As for density prediction model, based on dielectric mixing theoretical model, the dielectric constant value of asphalt concrete is calculated by the constituent and volume fraction of asphalt concrete, and is compared with measured value as well. A multiple nonlinear regression model is developed to relate the porosity, bitumen content, and the dielectric constant of the specimens at 7GHz. The statistical analysis indicates that the regression model is highly significant. This model will contribute to the development of non-destructive testing of density of asphalt concrete.
Keyword: Asphalt Concrete, Density, Dielectric Constant, Non-destructive Measurement.

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