Morphological character of coarse aggregate and its influence on high-temperature shear strength of asphalt mixture
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摘要: 采用60℃单轴贯入试验, 确定沥青混合料高温抗剪强度。使用数字图像处理技术, 从形状、棱角性和表面纹理对粗集料二维形态特征进行具体描述, 运用等效椭圆法和筛孔尺寸修正系数识别粗集料级配。结合MATLAB软件编写程序提取粗集料形态参数, 确定与沥青混合料高温抗剪强度相关的粗集料二维形态特征指标, 利用图像拓扑性质欧拉数定量评价粗集料骨架稳定性。研究结果表明: 随着粗集料的长宽比和偏心率的降低, 等效椭圆周长比和纹理指数的提高, 沥青混合料高温抗剪强度增加; 随着欧拉数的减小, 骨架密实型沥青混合料中粗集料骨架结构的稳定性增大, 高温抗剪强度增强。Abstract: The high-temperature shear strength of asphalt mixture was confirmed by using uniaxial penetration test at 60 ℃. The 2D morphological characters of coarse aggregate were described in terms of shape, angularity and surface texture by using digital image processing technology. The gradation of coarse aggregate was identified based on equivalent ellipse method and sieve size correction factor. The morphological characters of coarse aggregate were extracted by MATLAB, and some characters affecting the high-temperature shear strength of asphalt mixture were proved. Euler number of image in digital topology was applied to quantify the skeleton stability of coarse aggregate. Analysis result shows that the shear strength of asphalt mixture increases due to coarse aggregates with low aspect ratio and eccentricity, high angularity index of equal ellipse perimeter and surface texture parameter. As Euler number decreases, the skeleton structure of coarse aggregate in asphalt mixture with dense framework structure becomes steadier, which leads to higher high-temperature shear strength of asphalt mixture.
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表 1 混合料级配组成
Table 1. Compositions of mixture gradations
混合料类型 通过下列筛孔(方孔筛, mm) 的矿料质量百分率/% 19 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 AC16 100.0 97.5 82.5 68.0 52.5 41.0 29.5 22.0 16.0 11.0 6.0 SMA16 100.0 91.9 73.7 55.9 26.2 19.7 15.7 13.7 12.7 12.1 10.0 
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表 2 粗集料针片状含量
Table 2. Flat and elongated ratios of coarse aggregates
粗集料类型 Ⅰ Ⅱ Ⅲ Ⅳ 针片状含量/% 17.8 14.9 11.6 4.7
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表 3 沥青混合料高温抗剪强度
Table 3. High-temperature shear strengths of asphalt mixtures
混合料类型 AC16 SMA16 Ⅰ Ⅱ Ⅲ Ⅳ Ⅰ Ⅱ Ⅲ Ⅳ 油石比/% 5.3 5.2 4.9 4.7 6.6 6.5 6.2 5.9 抗剪强度/MPa 0.81 0.95 1.03 1.06 0.93 1.04 1.11 1.23
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表 5 级配识别结果
Table 5. Results of gradation recognition
颗粒粒径区间/mm 机械筛分含量/% 针片状含量/% 识别结果/% 等效圆法 最小外接正方形法 等效椭圆法 4.75~9.5 29.7 14.79 26.8 32.8 28.5 9.5~13.2 17.8 13.95 15.2 18.6 16.6 13.2~16 18.2 8.97 16.8 20.1 17.2 16~19 8.1 7.44 7.0 9.6 7.5
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表 6 筛孔修正系数
Table 6. Correction coefficients of sieve size
粗集料类型 横切面 纵切面 AC16 SMA16 AC16 SMA16 Ⅰ 0.884 0.897 0.837 0.862 Ⅱ 0.892 0.904 0.843 0.871 Ⅲ 0.903 0.910 0.849 0.890 Ⅳ 0.911 0.915 0.872 0.897
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表 7 粗集料总体形态特征
Table 7. Total morphological characters of coarse aggregates
混合料类型 形态特征指标 棱角性特征指标 纹理特征指标 长宽比 矩形度 偏心率 等效椭圆周长比 凸凹度 纹理指数 AC16 Ⅰ 1.965 0.625 0.842 1.261 0.882 2.602 Ⅱ 1.904 0.648 0.797 1.303 0.899 2.632 Ⅲ 1.814 0.638 0.781 1.379 0.899 2.832 Ⅴ 1.753 0.651 0.767 1.438 0.914 2.836 SMA16 Ⅰ 1.923 0.613 0.832 1.327 0.864 2.680 Ⅱ 1.899 0.647 0.807 1.376 0.897 2.751 Ⅲ 1.751 0.609 0.778 1.392 0.873 2.843 Ⅴ 1.736 0.655 0.746 1.567 0.905 2.888
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表 8 判定系数
Table 8. Determination coefficients
指标 长宽比 矩形度 偏心率 等效椭圆周长比 凸凹度 纹理指数 判定系数 0.786 0.142 0.834 0.883 0.170 0.833
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表 9 粗集料骨架评价结果
Table 9. Evaluation results of coarse aggregate skeletons
混合料类型 AC16 SMA16 Ⅰ Ⅱ Ⅲ Ⅳ Ⅰ Ⅱ Ⅲ Ⅳ 欧拉数 22 28 39 44 -69 -81 -114 -169
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