基于SCB和3D-DIC技术的既有沥青路面剩余寿命预估

Prediction on Residual Life for Existing Asphalt Pavement Based on SCB and 3D-DIC Technique

在改扩建项目中准确评价超服役周期高速公路沥青路面的剩余寿命,对于合理制订既有高速公路沥青路面的利用策略至关重要。从服役周期超过20 a的高速公路上钻取27个沥青混凝土芯样,并制作成54个半圆试件,分别进行半圆弯曲(SCB)断裂和半圆弯曲(SCB)疲劳试验,评价既有沥青混凝土路面的抗疲劳特性和剩余寿命。为解决传统测试方法无法实时捕捉沥青混凝土在高周疲劳试验中试件表面裂缝拓展问题,引入立体数字图像关联(3DDIC)技术监测试件表面应变场以及裂缝长度随疲劳荷载次数的演化趋势,结合K-d tree算法计算了每个疲劳荷载循环对应DIC图像中裂缝长度的变化。同时,采用双线性软化内聚区模型(CZM)确定沥青混凝土裂缝的应变阈值,从而保证了K-d tree算法计算裂缝长度的准确性。构建了Paris方程主曲线消除沥青混凝土开裂参数在不同应力比下的不一致性,在宽荷载域范围内表征各种路段沥青混凝土的抗疲劳性能。结果表明:既有沥青混凝土裂缝的应变阈值为1980με;随着应力比的增大,Paris方程A和n参数分别表现出波动增加和平稳下降趋势,而应力强度因子阈值呈平稳上升趋势;K84,K124,K165路段沥青面层剩余寿命分别为2.13E+08,3.57E+08,1.02E+07,除K165路段外,其他路段的剩余疲劳寿命均满足路面设计年限内交通量要求。

Accurately evaluating the residual life of the asphalt pavement of the over-service period expressway is essential to formulate pavement utilization strategies in reconstruction and expansion projects.27 asphalt concrete core specimens are drilled from the expressway with a service period of more than 20 a and made into 54 semicircular specimens,and the semi-circular bending(SCB)fracture and fatigue tests are performed to evaluate the fatigue resistance and residual life of the existing asphalt concrete pavement.In order to solve the problem that traditional test methods cannot capture the surface crack expansion of asphalt concrete specimens in high cycle fatigue test in real-time,stereo digital image correlation technology 3D-DIC is introduced to monitor the evolution trend of the strain field and crack length on the surface of asphalt concrete specimens with the number of fatigue loads.In addition,the change of crack length in the DIC image corresponding to each fatigue load cycle is effectively calculated by combining the K-d tree algorithm.Meanwhile,the bilinear softening cohesive zone model(CZM)is used to determine the strain threshold of asphalt concrete cracks,thereby ensuring the accuracy of the K-d tree algorithm to calculate the crack length.The Paris equation master curve is constructed to eliminate the inconsistency of cracking parameters of asphalt concrete under different stress ratios,and to characterize the fatigue resistance performance of asphalt concrete of various road sections within a wide load range.The result shows that(1)the strain threshold of asphalt concrete crack is 1980με;(2)with the increase of stress ratio,the Paris equation parameters A and n show trends of increasing fluctuation and steady decline respectively,while the threshold of stress intensity factor increases steadily;(3)the residual lives of the asphalt surface of section K84,K124 and K165 are 2.13E+08,3.57E+08 and 1.02E+07 respectively.Except section K165,the residual fatigue lives of other road sections meet the design expectations of the long-life pavement.