布敦岩沥青混凝土低温宏细观多尺度开裂特性

Macro-and micro-scale cracking characteristics of Bouton rock asphalt concrete under low temperature

为了从宏细观多尺度下研究布敦岩沥青混凝土在低温状态下的开裂特性,以施加短期老化(S-A)、长期老化(L-A)、紫外老化(U-A)、冻融循环(F-M)及盐冻融循环(SF-M)这5个不同路用环境因素的低温弯曲试验为基础,通过数字图像相关(digital image correlation,DIC)技术同步监测试验的开裂过程,从宏细观尺度对比分析了布敦岩沥青混凝土与基质及SBS改性沥青混凝土的低温开裂特性。其中,宏观尺度下采用弯曲应变能密度、弯曲系数来评价低温性能,细观尺度下采用裂纹长度、开裂关键节点来评价低温性能。结果表明:布敦岩沥青混凝土低温弯曲应变能密度大于基质沥青混凝土且接近SBS改性沥青混凝土,说明布敦岩沥青可以改善基质沥青混凝土低温开裂性能。由沥青混凝土的弯曲系数可知,布敦岩沥青混凝土在0℃和-10℃下与SBS改性沥青混凝土相似,属柔性开裂;在-20℃下与基质沥青混凝土相似,属于脆性开裂。通过分析试件的裂纹长度可知,布敦岩沥青混凝土的裂纹扩展长度大于基质沥青混凝土且该裂纹的变化服从三次多项式,对裂纹长度变化曲线进行分析得到其关键开裂长度,并根据反推的关键节点的临界应变能密度进一步确定布敦岩沥青具有延缓沥青混凝土开裂关键节点出现的优势。

In order to study the cracking characteristics of Bouton rock asphalt concrete at low temperature from macroscopic and microscopic scale respectively,the cracking process was monitored simultaneously by digital image correlation(DIC)technology based on low-temperature bending tests after undergoing five different road environmental factors:short-term aging(S-A),long-term aging(L-A),ultraviolet aging(U-A),freeze-thaw cycles(F-M)and salt freeze-thaw cycles(SF-M).The low-temperature cracking characteristics of Bouton rock asphalt concrete compared with matrix and SBS-modified asphalt concrete were analyzed in macro-and micro-scales,in which the bending strain energy density and bending coefficient were used to evaluate the low-temperature performance in macroscopic scale,and the crack length and key cracking nodes were used to evaluate the low-temperature performance in micro-scale.The results show that the low-temperature bending strain energy density of Bouton rock asphalt concrete is larger than that of matrix asphalt concrete and close to that of SBS modified asphalt concrete,which indicates that Bouton rock asphalt can improve the low-temperature cracking performance of matrix asphalt concrete.The bending coefficient of asphalt concrete shows that Bouton rock asphalt concretes is similar to SBS modified asphalt concrete at 0℃and-10℃with flexible cracking,and is similar to matrix asphalt concrete at-20℃with brittle cracking.By analyzing the crack length of the specimens,it can be seen that the crack extension length of Bouton rock asphalt concrete is larger than that of matrix asphalt concrete and the variation of the crack obeys a cubic polynomial.The crack length variation curve is analyzed to obtain the critical crack length,and the inverse critical strain energy density of the key cracking nodes further determines that Bouton rock asphalt has the advantage of delaying the appearance of the key cracking nodes of asphalt concrete.