基于破坏极限和损伤速率双约束的沥青抗疲劳开裂性能研究

Fatigue resistance of asphalt binder strongly affects the fatigue cracking performance of asphalt mixture; however, existing binder tests inadequately characterize the binder relevant properties. The goal of this study is to propose a binder parameter, which is governed by failure limit and damage rate, to effectively evaluate the binder fatigue cracking performance. Failure limit can be measured from the binder fracture energy (BFE) test, referring to the amount of energy a binder can absorb before fracture. Damage rate will be obtained by developing a BFE fatigue test, which involves applying the finite element method to determine the dimension of specimen essential part; designing mental pieces that can be used to avoid viscous flow in specimen nonessential parts; evaluating load characteristics including load shape, amplitude and rest period for purpose of separating elastic energy, delayed elastic energy, and determine damage associated dissipated energy without being affected by binder healing. After that, this study will establish a binder step-wise discontinuous crack growth model to investigate the combined effect of failure limit and damage rate on binder fatigue cracking performance; simulate the stress distribution ahead of the crack tip and the crack growth path to develop a binder fatigue cracking parameter. Finally, mixture fracture properties and fatigue cracking performance will be employed as the benchmarks to evaluate and calibrate the proposed binder parameter. It is anticipated that results from this study will improve the understanding on the mechanism of binder fatigue cracking distress and provide an effective binder parameter to select superior binder type, which can be used to prolong the pavement service life.

沥青的抗疲劳开裂性能直接影响沥青混合料的疲劳寿命，但现有试验无法对其做出准确评价。本研究拟提出一个考虑破坏极限和损伤速率双约束的沥青抗疲劳开裂性能指标。破坏极限用申请人已研发的Binder Fracture Energy(BFE)拉伸试验测得的断裂能量密度表征。损伤速率将通过继续研发BFE疲劳试验获得，内容包括：利用数值分析确定样本关键部位；设计贴片限制非关键部位粘性流动；设计循环荷载波形、峰值、荷载间隔来区分弹性能、延迟弹性能，排除沥青自愈，获得损伤消散能。在此基础上，本项目将建立沥青逐步不连续裂缝扩展模型来整合破坏极限和损伤速率对沥青抗疲劳开裂性能的双约束作用；模拟裂缝尖端应力场分布以及开裂路径来推导沥青疲劳寿命指标；通过沥青混合料的抗疲劳开裂性能对沥青指标进行检验和校准。预期成果：增强对疲劳机理的认识，从抗疲劳性能方面为合理选择沥青材料提供一个指标，并为延长道路疲劳寿命提供科学指导。

沥青的抗疲劳开裂性能直接影响沥青混合料的疲劳寿命，但现有试验无法对其做出准确评价。项目旨在提出一个考虑破坏极限和损伤速率双约束的沥青抗疲劳开裂性能指标，对沥青常温抗裂性能进行有效、准确的评价。项目共采用了6种沥青材料，包括3种不同软度的常规沥青和3种不同改性成分的改性沥青。研究的主要手段包括沥青断裂能量BFE试验、沥青线性振幅扫描LAS试验，以及沥青混合料间接拉伸SUPERPAVE-IDT试验。实验内容主要包括利用BFE试验和LAS试验对沥青的抗裂性能进行评价，并提出新的性能指标；以及通过Superpave-IDT试验对沥青混合料的常温抗裂性能进行评价，并为沥青的性能指标提供检验和校准信息。试验结果表明：1）现行AASHTO TP127破坏极限指标与新提出的损伤速率指标逆相关。与常规沥青相比，聚合物改性沥青的断裂能量值较大，而损伤速率值则较小；2）断裂能量参数重复性强，测量误差小，可以有效地区分不同沥青类型；3）现行AASHTO TP101规范和最新GR方法中两个沥青性能指标的一致性。基于这两个指标，除了橡胶改性沥青之外的5种沥青的排序相同，表明可以继续使用现行的TP101规范方法；4）考虑到沥青断裂能量与损伤速率逆相关，断裂能量参数本身与沥青混合料的疲劳寿命也展现出了极高的关联性，因此，本项目推荐使用AASHTO TP127沥青断裂能量指标对沥青的抗疲劳开裂性能进行表征，并指导研发和评价新型改性沥青。