Incorporating Size Effects into Multiscale Adhesion Modelling of Bitumen-Mineral Interfaces

英国的公路网总里程超过25万英里，为货物和服务的有效分配、经济安全和社会繁荣提供了手段。整个道路网络的资产价值为7500亿英镑，作为英国主要的交通基础设施，为道路使用者、商业和工业提供了至关重要的服务。然而，该网络需要不断升级、维护和修复，预计未来20年需要花费1810亿英镑。超过95%的铺砌道路由沥青混合物构成，其中包括三种主要成分，即矿物集料（微米至厘米），天然或添加填料（< 63微米）和沥青（膜厚10-20微米）。然而，尽管沥青混合料的劣化很重要，但人们从来没有完全了解或准确预测过沥青混合料的劣化。关键原因是目前评估和预测沥青与矿物集料之间粘附行为的方法没有考虑到不同材料尺寸尺度下的尺寸效应。这些尺寸效应主要来自沥青膜厚度、矿物表面粗糙度、气孔半径、沥青极性分布（分子尺寸）和矿物成分分布的变化。忽略这些尺寸效应，就无法准确预测沥青混合料的损伤，如材料断裂（交通荷载引起的疲劳开裂、非荷载相关的热开裂和年龄相关的开裂）、水分损伤敏感性（材料崩解和软化、剥离和微动）、凹坑和其他形式的严重表面劣化，这些都直接受沥青-矿物界面粘接性能的影响。该项目旨在开发一个整体的“粘附分析框架（AAF）”，重点是使用受尺寸影响的多尺度实验和建模方法，测量和预测沥青混合物中沥青（粘合剂）和矿物集料之间的界面粘附特性。结合实验技术、粘附理论和材料建模方法，确定尺寸相关和尺寸无关的材料特性，并将其从纳米尺度扩展到微观尺度到宏观尺度，以预测一系列沥青混合料类型的沥青-矿物界面粘合剂脱粘特性。该研究将结合显微镜和光谱成像以及纳米尺度的分子动力学（MD）模型来预测沥青-矿物界面的粘附性和一系列与尺寸无关的材料特性。粘弹性格里菲斯能量平衡原理将在微观尺度上应用，以产生基于力学的脱粘起裂准则，该准则结合了从纳米尺度MD模拟中获得的临界材料尺寸效应和与尺寸无关的材料特性。然后，通过结合不同材料和尺寸效应以及加载和环境条件的拉脱附着力和内聚性测试，验证理论沥青-矿物脱粘准则。最终的放大效应将处理裂纹（脱粘）扩展，该扩展是通过巴黎定律扩展模型开发的，该模型结合了纳米和微观尺度上确定的尺寸相关和尺寸无关的材料参数。然后，这些理论预测将通过一种新型的“三明治开裂”试验进行实验验证，该试验具有预制的初始开裂尺寸以及材料和条件变量。最后，所有这些不同的多尺度效应将被整合到多尺度模型层次中，用于预测粘合剂失效和整体材料响应，并作为基于web的开源软件和数据库交付。这款用户友好的软件将用于设计和生产更好、更持久的沥青材料，以确保这一关键国家资产的长期可持续性。

The UK's road network totals over 250,000 miles of paved roads providing a means for efficient distribution of goods and services, economic security and social prosperity. The entire road network has an asset value of £750 billion and as the UK's main transport infrastructure provides a vital service to road users, commerce and industry. However, the network requires constant upgrading, maintenance and rehabilitation with a predicted spend of £181bn required over the next 20 years.Over 95% of these paved roads are constructed from asphalt mixtures which comprise three principal components, namely, mineral aggregates (microns to centimetres), natural or added filler (< 63 microns) and bitumen (film thickness 10-20 microns). However, in spite of their importance, the deterioration of asphalt mixtures has never been fully understood or accurately predicted. The key reason is that the current means of assessing and predicting adhesive behaviour between the bitumen and the mineral aggregates does not account for size effects at the different material dimensional scales. These size effects result mainly from the variations of the bitumen film thickness, mineral surface roughness, air void radius, bitumen polarity distribution (molecular sizing) and mineral compositional distribution. Neglect of these size effects makes it impossible to accurately predict the asphalt mixture's distresses such as material fracture (traffic load induced fatigue cracking, non-load associated thermal cracking and age related cracking), moisture damage susceptibility (material disintegration and softening, stripping and fretting), potholes and other forms of severe surface deterioration, all of which are directly affected by the bitumen-mineral interfacial adhesive properties.The project aims to develop an overall 'adhesion analysis framework (AAF)' focusing on the measurement and prediction of interfacial adhesive properties between bitumen (binder) and mineral aggregates in asphalt mixtures using a size-affected multiscale experimental and modelling approach. Using a combination of experimental techniques, adhesion theories and material modelling approaches, size-dependent and size-independent material properties will be determined and scaled up from nano to micro to macroscale to predict the bitumen-mineral interface adhesive debonding properties of a range of asphalt mixture types. The research will use a combination of microscopy and spectroscopy imaging and molecular dynamics (MD) modelling at the nanoscale to predict bitumen-mineral interface adhesion and a range of size-independent material properties. The viscoelastic Griffith energy equilibrium principle will then be used at the microscale to produce a mechanics-based debonding initiation criterion incorporating the critical material size effects and the size-independent material properties obtained from the nanoscale MD simulations. The theoretical bitumen-mineral debonding criterion will then be verified by means of pull-off adhesion and cohesion testing incorporating different materials and size effects as well as loading and environmental conditions. The final scaling up effect will deal with crack (debonding) propagation developed through a Paris' law propagation model incorporating both size-dependent and size-independent materials parameters determined at the nano and microscales. These theoretical predictions will then be experimentally verified by a novel 'sandwich-cracking' test with prefabricated initial cracking dimensions together with material and conditioning variables. Finally, all these different multiscale effects will be incorporated into a multiscale modelling hierarchy for predicting adhesive failure and overall material response and delivered as a web-based opensource software and database. This user-friendly software will be used to design and produce better and long-lasting asphalt materials to ensure long-term sustainability of this key national asset.