Evaluation of the degradation of aggregates shape properties

ABSTRACT The aggregates shape properties (form, angularity, and surface texture) have an influence on the asphalt pavement surface texture, which is directly related to tire-pavement adhesion, to stability and to road safety. Due to the importance of studying these characteristics, this research has the main objective of evaluating the effect of aggregate degradation on their shape properties. In order to achieve this, the shape properties of aggregates with three different sizes were analyzed by means of traditional methods and also with the use of aDigital Image Processing (DIP) technique. These properties were analyzed with the use of the Aggregate Image Measurement System 2 (AIMS2), before and after the use of the Micro Deval (MD) and the Los Angeles abrasion equipment, besides the conventional test of uncompacted void content. The aggregates particles angularity values decreased during the degradation process for both equipment used in the analyses. The aggregates sphericity after the use of MD did not change significantly. This could be explained because smaller abrasive charges are used in this particular test. The surface texture evaluated after the Los Angeles abrasion test did not vary significantly, which can be explained due to the tendency of breakage during the test, a process that is more related changes in form conditions. Furthermore, the results showed that the aggregate size and the presence of water influenced the degradation processes of the aggregates. The combination of the characterization of aggregate shape properties by means of image techniques with the use of laboratorial mechanical processes that are capable of modifying these properties might be an adequate solution for the prediction of asphalt pavements performance in relation to adhesion loss throughout the time.

摘要
集料的形状特性（包括形态、棱角性与表面纹理）对沥青路面表面纹理具有显著影响，而路面表面纹理直接关联轮胎-路面黏附性能、路面结构稳定性及道路交通安全。鉴于上述特性研究的重要价值，本研究核心目标为评估集料降解过程对其形状特性的作用效果。为达成该研究目标，研究团队采用传统测试方法结合数字图像处理（Digital Image Processing, DIP）技术，针对三种不同粒径的集料开展形状特性分析。测试环节中，除开展常规的松装空隙率（uncompacted void content）试验外，还借助集料图像测量系统2（Aggregate Image Measurement System 2, AIMS2），分别在使用微型狄法尔磨耗试验机（Micro Deval, MD）与洛杉矶磨耗试验机前后，对集料的相关特性进行了量化表征。
分析结果表明，经两种磨耗设备的降解作用后，集料的棱角性数值均出现不同程度下降。经微型狄法尔磨耗试验机处理后的集料球形度未发生显著变化，这一现象可归因于该测试所采用的磨料粒径更小。洛杉矶磨耗试验后集料的表面纹理同样无明显改变，究其原因，该试验过程中的破碎作用更侧重于改变集料的形态特性。此外，研究结果还证实，集料粒径与水分的存在均会对集料降解过程产生影响。将图像技术表征集料形状特性的方法，与可调控集料形状特性的室内力学试验手段相结合，或可为预测沥青路面随时间推移产生黏附损失后的服役性能提供可行解决方案。