Structural Attributes in Cold Recycled Asphalt Mixes: Microstructure Insights

Document Type : Original Article

Authors
Hassan Ziari 1
Hossein Tavakoli 2
Mahdi Zalnezhad 3
1 Department of Civil Engineering, Iran University of Science and Technology (IUST), Tehran, Iran.
2 M.Sc., Student, Department of Civil Engineering, Iran University of Science and Technology (IUST), Tehran, Iran.
3 Ph.D., Student, Department of Civil Engineering, Iran University of Science and Technology (IUST), Tehran, Iran.
10.22034/road.2023.410558.2186
Abstract
This study provides a comprehensive exploration of the microstructure characteristics of cold recycled asphalt mixes, with a primary focus on their environmental benefits. Utilizing a suite of analytical techniques including Optical Microscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray diffraction, and Scanning Force Microscopy, the study delves into four pivotal microstructure facets: air voids and coarse aggregates, uniformity index, the impact of diverse additives, and the process of augmenting initial strength. The findings reveal that several factors, notably aggregate grading and compaction methodology, exert a notable influence on the microstructure of cold recycled mixes. Specifically, transitioning from fine to coarse grading amplifies void space within the cold asphalt mix. Moreover, both compaction methods and aggregate grading significantly alter the size and distribution of air voids. The study establishes that as grading shifts from fine to coarse, the uniformity of cold recycled asphalt mixes experiences a gradual decline. Additionally, the Superpave Gyratory compaction method emerges as the most effective among the three compaction methods considered. Furthermore, the investigation assesses the impact of diverse additives on microstructure and overall performance. Notably, optimal cement content for cold recycled asphalt, when using bitumen emulsion, is found to be in the range of 1-2%, ensuring resistance against cracking at low temperatures. In general, this research indicates the importance of considering the microstructure in the design and evaluation of cold recycled asphalt mixtures, which can help to develop sustainable asphalt mixtures
Keywords
cold asphalt
microstructure
cold recycled asphalt
scanning electron microscope
X-ray diffraction
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