The Evaluation Method of Particle Clustering Phenomena in RAP

Abstract

The particle clustering phenomena in reclaimed asphalt pavement (RAP) particles is one of the most important factors to affect the efficient recycling of asphalt concrete. In this study, the particle composition, clustering degree, crushing properties and clustering stability of RAP were studied by extraction test and cantabro-crushing test. It was found that the particles above 4.75 mm were composed mainly of small particles with a large degree of cluster and poor stability. The coarse particles (>4.75 mm) had a great influence on the variation of 4.75 mm sieve. Quantitative indexes of Percentage Loss rate (PL) and Stability Index (w) were proposed to evaluate the clustering degree and the stability of RAP. It provided a meaningful reference for the comparison of different RAP and the different crushing processes. In addition, the RAP could be divided into three kinds of structures, including weak cluster structure, strong cluster structure and old aggregate. The process of crushing the RAP was divided into three stages, which are weak structure-dominated, strong structure-dominated and the broken old aggregate. The weak structure had the largest degree of cluster and worst stability, resulting in a large variability of RAP, and it should be avoided in the crushing process.Appl. Sci. 2019, 9, 424 2 of 16 degradation was observed for the 40% RAP binder and RAP mixture when subjected to repeated loading [11]. Fakhri studied the glass fiber modified warm mix asphalt mixtures with high RAP content, and improved performance of the WMA mixture was shown due to the glass fiber and higher RAP percent [12]. Stimilli et al., proposed that an accurate mix design and the selection of adequate binder could overcome the potential drawbacks related to the use of high RAP percentage, given the possibility to produce suitable recycled mixtures [13]. The performance variability of recycled materials cannot be solved fully, and the reason is because there is a great variability of RAP [14-17]. The particle cluster phenomenon in RAP is one of the most important factors to affect the gradation variability and road performance of regenerated mixtures. Many studies had been carried out to investigate the clustering phenomena in regenerated asphalt mixtures. contended that the rheology, and in particular the complex modulus, could be used to study the cluster phenomenon in mixtures containing RAP [18]. In Bressi's more recent research, he concluded that the quantity and the quality of virgin aggregates play a significant role in the clusters' formation [19].According to related studies, the cluster level of different sources of RAP materials was quite different [20][21][22]. It could be affected by the pavement aging degree, material composition, gradation characteristics, milling equipment, milling temperature, pavement humidity, pavement layer and many other factors [23][24][25]. If the old asphalt mixtures were not broken fully, it would seriously affect the performance of the regenerated mixture and reduce the utilization rate of ...

An Analysis of Reclaimed Asphalt Pavement from a Single Source—Case Study: A Secondary Road in Romania

“…However, other research states that no geographical or regionalization of the properties of the RAP stockpiles could be made [26]. RAP clustering is analyzed in this research mainly because it is a very important factor that affects the performances of design gradation of recycled asphalt mixtures [6,9,15,[27][28][29][30]. Results of preceding research classify clusters according to the type of particle agglomeration structure into strong clusters, weak clusters, and old particle aggregate [29,31,32].…”

Identifying the mixing-induced homogeneity characteristics of asphalt mixtures containing reclaimed asphalt pavement (RAP) materials

“…Since then, many researchers progressively attached importance to the role of RAP clusters in recycled asphalt mixtures. Xu et al [19] classified RAP materials into three categories including weak structural agglomerates, strong structural agglomerates, and coarse aggregates. Besides, He also proposed loss rate (PL) and stability index (w) as quantitative indicators to estimate the degree of RAP agglomeration.…”

Analysis of different reclaimed asphalt pavements to assess the potentiality of RILEM cohesion test

“…RAP is the material resulting from the milling of asphalt concrete (AC) pavement layers and includes mineral aggregate, bitumen and air voids. It can appear in form of clusters (''pieces'' of AC with various sizes), single aggregate particles covered by bitumen and powder of bituminous mastic [1,2].…”