Abstract
The aggregate skeleton of hot-mix recycled asphalt mixture comprises reclaimed asphalt pavement (RAP) and new aggregate and is a complex skeleton system containing old and new aggregates. The RAP content in the mixture directly determines the mechanical response characteristics of the composite skeleton, thus affecting the road performance. In order to explore the effect of RAP content on the characteristics of composite skeleton, in this study, the contact points in the composite skeleton were classified into three types: new-new, new-old, and old-old. On the basis of digital image technology and weight analysis methods, the distribution characteristics of the contact type of AC-13 mixture skeletons with different RAP contents were investigated; the correlation between the weight parameters of the contact type and the macroscopic mechanical properties of the mixture was studied. The results indicate that grading is the main factor affecting the total number of contact points; with increasing RAP content, the overall trend of new-new contact points is decreasing; the old-old contact points increase monotonously and then rapidly after the RAP content reaching 40%; the new-old contact points increase first and then decrease with a peak corresponding to 30% RAP. With increasing number of new-old contact points, the mechanical indexes of the recycled asphalt mixture enhanced. The weight analysis method can more simply and clearly reflect the correlation between the contact type of coarse aggregate and the mechanical parameters of mixture. In the mixing ratio design of the recycled asphalt mixtures, choosing a mixture with more new-old contact points achieved better road performance; therefore, effectively increasing RAP content may be one of the potential ways to enhance road performance.
Highlights
At present, the waste and old asphalt mixture produced by China’s highway maintenance and repair reaches hundreds of millions of tons every year (Chen, 2011; Zhang et al, 2020)
Two-dimensional image processing technology based on charge-coupled device (CCD) digital camera
Since CCD digital photography and X-ray CT non-destructive scanning have different precision and scope of application, considering the image quality requirements in the study, CCD digital camera-based photography technology was adopted to obtain the cross-section information of asphalt mixture digital camera and the 2D or 3D image processing technology is based on X-ray CT (Cai, 2013)
Summary
The waste and old asphalt mixture produced by China’s highway maintenance and repair reaches hundreds of millions of tons every year (Chen, 2011; Zhang et al, 2020). Studies have shown that the RAP content of hot-mix recycled asphalt mixture is mostly controlled within the range 20–30%. High RAP content significantly reduces the durability of hot-mix recycled asphalt mixture (Valdés et al, 2011; Arshad and Qiu, 2013). Han et al (2019) considered that the RAP content of the recycled mixture significantly affects its performance. Zhang et al (2019) pointed out that the use of RAP, instead of natural aggregates, significantly enhanced the dynamic stability of the recycled asphalt mixture. According to the result of the three-point bending test, RAP weakens the cracking resistance of the recycled asphalt mixture at low temperature. Ma et al (2015) reported that RAP was beneficial to enhancing the water stability of warm mix asphalt and hot-mix Asphalt mixtures. Based on the in-lab test on mixtures, Pradyumna et al (2013) concluded that the addition of RAP can improve the performance of all the asphalt mixtures with 20% RAP
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