Optimization of technical measures for improving high-temperature performance of asphalt–rubber mixture

Chuan Xiao 0 1 Tianqing Ling 0 1 Yanjun Qiu 0 1 0 T. Ling School of Civil Engineering and Architecture, Chongqing Jiaotong University , Chongqing 400074, China 1 C. Xiao (&) Y. Qiu School of Civil Engineering, Southwest Jiaotong University , P.O. Box 520, No. 111 First North Section , 2nd Ring Road, Chengdu 610031, Sichuan, China Asphalt-rubber pavements often become damaged in high-temperature regions and appear rutted or wavy, and experience slippage. To improve the high-temperature performance of the asphalt-rubber mixture, technical measurements, such as, the optimal adjustment of gradation, technique of composite modification, and control of compaction were investigated. An optimal adjustment of aggregate gradation based on stone matrix asphalt improves the high-temperature stability of the asphaltrubber mixture significantly. Through composite modification, the effect of asphalt-rubber modification was enhanced, and the dynamic stability and relative deformation indices of the asphalt-rubber mixture were improved significantly. Furthermore, compaction parameters had a significant influence on the high-temperature stability of the asphalt-rubber mixture. The rolling times for compacting the asphalt-rubber mixture should be controlled to within 18-20 round-trips at a molding temperature at 180 C; if the rolling time is a 12 round-trip, the compaction temperature of the asphalt-rubber mixture should be controlled between 180 and 190 C. 1 Introduction Rapid growth of waste tires is a serious environmental problem because of their highly resistant chemical, biological, and physical properties. Many approaches have been considered to encourage the sustainable development. Using crumb rubber in asphalt, which initiated with the motivation to improve the binder properties, is one of the practical ways to tackle the increasing waste tires. In general, the approaches used to incorporate crumb rubber modifier (CRM) in road paving materials are classified as the dry method and the wet method [2]. Wet method is applied in most of the rubberized asphalt projects in China, which entails adding the crumb rubber to the binder before mixing it with aggregate [3]. The behavior of asphaltrubber with wet method depends on several factors, such as, the origin, fabrication process and grain size distribution of the crumb rubber, the type of base asphalt binder used in the mixture, and the temperature and time of the mixing process. Anderson et al. [4] investigated the rheological and physical properties of binders modified with rubber, for rubber contents below 20 % by weight. Huang et al. [5] and Shen and Amirkhanian [6] suggested the optimal preparation of asphaltrubber according to comparative tests on material properties of asphalt binder. In pavement destruction, asphaltrubber has become increasingly attractive in the applications, such as, open graded friction course (OGFC), stress absorption membrane interlayer (SAMI), and super silent pavement (SSP) [2]. The asphaltrubber pavements exhibit unique advantages in reducing pavement thickness, delaying reflection cracking, and decreasing traffic noise [7, 8]. However, an obvious problem in the application of the asphaltrubber mixture is the lack of high-temperature stability used as structural layer, which could cause serious rutting under recycled vehicle loading. The indices, such as, viscosity, penetration, and softening point show that the asphaltrubber shows excellent performance at high-temperature [9]. However, because of the interference of asphaltrubber and aggregate during the compacting process and the low stiffness modulus and deformation characteristics of the asphaltrubber mixture [8, 10], it is difficult to meet the desired demands when applying asphaltrubber pavement in high-temperature regions. Furthermore, there is no unified technical specification for asphaltrubber in China resulting in significant discrepancies in aggregate gradation, asphalt content, and mineral filler content when paving with asphaltrubber mixture [1113]. Improvements in the hightemperature performance of asphaltrubber pavements are critical when they are applied in high-temperature regions and under heavy traffic conditions in China. In this paper, we investigate the high-temperature stability of an asphaltrubber mixture based on internal and external factors. At first, the optimal gradation was adjusted in the rutting tests with dynamic stability and relative deformation as evaluation indices. Then, the scheme of compound modification and optimization of the compaction parameters were analyzed to improve the high-temperature stability of the asphaltrubber mixture. To obtain a reasonable scheme of compound modification, comparative tests of high-temperature performance were conducted between different binders and mixtures. The effects of rolling time and molding temperature on air void volume and the dynamic stability (DS) were investigated to determine optimal compaction parameters. 2 Test materials 2.1 Material properties of asphaltrubber SK 70# base asphalt and crumb rubber (30 mesh size) were used to produce asphaltrubber for comparative tests of asphaltrubber performance. The test methods followed Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering from the industry standard of China (JTG E20-2011) [14] with main performance indices listed in Table 1. Table 1 Properties of asphaltrubber Performance index Note The code of test method followed JTG E20-2011 [14] 2.2 Material properties of aggregate and filler The test methods followed Test Methods of Aggregate for Highway Engineering (JTG E42-2005) and the main indices of the aggregate and mineral filler in the asphalt rubber mixtures are listed in Tables 2 and 3, respectively. 3 Test method and analysis 3.1 Optimization of aggregate gradation 3.1.1 Gradation-type selection Based on the broad overview of a typical gradation type for an asphaltrubber mixture, AR-AC-13 (based on Arizona standards [2, 12]), SMA-13 (traditional stone matrix asphalt [15]), and AC-13 (dense-graded asphalt mixture [15]) were chosen as research materials on which to conduct the rutting tests. Figure 1 shows the aggregate gradations of different mixtures. The rutting tests on the different asphalt mixtures followed Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) with parameters listed in Table 4. The rutting test results for the different asphalt mixtures are given in Table 5. Table 5 shows that the preferential order of the three kinds of mixtures based on high-temperature performance is: SMA-13 [ AR-AC-13 [ AC-13. This occurs because of the different characteristics of the mixtures. Because AC-13 is a suspend-dense structure mixture, there is interference between the asphaltrubber binder and the aggregate during compaction. This type of mixture is difficult to compact completely with asphaltrubber. This most likely ex (...truncated)