Chengwei Xing , Mingchen , Lingxiao Liu and Ruikang Yang Chengwei Xing , Mingchen , Lingxiao Liu and Ruikang Yang 1 Key Laboratory for Special Area Highway Engineering of Ministry of Education, Chang'an University, 1 长安大学特殊领域公路工程教育部重点实验室、South 2nd Ring Road Middle Section, Xi'an 710064, China; xingcw@chd.edu.cn 中国西安市南二环中段，710064；xingcw@chd.edu.cn2 School of Highway, Chang'an University, South 2nd Ring Road Middle Section, Xi'an 710064, China 2 中国西安市南二环中段长安大学公路学院 邮编：7100643 The Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, 3 同济大学道路与交通工程教育部重点实验室、Shanghai 201800, China 中国上海 2018004 China State Construction Engineering (Hong Kong) Limited, Hong Kong, China; lingxiao.liu@cohl.com 4 中国建筑工程（香港）有限公司，中国香港；lingxiao.liu@cohl.com* Correspondence: littleming@tongji.edu.cn (M.L.); rkyang@tongji.edu.cn (R.Y.) * 通讯：littleming@tongji.edu.cn (M.L.); rkyang@tongji.edu.cn (R.Y.)
Citation: Xing, C.; Li, M.; Liu, L.; Yang, R. Long-Term Aging Behavior of Plastic/Styrene Butadiene Rubber (SBR) Composite Modified Bitumen. Materials 2023, 16, 4567. https:// doi.org ma16134567 引用：Xing, C.; Li, M.; Liu, L.; Yang, R. Plastic/Styrene Butadiene Rubber (SBR) Composite Modified Bitumen.材料 2023，16，4567。https:// doi.org ma16134567
Academic Editor: Yue Xiao 学术编辑：肖玥
Received: 18 May 2023 收到：2023 年 5 月 18 日
Revised: 8 June 2023 修订日期：2023 年 6 月 8 日
Accepted: 20 June 2023 接受： 2023 年 6 月 20 日
Published: 24 June 2023 出版日期：2023 年 6 月 24 日
Abstract 摘要
The reuse of recycled waste plastics has long been attempted in pavement engineering as bitumen modifier. It was revealed that waste plastics can significantly enhance the high-temperature performance of bitumen and bitumen mixtures. Even so, the application of waste plastics as a bitumen modifier is still not widespread. This is attributable to the generally poor low-temperature performance of plastic-modified bitumen, which often fails to meet specification requirements. For this purpose, styrene butadiene rubber (SBR) was selected to improve the low-temperature performance of plastic-modified bitumen. However, due to the long-term aging process, the composite and structure of the modified bitumen will change, which negatively impacts its performance. The objective of this study is to investigate the long-term aging behavior of plastic/SBR composite-modified bitumen. For this purpose, waste polyethylene was used as a plastic modifier and was mixed with base bitumen and 3% SBR at ratios and 7.5%. The rheological properties and molecular weight distribution of base bitumen, plastic and plastic/SBR-modified bitumen before and after long-term aging were measured. Results show that the incorporation of plastic can improve the complex modulus, rutting factor and percent recovery of bitumen and reduce the non-recoverable creep compliance of the bitumen, indicating the modification process enhances the high-temperature performance of bitumen. The enhancement effect is more pronounced with the increase of plastic content. For modified bitumen with plastic modifier, the complex modulus of modified bitumen is increased by compared to base bitumen. The addition of 3% SBR modifier can further improve the high-temperature performance of the modified bitumen. In addition, the modification process also increases the large molecule size percentage (LMSP) and weight average molecular weight of bitumen. Compared with weight average molecular weight, the LMSP correlates well with the rheological properties of modified bitumen. In accordance with the complex modulus, using the LMSP and weight average molecular weight of bitumen before and after aging, the corresponding aging index was calculated. The quantitative results showed that the addition of plastic modifier can improve the aging resistance of bitumen, but the enhancement effect is not as obvious as that of SBR modifier. 回收废塑料作为沥青改性剂在路面工程中的再利用尝试由来已久。研究表明，废塑料可以显著提高沥青和沥青混合物的高温性能。尽管如此，废塑料作为沥青改性剂的应用仍不广泛。这是因为塑料改性沥青的低温性能普遍较差，往往达不到规范要求。为此，人们选择丁苯橡胶（SBR）来改善塑料改性沥青的低温性能。然而，由于长期老化过程，改性沥青的复合材料和结构会发生变化，从而对其性能产生负面影响。本研究的目的是调查塑料/丁苯橡胶复合改性沥青的长期老化行为。为此，使用废聚乙烯作为塑料改性剂，并与基质沥青和 3% 的 SBR 按 和 7.5% 的比例混合。测量了长期老化前后基质沥青、塑料和塑料/丁苯橡胶改性沥青的流变特性和分子量分布。结果表明，掺入塑料可以提高沥青的复合模量、车辙系数和恢复率，降低沥青的不可恢复蠕变顺应性，表明改性过程提高了沥青的高温性能。随着塑料含量的增加，增强效果更加明显。对于使用 塑料改性剂的改性沥青，改性沥青的复合模量比基础沥青提高了 。添加 3% 的 SBR 改性剂可进一步提高改性沥青的高温性能。此外，改性过程还提高了沥青的大分子尺寸百分比（LMSP）和重量平均分子量。与重量平均分子量相比，大分子尺寸百分比与改性沥青的流变性能密切相关。根据复合模量，利用老化前后沥青的大分子百分率和重量平均分子量，计算出相应的老化指数。定量结果表明，添加塑性改性剂可提高沥青的抗老化性能，但其提高效果不如 SBR 改性剂明显。
In recent years, the recycling of waste materials has received increasing attention [1-4]. As the consumption of plastic products has increased, the amount of waste plastic has also increased [5-7]. It is estimated that the global production of waste plastics amounts to 300 million tons, but less than of waste plastics are recycled. Most waste plastics are landfilled or incinerated, which causes serious environmental pollution problems. In recent 近年来，废旧材料的回收利用受到越来越多的关注 [1-4]。随着塑料制品消费量的增加，废塑料的数量也在增加 [5-7]。据估计，全球废塑料产量达 3 亿吨，但只有不到 的废塑料得到回收利用。大部分废塑料被填埋或焚烧，造成了严重的环境污染问题。近年来
years, there have been many attempts to recycle waste materials in the field of pavement engineering, and the reuse of waste plastics as modifiers for bitumen has become a major application trend [8-10]. Related studies have revealed that waste plastics can significantly enhance the high-temperature performance of bitumen and its mixtures. For instance, with the aid of the multiple stress creep recovery (MSCR) test, Al-Abdul et al. [11] investigated the effects of three kinds of waste plastics modifiers (recycled polypropylene and low- and high-density polyethylene) on the high-temperature performance of composite-modified bitumen. Their findings have shown that the addition of waste plastics can affect the percentage recovery and non-recoverable creep of bitumen and hence significantly improve the high performance of bitumen [11]. 多年来，路面工程领域一直在尝试对废料进行回收利用，废塑料作为沥青改性剂的再利用已成为一种主要的应用趋势[8-10]。相关研究表明，废塑料可以显著提高沥青及其混合物的高温性能。例如，Al-Abdul 等人[11] 借助多应力蠕变恢复（MSCR）试验，研究了三种废塑料改性剂（再生聚丙烯、低密度和高密度聚乙烯）对复合改性沥青高温性能的影响。研究结果表明，添加废塑料可影响沥青的回收率和不可回收蠕变率，从而显著改善沥青的高性能[11]。
Nevertheless, waste plastic-modified bitumen is still not extensively used in practical engineering. There are various reasons why waste plastic-modified bitumen is not yet widely used. Firstly, there are many different types of waste plastics, and their chemical composition varies, which leads to large differences in performance between different forms of plastic-modified bitumen and its mixtures. Secondly, due to the high modulus of waste plastic-modified bitumen, pavement made from it is prone to cracking at low temperatures . In particular, because the low temperature ductility of plastic-modified bitumen struggles to meet the requirements of the relevant specifications, it greatly limits the widespread use of plastic-modified bitumen. For this reason, the incorporation of rubber materials such as crumb rubber, styrene-butadiene-styrene (SBS) and styrene butadiene rubber (SBR) is commonly adopted to improve the low-temperature performance of waste plastic-modified bitumen [14-16]. Considering that composite modification using SBR can change the chain rigidity and crosslink density of composite materials, SBR is an effective modifier commonly used to enhance the low-temperature performance of modified bitumen in practical engineering [17,18]. Ren et al. [18] investigated the effect of the addition of the SBR modifier on the low-temperature crack resistance of gilsonite-modified bitumen using the blending beam rheometer (BBR) test and found that the addition of SBR is a valuable way to improve the low-temperature PG grade of gilsonite-modified bitumen. Liu et al. [19] used SBR modifier to enhance the low-temperature performance of Buton rock-modified bitumen mixtures and revealed that the bending strength and maximum bending strain of SBR/Buton rock composite-modified bitumen mixtures at were increased by and , respectively, following the addition of SBR. As such, using SBR to modify bitumen is an effective solution to enhance the low-temperature performance of waste plastic-modified bitumen. 然而，废塑料改性沥青在实际工程中仍未得到广泛应用。废塑料改性沥青尚未得到广泛应用的原因是多方面的。首先，废塑料种类繁多，化学成分各异，导致不同形式的塑料改性沥青及其混合物之间性能差异较大。其次，由于废塑料改性沥青的模量较高，用其铺设的路面在低温下容易开裂 。特别是由于塑性改性沥青的低温延展性难以达到相关规范的要求，大大限制了塑性改性沥青的广泛使用。因此，为了改善废塑料改性沥青的低温性能，通常采用加入橡胶材料的方法，如橡胶屑、丁苯橡胶（SBS）和丁苯橡胶（SBR）[14-16]。考虑到使用丁苯橡胶进行复合改性可以改变复合材料的链刚度和交联密度，丁苯橡胶是实际工程中常用的提高改性沥青低温性能的有效改性剂[17,18]。Ren 等人[18]利用掺合梁流变仪（BBR）试验研究了添加 SBR 改性剂对栅极石改性沥青低温抗裂性能的影响，发现添加 SBR 是提高栅极石改性沥青低温 PG 级性能的重要途径。Liu 等人[19]使用丁苯橡胶改性剂来提高布顿岩改性沥青混合物的低温性能，结果表明，添加丁苯橡胶后，丁苯橡胶/布顿岩复合改性沥青混合物在 条件下的抗弯强度和最大弯曲应变分别提高了 和 。因此，使用丁苯橡胶改性沥青是提高废塑料改性沥青低温性能的有效解决方案。
In addition to low-temperature performance, the effect of aging on waste plasticmodified bitumen is also of concern. During the service life of bitumen pavement, bitumen is subject to aging due to multiple environmental factors [20-24]. After aging, bitumen becomes hardened and brittle, while the chemical composition of the bitumen also changes significantly [25-27]. It cracks and breaks easily under the action of external forces and fails to continue to perform its original role of bonding. Therefore, the aging behavior of modified bitumen has been a focus of interest for researchers. By comparing the rheological and chemical properties of SBS-modified bitumen, Lin et al. [28] suggested that the addition of a modifier can retard the aging of bitumen. However, most of the existing research on the long-term aging behavior of bitumen has focused on the more commonly used types of modified bitumen, such as SBS-modified bitumen. There are relatively few studies on the long-term aging behavior of plastic-modified bitumen. In addition, the aging behavior of composite-modified bitumen is more complicated than that of single-modified bitumen. Wang et al. [29] investigated the evolution of the rheological and chemical properties of SBS-modified bitumen and terminal blend rubberized/SBS composite-modified bitumen due to long-term aging and pointed out that the incorporation of terminal blend rubberized bitumen slows the aging rate of SBS-modified bitumen. As such, it is useful to investigate the long-term aging behavior of plastic/SBR composite-modified bitumen. 除低温性能外，老化对废塑料改性沥青的影响也值得关注。在沥青路面的使用寿命期间，沥青会受到多种环境因素的影响而老化[20-24]。老化后，沥青会变硬、变脆，同时沥青的化学成分也会发生显著变化 [25-27]。在外力作用下，沥青很容易开裂和断裂，无法继续发挥其原有的粘结作用。因此，改性沥青的老化行为一直是研究人员关注的焦点。Lin 等人[28]通过比较 SBS 改性沥青的流变和化学特性，认为添加改性剂可以延缓沥青的老化。然而，现有关于沥青长期老化行为的研究大多集中在 SBS 改性沥青等较常用的改性沥青类型上。关于塑性改性沥青长期老化行为的研究相对较少。此外，与单一改性沥青相比，复合改性沥青的老化行为更为复杂。Wang 等人[29]研究了 SBS 改性沥青和端掺橡胶/SBS 复合改性沥青在长期老化过程中的流变学和化学性质的变化，指出端掺橡胶沥青会减缓 SBS 改性沥青的老化速度。因此，研究塑料/SBR 复合改性沥青的长期老化行为很有帮助。
The objective of this study is to analyze the long-term aging behavior of plastic/SBR composite-modified bitumen. For this purpose, the waste plastic and SBR modifiers were 本研究旨在分析塑料/丁苯橡胶复合改性沥青的长期老化行为。为此，将废塑料和丁苯橡胶改性剂混合在一起。
first mixed with base bitumen to prepare the composite-modified bitumen. Following this, the prepared modified bitumen was subject to a pressure aging vessel (PAV) test to simulate long-term aging during service life. Then, temperature sweep and multiple stress creep recovery tests of the virgin and long-term aged modified bitumen were conducted to evaluate the evolution of the rheological properties of bitumen. At the same time, the evolution of the chemical composition of prepared bitumen was tested with the aid of gel permeation chromatography (GPC). Finally, the correlation between the rheological properties and chemical properties of waste plastic/SBR composite-modified bitumen was analyzed. 首先与基质沥青混合，制备复合改性沥青。然后，对制备好的改性沥青进行压力老化容器（PAV）试验，以模拟其在使用过程中的长期老化。然后，对原生沥青和长期老化改性沥青进行温度扫描和多应力蠕变恢复试验，以评估沥青流变特性的演变。同时，利用凝胶渗透色谱法（GPC）测试了制备的沥青化学成分的变化。最后，分析了废塑料/丁苯橡胶复合改性沥青的流变特性和化学特性之间的相关性。
2. Materials and Methods 2.材料和方法
First, a brief description of the materials and methods used in this study is given. Meanwhile, to facilitate the reader's understanding, Table 1 summarizes the abbreviations used in this studies. 首先，简要介绍了本研究使用的材料和方法。同时，为了便于读者理解，表 1 总结了本研究中使用的缩写。
Table 1. Abbreviations used in this studies. 表 1.本研究中使用的缩略语。
Abbreviations
Full Description 完整说明
SBR
Styrene butadiene rubber 丁苯橡胶
SBS
Styrene-butadiene-styrene
GPC
Gel permeation chromatography 凝胶渗透色谱法
MSCR
Pressure aging vessel 压力老化容器
TS
Multiple stress creep recovery 多应力蠕变恢复
LMSP
Temperature sweep 温度扫描
CAI
Large molecule size percentage 大分子尺寸百分比
LAI
Complex modulus aging index 复模量老化指数
MAI
Large molecular size distribution aging index 大分子尺寸分布老化指数
2.1. Materials 2.1.材料
In this study, the plastic modifier selected is a common household waste polyethylene material. The waste plastic modifier is mixed with a kind of PG 64-22 base bitumen to prepare the plastic-modified bitumen. The contents of waste plastic in the modified bitumen are and by weight. In addition, a kind of commercial SBR latex provided by a local company is used as modifier to enhance the low-temperature performance of plastic-modified bitumen. The Mooney viscosity of latex is . The content of SBR modifier in the composite-modified bitumen is by weight, Table 2 shows the basic properties of bitumen used in this study. 本研究选用的塑料改性剂是一种常见的家用废聚乙烯材料。废塑料改性剂与一种 PG 64-22 基质沥青混合，制备塑料改性沥青。按重量计，改性沥青中废塑料的含量分别为 和 。此外，还使用了当地一家公司提供的一种商用 SBR 胶乳作为改性剂，以提高塑料改性沥青的低温性能。胶乳的门尼粘度为 。 表 2 显示了本研究中使用的沥青的基本特性。
Table 2. Basic properties of bitumen. 表 2.沥青的基本特性
Properties
Results
Test Method
Penetration
67.8
ASTM D5
Softening point 软化点
48.3
ASTM D36
Ductility
ASTM D113
Rotary viscosity 旋转粘度
0.41
ASTM D4402
2.2. Methods 2.2.方法
2.2.1. Preparation Process of Composite Modified Bitumen 2.2.1.复合改性沥青的制备工艺
The detailed preparation process for modified bitumen is as follows: First, the base bitumen is heated to , and the weighed waste plastic modifier and by weight) is added to the heated bitumen. At this temperature, the plastic is left to swell for approximately . During the swelling process, a glass rod is used for stirring to disperse the plastic modifier into small pieces. Following this, the swollen bitumen is subjected to shearing using a high-speed shear at for ; the shear speed is set as . For plastic/SBR-modified composite bitumen, the weighed SBR (3% by 改性沥青的具体制备过程如下：首先，将基础沥青加热至 ，然后将称重后的废塑料改性剂 和 （按重量计）加入加热后的沥青中。在此温度下，塑料会膨胀约 。在膨胀过程中，使用玻璃棒进行搅拌，将塑料改性剂分散成小块。 然后，在 的高速剪切机上对溶胀的沥青进行剪切，剪切速度设定为 。对于塑料/丁苯橡胶改性的复合沥青，称量的丁苯橡胶（3% by
weight) is then added into the plastic bitumen for another high-speed shear process. The shear temperature is set as and the shear speed is set as . Finally, the mixed modified bitumen is stored at ambient temperature in preparation for testing. 然后在塑性沥青中加入沥青，再进行一次 高速剪切。剪切温度设定为 ，剪切速度设定为 。最后，将混合改性沥青储存在环境温度下，以备测试。
2.2.2. Aging Methods 2.2.2.老化方法
The long-term aging of base and modified bitumen is simulated via PAV test according to AASHTO R28. The parameters in the PAV test are set as follows: the aging temperature is controlled as and the aging period is set as . This aging condition is regarded as simulating the aging process of bitumen pavements over a period of 5 to 10 years. Before PAV test, an 85-min rolling thin film oven test was conducted at for base and modified bitumen according to AASHTO T240 to simulate the short-term aging of bitumen during mixing and paving. Table 3 presents the detailed preparation process of bitumen used in this study and their identifications. 根据 AASHTO R28，通过 PAV 试验模拟基质沥青和改性沥青的长期老化。PAV 试验的参数设置如下：老化温度控制为 ，老化周期设置为 。这种老化条件被视为模拟沥青路面 5 至 10 年的老化过程。在进行沥青摊铺试验前，根据 AASHTO T240，在 对基层沥青和改性沥青进行了 85 分钟的滚动薄膜烘箱试验，以模拟沥青在搅拌和摊铺过程中的短期老化。表 3 列出了本研究中使用的沥青的详细制备过程及其标识。
Table 3. Detailed preparation process of bitumen used in this study and their identifications. 表 3.本研究中使用的沥青的详细制备过程及其标识。
Bitumen
Waste Plastic 废塑料
Modifier
SBR
Long-Term
Aging
Identifications
-
-
-
Base-VIR
-
-
PAV
Base-PAV
-
-
-
PAV
-
Base bitumen
PAV
-
-
6-VIR
-
PAV
6-PAV
-
6R-VIR
PAV
6R-PAV
-
-
-
PAV
7.5-PAV
-
PAV
7.5R-PAV
2.2.3. Temperature Sweep (TS) Test 2.2.3.温度扫描 (TS) 测试
The complex modulus and phase angle of base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen before and after long-term aging at and , respectively, were measured via TS test. To compare the variation patterns of the complex modulus and phase angle of the bitumen samples under different aging conditions, the same test parameters were used for all samples. The bitumen samples were loaded in controlled-strain mode with a sinusoidal oscillation load. The strain levels are all . 通过 TS 试验分别测量了在 和 长期老化前后的基体沥青、塑料改性沥青和塑料/丁苯橡胶复合改性沥青的复模量 和相位角 。为了比较不同老化条件下沥青样品复模量和相位角的变化规律，所有样品都采用了相同的测试参数。沥青样品在受控应变模式下以 正弦振荡载荷加载。应变水平均为 。
2.2.4. Multiple Stress Creep Recovery (MSCR) Test 2.2.4.多应力蠕变恢复（MSCR）试验
The MSCR test is an improved test method based on the repeated creep recovery test, which is primarily used to evaluate the high-temperature performance and elastic response of bitumen materials. Based on ASSHTO TP-350, MSCR tests were performed on the base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen before and after long-term aging at and . In each MSCR test, twenty creep-and-recovery cycles at stress were first conducted on the prepared bitumen sample, followed by ten creep-and-recovery cycles at stress. Each creep-andrecovery process consists of a creep process and a recovery process. The time-strain data during the creep-and-recovery process was automatically collected by the dynamic shear rheometer. Based on the collected data, the following indicators were calculated. MSCR 试验是在重复蠕变恢复试验基础上改进的试验方法，主要用于评估沥青材料的高温性能和弹性响应。根据 ASSHTO TP-350，在 和 长期老化前后，对基本沥青、塑料改性沥青和塑料/丁苯橡胶复合改性沥青进行了 MSCR 试验。在每次 MSCR 试验中，首先对制备好的沥青样品在 应力下进行二十次蠕变-恢复循环，然后在 应力下进行十次蠕变-恢复循环。每个蠕变-恢复过程包括 蠕变过程和 恢复过程。蠕变-恢复过程中的时间应变数据由动态剪切流变仪自动采集。根据收集到的数据计算出以下指标。
where presents the percent recovery, represents non-recoverable creep compliance, presents peak strain, presents unrecovered strain, refers to the applied shear stress in . 其中 表示恢复百分比， 表示不可恢复的蠕变顺应性， 表示峰值应变， 表示未恢复应变， 指 中的施加剪应力。
2.2.5. GPC Test 2.2.5.GPC 试验
The GPC is an effective instrument for separating substances to be measured according to their molecular weight. During the GPC test, the sample solution flows slowly across the column containing the porous gel. The smaller the molecules, the simpler it is for molecules to enter the micro-pores inside the gel. Thus, smaller molecules pass through the column more slowly and are retained in the column longer. In contrast, the larger molecules have difficulty entering the microporous pores and are therefore the first to exit the column and be detected. The retention times in the chromatograms range from short to long, corresponding to the size of the molecules from large to small. GPC 是一种根据分子量分离待测物质的有效仪器。在 GPC 测试过程中，样品溶液缓慢流过含有多孔凝胶的色谱柱。分子越小，越容易进入凝胶内部的微孔。因此，小分子通过色谱柱的速度更慢，在色谱柱中保留的时间更长。与此相反，较大的分子很难进入微孔，因此会最先离开色谱柱并被检测出来。色谱图中的保留时间从短到长，与分子的大小从大到小相对应。
In this study, the GPC test was performed on base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen to evaluate the evolution of the molecular weight distribution of bitumen due to long-term aging. To prepare the bitumen sample for the GPC test, the selected samples were first dissolved in tetrahydrofuran solution; the concentration of the solutions was all controlled to . The bitumen and tetrahydrofuran solution was soaked for one day and then filtered through a sieve. The filtered sample was then injected into the GPC instrument to obtain its molecular weight distribution chromatogram. 本研究对基本沥青、塑料改性沥青和塑料/SBR 复合改性沥青进行了 GPC 测试，以评估沥青分子量分布因长期老化而发生的变化。为了制备用于 GPC 测试的沥青样品，首先将选定的样品溶解在四氢呋喃溶液中；溶液的浓度均控制在 。将沥青和四氢呋喃溶液浸泡一天，然后用 筛过滤。然后将过滤后的样品注入 GPC 仪器，以获得其分子量分布色谱图。
3. Results and Discussion 3.结果与讨论
3.1. Evaluation of Complex Modulus 3.1.复模量的评估
Figure 1 presents the complex modulus of different bitumen samples before and after long-term aging at and , respectively. It can be seen from the figure that as the temperature increases, the complex modulus of bitumen sample tends to decrease. The development of complex modulus is attributed to the increase in temperature intensifying the irregular movement of bitumen molecules. As such, less stress is required for the same strain response, reducing the resistance of bitumen to external forces, which finally expresses a reduction in the complex modulus. In addition, the addition of waste plastic increases the complex modulus of the base bitumen. Using as an example, the addition of and plastic modifier to the base bitumen increases the complex modulus by and , respectively. The increase in complex modulus is more pronounced with increasing amounts of plastic incorporated. The incorporation of SBR modifier does not only increase the complex modulus of plasticmodified bitumen. The above results suggest that the integrated modification enhances the permanent deformation resistance of bitumen. 图 1 显示了不同沥青样品在 和 长期老化前后的复模量 。从图中可以看出，随着温度的升高，沥青样品的复模量呈下降趋势。复合模量的变化是由于温度的升高加剧了沥青分子的不规则运动。因此，相同的应变反应所需的应力较小，从而降低了沥青对外力的抵抗能力，最终导致复合模量的降低。此外，废塑料的加入也会增加基础沥青的复合模量。以 为例，在基质沥青中加入 和 塑料改性剂后，复模量分别增加了 和 。复合模量的增加随着塑料添加量的增加而更加明显。SBR 改性剂的加入不仅增加了塑料改性沥青的复合模量，还增加了复合模量。上述结果表明，综合改性增强了沥青的抗永久变形能力。
After long-term aging, the complex modulus of different modified bitumen increases substantially. In existing studies, the resistance of bitumen to aging is usually evaluated via complex modulus aging index (CAI), which is the ratio of complex modulus of bitumen after aging to that of bitumen before aging. In this study, to compare the aging resistance of different bitumen samples, the CAI of base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen were calculated; results are shown in Table 4. As can be seen from the table, the CAI of base bitumen is the highest, indicating that after longterm aging, the complex modulus of base bitumen varies most significantly. In contrast, the aging index CAI of bitumen gradually decreases with the incorporation of plastic modifier Using as an example, the addition of and plastic modifier to the base bitumen decreases the CAI by and , respectively. The decrease in CAI becomes more pronounced as the amount of plastic modifier is increased. This indicates that the addition of plastic modifier has improved the aging resistance of bitumen. In addition, the integrate modification of plastic and SBR resulted in the smallest CAI for 经过长期老化后，不同改性沥青的复模量会大幅增加。现有研究通常通过复模量老化指数（CAI）来评价沥青的抗老化性，即老化后沥青的复模量与老化前沥青的复模量之比。在本研究中，为了比较不同沥青样品的抗老化性能，计算了基质沥青、塑料改性沥青和塑料/SBR 复合改性沥青的 CAI，结果如表 4 所示。从表中可以看出，基质沥青的 CAI 最高，说明经过长期老化后，基质沥青的复合模量变化最大。相反，沥青的老化指数 CAI 会随着塑料改性剂的加入而逐渐降低。以 为例，在基质沥青中加入 和 塑料改性剂后，CAI 分别降低了 和 。随着塑料改性剂用量的增加，CAI 的降低幅度也越来越大。这表明塑料改性剂的添加提高了沥青的抗老化性能。此外，塑料和丁苯橡胶混合改性后，沥青的 CAI 值最小。
composite-modified bitumen. The CAI of SBR/plastic composite-modified bitumen is far less than that of plastic-modified bitumen, indicating that compared with plastic, the application of SBR is more effective in improving the aging resistance of bitumen. For plastic/SBR composite-modified bitumen with and plastic inclusion, the aging index CAI is only around 2.5 . As such, and plastic inclusion are recommended to produce plastic/SBR composite-modified bitumen to obtain the bitumen with excellent aging resistance. 复合改性沥青。丁苯橡胶/塑料复合改性沥青的 CAI 远远低于塑料改性沥青，这表明与塑料相比，丁苯橡胶的应用在提高沥青的抗老化性能方面更为有效。对于含有 和 塑料的塑料/丁苯橡胶复合改性沥青，其老化指数 CAI 仅为 2.5 左右。因此，建议使用 和 加入塑料来生产塑料/丁苯橡胶复合改性沥青，以获得抗老化性能优异的沥青。
In addition complex modulus, the phase angle of bitumen samples also can be obtained via TS test, which reflects the hysteresis of strain to stress. Figure 2 presents the phase angle of bitumen samples before and after aging at and , respectively. It can be concluded from the figure that as the temperature rises, the phase angle of bitumen increases, but the increase is not obvious. The addition of plastic modifier reduces the phase angle of bitumen and the decrease becomes apparent with increasing plastic content. Similarly, the addition of SBR modifier further lowers the phase angle of the modified bitumen. This is achieved due to the addition of modifiers creating a support network in the modified bitumen, which leads to an enhanced elastic response for modified bitumen. 除复模量外，沥青样品的相位角也可通过 TS 测试获得，它反映了应变对应力的滞后性。图 2 分别显示了沥青样品在 和 老化前后的相位角。从图中可以得出结论：随着温度的升高，沥青的相角会增大，但增大的幅度并不明显。塑料改性剂的加入会减小沥青的相角，并且随着塑料含量的增加，相角减小的趋势会变得明显。同样，添加 SBR 改性剂会进一步降低改性沥青的相角。这是由于改性剂的加入在改性沥青中形成了一个支撑网络，从而增强了改性沥青的弹性响应。
After long-term aging, the phase angle of the bitumen is substantially reduced. This is due to the content of polar components such as asphaltenes increasing as the bitumen ages and the elastic response of bitumen is higher after aging. This pattern also applies to plastic-modified bitumen and plastic/SBR composite-modified bitumen with different plastic content, indicating that the aging of modified bitumen results in an increase in elastic response of composite-modified bitumen. 经过长期老化后，沥青的相位角大大减小。这是由于沥青中的极性成分（如沥青质）含量随着沥青的老化而增加，老化后沥青的弹性响应更高。这一规律也适用于不同塑料含量的塑料改性沥青和塑料/丁苯橡胶复合改性沥青，表明改性沥青的老化会导致复合改性沥青的弹性响应增加。
3.3. Evaluation of Rutting Factor 3.3.车辙系数评估
After obtaining the complex modulus and phase angel of bitumen, the rutting factor of bitumen was obtained, which is proven to correlate well with the high-temperature performance of bitumen. Figure 3 presents the rutting factor of bitumen before and after aging. As can be seen from the figure, the application of plastic improves the rutting factor of bitumen at different temperatures, and the increase in the rutting factor is more pronounced as the content of plastic increases, indicating the addition of plastic improves the high-temperature rutting resistance of bitumen. In addition, the addition of SBR does not lessen the improvement of the plastic on the high-temperature performance of the bitumen. On the contrary, the addition of SBR further improves the high-temperature performance of waste plastic-modified bitumen. After long-term aging, the rutting factor of bitumen increases obviously with the highest rutting factor of 7.5-PAV, indicating the temperature performance enhancement after bitumen long-term aging. It applies to all base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen. 在得到沥青的复模量和相位天使后，就得到了沥青的车辙系数，该系数被证明与沥青的高温性能有很好的相关性。图 3 显示了老化前后沥青的车辙系数。从图中可以看出，塑料的应用改善了沥青在不同温度下的车辙系数，而且随着塑料含量的增加，车辙系数的增加更为明显，这表明塑料的添加改善了沥青的高温抗车辙性能。此外，丁苯橡胶的添加并没有削弱塑料对沥青高温性能的改善作用。相反，丁苯橡胶的加入进一步提高了废塑料改性沥青的高温性能。长期老化后，沥青的车辙系数明显增加，其中 7.5-PAV 的车辙系数最高，说明沥青长期老化后的高温性能得到了提高。该研究适用于所有基质沥青、塑料改性沥青和塑料/SBR 复合改性沥青。
(a)
(b)
Figure 3. Cont. 图 3.图 3
(c)
(d)
(e)
Figure 3. Rutting factor of bitumen before and after aging at: (a) ; (b) ; (c) ; (d) ; (e) . 图 3.沥青老化前后的车辙系数，见图 3：(a) ； (b) ； (c) ； (d) ； (e) 。
3.4. Evaluation of Percent Recovery and Non-Recoverable Creep Compliance 3.4.评估恢复百分比和不可恢复蠕变符合性
The percent recovery of different bitumen samples at 0.1 and at five temperatures are measured via MSCR test, which characterizes the elastic deformation capacity of bitumen; results are shown in Figure 4. It can be concluded from the figure that for base bitumen, the percent recovery is low at both 0.1 and stress. Modification with plastic or SBR modifier leads to improved percent recovery of bitumen. In comparison, the modification of SBR plays a more vital role in improving the percent recovery of bitumen. Following the long-term aging process, the percent recovery of all base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen increases at five temperatures. For base bitumen, the recovery rate of bitumen after aging is still at a low level. For plastic-modified or plastic/SBR composite-modified bitumen, the improvement of recovery rate at 0.1 and after long-term aging is pronounced. Especially for 7.5R-PAV, the percent recovery of bitumen is close to . 通过 MSCR 试验测量了不同沥青样品在 0.1 和 五种温度下的恢复百分比，该试验表征了沥青的弹性变形能力；结果如图 4 所示。从图中可以得出结论，对于基质沥青，在 0.1 和 应力下的恢复百分比都很低。使用塑料或 SBR 改性剂进行改性可提高沥青的恢复百分率。相比之下，丁苯橡胶改性在提高沥青回收率方面的作用更大。在长期老化过程中，所有基质沥青、塑料改性沥青和塑料/丁苯橡胶复合改性沥青的回收率在五个温度下均有所提高。对于基质沥青，老化后的沥青回收率仍处于较低水平。对于塑料改性沥青或塑料/丁苯橡胶复合改性沥青，在 0.1 和 温度下长期老化后的回收率明显提高。特别是 7.5R-PAV 的沥青回收率接近 。
Figure 5 shows the non-recoverable creep compliance of bitumen at 0.1 and . It is generally accepted that the non-recoverable creep compliance of bitumen correlates well with the resistance to rutting of modified bitumen at high temperature. The lower the non-recoverable creep compliance, the better the high-temperature performance of the bitumen. As concluded from the figure for base bitumen, the non-recoverable creep compliance values and are high, indicating the high-temperature performance of base bitumen is weak. In contrast, the addition of the plastic modifier reduces the non-recoverable creep compliance of bitumen. The decrease in non-recoverable creep compliance is evident as the amount of plastic modifier content increases. The additional incorporation of SBR further reduces the non-recoverable creep compliance of plasticmodified bitumen. Especially for R-VIR, the non-recoverable creep compliance at 图 5 显示了沥青在 0.1 和 条件下的不可恢复蠕变顺应性。一般认为，沥青的不可恢复蠕变顺应性与改性沥青在高温下的抗车辙能力密切相关。不可恢复蠕变顺应性越低，沥青的高温性能越好。从图中可以看出，基质沥青的不可恢复蠕变顺应性值 和 较高，表明基质沥青的高温性能较弱。相反，添加塑性改性剂后，沥青的不可恢复蠕变顺应性降低。随着塑料改性剂含量的增加，不可恢复的蠕变顺应性明显下降。加入丁苯橡胶后，塑性改性沥青的不可恢复蠕变顺应性进一步降低。特别是对于 R-VIR，在温度为 0.5℃时的不可恢复蠕变顺应性为 0.5%。
0.1 and is close to 0 . As such, the higher plastic and SBR content is recommended to improve the high-temperature performance of bitumen. After long-term aging, the and of all base bitumen, plastic-modified bitumen and plastic/SBR compositemodified bitumen decreases dramatically. Especially for plastic-modified bitumen and plastic/SBR composite-modified bitumen, the and of bitumen after aging are close to 0 . As such, for modified bitumen, the high-temperature rutting resistance of bitumen after long-term aging is not a concern. To improve the performance of plasticmodified bitumen, existing studies have tried adding recycled crumb rubber to plastic bitumen. The reported findings in their studies suggested the incorporation of content crumb rubber to plastic-modified bitumen increased non-recoverable creep compliance at of bitumen at by [30]. The high-temperature performance of bitumen decreased after composite modification with crumb rubber and plastic. For comparison, the incorporation of 3% SBR to plastic-modified bitumen reduced non-recoverable creep compliance at of bitumen at by . The above results show that the composited modification of SBR is more beneficial for the high-temperature performance of bitumen compared to crumb rubber. 0.1， 接近 0 。因此，建议提高塑料和 SBR 的含量，以改善沥青的高温性能。经过长期老化后，所有基质沥青、塑料改性沥青和塑料/丁苯橡胶复合改性沥青的 和 都会急剧下降。尤其是塑料改性沥青和塑料/SBR 复合改性沥青，老化后的 和 都接近 0。因此，对于改性沥青来说，长期老化后沥青的高温抗车辙性能并不令人担忧。为改善塑性改性沥青的性能，现有研究尝试在塑性沥青中添加再生橡胶屑。他们的研究结果表明，在 塑料改性沥青中加入 含量的橡胶屑，可使沥青在 时的不可恢复蠕变顺应性提高 [30]。用橡胶屑和塑料进行复合改性后，沥青的高温性能有所下降。相比之下，在 塑料改性沥青中加入 3% 的丁苯橡胶后，沥青在 的不可恢复蠕变顺应性降低了 。上述结果表明，与橡胶屑相比，丁苯橡胶的复合改性更有利于提高沥青的高温性能。
3.5. Evaluation of Molecular Weight Distribution 3.5.分子量分布评估
Figure 6 shows the molecular weight distribution chromatograms of bitumen before and after aging. As can be seen from the figure for bitumen samples, there is a rising peak in the chromatogram around 21 to (corresponding to molecular weights of about 17,800 to 11,000 Daltons). The elevation of the peak at 21 to is higher in the chromatogram of the modified bitumen compared to the base bitumen. This indicates that a molecular aggregation process takes place during the modification process. The ongoing aggregation of small molecules into large molecules leads to an increase in the content of 图 6 显示了老化前后沥青的分子量分布色谱图。从图中可以看出，沥青样品的色谱图在 21 至 （对应分子量约为 17,800 至 11,000 道尔顿）附近出现了一个上升峰。与基质沥青相比，改性沥青色谱图中 21 至 处峰值的升高幅度更大。这表明在改性过程中发生了分子聚集过程。小分子不断聚合成大分子，导致沥青中的沥青质含量增加。
large molecular weight substances. After long-term aging, the higher peaks at 21 to for different bitumen chromatograms are found, suggesting the small molecule aggregation process also occurs during the long-term aging of bitumen. 大分子量物质。经过长期老化后，不同沥青色谱在 21 至 处出现较高的峰值，这表明沥青在长期老化过程中也会出现小分子聚集过程。
Figure 6. Molecular weight distribution chromatograms of bitumen before and after aging. 图 6.老化前后沥青的分子量分布色谱图。
To quantify the bitumen chromatogram, Li et al., [31,32] divided the bitumen chromatogram into large, medium and small molecules based on molecular weight. A schematic diagram of the division is shown in Figure 7. Using this chromatogram division method, the large molecule size (LMS) percentage of bitumen can be calculated from the following Equation (3). 为了量化沥青色谱图，Li 等人[31,32]根据分子量将沥青色谱图分为大、中、小分子。划分示意图如图 7 所示。利用这种色谱划分方法，可根据以下公式（3）计算出沥青的大分子尺寸（LMS）百分比。
where LMSP represents the large molecule size percentage in bitumen, . 其中，LMSP 表示沥青中的大分子尺寸百分比， 。
Figure 7. Schematic diagram of the division. 图 7.分部示意图。
The corresponding LMSP of base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen before and after long-term aging is calculated via Equation (3); results are shown in Figure 8. It is quite clear from the figure that the LMSP of bitumen increases after the modification by plastic and SBR. The addition of and plastic modifier to the base bitumen increases the LMSP by and . In addition, the addition of SBR to VIR, 6-VIR and 7.5-VIR increases the LMSP by , and , respectively. In addition, the LMSP of bitumen also increases with longterm aging. This indicates that the aggregation of small molecules occurs during the both modification and aging process of bitumen. 通过公式（3）计算出基本沥青、塑料改性沥青和塑料/丁苯橡胶复合改性沥青在长期老化前后相应的 LMSP；结果如图 8 所示。从图中可以明显看出，沥青经塑料和丁苯橡胶改性后，其 LMSP 有所提高。在基质沥青中添加 和 塑料改性剂后，沥青的 LMSP 分别增加了 和 。此外，在 VIR、6-VIR 和 7.5-VIR 中添加 SBR 后，沥青的 LMSP 分别增加了 、 和 。此外，沥青的 LMSP 也随着长期老化而增加。这表明在沥青的改性和老化过程中都会出现小分子聚集现象。
Figure 8. LMSP of bitumen before and after long-term aging. 图 8.长期老化前后沥青的 LMSP。
In addition to the LMSP of bitumen, the GPC test also gives the weight average molecular weight of the sample, which is derived via the following equation. is currently believed to reflect changes in large molecule size in the bitumen samples. Figure 9 presents the weight average molecular weight of base bitumen, plastic and plastic/SBR composite-modified bitumen before and after aging. As can be seen from the figure, the of bitumen slightly increases with the modification by plastic. The addition of , and plastic modifier to the base bitumen increases the by and , respectively. However, the lifting effect is not as effective as that with SBR modification. The addition of SBR to the 4.5-VIR, 6-VIR and 7.5-VIR increases the by and ,respectively. In addition, the of bitumen increases after a long-term aging process, which is due to the aggregation of small molecules after aging. 除了沥青的 LMSP 外，GPC 测试还能给出样品的重量平均分子量 ，该值通过以下公式得出。目前认为 反映了沥青样品中大分子尺寸的变化。图 9 显示了老化前后基质沥青、塑料和塑料/SBR 复合改性沥青的重量平均分子量。从图中可以看出，随着塑料的改性，沥青的 略有增加。在基质沥青中添加 、 和 塑料改性剂后， 分别增加了 和 。但是，其提升效果不如 SBR 改性效果好。在 4.5-VIR、6-VIR 和 7.5-VIR 中添加 SBR 后， ，分别增加了 和 。此外，沥青的 在长期老化后会增加，这是由于老化后小分子聚集所致。
where, represents the molecular weight; represents the weight of molar mass . 其中， 代表分子量； 代表摩尔质量的重量 。
Figure 9. of bitumen before and after long-term aging 图 9. 长期老化前后的沥青
To evaluate the aging resistance of bitumen in terms of the change in molecular size, two evaluation indexes, the large molecular size aging index (LAI) and the molecular weight aging index (MAI) (Equations (5) and (6)), are proposed. Table 5 presents the LAI and MAI of base bitumen, plastic-modified bitumen and plastic/SBR composite-modified bitumen. It can be concluded from the table that the base bitumen has the highest and MAI. For , the addition of and plastic modifier to the base bitumen decreases LAI by and , respectively. For MAI, the addition of and plastic modifier to the base bitumen decreases MAI by and , respectively, indicating that the base bitumen is less resistant to aging. The LAI and MAI of plastic- 为了从分子尺寸变化的角度评价沥青的耐老化性，提出了两个评价指标，即大分子尺寸老化指数（LAI）和分子量老化指数（MAI）（等式（5）和（6））。表 5 列出了基本沥青、塑料改性沥青和塑料/SBR 复合改性沥青的 LAI 和 MAI。从表中可以得出结论，基本沥青的 和 MAI 最高。就 而言，在基质沥青中添加 和 塑料改性剂后，LAI 分别降低了 和 。就 MAI 而言，在基质沥青中添加 和 塑料改性剂会使 MAI 分别降低 和 ，这表明基质沥青的抗老化能力较弱。塑料改性剂的 LAI 和 MAI
modified bitumen and plastic/SBR composite-modified bitumen are lower, indicating that the addition of modifiers improves the aging resistance of the bitumen. 改性沥青和塑料/丁苯橡胶复合改性沥青的抗老化性能较低，表明添加改性剂可提高沥青的抗老化性能。
where are the evaluation indexes; is the of bitumen before aging,%; is the LMSP of bitumen after aging,%. is the weight average molecular weight of bitumen before aging; is the weight average molecular weight of bitumen after aging; 其中 为评价指标； 为老化前沥青的 ，%； 为老化后沥青的 LMSP，%。 为老化前沥青的重量平均分子量； 为老化后沥青的重量平均分子量；
Table 5. LAI and MAI of different bitumen. 表 5.不同沥青的 LAI 和 MAI。
3.6. Correlation between Molecular Weight and Rheological Properties 3.6.分子量与流变特性之间的相关性
To analyze the effect of molecular weight on the rheological properties of plastics and plastic/SBR-modified bitumen, correlations between and rutting factor, at of plastic and plastic/SBR-modified bitumen were established using Pearson correlation analysis. Table 6 shows the correlation between and rheological properties of bitumen. As can be seen from the table, the and rheological properties of plastic and plastic/SBR-modified bitumen do not show a good linear correlation. This is due to the use of a 0.45 -micron filter to filter the dissolved bitumen sample prior to the experiment. The size of the plastic particles is greater than , so so the plastic phase will still remain on the filter after filtration. Thus, the measured via GPC does not provide a realistic representation of the of the plastic-modified bitumen. In contrast, the LMSP captures the molecular weight distribution of bitumen, rather than the actual molecular weight. Thus, the LMSP exhibits a better correlation with the rheological properties of modified bitumen. This indicates that the molecular weight distribution of bitumen affects its rheological properties to some extent. 为了分析分子量对塑料和塑料/SBR 改性沥青流变性能的影响，使用 Pearson 相关分析法建立了塑料和塑料/SBR 改性沥青的 与车辙系数、 在 之间的相关关系。表 6 显示了 与沥青流变特性之间的相关性。从表中可以看出， 与塑料沥青和塑料/丁苯橡胶改性沥青的流变性能没有很好的线性关系。这是因为在实验前使用了 0.45 微米的过滤器来过滤溶解的沥青样品。塑料颗粒的尺寸大于 ，因此过滤后塑料相仍会留在过滤器上。因此，通过 GPC 测得的 并不能真实反映塑料改性沥青的 。相比之下，LMSP 捕获的是沥青的分子量分布，而不是实际分子量。因此，LMSP 与改性沥青的流变特性具有更好的相关性。这表明，沥青的分子量分布会在一定程度上影响其流变特性。
Table 6. Correlation between molecular weight and rheological properties. 表 6.分子量与流变特性之间的相关性。
Bitumen Type
Regression Equation 回归方程
0.71
Plastic-modified bitumen 塑料改性沥青
0.74
0.48
0.62
Plastic/SBR-modified 塑料/改性丁苯橡胶
0.84
bitumen
0.75
0.53
0.37
4. Conclusions 4.结论
With the aid of DSR and GPC tests, the rheological properties and molecular weight distribution of base bitumen, plastic, and plastic/SBR-modified bitumen before and af- 借助 DSR 和 GPC 试验，研究了基质沥青、塑料和塑料/SBR 改性沥青在使用前和使用后的流变性能和分子量分布。
ter long-term aging were measured. According to the measured results, the following conclusions were summarized: 测量的结果表明，"钙钛矿 "的长期老化率为 0.5%。根据测量结果，总结出以下结论：
Modification by plastic improves the high-temperature performance of bitumen. It increases complex modulus, rutting factor and percent recovery of bitumen while it decreases the phase angle and non-recoverable creep compliance of bitumen. The integrate modification of plastic and SBR generates an elastic supporting network of bitumen, further enhancing the high-temperature performance of modified bitumen. The enhancement effect is more pronounced with increasing plastic inclusion. 塑料改性可改善沥青的高温性能。它提高了沥青的复合模量、车辙系数和恢复率，同时降低了沥青的相位角和不可恢复蠕变顺应性。塑料和丁苯橡胶的混合改性产生了沥青的弹性支撑网络，进一步提高了改性沥青的高温性能。随着塑料添加量的增加，增强效果更加明显。
The aggregation of small molecules occurs during the modification by plastic and SBR, as the large size molecule percentage in bitumen increases. During the long-term aging process, the small molecules in the bitumen also undergo aggregation reactions, and the LMSP and of bitumen increases. 在塑料和 SBR 改性过程中，随着沥青中大尺寸分子比例的增加，小分子会发生聚集。在长期老化过程中，沥青中的小分子也会发生聚集反应，沥青的 LMSP 和 也会增加。
For all three plastic-modified bitumen, the CAI, LAI and MAI are smaller than those of base bitumen. The aging resistance of bitumen is improved by an average of about after the addition of plastic modifiers, and it improves more significantly with increasing plastic content. After the addition of SBR modifier, the aging resistance of modified bitumen is further improves. 所有三种塑料改性沥青的 CAI、LAI 和 MAI 都小于基质沥青。添加塑料改性剂后，沥青的抗老化性能平均提高了约 ，而且随着塑料含量的增加，抗老化性能的提高更为显著。添加 SBR 改性剂后，改性沥青的耐老化性进一步提高。
The and rheological properties of plastic and plastic/SBR-modified bitumen do not correlate well, with correlation coefficients less than 0.6. In contrast, the LMSP of bitumen exhibits a better correlation with rheological properties of the modified bitumen, with correlation coefficients exceeding 0.7 . The molecular weight distribution of bitumen affects its rheological properties to some extent. 与塑性沥青和塑料/SBR 改性沥青的流变特性相关性不高，相关系数小于 0.6。相比之下，沥青的 LMSP 与改性沥青流变特性的相关性较好，相关系数超过 0.7。沥青的分子量分布在一定程度上影响其流变特性。
It is recommended to use SBR for composite modification of plastic-modified bitumen, which improves the high-temperature performance and aging resistance of modified bitumen. However, only one plastic modifier was utilized in this study. Future study is envisaged to verify the applicability of this rule using more types of plastic modifiers. 建议使用丁苯橡胶对塑料改性沥青进行复合改性，以提高改性沥青的高温性能和耐老化性。不过，本研究只使用了一种塑料改性剂。今后的研究计划使用更多类型的塑料改性剂来验证这一规则的适用性。
Author Contributions: Conceptualization, C.X. and M.L.; methodology, C.X. and M.L.; formal analysis, C.X. and L.L.; data curation, C.X.; writing-original draft preparation, C.X., M.L. and R.Y. All authors have read and agreed to the published version of the manuscript. 作者贡献：构思，C.X.和M.L.；方法，C.X.和M.L.；形式分析，C.X.和L.L.；数据整理，C.X.；写作-原稿准备，C.X.、M.L.和R.Y.。所有作者均已阅读并同意手稿的出版版本。
Funding: This work was funded by the Fundamental Research Funds for the Central Universities, CHD (Project No. 300102212104) 资助：本研究由中央高校基本科研业务费资助（项目编号：300102212104）。
Institutional Review Board Statement: Not applicable. 机构审查委员会声明：不适用。
Informed Consent Statement: Not applicable. 知情同意声明：不适用。
Data Availability Statement: The data presented in this study are available on request from the corresponding author. 数据提供声明：本研究中的数据可向通讯作者索取。
Conflicts of Interest: The authors declare no conflict of interest. 利益冲突：作者声明无利益冲突。
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