针对乳化沥青与泡沫沥青冷再生技术发展过程中的关键问题，介绍了冷再生技术的发展现状，分析了乳化沥青与泡沫沥青混合料的材料组分性能，总结了冷再生沥青混合料配合比设计方法和路面结构设计方法，论述了相关路用性能演化规律以及施工工艺和施工设备，提出了冷再生技术的未来发展趋势。研究结果表明：冷再生沥青混合料的材料组成成分间相互作用机制及强度破坏机理复杂，回收沥青混合料来源和掺量以及沥青老化程度、沥青以及外加剂种类及含量均会显著影响冷再生沥青混合料的材料性能；不同的冷再生沥青混合料设计方法在级配选择、沥青等级、成形方法、养护方式以及性能评价指标等方面差别较大，大多采用试验测试法指导配合比设计；冷再生沥青路面设计方法经历了从经验法到力学－经验法的转变，通常将冷再生材料视为无黏结颗粒材料或者沥青黏结材料进行结构设计，目前仍缺乏符合冷再生沥青混合料材料特性的力学失效设计准则；在工程应用方面，应充分考虑冷再生结构层位及力学响应，明确抗车辙、抗水损害、抗疲劳和低温抗开裂的性能需求，以指导冷再生沥青混合料的材料组成设计；未来应从施工工艺和材料组成两方面加强冷再生沥青混合料性能优化研究，建立以力学指标为基础的养生时间评估体系，完善适用于气候条件的冷再生结构层施工规范，加强现场试验的数据检测和收集工作，实现对冷再生沥青路面结构设计方程的有效标定。

　　In view of the key problems in the development of cold recycling technology of emulsified asphalt and foam asphalt, this paper introduces the development status of cold recycling technology, analyzes the material composition performance of emulsified asphalt and foam asphalt mixture, summarizes the mix proportion design method and pavement structure design method of cold recycling asphalt mixture, discusses the evolution law of relevant road performance, construction technology and construction equipment, and puts forward the future development trend of cold recycling technology. The research results indicate that the interaction mechanism and strength failure mechanism between the material components of cold recycled asphalt mixture are complex. The source and dosage of recycled asphalt mixture, as well as the degree of asphalt aging, the type and content of asphalt and additives, will significantly affect the material properties of cold recycled asphalt mixture; Different design methods for cold recycled asphalt mixtures vary greatly in terms of gradation selection, asphalt grade, forming method, curing method, and performance evaluation indicators. Most of them use experimental testing methods to guide mix design; The design method of cold recycled asphalt pavement has undergone a transformation from empirical method to mechanical empirical method. Cold recycled materials are usually regarded as non bonded granular materials or asphalt bonding materials for structural design. Currently, there is still a lack of mechanical failure design criteria that meet the characteristics of cold recycled asphalt mixture materials; In terms of engineering applications, the cold recycling structure layer and mechanical response should be fully considered, and the performance requirements for anti rutting, anti water damage, anti fatigue, and low-temperature anti cracking should be clarified to guide the material composition design of cold recycling asphalt mixtures; In the future, research on optimizing the performance of cold recycled asphalt mixtures should be strengthened from two aspects: construction technology and material composition. A health time evaluation system based on mechanical indicators should be established, and construction specifications for cold recycled structural layers suitable for Chinese climate conditions should be improved. Data detection and collection work for on-site testing should be strengthened to achieve effective calibration of the design equation for cold recycled asphalt pavement structures.

　　针对乳化沥青与泡沫沥青冷再生技术发展过程中的关键问题，介绍了冷再生技术的发展现状，分析了乳化沥青与泡沫沥青混合料的材料组分性能，总结了冷再生沥青混合料配合比设计方法和路面结构设计方法，论述了相关路用性能演化规律以及施工工艺和施工设备，提出了冷再生技术的未来发展趋势。研究结果表明：冷再生沥青混合料的材料组成成分间相互作用机制及强度破坏机理复杂，回收沥青混合料来源和掺量以及沥青老化程度、沥青以及外加剂种类及含量均会显著影响冷再生沥青混合料的材料性能；不同的冷再生沥青混合料设计方法在级配选择、沥青等级、成形方法、养护方式以及性能评价指标等方面差别较大，大多采用试验测试法指导配合比设计；冷再生沥青路面设计方法经历了从经验法到力学－经验法的转变，通常将冷再生材料视为无黏结颗粒材料或者沥青黏结材料进行结构设计，目前仍缺乏符合冷再生沥青混合料材料特性的力学失效设计准则；在工程应用方面，应充分考虑冷再生结构层位及力学响应，明确抗车辙、抗水损害、抗疲劳和低温抗开裂的性能需求，以指导冷再生沥青混合料的材料组成设计；未来应从施工工艺和材料组成两方面加强冷再生沥青混合料性能优化研究，建立以力学指标为基础的养生时间评估体系，完善适用于气候条件的冷再生结构层施工规范，加强现场试验的数据检测和收集工作，实现对冷再生沥青路面结构设计方程的有效标定。

　　In view of the key problems in the development of cold recycling technology of emulsified asphalt and foam asphalt, this paper introduces the development status of cold recycling technology, analyzes the material composition performance of emulsified asphalt and foam asphalt mixture, summarizes the mix proportion design method and pavement structure design method of cold recycling asphalt mixture, discusses the evolution law of relevant road performance, construction technology and construction equipment, and puts forward the future development trend of cold recycling technology. The research results indicate that the interaction mechanism and strength failure mechanism between the material components of cold recycled asphalt mixture are complex. The source and dosage of recycled asphalt mixture, as well as the degree of asphalt aging, the type and content of asphalt and additives, will significantly affect the material properties of cold recycled asphalt mixture; Different design methods for cold recycled asphalt mixtures vary greatly in terms of gradation selection, asphalt grade, forming method, curing method, and performance evaluation indicators. Most of them use experimental testing methods to guide mix design; The design method of cold recycled asphalt pavement has undergone a transformation from empirical method to mechanical empirical method. Cold recycled materials are usually regarded as non bonded granular materials or asphalt bonding materials for structural design. Currently, there is still a lack of mechanical failure design criteria that meet the characteristics of cold recycled asphalt mixture materials; In terms of engineering applications, the cold recycling structure layer and mechanical response should be fully considered, and the performance requirements for anti rutting, anti water damage, anti fatigue, and low-temperature anti cracking should be clarified to guide the material composition design of cold recycling asphalt mixtures; In the future, research on optimizing the performance of cold recycled asphalt mixtures should be strengthened from two aspects: construction technology and material composition. A health time evaluation system based on mechanical indicators should be established, and construction specifications for cold recycled structural layers suitable for Chinese climate conditions should be improved. Data detection and collection work for on-site testing should be strengthened to achieve effective calibration of the design equation for cold recycled asphalt pavement structures.

　　引言

　　Introduction

　　进入２１世纪以来，国内道路建设规模和建设速度持续增 长。近年来随着公路设计服务年限的临近，各地道路陆续出现一系列病害，由此导致道路养护里程和养护规模急速增长，在此过程中不可避免地产生大量的沥青铣刨料，其中包括回收沥青混合料（ＲｅｃｙｃｌｅｄＡｓｐｈａｌｔＰａｖｅｍｅｎｔ，ＲＡＰ）以及回收水泥稳定基层料［１－２］。露天堆放、填埋等传统处理方法会造成环境污染以及资源浪费。此外，随着天然集料和沥青材料的供应紧缺和上涨，对道路建设成本以及施工进度产生了一定的负面影响，因此，再生技术得到了广泛的关注和应用［３－４］。再生技术主要包括热再生技术和冷再生技术。相比于热再生，冷再生技术通常采用乳化沥青或泡沫沥青作为沥青胶结料，在常温下进行拌和和压实，可降低沥青胶结料的初始老化［５］，且能量消耗仅为生产同等沥 青 混 合 料 的 ２０％～４０％［６－７］，具 有节 能、可持续性强和经济效益高等优势。根据施工工艺、铣刨深度以及拌和场地的不同，冷再生技术细分为就地 冷 再 生（ＣｏｌｄＩｎ－Ｐ１ａｃｅＲｅｃｙｃｌｉｎｇ，ＣＩＲ）、厂拌冷再生（ＣｏｌｄＣｅｎｔｒａｌＰｌａｎｔＲｅｃｙｃｌｉｎｇ，ＣＣＰＲ）和全深式冷再生（ＦｕｌｌＤｅｐｔｈＲｅｃｙｃｌｉｎｇ，ＦＤＲ）。冷再生技术经过几十年的发展已被世界各国广泛应用，在美国、加拿大、法国、德国、澳大利亚等已较为成熟。目前冷再生技术主要应用于轻交通等级的路面修复，弗吉尼亚州交通部的研究表明冷再生技术对于重交通道路的修复也具有明显的适用性和显著的成本效益［８］。

　　Since the beginning of the 21st century, the scale and speed of domestic road construction have continued to grow. In recent years, as the service life of highway design approaches, a series of road diseases have emerged in various regions, leading to a rapid increase in road maintenance mileage and scale. In this process, a large amount of asphalt milling materials are inevitably generated, including recycled asphalt pavement (RAP) and recycled cement stabilized base materials [1-2]. Traditional methods such as open-air stacking and landfilling can cause environmental pollution and waste of non renewable resources. In addition, with the shortage and price increase of natural aggregates and asphalt materials, it has had a certain negative impact on road construction costs and construction progress. Therefore, recycling technology has received widespread attention and application [3-4]. Regeneration technology mainly includes hot regeneration technology and cold regeneration technology. Compared with hot recycling, cold recycling technology usually uses emulsified asphalt or foam asphalt as asphalt binder. Mixing and compaction at normal temperature can reduce the initial aging of asphalt binder [5], and the energy consumption is only 20%~40% of the production of the same asphalt mixture [6-7]. It has the advantages of energy conservation, environmental protection, strong sustainability and high economic benefits. According to different construction techniques, milling depths, and mixing sites, cold recycling technology is divided into on-site cold recycling (CIR), factory mixed cold recycling (CCPR), and full depth recycling (FDR). Cold regeneration technology has been widely applied in countries around the world after decades of development, and has become relatively mature in countries such as the United States, Canada, France, Germany, and Australia. At present, cold recycling technology is mainly applied to the repair of light traffic grade road surfaces. Research by the Virginia Department of Transportation has shown that cold recycling technology also has significant applicability and cost-effectiveness for the repair of heavy traffic roads [8].

　　目前，众多学者主要从冷再生沥青混合料的材料组成性能分析、混合料配合比设计方法和路面结构设计方法、混合料路用性能分析以及施工技术和施工装备等方面对冷再生技术开展研究。冷再生沥青混合料材料组成及其相互作用机制复杂，众多学者主 要 研 究 ＲＡＰ 料、乳 化沥 青／泡 沫 沥 青 胶 结 料，水泥／石灰添加剂等因素对冷再生沥青混合料性能的影响。研究结果表明，ＲＡＰ料变异性大，ＲＡＰ料来源、沥青老化程度及 ＲＡＰ料掺量都会影响冷再生沥青混合料性能，此外，泡沫沥青和乳化沥青作为胶结料的混合料强度形成机理以及水泥和石灰对混合料力学性能提升效果也存在差异［９］，冷再生沥青混合料的材料组分相互作用机制和强度破坏机理有待进一步明确，因此，在世界范围内尚未形成统一的冷再生沥青混合料配合比设计方法和路面结构设计方法。国外通常采用的配合比设计方法有 ＡＡＳＨＴＯ 修正马歇尔法、Ｈｖｅｅｍ 设计法、俄勒冈州设计法、ＡＩ设计法等［１０］。发布了《公路沥青路面再生技术规范》（ＪＴＧ／Ｔ５５２１—２０１９），并 在２０１９年 进行 了 修 订，规定了采用双面击实５０＋２５次的马歇尔法。此外，路面结构设计方法存在冷再生路面破坏失效准则不统一、模型预估值与路面检测值不匹配等问题。以上原因制约了冷再生技术的广泛应用。本文总结了冷再生技术类别及发展现状、乳化沥青和泡沫沥青混合料材料组成性能分析、配合比设计及路面结构设计方法、路用性能分析以及冷再生技术工艺和施工设备等研究现状，并对相关技术方法进行了对比分析，提出了冷再生技术的关键研究问题和未来发展趋势，旨在进一步促进冷再生技术在实际工程中的应用。

　　At present, many scholars mainly conduct research on cold recycling technology from the aspects of material composition and performance analysis of cold recycled asphalt mixture, mixture mix design method and pavement structure design method, mixture road performance analysis, as well as construction technology and equipment. The composition of cold recycled asphalt mixture and its interaction mechanism are complex. Many scholars mainly study the influence of RAP material, emulsified asphalt/foam asphalt binder, cement/lime additives and other factors on the performance of cold recycled asphalt mixture. The research results show that RAP material has great variability. The source of RAP material, asphalt aging degree and the amount of RAP material will affect the performance of cold recycled asphalt mixture. In addition, the strength formation mechanism of mixture with foam asphalt and emulsified asphalt as binder and the improvement effect of cement and lime on the mechanical performance of mixture are also different [9]. The interaction mechanism of material components and strength destruction mechanism of cold recycled asphalt mixture need to be further clarified. Therefore, there is no unified mix design method of cold recycled asphalt mixture and pavement structure design method in the world. The commonly used mix design methods abroad include AASHTO modified Marshall method, Hveem design method, Oregon design method, AI design method, etc. [10]. China has released the "Technical Specification for Highway Asphalt Pavement Recycling" (JTG/T5521-2019) and revised it in 2019, stipulating the use of Marshall method with double-sided compaction of 50+25 times. In addition, there are some problems in the pavement structure design method, such as the failure criteria of cold recycled pavement are not unified, and the predicted values of the model do not match the measured values of the pavement. The above reasons restrict the widespread application of cold regeneration technology. This paper summarizes the category and development status of cold recycling technology, composition and performance analysis of emulsified asphalt and foam asphalt mixture materials, mix design and pavement structure design methods, road performance analysis, cold recycling technology process and construction equipment, and other research status.

　　１冷再生技术发展现状

　　1. Development Status of Cold Recycling Technology

　　1.1 北美

　　1.1 North America

　　美国早在１９１５年开展冷再生技术研究，但在１９７４年 前 开 展 的 相 关 试 验 研 究 较 少，在 ２０ 世 纪７０年代后逐步得到推 广 应 用［１１］。截 止１９８５年 底，宾夕法尼亚交通部完成了包括就地冷再生、厂拌冷再生和全深式冷再生在内的大约９０个冷再生项目，旨在推动冷再生在基层应用建立标准规范，并为相关工程项目提供施工技术指导。自１９８４年以来，美国交通部开展了１２０余项就地冷再生项目，并持续对该技术的施工工艺和材料性能进行评估。到２０世纪８０年代末，美国沥青再生料用量已占到全部沥青混合料的一半。堪萨斯州交通部自１９８６年采用冷再生技术修复路面，并在１９９０～１９９２年期间修建了４条试验 路。截 １９９６年，爱 荷华 州 已 完 成９７个就地冷再生项目［１２］。美国２５个州的沥青再生料使用 规 模 已 达 到 近 ２ 亿 吨。Ｍｏｒｉａｎ 等［１３］介 绍 了美国宾夕法尼亚州４４条实施冷再生技术的路段使用情况，调查结果显示冷再生路面抗反射裂缝性能较传统热拌混合料直接加铺的方式提高了１～２倍，且成本低于其２／３。

　　The United States first conducted research on cold regeneration technology in 1915, but there were relatively few related experimental studies conducted before 1974, and it gradually gained promotion and application after the 1970s [11]. By the end of 1985, the Pennsylvania Department of Transportation had completed approximately 90 cold recycling projects, including on-site cold recycling, factory mixed cold recycling, and full depth cold recycling, aimed at promoting the establishment of standard specifications for cold recycling applications at the grassroots level and providing construction technical guidance for related engineering projects. Since 1984, the US Department of Transportation has carried out over 120 on-site cold recycling projects and continuously evaluated the construction process and material properties of this technology. By the late 1980s, the use of recycled asphalt in the United States had accounted for half of all asphalt mixtures. The Kansas Department of Transportation has been using cold recycling technology to repair road surfaces since 1986 and built four test roads between 1990 and 1992. As of 1996, Iowa had completed 97 on-site cold recycling projects. The use of asphalt recycled materials in 25 states in the United States has reached nearly 200 million tons. Morian et al. [13] introduced the usage of cold recycling technology in 44 road sections in Pennsylvania, USA. The survey results showed that the anti reflective crack performance of cold recycled pavement was 1-2 times higher than that of traditional hot mix direct paving, and the cost was less than 2/3 of it.

　　美国沥青路面协会年度调查显示，２０１８年９９％以上的 ＲＡＰ料被回收利用［１４］。目 前，美 国 联 邦 公 路 局 颁 布 了 ＦｅｄｅｒａｌＬａｎｄｓＨｉｇｈｗａｙＳｐｅｃｉｆｉｃａｔｉｏｎｓ，并对ＣＩＲ和ＦＤＲ两种再生工艺进行了规范，此外全美目前有４１个州少颁布了一种冷再生技术规范；加拿大１０个省或地区中有３个省或地区制定了有关冷再生的技术规范。北美地区 的 冷 再 生 技 术 规 范 的 制 定 情 况 如 图 １ 所示［１５］，共涉及８３个冷再生技术规范，其中大约５４％（４５个规范）规 范 了 ＣＩＲ，１７％（１４ 个 规范）规 范 了ＣＣＰＲ，２９％（２４个规范）规范了 ＦＤＲ。ＲＡＰ料除了应用于沥青混合料，还作为碎石材料应用于道路建设。工程实践已证明 ＲＡＰ料可应用于无黏结 基 层 材 料 和 底 基 层 材 料，但 ＲＡＰ 料 级配是 限 制 其 应 用 的 主 要 因 素。美 国 ４９ 个 州 已 将ＲＡＰ料应用于沥青混合料中，包括佛吉尼亚州在内的１３个州应用于基层，其中４个州应用于底基层，２个州应用于稳定基层材料和路肩集料［１６］。总体来说，将 ＲＡＰ 料 应用于级配碎石基层和底基层具有良好的路用性能。

　　The annual survey of the National Asphalt Pavement Association in the United States shows that more than 99% of RAP materials were recycled in 2018 [14]. At present, the Federal Highway Administration of the United States has issued the Federal Lands Highway Specifications and standardized the CIR and FDR recycling processes. In addition, there are currently 41 states in the United States that have issued at least one cold recycling technology specification; Three out of ten provinces or territories in Canada have established technical specifications for cold regeneration. The development of cold regeneration technology specifications in North America is shown in Figure 1 [15], involving a total of 83 cold regeneration technology specifications, of which approximately 54% (45 specifications) regulate CIR, 17% (14 specifications) regulate CCPR, and 29% (24 specifications) regulate FDR. RAP material is not only used in asphalt mixtures, but also as crushed stone material in road construction. Engineering practice has proven that RAP material can be applied to non bonded base materials and sub base materials, but the gradation of RAP material is the main factor limiting its application. Forty nine states in the United States have applied RAP material to asphalt mixtures, including 13 states including Virginia for base use, with 4 states for subbase and 2 states for stabilizing base materials and shoulder aggregates [16]. Overall, applying RAP material to graded crushed stone base and subbase has good road performance.

　　１.2 欧洲

　　1.2 Europe

　　２０世纪７０年代中期，德国、荷兰以及芬兰等陆 续 开 展 了 路 面 再 生 料 的 研 究。欧 盟 颁 布 的ＷａｓｔｅＦｒａｍｅｗｏｒｋＤｉｒｅｃｔｉｖｅ（２００８／９８／ＥＣ）中 明确了沥青再生技术的重要性，到２０２０年非危害性建筑垃圾（包括 沥 青 垃 圾）的 回 收 率 应 达 到７０％。德 国目前 已 实 现 了 将１００％ＲＡＰ 料 回收 再 利 用。芬 兰将路面再生材料主要应用于轻交通等级路面的面层和基层，近年来逐渐应用于高等级公路［１７］。法国将冷再生技术推广于高速公路和主要交通道路的修复工程。比利时于１９８９年引进了冷再生技术，并在１９８９～２００１ 年 修 复 了 ３０ 万 平 方 米 的 再 生 路面［１８］。在冷再生沥青混合料的规范标准方面，英国总结了 ＲＡＰ料在道路修复和泡沫沥青结构层中的应用情况，《公路工程规范》的第９４７和９４８条中规范了就地冷再生和厂拌冷再生的设计流程，对配合比设计方法以及冷再生沥青路面的预期刚度模量提供指导［１９］。1.3

　　In the mid-1970s, countries such as Germany, the Netherlands, and Finland successively conducted research on road recycled materials. The Waste Framework Directive (2008/98/EC) issued by the European Union emphasizes the importance of asphalt recycling technology, and by 2020, the recycling rate of non hazardous construction waste (including asphalt waste) should reach 70%. Germany has currently achieved the recycling and reuse of 100% RAP materials. Finland mainly applies recycled pavement materials to the surface and base layers of light traffic grade pavements, and has gradually applied them to high-grade highways in recent years [17]. France will focus on promoting cold recycling technology in the repair projects of highways and major transportation roads. Belgium introduced cold recycling technology in 1989 and repaired 300000 square meters of recycled road surfaces from 1989 to 2001. In terms of specifications and standards for cold recycled asphalt mixture, the UK summarized the application of RAP material in road repair and foam asphalt structural layer. Articles 947 and 948 of the Highway Engineering Specifications standardize the design process of in situ cold recycling and plant mix cold recycling, providing guidance for mix design methods and the expected stiffness and modulus of cold recycled asphalt pavement [19]. 1.3 China

　　截２０２１年末， 公 路 总 里 程５２８万 ，随着公路里程的增加，公路养护投入不断加大。交通部《公路网规划（２０１３～２０３０年）》指出，９７％的国道、省道及县乡道将进行升级改造，公路养护设备和服务市场规模达２０００亿人民币。建设较早的高等级公路多为半刚性基层沥青路面，由于沥青面层较薄，道路易发生结构性损伤，在道路养护过程中通常将沥青面层铣刨破碎后对半刚性基层进行处治。从１９９８年开始对冷再生沥青混合料进行大规模的研究和应用工作，经过多年的研究和推广已在高等级公路或干线公路得到一定程度的应用。２００７年之前，冷再生沥青混合料主要应用于高速公路的基层和底基层，近几年逐步推广应用下面层。２０１０年后，对泡沫沥青的研究越来越多，截２０１７年泡沫沥青已分别在江苏、浙江、湖北、广 东、江西以及天津等地得到一定规模的应用［２０］。２０１７年和２０１８年包茂高速陕蒙段和青银高速靖王段的路面大修工程，将乳化沥青厂拌冷再生作为下面层进行大面积推广应用，共利用了路面铣刨料约３０万吨，经济效益与环境效益显著［２１］。《“十四五”公路养护管理发展纲要》提出了大力推动废旧路面材料、工业废弃物等再生利用，提升资源利用效率。目前高速公路沥青路面材料循环利用率为９５％，普通国省道沥青路面材料循环利用率为８０％。１.4 冷再生技术对比分析

　　As of the end of 2021, the total length of highways in China was 5.28 million kilometers, and with the increase of highway mileage, investment in highway maintenance continues to increase. The National Highway Network Plan (2013-2030) issued by the Ministry of Transport states that 97% of China's national highways, provincial highways, and county and township roads will be upgraded and renovated, and the market size of highway maintenance equipment and services will reach 200 billion yuan. China's early construction of high-grade highways mostly used semi-rigid base asphalt pavement. Due to the thin asphalt surface layer, the road is prone to structural damage. In the process of road maintenance, the asphalt surface layer is usually milled and crushed before treating the semi-rigid base layer. China has been conducting large-scale research and application of cold recycled asphalt mixture since 1998, and after years of research and promotion, it has been applied to a certain extent on high-grade highways or main roads in China. Before 2007, cold recycled asphalt mixture was mainly used for the base and subbase of highways, and in recent years, it has gradually been promoted and applied to the lower layers. Since 2010, more and more research has been done on foam asphalt in China. As of 2017, foam asphalt has been applied in Jiangsu, Zhejiang, Hubei, Guangdong, Jiangxi, Tianjin and other places on a certain scale [20]. In 2017 and 2018, the road surface overhaul projects of the Shaanxi Inner Mongolia section of the Baomao Expressway and the Jingwang section of the Qingyin Expressway promoted the large-scale application of emulsified asphalt plant mixed cold recycling as the lower layer, using a total of about 300000 tons of road milling materials, with significant economic and environmental benefits [21]. The "14th Five Year Plan for the Development of Highway Maintenance Management" proposes to vigorously promote the recycling of waste road materials, industrial waste, and other materials to improve resource utilization efficiency. At present, the recycling rate of asphalt pavement materials on Chinese highways is 95%, and the recycling rate of asphalt pavement materials on ordinary national and provincial roads is 80%. 1.4 Comparative analysis of cold regeneration technology

　　表１总结分析了３种冷再生技术适用的病害处治形式，参 照 《公路沥青路面预防养护技术规范》（ＪＴＧ／Ｔ５１４２－０１—２０２１）对病害形式分类为路表病害、变形 类 病 害 和 裂 缝 类 病 害 ３ 种 形 式［２２］。表 １中：√为适用；Δ为可用；×为不；上标ａ表示如果病害只发生在道路表层，可直接设置加铺层，或者进行就地冷再生处理；上标ｂ表示尽管该再生方式可处治该类型病害，但经济性较差，不采用；上标ｃ表示需对下承层进行加固处理；上标ｄ表示如果路基承载能力不足，可采取水泥、石灰等化学改良方法进行加固处理。

　　Table 1 summarizes and analyzes three types of disease treatment forms applicable to cold recycling technology. Referring to the "Technical Specification for Preventive Maintenance of Asphalt Pavement on Highways" (JTG/T5142-01-2021), the disease forms are classified into three types: surface diseases, deformation diseases, and crack diseases [22]. In Table 1: √ is applicable; Δ is available; X is not recommended; The superscript 'a' indicates that if the disease only occurs on the surface of the road, an additional layer can be directly added or on-site cold recycling treatment can be carried out; The superscript b indicates that although this regeneration method can treat this type of disease, its economy is poor and it is not recommended to use it; The superscript c indicates the need for reinforcement treatment of the underlying layer; The superscript d indicates that if the bearing capacity of the roadbed is insufficient, chemical improvement methods such as cement and lime can be used for reinforcement treatment.

　　２冷再生沥青混合料材料组成性能分析

　　Analysis of Composition and Performance of Cold Recycled Asphalt Mixture Materials

　　冷再生沥青混合料的材料组成复杂，包含 ＲＡＰ料、新集料、乳化沥青／泡沫沥青、水泥等组分，各组成成分的力学性能及相对含量的变化会影响混合料的力学性能，因此，有必要对冷再生沥青混合料的组成成分进 行 性 能 及 力 学 评 估。本 文 选 取 ＲＡＰ 料、乳化沥青／泡沫沥青胶结料以及水泥／水泥外添剂进行组分性能分析。2.1 ＲＡＰ料

　　The material composition of cold recycled asphalt mixture is complex, including RAP material, new aggregate, emulsified asphalt/foam asphalt, cement and other components. The change of mechanical properties and relative content of each component will affect the mechanical properties of the mixture. Therefore, it is necessary to conduct performance and mechanical evaluation on the components of cold recycled asphalt mixture. In this paper, RAP material, emulsified asphalt/foam asphalt binder and cement/cement additive are selected for component performance analysis. 2.1 RAP material

　　ＲＡＰ料中的粗集料颗粒假定具有较好的强度和抗变形能力，由细集料和老化沥青胶浆组成的老化砂浆具有一定的脆性和塑性，这取决于沥青的老化和氧化程度以及温度等因素。同时，三轴蠕变试验的相关结果也验证了 ＲＡＰ料具有一定的黏性和温度依赖性，老化沥青能够影响冷再生沥青混合料力学性能，因此，在冷再生沥青混合料配合比设计中应充分考虑 ＲＡＰ料性能，分析老化沥青性能，以确定沥青掺量。ＪＴＧ／Ｔ５５２１—２０１９中规定了沥青路面回收料的取样与试验分析方法，在回收料使用前对 ＲＡＰ料 的含 水 率、级 配、砂 当 量、沥 青 含 量及性能、抽提后的旧集料级配及集料性质进行测试。众多学者主要从 ＲＡＰ料来源、沥青老化程度、ＲＡＰ掺量等方面研究 ＲＡＰ料对冷再生沥青混合料的性能影响。不同 来 源 的 ＲＡＰ 料 主要 在 级 配 组 成、老 化 沥青砂浆性能方面存在差异。沥青路面在长期荷载作用下会发生集料颗粒破损，以及受铣刨、破碎和存储等流程的影 响，导 致 ＲＡＰ 料 具有 更 多 的 细 集 料 成分［２３－２４］。此外，由于 老 化 沥 青 的 黏 结 作 用，ＲＡＰ 料存在大量虚假颗粒团，在混合料压实过程中虚假颗粒团会发生破裂，从而改变混合料的设计级配，其中细颗粒中的 虚 假 颗 粒 团 成 分 高 于 粗 颗 粒［２５］，因 此，在应用前应对其颗粒团聚特性进行评估。

　　The coarse aggregate particles in RAP material are assumed to have good strength and deformation resistance, while the aged mortar composed of fine aggregate and aged asphalt binder has certain brittleness and plasticity, which depend on factors such as the aging and oxidation degree of asphalt and temperature. At the same time, the relevant results of the triaxial creep test also verified that RAP material has certain viscosity and temperature dependence, and aged asphalt can affect the mechanical properties of cold recycled asphalt mixture. Therefore, in the design of the mix proportion of cold recycled asphalt mixture, the performance of RAP material should be fully considered, and the performance of aged asphalt should be analyzed to determine the optimal asphalt dosage. JTG/T5521-2019 specifies the sampling and testing analysis methods for recycled asphalt pavement materials. Prior to the use of recycled materials, the moisture content, gradation, sand equivalent, asphalt content and properties of RAP materials, as well as the gradation and properties of extracted old aggregates, are tested. Many scholars have mainly studied the influence of RAP materials on the performance of cold recycled asphalt mixtures from the aspects of RAP material source, asphalt aging degree, RAP dosage, etc. RAP materials from different sources mainly have differences in grading composition and performance of aged asphalt mortar. Asphalt pavement will experience aggregate particle damage under long-term load, as well as the influence of milling, crushing, and storage processes, resulting in RAP materials having more fine aggregate components [23-24]. In addition, due to the bonding effect of aged asphalt, RAP material contains a large number of false particle clusters. During the compaction process of the mixture, the false particle clusters will break, thereby changing the design gradation of the mixture. The composition of false particle clusters in fine particles is higher than that in coarse particles [25]. Therefore, its particle aggregation characteristics should be evaluated before application.

　　此外，不同来源的 ＲＡＰ料表面裹附的老化沥青砂浆差异较大，包括沥青种类、沥青含量及矿粉性能等因素，并且沥青是一 种 温 度 敏 感 性 材 料，不 同 ＲＡＰ 料 在同一温 度 下 的 性 能 各 异。ＲＩＬＥＭ 技 术 委 员 会 在２３７－ＳＩＢＴＧ６技术方法中提出采用破碎试验评价不同级配 区 间 ＲＡＰ 料 在 击 实 荷 载 下 的 颗 粒 细 化 特征，基于通过１．６ｍｍ 筛孔尺寸通过率对不同来源的 ＲＡＰ 料 进 行 初 步 分 档；其 次 开 展 不 同 温 度 下ＲＡＰ料破碎试验，基于不同温度与５ ℃的１．６ｍｍ筛孔通过率 的 比 值 表 征 ＲＡＰ 料 的温 度 敏 感 性，以反映老化沥青在冷再生沥青混合料中黏聚程度，并对 ＲＡＰ料进行二 次 分 档，进 而 对 不 同 来 源 的 ＲＡＰ料进行有效的质量控制［２５－２７］。不同使用年限的 ＲＡＰ料对冷再生沥青混合料性能的影响主要在于沥青老化程度的差异，使用年限越长，沥青老化程度越高。研究表明：沥青老化能够提高新旧沥青的黏结程度［２８－２９］，并随着老化程度的增加而降 低［３０］。沥 青老 化 导 致 混 合 料 空 隙 率 增大，间接劈裂强度、断裂能和水稳定性下降，高温稳定性增加［３１－３２］。以 上可 知，由 于 ＲＡＰ 料 中老 化 沥青的存在，导 致 ＲＡＰ 料 在荷 载 作 用 下 更 易 发 生 变形或断裂；随着 ＲＡＰ料掺量的增大，再生沥青路面的整体路用性能呈下降趋势［３３－３４］。

　　In addition, the aged asphalt mortar coated on the surface of RAP materials from different sources varies greatly, including factors such as asphalt type, asphalt content, and mineral powder properties. Moreover, asphalt is a temperature sensitive material, and the performance of different RAP materials varies at the same temperature. The RILEM Technical Committee proposed in the 237-1IBTG6 technical method to evaluate the particle refinement characteristics of RAP materials with different grading ranges under compaction loads using crushing tests, and to preliminarily classify RAP materials from different sources based on the pass rate through a 1.6mm sieve size; Secondly, RAP material crushing tests were conducted at different temperatures, and the temperature sensitivity of RAP material was characterized based on the ratio of 1.6mm sieve pass rate at different temperatures to 5 ℃, in order to reflect the degree of agglomeration of aged asphalt in cold recycled asphalt mixture. RAP material was further divided into two grades to effectively control the quality of RAP material from different sources [25-27]. The influence of RAP materials with different service lives on the performance of cold recycled asphalt mixtures mainly lies in the difference in the degree of asphalt aging. The longer the service life, the higher the degree of asphalt aging. Research has shown that asphalt aging can improve the adhesion between new and old asphalt [28-29], and decrease with increasing aging [30]. Asphalt aging leads to an increase in the void fraction of the mixture, a decrease in indirect splitting strength, fracture energy, and water stability, and an increase in high-temperature stability [31-32]. As can be seen from the above, the presence of aged asphalt in RAP material makes it more prone to deformation or fracture under load; With the increase of RAP content, the overall road performance of recycled asphalt pavement shows a downward trend [33-34].

　　针对老化沥 青，杨建萍［３５］研究了 ＲＡＰ 料中沥青分布、沥青 含 量 分布规律并提出了沥青变异性控制模型，建立了评价老化沥青对新沥青选取影响的波动范围评价方法。众多学者对冷再生沥青混合料中 ＲＡＰ料掺量进行研究。随 着 ＲＡＰ 料 掺量 增 大，冷 再 生 沥 青 混合料内部孔隙率增大，降低了抗开裂性能、水稳定性和高温稳定性［３１］。目前，越来越多的学者研究大掺量 ＲＡＰ料 的 冷 再 生 沥 青 混 合 料 力 学 性 能 的 适 用性［３６］。Ｄｏｎｇ等［３７－３８］研 究 表 明 １００％ ＲＡＰ 料 掺 量的试件相比密级配基层材料试件具有更高的刚度、回弹 模 量，但 抗 剪 强 度 较 低，抗 变 形 能 力 较 差。将ＲＡＰ料作为无黏 结 基 层 材 料 时，随 着 ＲＡＰ 料 掺量的增 加，加 州 承 载 比 （ＣａｌｉｆｏｒｎｉａＢｅａｒｉｎｇ Ｒａｔｉｏｎ，ＣＢＲ）降低，在外力作用下呈现一定的蠕变特性，这主要是由于在荷载作用下老化沥青砂浆发生接触滑移。根据澳大利亚等的实践经验，建议在工程应用中掺入一定比例的新料以达到强度和变形的规范要求，ＲＡＰ 料 掺量 建 议 不 超 过５０％［３９］。在 实际工程中应基于冷再生沥青结构层位对其相应的力学指标进行测试，建立冷再生沥青混合料性能指标与ＲＡＰ料掺量的定量关系，并根据道路等级对应的混合料性能要 求 严 格 控 制 ＲＡＰ 料 掺量，以 满 足 结 构设计规范要求的材料性能［４０－４４］。

　　Regarding aged asphalt, Yang Jianping [35] studied the distribution and content of asphalt in RAP materials, proposed an asphalt variability control model, and established a fluctuation range evaluation method to assess the impact of aged asphalt on the selection of new asphalt. Numerous scholars have conducted research on the dosage of RAP in cold recycled asphalt mixtures. With the increase of RAP content, the internal porosity of cold recycled asphalt mixture increases, which reduces the cracking resistance, water stability, and high temperature stability [31]. At present, more and more scholars are studying the applicability of mechanical properties of cold recycled asphalt mixtures with high RAP content [36]. Dong et al. [37-38] found that specimens with 100% RAP content have higher stiffness and rebound modulus compared to specimens with dense graded base materials, but lower shear strength and poorer deformation resistance. When RAP material is used as a non bonded base material, as the RAP content increases, the California Bearing Ratio (CBR) decreases and exhibits certain creep characteristics under external forces, mainly due to contact slip of aged asphalt mortar under load. Based on the practical experience of countries such as Australia, it is recommended to add a certain proportion of new materials in engineering applications to meet the specifications for strength and deformation. The recommended RAP material content should not exceed 50% [39]. In practical engineering, the corresponding mechanical indicators of cold recycled asphalt should be tested based on its structural layer, and a quantitative relationship between the performance indicators of cold recycled asphalt mixture and the RAP content should be established. The RAP content should be strictly controlled according to the performance requirements of the road grade corresponding to the mixture, in order to meet the material properties required by the structural design specifications [40-44].

　　2.2 沥青胶结料

　　2.2 Asphalt binder

　　乳化沥青和泡沫沥青是冷再生沥青混合料常用的胶结料类型，除了为冷再生沥青混合料提供黏结强度外，还有助于再生和软化老化沥青。泡沫沥青和乳化沥青中含有一定量的水分，在常温下具有一定的流动性从而实现常温拌和。冷再生沥青混合料由于水分的存在，导致初始强度低，但随着养护时间增长和水分挥发，混合料强度逐渐增大。2.2.1泡沫沥青泡沫沥青是冷再生沥青混合料常用的胶结料，自２０世纪７０年代后被广泛用作冷再生材料的再生剂和黏结剂。泡沫沥青是在高温条件下在发泡装置中加入高温沥青和一定比例的水，将水与高温沥青混合后形成蒸汽，促使沥青迅速膨胀生成泡沫状，如图２所示［４５］。发 泡效 果 的 主 要 技 术 指 标 为 膨 胀 期和半衰期，通常认为膨胀率高、半衰期长的泡沫沥青质量较好。为充分评价泡沫沥青的发泡质量，国内外提出了多种评价方法，包括发泡指数以及从能量角度确定发泡条件和发泡特性，研究表明发泡剂种类、温 度、气压和外加水对发泡性能具有显著影响［４１－４２］。升高温度能够降低沥青黏度，提高发泡膨胀率［４３］，发泡温度为１５０ ℃～１７０ ℃［４４］；同 时，随着用水量的 增 加，膨 胀 率 逐 渐 增 大，半 衰 期 逐 渐 降低［４４］。此外，李强等［４］对比了３种发泡剂对沥青发泡特性的影响，结果表明十六烷基三甲基溴化铵发泡剂表现出更优的发泡特性，且成型的再生混合料力学强度。１９５６年泡沫沥青在爱荷华州的基层修复中作为稳定 剂 被 使 用。１９６８年美孚石油改善了 泡沫沥青的生产工艺，促进了泡沫沥青的发展。２０世纪７０年代，泡沫沥青技术被广泛应用于许多。２０世纪８０年代初，美国对泡沫沥青再生技术进行了系统的研究，并实施了一批现场试验段。

　　Emulsified asphalt and foam asphalt are common types of binders for cold recycled asphalt mixture. In addition to providing bond strength for cold recycled asphalt mixture, they also help to regenerate and soften aging asphalt. Foam asphalt and emulsified asphalt contain a certain amount of water and have a certain fluidity at room temperature to achieve mixing at room temperature. Due to the presence of moisture, the initial strength of cold recycled asphalt mixture is low, but as the curing time increases and moisture evaporates, the strength of the mixture gradually increases. 2.2.1 foam asphalt foam asphalt is a common binder for cold recycled asphalt mixture, and has been widely used as a regenerant and binder for cold recycled materials since the 1970s. Foam asphalt is to add high temperature asphalt and a certain proportion of water into the foaming device under high temperature conditions, mix water with high temperature asphalt to form steam, and promote the asphalt to expand rapidly to form foam, as shown in Figure 2 [45]. The main technical indicators of foaming effect are expansion period and half life. Generally, foam asphalt with high expansion rate and long half life is considered to be of good quality. In order to fully evaluate the foaming quality of foam asphalt, experts at home and abroad have proposed a variety of evaluation methods, including foaming index and determination of optimal foaming conditions and foaming characteristics from the perspective of energy. Research shows that the type of foaming agent, temperature, air pressure and added water have a significant impact on the foaming performance [41-42]. Raising the temperature can reduce the viscosity of asphalt and increase the foaming expansion rate [43]. The optimal foaming temperature is between 150 ℃ and 170 ℃ [44]; Meanwhile, as the water usage increases, the expansion rate gradually increases and the half-life gradually decreases [44]. In addition, Li Qiang et al. [4] compared the effects of three foaming agents on the foaming characteristics of asphalt, and the results showed that hexadecyltrimethylammonium bromide foaming agent exhibited better foaming characteristics, and the formed recycled mixture had the best mechanical strength. In 1956, foam asphalt was first used as a stabilizer in the base course repair in Iowa. In 1968, Mobil Petroleum improved the production process of foam asphalt and promoted the development of foam asphalt. In the 1970s, foam asphalt technology was widely used in many countries. In the early 1980s, the United States carried out a systematic study on the recycling technology of foam asphalt, and implemented a number of on-site test sections.

　　在２０世纪末，国外泡沫沥青冷再生技术已相对成熟。２０１６年弗吉尼亚州 交 通 部 开 展 了 １００％ＲＡＰ 掺 量的 泡 沫沥青混合料替代传统沥青基层的试验段，后期调查结果显示路面未出现明显的开裂或车辙病害［４６］。２０１３年马里兰 州 公 路 管 理 局 制 定 了 泡 沫 沥 青 稳 定基层材料的技术指南，包括配合比设计、材料选择、现场施工以及质量控制等环节［４７］。从２０世纪９０年代开始对泡沫沥青冷再生技术进行研究和应用。以国内典型工程———北京市卢丘路大修工程为例［４８］，现场工程应用情况表明泡沫沥青再生混合料具有较高的模量、较小的温度收缩应力和良好的抗疲劳性能，可用于基层以减少路面反射裂缝；半刚性基层上加铺冷再生结构层形成的复合结构性能稳定，强度较高；泡沫沥青混合料适用于交通量较小的高速公路。随着泡沫沥青含量增多，冷再生沥青混合料的水稳定性和劈裂强度均呈现先增高后降低的趋势，且养生方式的差异会影响混合料终的力学性能［２０］。2.2.2 乳化沥青乳化沥青是将高温熔融后流动状态的沥青加入含有乳化剂的皂液中，通过机械高速剪切作用，使沥青变成微小颗粒并分散在含有稳定剂－乳 化剂 的 水溶液中，形成一种较稳定的水包油结构。评判乳化沥青的指标包括破乳速度、筛上残留物（１．１８ｍｍ）、黏度以及蒸发残留物等。

　　At the end of the 20th century, the cold recycling technology of foam asphalt abroad was relatively mature. In 2016, the Virginia Department of Transportation carried out a test section in which 100% RAP foam asphalt mixture was used to replace the traditional asphalt base, and the later investigation results showed that there was no obvious cracking or rutting disease on the pavement [46]. In 2013, Maryland Highway Administration formulated a technical guide for foam asphalt stabilized base course materials, focusing on mix design, material selection, on-site construction and quality control [47]. China began to research and apply the cold recycling technology of foam asphalt in the 1990s. Taking Beijing Luqiu Road Overhaul Project, a typical domestic project, as an example [48], the field engineering application shows that foam asphalt recycled mixture has high modulus, low temperature shrinkage stress and good fatigue resistance, which can be used for base course to reduce pavement reflection cracks; The composite structure formed by adding a cold recycled structural layer on a semi-rigid base has stable performance and high strength; Foam asphalt mixture is suitable for expressway with small traffic volume. With the increase of foam asphalt content, the water stability and splitting strength of cold recycled asphalt mixture show a trend of first increasing and then decreasing, and the difference in curing methods will affect the final mechanical properties of the mixture [20]. 2.2.2 Emulsified Asphalt Emulsified asphalt is the process of adding high-temperature melted and flowing asphalt to a soap solution containing emulsifiers. Through mechanical high-speed shearing, the asphalt is transformed into small particles and dispersed in an aqueous solution containing stabilizers and emulsifiers, forming a relatively stable water in oil structure. The indicators for evaluating emulsified asphalt include demulsification speed, residue on the sieve (1.18mm), viscosity, and evaporation residue.

　　在适当的制备工艺和存储条件下，乳化沥青可存储几个月。在乳化沥青冷再生沥青混合料强度形成机理方面，乳化沥青液滴表面带有电荷，当沥青乳液与集料颗粒表面电荷电性相反时，由于异性电荷相吸，使胶结料与集料的界面黏结强度增大，不同类型沥青乳液与集料的相容性如表２［７］所示。当沥青乳液与集料 混合接触时，沥青倾向于与水分发生分离并黏附在集料颗粒表面，该过程称为破乳。图３示意了乳化沥青混合料的２种破坏模式：在养护初期，由于沥青乳液－水泥砂浆相与集料界面存在水膜，是混合料发生断裂的强度薄弱界面，黏附破坏为主要破坏模式；随着养护时间增加，在水泥水化反应、乳化沥青破乳的持续进行以及水分挥发作用下，沥青聚集成膜并均匀裹附在集料表面，界面黏附强度超过了沥青砂浆的黏聚强度，砂浆相的黏聚破坏成为主要破坏模式。对于厂拌冷再生技术，破乳时间需大于冷再生沥青混合料拌和、运输以及摊铺碾压时间，避免乳化沥青提前破乳并造成混合料的和易性下降。此外，乳化沥青混合料中通常加入一定比例的水泥，水泥与水分发生水化反应，加速了破乳过程；水化产物与破乳后的沥青形成加筋结构，进一步提高了冷再生沥青混合料的强度［４９］。

　　Under appropriate preparation processes and storage conditions, emulsified asphalt can be stored for several months. In terms of strength formation mechanism of emulsified asphalt cold recycled asphalt mixture, the surface of emulsified asphalt droplets is charged. When the surface charge of asphalt lotion is opposite to that of aggregate particles, the interfacial bonding strength of binder and aggregate will increase due to the absorption of anisotropic charges. The compatibility of different types of asphalt lotion with aggregates is shown in Table 2 [7]. When asphalt lotion is mixed with aggregate, asphalt tends to separate from water and adhere to the surface of aggregate particles. This process is called demulsification. Figure 3 shows two failure modes of emulsified asphalt mixture: at the initial stage of maintenance, there is a water film between the asphalt lotion cement mortar phase and the aggregate interface, which is the weak strength interface where the mixture breaks, and adhesion failure is the main failure mode; As the curing time increases, under the continuous hydration reaction of cement, emulsion breaking of emulsified asphalt, and water evaporation, asphalt aggregates into a film and uniformly adheres to the surface of the aggregate. The interfacial adhesion strength exceeds the cohesive strength of asphalt mortar, and the cohesive failure of mortar phase becomes the main failure mode. For the factory mixed cold recycling technology, the demulsification time should be greater than the mixing, transportation, and paving rolling time of the cold recycled asphalt mixture to avoid premature demulsification of emulsified asphalt and reduce the workability of the mixture. In addition, a certain proportion of cement is usually added to emulsified asphalt mixture, which undergoes hydration reaction with water to accelerate the demulsification process; The hydration products form a reinforced structure with the emulsified asphalt, further improving the strength of the cold recycled asphalt mixture [49].

　　李云良等［５０］研究了不同 水泥－乳化沥青比例下复合胶浆的老化试验及频率扫描试验，结果表明不同相对含量的水泥－沥青乳液的老化性能具有明显差异，在混合料设计中应进行考虑。此外，借鉴热拌沥青路面工程中使用改性沥青的工程经验，可以采用改性乳化沥青以获得更加优良的路用性能，提高冷再生沥青结构层的应用层位。郑俊秋［５１］制备了３种普通乳化沥青以及改性乳化沥青，结果表明改性乳化沥青能够显著改善高温和低温性能。2.2.3性能对比分析对于乳 化 沥 青 混 合 料，乳 化 沥 青 吸 附 聚 集 成膜并均匀 裹 附 在 集 料 表 面，水 泥 水 化 加 速 了 乳 化沥青破乳，同时生成针状和簇状的水化产物与沥青相互 交 织，形 成 空 间 网 络 结 构。泡 沫 沥 青 在 集料表面呈非连续 分 布，具 有 局 部 黏 结 的 点 焊 特 征，除了受基质沥青性能和水分影响外，仍 受 沥 青 与填（细）料的裹附均 匀 程 度 以 及 胶（砂）浆 的 点 状 分布状态影 响［５２－５３］。

　　Li Yunliang et al. [50] studied the aging test and frequency scanning test of composite mortar under different cement asphalt emulsion ratios. The results show that the aging performance of cement asphalt lotion with different relative contents has obvious differences, which should be considered in the mixture design. In addition, drawing on the engineering experience of using modified asphalt in hot mix asphalt pavement projects, modified emulsified asphalt can be used to achieve better road performance and improve the application level of cold recycled asphalt structural layers. Zheng Junqiu [51] prepared three types of ordinary emulsified asphalt and modified emulsified asphalt, and the results showed that modified emulsified asphalt could significantly improve high and low temperature performance. 2.2.3 Performance Comparison Analysis: For emulsified asphalt mixtures, emulsified asphalt adsorbs and aggregates into a film, which uniformly adheres to the surface of the aggregate. Cement hydration accelerates the demulsification of emulsified asphalt, while generating needle shaped and cluster shaped hydration products that interweave with asphalt, forming a spatial network structure. The foam asphalt is distributed discontinuously on the aggregate surface and has the characteristics of spot welding of local bonding. In addition to the influence of the performance and moisture of the base asphalt, it is also affected by the uniformity of the coating of asphalt and filler (fine) materials and the spot distribution of mortar (sand) [52-53].

　　２种沥青的黏结特性导致 冷 再生沥青混合料的受力特征具有差异，进 而 影 响 混合料性能。相同沥青掺量的泡沫沥青混合料的孔隙率、抗水损害、抗低温开裂性优于乳化沥青混合料［５４］。随着沥青掺量的增加，乳化沥青混合料的刚度模量呈下降趋势，泡沫沥青混合料呈增大趋势，这主要是由于２种再生剂对于冷再生沥青混合料强度形成机理存在差异性。乳化沥青中含有大量的水，以流体形式包裹细 集 料 和 粗 集 料。随 着 乳 化 沥 青 含 量 的 增加，沥青以润滑剂的形式降低了集料间的摩阻力，导致刚度模量降低。相反，泡沫沥青与矿粉和细集料形成沥青砂浆，再与粗集料黏结形成强度，沥青与粗集料呈点接触状态。增加沥青含量可增加泡沫沥青混合料 内 部 的 黏 结 界 面，从 而 提 高 刚 度 模 量。基于２种沥青在混合料内部的分布特点，乳化沥青混合料具有显著的温度和频率依赖特性［５３，５５］。

　　The bonding characteristics of two types of asphalt lead to differences in the stress characteristics of cold recycled asphalt mixtures, which in turn affect the performance of the mixture. The porosity, water damage resistance and low-temperature cracking resistance of foam asphalt mixture with the same asphalt content are better than those of emulsified asphalt mixture [54]. With the increase of asphalt content, the stiffness modulus of emulsified asphalt mixture decreases, while that of foam asphalt mixture increases. This is mainly due to the difference in the strength formation mechanism of the two kinds of regenerants for cold recycled asphalt mixture. Emulsified asphalt contains a large amount of water, which wraps fine and coarse aggregates in a fluid form. With the increase of emulsified asphalt content, asphalt reduces the frictional resistance between aggregates in the form of lubricant, resulting in a decrease in stiffness modulus. On the contrary, foam asphalt first forms asphalt mortar with mineral powder and fine aggregate, and then forms strength with coarse aggregate. Asphalt and coarse aggregate are in point contact. Increasing the asphalt content can increase the bonding interface inside foam asphalt mixture, thus improving the stiffness modulus. Based on the distribution characteristics of two types of asphalt inside the mixture, emulsified asphalt mixture has significant temperature and frequency dependence characteristics [53, 55].

　　2.3 化学添加剂

　　2.3 Chemical additives

　　水泥等稳定剂加入冷再生材料，不仅可以作为填料改善级配，还可以提高冷再生的早期强度和长期性能，且外添剂含量和性能也会对冷再生沥青混合料的力学性能产生较大影响［５６］。2.3.1水泥众多学者研究了水泥及水泥水化产物对冷再生混合料强度特性的影响，冷再生沥青混合料中通常加入１．０％～２．５％的水泥以提高混合料的早期强度、高温稳定性［５７－５８］，并可作为添加剂以增强砂浆与集料的黏结性，提高抗水损害性能［５９－６０］。其次，水泥可提高冷再生沥青混合料的无侧限抗压强度、间接抗拉强度、回 弹 模 量 和 抗 车 辙 性 能 等 力 学 性 能［５８］，但水泥掺量与冷再生沥青混合料力学性能的提高幅度并非呈线 性 正 相 关。以 水 泥－乳 化沥 青 混 合 料 为例，当水泥掺量超过２％，冷再生沥青混合料的间接拉伸强度 增 强 效 果 较 小［６１］。Ｘｉａｏ等［５８］研 究表 明，当乳化 沥 青 掺 量 为８％，水 泥 掺 量 由０增 加 到４％时，其间接抗 拉 强 度 先 增 大 后 减 小，水 泥 掺 量 约 为３％时，抗压强度和回弹性模量。虽然水泥能够多方面地提升冷再生沥青混合料性能，但是不利于抗疲劳性能和低温开裂，尤其对于冷再生混合料应用于基层或者下面层，对抗疲劳性能具有一定的要求。

　　Adding stabilizers such as cement to cold recycled materials can not only improve the gradation as fillers, but also enhance the early strength and long-term performance of cold recycled asphalt mixtures. Moreover, the content and performance of external additives can also have a significant impact on the mechanical properties of cold recycled asphalt mixtures [56]. 2.3.1 Many scholars have studied the influence of cement and cement hydration products on the strength characteristics of cold recycled asphalt mixtures. Usually, 1.0% to 2.5% cement is added to cold recycled asphalt mixtures to improve the early strength and high-temperature stability of the mixture [57-58], and can be used as an additive to enhance the bonding between mortar and aggregate, and improve the resistance to water damage [59-60]. Secondly, cement can improve the mechanical properties such as unconfined compressive strength, indirect tensile strength, rebound modulus, and rutting resistance of cold recycled asphalt mixtures [58], but the increase in cement content is not linearly positively correlated with the improvement in mechanical properties of cold recycled asphalt mixtures. Taking cement emulsified asphalt mixture as an example, when the cement content exceeds 2%, the indirect tensile strength enhancement effect of cold recycled asphalt mixture is relatively small [61]. Xiao et al. [58] found that when the emulsified asphalt content is 8% and the cement content increases from 0% to 4%, its indirect tensile strength first increases and then decreases. When the cement content is about 3%, the compressive strength and elastic modulus are the highest. Although cement can improve the performance of cold recycled asphalt mixture in various aspects, it is not conducive to fatigue resistance and low-temperature cracking, especially for the application of cold recycled mixture in the base or lower layer, which has certain requirements for fatigue resistance.

　　为保证冷再生沥青混合料的低温抗开裂性能，水泥掺量应低于２％［６２－６４］。对于冷再生混合料的抗疲劳性能，以乳化沥青沥青混合料为例，研究表明其疲劳性能取决于初始应变水平，当微应变低于３００με时，水泥有利于提高疲劳寿 命，应 变水平高于３００με时 则相 反［６５－６６］。冷再生沥青混合料应用于基 层 时，其应变水平通常低于 ２００με，因此，在冷再生沥青路面设计方法中应充分对其进行研究，提出符合冷再生沥青混合料材料特性的疲劳失效设计准则。美国沥青学会建议将水泥用量限制在１％，将水泥掺量确定为１．５％，以降低水泥对疲劳性能的弱化影响，但在其他相关研究中也提出可采用３％的水泥掺量［６５，６７］。以上总结了水泥对于冷再生沥青混合料性能的影响，并以乳化沥青或者泡沫沥青混合料的试验结果进行了分析论述。水泥对于乳化沥青混合料和泡沫沥青混合料力学性能的影响规律较为一致，由于乳化沥青和泡沫沥青混合料的强度形成机理存在差异，以及其他材料组分性能及相对含量的差异会影响水泥掺量。2.3.2石灰石灰通常作为一种活性添加剂，通常以熟石灰和石灰浆的形式加入冷再生沥青混合料以改善其力学性能［６８－６９］，熟石灰是常见的一种添加剂，添加量通常为集料质量的１％～３％［７０］。熟石灰相比于普通的石灰石矿粉填料具有更高的孔隙率，石灰石矿粉压实后孔隙率通常为３０％～３４％，而熟石灰孔隙率通常为６０％～７０％。其次，熟石灰作为一种填料对沥青的增果高于普通填料［６７］。

　　To ensure the low-temperature anti cracking performance of cold recycled asphalt mixture, the cement content should be less than 2% [62-64]. For the fatigue resistance of cold recycled mixtures, taking emulsified asphalt mixtures as an example, research has shown that their fatigue performance depends on the initial strain level. When the micro strain is below 300 μ ε, cement is beneficial for improving fatigue life, while when the strain level is above 300 μ ε, the opposite is true [65-66]. When cold recycled asphalt mixture is applied to the base layer, its strain level is usually below 200 μ ε. Therefore, in the design method of cold recycled asphalt pavement, it should be fully studied and fatigue failure design criteria that meet the material characteristics of cold recycled asphalt mixture should be proposed. The American Asphalt Institute recommends limiting the cement content to 1%, while China sets the cement content at 1.5% to reduce the weakening effect of cement on fatigue performance. However, other related studies have also suggested using a cement content of 3% [65,67]. The above summarizes the influence of cement on the performance of cold recycled asphalt mixture, and analyzes and discusses the test results of emulsified asphalt or foam asphalt mixture. The influence of cement on the mechanical properties of emulsified asphalt mixture and foam asphalt mixture is relatively consistent. Due to the difference in the strength formation mechanism of emulsified asphalt and foam asphalt mixture, and the difference in the performance and relative content of other material components, the optimal cement content will be affected. 2.3.2 Lime is usually used as an active additive, usually added to cold recycled asphalt mixtures in the form of hydrated lime and lime slurry to improve their mechanical properties [68-69]. Hydrated lime is the most common additive, usually added in an amount of 1% to 3% of the aggregate mass [70]. Compared to ordinary limestone powder fillers, hydrated lime has a higher porosity. The porosity of compacted limestone powder is usually 30% to 34%, while the porosity of hydrated lime is usually 60% to 70%. Secondly, as a filler, hydrated lime has a higher reinforcing effect on asphalt than ordinary fillers [67].

　　研究表明，以填料与沥青的质量比为指标，将针入 度（单 位１０－１ ｍｍ）为２００的沥青软化点提高２０ ℃，熟石灰与沥青的比值为０．７～１．０，而矿粉填料的质量比为１．５～２．５。熟石灰在美国得到关注和研究，被 用 于热拌沥青混合料中以提高其抗水损害和冻融破坏，同时还能够提 高 混 合 料 的 模 量 及 抗 车 辙、抗 疲劳性能，增强混合料的耐久性［７１］。这 主要 是 由 于熟石灰能够改善集料与沥青的黏附状态，游 离 的钙离子沉 积 在 集 料 表 面，促 进 与 沥 青 中 的 酸 性 物质发生物化反应，增 强 集 料 与 沥 青 的 黏 结 强 度，进而提高抗水损害性能［６８］，这一现象对酸性集料尤为明显。其次，相关室内试验和现场调研结果表明，石灰能够降低冷再生沥青混合料孔隙率，从而提高混合料抗拉强度、抗变形能力和刚度，但石灰浆增果更优［７２－７４］。以上总结了石灰的物理特性以及与沥青胶结料的化学反应特性，揭示了石灰对冷再生混合料性能的影响机理，该方面的总结同样适用于乳化沥青和泡沫沥青等多种沥青胶结料的冷再生沥青混合料。

　　Research has shown that using the mass ratio of filler to asphalt as an indicator, the softening point of asphalt with a penetration degree (unit 10-1mm) of 200 can be increased by 20 ℃. The ratio of hydrated lime to asphalt is 0.7-1.0, while the mass ratio of mineral powder filler is 1.5-2.5. Hydrated lime first received attention and research in the United States, and was used in hot mix asphalt mixtures to improve their resistance to water damage and freeze-thaw failure, as well as to increase the modulus, rutting resistance, and fatigue resistance of the mixture, enhancing its durability [71]. This is mainly due to the fact that hydrated lime can improve the adhesion state between aggregates and asphalt. Free calcium ions deposit on the surface of aggregates, promote biological reactions with acidic substances in asphalt, enhance the bonding strength between aggregates and asphalt, and thus improve the water damage resistance performance [68]. This phenomenon is particularly evident for acidic aggregates. Secondly, relevant indoor tests and on-site investigations have shown that lime can reduce the porosity of cold recycled asphalt mixtures, thereby improving the tensile strength, resistance to permanent deformation, and stiffness of the mixture. However, lime slurry has a better reinforcement effect [72-74]. The above summarizes the physical characteristics of lime and the chemical reaction characteristics with asphalt binder, and reveals the influence mechanism of lime on the performance of cold recycled asphalt mixture. The summary in this aspect is also applicable to cold recycled asphalt mixture of various asphalt binders such as emulsified asphalt and foam asphalt.

　　2.3.3性能对比分析水泥的主要成分为硅酸二钙和硅酸三钙，与水发生水化反应生成水化硅酸钙和氢氧化钙，其中水化硅酸钙是形成强度的主要物质。熟石灰的主要成分为氢氧化钙，其比表面积约为水泥的１０倍，可为乳化沥青或泡沫沥青提供较好的分散相，但遇水不发生水化反应。２种活性填料对冷再生沥青混合料的强度性能具有显著差异，主要表现为：

　　2.3.3 Performance Comparison Analysis The main components of cement are dicalcium silicate and tricalcium silicate, which react with water to form hydrated calcium silicate and calcium hydroxide. Hydrated calcium silicate is the main substance that forms strength. The main component of hydrated lime is calcium hydroxide, whose specific surface area is about 10 times that of cement. It can provide a better dispersion phase for emulsified asphalt or foam asphalt, but it will not react with water. There is a significant difference in the strength performance of cold recycled asphalt mixture between two types of active fillers, mainly manifested as:

　　（１）加入水泥可显著提高冷再生沥青混合料的模量，但熟石灰的强度提升效果不显著［７５－７６］，当需要提高早期及长期强度时建议添加水泥；（２）加入水泥的冷再生沥青混合料不具有应力依赖性，混合料呈现胶结材料的特征，加入熟石灰的混合料具有较为明显的应力依赖性，即模量随围压改变而变化，更多呈现无黏结颗粒材料特性［５３］；（３）水 泥作为添加剂的冷再生沥青混合料在高应变水平下的抗疲劳性能较差［７３］，在工程设计时应充分考虑冷再生结构层的应力及应变水平，以防止疲劳开裂；（４）在潮湿多雨环境里建议采用水泥稳定剂并适当提高用量，以提高抗水损害能力。由此可见，在冷再生沥青混合料材料设计过程中应充分考虑当地气候条件、冷再生材料所应用的结构层位及其对应的性能需求，以选择合适的添加剂。如果要求提高冷再生沥青混合料的早期强度且具有较好的抗水损害和抗变形能力，建议采用水泥作为外加剂［６８］。2.4冷再生材料组分相互作用机制

　　(1) Adding cement can significantly improve the modulus of cold recycled asphalt mixture, but the strength improvement effect of hydrated lime is not significant [75-76]. It is recommended to add cement when early and long-term strength needs to be improved; (2) The cold recycled asphalt mixture with added cement does not have stress dependence, and the mixture exhibits the characteristics of a bonding material. The mixture with added hydrated lime has a more obvious stress dependence, that is, the modulus changes with the change of confining pressure, and more exhibits the characteristics of a non bonding particle material [53]; (3) The anti fatigue performance of cold recycled asphalt mixture with cement as an additive is poor at high strain levels [73]. In engineering design, the stress and strain levels of the cold recycled structural layer should be fully considered to prevent fatigue cracking; (4) In humid and rainy environments, it is recommended to use cement stabilizers and increase their dosage appropriately to enhance their resistance to water damage. From this, it can be seen that in the design process of cold recycled asphalt mixture materials, local climate conditions, the structural layers and corresponding performance requirements of the cold recycled materials should be fully considered to select appropriate additives. If it is required to improve the early strength of cold recycled asphalt mixture and have good resistance to water damage and permanent deformation, it is recommended to use cement as an admixture [68]. 2.4 Interaction mechanism of components in cold recycled materials

　　沥青与水泥相互作用形成复合胶浆，决定了冷再生沥青混合料的流变特性和力学属性。由图４［６１，７７］所示的冷再生沥青复合胶浆微观形貌可以看出：水泥水化生成的水化产物包括针刺状钙矾石，板状氢氧化钙晶体以及纤维状水化硅酸钙 凝 胶，沥青与水化产物相互交织并附着在水化产物表面，针状的钙矾石晶体刺破沥青膜。此外，沥青能够包裹一部分水泥颗粒，阻碍其进一步发生水化反应。研究表明水泥与沥青的相对含量的变化会影响冷再生沥青混合料的力学特性，当沥青与水泥质量比大于１且水泥用量低于１％时可视为沥青稳定类材料，当质量比大于１且水泥用量大于１％时可视为水泥稳定类材料［５６］。沥青－水泥复合胶浆与旧料和新料可形成不同的界面形态，水泥水化产物能够增强砂浆相与集料间的黏附性，界面性能的强弱决定了混合料破坏模式。其次，沥青与水泥的加入时机能够改变界面形式和界面强度进而影响冷再生沥青混合料性能。在传统的施工工艺中，通常将水泥和乳化沥青／泡沫沥青依次加入并与集料进行拌和，会使集料表面包裹一层水泥水化产物，界面过渡区内呈现较多的微裂纹，不利于冷再生沥青混合料的抗裂性能和抗水损害。温彦凯等［２８，７８］研究表明，将水泥、乳化沥青／泡沫沥青和矿粉先充分拌和，形成各相分散均匀的复合胶浆再与集料进行拌和，通过扫描电子显微镜测试观测到复合胶浆在集料表面可形成较好的浸润和黏附效果，从而提高冷再生沥青混合料的力学性能。由于 ＲＡＰ料表层存在老化沥青，沥青具有疏水性特性，阻碍了 ＲＡＰ料 内部微孔隙对水的吸收，因此，ＲＡＰ料 对外加水的吸收程度低于新集料。

　　The interaction between asphalt and cement forms a composite slurry, which determines the rheological and mechanical properties of cold recycled asphalt mixtures. It can be seen from the microscopic morphology of cold recycled asphalt composite mortar shown in Figure 4 [61, 77] that the hydration products generated by cement hydration include needle like ettringite, plate like calcium hydroxide crystal and fibrous calcium silicate hydrate gel. The asphalt and hydration products are intertwined and attached to the surface of the hydration products, and needle like ettringite crystal punctures the asphalt film. In addition, asphalt can encapsulate some cement particles, hindering their further hydration reaction. Research has shown that changes in the relative content of cement and asphalt can affect the mechanical properties of cold recycled asphalt mixtures. When the mass ratio of asphalt to cement is greater than 1 and the cement content is less than 1%, it can be considered as asphalt stabilized material. When the mass ratio is greater than 1 and the cement content is greater than 1%, it can be considered as cement stabilized material [56]. Asphalt cement composite mortar can form different interface shapes with old and new materials. Cement hydration products can enhance the adhesion between mortar and aggregate, and the strength of interface performance determines the failure mode of the mixture. Secondly, the timing of adding asphalt and cement can change the interface form and strength, thereby affecting the performance of cold recycled asphalt mixtures. In the traditional construction process, cement and emulsified asphalt/foam asphalt are usually added in turn and mixed with the aggregate, which will make the aggregate surface wrapped with a layer of cement hydration products, and there are many microcracks in the interface transition zone, which is not conducive to the crack resistance and water damage resistance of cold recycled asphalt mixture. Wen Yankai et al. [28, 78] research shows that cement, emulsified asphalt/foam asphalt and mineral powder are fully mixed to form a composite mortar with evenly dispersed phases and then mixed with the aggregate. Through scanning electron microscope testing, it is observed that the composite mortar can form a better wetting and adhesion effect on the surface of the aggregate, thus improving the mechanical properties of cold recycled asphalt mixture. Due to the presence of aged asphalt on the surface of RAP material, which has hydrophobic properties, it hinders the absorption of water by the internal micropores of RAP material. Therefore, the absorption of water by RAP material is lower than that of new aggregate.

　　Ｍａ等［６１］研究表明 ＲＡＰ料抽提后的比表面积约为抽提前的３倍，因此，沥青含量和含水量会随着ＲＡＰ料掺量的增加而降低［７９］，如图５［８０］所示，图中沥青含量与 ＲＡＰ料含量均为质量百分含量。在恒定水灰比下具有更多的自由水与水泥胶凝材料发生反应，从而提高水化反应程度。其次，ＲＡＰ料内部集料颗粒与老化沥青的界面黏结强度较差，以上原因都会降低冷再生沥青混合料抗开裂性能［６１，８０］。由以上分析可知，冷再生沥青混合料材料组分及其相互作用机制复杂，界面形式多变，ＲＡＰ料掺量及性能、添加剂以及沥青胶结料类型和含量等都会影响冷再生沥青混合料的力学性能。在工程应用前，应对各材料组分进行测试与表征，基于性能需求对冷再生沥青混合料进行组分设计和试验验证。3 冷再生沥青混合料配合比及路面设计方法

　　Ma et al. [61] found that the specific surface area of RAP material after extraction is about three times that of pre extraction. Therefore, the optimal asphalt content and moisture content will decrease with the increase of RAP material content [79], as shown in Figure 5 [80], where the asphalt content and RAP material content are both mass percentage contents. At a constant water cement ratio, there is more free water to react with cement cementitious materials, thereby increasing the degree of hydration reaction. Secondly, the interface bonding strength between RAP aggregate particles and aged asphalt is poor, which can reduce the cracking resistance of cold recycled asphalt mixtures [61, 80]. From the above analysis, it can be seen that the components and interaction mechanisms of cold recycled asphalt mixture materials are complex, and the interface forms are varied. The dosage and performance of RAP material, additives, and the type and content of asphalt binder can all affect the mechanical properties of cold recycled asphalt mixture. Before engineering application, each material component should be tested and characterized, and the composition design and experimental verification of cold recycled asphalt mixture should be based on performance requirements. Mix proportion and pavement design method of cold recycled asphalt mixture

　　由于冷再生沥青混合料中存在 ＲＡＰ料和水泥基稳定剂等组成成分，传统的沥青混合料设计方法难以适用于冷再生沥青混合料。目前，关于冷再生材料的路面设计方法以及混合料设计方法得到众多学者的研究，各国提出了不同的冷再生沥青混合料设计方法和路面结构设计方法，但尚未形成统一的设计方法［８１］。3.1 冷再生沥青混合料设计方法

　　Due to the presence of RAP and cement-based stabilizers in cold recycled asphalt mixtures, traditional asphalt mixture design methods are difficult to apply to cold recycled asphalt mixtures. At present, many scholars have studied the pavement design methods and mixture design methods of cold recycled materials. Different countries have proposed different design methods for cold recycled asphalt mixtures and pavement structures, but a unified design method has not yet been formed [81]. 3.1 Design Method for Cold Recycled Asphalt Mixture

　　3.1.1国外代表性配合比设计方法美国部分州和研究机构根据热拌沥青混合料设计方法，形成了不同的冷再生沥青混合料设计方法。主要分为经验公式法和试验测试法２种，其中基于经验公式法的设计理论包括美国沥青协会的 ＡＩ设计法［８２］和俄勒冈州设计法，基于试验测试法的设计理论包括 ＡＡＳＨＴＯ 修 正马 歇 尔 法（Ｍａｒｓｈａｌｌ法）、Ｈｖｅｅｍ 设计法、宾夕法尼亚州设计法、Ｓｕｐｅｒｐａｖｅ设计法，各种设计方法的汇总如表３所 示［２１，８３－８４］。经验公式法相比于试验测试法设计步骤较简略，测试过程较简单，主 要 是 基 于 ＲＡＰ 料 中老 化 沥 青 的 性能指标预估乳化沥青含量，但是试验结果的可靠性较低。试验测试法是基于力学性能测试确定沥青含量和含水量，主要分为２个方面：其一是密度法，即根据冷再生沥青混合料试件的相对密度确定沥青含量；其二是强度法，即根据冷再生混合料的回弹模量、劈裂强度、马歇尔稳定度和水稳定性等指标确定沥青含量。

　　3.1.1 Representative foreign mix design methods: Some states and research institutions in the United States have developed different design methods for cold recycled asphalt mixtures based on the design methods for hot mix asphalt mixtures. There are mainly two types of design methods: empirical formula method and experimental testing method. The design theory based on empirical formula method includes the AI design method of the American Asphalt Institute [82] and the Oregon design method. The design theory based on experimental testing method includes AASHTO modified Marshall method (Marshall method), Hveem design method, Pennsylvania design method, Superpave design method. The summary of various design methods is shown in Table 3 [21, 83-84]. The empirical formula method has simpler design steps and testing process compared to the experimental testing method. It mainly estimates the optimal emulsified asphalt content based on the performance indicators of aged asphalt in RAP material, but the reliability of the test results is lower. The experimental testing method is based on mechanical performance testing to determine the optimal asphalt content and moisture content, mainly divided into two aspects: one is the density method, which determines the optimal asphalt content based on the maximum relative density of cold recycled asphalt mixture specimens; The second method is the strength method, which determines the optimal asphalt content based on indicators such as the rebound modulus, splitting strength, Marshall stability, and water stability of cold recycled mixtures.

　　不同的冷再生沥青混合料设计方法在级配选择、沥青等级、成形方法、养护方式以及性能评价指标等方面差别较大，但基本都是基于试验测试法指导混合料配合比设计。在总结国内外冷再生沥青混合料配合比设计方法的基础上，表４对比分析了通常采用的 Ｍａｒｓｈａｌｌ、Ｓｕｐｅｒｐａｖｅ和 Ｈｖｅｅｍ 法的优缺点［８４］。常见冷再生沥青混合料的压实方法有冲击法（马歇尔压实、普氏压实）、揉压法（旋转压实、线性碾压）以及振动法，不同的压实方法能够对沥青含量和含水量产生差异，从而影响混合料的体积参数和力学性能［８５－８６］。目前，国内外学者主要开展不同压实方法对冷再生沥青混合料性能影响的研究。Ｍｅｎｅｓｅｓ等［８６］研究表明旋转压实试件的孔隙含量变异系数小，马歇尔压实试件的孔隙率变异性，普氏压实法会导致内部集料破碎，优先采用旋转压实方法；Ｊｉａｎｇ等［８７］对比分析了 Ｍａｒｓｈａｌｌ压实和振动压实，研究表明振动压实成型试件的含水量和 沥 青 含 量 比 Ｍａｒｓｈａｌｌ试 件分 别 降 低 了１１％和９％，具有更 好 的 水 稳 定 性，抗 开 裂、抗 车 辙和抗疲劳性能。与重型压实相比，旋转压实成型的冷再生沥青混合料试件的含水量降低了１８％，密度提高了３．５％［８５］。

　　Different design methods for cold recycled asphalt mixtures vary greatly in terms of gradation selection, asphalt grade, forming method, curing method, and performance evaluation indicators, but they are mostly based on experimental testing methods to guide the mix design of the mixture. On the basis of summarizing the mix design methods of cold recycled asphalt mixtures at home and abroad, Table 4 compares and analyzes the advantages and disadvantages of the commonly used Marshall, Superpave, and Hveem methods [84]. The common compaction methods for cold recycled asphalt mixtures include impact compaction (Marshall compaction, Proctor compaction), kneading compaction (rotary compaction, linear rolling), and vibration compaction. Different compaction methods can result in differences in the optimal asphalt content and moisture content, thereby affecting the volume parameters and mechanical properties of the mixture [85-86]. At present, domestic and foreign scholars mainly conduct research on the influence of different compaction methods on the performance of cold recycled asphalt mixtures. The study by Meneses et al. [86] showed that the coefficient of variation of pore content in rotary compaction specimens was the smallest, while the coefficient of variation of pore content in Marshall compaction specimens was the largest. The Proctor compaction method would cause internal aggregate fragmentation, and the rotary compaction method was recommended as the preferred method; Jiang et al. [87] compared and analyzed Marshall compaction and vibration compaction. The study showed that the optimal moisture content and asphalt content of vibration compaction formed specimens were reduced by 11% and 9% respectively compared to Marshall specimens, exhibiting better water stability, cracking resistance, rutting resistance, and fatigue resistance. Compared with heavy compaction, the optimal moisture content of cold recycled asphalt mixture specimens formed by rotary compaction decreased by 18% and the density increased by 3.5% [85].

　　目前，众多学者 主 要 通 过 比较体积参数和力学性能对不同压实方法进行定量化评价，然而配合比设计旨在冷再生沥青混合料工程应用前对其进行测试，以预测沥青路面性能，因此，的试件成型方式应符合现场压实后混合料的相应指标。Ｌｉｕ等［８８］将现场岩样与室内成型方法进行对 比，提出符合冷再生基层现场压实条件的成型方法，即大Ｍａｒｓｈａｌｌ试件的初次压实为１５０次，二次压实为７５次，旋转压 实 次 数 为３０＋１５；Ｏｒｏｓａ等［８９］比较了静 态 压 实、旋转压实和马歇尔压实法成型试件 的 体 积 指 标，并与现场压实目标值进行了对比分 析，验证了旋转压实法能够较好反映现场压实水 平；Ｍａｒｔíｎｅｚ－Ｅｃｈｅｖａｒｒíａ等［９０］提 出了 一 种室内压实 方 法，以与现场压实后的冷再生沥青结构层密度 保 持 一 致，并对比分析了现场芯样与成型试样的 动 态 模 量，验证了所提出压实方法的适用性。由以 上 分 析 可 得， 佳 成 型 方 法 应 与 现 场压实后的混合料体 积 参 数 和 力 学 性 能 具 有 较 好 的一致性，以更好地反映冷再生材料在实际服役状态下的性能优劣。冷再生沥青混合料的室内养生过程主要是为了模拟现场冷再生沥青结构层的固化条件，以确定上铺沥青结构层和开放交通的时间。养生条件决定了冷再生沥青试件在养护过程中的强度增长，其主要包括养 生 时 间、温 度 和 湿 度。

　　At present, many scholars mainly quantitatively evaluate different compaction methods by comparing volume parameters and mechanical properties. However, mix design aims to test cold recycled asphalt mixtures before their engineering application to predict asphalt pavement performance. Therefore, the optimal specimen forming method should comply with the corresponding indicators of the compacted mixture on site. Liu et al. [88] compared on-site rock samples with indoor forming methods and proposed a forming method that meets the on-site compaction conditions for cold recycled base layers, namely, the initial compaction of the large Marshall specimen is 150 times, the secondary compaction is 75 times, and the rotational compaction is 30+15 times; Orosa et al. [89] compared the volume indices of static compaction, rotary compaction, and Marshall compaction method formed specimens, and compared and analyzed them with the on-site compaction target values, verifying that the rotary compaction method can better reflect the on-site compaction level; Mart í nez Echevarr í a et al. [90] proposed an indoor compaction method to maintain consistency with the density of cold recycled asphalt structural layers after on-site compaction, and compared and analyzed the dynamic modulus of on-site core samples and formed samples to verify the applicability of the proposed compaction method. From the above analysis, it can be concluded that the optimal molding method should have good consistency with the volume parameters and mechanical properties of the compacted mixture on site, in order to better reflect the performance advantages and disadvantages of cold recycled materials in actual service conditions. The indoor curing process of cold recycled asphalt mixture is mainly to simulate the solidification conditions of the on-site cold recycled asphalt structural layer, in order to determine the time for laying the asphalt structural layer and opening traffic. The curing conditions determine the strength growth of cold recycled asphalt specimens during the curing process, mainly including curing time, temperature, and humidity.

　　Ｌｅｅ等［９１］开 展 了 如图６所示的无密封养护、半密封养护和全密封养护３种室内养护方法，对应的强度增长规律如下。（１）无密封养护：２５ ℃、４０ ℃和６０ ℃烘箱内分别固化２ｄ，含水率降０，间 接 抗 拉 强 度 持 续 增 长２８ｄ。室温养护１０ｈ，间 接抗 拉 强 度 没 有 增 加，间 接抗拉强 度 与 含 水 率 之 间 无 相 关 性；从 １０ｈ 增 加到５０ｈ，间接抗拉强度有所增加。（２）半密封养护：室内养护１２ｈ后，间接抗拉强度没有增加，从１２ｈ增加到１４ｄ，间接抗拉强度有所增加；在相同含 水 率 下，部 分 固 化１４ｄ试 件的 间接抗拉强度高于７ｄ的试件。（３）全密封养护：随着养生时间增加，间接抗拉强度增大；４０ ℃烘箱中养护１４ｄ，当试样初始含水率低于１．５％时，试样间接抗拉强度提高；初始含水率高于１．５％时，间接抗拉强度没有增加。

　　Lee et al. [91] conducted three indoor maintenance methods as shown in Figure 6: unsealed maintenance, semi sealed maintenance, and fully sealed maintenance. The corresponding strength growth patterns are as follows. (1) Unseal curing: Cured in ovens at 25 ℃, 40 ℃, and 60 ℃ for 2 days, with a moisture content reduced to 0, and indirect tensile strength continuously increased for 28 days. After 10 hours of room temperature curing, there was no increase in indirect tensile strength, and there was no correlation between indirect tensile strength and moisture content; The indirect tensile strength increased from 10h to 50h. (2) Semi sealed maintenance: After 12 hours of indoor maintenance, the indirect tensile strength did not increase. However, when it increased from 12 hours to 14 days, the indirect tensile strength increased slightly; At the same moisture content, the indirect tensile strength of partially cured 14d specimens is higher than that of 7d specimens. (3) Fully sealed maintenance: As the maintenance time increases, the indirect tensile strength increases; After curing in a 40 ℃ oven for 14 days, the indirect tensile strength of the sample increases when the initial moisture content of the sample is below 1.5%; When the initial moisture content is higher than 1.5%, the indirect tensile strength does not increase.

　　3.1.2国内配合比设计方法参考了国内外相关设计方法和工程应用情况，明确了采用马歇尔设计方法指导冷再生沥青混合料配合比设计。但是，已有的冷再生项目工程中对采用马歇尔压实成型还是旋转压实成型并没有形成统一标准。相对于马歇尔成型方式，旋转压实能够 更 好 地 模 拟 冷 再 生 路 面 的 现 场 碾 压 过 程。Ｗｅｉ等［９２］研究了旋转压实成型方法在乳化沥青混合料中的应用，并根据劈裂强度对相关技术参数进行优化。ＪＴＧ／Ｔ５５２１—２０１９中冷再生配合比设计方法采用双面击 实５０＋２５次 的马 歇 尔 法，养 生 条 件 为６０℃烘箱中少４０ｈ，采用１５℃劈裂强度或马歇尔稳定度指标以确定乳化沥青用量。马歇尔设计方法是目前世界上应用为广泛的一种沥青混合料设计方法。它的优点是对混合料的体积指标都有着明确的要求，且设备便宜、操作简单。3.2冷再生沥青路面结构设计方法

　　3.1.2 Domestic Mix Proportion Design Method China has referred to relevant design methods and engineering applications at home and abroad, and clarified the use of Marshall design method to guide the mix proportion design of cold recycled asphalt mixtures. However, there is no unified standard for using Marshall compaction or rotary compaction in existing cold recycling projects in China. Compared to the Marshall molding method, rotary compaction can better simulate the on-site rolling process of cold recycled pavement. Wei et al. [92] studied the application of rotary compaction molding method in emulsified asphalt mixtures and optimized relevant technical parameters based on splitting strength. The JTG/T5521-2019 intercooled regeneration mix design method adopts the Marshall method of double-sided compaction 50+25 times, and the curing conditions are at least 40 hours in a 60 ℃ oven. The 15 ℃ splitting strength or Marshall stability index is used to determine the optimal emulsified asphalt dosage. The Marshall design method is currently the most widely used asphalt mixture design method in the world. Its advantage is that it has clear requirements for the volume index of the mixture, and the equipment is cheap and easy to operate. 3.2 Design Method for Cold Recycled Asphalt Pavement Structure

　　在冷再生技术规范指导方面，１９８１年美国交通运输研究委员会出版了《路面废料再生指南》，随后沥青协会在１９８３年出版了《沥青路面冷拌再生技术手册》。日本道路协会在１９８４年颁布了《路面废旧材料再生利用技术指南》，并在２００４年出版了《路面回收指南》。南非在２００９年颁布了《沥青稳定类再生设计和施工技术指南》，详细介绍了冷再生沥青混合料配合比设计、结构设计以及施工方法等。冷再生路面结构设计方法作为冷再生技术推广应用的重要组成部分，在国内外大致可分为２类：一类是以工程经验和室内试验为依据的经验设计法，典型的经验设计法有 ＣＢＲ法和 ＡＡＳＨＴＯ 法；另一类是以力学分析为基 础，考 虑 交 通、环境以及材料特性的力学－经验法，包括 ＭＥＰＤＧ 和 ＡＡＳＨＴＯ２０１５。路面设计方法的发展也经历了从经验法到力学－经 验法的转变，目前冷再生沥青路面的结构设计方法大多以沥青路面结构设计方法为基础。以下介绍几种典型的冷再生沥青路面结构设计方法。

　　In terms of guidance on cold recycling technology specifications, the Transportation Research Board of the United States published the "Guidelines for Road Waste Recycling" in 1981, followed by the Asphalt Institute publishing the "Handbook for Cold Mix Recycling Technology of Asphalt Pavement" in 1983. The Japan Road Association issued the "Technical Guidelines for the Recycling of Road Waste Materials" in 1984 and published the "Road Recycling Guidelines" in 2004. In 2009, South Africa issued the "Guidelines for Design and Construction Technology of Asphalt Stabilized Recycled Asphalt", which detailed the mix design, structural design, and construction methods of cold recycled asphalt mixtures. The design method of cold recycling pavement structure, as an important component of the promotion and application of cold recycling technology, can be roughly divided into two categories at home and abroad: one is the empirical design method based on engineering experience and indoor testing, and typical empirical design methods include CBR method and AASHTO method; Another type is based on mechanical analysis, considering traffic, environment, and material properties using mechanical empirical methods, including MEPDG and AASHTO2015. The development of pavement design methods has also undergone a transition from empirical methods to mechanics empirical methods. Currently, most structural design methods for cold recycled asphalt pavements are based on asphalt pavement structural design methods. The following introduces several typical design methods for cold recycled asphalt pavement structures.

　　3.2.1经验法（１）ＡＡＳＨＴＯ 结构层系数设计法：针对冷再生沥青路面结构设计并未提出针对性的设计方法，加铺层厚度设计仍依托于结构数，加铺层厚度计算包括冷再生层和加铺层。结构数ａ的计算公式为乳化沥青混 合 料 的 推 荐 结 构 层 系 数 为０．２８～０．３５［９３－９４］，泡 沫 沥 青 混 合 料 的 推 荐 结 构 层 系 数 为０．３６～０．３９［９５］，相关研究中全深式冷再生沥青混合料的值为０．２５～０．４１［９６］，沥青混合料的结构层系数约为０．５。其 中结 构 层 系 数 可 以 通 过 有 效 结 构 数 进 行 表征，有 效 结 构 数 Ｓ 是基于落锤式弯沉仪 （ＦａｌｌｉｎｇＷｅｉｇｈｔＤｅｆｌｅｃｔｏｍｅｔｅｒ，ＦＷＤ）测试反演路基上方所有结构层的有效模量进行定量化计算，表示为（２）美国加利福尼亚州采用碎石当量法定义了各结构层材料在承受相同荷载作用下的碎石当量厚度。特定结构层的碎石当量厚度Ｇ 为（３）南非设计法：基于 ＡＡＳＨＴＯ 结构数的设计原理，南非提出了路面数设计法，将沥青面层、水泥混凝土等胶结材料、沥青稳定材料、无黏结材料和路基土的材料属性进行材料性能等级划分，并基于路面结构层从上下刚度依次递减的原则，提出了层间模量比。具体设计步骤如下。步骤１：计算路基等效长期刚度，考虑气候因素的湿度调整因子和厚度系数。步骤２：基于层间模量比依次计算路基上方各结构层模量，即该结构层的支撑层模量乘以模量比，取计算模量和允许模量的较小值。步骤３：对于沥青混合料和沥青稳定类材料（包含泡沫沥青混合料和乳化沥青混合料），需乘以厚度调整系数。

　　3.2.1 Empirical Method (1) AASHTO Structural Layer Coefficient Design Method: No targeted design method has been proposed for the structural design of cold recycled asphalt pavement. The design of overlay thickness still relies on the number of structures, and the calculation of overlay thickness includes both cold recycled layer and overlay layer. The calculation formula of structure number a is that the recommended structure layer coefficient of emulsified asphalt mixture is 0.28~0.35 [93-94], the recommended structure layer coefficient of foam asphalt mixture is 0.36~0.39 [95], the recommended value of full depth cold recycling asphalt mixture in relevant studies is 0.25~0.41 [96], and the structure layer coefficient of asphalt mixture is about 0.5. The structural layer coefficient can be characterized by the effective structure number, which S is quantitatively calculated based on the effective modulus of all structural layers above the roadbed inverted by the Falling Weight Deflectometer (FWD) test. It is expressed as (2) California, USA uses the gravel equivalent method to define the equivalent thickness of each structural layer material under the same load. The equivalent thickness G of crushed stone for a specific structural layer is (3) South African design method: Based on the design principle of AASHTO structural number, South Africa proposed the pavement number design method, which divides the material properties of asphalt surface layer, cement concrete and other bonding materials, asphalt stabilizing materials, non bonding materials and subgrade soil into material performance grades. Based on the principle of decreasing stiffness from top to bottom of the pavement structural layer, the interlayer modulus ratio is proposed. The specific design steps are as follows. Step 1: Calculate the equivalent long-term stiffness of the roadbed, taking into account the humidity adjustment factor and thickness coefficient of climate factors. Step 2: Calculate the modulus of each structural layer above the roadbed based on the interlayer modulus ratio, that is, multiply the modulus of the supporting layer of the structural layer by the modulus ratio, and take the smaller of the calculated modulus and the maximum allowable modulus. Step 3: For asphalt mixture and asphalt stabilized materials (including foam asphalt mixture and emulsified asphalt mixture), the thickness adjustment coefficient shall be multiplied.

　　步骤４：对于基层材料，模量需乘以基层可靠度因子。步骤５：计算所有结构层贡献值总和，即路面数。步骤６：根据道路等级和路面数，确定标准轴载作用下的路面承载能力。

　　Step 4: For the base material, the modulus needs to be multiplied by the base reliability factor. Step 5: Calculate the total contribution value of all structural layers, i.e. the number of road surfaces. Step 6: Determine the minimum bearing capacity of the road surface under standard axle load based on the road grade and number of road surfaces.

　　3.2.2力学－经验法力学－经验法是基于结构力学和材料模型来分析施加荷载时路面结构内部响应的应力、应变和挠度，通过传递函数将应力、应变或挠度与结构性能（荷载重复到破坏的次数）建立关联，传递函数是一种经验关系，来自研究和／或路面性能数据。路面分析模型一般采用弹性层状体系理论，输入参数包括结构层厚和各结构层材料对应的弹性模量和泊松比。力学－经验法能够对已有的路面结构层进行有效建模和分析，对冷再生沥青路面设计具有显著优势。目前，尚未形成针对冷再生沥青路面的设计方法，力学－经验法将冷再生沥青混合料视为一种无黏结基层材料，需确定回弹模量并作为力学输入值［８］。然而，冷再生沥青混合料具有一定的黏弹性力学特性，是一种介于无黏结颗粒材料与沥青混合料的路面材料。以全深式冷再生为例，研究表明将冷再生结构层视为沥青黏结层或是无黏结材料层对路面性能具有显著影响［９６］。对冷再生沥青路面结构设计方法的研究较少，主要基于《公路沥青路面设计规范》（ＪＴＧ　Ｄ５０—２０１７）进行结构设计。目前，越来越多的学者将冷再生沥青混合料作为一种沥青黏结材料进行路面结构设计。当冷再生沥青材料作为基层和下面层时，在荷载作用下冷再生结构层底部受拉，需要对其疲劳寿命进行验算；其次，冷再生沥青材料在荷载作用下会发生车辙变形，也需要对其变形进行验算。目前，冷再生沥青结构层的车辙预估模型和疲劳设计方程大多采用基于热拌沥青混合料的路面设计准则，但是冷再生沥青材料与传统热拌沥青混合料的性能具有一定差异，传统沥青路面结构设计准则对冷再生沥青结构层的适用性仍需进一步研究［９７］。Ｇｕ等［８］将冷再生沥青结构层作为基层，并考虑了其黏弹性力学特性，建立了符合冷再生沥青路面的车辙预估模型和疲劳损伤模型。以如图７［８］所示的车辙预估模型为例，车辙预测深度约为现场检测值的２倍（Ｅ、Ｆ分别为乳化沥青、泡沫沥青，Ｐ、Ｍ分别为预测值、现场检测值），该现象主要是由于力学－经验法的模型校正系数存在偏差，以及室内试验养护方法未能真实反映冷再生沥青混合料的养护过程。传统的疲劳设计方程是基于弹性假设的线性损伤累计，假定在疲劳损伤过程中沥青混合料模量为定值，在控制应力模式下材料内部产生固定的应变水 平，未考虑冷再生沥青混合料的非线性损伤演化。针对冷再生沥青混合料疲劳准则的研究，Ｋｕｎａ等［９８］提出了如图８所示的基于混合料刚度演化的疲劳寿命分阶段累加设计方法，将 刚 度演化过程 划 分 成 多 个 区 间，假 定 每 个 区 间 的 刚 度为该区间的均值，依 次 计 算 各 区 间 内 的 疲 劳 寿 命，并进行累加。

　　3.2.2 Mechanics Empirical Method Mechanics empirical method is based on structural mechanics and material models to analyze the stress, strain, and deflection of the internal response of pavement structures when loads are applied. It establishes a correlation between stress, strain, or deflection and structural performance (the number of times the load is repeated to failure) through a transfer function, which is an empirical relationship derived from research and/or pavement performance data. The pavement analysis model generally adopts the theory of elastic layered system, and the input parameters include the thickness of the structural layer and the corresponding elastic modulus and Poisson's ratio of each structural layer material. The mechanics experience method can effectively model and analyze existing pavement structural layers, which has significant advantages in the design of cold recycled asphalt pavement. At present, there is no design method for cold recycled asphalt pavement. The mechanical empirical method considers cold recycled asphalt mixture as a non bonded base material, and the rebound modulus needs to be determined as the mechanical input value [8]. However, cold recycled asphalt mixture has certain viscoelastic mechanical properties and is a pavement material that falls between non bonded granular materials and asphalt mixtures. Taking full depth cold recycling as an example, research has shown that treating the cold recycling structural layer as either an asphalt bonding layer or a non bonding material layer has a significant impact on pavement performance [96]. There is relatively little research on the design method of cold recycled asphalt pavement structure in China, mainly based on the "Design Specification for Highway Asphalt Pavement" (JTGD50-2017) for structural design. At present, more and more scholars are using cold recycled asphalt mixture as an asphalt bonding material for pavement structure design. When cold recycled asphalt material is used as the base and lower layer, the bottom of the cold recycled structural layer is subjected to tension under load, and its fatigue life needs to be verified; Secondly, cold recycled asphalt materials will undergo rutting deformation under load, and its permanent deformation also needs to be verified. At present, most of the rutting prediction models and fatigue design equations for cold recycled asphalt structural layers adopt pavement design criteria based on hot mix asphalt mixtures. However, the performance of cold recycled asphalt materials differs from that of traditional hot mix asphalt mixtures, and the applicability of traditional asphalt pavement structural design criteria to cold recycled asphalt structural layers still needs further research [97]. Gu et al. [8] used the cold recycled asphalt structural layer as the base layer and considered its viscoelastic mechanical properties, establishing a rutting prediction model and fatigue damage model that are suitable for cold recycled asphalt pavement. Taking the rut prediction model as shown in Figure 7 [8] as an example, the rut prediction depth is about twice the field detection value (E and F are emulsified asphalt and foam asphalt respectively, P and M are the prediction value and field detection value respectively). This phenomenon is mainly due to the deviation of the model correction coefficient of the mechanical empirical method, and the failure of the indoor test maintenance method to truly reflect the maintenance process of cold recycled asphalt mixture. The traditional fatigue design equation is based on the linear damage accumulation assumption of elasticity, assuming that the modulus of asphalt mixture is constant during the fatigue damage process, and a fixed strain level is generated inside the material under controlled stress mode, without considering the nonlinear damage evolution of cold recycled asphalt mixture. Kuna et al. [98] proposed a phased cumulative design method for fatigue life of cold recycled asphalt mixtures based on the evolution of mixture stiffness, as shown in Figure 8. The stiffness evolution process is divided into multiple intervals, and assuming that the stiffness of each interval is the mean of that interval, the fatigue life within each interval is calculated sequentially and accumulated.

　　3.2.3冷再生沥青路面设计存在的问题结构数、碎 石 当 量 法 及 路 面 数 设 计 法 是 经 验性的设计方法。结 构 数 和 碎 石 当 量 法 基 于 一 定 的标准值粗略地将冷 再 生 沥 青 混 合 料 强 度 性 能 进 行等效系数 的 折 减，并未考虑路面结构整体的受力特性和结 构 层 合 理 设 置；路 面 数 设 计 法 考 虑 了 路面结构的 整 体 受 力 特 性，基 于 大 量 路 面 结 构 性 能检测数据对各结构层模量进行了有效规范。以 上经验法均未考虑冷 再 生 材 料 在 长 期 服 役 过 程 中 的刚度性能演化。研究表 明，冷 再 生 沥 青 混 合 料 的 抗 疲 劳 性 能低于热拌 沥 青 混 合 料，且在道路结构中多应用于基层，在 交 通 荷 载 作 用 下 易 发 生 疲 劳 裂 缝。对 于力学经验 法，目前针对冷再生沥青路面的疲劳方程研究较 少，普遍按照热拌沥青混合料的设计方法进行 疲 劳 设 计，未 能 充 分 考 虑 其 抗 疲 劳 性 能。主要原因 在 于：１）由于冷再生沥青混合料材料组成复杂，其强度组成机理与传统的热拌沥青混合料差异较大，在服 役 前 期 随 着 时 间 增 长，强 度 仍 出现一定程 度 的 提 高，以上因素导致冷再生沥青混合料在全寿命周期 内 的 强 度 演 化 和 失 效 机 理 目 前尚未充分 明 确，如果按照传统热拌沥青混合料的疲劳设计准则进行路面设计，会 导 致 计 算 得 到 的冷再生基 层 厚 度 过 大；２）缺少充足的冷再生沥青路面现场 疲 劳 失 效 数 据，无 法 对 室 内 疲 劳 方 程 进行有效标定。冷再生沥青路面设计研究应着重考虑冷再生材料自身材料属性和结构层受力特性，深入研究不同材料组分影响下冷再生沥青混合料的强度特性和破坏机理，建立符合冷再生沥青混合料特性的力学失效设计准则，并系统开展大量的冷再生沥青路面现场检测，基于现场检测数据对其路面设计准则进行校正，以建立真正符合冷再生沥青路面的结构设计方法。

　　3.2.3 Problems in the design of cold recycled asphalt pavement: The structural number, gravel equivalent method, and pavement number design method are empirical design methods. The structural number and gravel equivalent method roughly reduce the strength performance of cold recycled asphalt mixture by equivalent coefficients based on certain standard values, without considering the overall stress characteristics of the pavement structure and the reasonable setting of structural layers; The pavement design method considers the overall stress characteristics of the pavement structure and effectively regulates the modulus of each structural layer based on a large amount of pavement structure performance testing data. The above empirical methods did not consider the stiffness performance evolution of cold recycled materials during long-term service. Research has shown that the fatigue resistance of cold recycled asphalt mixture is lower than that of hot mix asphalt mixture, and it is mostly used in the base layer of road structures, which is prone to fatigue cracks under traffic loads. For the empirical method of mechanics, there is currently little research on the fatigue equation of cold recycled asphalt pavement. The fatigue design is generally based on the design method of hot mix asphalt mixture, and its anti fatigue performance has not been fully considered. The main reason is that: 1) Due to the complex composition of cold recycled asphalt mixture materials, their strength composition mechanism is significantly different from that of traditional hot mix asphalt mixture. In the early stage of service, as time increases, the strength still shows a certain degree of improvement. The above factors have led to the strength evolution and failure mechanism of cold recycled asphalt mixture throughout its life cycle, which is currently not fully understood. If the pavement design is carried out according to the fatigue design criteria of traditional hot mix asphalt mixture, it will result in the calculated thickness of the cold recycled base layer being too large; 2) Lack of sufficient on-site fatigue failure data for cold recycled asphalt pavement makes it impossible to effectively calibrate indoor fatigue equations. The research on the design of cold recycled asphalt pavement should focus on the material properties and structural layer stress characteristics of cold recycled materials, deeply study the strength characteristics and failure mechanism of cold recycled asphalt mixtures under the influence of different material components, establish mechanical failure design criteria that conform to the characteristics of cold recycled asphalt mixtures, and systematically carry out a large number of on-site inspections of cold recycled asphalt pavement. Based on the on-site inspection data, the pavement design criteria should be corrected to establish a structural design method that truly conforms to cold recycled asphalt pavement.

　　4 冷再生沥青混合料路用性能研究

　　Research on the Road Performance of 4 Cold Recycled Asphalt Mixtures

　　为了对冷再生材料的力学特性和应用效果进行定量化的评价，国内外学者进行了大量冷再生沥青混合料路用性能试验研究。4.1车辙性能

　　In order to quantitatively evaluate the mechanical properties and application effects of cold recycled materials, scholars at home and abroad have conducted a large number of experimental studies on the road performance of cold recycled asphalt mixtures. 4.1 Rutting performance

　　车辙是高温条件下在载荷反复作用下引起的变形累积，刚度较大的沥青混合料具有更强的抗车辙性能。冷再生材料主要应用于基层、底基层以及下面层，提高冷再生材料的强度可以为沥青面层提供足够的支撑力，从而减小路面纵向裂缝。目前，研究冷再生沥青混合料车辙性能的主要试验方法包括动态模量试验、马歇尔稳定度、重复加载试验、三轴动态蠕变 试 验、汉 堡 车 辙 仪 等［９９－１０１］。同 时，乳化沥青／泡沫沥青及其沥青胶浆作为冷再生材料的胶结料，其抗变形能力也对冷再生沥青混合料的性能影响较大。Ｖｉｇｎａｌｉ等［１０２］采用了温度扫描试验和多重应力蠕变恢复试验表征冷再生胶浆材料的抗变形能 力；汪 德 才 等［１０３］采用车辙因子指标评价乳化沥青残留物的高温抗变形能力；Ｒｅｚａｅｉ等［１０４］对比分析 了 ９ 种冷再生材料的车辙性能，试 验 结果表明较高马歇尔 模 数 的 冷 再 生 材 料 具 有 更 好 的抗车辙性能，与汉 堡 车 辙 试 验 结 果 一 致，骨 料 粒 径分布对车 辙 性 能 影 响 较 大，密 级 配 混 合 料 抗 车 辙性能优于开级 配；Ｇｕ等［８］对比分析了厂拌冷再生和就地冷再生沥青混合料的抗车辙性能，级 配 较粗的 厂 拌 冷 再 生 混 合 料 的 抗 车 辙 性 能 更 佳。

　　Rutting is a permanent deformation accumulation caused by repeated loading under high temperature conditions, and asphalt mixtures with higher stiffness have stronger resistance to rutting. Cold recycled materials are mainly used in the base layer, sub base layer, and lower surface layer. Improving the strength of cold recycled materials can provide sufficient support for the asphalt surface layer, thereby reducing longitudinal cracks in the road surface. At present, the main experimental methods for studying the rutting performance of cold recycled asphalt mixtures include dynamic modulus test, Marshall stability test, repeated loading test, triaxial dynamic creep test, Hamburg rutting instrument, etc. [99-101]. At the same time, emulsified asphalt/foam asphalt and its asphalt mortar, as the binder of cold recycled materials, have a greater impact on the performance of cold recycled asphalt mixture in terms of its permanent deformation resistance. Vignali et al. [102] used temperature scanning tests and multiple stress creep recovery tests to characterize the resistance to permanent deformation of cold recycled adhesive materials; Wang Decai et al. [103] evaluated the high-temperature deformation resistance of emulsified asphalt residues using the rutting factor index; Rezaei et al. [104] compared and analyzed the rutting performance of 9 cold recycled materials. The experimental results showed that cold recycled materials with higher Marshall modulus had better rutting resistance, consistent with the Hamburg rutting test results. The particle size distribution of aggregates had a greater impact on rutting performance, and the rutting resistance of dense graded mixtures was better than that of open graded mixtures; Gu et al. [8] compared and analyzed the anti rutting performance of factory mixed cold recycled and on-site cold recycled asphalt mixtures, and found that the coarse-grained factory mixed cold recycled mixture had better anti rutting performance.

　　此外，厂拌冷再生可 以 对 ＲＡＰ料的变异性进行有效控制，相关研究结果表明厂拌泡沫沥青混合料的抗车辙性能高于热拌沥青混合料，乳 化 沥 青 混 合料稍差于热拌混 合 料。其他研究表明泡沫沥青混合料的模量高于乳化沥青混合料，间 接 反 映 出 泡沫沥青混合料具有更好的 抗 车 辙 性 能［５５］。这 主要是由于沥青在混合料中分布方式的差异，泡 沫 沥青混合料以点焊方式与集料进行黏合，而 乳 化 沥青主要是以沥青膜的形式包裹在集料表面，在 外力荷载作用下乳化 沥 青 混 合 料 更 易 发 生 集 料 间 的滑移，从而造成 较 大 的 车 辙。高 超［１０５］开 展了 常 温条件下 ＭＭＬＳ３加速加载试验，并对试件 进 行Ｘ射线无损扫 描，表明车辙变形主要是由于泡沫砂浆试件压密变形和集料在空间方向上的位移调整；Ｂａｂａｇｏｌｉ等［１０６］采用马歇尔稳定度、动 态 蠕 变 及 车轮试验评价水泥及石灰 对 ＳＢＳ改 性乳 化 沥 青 混 合料的影响，加入水 泥 和 石 灰 能 够 降 低 空 隙 率，提 高了马歇尔稳定度和抗 变 形 能 力；其 次，ＲＡＰ料降低了冷再 生 沥 青 混 合 料 的 热－黏弹性力学特性，相比于传统热拌沥 青 混 合 料 具 有 更 好 的 抗 永 久 变形 能 力［１０７］，但其抗车辙性能随着 ＲＡＰ料 的 增 加而降低［１０８］。4.2抗水损害性能

　　In addition, plant mix cold recycling can effectively control the variability of RAP mixture. Relevant research results show that the anti rutting performance of plant mix foam asphalt mixture is higher than that of hot mix asphalt mixture, and the emulsified asphalt mixture is slightly worse than that of hot mix asphalt mixture. Other studies show that the modulus of foam asphalt mixture is higher than that of emulsified asphalt mixture, which indirectly reflects that foam asphalt mixture has better rutting resistance [55]. This is mainly due to the difference in the distribution of asphalt in the mixture. foam asphalt mixture is bonded to the aggregate by spot welding, while emulsified asphalt is mainly wrapped on the surface of the aggregate in the form of asphalt film. Under the external force load, emulsified asphalt mixture is more likely to slip between aggregates, resulting in large rutting. Gaochao [105] carried out the accelerated loading test of MMLS3 at room temperature, and carried out X-ray non-destructive scanning on the specimens. It showed that the rutting deformation was mainly due to the compaction deformation of foam mortar specimens and the displacement adjustment of aggregates in the spatial direction; Babagoli et al. [106] evaluated the effects of cement and lime on SBS modified emulsified asphalt mixture using Marshall stability, dynamic creep, and wheel tests. The addition of cement and lime can reduce porosity, improve Marshall stability, and enhance resistance to permanent deformation; Secondly, RAP material reduces the thermal viscoelastic mechanical properties of cold recycled asphalt mixture, and has better resistance to permanent deformation compared to traditional hot mix asphalt mixture [107]. However, its anti rutting performance decreases with the increase of RAP material [108]. 4.2 Water damage resistance performance

　　冷再生材料中加入乳化沥青或泡沫沥青，其中水分随着养护龄期的增加而逐渐挥发，该过程会导致冷再生材料内部留下水分挥发后的微空隙，该部分空隙会在路面服役期内发生水分汇集，从而对冷再生材料产 生 水 损 害，造 成 各 项 力 学 性 能 的 衰 减。ＪＴＧ／Ｔ５５２１—２０１９采用冻融劈裂强度比、干 湿劈裂强度比作为控制冷再生材料水损害的控制指标，同时其他众多学者也采用马歇尔稳定度、间接拉伸强度、回弹模量、无侧限抗压强度等指标评价冷再生沥青混 合 料 的 水 稳 性［１０９－１１２］。此 外，表面 能 试 验 用于评价胶结料与集料的裹附程度及裹附质量，也被用于评价冷再生沥青混合料的水稳定性［１１３］。冷再生沥青混合料发生水损害后，材料内部出现微裂缝，导致空隙增大以及劈裂强度、模量及抗疲劳性能等降低［１１１］。在冻融循环过程中产生的膨胀应力、内应力以及温度应力破坏水泥水化产物的立体网状结构，微空隙数目减少，而大体积空隙数目显著增多［１１４］，降低了集料与沥青间的黏结性，造成混合料的抗剪性能衰减［１１１］。相关研究结果表明 ＲＡＰ料掺量是影响冷再生沥青混合料水稳定性的主要因素，水稳定性 随 着 ＲＡＰ 料 的掺 量 呈 先 增 大 后 减 小的趋势［１１０］。考虑到集 料 类 型 的 影 响，ＲＡＰ料 与沥青黏附效 果 差，其水稳性远低于常规的花岗岩和石灰岩 集 料 类 型［１１３］。熟 石 灰 或 硅 酸 盐 水 泥 不 仅可以作为冷再生材料的矿物掺合料，其 含 有 氢 氧化钙和其 他 碱 性 成 分，遇水发生水化作用并与沥青形成复 合 胶 浆，两者交互作用增强了沥青与集料的黏结 力，从而提高了冷再生沥青混合料的水稳 定 性［３０，１１２，１１５］，但 是水 泥 掺 量 超 过１．５％后 抗水损害性能 的 增 强 效 果 变 小［１１０］；此 外，添 加 聚 合 物外加剂能够提高冷再生沥青混合料的水稳性［１１３］。4.3抗疲劳开裂性能

　　Emulsified asphalt or foam asphalt is added to the cold recycled materials, and the moisture in the cold recycled materials gradually evaporates with the increase of the curing age. This process will lead to micro voids left inside the cold recycled materials after the moisture volatilization. This part of voids will collect moisture during the service life of the pavement, thus causing water damage to the cold recycled materials, causing the attenuation of various mechanical properties. JTG/T5521-2019 uses freeze-thaw splitting strength ratio and dry wet splitting strength ratio as control indicators for water damage in cold recycled materials. At the same time, many other scholars have also used Marshall stability, indirect tensile strength, rebound modulus, unconfined compressive strength and other indicators to evaluate the water stability of cold recycled asphalt mixtures [109-112]. In addition, surface energy tests are used to evaluate the degree and quality of adhesion between binders and aggregates, as well as to evaluate the water stability of cold recycled asphalt mixtures [113]. After water damage occurs in cold recycled asphalt mixture, micro cracks appear inside the material, resulting in increased voids and decreased splitting strength, modulus, and fatigue resistance [111]. The expansion stress, internal stress, and temperature stress generated during the freeze-thaw cycle damage the three-dimensional network structure of cement hydration products, resulting in a decrease in the number of micro voids and a significant increase in the number of large volume voids [114]. This reduces the adhesion between aggregates and asphalt, leading to a decline in the shear performance of the mixture [111]. The relevant research results indicate that the dosage of RAP material is the main factor affecting the water stability of cold recycled asphalt mixture, and the water stability shows a trend of first increasing and then decreasing with the dosage of RAP material [110]. Considering the influence of aggregate types, RAP material has poor adhesion to asphalt and its water stability is much lower than conventional granite and limestone aggregate types [113]. Hydrated lime or Portland cement can not only be used as mineral admixtures for cold recycled materials, but also contain calcium hydroxide and other alkaline components. When it comes into contact with water, it undergoes hydration and forms a composite slurry with asphalt. The interaction between the two enhances the adhesion between asphalt and aggregate, thereby improving the water stability of cold recycled asphalt mixtures [30112115]. However, the enhancement effect of water damage resistance decreases when the cement content exceeds 1.5% [110]; In addition, adding polymer additives can improve the water stability of cold recycled asphalt mixtures [113]. 4.3 Fatigue cracking resistance performance

　　冷再生材料目前在国内工程应用中主要应用于基层和底基层，为了保证冷再生材料具有足够承载能力，通常采用掺入１．０％～２．５％水泥以提高冷再生结构层的抗变形能力，但同时也导致其脆性增加，在一定程度上降低了其抗疲劳性能。目前，关于冷再生沥青混合料疲劳性能的研究主要集中于疲劳试验方法、破坏特征、寿命预估以及控制指标等方面。冷再生沥青混合料的疲劳试验通常采用间接拉伸疲劳试 验、四 点 弯 曲 试 验［１１６－１１７］、盘 状紧 凑 拉 伸［１１８］和半圆弯曲试 验［１１９］等 方法，采取应力控制模式或者应变控制模式［１２０］。常用的性能分析指标包括断裂能［１１８］、抗拉强度、耗散能等指标。通过冷再生路面裂缝调查结果发现，室内试验的断裂能指标与冷再生 路 面 的 横 向 裂 纹 数 量 具 有 较 好 的 相 关 性。

　　Cold recycled materials are currently mainly used in domestic engineering applications for base and sub base layers. In order to ensure that cold recycled materials have sufficient bearing capacity, 1.0% to 2.5% cement is usually added to improve the deformation resistance of the cold recycled structural layer. However, this also leads to an increase in its brittleness, which to some extent reduces its fatigue resistance. At present, research on the fatigue performance of cold recycled asphalt mixtures mainly focuses on fatigue testing methods, failure characteristics, life estimation, and control indicators. The fatigue test of cold recycled asphalt mixture usually adopts methods such as indirect tensile fatigue test, four point bending test [116-117], disc compact tensile test [118], and semi-circular bending test [119], and adopts stress control mode or strain control mode [120]. Common performance analysis indicators include fracture energy [118], tensile strength, dissipated energy, and other indicators. Through the investigation of cracks in cold recycled pavement, it was found that the fracture energy index of indoor tests has a good correlation with the number of transverse cracks in cold recycled pavement.

　　Ｔｅｓｈａｌｅ等［１２１］采用断裂能为指标，研究了盘状紧凑拉伸和半圆弯曲断裂试验方法对评价就地冷再生混合料抗裂性 能 的 适 用 性；孙 立 军 等［１２２］采 用劈 裂 强度试验和应力控制模式的劈裂疲劳试验对比研究了在役冷再生沥青混合料与新成型乳化沥青混合料的疲劳损伤特 性；汪 德 才 等［１１９］采用间接拉伸疲劳试验研究了不同的应力水平、材料组成及掺量对冷再生沥青混合料疲劳性能的影响，结果表明乳化沥青性能、ＲＡＰ掺量对疲劳寿命的影响为显著，应力水平和水泥用量的影响小，其中，冷再生试件断裂能随着 ＲＡＰ料掺量 的 增 加 先 增 大 后 减 小，当 ＲＡＰ料掺量超过１０％时，冷再生试件的断裂能相比常规热拌混合料显著降低［１２３］；严金海等［１２４］采用间接拉伸疲劳试验对比分析了有无水泥掺量下乳化沥青混合料的断裂特性和疲劳寿命，结果表明其疲劳破坏形式为塑性破坏，在低应力和低应变水平下抗疲劳性能优于无水泥添加的乳化沥青混合料，而在高应力和高应变水平下却相反［１２５－１２６］。

　　Teshale et al. [121] used fracture energy as an indicator to study the applicability of disc compact tensile and semi-circular bending fracture test methods for evaluating the crack resistance of in-situ cold recycled mixtures; Sun Lijun et al. [122] compared the fatigue damage characteristics of in-service cold recycled asphalt mixture and newly formed emulsified asphalt mixture using splitting strength test and stress control mode splitting fatigue test; Wang Decai et al. [119] used indirect tensile fatigue tests to study the effects of different stress levels, material compositions, and dosages on the fatigue performance of cold recycled asphalt mixtures. The results showed that emulsified asphalt performance and RAP dosage had the most significant impact on fatigue life, while stress levels and cement dosage had the smallest impact. Among them, the fracture energy of cold recycled specimens increased first and then decreased with the increase of RAP dosage. When the RAP dosage exceeded 10%, the fracture energy of cold recycled specimens significantly decreased compared to conventional hot mix mixtures [123]; Yan Jinhai et al. [124] used indirect tensile fatigue tests to compare and analyze the fracture characteristics and fatigue life of emulsified asphalt mixtures with and without cement content. The results showed that its fatigue failure mode was plastic failure, and its fatigue resistance was better than that of emulsified asphalt mixtures without cement addition at low stress and low strain levels, but the opposite was true at high stress and high strain levels [125-126].

　　对于沥青黏结剂种类，泡沫沥青混合料在低应力水平下疲劳寿命较高，疲劳损伤表现为脆性断裂；乳化沥青混合料在高应力水平下疲劳寿命较高，疲劳损伤表现为塑性破坏［５５］。这主要是 由 于 泡 沫 沥 青 混 合 料 在 相 同 沥 青掺量下强度更高，具有类似于半刚性材料的力学特性；乳化沥青能够较均匀地裹附在集料表面，具有较为明显的黏弹性力学特性，在高应力水平下抗疲劳性能更佳。4.4 低温性能

　　For the type of asphalt binder, the fatigue life of foam asphalt mixture is higher at low stress level, and the fatigue damage is brittle fracture; Emulsified asphalt mixture has a higher fatigue life under high stress levels, and fatigue damage manifests as plastic failure [55]. This is mainly due to the higher strength of foam asphalt mixture under the same asphalt content, which has mechanical properties similar to semi-rigid materials; Emulsified asphalt can be uniformly coated on the surface of aggregates, with obvious viscoelastic mechanical properties and better fatigue resistance under high stress levels. 4.4 Low temperature performance

　　对于冷再生材料低温性能的研究，通常采用间接拉伸蠕变试验，研究低温下材料的强度和蠕变柔量［１２３］；除此之外，低温开裂和抗疲劳开裂数据可以作为 ＭＥＰＤＧ 的 输入 参 数 来 预 测 路 面 病 害。老 化的 ＲＡＰ料能够 提 高 冷 再 生 沥 青 混 合 料 的 刚 度，同时会增强低温脆性。Ｂｅｈｎｉａ等［１２３］采用声发射技术表征了冷再 生 试 件 的 脆 化 温 度，加 入 ＲＡＰ 料 试件的脆化温度高于相同沥青和新集料组成的热拌沥青混合料，这主 要 是 由 于 ＲＡＰ 料 中的 老 化 沥 青 增 加了冷再生材 料 的 脆 性 特 性，但 不 同 ＲＡＰ 料 掺量 的冷再生沥青混合料脆化温度差异较小；Ｙａｎ等［１２７］研究表明加入１％～２％的 水泥 可 以 提 高 乳 化 沥 青混合料的高温稳定性和低温抗裂性，但水泥掺量超过１．５％时，其 低温 抗 开 裂 性 能 增 加 到 大 值 后 随之降低；徐金枝等［６２］开展了不同泡沫沥青和水泥含量的冷再生低温抗裂试验，结果表明冷再生材料的低温柔韧性随泡沫沥青用量的增加而增大，但随着水泥用量的增加而呈抛物线变化规律，因此，当水泥掺量超过一定水平时，冷再生沥青混合料具有更高的低温脆性。4.5小结

　　For the study of low-temperature performance of cold recycled materials, indirect tensile creep tests are usually used to investigate the strength and creep compliance of materials at low temperatures [123]; In addition, low-temperature cracking and fatigue cracking data can be used as input parameters for MEPDG to predict road surface diseases. Aging RAP material can improve the stiffness of cold recycled asphalt mixture and enhance low-temperature brittleness. Behnia et al. [123] used acoustic emission technology to characterize the brittleness temperature of cold recycled specimens. The brittleness temperature of specimens with RAP added was higher than that of hot mix asphalt mixtures composed of the same asphalt and new aggregate. This is mainly due to the increased brittleness of cold recycled materials caused by aged asphalt in RAP, but the difference in brittleness temperature of cold recycled asphalt mixtures with different RAP content is small; Yan et al. [127] found that adding 1% to 2% cement can improve the high-temperature stability and low-temperature crack resistance of emulsified asphalt mixtures. However, when the cement content exceeds 1.5%, its low-temperature crack resistance increases to its maximum value and then decreases; Xu Jinzhi et al. [62] carried out cold recycling low temperature crack resistance tests with different foam asphalt and cement content, and the results showed that the low temperature flexibility of cold recycling materials increased with the increase of foam asphalt content, but it showed a parabolic change law with the increase of cement content. Therefore, when the cement content exceeded a certain level, the cold recycling asphalt mixture had higher low-temperature brittleness. 4.5 Summary

　　由以上分析可知，冷再生沥青混合料的材料组成及性能决定了其路用性能。密级配和粗级配的混合料骨架结构有助于提高冷再生沥青混合料的抗车辙性能。相比 对 无 ＲＡＰ 料 的混 合 料 试 件，ＲＡＰ 料能够提高冷再生沥青混合料的抗车辙性能，并随着ＲＡＰ料 掺量 的 增 加 呈 降 低 趋 势，但 不 利 于 抗 水 损害、抗疲劳以及低温开裂性能。添加水泥和石灰能够增加冷再生沥青混合料的刚度，提升抗车辙性能，且作为一种外加剂能够改善集料与沥青的黏附效果，增强抗水损害性能；低应力应变水平下添加水泥和石灰有利于提高抗疲劳性能，高应力应变水平下则相反；低温开裂性能随着水泥和石灰掺量的增加呈先增长、后降低的趋势。由于乳化沥青和泡沫沥青在冷再生沥青混合料中分布方式的差异，在其他条件相同下，泡沫沥青混合料的模量高于乳化沥青混合料，抗车辙性能更佳。此外，泡沫沥青混合料在低应变水平下的抗疲劳性能更佳，而高应变水平下乳化沥青混合料的抗疲劳性能更优。

　　From the above analysis, it can be concluded that the material composition and performance of cold recycled asphalt mixture determine its road performance. The skeleton structure of dense and coarse graded mixtures helps to improve the anti rutting performance of cold recycled asphalt mixtures. Compared to specimens without RAP material, RAP material can improve the anti rutting performance of cold recycled asphalt mixture, and shows a decreasing trend with the increase of RAP material content. However, it is not conducive to water damage resistance, fatigue resistance, and low-temperature cracking performance. Adding cement and lime can increase the stiffness of cold recycled asphalt mixture, enhance its resistance to rutting, and as an additive, improve the adhesion between aggregate and asphalt, enhancing its resistance to water damage; Adding cement and lime at low stress-strain levels is beneficial for improving fatigue resistance, while the opposite is true at high stress-strain levels; The low-temperature cracking performance shows a trend of first increasing and then decreasing with the increase of cement and lime content. Due to the difference in distribution of emulsified asphalt and foam asphalt in cold recycled asphalt mixture, the modulus of foam asphalt mixture is higher than that of emulsified asphalt mixture under the same other conditions, and the rutting resistance is better. In addition, the anti fatigue performance of foam asphalt mixture is better at low strain level, while the anti fatigue performance of emulsified asphalt mixture is better at high strain level.

　　由此可 见，冷 再 生 沥 青 混 合 料 的 材 料 组 成 对其力学性能影响的差异较大，在 实 际 工 程 中 应 充分考虑冷再生材料所在的结构层位，分 析 其 力 学响应以及对应的力学失效模式，明 确 关 键 性 能 需求。当冷再生沥青 混 合 料 应 用 于 面 层 并 作 为 主 要承载层时，应充分 考 虑 其 抗 车 辙 性 能，开 展 室 内 试验明确 ＲＡＰ料掺量 与 车 辙 变 形 的 对 应 关 系，水 泥和石灰作为外加剂可提高混合料的刚度和强度。相反，当冷再生沥 青 混 合 料 作 为 结 构 基 层 时，应 严格控制水 泥 和 石 灰 掺 量，以 防 止 服 役 期 内 过 早 出现疲劳裂缝。5 冷再生技术施工工艺及施工设备

　　From this, it can be seen that the material composition of cold recycled asphalt mixture has a significant impact on its mechanical properties. In practical engineering, the structural layer where the cold recycled material is located should be fully considered, and its mechanical response and corresponding mechanical failure modes should be analyzed to clarify key performance requirements. When cold recycled asphalt mixture is applied to the surface layer and used as the main bearing layer, its anti rutting performance should be fully considered. Indoor tests should be conducted to clarify the corresponding relationship between RAP content and rutting deformation. Cement and lime as additives can improve the stiffness and strength of the mixture. On the contrary, when cold recycled asphalt mixture is used as the structural base, the cement and lime content should be strictly controlled to prevent premature fatigue cracks during service life. 5 Cold Recycling Technology Construction Process and Equipment

　　5.1 冷再生技术施工工艺

　　5.1 Cold Recycling Technology Construction Process

　　冷再生沥青路面施工工艺是实现预期路面性能的关 键 步 骤。以 就 地 冷 再 生 技 术 为 例，主 要 包括施工准备、铣刨拌和、摊铺碾压、养生等步骤。

　　The construction process of cold recycled asphalt pavement is a key step in achieving the expected pavement performance. Taking on-site cold recycling technology as an example, it mainly includes steps such as construction preparation, milling and mixing, paving and rolling, and curing.

　　（１）施工准备施工前为保证施工性，需提前封闭交通并设置提醒牌，对施工路段进行清扫。其次，若原路面存在病害，要对路面病害进行预处理。根据设计要求计算所需水泥用量并采用撒布机在路面进行铺撒，如需添加一定级配要求的碎石，将碎石按照设计量均匀撒布在路面上。

　　(1) Before construction preparation, in order to ensure construction safety, it is necessary to close traffic and set up reminder signs in advance, and clean the construction section. Secondly, if there are defects on the original road surface, pre-treatment of the road surface defects is necessary. According to the design requirements, calculate the required amount of cement and use a spreader to spread it on the road surface. If it is necessary to add crushed stones with certain grading requirements, evenly spread the crushed stones on the road surface according to the design amount.

　　（２）铣刨拌和利用冷再生机推动洒水车和再生剂胶结料罐车前进，使 ＲＡＰ 料、新 料、再生 剂 和 水 均 匀 拌 和。应综合考虑路面损害状况、铣刨深度、再生层厚度等因素，合理确定再生机组前进速度，一 般 控 制 在 ３～６ｍ·ｍｉｎ－１。每段铣刨长度控制在８０～１００ｍ，在再生机起步开始作业和结束作业处，安排人员及时整平，防止影响接缝处的平整度和密实性。纵向接缝搭接宽度不宜小于１００ｍｍ。

　　(2) Milling and mixing utilize cold regeneration energy to drive the sprinkler truck and the recycling agent binder tank truck forward, ensuring even mixing of RAP material, new material, recycling agent, and water. The forward speed of the regeneration unit should be reasonably determined by considering factors such as road damage, milling depth, and thickness of the regeneration layer, and generally controlled at 3-6m · min-1. The length of each milling section should be controlled between 80-100m. At the starting and ending points of the regeneration machine, personnel should be arranged to level it in a timely manner to prevent affecting the flatness and compactness of the joints. The longitudinal seam overlap width should not be less than 100mm.

　　（３）摊铺碾压摊铺机应均匀、连续，速度宜控制在２～４ｍ·ｍｉｎ－１范围内，摊铺宽度应与再生铣刨宽度保持一致。摊铺能力应与再生能力基本匹配，应在水泥初凝时间内完成材料摊铺压实。松铺系数应根据试验段的结果确定。摊 铺 完 成 后 采 用 钢 轮 振 动 压 路 机 进 行 初压，速度宜为１．５～３．０ｋｍ·ｈ－１，碾压２～３遍；随后采用钢轮振动压路机进行复压，碾压４～６遍，速度宜为２～４ｋｍ·ｈ－１；采用胶轮压路机终压４～６遍，速度 宜 为２～４ｋｍ·ｈ－１。就 地冷 再 生 技术的完整施工工艺见图９。

　　(3) The paving and rolling paving machine should be uniform and continuous, and the speed should be controlled within the range of 2-4m · min-1. The paving width should be consistent with the width of the regenerated milling machine. The paving capacity should be basically matched with the regeneration capacity, and the material paving and compaction should be completed within the initial setting time of cement. The coefficient of looseness should be determined based on the results of the test section. After the paving is completed, a steel wheel vibratory roller should be used for initial compaction at a speed of 1.5-3.0 km · h-1, with 2-3 passes of rolling; Subsequently, a steel wheel vibratory roller is used for re compaction, rolling 4-6 times at a speed of 2-4 km · h-1; Finally, a rubber roller should be used for 4-6 passes of final compaction, with a speed of 2-4 km · h-1. The complete construction process of on-site cold recycling technology is shown in Figure 9.

　　（４）养生冷再生层宜在封闭交通的条件下进行养生，养生时间不宜小于７ｄ，不应少于４８ｈ。当满足下述２个条件时可提前结束养生：再生层使用φ１５０ｍｍ 钻头的钻芯机可取出完整的芯样；再生层含水率低于２％。与就地冷再生技术相比，厂拌冷再生技术是将铣刨的 ＲＡＰ料运输拌合站，并按照配合比进行冷再生沥青混合料拌和，然后运输施工现场进行摊铺碾压。车辆数要满足机组出料和摊铺速度相互协调，机组和施工现场不宜过远，车顶裸露的混合料需进行覆盖以减少水分蒸发损失。混合料采用摊铺机摊铺，熨平板无需加热，振频和振幅以高频低幅为宜，初始密实度达到８５％以上，速度控制在２～４ｍ·ｍｉｎ－１。碾压速度应均匀，初压速度宜为１．５～３．０ｋｍ·ｍ－１，复压和终压速 度 宜 为２～４ｋｍ·ｍ－１。同 时，需配备一台小型振动压路机，以保证边角处的压实度。对于冷再生结构层养生条件，不同的现场条件（温度、湿度、风速、降雨等）、冷再生沥青混合料组分（ＲＡＰ 料 性 能、胶 结 料 以 及 活 性 填 料 类 型 和 含 量等）、结构层特性（冷再生结构层厚度、密度、初始含水率）都会对冷再生结构层的强度增长产生影响。

　　(4) The cold regeneration layer for health preservation should be carried out under closed traffic conditions, and the health preservation time should not be less than 7 days and not less than 48 hours. When the following two conditions are met, the health preservation can be ended in advance: the regeneration layer can use a core drilling machine with a diameter of 150mm drill bit to extract complete core samples; The moisture content of the regeneration layer is less than 2%. Compared with on-site cold recycling technology, factory mixed cold recycling technology transports the milled RAP material to the mixing station, mixes the cold recycled asphalt mixture according to the mix proportion, and then transports it to the construction site for paving and rolling. The number of vehicles should be coordinated with the discharge and paving speed of the unit, and the unit and construction site should not be too far apart. The exposed mixture on the roof should be covered to reduce water evaporation loss. The mixture is spread using a paver, and the ironing board does not require heating. The vibration frequency and amplitude should be high and low, with an initial density of over 85% and a speed controlled between 2-4m · min-1. The compaction speed should be uniform, with an initial compaction speed of 1.5-3.0km · m-1 and a secondary and final compaction speed of 2-4km · m-1. At the same time, a small vibratory roller is required to ensure compaction at the corners. For the curing conditions of cold recycled structural layers, different on-site conditions (temperature, humidity, wind speed, rainfall, etc.), cold recycled asphalt mixture components (RAP material performance, binder and active filler type and content, etc.), and structural layer characteristics (cold recycled structural layer thickness, density, initial moisture content) will all have an impact on the strength growth of cold recycled structural layers.

　　此外，研究表明当含水率趋于稳定后，冷再生结构层的强度性能仍会持续增长。目前，冷再生技术规范主要基于控制养护时间和含水率的施工经验确定开放交通以及加铺上层结构，未充分考虑与路面承载性能直接相关的刚度 和 强 度 的 要 求，将含水率作为养生条件具有一定的局限性，因此，建议将 ＦＷＤ／轻型落锤弯沉仪（ＬｉｇｈｔＷｅｉｇｈｔＤｅｆｌｅｃｔｏｍｅｔｅｒ，ＬＷＤ）作为评价冷再生结构层承载性能的评判方法，即以力学性能的变化来评估养生程度并确定养生时间，而不是依赖于含水率的测量。其次，应完善符合气候条件的冷再生结构层施工环境条件规范。以美国各州规范为例［１２８］，科罗拉多州和堪萨斯州交通部门规定大气温度应高于１３℃，印第安纳州规定路表温度应高于１３ ℃且夜间温度应高于２ ℃，纽约州规定当空气或地表温度低于７ ℃或作业开始后２４ｈ内低于４ ℃时不允许进行施工。5.2 冷再生技术施工设备

　　In addition, studies have shown that when the moisture content stabilizes, the strength performance of the cold regenerated structural layer will continue to increase. At present, the specifications for cold recycling technology are mainly based on the construction experience of controlling maintenance time and moisture content to determine open traffic and adding upper structures, without fully considering the requirements for stiffness and strength directly related to the pavement bearing performance. Using moisture content as a maintenance condition has certain limitations. Therefore, it is recommended to use FWD/Light Weight Deflectometer (LWD) as the evaluation method for evaluating the bearing performance of cold recycling structural layers, that is, to evaluate the degree of maintenance and determine the maintenance time based on changes in mechanical properties, rather than relying on the measurement of moisture content. Secondly, it is necessary to improve the environmental conditions for the construction of cold recycling structural layers that meet the climate conditions in China. Taking the regulations of various states in the United States as an example [128], the transportation departments of Colorado and Kansas stipulate that the atmospheric temperature should be higher than 13 ℃, Indiana stipulates that the road surface temperature should be higher than 13 ℃ and the nighttime temperature should be higher than 2 ℃, and New York state stipulates that construction is not allowed when the air or surface temperature is below 7 ℃ or below 4 ℃ within 24 hours after the start of the operation. 5.2 Cold Recycling Technology Construction Equipment

　　国外关于就地冷再生设备的生产公司主要有美国卡特皮勒公司、德国宝马公司、法国奔能公司以及德国维特根公司，其中维特根公司是世界上、的再生设备厂家。近年来，国内工程机械厂家也逐渐重视冷再生机的研发和生产。山东公路机械厂研发出 具 有 国 际 先 进 水 平 的 ＬＺＳ２４００就 地冷再生机，西安筑路机械公司研发了就地冷再生拌合机 ＣＲ２５００，徐工研发了新款再生设备－ＸＬＺ２３０Ⅱ路面冷再生机。与国外再生机相比，国产冷再生机在品种类型和总体性能方面都存在一定的差距。通过多年的研发和改进，目前冷再生机能够实现铣拌转子在和小转速之间无极调速，增大了冷再生铣刨深度。目前，市场上主要以维特根的 ＷＲ２５００Ｓ和ＷＲ２０００为主［４５］。维特根wr250再生机全深式冷再生技术是就地冷再生技术的一种，主要在再生层厚方面与常规的就地冷再生技术存在差 异，铣 刨 深 度 取 决 于 铣 刨 机 的 类 型 和 功 率。Ｐａｖｅｍｅｎｔ公司开发的铣刨机回收系统深度可达５４８．６４ｃｍ，维特根公司研发的 Ｗ３８０Ｃｒｉ再生机能够修复３５０ｍｍ 深度的病害，都 能 够 较 好 地 满 足全深式冷再生的要求。关于就地冷再生设备研究方面，主要集中在转子刀具的布置特点与土壤切削理论，开展冷再生机铣削转子刀具在工作过程中动力学方面的研究。维特根w380cr再生机施工中的w380cr再生机组厂拌冷再生技术是将 ＲＡＰ料运输拌合站进行拌和，可使用间歇式、滚筒式或连续式拌和设备。连续式拌和设备是应用广的一种，以德国维特根公司生产的连续式拌和再生设备 ＫＭＡ２００为知名。国内具有代表性的设备有中交西筑的 ＣＲＳ３００厂拌冷再生搅拌设备，采用二次搅拌技术，实现了乳化沥青混合料性能更加稳定；高远圣工的 ＧＹＣＢＬ２００型 厂拌冷再生设备具有搅拌力度大、效率高、混合均匀等特点；铁拓 ＴＣＭ２５０型厂拌冷再生设备解决了小掺量添加剂搅拌不均匀问题。目前，关于厂拌冷再生设备研究方面，主要集中在设备结构与拌和时间、拌和均匀性间关系的研究。维特根KMA厂拌设备中交西筑的 ＣＲＳ３００设备６冷再生技术未来发展展望

　　The main foreign companies producing on-site cold recycling equipment include Caterpillar from the United States, BMW from Germany, Benen from France, and Wittgen from Germany. Among them, Wittgen is the world's largest and most advanced manufacturer of recycling equipment. In recent years, domestic construction machinery manufacturers have gradually attached importance to the research and production of cold recycling machines. Shandong Highway Machinery Factory has developed the internationally advanced LZS2400 on-site cold recycling machine, Xi'an Road Construction Machinery Company has developed the on-site cold recycling mixing machine CR2500, and XCMG has developed a new recycling equipment - XLZ230II pavement cold recycling machine. Compared with foreign regeneration machines, there is a certain gap in the variety and overall performance of domestic cold regeneration machines. Through years of research and development and improvement, the current cold regeneration technology can achieve infinite speed regulation of milling and mixing rotors between maximum and minimum speeds, increasing the maximum milling depth of cold regeneration. At present, the market is mainly dominated by Wirtgen's WR2500S and WR2000 [45]. The full depth cold regeneration technology of the Wirtgen WR250 regeneration machine is a type of in-situ cold regeneration technology, which mainly differs from conventional in-situ cold regeneration technology in terms of regeneration layer thickness. The milling depth depends on the type and power of the milling machine. The maximum depth of the milling machine recycling system developed by Pavement can reach 548.64cm, and the W380Cri regeneration machine developed by Wittgen can repair defects at a depth of 350mm, both of which can meet the requirements of full depth cold regeneration. Regarding the research on on-site cold recycling equipment, the main focus is on the layout characteristics of rotor cutting tools and soil cutting theory, and the study of the dynamics of cold recycling machine milling rotor cutting tools during the working process. The w380cr regeneration unit cold mixing regeneration technology in the construction of the Wittgen w380cr regeneration machine is to transport RAP materials to the mixing station for mixing, which can use intermittent, drum or continuous mixing equipment. Continuous mixing equipment is the most widely used type, with the KMA200 continuous mixing and recycling equipment produced by the German company Wittgen being the most well-known. Representative equipment in China includes the CRS300 plant mixing cold recycling mixing equipment from CCCC West Construction, which uses secondary mixing technology to achieve more stable performance of emulsified asphalt mixture; The GYCB200 factory mixing cold recycling equipment from Gaoyuan Shenggong has the characteristics of high mixing force, high efficiency, and uniform mixing; The Tietuo TCM250 plant mixing cold recycling equipment solves the problem of uneven mixing of small dosage additives. At present, research on cold recycling equipment for factory mixing mainly focuses on the relationship between equipment structure, mixing time, and mixing uniformity. Future Development Prospects of CRS300 Equipment 6 Cold Recycling Technology in Jiaoxi Construction of Wirtgen KMA Plant Mixing Equipment

　　冷再生技术经过几十年的技术研究和工程应用，在材料性能、设计方法和工程经验方面均取得一系列重要进展，但仍有一些关键技术需继续开展研究。

　　After decades of technical research and engineering application, cold recycling technology has made significant progress in material properties, design methods, and engineering experience. However, there are still some key technologies that need to be further studied.

　　（１）冷再生结构层施工完成后需要较长的养护周期，在后续研究中可考虑从材料和工艺两方面提升冷再生沥青混合料的早期性能。一方面可以添加减水剂、低聚物等外加剂，通过改进材料以提高冷再生沥青混合料的早期强度和长期性能。其次，可以开展生产拌和顺序和现场压实工艺的优化研究，优化拌和工艺可以改善 混 合 料 内 部 砂 浆 形 态 及 砂 浆－集料的界面黏附强度，优化现场压实工艺可以提高冷再生层密实度并降低内部空隙，以提高冷再生沥青混合料的强度特性和长期性能。

　　(1) After the construction of the cold recycled structural layer is completed, a longer curing period is required. In subsequent research, it is possible to consider improving the early performance of the cold recycled asphalt mixture from both material and process aspects. On the one hand, additives such as water reducing agents and oligomers can be added to improve the early strength and long-term performance of cold recycled asphalt mixtures by improving the materials. Secondly, research can be conducted on optimizing the production mixing sequence and on-site compaction process. Optimizing the mixing process can improve the internal mortar morphology of the mixture and the interfacial adhesion strength between mortar and aggregate. Optimizing the on-site compaction process can improve the compactness of the cold recycled layer and reduce internal voids, thereby enhancing the strength characteristics and long-term performance of the cold recycled asphalt mixture.

　　（２）继续开展冷再生沥青路面结构设计方法的研究：开展冷再生结构层位的温度分布、频率响应以及力学分析方面的研究，获取符合冷再生结构层位受力特性的力学响应，是开展冷再生沥青路面结构力学分析的关键；开展冷再生沥青路面疲劳寿命预估方程的研究，加强现场试验路的数据检测和收集工作，对疲劳方程进行现场标定，以指导冷再生路面结构设计。

　　(2) Continuing the research on the design method of cold recycled asphalt pavement structure: conducting research on the temperature distribution, frequency response, and mechanical analysis of cold recycled structure layers, obtaining mechanical responses that conform to the stress characteristics of cold recycled structure layers, is the key to conducting mechanical analysis of cold recycled asphalt pavement structure; Conduct research on the fatigue life prediction equation for cold recycled asphalt pavement, strengthen data detection and collection on on-site test roads, calibrate the fatigue equation on site to guide the structural design of cold recycled pavement.

　　7结语

　　7 Conclusion

　　（１）冷再生沥青混合料材料组分相互作用机制复杂，ＲＡＰ料 来源、沥 青 老 化 程 度、ＲＡＰ 掺 量会 影响沥 青 含 量、ＲＡＰ 料－沥 青界 面 强 度 以 及 混 合料整体力学性能，因此，在工程应用前应对 ＲＡＰ料进行的测试和表征。

　　(1) The interaction mechanism between the components of cold recycled asphalt mixture materials is complex. The source of RAP material, the degree of asphalt aging, and the RAP dosage will affect the optimal asphalt content, RAP asphalt interface strength, and overall mechanical properties of the mixture. Therefore, comprehensive testing and characterization of RAP material should be carried out before engineering application.

　　（２）乳化沥青和泡沫沥青作为胶结料在冷再生沥青混合料强度形成机理方面存在差异，水泥、石灰外加剂种类及相对含量对混合料的性能提升效果也具有显著差异。在工程应用中应根据性能需求对冷再生沥青混合料进行合理设计和试验验证。

　　(2) Emulsified asphalt and foam asphalt, as binders, have differences in the strength formation mechanism of cold recycled asphalt mixture, and the types and relative contents of cement and lime admixtures also have significant differences in improving the performance of the mixture. Reasonable design and experimental verification of cold recycled asphalt mixture should be carried out according to performance requirements in engineering applications.

　　（３）目前尚未形成统一的冷再生沥青混合料配合比设计方法和路面结构设计方法，国内外大多采用 Ｍａｒｓｈａｌｌ、Ｓｕｐｅｒｐａｖｅ和 Ｈｖｅｅｍ 配合比设计方法和 力 学－经 验 法 路 面 结 构 设 计 方 法，中 国 采 用Ｍａｒｓｈａｌｌ配合比设 计 方 法 和 力 学－经 验法 的 路 面 设计方法，在进行冷再生沥青路面设计时应对其车辙变形和疲劳寿命进行验算。

　　(3) At present, there is no unified method for designing the mix proportion and pavement structure of cold recycled asphalt mixture. Most domestic and foreign countries adopt Marshall, Superpave, and Hveem mix proportion design methods and mechanical empirical pavement structure design methods. China adopts Marshall mix proportion design method and mechanical empirical pavement design method. When designing cold recycled asphalt pavement, its rutting deformation and fatigue life should be verified.

　　（４）材料组分性能和相对含量的变化会对冷再生沥青混合料的抗车辙、抗水损害、抗疲劳开裂及低温性能产生影响，充分考虑冷再生材料所在的结构层位，分析其力学响应以及对应的力学失效模式，明确关键性能需求。当冷再生沥青混合料应用于面层并作为主要承载层时，应充分考虑其抗车辙性能；当作为结构基层时，应严格控制水泥和石灰掺量，以防止服役期内过早出现疲劳裂缝。

　　(4) The changes in the properties and relative content of material components will have an impact on the anti rutting, anti water damage, anti fatigue cracking, and low-temperature performance of cold recycled asphalt mixtures. It is necessary to fully consider the structural layer where the cold recycled material is located, analyze its mechanical response and corresponding mechanical failure modes, and clarify the key performance requirements. When cold recycled asphalt mixture is applied to the surface layer and used as the main bearing layer, its anti rutting performance should be fully considered; When used as a structural base, the dosage of cement and lime should be strictly controlled to prevent premature fatigue cracks during service life.

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