【作者】 徐金枝；

【导师】 郝培文；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2007， 博士

【摘要】 对沥青路面废旧材料进行再生利用,可以有效提高资源利用率,保护生态环境,符合国家提出的发展循环经济、实现可持续发展的战略方针。因此,对沥青路面再生技术进行研究具有重要的意义。泡沫沥青是近年来兴起的一种冷再生稳定剂,用其稳定的再生混合料在材料性能、经济性以及环保性等方面具有独特的优势和发展前景。但到目前为止有关泡沫沥青冷再生混合料的材料特性、破坏机理等的研究十分有限,泡沫沥青再生混合料的设计也主要依赖于经验,这些均限制了泡沫沥青冷再生技术的推广应用。本文从泡沫沥青与泡沫沥青冷再生混合料的材料组成出发,旨在通过大量室内试验,对泡沫沥青冷再生混合料的物理力学性能以及使用性能进行系统深入的研究,以实现泡沫沥青冷再生混合料的优化设计,从而改善其各项性能,进而推动泡沫沥青冷再生技术的研究与应用。沥青发泡特性是影响泡沫沥青冷再生混合料性能的关键因素。本文选用不同等级的沥青进行发泡特性试验分析,研究沥青发泡特性的评价指标与方法、发泡剂对沥青发泡特性的影响以及沥青基本性质与其发泡特性之间的相关性。结果表明:发泡指数FI在一定范围内增大反映出沥青发泡特性的改善,但并非FI越大泡沫沥青的发泡特性就越好,FI不能代替膨胀率和半衰期两个基本指标单独用于泡沫沥青的设计与评价,而应将其作为一种辅助或补充指标,与膨胀率和半衰期相结合共同对泡沫沥青进行合理设计与评价;发泡剂可显著延长泡沫沥青的半衰期,但其对膨胀率影响较小;沥青的动力粘度指标与其发泡特性之间具有较好的相关性,PI、沥青的三大指标、密度、老化后的性质以及沥青等级等与其发泡特性之间相关性较小。通过筛分试验研究了不同条件下泡沫沥青冷拌混合料中沥青的分散性状,分析表明:设计中如不能合理控制泡沫沥青发泡特性、矿料温度、矿料级配组成以及混合料拌和水量等因素,将会造成沥青分散不均匀甚至结团现象,影响泡沫沥青冷拌混合料的相关性能;泡沫沥青均匀分散的混合料中,沥青主要裹覆＜1.18mm的细集料,尤其是＜0.3mm的细集料部分,形成泡沫沥青砂浆并将大粒径集料以点焊的形式粘结成整体。通过变化不同的沥青发泡特性以及矿料温度,研究其对泡沫沥青再生混合料力学性能的影响,结果表明:两因素对泡沫沥青再生混合料的ITS与UCS均具有显著影响,且沥青发泡特性的评价指标膨胀率与半衰期相比,膨胀率对再生混合料力学强度特性的影响更为显著,据此提出在沥青发泡特性的优化设计中,应偏向于按膨胀率较大相应选择最佳沥青发泡条件。水是泡沫沥青冷再生混合料关键的设计指标之一。本文设计了泡沫沥青稳定新料与旧料形成的不同类型混合料,研究泡沫沥青冷拌混合料的拌和用水量问题。分析表明:混合料的最佳拌和用水量随其组成中填料含量的增多而一定程度增大,根据研究结果推荐了不同类型及组成的泡沫沥青冷拌混合料适宜拌和用水量范围及最佳拌和用水量。矿料级配组成是影响泡沫沥青冷再生混合料性能的另一关键因素。本文设计了具有不同细料组成及不同粗料组成的泡沫沥青冷拌混合料,通过对其抗拉、抗压与抗剪等力学性能的研究发现:泡沫沥青混合料的最佳沥青用量与混合料中的填料含量密切相关,与热拌沥青混合料相比,泡沫沥青混合料具有相对较大的粉胶比;提高细料部分的密实程度可显著改善泡沫沥青冷拌混合料的各项力学性能;粗料部分组成的变化对最佳泡沫沥青用量基本无影响,对混合料的力学性能影响则较小;针对不同级配的研究结果,相应修正了Wirtgen推荐的泡沫沥青稳定材料级配范围;此外,通过研究关键筛孔的级配变异敏感性,推荐了泡沫沥青冷拌混合料施工中关键筛孔的允许波动范围。泡沫沥青再生层的强度、刚度等力学性能受多种因素影响。本文从内外因两方面对泡沫沥青再生混合料的力学性能进行了试验分析,结果表明:沥青旧料掺量、泡沫沥青与水泥用量以及温度、养生、压实方法等对泡沫沥青再生混合料的抗拉、抗压、抗剪强度以及抗压回弹模量具有显著影响;泡沫沥青再生混合料力学性能的温度敏感性低于热拌沥青混合料。永久变形性能是泡沫沥青再生结构层使用中的重要性能之一。本文采用动态压缩蠕变试验分析了不同材料组成对泡沫再生混合料永久性能的影响,结果表明:一定程度增大水泥用量、矿料组成中的细料含量以及减小泡沫沥青用量,可提高泡沫沥青再生混合料的抗变形能力;在合理设计混合料级配组成的条件下,路面各结构层均可再生利用形成变形能力满足要求的再生混合料;泡沫沥青再生混合料的抗永久变形性能优于热拌沥青混合料;此外,泡沫沥青再生混合料蠕变试验的加载段可采用Burgers模型进行理想的拟合,从而获得泡沫沥青再生混合料的相关粘弹性参数。抗疲劳性能是泡沫沥青再生混合料铺筑路面基层或底基层时必须优化设计的关键性能。本文采用间接拉伸劈裂疲劳试验分析了不同材料组成对泡沫沥青再生混合料疲劳性能的影响,分析表明:水泥在小掺量条件下增多时有助于提高再生混合料的抗疲劳性能;最佳泡沫沥青用量下再生混合料可具有良好的抗疲劳性能以及强度与变形能力;改善沥青的发泡特性可相应提高再生混合料的抗疲劳性能;二灰砂砾基层材料形成的泡沫沥青再生混合料抗疲劳性能较差,将其与面层沥青旧料混合再生后形成的混合料性能有效改善;泡沫沥青再生混合料的抗疲劳性能介于半刚性基层材料与热拌沥青混合料之间。最后本文对泡沫沥青冷再生路面的施工工艺进行了研究,提出了泡沫沥青冷再生工程的施工质量检查方法与标准,并通过工程实例的验证得出,经合理设计与施工的泡沫沥青再生层具有良好的结构承载力,可作为高等级公路的基层或底基层。更多还原

【Abstract】 Recycling of asphalt pavements can effectively enhance the use of resources, protect ecological environment and accords with the national strategy of developing cycling economy and realizing sustainable development. Therefore, research on the technology of asphalt pavement recycling is of great significance.Foamed asphalt is a kind of cold recycling stabilizing agent, which gains more and more acceptance in recent years. Recycled mixes stabilized with foamed asphalt possess advantages in terms of performance, economy and environment protection. However, studies about the behaviors and distress mechanisms of foamed asphalt cold recycled mix have still been limited at present, and mix design also mainly depends on experience, which hold back the popularity of foamed asphalt cold recycling technology.From foamed asphalt and foamed asphalt cold mix composition point of view, this paper, through a lot of laboratory experiments and relative analysis, aims to systematically study the mechanical properties and pavement performances of foamed asphalt cold mix, so as to optimize its design, improve its various performances and promote relative research and practice for the technology.Foamability of asphalt is a key factor influencing properties of foamed asphalt cold recycled mix. The paper selected asphalts with different penetration grades to carry out foaming experiments, so as to determine the evaluation indexes and method for asphalt foamablity, and the relationship between basic characteristics of asphalt and its foamablity. It was confirmed that increase of foam index (FI) within a certain range reflects the improvement of foaming properties. However, it does not necessarily mean that the bigger the value of FI, the better the foam characteristics is. Not be used as a substitute for expansion ratio and half-life, FI should be considered as a complementary index for the design and evaluation of foamed asphalt together with expansion ratio and half-life. Foamant additive can significantly extend half-life of foamed asphalt, but has little bearing on expansion ratio. Dynamic viscosity of asphalt was found to have a comparatively good correlation with its foaming characteristics. Whereas other basic properties, such as PI, penetration, softening point, elongation, specific gravity, characters after aging, penetration grade and etc, show a little correlation with foaming properties.The dispersion of foamed asphalt within cold mix was studied by sieve analysis. The results showed that if some factors, such as asphalt foamability, temperature and gradings of mineral aggregates, mixing moisture content and etc, cannot be reasonably controlled in mix design, asphalt may fail to disperse evenly or conglomerate in mix, leading to an adverse effect on mix properties. Among the mix where asphalt disperses evenly, asphalt mainly coats fine aggregates passing through 1.18mm sieve, especially those passing through 0.3mm sieve and form foamed asphalt motar, which adhere to larger aggregates and bond them together in a manner of "point".Mixing moisture content is one of the pivotal parameters in foamed asphalt mix design. The paper designed different kinds of foamed asphalt mixes with original aggregates and recycled asphalt pavements as well to study the proper moisture contents in mixing of foamed asphalt mixes. The analysis showed that mixing moisture content increases with the increase of filler content within a certain degree. Reasonable ranges of mixing moisture content and optimum moisture contents for foamed asphalt mixes with various kinds and gradings were proposed accordingly.Grading of mineral aggregate is another key factor which affects foamed asphalt cold recycled mix performance. The paper designed foamed asphalt mixes with different fine and coarse fraction gradings and studied their tensile, compression, shear strength separately. It is indicated that optimum foamed asphalt content is closely related to filler content and foamed asphalt mix has a higher filler to asphalt ratio than HMA. Enhancement of fine fraction density can remarkably improve the mechanical properties of foamed asphalt mix. However, change of coarse fraction grading has little bearing on optimum asphalt content and mechanical properties of mix. The grading envelope recommended by Wirtgen was modified accoding to the results concluded in the paper. Besides, the variation sensitivity of key sieves were investigated and the allowable variation ranges in construction were suggested accordingly.Strength and rigidity properties of foamed asphalt recycled mix are influenced by many factors. The paper carried out relative studies from internal and external aspects. It was shown that foaming characteristics, mineral aggregate temperature, amounts of recycled mix, foamed asphalt and cement, curing and compaction method, determing temperature and etc, all have significant influence on strength characters and compression resilient modulus of foamed asphalt recycled mix. In addition, temperature sensitivity of mechanical properties for foamed asphalt recycled mix is less than HMA.Permanent deformation is one of the important performance of foamed asphalt recycled pavements. The paper adopted dynamic compression creep test to analyze the effect of mix composition on its permanent deformation response. It was found that increasing amounts of cement and fine fraction or decreasing foamed asphalt content at a certain degree, can improve the deformation resistance of foamed asphalt recycled mix. By reasonably designing mix grading, materials of every layer in pavement structures can be recycled with foamed asphalt with satisfied deformation resistance. Foamed asphalt recycled mix has superior deformation resistance over HMA. Loading stage of creep testing for foamed asphalt recycled mix was also found to be well simulated by Burgers model, with the visco-elastic parameters for recycled mix can be acquired.Fatigue resistance is a paramount performance needed to be optimized for foamed asphalt recycled mixes, which are used for base or subbase layers in pavements. The paper chose indirect tensile fatigue test to study the influence of different material compositions on fatigue characteristics of recycled mixes. It was indicated that increase of cement at a small amount is beneficial to the improvement of fatigue resistance for recycled mixes. Optimum foamed asphalt content can make the recycled mixes have relatively good fatigue resistance, strength and flexibility. Enhancement of foaming properties can also improve fatigue characteristics of recycled mixes. Gravel treated with lime and fly ash forms recycled mix with inferior fatigue reponse, but mixing with RAP can effectively ameliorate its performance. Fatigue resistance for foamed asphalt recycled mixes fall between semi-rigid material and HMA.At last, the paper studied the construction technics of foamed asphalt recycled pavements. The corresponding inspection methods and standards for construction quality are suggested. An actual project demonstrated that reasonably designed foamed asphalt recycling layers have favorable structural capability and can be used for base or subbase layers of high class pavements.更多还原