Heat transfer model for microwave hot in-place recycling of asphalt pavements

In order to solve for temperature fields in microwave heating for recycling asphalt mixtures, a two-dimensional heat transfer model for the asphalt mixtures within the heating range is built based on the theory of unsteady heat conduction. Four onedimensional heat transfer models are established for the asphalt mixtures outside the heating range, which are simplified into four half-infinite solids. The intensity of the radiation electric field is calculated through experiment by using heating water loads. It is suggested that the mathematical model of boundary conditions can be established in two ways, which are theoretical deduction and experimental reverse. The actual temperature field is achieved by fitting temperatures of different positions collected in the heating experiment. The simulant temperature field, which is solved with the Matlab PDE toolbox, is in good agreement with the actual temperature field. The results indicate that the proposed models have high precision and can be directly used to calculate the temperature distribution of asphalt pavements.

Numerical simulation analysis on multi-layer low-temperature heating method of asphalt pavement in hot in-place recycling

Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling(HIR).To improve the heating speed of asphalt pavement in HIR,based on the numerical analysis model of asphalt mixture heating process,a new multi-layer low-temperature heating method(MLHM)was proposed.Considering input heat flux,the thermal capacity and thermal resistance of asphalt mixture,the heat transfer model was established based on energy conservation law.By heating the asphalt mixture in layers,it changes the situation that the heat energy can only be input from the upper surface of the asphalt mixture pavement.Through the simulation of the heating method of asphalt mixture in the existing technology,the result shows that the existing heating methods lead to serious aging or charring of the asphalt mixture.By MLHM,the upper and the bottom of the asphalt mixture are heated at the same time,and the heating temperature is lower than other heat methods,which not only reduces the heating thickness and increases the heating area of the asphalt mixture pavement,but also improves the heating speed,saves the energy resource and ensures the heating quality.Especially,by MLHM,the heating uniformity is better and speed is faster.

The Characteristics of Asphalt Mixture in the System of Full Thickness Cold In-place Recycling

A new research method was proposed（A/S method） to study the components and properties of reclained asphalt mixture（RAP）. The RAP was divided into two main parts, one was marked with A that included all the reclaimed old asphalt materials（including some parts of particle materials covered by asphalt）, the other was marked with S which mainly included works soil in the road structure. The actual working conditions were simulated by this kind of new method, and the adaption between the RAP properties, A/S, and the content of cementitious materials were studied. The research indicated that the real working condition could be simulated effectively by means of A/S method. It was also showed that high content of cement could improve the overall performance of RAP significantly, but it would have a negative effect on the properties of RAP if the types and sizes of aggregate particles in RAP mixture were too single. The optimum water content and maximum dry density could not be regarded as the primary basis to evaluate the overall performance of RAP, when S=0 in the experiments, although the maximum density of samples was bigger than that with A/S=1/1, the samples were not strong enough and they were easy to collapse, which indicated that component design of RAP played a great role in improving the overall properties of RAP and the comprehensive tests should be considered to evaluate the stability of RAP. Low frequency load in high temperature environment had the negative effect on the overall stability of RAP, and factors such as the loading state of the materials, the hydration degree of cementitious materials, and the aggregate gradation in the mixture were the determining factors for improving the overall performance of RAP.

Cold In-Place Recycling as a Sustainable Pavement Practice

Pavement rehabilitation and reconstruction methods with CIR （cold in-place recycling） are alternatives that can effectively reduce the high stresses and waste produced by conventional pavement strategies. An attempt was made to predict the performance, particularly low-temperature cracking resistance characteristics of CIR mixtures. These were prepared with the mix design procedure developed at the URI （University of Rhode Island） for the FHWA （Federal Highway Administration） to reduce wide variations in the application of CIR mixtures production. This standard was applied to RAP （reclaimed asphalt pavement） to produce CIR mixtures with CSS-Ih asphalt emulsion as the additive. By adjusting the number of gyrations of the SGC （Superpave gyratory compactor） for compaction, the field density of 130 pcf was represented accurately. To secure a base line, HMA （hot mix asphalt） samples were produced according to the Superpave volumetric mix design procedure. The specimens were tested using the IDT （indirect tensile） tester according to the procedure of AASHTO T 322 procedure at temperatures of-20, -10 and 0 ℃ （-4, 14, and 32°F, respectively）. The obtained results for the creep compliance and tensile strength were used as input data for the MEPDG （mechanistic empirical pavement design guide）. The analysis results indicated that no thermal or low-temperature cracking is expected over the entire analysis period of 20 years for both HMA and CIR mixtures. Thus, it appears that CIR is a sustainable rehabilitation technique which is also suitable for colder climates, and it is recommended to conduct further investigation of load-related distresses such as rutting and fatigue cracking.

Performance of RAP in the System of Cold Inplace Recycling of Asphalt Pavement

The property of reclaimed asphalt pavement（RAP） mixture will be affected mainly by composition of old asphalt/soil and cement content in CIR system. We studied the relationship between A/S and cementitious materials. It showed that if there was no soil in RAP, the unconfined compressive strength was only from 0.18 MPa to 1.07 MPa even if adding cement was from 2% to 6%, and RAP samples collapsed during conserving in water. The optimum water content rose from 6.5% to 11% with the declining of A/S from S=0 to A/S=1/5. Five RAP samples all got the maximum compressive strength when A/S=5/5, and the maximum compressive strength of the samples adding 6% cement was 3.17 MPa. It showed that the capacity of RAP was not only affected by A/S, but also by the content of cement. The dynamic modulus of RAP will increase with the rise of loading frequency and decrease with the temperature rising. SEM test showed that C-S-H interlacing formed the netted structure, and it enwrapped the aggregate and improved the strength of RAP.

沥青路面就地热再生混合料再生剂用量及级配优化

为提升再生沥青混合料级配、新沥青混合料掺量的准确性,保障再生沥青混合料的综合性能,从旧沥青混合料的沥青含量、回收沥青的性能、旧混合料的级配方面进行了深入剖析,采用骨架密实设计法设计了再生沥青混合料级配,试验了新沥青混合料的用量,最后开展了再生沥青混合料高温、低温、水稳定性试验。通过就地热再生沥青混合料的优化设计,确认再生沥青混合料的合成级配宜采用骨架密实型且较低空隙率的混合料,再生剂用量为旧沥青混合料质量的4%,混合料的高温、低温、水稳定性能均与热拌沥青混合料性能相当,最后提出了施工过程中级配变异时应及时采取变异策略。

废旧沥青混合料厂拌热再生技术综述

本文对废旧沥青混合料(RAP)厂拌热再生技术各环节关键技术问题和最新研究成果进行综述。分析了沥青老化机理和老化后的多尺度变化规律,总结基质沥青和SBS改性沥青的再生方法与再生剂研究进展。通过分析RAP的性能特点和变异性,引入了最新的预处理技术。评述了厂拌热再生沥青混合料和沥青路面的性能特点,对比了间歇式和连续式厂拌设备及工艺,介绍了工程应用情况和效益,明确了厂拌热再生技术在节能减排、经济环保方面的优势。本文在分析现有厂拌热再生技术最新研究进展的同时,提出了存在的问题和未来发展方向,助力厂拌热再生技术的革新和推广应用。

就地热再生技术在江苏省高速公路的应用研究

就地热再生是一种绿色环保的路面养护技术,可以有效修复沥青路面车辙、裂缝等病害。江苏省高速公路从2003年开始应用该技术,至今已应用1 997 km。基于该部分路段的相关养护数据,分析了就地热再生技术的服役时间,并对服役时间进行了影响因素分析。结果表明:就地热再生技术在江苏高速公路的服役寿命一般在4~6年。原路面上面层的级配对热再生技术的服役时间影响不显著,而原路面服役时间、交通等级、中面层沥青种类的影响显著。

VE改性剂在普通沥青路面复拌就地热再生工程中的应用研究

本文以广东省某高速公路为依托,通过对路面技术状况、结构强度的调查,结合历年养护情况,分析了路面病害产生的主要原因;研究了旧路面沥青混合料的组成及再生材料的性能,确定了再生剂的添加比例;对比分析了VE改性沥青、普通沥青、PG76沥青各项指标结果,研究了VE改性剂对普通沥青混合料路用性能的提升效果。

太佳高速公路沥青路面就地热再生适用性及效益分析

为研究高速公路沥青路面就地热再生技术在山西太佳高速公路养护中的适用性,对该高速公路上面层取样后做筛分、抽提试验,确定了再生剂的用量、新沥青混合料用量及新沥青混合料油石比,随后完成了200 m就地热再生路面铺筑工作,通过检测渗水系数、构造深度、平整度、压实度指标,结果均符合试验要求,最后开展了沥青路面就地热再生与铣刨加铺新沥青混合料单价对比,得出就地热再生的成本费用约为铣刨加铺新沥青混合料费用的1/3。

沥青路面就地热再生加热温度场监测与分析方法研究

本文提出了基于红外热像仪采集路表红外热像图的方法来监测就地热再生过程中不同阶段的加热温度情况,并建立以路表温度代表值、温度高于200℃比例、温度横向变异系数以及温度纵向耗散速率为评价指标的分析方法。同时基于此监测与分析方法对明火加热、红外热辐射以及热风循环三种加热方式的就地热再生加热温度场进行了比较分析。研究结果表明采用本文提出的监测与分析方法可以更全面有效地掌握就地热再生过程中路表加热温度场的情况,从而更好地指导就地热再生的质量控制。

基于OWA算子的RAP料铣刨回收工艺优化

由于国内针对铣刨技术研究起步较晚,缺乏相关的技术经验,因此在以往的旧沥青路面铣刨过程中,铣刨工艺参数的设置往往根据施工经验确定,主观因素较强,影响RAP料质量。为解决因为铣刨工艺不当,而造成RAP料质量差的问题,本文采用OWA算子,综合考虑细化度与假骨料率两个指标,研究了不同混合料的最优铣刨速度,优化了不同沥青混合料的铣刨工艺参数。结果表明:①AK-13的最优铣刨速度为15m/min;②AK-16的最优铣刨速度为12m/min;③AC-20的最优铣刨速度为7m/min。

基于旧路改造的厂拌热再生应用研究

在沥青路面再生利用中,采用厂拌热再生工艺,既经济又环保,性能稳定。以某公路工程为实例,研究了厂拌热再生混合料的配合比设计方法、施工工艺及其路用性能。研究表明,与新拌沥青混合料相比较,厂拌热再生沥青混合料性能好、强度高、抗车辙能力强,而且有效提高了沥青路面废旧材料的回收利用率,节约了工程成本,具有很大的推广价值。

沥青路面热再生施工技术与质量控制措施分析

为提升路面使用质量,满足车辆行驶安全需求,促进路面建设领域的高效发展,文章对沥青路面热再生技术进行分析,根据国内对热再生技术的应用,综合现场路面施工建设情况,从沥青路面热再生、施工准备、拌和、摊铺、碾压等方面翔实研讨了沥青路面热再生施工技术,最后提出了相应的质量控制措施,以供参考与借鉴。

厂拌热再生技术在沥青路面养护工程中的应用

文章分析了厂拌热再生技术对路面性能、施工效率及环境保护的影响。通过实际工程项目,采用厂拌热再生技术对废旧沥青路面进行处理。对再生沥青混合料的性质进行了详细分析,并优化了拌和及施工工艺。通过对比实验和性能测试,评估了再生路面的高温稳定性、低温韧性等关键指标。应用厂拌热再生技术后,路面的抗压强度平均提高了20%以上,与传统方法相比,施工周期缩短了约50%,提高了养护效率。该技术不仅提升了路面性能、提高了施工效率,还对环境保护做出了积极贡献。

基于冷添加下的厂拌热再生沥青混合料在广州市政道路中的研究与应用

依托广州市政道路养护工程项目,研究探讨了冷添加下厂拌热再生沥青混合料在广州地区的工程应用。开展了废旧沥青路面材料(RAP)冷添加的厂拌热再生沥青混合料配合比设计、生产工艺优化,并对再生沥青混合料的高温性能、水稳定性能、抗疲劳性能进行检验。试验结果表明:合理的材料设计和生产工艺优化,可保证冷添加下厂拌热再生沥青混合料的路用性能稳定,可在实际工程中推广使用。

Application and Research on Plant-Mixed Thermal Regeneration Technology of RAP Asphalt Mixtures

When the plant-mixed thermal regeneration technology is adopted for the waste asphalt pavement mixtures,its performance can basically reach the level of freshly-mixed asphalt concrete,which can be used for paving the middle and lower layers of road pavements of various grades.Through the research and application of plant-mixed thermal regeneration technology based on China's Kunming-Yuxi Expressway Pavement Overhaul Project,this paper summarizes relevant technical points and effectively advocates the promotion and application of this technology in highway maintenance.

RAP掺量与新旧沥青融合程度对热再生混合料性能的影响

通过变化RAP掺量为20%~50%试验,研究常规未知新旧沥青融合状态与模拟新旧沥青100%融合状态下热再生混合料高温及低温性能、水稳定性、抗疲劳性能。结果表明:两种融合状态下,热再生混合料抗车辙性能均随RAP掺量增大而提高,低温抗裂性能和水稳定性均随RAP掺量增大而降低。新旧沥青融合程度和RAP掺量对热再生混合料的高温及低温性能、水稳定性、抗疲劳耐久性能有显著影响。与常规拌和工艺相比,新旧料100%融合工艺制备的热再生混合料其高温稳定性稍差,但具有更好的低温抗裂性能、水稳定性和抗疲劳耐久性能,配合比设计时应考虑新旧沥青融合程度对高RAP掺量热再生混合料路用性能与抗疲劳耐久性能的影响。

响应面法优化大比例厂拌热再生混合料参数

为对大比例厂拌热再生沥青混合料的工艺参数进行优化设计,选取再生料(reclaimed asphalt pavement, RAP)掺量,再生料预热温度,以及再生剂掺量为试验变量,选取动稳定度,低温小梁弯曲最大弯拉应变,以及冻融劈裂强度比为响应变量。使用Design-Expert软件中的Box-Behnken响应面优化设计方法,进行三因素三水平优化设计。其中,动稳定度,最大弯拉应变和冻融劈裂强度比分别作为混合料高温稳定性,低温抗裂性和水稳定性的衡量指标。再生料掺量选取20%~40%,再生料预热温度选取100~140℃,再生剂掺量选取6%~10%,响应变量均以最大值为优进行优化设计。结果表明:再生料掺量对于3个响应变量都有显著影响,而再生料预热温度和再生剂掺量对动稳定度和低温小梁弯曲最大弯拉应变有较大影响,对冻融劈裂强度比影响较小。优化得到最优解的再生料掺量为25.69%,再生料预热温度为131.59℃,再生剂掺量为8.29%。此时动稳定度为3 224.35次/mm,最大弯拉应变为2 870.37με,冻融劈裂强度比为89.230 1%。且使用优化后的工艺参数进行试验,得到的结果与预测结果的误差都小于3%,证明优化结果可靠有效。

高掺量改性RAP热再生沥青混合料低温抗裂性能宏微观机理

旨在研究再生剂和改性剂提升高掺量沥青混合料回收料(reclaimed asphalt pavement,RAP)热再生沥青混合料低温抗裂性能的宏微观机理,进而弥补其低温抗裂性能不足的显著缺陷,设计了3种改性剂配比方案(8%再生剂1、8%再生剂2、4%再生剂2+4%改性剂),开展了高掺量改性RAP热再生沥青混合料室内小梁弯曲试验,分析了混合料的宏观断裂行为特征,进而基于近场动力学理论建立了相应的数值模型,揭示了混合料内部裂纹萌生与扩展的微观机理以及不同改性剂的作用机理。结果表明,双外加剂(再生剂和改性剂)配比下高掺量RAP再生沥青混合料的破坏应变、劲度模量、应变能密度等低温抗裂性能指标均优于单独使用再生剂,近场动力学理论可较好地模拟再生沥青混合料的低温开裂行为;再生剂可显著提升旧沥青界面处的黏结能力,再生剂1使试件底部应力分布更为均匀,再生剂2恢复旧沥青黏结能力的效果更优;而改性剂则提升沥青的整体性能,且对新沥青的性能提升更加明显;相较于单独使用再生剂,双外加剂可恢复旧沥青性能并提升沥青整体的黏性,有效弥补高掺量RAP再生混合料低温抗裂性能不足的缺陷。