Cement-fly Ash Stabilization of Cold In-place Recycled (CIR) Asphalt Pavement Mixtures for Road Bases or Subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement （RAP） aggregate and stabilized soil （S） for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent （MA） on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy（SEM） images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

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.

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.

Asphalt Pavement Cold Recycling and Basic Characteristics of RAP Materials and their application

In the developed countries significant proportion of reclaimed asphalt pavement(RAP)materials are used in the construction of pavements.Until recently,milled asphalt from old roads was sent to tip as waste.However,in recent years there has been increased use of waste materials in many road projects within the capital city and federal road network.Use of RAP materials is relatively new to Ethiopia and understanding its characteristics and related technology with all its potential environmental,economic and social benefits is important.Cold recycling is desired due to its potential economic benefit.In this study characteristics of RAP materials are assessed both from literature and laboratory investigations in order to better understand its performance and use.Questionnaire survey was undertaken to identify factors that are hindering recycling of materials in pavements in Ethiopia and what is to be done to overcome these factors.A policy statement is derived to support a quick start and implementation of asphalt pavement recycling in Ethiopia.Currently,a huge asphalt pavement network is being constructed and virgin construction material exploration and import materials such as bitumen is costing the country a lot of money.Over USD 7 Billion worth asphalt pavement have been constructed over the last 23 years to serve the public and freight transport,which requires about USD 176 million annually for maintenance and rehabilitation works.Therefore,any saving obtained from recycling will have meaningful impact on cost saving and environment preservation.

乳化沥青冷再生混和料设计与施工关键技术分析

在现有乳化沥青冷再生沥青混合料配合比设计方法的基础上,介绍了乳化沥青混合料强度形成过程,结合某养护改善工程的实际情况,对规范中要求的二次成型的设计方法与一次成型方法进行了论证分析,提出了二次成型设计方法的差异性与不足,并通过施工过程中现场机械的碾压成型方案进一步论证,在此基础上推荐采用旋转压实仪进行设计,乳化沥青再生混合料一次碾压(乳化沥青破乳完成前压实)成型的施工工艺。

混杂废旧纤维对乳化沥青冷再生混合料的性能优化研究

为提高含再生剂乳化沥青冷再生混合料的性能,选用木质素纤维及废旧玻璃纤维作为混杂纤维进行配比优化设计。采用室内车辙试验、低温弯曲试验、间接拉伸模量以及疲劳试验,研究了两种纤维的混杂比例及掺量对乳化沥青冷再生混合料路用性能和力学性能的影响。基于主成分分析方法分析了混杂纤维乳化沥青冷再生混合料的综合性能,并建立了相应的综合得分评价模型。结果表明,相对于使用单一纤维,混杂纤维的应用进一步提高了乳化沥青冷再生混合料的高温抗车辙能力以及低温抗裂能力,改善了其疲劳性能。此外,纤维的混杂比例因素对乳化沥青冷再生混合料的性能影响占到80.114%,而混杂纤维掺量对其综合性能的影响占到14.002%,定量说明两种纤维的混杂比例对乳化沥青冷再生混合料的综合性能有着更显著影响。推荐混杂纤维掺加量为0.3%,M玻璃纤维∶M木质素纤维为7∶3时,乳化沥青冷再生混合料的综合性能最佳。

沥青混合料就地再生施工工艺分析

针对沥青路面的修复问题介绍了沥青混合料就地再生技术的方法、原理及再生工艺,分析和比较了沥青混合料就地冷再生和就地热再生工艺设备及施工工艺,对其特点及应用范围进行了总结和归纳。

基于灰色关联分析法的泡沫沥青冷再生混合料优化设计

结合泡沫沥青冷再生混合料的室内试验,探讨泡沫沥青再生二灰碎石混合料的设计及其优化方法。结果表明:采用马歇尔方法设计的泡沫沥青冷再生二灰碎石混合料,15℃干劈裂强度为0.65 MPa,满足路面基层强度要求;沥青用量对湿劈裂强度影响最为显著,干湿劈裂强度比的影响最小。基于灰色关联度方法,优化了泡沫沥青再生二灰碎石混合料设计方法,确定了最佳油石比。