Evaluation of reclaimed asphalt pavement binder stiffness without extraction and recovery

A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement （RAP） binder was developed. In the testing procedure, the SuperpaveTM Bending Beam Rheometer （BBR） with special modifications and binder blending charts by Asphalt Institute were utilized. Modifications involved the development of a new kind of sample mold and different testing parameters were made to BBR testing procedure to capture the theological properties of bitumen mortars produced by mixing fresh binder with fine RAP materials or RAP aggregate. The stiffness relationship between binder and bitumen mortar was established based on the BBR test results. The blended binder stiffness in bitumen RAP mortar was estimated from the RAP mortar stiffness based on the binder-mortar relationship. And finally, the RAP binder stiffness was estimated from the blended binder and fresh binder stiffness based on the blending charts by Asphalt Institute. The results indicate that the new procedure can capture the rheological properties of bitumen mortar and can be used to estimate the low temperature stiffness of RAP binder without binder extraction and/or any chemical treatments.

Recent developments in asphalt-aggregate separation technology for reclaimed asphalt pavement

Reclaimed asphalt pavement(RAP)has significant recycling value because it contains nonrenewable resources including asphalt and aggregate.However,thus far,only a small part of RAP materials can be used in the con-struction of recycled asphalt pavement,and the usage is regarded as a low-value utilization in the underlying layers.One of the most important reasons for this shortcoming is the problem of false particle size and pseudo gradation of RAP materials.Therefore,identifying suitable asphalt-aggregate separation technology is essential for improving the utilization of RAP materials in recycled asphalt mixture and enhancing the construction quality of recycled asphalt pavement.To address this,the paper performed a systematic review of asphalt-aggregate separation technologies for processing RAP materials and their prospects.Firstly,based on the composition of the asphalt mixture and the characteristics of RAP materials after aging,the key RAP separation technologies were proposed.Then,the concept,principle,and implementation methods of physical,chemical,and biological sep-aration methods of RAP materials were comprehensively analyzed.Moreover,the advantages and disadvantages of various separation technologies were discussed by comparing them with the related technologies in the petrochemical industry.The application prospects of various asphalt-aggregate separation methods for RAP materials can provide a reference for upgrading and expanding solid waste recycling technology for asphalt pavement.

Evaluation of asphalt mixture behavior incorporating warm mix additives and reclaimed asphalt pavement

Incorporation of warm mix asphalt （WMA） and reclaimed asphalt pavement （RAP） has benefited the asphalt industry in many ways such as reducing the demand for virgin materials, lowering energy requirement during the asphalt production and construction, in addition to reducing greenhouse-gas emissions. This study evaluated the effects of Evotherm and RH-WMA and RAP on mixtures＇ behavior in terms of the compaction energy index （CEI）, indirect tensile strength （ITS） and resilient modulus. The results showed that warm mix additives reduced the CEI, ITS and resilient modulus; while RAP increased the corresponding values. Statistical analysis showed that mixtures incorporating Evotherm and RAP had significant effects on CEI, while the effects of RH-WMA on the corresponding value were found to be statistically insignificant. General Linear Model showed that Evotherm, RAP and RH-WMA exhibited no significant effects on the ITS and resilient modulus. The one-way analysis of variance showed that Evotherm influenced mixture behavior significantly, while RAP and RH-WMA effects were found to be statistically insignificant. Regression equations with high accuracy levels were proposed to predict CEI, ITS and resilient modulus with respect to modification of mixture variables such as mix constituents （Evotherm, RH-WMA, and RAP） and compaction temperature.

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.

Sustainable Asphalt Concrete Containing RAP and Coal Gangue Aggregate:Performance,Costs,and Environmental Impact

The shortage of natural aggregates is becoming a severe problem in the pavement industry globally.To address this issue,in this study,an effort was made to use reclaimed asphalt pavement(RAP)and coal gangue(CG)as coarse and fine aggregate,respectively for producing the hot mix asphalt(HMA).As the replacement of natural aggregate,there were seven types of HMA containing 20%and 40%RAP coarse aggregate content,and 10%and 25%CG fine aggregate content were designed and prepared.In addition,Marshall Stability test,rutting resistance test,immersion Marshall test,freezing-thaw splitting test,moisture-induced sensitivity test,and low-temperature semicircle bending test were conducted.The results show that the properties of the asphalt mixture containing both RAP and CG meet the Chinese specification through it is slightly lower than the virgin asphalt mixture.Furthermore,the addition of 40%RAP coarse aggregate and 25%CG fine aggregate to asphalt mixes can significantly reduce manufacturing costs,energy consumption,and CO_(2)emissions by 29.4%,19.8%,and 21.9%,respectively,compared to the virgin asphalt mixture.The finding of this study contributes to current knowledge by investigating the feasibility of jointly using the RAP and CG in asphalt mixture,which could be interested by both industry and academic society.

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.

Influence of rejuvenators on bitumen ageing in hot recycled asphalt mixtures

The use of reclaimed asphalt pavement （RAP） in new hot mix asphalt （HMA） by means of hot recycling techniques generates the advantage linked to the exploitation of both lytic and bituminous component, consequently leading to the decrease of both virgin aggregates and bitumen supplying. However, many agencies and public administration authorise RAP percentages ranges from 10% to 30% in hot recycling. The main reason for such a low amount of allowable RAP content is related to the aged bitumen contained in the RAP materials, which is more brittle than a virgin bitumen leading to a final mixture more susceptible to fatigue, thermal and reflection cracking. The use of rejuvenators has the potential to restore rheology and chemical components of aged RAP bitumen, thus allowing a significant increase in the amount of RAP to be properly implemented in HMA. The experimental investigation is described in this paper and carried out through a dynamic shear rheometer （DSR） which provides the rheological characterisation of a paving grade bitumen during its overall service life including its reuse in hot recycling by adopting different rejuvenators. Results show that rejuvenators modify bitumen chemistry and consequently rheology by enhancing the viscous response. Moreover, it was observed that oxidation is less harmful, in terms of stiffness increase, on the 50/50 aged bitumen - virgin bitumen blends （rejuvenated or not） than on the virgin bitumen. Moreover, the addition of a rejuvenator in a bituminous blend containing 50% of bitumen reactivated from RAP could lead to a corresponding composite bituminous phase less subjected to ageing phenomena and even less stiff at the end of service life than the associated virgin bitumen alone.

Mix design,development,production and policies of recycled hot mix asphalt:A review

Worldwide,flexible pavements are the paramount type of pavements.These national assets can be recycled to serve the next design life without the need to dispose of them in landfill.The old/distressed,flexible pavement material is called,reclaimed asphalt pavement(RAP)material.In view of the sustainable development practice,100%RAP should be recycled.However,the practical range of RAP incorporation in a drum mix plant ranges from 10%to 50%whereas in a batch mix plant,it is 10%-35%.In a batch mix plant,incorporation of the hot dried RAP(instead of cold RAP feeding)can increase the RAP incorporation level by 20%.Studies recommended that the rejuvenator should be added over the RAP material instead adding with the base binder.The addition of rejuvenator on the RAP conveyor belt(to the pug mill),provided sufficient time for rejuvenating the aged binder coating over RAP aggregates.Further,a thorough knowledge of the mix design process of recycled hot mix asphalt(RAP-HMA)is essential to produce a durable mix.For high RAP content(>20%),the RAP binder properties are important for the mix design process.However,very limited studies discussed(in detail)the recovery process of the RAP binder.The review article through light on the binder recovery process,method of RAP gradation,specific gravity determination for RAP material,minimum desirable properties of the RAP material etc.This review paper also provides a narrative review of the historical development of RAP-HMA technology,technical aspects related to the procurement of RAP material,mix design and production of the recycled mix.Moreover,the international&national policies/laws for construction and demolition waste are discussed.