Long-term performance of recycled asphalt mixtures containing high RAP and RAS

The application of reclaimed asphalt pavement(RAP)and reclaimed asphalt shingles(RAS)on asphalt pavement can reduce the asphalt paving cost,conserve energy and protect the environment.However,the use of high contents of RAP and RAS in asphalt pavement may lead to durability issues,especially the fatigue cracking and thermal cracking.It is necessary to conduct a series of analyses on asphalt mixtures containing high RAP and RAS,and seek methods to enhance their long-term performance.This paper provides a comprehensive over-view of the long-term performance of recycled asphalt mixtures containing high contents of RAP and RAS.The findings in this research show that rutting resistance of high recycled asphalt mixtures is not a concern,whereas their resistance to fatigue and thermal cracking is not conclusive.Recycling agents can be used to improve the thermal cracking resistance of high recycled asphalt mixtures.An optimum decision on recycling agents will improve the durability properties of high recycled asphalt mixtures.It is recommended that to use a balanced mixture design approach with testing of the blended asphalt binders will provide better understanding of long-term performance of recycled asphalt mixtures containing high RAP and RAS.

On the Use of Recycled Asphalt and Trinidad Lake Asphalt(TLA)for the Preparation of High Modulus Asphalt Concrete

Rutting of asphalt pavement occurs earlier and is more serious under the increasingly heavy traffic load conditions that can be found in subtropical monsoon climate regions.High modulus asphalt concrete(HMAC)with excellent anti-rutting and anti-fatigue properties is generally used to mitigate this issue.Given the relatively high cost of the additives used in this type of asphalt,in this study the feasibility of using recycled asphalt mixture(RAP)and Trinidad lake asphalt(TLA)for the preparation of HMAC is considered.The mineral composition of the RAP is first analyzed,then the TLA modified asphalt with different levels of RAP content is used to assess the effect of RAP on the performance of the mixture.Finally,the high-temperature rheological properties of extracted bitumen and the adhesion characteristic between mineral and bitumen are analyzed.The results show that after RAP combustion,the yellowish and greyish minerals display different alkalinity values,while the greyish mineral exhibits an improved ability to combine with bitumen.Thus,RAP can significantly enhance the high-temperature rutting resistance of TLA modified asphalt mixtures.The aged bitumen in RAP makes the mixed binder harder and improves its rheological properties at high temperatures.

Evaluation of rutting and low-temperature cracking resistancesof warm-mix recycled asphalt bindersunder the secondary aging condition

The rutting and low-temperature resistances of warm-mix recycled asphalt binders under the secondary aging condition were measured by the dynamic shear rheometer test and bending beam rheometer test.Effects of different types of warm-mix asphalt(WMA)technologies and additives were evaluated.Aging and improvement mechanisms were investigated by the Fourier transform infrared spectroscopy test.It is found that recycled binders after the secondary aging are more resistant to rutting and less resistant to low-temperature cracking.The two warm-mix asphalt technologies have opposite effects.Using the Sasobit WMA significantly improves the rutting resistance and reduces the low temperature resistance for the recycled binders due to its morphological change at different temperatures.The rutting factor values of recycled asphalt binders with the Sasobit additive increase by 4.6 to 5.6 times.However,using the Evotherm WMA causes the deterioration of the rutting resistance due to the structural lubrication effect.The rutting factor values of recycled asphalt binders with the Evotherm additive show the reduction of 52%to 62%.It is recommended to add the styrene butadiene rubber latex or crumb rubber powder into the warm-mix recycled asphalt binders to simultaneously improve the rutting and low-temperature cracking resistances.

Evaluation of Mixture Performance Recycled Asphalt Pavement Materials as Base Layer with or without Rejuvenator into the Asphalt

The binder properties were determined in accordance with Chinese standard such as ductility test, which allowed to measure the distance in centimeters that a standard briquette of asphalt had been stretched before breaking. Then, penetration test was carried out in order to know some properties of the asphalt, which are the hardness and the softness. Finally, softening point test was carried out in order to determine the temperature at which the bitumen attains a particular degree of softening under the specification of the test. According to Chinese standard for performance tests, firstly, Marshall test was carried out in order to measure the theoretical density, air voids, voids filled with asphalt, stability, flow, and voids in mineral aggregate of asphalt specimens. Secondly, Freeze-thaw splitting test was carried out in order to determine Splitting strength ratio. Finally, dynamic stability (rutting) test was carried out to determine average dynamic stability. Beside the tests carried out, the gradation of the extracted aggregate in accordance with American Association of State Highway and Transportation Officials was carried out to determine the dimensions of the particles weight distribution. Furthermore, both the percentage of recycled asphalt pavement materials and binder in mixture were determined to know how much of the new material during the mixture was needed. However, two specimens were used to evaluate the performance of recycled asphalt pavement materials. One specimen of recycled asphalt pavement materials was ten years old, and another one of recycled asphalt pavement materials was five years old. The results show that the conditions of the environment such as moisture, temperature, and age, decrease the ductility and penetration properties of binder when increase the softening point property of binder. Then the gradation of recycled asphalt pavement aggregate is of the required values to reuse in the mixture, while the flow ratio, the splitting strength ratio, and the dynamic stability ratio, are less than the required value test. With regard to the properties of mixture of recycled asphalt pavement material binder with rejuvenator, the results show that when the penetration and ductility versus percentage of rejuvenator increase, softening point versus percentage of rejuvenator decreases. Also, when the bitumen and rejuvenator percentage increase, the air voids decrease. Consequently, voids filled with asphalt and voids in the mineral aggregate increase. Moreover, the theoretical density and stability values decrease in a mixture containing four-point fifty percent to six percent of bitumen and rejuvenator, whereas the flow values increase. More interestingly, with four percent to four-point fifty percent mixture ratio of bitumen and rejuvenator, density, stability, and flow values increase. The splitting strength ratio values of mixtures and the dynamic stability test (rutting test) values of mixtures with forty percent of specimen one and specimen two respectively are greater than the required value of the standard test. In addition, the high percentage of rejuvenator increases the rut of pavement, in the same manner, the low percentage of rejuvenator induces low rut. In conclusion, the binder content from recycled materials without rejuvenator seems not be sufficient to be reused on the new pavement while the aged recycled material seems to be performed better than no aged recycled material with rejuvenator into bitumen. Then, the rejuvenator can influence the bitumen properties and performance of the pavement. Finally, the pavement made by only recycled pavement materials as a base layer appears to be more economical but cannot be more effective than the pavement made by mixture of new and recycled pavement materials as a base layer.

The Effect of Bio-Oil on High-Temperature Performance of Bio-Oil Recycled Asphalt Binders

Bio-oil recycled asphalt binders in road engineering can help solve the problem of oil shortage and reduce the environmental pollution and sustainability.This paper investigated the road performance of the aged asphalt binder by adding bio-oil so that the aged asphalt binder could be reused to reach purpose of reuse.The residual soybean oil was selected as rejuvenator and blended with aged asphalt binder at 0%,2%,4%,and 6%,respectively.The results showed that bio-oil increased the penetration of aged asphalt binder,the penetration of bio-oil recycled asphalt binder with a bio-oil content of 6%reached the standard of 70#matrix asphalt binder.The addition of bio-oil reduced the viscosity,mixing and compaction temperature of aged asphalt binder.As a common knowledge,bio-oil helps to increase the lightweight components of the aged asphalt binder,which diminishes the high-temperature rutting resistance of bio-oil recycled asphalt binders.The high-temperature deformation resistance of bio-oil recycled asphalt binders had not decreased linearly with the bio-oil dosage.Meanwhile,the hightemperature performance of the bio-oil recycled asphalt binder with a 6%bio-oil was superior to matrix asphalt binder.Bio-oil increased the light components of the aged asphalt binder,thus reducing the high-temperature rheological properties of bio-oil recycled asphalt binders as the bio-oil dosage increases.The above test results showed that the bio-oil could restore the aged asphalt binder to the initial level to reach the reuse target.

Characterization of subgrade soil mixed with recycled asphalt pavement

Due to awareness to greener environment, use of recycled asphalt material has become popular in asphalt pavement industry. The use of recycled asphalt pavement （RAP） ma- terials in subgrade soil can be an additional scope of utilizing RAP. This study investigates the effect of RAP on the resilient modulus （MR） of subgrade soils mixed with RAP materials. Note that MR is the principal material input parameter for designing asphalt pavement using the recent mechanistic-empirical pavement design software. As a first step of the current study, different percentages of RAP and moisture were thoroughly mixed with subgrade soils. Then, the MR of these RAP mixed soils were determined using the AASHTO T 307 （1999） at different stress levels in the laboratory. Results show that the MR of RAP mixed soil increases with the applied deviatoric and bulk stresses, however, it is less sensitive to applied confining pressure. Use of RAP materials has made the soils stiff enough not to respond to the confining pressure. As expected, the MR value reaches a maximum at the optimum moisture content and increases linearly with RAP content. The MR values and characteristics of the RAP mixed subgrade soils, as determined by the current study, can be used for subgrade design and stabilization using RAP for better pavement design.

Performance evaluation and chemical property analysis of RWMA binders with 100% artificial reclaimed asphalt

The performance evaluation and chemical property analysis of the recycled warm mix asphalt （RWMA） binders containing 100% artificial reclaimed asphalt （ RA） are presented, and the combined effects of different percentages of the rejuvenator and warm mix additive （WMA） additives on RWMA binders are analyzed through laboratory tests. Three types of WMA additives ad one commercial rejuvenator named GST were selected to restore the artificial RA. The laboratory performace tests including the penetration test, softening test ad rotary, viscosity （RV） test were carried out. In addition, the Fourier transform infrared spectroscopy （FTIR） test was performed to explore the chemical property of RWMA binders. The results of the performance tests indicate that the rejuvenator GST has the ability to restore the artificial RA; choosing the optimum content of WMA additives and rejuvenator is the key to restoring 100% artificial RA, since the combined effects of them play an important role in determining the basic laboratory performance of RWMA binders. The FTIR tests show that the process of recycling mainly adjusts the chemical component of aged asphalt and no remarkable change is observed in the FTI1R spectra of RWMA binders in terms of chemical functional groups with the introduction of WMA additives.

Diffusion and Regeneration Mechanism of Waste Composite Oils Rejuvenator in Aged Asphalt

The physical performance of recycled asphalt was used as the main evaluation index to study the optimal range of a self-made rejuvenator.Through the penetration,viscosity and gel permeation chromatography(GPC)tests,the diffusion degree of the rejuvenator under different temperatures and time process was analyzed,and the diffusion efficiency of the rejuvenator was evaluated from the macro and micro perspective.The regeneration mechanism of the rejuvenator in the aged asphalt was also analyzed using the Fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM)and chemical composition tests.The research results showed that the optimum rejuvenator content was about 3%.Higher temperature and longer time were beneficial to improving the permeability and diffusion of the rejuvenator.During the aging process,the light components were reduced,and more macromolecular asphaltenes were generated as well as a large number of carbonyl and sulfoxide.After diffusion and regeneration,the light components in the asphalt were supplemented,the wrinkles and gullies of the aged asphalt were almost improved to the surface state of the matrix asphalt.

Development and Validation of a Laboratory Aging Method for the Accelerated Simulation of Reclaimed Asphalt

The paper presented first results elaborated during the European Research Project Re-road which aims at the development of techniques for increasing the recycling rates of reclaimed asphalt. During service life surface asphalt courses are subjected to aging due to oxidation effects which causes the hardening of the binder and thereby a change in the chemical, physical and mechanical properties of the material. Surface courses often contain highly modified binders as well as special additives for improving the performance characteristics. As these layers inhibit the shortest service lives compared to other road construction layers every year high amounts of reclaimed surface asphalt are available for recycling. The question is raised how the reclaimed asphalt consisting of high quality and costly material components can be recycled for optimal added value. To analyze the asphalt mix service life performance and its recyclability during mix design a laboratory method was developed to simulate the real in-situ aging. First the effects of site aging on the binder and asphalt characteristics were presented. Three laboratory aging methods were discussed which aimed the accelerated aging which meets similar property changes as site aging. At last the effects of two different laboratory aging methods on the same SMA mixture were compared.

The Development of Recycling Agent for Asphalt Pavement

A type of recycling agent was developed and its use for modifying used asphalt is described.The results show that the viscosity and three main properties of the aged asphalt were remarkably improved.With 5% - 7% content of recycling agent, the main properties of recycled asphalt comported with China GB asphalt standard AH-70 and the recycled asphalt concrete could be used as high grade highway.Furthermore,the recycling mechanism of the aged asphalt is discussed.

Quantitative characterization of fusion state of virgin and aged asphalt using nano-ferrous ferric oxide tracer

The exact evaluation of the fusion rate of virgin and aged asphalt is essential to optimize the performance of the recycled asphalt mixture.The fusion rate index was developed by tracing the distribution of tracer asphalt,which contains nano-ferrous ferric oxide(nano-Fe_(3)O_(4))tracer.Laboratory fusion simulation tests were performed on three types of asphalt to obtain different fusion states,and fatigue tests were performed to evaluate the influence of the fusion rate on the fatigue life of the recycled asphalt.It was found that the tracer asphalt containing 4%nano-Fe_(3)O_(4)shows the optimal trace effect,and the developed fusion rate index can quantitatively characterize the influence of different factors on the fusion state of the recycled asphalt.The fusion state is closely related to the fatigue performance of recycled asphalt,and the fusion rate index can fairly evaluate its fatigue performance.The relationship between the fusion rate and the fatigue life of recycled asphalt depends on the factors that cause the fusion rate variation.Under the influence of the amount of rejuvenator,the fatigue life of recycled asphalt grows exponentially with increasing fusion rate due to enhancement of molecular motion as well as a supplement of lightweight components.Under the influence of heat preservation treatment,fatigue life increases linearly with increasing fusion rate.The proposed fusion rate index can be utilized to quantitatively characterize the fusion state of virgin and aged asphalt,thus providing a simple way to guide the practical application of recycled asphalt.

Green Road Construction Technologies in Guangzhou

Total road pavement in Guangzhou reaches 77×10~6m^2.Its huge maintenance and potential rehabilitation calls for a green road system.This paper presents a discussion,first about green road construction technologies together with their applications and development like reclaimed asphalt pavement,rubberized asphalt pavement,and warm mix asphalt; and then,about the key obstacles for promotion and activities,primarily for green road promotion,in the perspectives of the current technical and application situations in China and separately in Guangzhou.Based on environmental and conditional analysis,as well as a development expectation from an industrial viewpoint,this paper creates a development trend of green road technologies.