Recycled Asphalt Mixtures Research Articles

Performance evaluation of recycled asphalt mixtures with various percentages of RAP from the rotary decomposition process

This paper conducted an experimental study to evaluate the performance of recycled asphalt mixtures containing various percentages of reclaimed asphalt pavement (RAP). The variabilities and properties of RAP materials from the rotary decomposition process were determined first, through which the RAP materials were mainly decomposed in three stages including reclaimed stone aggregates barely containing asphalt, and asphalt-rich mortar sand. The results demonstrated that the mineral grading and asphalt percentage of decomposition products were stable. Then, the design aggregate gradation of AC − 20F was selected and its optimum asphalt content (OAC) was obtained using the Marshall mix design method. In addition, the laboratory performance, including the high-temperature performance, low-temperature crack resistance, moisture susceptibility and dynamic modulus tests, of recycled asphalt mixtures with varying RAP contents was conducted. The test results indicated that when the RAP content increased, the rutting resistance improved, but the crack resistance at low temperature and moisture damage susceptibility worsened. The RAP content had an effect on the dynamic modulus, especially at a lower loading frequency (high temperature). And the dynamic modulus of recycled asphalt mixtures increased with the loading frequency increasing and temperature decreasing. The dynamic modulus of the recycled asphalt mixture under standard conditions (20 °C and 10 Hz) was determined to be 11500–13000 MPa. The recycled asphalt mixture with higher percentages of RAP (more than 40%) was applicable to be used as a high modulus asphalt mixture (HMAM) in the future based on the results of the dynamic modulus test. Finally, an empirical predictive model of the dynamic modulus for recycled asphalt mixtures was established.

Performance characterization and enhancement mechanism of recycled asphalt mixtures involving high RAP content and steel slag

Reutilization of reclaimed asphalt pavement (RAP) is conducive to achieving carbon peak and neutrality goals and establishing a resources recycling system for road engineering. Previous studies have indicated that recycled asphalt mixtures with RAP content exceeding 30% seem inappeasable in upper surface of asphalt pavement due to their inferior skid resistance and endurance. While steel slag, a solid waste with excellent mechanical properties and high alkalinity, can elevate performances of asphalt mixture. Recycled asphalt mixtures involving 50%, 60% and 70% RAP content and steel slags were prepared firstly, and their road performances were characterized. Properties discrepancies existing in microstructure and geometric characteristics of steel slag and basalt and their interfacial properties with asphalt were discussed. The results indicate that incorporating steel slag in recycled asphalt mixtures with 70% RAP content reveals a desirable performances indexes in contrast to basalt. The adhesion and mechanical performance of recycled asphalt mixtures can be significantly enhanced by steel slag due to its honeycomb porous structure, larger angularity, lower sphericity and higher texture. Steel slag and recycled asphalt demonstrate lower spalling rate under hydrodynamic pressure and larger adhesive destructive force compared with basalt, resulting in superior moisture susceptibility and cracking resistance for recycled asphalt mixtures.

Environment-friendly recycled asphalt pavement design for road maintenance applications.

Potholes are one of the most common road distresses in Kuwait especially after winter season in 2018. Pavement deterioration rate significantly increases as the pavement exposes to moisture. Paving road requires using high-quality materials. This paper aims to investigate the feasibility of using recycled asphalt pavement in hot mix asphalt (HMA) design. Questionnaires and a series of laboratory tests were conducted to analyze the effects of pores on the society and test the recycled and the regular mixtures performance to choose the best option regarding it. Marshal test portrayed that the recycled mixture has a high stability and flow. According to the tensile strength ratio test requirements which set a minimum ratio of 75%, it is recommended to reduce the proportion of recycled aggregate. The Hamburg wheel tracker (HWTD) test proved that the recycled asphalt mixture has a low rutting depth for wet and dry samples compared to the general one. On the other hand, the wet recycled mixture requires a reduction by of 20% to satisfy the specifications. The physical properties for both mixtures were compared, and the voids filled with asphalt (VFA) and voids in mineral aggregate (VMA) of the recycled mixture are lower than those in the regular mixture. The recycled mixture reveals a higher efficiency in saving costs and improving mixtures used for potholes maintenance activities. All the results proved that the mixtures consisting of recycled asphalt are most preferred since they are affordable and perform reasonably well compared to mixtures made of regular asphalt. As a future work, smaller percentages of recycled aggregate should be tested to check the robustness and sustainability of the designed recycled asphalt mixture using different tests such as Hamburg wheel tracker test (wet samples) and indirect tensile strength test. Furthermore, more experiments can be run to test other mix parameters and properties such as durability.

Functionalization of Smart Recycled Asphalt Mixtures: A Sustainability Scientific and Pedagogical Approach

The sustainable development of our societies demands strong efforts on scientific and technological research while informing and educating students and the general population. Air pollution and road safety hazards constitute two main public health problems that are insufficiently addressed pedagogically. With this work, we aim to contribute to tackeling the problem by presenting the results of scientific research on the development of photocatalytic, superhydrophobic, and self-cleaning recycled asphalt mixtures to achieve an eco-social friendly and smart material able to mitigate socioenvironmental impacts. The functionalization of asphalt is implemented by spraying particles’ solutions over a conventional AC 10, then evaluated by dye degradation and wettability. Firstly, different particles’ solutions (with nano-TiO2 and/or micro-PTFE under water, ethyl alcohol, and dimethyl ketone) were sprayed to select the best solution (BS), which was composed of TiO2-PTFE (4 g/L each) in ethyl alcohol. Two successive spraying coatings (diluted epoxy resin and BS) were performed over conventional and recycled AC 10 (with reclaimed asphalt pavement and steel slags). Their efficiency decreases with the highest resin amounts. The best results were obtained with 0.25 g resin and BS. For the lowest resin amount, all mixtures achieved superhydrophobicity and performed similarly regarding wettability.

Study on the Effect of Regeneration Agent on the Viscosity Properties of Aged Asphalt.

China’s highway asphalt pavement has entered the stage of major repair, and improving the utilization rate of recycled asphalt pavement (RAP) is the main issue. The key link affecting the performance of recycled asphalt mixtures is the regeneration of aged asphalt, and the effect of the regenerant dosing on the high-temperature performance and viscosity of aged asphalt is the main content to be studied in this research. The aging behavior of asphalt seriously affects the roadworthiness of asphalt mixtures. In this study, we investigated the effect of changes in the microscopic properties of the aged asphalt on its viscosity properties during regeneration using gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) as well as Brinell viscosity tests. This study simulated asphalt aging by the RTFOT test, and then we obtained an aged asphalt with a needle penetration of 30. We prepared different regenerated asphalts by adding regeneration agent with doses of 2%, 4%, and 6% to the aged asphalt. The results showed that the regeneration agent could effectively reduce the viscosity of the aged asphalt, which can play a positive role in improving the construction and ease of the aged asphalt. Rejuvenation agents affected the aging asphalt sulfoxide and carbon group indices. Moreover, rejuvenation agents can also significantly reduce the intensities of their characteristic functional group indices. The results of the AFM test showed that the increase in the dose of regeneration agent increased the number of the asphalt bee-like structures and decreased the area of individual bee-like structures. The results of the GPC test were consistent with the results of the AFM test, and the increase in the dose of regeneration agent reduced the asphalt macromolecule content. The viscosity properties and microstructure of the aged asphalt changed positively after the addition of the regeneration agent, indicating that the regeneration agent had a degrading and diluting effect on macromolecules.

Hot recycled asphalt mixtures with the incorporation of milled material: analysis of the mechanical performance and economic presumption in the applicability of the technique

The paving technique ensures the guarantee of functional traffic conditions, optimizing the performance of the structure in providing travel with comfort and safety. Considering that due to time and the action of traffic, when the pavement reaches the end of its useful life, interventions are necessary, aiming at a gain in serviceability, comprised of the thinning of the coating, generating waste, for later execution of a new layer, which can be recycled. This recurrent technique for road pavements has been widely applied to the use of RAP (reclaimed asphalt pavement), to compose new layers of pavement, given its mechanical performance, especially in terms of permanent deformation, and given the sustainable and economical premise. The paper sought to evaluate, using a laboratory study, the mechanical performance of hot recycled asphalt mixtures with the incorporation of 25%, 45%, and 100% of RAP, and to perform an economic analysis of the applicability of the technique. The dosage methodology occurred according to the Superpave specification whose results listed a significant gain in stiffness, and good mechanical performance with proportionality in the values obtained according to the incorporation rate of RAP. As for the economic analysis, it was observed that the costs of applicability of the technique are related to the percentage of incorporation in mass and the logistical costs of processing, which may be lower than or higher than that of a conventional mixture. Above all, the results were satisfactory to prove the feasibility of the technique in paving works.

Characterization of Nanoscopic Crack Propagation at Virgin-Aged Binder Interface in Asphalt Containing Recycled Asphalt Mixture Based on Molecular Dynamics Simulations

Characterization of Nanoscopic Crack Propagation at Virgin-Aged Binder Interface in Asphalt Containing Recycled Asphalt Mixture Based on Molecular Dynamics Simulations

Influence of Mobilized Rap Content on Effective Binder Quality and Performance of 100% Hot In-Place Recycled Asphalt Mixtures

Influence of Mobilized Rap Content on Effective Binder Quality and Performance of 100% Hot In-Place Recycled Asphalt Mixtures

Research on the Impact of Recycled Asphalt Mixture on Road Performance Based on New Thermal Recycling

Different binder content to RAP Regeneration SBS modified asphalt mixture for road performance to SBS modified asphalt (I-D type) as an index, determine the optimum dose of new heat regenerating agent and different RAP regeneration, and prepared different recycled asphalt, which have differences in RAP content. The performance of recycled asphalt mixture with different RAP content was evaluated by freeze-thaw splitting test. Rut test and Low temperature trabecular bending test. The correlation between RAP content and pavement performance was analyzed by grey system correlation analysis method. According to the experimental verification results, it can be known that increasing the content of RAP material can improve the high-temperature performance of reclaimed asphalt, but will result in a qualitative decrease in low-temperature performance and water temperature, but the above-mentioned performance can reach the required level, Shows that new heat regenerators play a role in the road performance of RAP materials, and for the RAP material utilization ratio of more than 50%, as for the gray correlation analysis, it can be found that there is a close correlation between the low-temperature performance of recycled asphalt mixture and the content of RAP material. The low temperature cracking resistance of asphalt mixtures will change significantly due to the slight changes in RAP materials.

Comparative Environmental Analysis of Pavement Structures with Recycled Asphalt Mixtures Produced in Brazil and in Switzerland

Comparative Environmental Analysis of Pavement Structures with Recycled Asphalt Mixtures Produced in Brazil and in Switzerland

3D Finite Element Model for Recycled Asphalt Mixtures with High Percentages of Reclaimed Asphalt Pavement Rutting Simulation

3D Finite Element Model for Recycled Asphalt Mixtures with High Percentages of Reclaimed Asphalt Pavement Rutting Simulation

Research on interfacial zone failure of asphalt mixture mixed with recycled aggregates

Construction and demolition wastes (CDW) is a complex mixture containing cement mortar and mineral aggregate, recycled aggregates (RA) are further prepared by CDW after the crushing process. Investigating the effect of RA on interfacial zone failure of asphalt mixture is beneficial to promote the utilization of CDW in pavement engineering. Firstly, RA without strengthening treatment was used to prepare recycled aggregate asphalt mixture (RAAM), then the physical and mechanical properties of RA and RAAM were studied using microstructure analysis and performance tests. To comprehensively understand the influence of RA percentage on interface damage, the interfacial zone in RAAM was classified into cement mortar interface and natural aggregate interface. Results show that the attached cement mortar of RA is a porous material and leads to a weak interface adhesion with asphalt mortar. The cement mortar interface presents greater porosity and lesser modulus compared with the natural aggregate interface. Increasing RA percentage causes more interface failure during deformation, and the damage of cement mortar and its interface with asphalt mortar are the primary resources of failure. According to numerical simulation for fracture processing, the influence of replacing natural aggregate with RA on energy consumption is obvious, and it increases the average stress value of the interface. This study shows that RA can be used as an effective alternative for natural aggregate after enhancing its attached cement mortar.

The study of the feasibility of using recycled steel slag aggregate in hot mix asphalt

Significant growth in the road network around the world has increased the need for pavement materials. The growing demand for producing original asphalt pavements from non-renewable natural resources can deplete natural resources, cause environmental issues, and consume significant amounts of energy. The idea of using waste materials such as steel slag or reusing recycled aggregated of old pavements was evaluated to increase the sustainability of pavements. Rutting resistance, marshall stability, moisture susceptibility, resilient modulus, and fatigue life of slag and conventional asphalt mixtures containing different percentages (0, 25, 50, and 75 wt%) of (Recycled Asphalt Pavement) RAP or slag aggregates were compared to evaluate the mechanical performance of recycled asphalt with slag aggregate, The recycled asphalt mixtures were rejuvenated by 3 or 6 wt% of automobile waste oil. The results showed that slag asphalt had a better performance in all areas. Additionally, replacing the original aggregate with RAP or recycled slag improved marshall stability, tensile strength, and rutting resistance of the asphalt or slag asphalt mixture. Using higher percentages of the recycled aggregate resulted in further improvements. The fatigue life of the recycled samples increased under loading with low strain level when higher percentages of the recycled aggregate were replaced, but it reversed at higher strains. Finally, the results indicated that using recycled steel slag for producing hot mix asphalt could produce a more durable asphalt in comparison to using RAP.

Assessing the Asphalt Binder Film Thickness in Recycled Asphalt Mixtures Using Micro-Level Techniques.

Adequate asphalt binder film thickness (ABFT) delivers skeletal integrity in recycled asphalt mixtures, resulting in long-lasting roadways when exposed to traffic and environment. The inaccurate measurement of ABFT and the consequences of not having adequate film thickness model has substantially introduced discrepancies in predicting actual performance of recycled asphalt mixtures. Expansion of the ultra-modern expertise and SuperPave requirements necessitate the revision of authentic ABFT at micro-level. The current study identifies the weaknesses of the current methods of estimating ABFT and provides results that are reliable and useful, using modern measurement methods. Using scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS), this study measures the ABFT around the tiniest particle of 0.2 μm magnitude, entrenched in asphalt mastic in recycled asphalt mixtures. The ABFT, obtained through image analysis, is compared with those obtained through available analytical models. The study utilizes different asphalt mixtures, containing varying proportions of recycled asphalt mixture and rejuvenators. The aggregate, virgin, and recycled binders were characterized in terms of physical and rheological properties, respectively. Marshall mix design was carried out for the conventional and recycled mixture, containing 40%, 50%, and 60% recycled materials, rejuvenated with 3%, 6%, 9%, and 12% waste engine oil (WEO) at a mixing temperature of 160 °C, based on viscosity of the virgin and rejuvenated binder. ABFT was assessed through analytical models and image analysis for the aforesaid recycled asphalt mixtures, prepared at optimum binder and rejuvenator content as per protocol outlined in ASTM D1559. The analytical estimation of ABFT, in the aforesaid recycled asphalt mixtures, revealed that the ABFT fluctuates from 6.4 μm to 13.7 microns, with a significant association to recycled asphalt mixture and rejuvenator content. However, the image analysis revealed that the ABFT, in the aforesaid recycled asphalt mixtures, fluctuates from 0.4 μm to 2 microns, without any association to recycled asphalt mixture or rejuvenator content. The image analysis indicated that the recycled asphalt mixtures typically comprise of mortar, happening in uneven shape, and are used to grip large aggregates. The asphalt mastic, a blend of bitumen and mineral filler, was found to be an interlocking agent, used to grasp only fine particles in asphalt mortar. The asphalt binder film was discovered to be a deviating stand-alone entity that only exists around the mineral fillers in the asphalt mastic as a non-absorbed binder, occupying an imprecise space of 0.4 μm to 2 microns, among the filler particles. The current findings will be useful to design asphalt pavements through the aforesaid precise limit of SEM-based ABFT rather than traditionally measured ABFT to predict the actual performance of recycled asphalt mixtures.

Characterization of fatigue performance of the warm‐mix recycled asphalt mixture using different models

AbstractThe fatigue performance of different warm‐mix recycled asphalt mixtures was evaluated by the semicircular bend (SCB) test. A delayed oven heating (DOH) method was developed to simulate the long‐term ageing in the laboratory. The effects of recycling plans, reclaimed asphalt pavement (RAP) content, and ageing levels on the tensile strength and fatigue resistance were investigated. The fatigue life of the warm‐mix recycled asphalt mixture was characterized by the phenomenological, dissipated energy, and the ratio of dissipated energy change (RDEC) models, respectively. The results show that the use of the warm‐mix asphalt (WMA) technology causes a reduction of the fatigue performance for the recycled asphalt mixture, which can be compensated by the addition of styrene–butadiene rubber (SBR) latex. As the RAP content or long‐term ageing time increases, the fatigue life significantly decreases. The dissipated energy model with the unified model coefficients can predict the fatigue lives for different warm‐mix recycled asphalt mixtures.

Stiffness assessment of cold recycled asphalt mixtures – Aspects related to filler type, stress state, viscoelasticity, and suction

Cold recycling is an advantageous technique, from economic and environmental perspectives, for asphalt pavement rehabilitation, interventions, and maintenance. Additional investigation is still needed for the widespread of the technique. Some of the issues evolve predicting the recycled material mechanical behavior and performance along its service life. Therefore, stiffness assessment (through triaxial resilient modulus and dynamic modulus tests) and suction tests were performed to better understand the cold recycled asphalt mixture (CRAM) behavior. This paper covered an investigation of the suction pressure phenomenon and its effects regarding the stiffness of emulsion-stabilized cold recycled asphalt mixtures, considering different fillers. A non-contact suction test method was proposed for CRAM compacted specimens in a way to enable total suction readings. Further theoretical analysis, key literature review, and discussions were presented. Some of the findings of the work are: (i) CRAM’s stiffness may present similar behavior of a granular material, with confining pressure dependence, and at the same time, presents a temperature/frequency dependence (as asphaltic materials); (ii) suction phenomenon may be responsible for part of the stiffness of CRAM; (iii) the filler type (even in small percentage) affects the mechanical behavior of CRAM.

Preliminary Study on New Alternative Binders through Re-Refined Engine Oil Bottoms (REOBs) and Industrial By-Product Additives.

Recent studies have worked towards addressing environmental issues such as global warming and greenhouse gas emissions due to the increasing awareness of the depletion of natural resources. The asphalt industry is seeking to implement measures to reduce its carbon footprint and to promote sustainable operations. The reuse of several wastes and by-products is an example of a more eco-friendly activity that fulfils the circular economy principle. Among all possible solutions, the road pavement sector encourages, on one hand, the use of recycled materials as a partial replacement of the virgin lithic skeleton; on the other hand, it promotes the use of recycled materials to substituting for a portion of the petroleum bituminous binder. This study aims to use Re-refined Engine Oil Bottoms (REOBs) as a main substitute and additives from various industrial by-products as a full replacement for virgin bitumen, producing high-performing alternative binders. The REOBs have been improved by utilizing additives in an attempt to improve their specific properties and thus to bridge the gap between REOBs and traditional bituminous binders. An even larger amount of virgin and non-renewable resources can be saved using these new potential alternative binders together with the RAP aggregates. Thus, the reduction in the use of virgin materials is applied at the binder and the asphalt mixture levels. Rheological, spectroscopic, thermogravimetric, and mechanical analysis were used to characterize the properties, composition, and characteristics of the REOBs, REOB-modified binders, and asphalt mixes. Thanks to the rheological investigations of possible alternative binders, 18 blends were selected, since they behaved like an SBS-modified bitumen, and then they were used for producing the corresponding asphalt mixtures. The preliminary mechanical analysis of the asphalt mixtures shows that six mixes have promising responses in terms of stiffness, tensile resistance, and water susceptibility. Nevertheless, the high variability of recycled materials and by-products has to be taken into consideration during the definition of alternative binders and recycled asphalt mixtures. In fact, this study highlights the crucial effects of the chemical composition of the constituents and their compatibility on the behaviour of the final product. This preliminary study represents a first attempt to define alternative binders, which can be used in combination with recycled aggregates for producing more sustainable road materials. However, further analysis is necessary in order to assess the durability and the ageing tendency of the materials.

Investigation on the mechanism and performance of asphalt and its mixture regenerated by waste engine oil

Waste engine oil (WEO) is planned to be used as a regenerating agent for asphalt pavement materials to regenerate the reclaimed asphalt pavement (RAP) and recovery their road performance. To enhance the modification effect of WEO on the road performance of asphalt mixture, the furfural extraction oil and epoxy resin are added to compound with the WEO as well. The modern testing techniques were used to reveal the mechanism of WEO-RA from the microscopic scale. The macroscopic properties of asphalt such as the physical, rheological and anti-aging properties of asphalt were investigated to study the regeneration effect of WEO on the technical performance of aged asphalt. The road performance and mechanical properties of recycled asphalt mixtures were investigated extensively. The results show that WEO can be used to recovery the aged asphalt by modifying its components, the modification of WEO on aged asphalt is a physical way. The thermal stability of WEO regenerated asphalt (WEO-RA) is slightly worse than that of the original asphalt, but the WEO-RA has good thermal stability. Physical and high-temperature rheological performance of WEO-RA is almost the same with original asphalt. The low-temperature property rheological performance WEO-RA is two PG better than that of original asphalt. The long-term anti-aging performance of WEO-RA is as good as original asphalt. The performance of WEO-RA has good storage stability. The asphalt mixtures with 0–50% RAP meet the road performance requirement, what’s more, the both the high-temperature and low-temperature performance of asphalt mixture are enhanced with different contents of RAP regenerated by WEO.

High-temperature creep and low-temperature relaxation of recycled asphalt mixtures: Evaluation and balanced mix design

In this study, high-temperature creep and low-temperature relaxation performance of recycled asphalt mixtures, with different contents of reclaimed asphalt pavement (RAP), rejuvenator, and virgin asphalt, were evaluated. The creep index (εp/FN) and relaxation index (ts) were selected as evaluation indices of prepared samples. Based on the comparison of εp/FN and ts of the recycled asphalt mixture and virgin asphalt mixture, a new balance design method was proposed. The results showed that εp/FN increased gradually with the increase of rejuvenator and virgin asphalt when the RAP content was constant, while ts was decreased. It indicated that the high-temperature creep performance of the recycled asphalt mixture was improved, but the low-temperature relaxation performance became poor. The high-temperature creep and low-temperature relaxation evaluation indices could be directly compared, and the accuracy of the comparison results was improved. Therefore, the proposed balanced design was developed based on the comparison of the absolute value by mathematical formulas, which was not only simple or intuitive but also easy to operate. When the RAP content was less than 30 %, the optimum balance point of the high-and low-temperature performance was lmin. When the RAP content was 50 %, the best low-temperature relaxation performance point was the optimum balance point with the prerequisite of a good high-temperature creep performance. It is a new method to analyze the high-and low-temperature performance of recycled asphalt mixtures, which is of great significance to improve the durability of the recycled asphalt pavement.

Study of the quantification of recycled binder activity in asphalt mixtures with RAP

Many environmental and economic benefits can be achieved by employing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures. However, due to the high stiffness and brittleness of recycled materials, cracking issues may arise when utilizing them at high contents. Recycled binder activity is one of the primary factors that influences the performance of recycled asphalt pavements. Recycled binder activity represents the amount of RAP or RAS binder that becomes active at production temperatures for mixing with the virgin binder. Previous studies have indicated that recycled binders are only partially active; however, the majority of state department of transportation’s assume full activity. Designing recycled asphalt mixtures under the assumption of full recycled binder activity may result in mixtures with insufficient binder content and thus increasing the susceptibility for cracking and moisture damage. This paper compares two recycled binder activity quantification methods; the first method quantifies activity using recycled asphalt mixtures of virgin and RAP materials, while the second method uses 100 percent recycled materials. The two methods showed to produce relatively similar recycled binder activity values; however, the use of 100 percent RAP materials showed to be a more promising approach due to its practicality.