Reclaimed Asphalt Pavement Materials Research Articles

Influence of Confinement Pressure on the Mechanical Response of Emulsified Cold-Recycled Mixtures

Cold recycling of asphalt pavement is an effective rehabilitation technique in terms of saving natural resources and cost of construction. The current study focuses on cold-recycled asphalt mixture designated as emulsified cold-recycled mixture (ECRM) that contains 100% reclaimed asphalt pavement material and slow-setting asphalt emulsion. Here, a repeated haversine compression test is conducted with and without confinement pressure at six temperatures (0°C, 10°C, 20°C, 30°C, 40°C, and 50°C) and 10 frequencies (25, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, and 0.01 Hz). The stress–strain–time response of ECRM is investigated, and it is observed that the influence of confinement pressure is negligible in the temperature range of 0°C–10°C, whereas it is significant at temperature 30°C and higher, irrespective of the frequency of loading. However, at 20°C, the influence of confinement pressure is negligible at higher frequencies (25–10 Hz), and it is significant at lower frequencies (less than 10 Hz). The viscoelastic response of ECRM is seen at all temperature, frequency, and confinement conditions of loading from the analyzed Lissajous plots. The dynamic modulus and phase angle are computed using the regression and the fast Fourier-transform (FFT) methods. The dynamic modulus and phase angle master curve is then generated using a free-shifting approach and a model-based approach. The model-based approach involves the numerical solution of the exact Kramers–Kronig relations combined with the generalized logistic sigmoidal model. The FFT-based dynamic modulus is used to construct a master curve with the generalized logistic sigmoidal model. Such a model-based master curve resulted in excellent predictive capabilities for dynamic modulus, and hence it is suggested for ECRM.

Analysis and assessment of respirable particles in asphalt pavement recycling from perspectives of workers’ health

Different groups of people are exposed to respirable particles in recycling asphalt pavement materials. In evaluating the health issues of such particles posed to construction workers, existing studies mainly focus on respirable crystalline silica but rarely address the organic fractions. In this study, respirable particles in reclaimed asphalt pavement (RAP) materials were collected from different sources and analyzed to determine their morphology, elemental composition, organic content, and the content and type of polycyclic aromatic hydrocarbons (PAHs). Focus is placed on the analysis of PAHs in the particles, for which the hazards are assessed using benzo[a]pyrene toxic equivalent concentration. The respirable particles are found to contain much richer asphalt content than RAP mixtures. A variety of PAHs can be found in the particles, especially those with a large number of aromatic rings (>3). Moreover, very old RAP materials contain more PAHs, due to the oxidation reaction of the hydrocarbons in asphalt binder. Based on the analysis data and reported exposure levels to such particles in milling asphalt pavements, it is concluded that the health risks posed by such particles cannot be neglected. Mitigation measures and personal protective equipment are recommended to be used in producing and handling RAP materials.

Utilization of Reclaimed Asphalt Pavement Material in Wet Mix Macadam (W.M.M)

Reclaimed asphalt pavement (RAP) is one of the innovative and effective technologies in many places in the world. The utilization of RAP is rapidly increasing popularity and becoming an emerging technique in India. As per IRC-120:2015, removing or reprocessing pavement materials containing aggregates that are bitumen coated is termed as RAP. These materials are gained through a process in which the existing surface pavement is reclaimed and reused after processing for reconstruction, resurfacing, or repaving. Well graded and high-quality aggregate are achieved from this process. Proper utilization of RAP with specified properties and specified percentages, not only serve as an alternative useful pavement material but also helps in reducing the usage of natural construction material, that will directly reduce the overall cost of projects. By conducting tests as per MoRTH specifications (5th Revision), the various characteristics of RAP material and fresh aggregates are observed. The main objective of the study is to carry out the performance tests: Modified Proctor test on fresh material as well as on material mixed with reclaimed asphalt pavement i.e. 10%, 20%, and 30% of total mix and to achieve optimum moisture content and maximum dry density by using Modified Proctor Test. Attempts are carried out to design a new pavement using Indian Road Congress (I.R.C-37:2018) guidelines and utilization of RAP material. Economic benefits are calculated in terms of fresh and RAP (10%, 20%, and 30%) mix material 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.

Durability and Mechanical Properties of Roller Compacted Concrete Containing Coarse Reclaimed Asphalt Pavement

The feasibility of utilizing Reclaimed Asphalt Pavement (RAP) as a replacement for coarse aggregates in Roller Compacted Concretes (RCCs) was assessed. This replacement was performed in different volumetric percentages (25%, 50%, 75%, and 100%). During this process, RAP materials were subject to abrasion and impact in the Los Angeles drum and mixer before being added to the mixture. Compressive strength, splitting tensile strength, flexural strength, crack propagation, Ultrasonic Pulse Velocity (UPV), electrical resistivity, density, and water absorption (in 7, 28, and 90 days of age) tests were done on all mixtures. Results show that utilizing RAP in RCC can cause a drop in the mechanical properties, but it has positive effects on crack propagation of the specimens due to their increased toughness. Increasing the amount of RAP in the mixtures has increased their electrical resistivity, likely owing to the hydrophobic properties of RAP, which causes prevention from connecting pores to each other. The relationship between the mechanical properties and UPV of the mixtures was analysed using regression models. Moreover, one- and two-way ANOVA (analysis of variance) tests were performed on the results at a 95% confidence level. Finally, replacing the coarse aggregates with RAP only up to 75% is suggested if pre-processing is performed.

Development of ternary binder mixing formulation for asphalt pavement recycling

ABSTRACT Recycling agents (as softening agents or, rejuvenators) are being widely used in the asphalt recycling process. At the binder level, recycling therefore involves three constituents, namely, virgin binder, aged binder (arising out of reclaimed asphalt pavement materials) and the recycling agent – making it a ternary binder blend. Limited literature is available on the ‘mixing formula’ for ternary binder blend that can be used to predict the resultant physical property of the blend, when the proportion and physical property of each of these three binders are given. The objective of the present research is to explore a suitable ternary mixing formula (relevant to hot asphalt recycling process) based on empirical observations in the laboratory. In this work, four different types of recycling agents (two softening agents and two rejuvenators) are used, and the complex viscosity is taken as the physical property. Temperature and frequency are also included as variables as an effort to improve the robustness of the suggested equation. Subsequently, a generalised equation is developed for the prediction of complex viscosity at any given temperature and frequency and the same is validated for the ternary binder mix dealt in the present study.

Direct use of RAPM in laboratory study on diffusion between asphalt binders

The present work reports a laboratory study on the asphalt binder diffusion with reference to the hot asphalt recycling. Generally, in diffusion-related studies on asphalt binder either artificially aged or, a chemically extracted binder from reclaimed asphalt pavement material (RAPM) is used. In the present study, an experimental set-up is proposed to directly use RAPM in the diffusion process. The application potentials of the FTIR-ATR and the AFM, for studying the asphalt binder diffusion process and estimation of the coefficient of diffusion, are also investigated. Based on the limited data observed and idealisations considered, the diffusion coefficient for the binder-pair used in the study is obtained in the order of 10−9 m2/s, and its value is observed to increase with the increase of temperature.

Influence of the Performance of Reclaimed Asphalt Pavement (RAP) Material on Bituminous Mix

The utilization of reclaimed asphalt pavement (RAP) material to prepare a durable bituminous concrete (BC) mixture, used for flexible pavement surface courses is a challenging task in this investigation. RAP material is one of the latest substitutes for virgin aggregate and virgin binder of the bituminous mix. Using RAP material in flexible pavements can improve the engineering properties of bituminous mix and is also beneficial for economic and environmental. To execute such study, virgin aggregate (VA) has been replaced by 0, 10, 20, 30, 40, 50, 60, 75, and 100% of RAP material, respectively, in the cited mix with 2% Ordinary Portland Cement (OPC) as mineral filler. To characterize the RAP material, several laboratory tests such as specific gravity test, water absorption test, shape test, impact test, Los-Angeles abrasion test and, advanced tests as X-RF, X-RD, and GPC test, etc. have been employed. However, to assess the durability and strength of RAP enriched BC mix, Marshall stability test, modified Marshall immersion test, indirect tensile strength (ITS) test and, Cantabro abrasion test has been conducted. Marshall stability test, modified Marshall immersion test, ITS test, and Cantabro abrasion test is explored that 50% RAP modified bituminous mix has the capability to best perform than the other studied mix in terms of durability and strength. Because the molecular bonding of carbonyl compound between aged and virgin binder is suspected in the mix improvement factor that leads to the longer span life of the RAP modified flexible pavement.

Rheological behavior of asphalt binders and fatigue resistance of SMA mixtures modified with nano-silica containing RAP materials under the effect of mixture conditioning

Due to the environmentally associated issues regarding the construction or rehabilitation of asphalt pavements with merely virgin materials, researchers have proposed the re-utilization of the reclaimed asphalt pavement (RAP) materials. However, their adoption in asphalt pavements is detrimental to the fatigue performance of asphalt pavements. For this, modifying asphalt binders with nanoparticles has been one of the successful choices among researchers. In this study, different compounds of asphalt binders and stone matrix asphalt (SMA) mixtures containing 20%, 30%, 40%, and 50% RAP materials modified with 2%, 4%, and 6% nano-silica were prepared. Moreover, the rheological behavior of each mix was evaluated using several tests, including rotational viscosity (RV) considering the flow activation energy (FAE) method, frequency sweep, Multiple Stress Creep Recovery (MSCR), Linear Amplitude Sweep (LAS), and Bending Beam Rheometer (BBR). Besides, the fatigue performance of aged SMA mixtures was investigated using the four-point beam fatigue (4 PB) test. The results indicated that the temperature susceptibility of binders was decreased by the addition of nano-silica and RAP binder. Also, according to the MSCR and frequency sweep tests results, the rutting resistance of modified binders with the RAP binder was superior to that of the base binder. Besides, due to the establishment of a network by nano-silica within the structure of the asphalt binder in which the functional groups of asphalt binder interact with nanoparticles, the modified binders with RAP binder outperformed their unmodified counterparts regarding the fatigue life. Also, aging had a less detrimental impact on the fatigue life of the RAP contained SMA mixtures. However, the low-temperature performance of binders was degraded by the addition of nano-silica.

A method for characterising RAP degree of binder activity

Most transportation agencies in the United States continue to assume reclaimed asphalt pavement (RAP) contributes 100% of its binder to a new asphalt concrete (AC) mixture despite mounting evidence to the contrary, leading to mixtures with insufficient binder and resulting in workability and durability issues. This research assessed the practicality of estimating a realistic reduced RAP binder activity for consideration in AC mixture design based on indirect tensile (IDT) strength testing of 100% RAP mixtures. The concept and methodology of the Degree of Binder Activity (DoA) was reviewed, modified, and estimated for RAP materials from six states with varying climates in the United States. Pending further validation, the DoA methodology was determined to be practical for inclusion in existing mixture design methods.

Influence of shotblasting treatment on asphalt pavement performance

ABSTRACT The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. This study selected six pavement sections with low skid resistance from the National Center for Asphalt Technology Test Track for shotblasting abrasion. These sections included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four coarse aggregate types (limestone, granite, dolomite and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure the surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking and surface roughness were periodically monitored. The test results indicated that shotblasting treatment was effective in improving the friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and coarse aggregate type.

A laboratory study of the effect of fiberglass additive on the behavioural properties of RAP asphalt mixtures

The increase in the amount of reclaimed asphalt pavement (RAP) and environmental concerns for bitumen production have contributed to the use of RAP in road construction and maintenance. The use of higher than 15% of RAP adversely affects the physical and rheological properties of the asphalt binder and the mechanical properties of mixtures. Therefore, the use of bitumen and asphalt mixture improver were necessary to reduce the negative effects generated with the use of RAP. This paper aims to study the effect of fiberglass (FG) (0.5%, 1.0%, 1.5%, and 2%) on the mechanical properties of asphalt concrete containing 25%, 50% RAP and 9% waste engine oil. The performance of RAP asphalt mixtures incorporated with FG was evaluated using the Marshall stability test, moisture susceptibility test, and immersion wheel rutting test. The results indicated that the use of FG and RAP materials to rejuvenated asphalt mixtures resulted in an increase in the values of Marshall stability and rutting resistance. Moreover, the study revealed that increasing the content of RAP material and FG results in increased resistance of asphalt to moisture damage. This paper concluded that using 0.15% of FG and 50% RAP materials gives the best results.

Sustainability of using reclaimed asphalt pavement: based-reviewed evidence

The concept of sustainability is considered essential in the development of the asphalt mixtures industry, due to its economic and environmental benefits. This study attempts to highlight the potential benefits of sustainability using Reclaimed Asphalt Pavement (RAP). It reviews previous studies conducted on RAP to obtain the most important characteristics in how to use the optimal content of RAP and its effect on some basic properties such as resilient modulus, susceptibility to moisture, permanent deformation, and fatigue. This study mainly focuses on the advantages of using RAP materials in hot mix asphalt (HMA). The results indicated that adding 30% of RAP to virgin asphalt mixtures gives the best performance in terms of the most studied characteristics.

The Influence of Mixing Conditions on the Macro-Scale Homogeneity of Asphalt Mixtures Blended with Reclaimed Asphalt Pavement (RAP).

The homogeneity of asphalt mixtures blended with reclaimed asphalt pavement (RAP) is affected by many factors. Due to the complicated compositions of recycled asphalt mixtures, the inhomogeneity issue might cause insufficient mechanical properties of asphalt mixtures, even though a design method was appropriately adopted. Therefore, it is of great significance to study the influence of mixing conditions on the homogeneity of asphalt mixtures blended with RAP materials. This study focused on the macro-scale homogeneity of produced asphalt mixtures. Specifically, asphalt mixtures incorporated with 40% RAP content were produced in a laboratory using different mixing times and mixing temperatures. A multi-direction indirect tensile stiffness modulus (ITSM) test was proposed to quantify the homogeneity of produced samples. In addition, the digital image processing (DIP) method was used to identify the distribution of aggregates and RAP binder. The results indicated that the influence of mixing time on the macro-homogeneity of asphalt mixtures indicated that a longer mixing time was favorable for the material dispersion. The influence of mixing temperature mainly rested on two perspectives. One was that the temperature variation induced the change of binder viscosity. The other was that the temperature influences the diffusion process between RAP binder and new bitumen, which further affected the mechanical performance of produced asphalt mixtures.

The impact of aging heterogeneities within RAP binder on recycled asphalt mixture design

The degree of binder activation in reclaimed asphalt pavement (RAP) is a critical aspect that should be considered in the design of recycled asphalt mixtures. It is widely believed that binder from RAP is less than 100% activated, which implies that part of the RAP binder will be inactive in the mixing process. It is important to quantitatively assess whether there is any significant difference between the active and the inactive binder as typical recycled mixture design insinuates 100% binder activation and complete homogenization of the virgin and RAP binder. The objective of this study is to evaluate aging heterogeneities within RAP binder as an imperative step to improve the design of recycled asphalt mixtures. Stages of binder extraction were performed on six RAP materials to artificially activate different RAP binder layers. After each extraction, the binder recovered was evaluated in terms of its rheological properties, polarity-based fractions, and Fourier transform infrared spectroscopy. Based on the results, an asphalt mix design was simulated using different RAP percentages considering the impact of RAP binder aging heterogeneities. Overall, the analysis implied that it may not be a realistic assumption to consider full RAP binder homogeneity. Based on the simulation performed, blending charts used to design recycled asphalt mixtures should be ideally based on the active RAP binder properties instead of the properties of the RAP binder after complete binder extraction. This would facilitate in choosing the correct virgin binder when the partial RAP binder activation scenario is considered.

Investigating Degree of Blending Between Reclaimed Asphalt Pavement and Virgin Binder Using Atomic Force Microscopy and Focused Ion Beam

Adding reclaimed asphalt pavement (RAP) into asphalt mixes is a common practice and has many merits such as reducing costs and emissions. In recent decades, many state highway agencies have embarked on investigating asphalt mixes with high RAP content. As the RAP content increases, understanding how well the RAP binder blends with virgin binder becomes more crucial. Lack of knowledge on how much of the residual RAP binder actively blends with virgin binder during production is one of the reasons preventing full exploitation of RAP materials. Obviously, the amount of aged RAP binder blending into virgin binder affects the properties of asphalt mixes. A study was undertaken to investigate the degree of blending, that is, the amount of RAP binder blended with virgin binder, through atomic force microscopy (AFM) and focused ion beam (FIB). The AFM measurements were conducted on both binder samples and RAP aggregate samples; the former consisted of extracted and recovered RAP binder, virgin binder, and blended binder, while the latter covered blended RAP aggregate and virgin binder samples. AFM measurements on binders indicated that blended RAP and virgin binder, at the blending zone between RAP and virgin binder, has moduli between that of pure RAP binder and pure virgin binder. AFM was also explored to investigate the degree of blending using RAP aggregate and virgin binder, but preparation of acceptable samples for such work was not possible, in spite of extensive work in preparation of such samples through mechanical polishing and FIB.

Effect of Emulsified Asphalt Content on Creep Behavior and Mechanical Properties of Cold Recycled Emulsified Asphalt Bases

Since the beginning of the 21st century, the rapid development of road infrastructure has facilitated enhanced mobility and accessibility that has caused environmental degradation due to the continuous extraction of natural aggregates. To address this increasing problem, recycled aggregates and Reclaimed Asphalt Pavement (RAP) materials have been utilized in road construction worldwide. The studies related to various emulsified asphalt contents on permanent deformation and other parameters are limited. This study examined the performance characteristics of cold recycled emulsified asphalt bases with RAP materials in different proportions, i.e., 25%, 50%, and 75%, and evaluated in terms of the indirect tensile strength, tensile strength ratio, density, water loss, and permanent deformation at lower and higher emulsified asphalt contents than optimum. The results demonstrated that the total residual binder content influences the permanent deformation characteristics of cold mixes. There was no significant variation in the durability and strength with the RAP at the optimum emulsified asphalt content. But, the emulsified asphalt contents other than optimum influence the strength, density, and permanent deformation. The logarithmic and power-law models are best suited to predict the first-stage permanent deformation of cold mixes.

Recycling Aged Asphalt Using Hard Asphalt Binder for Hot-Mixing Recycled Asphalt Mixture

Increasing the content of reclaimed asphalt pavement material (RAP) in hot-mix recycled asphalt mixture (RHMA) with a satisfactory performance has been a hot topic in recent years. In this study, the performances of Trinidad lake asphalt (TLA), virgin asphalt binder, and aged asphalt binder were first compared, and then the modification mechanism of TLA on virgin asphalt and aged asphalt was explored. Furthermore, the RHMA was designed in accordance with the French norm NF P 98-140 containing 50% and 100% RAP, and their high-temperature stability, low-temperature cracking resistance, and fatigue performances were tested to be compared with the conventional dense gradation AC-20 asphalt mixture. The results show that the addition of TLA changes the component proportion of virgin asphalt binder, but no new functional groups are produced. The hard asphalt binder modified by TLA has a better rutting resistance, while the fatigue and cracking resistance is lower, compared to both aged and virgin asphalt. The high-modulus design concept of RHMA is a promising way to increase the RAP content in RHMA with acceptable performance. Generally, the RHMA with 50% RAP has similar properties to AC-20. And, when the RAP content reaches 100%, the high- and low-temperature performance and anti-fatigue performance of RHMA are better than AC-20 mixture. Thus, recycling aged asphalt using hard asphalt binder for hot-mixing recycled asphalt mixture to increase the RAP content is feasible.

Performance analysis of cement treated base layer by incorporating reclaimed asphalt pavement material and chemical stabilizer

Milling of an existing pavement after it's service life engenders massive production of reclaimed asphalt pavement material (RAPM), which may cause disposal issues. The current study highlights the sustainable valorization of RAPM in the cement-treated base (CTB) layer by incorporating chemical stabilizers by the full-depth reclamation (FDR) method. CTB mix was prepared in the laboratory by using 100% RAPM with varying cement and chemical admixture content. In order to identify the effect of different content of cement and chemical stabilizer on the laboratory measured different engineering properties of CTB mix were evaluated. Furthermore, to impart more insights on the laboratory-designed CTB mix under actual traffic conditions, the test track was also laid and being monitored by the durability properties of fields sample and falling weight deflectometer (FWD) analysis. Four cement contents of 3.5, 4.0, 4.5, and 5 percent and five chemical stabilizer contents of 0, 3.0, 3.5, 4.0, and 4.5 percent by weight of cement were added. From obtained data, it can be concluded that mix prepared with 4.5% cement and 4% chemical stabilizer provides the best result in terms of strength parameters and durability properties of studied samples. FWD data advocates that constructed pavement with a designed CTB layer imparts low fatigue behavior as compared with the performance criteria prescribed in Indian Roads Congress (IRC) guidelines. Our study accentuated that 100% recycling of RAPM in FDR technology can be a viable solution as the comprehensive cost analysis showed a 45% cost reduction for the proposed mix by incorporating studied materials.

Functional and environmental impacts of the use of reclaimed asphalt pavement materials and of foamed asphalt

Environmental safety related to asphalt mixing plants has been a growing concern due to the high temperature of asphalt mixture production resulting in a lot of energy used and much air pollutants released. Asphalt mixtures with foamed bitumen and RAP can reduce this problem. This paper deals with their functional and environmental effects. In the paper, it was introduced that the hot mix asphalt mixtures bound by foamed bitumen and containing RAP materials provides a good workability, in comparison to “traditional” hot mix asphalt mixtures. However, producing foamed bitumen needs special technological steps before using it as asphalt binder. The use of RAP materials reduces environmental harm and construction costs, besides it preserves the limited resources of stone, sand and gravel.