Recycled Asphalt Pavement Research Articles

Flexible pavement construction using different waste materials: A review

Flexible pavement is the most preferred pavement system for road construction. In achieving the goal of becoming a developed country, industrialization and construction activities are increasing daily in a developing country like India. Today's ever-growing demand for the supply of exhaustible natural resources is one of the significant challenges of the global pavement industry. Wrenching out and generation of these virgin materials is an unsustainable practice. Further, rapid industrialization and infrastructure development leads to the generation of different waste materials. Uncontrolled waste management causes various health hazards and leads to environmental pollution. Also, the open dumping of these wastes requires a huge landfill area and minimizes the land available for further development. Detailed laboratory investigation conducted by various researchers showed the usage of industrial waste in unbound base and sub-base layers of pavements in the form of coarse aggregates, fine aggregates, and mineral fillers. Utilization of recycled or already used materials and natural aggregates provides an economical, efficient and sustainable construction technique without compromising the strength and durability characteristics of pavement. Various studies have established that secondary material provides an efficient waste disposal technique, reduces the demand for conventional materials, and reduces the overall construction cost. Asphalt pavements and construction and demolition wastes are among the primary sources of reclaimed aggregates. The recycled material is first extracted from its source, processed, and then made suitable for further pavement construction utilization. This paper provides an overview of such recycled materials that have been successfully used in sub-base and base layers of flexible pavement. Further, this review paper is expected to address several major issues with the usage of Recycled Asphalt Pavement (RAP) in unbound layers of flexible pavements, and it will encourage researchers and highway agencies across the globe to develop a framework for the efficient use of RAP in pavement construction.

Characterization of Recycled Asphalt Pavement with Known Source History

Characterization of Recycled Asphalt Pavement with Known Source History

Evaluation of recycled asphalt pavement in Colombia

Reclaimed asphalt pavements are obtained from existing pavements through recovery techniques and are used for new asphalt mixtures production with the inclusion of virgin aggregates and asphalt cement, constituting environmentally friendly mixtures at a lower total cost, by requiring fewer quantities of new materials. This research, unlike the studies found on the subject, focuses on the study of reclaimed asphalt pavement by analyzing its granulometric distribution and asphalt cement content. For this purpose, representative reclaimed asphalt pavement samples were taken from four Colombia cities, to verify their heterogeneity. The obtained reclaimed asphalt pavement was analyzed in the laboratory, to obtain the material granulometric distribution, through extraction and asphalt content tests, following Colombian regulations from the “Instituto Nacional de Vías”. The results show that the granulometry of all cities has a central tendency (average) that moves towards an upper limit in the 2 mm particles. When analyzing the granulometry separately of the four cities, it is observed that they present a different trend in their granulometry, which shows their heterogeneity. The asphalt cement content presented values between 4.0% and 5.0%.

Advanced characterisation of multi-recycled warm asphalt pavement (MRWAP) with high content of recycled asphalt pavement

The main results of the French collaborative project Improvmure, funded by the National Research Agency are presented. A very wide study was performed on bituminous mixtures produced on experimental sites or in laboratory at different scales (semi-industrial process or lab process). Objectives were to evaluate the influence of the recycling rate (0%, 40% and 70%), the number of successive recycling cycles (from 1 to 3 cycles), and the manufacturing process (hot mix or warm mix using additives or foamed bitumen). The impact was studied in laboratory on the emitted fumes during the production process, on the properties used for mix design (compactability, water sensitivity, complex modulus at 15°C/10 Hz, fatigue), on advanced thermomechanical behaviour (linear viscoelasticity, crack behaviour at low temperature, crack propagation) and on surface properties (skid resistance). The paper gathers many valuable results, showing the possibility to recycle bituminous mixtures multiple times, at high rates and with warm manufacturing process.

Performance Improvement of Recycled Asphalt Pavements via Quality Control of Extracted RAP Aggregate Gradation

Performance Improvement of Recycled Asphalt Pavements via Quality Control of Extracted RAP Aggregate Gradation

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.

Effect of glass fibers and waste engine oil on the properties of RAP asphalt concretes

ABSTRACT The increase in the cost of virgin materials and the environmental sustainability have contributed to increasing the incentive to use asphalt mixtures containing high percentages of recycled asphalt pavement (RAP). However, the use of high percentage of RAP into virgin asphalt mixture could negatively affect the performance of some properties of asphalt mixtures. Thus, using an appropriate additive to offset the negative effect of RAP could lead to an increase in the amount of RAP in asphalt mixtures. Therefore, this study aimed to evaluate the effect of using glass fiber (GF) with different contents (0.0%, 0.1%, 0.2%, and 0.3%) as an additive on the performance of asphalt mixtures containing RAP materials (60%, 70%, and 80%) and rejuvenated with waste engine oil (WEO) i.e., 6%, 9%, and 12%. The performance of RAP mixtures incorporating GF was evaluated using the indirect tensile strength test (ITS), resilient modulus test, and moisture susceptibility test. Hamburg wheel track testing was done to evaluate the rutting performance of the 70% RAP mixture. The results showed that the GF modification enhanced the ITS, rutting resistance, moisture susceptibility, and resilient modulus of rejuvenated mixtures. It was also found that the GF content of 0.2% was the optimum.

Effect of marshal and gyratory compaction methods on cracking characteristics of hot mix asphalt concrete materials under all three basic modes of fracture

Asphalt mixtures in the laboratory scale studies are often compacted and manufactured using two well-known methods namely gyratory and marshal methods. Due to differences in compaction procedure, employing any of these methods can affect the overall strength and mechanical properties (such as the fracture toughness and cracking resistance) of hot mix asphalt (HMA) materials. Understanding the effect of compaction method on cracking behavior of asphalt mixtures can provide good insights for estimating the long-term performance of pavements and roads. Therefore, in this research the effect of HMA compaction method is studied experimentally on modes I, II and III cracking behavior and fracture toughness values using the edge notch disc bend (ENDB) specimen. In addition, the effect of adding recycled asphalt pavement (RAP) material is also studied on the fracture behavior. Accordingly several HMA mixtures compacted with both marshal and gyratory methods and containing 0 and 50 % RAP material are tested at a fixed low temperature of −25 °C and the corresponding values of KIc, KIIc and KIIIc as well as the work of fracture values under all three basic modes of loading are obtained. The experimental results show the noticeable effects of loading mode, RAP content and compaction method on the fracture behavior of tested HMA materials. In general, adding RAP material reduces the fracture toughness values for all loading modes. However, compaction method has different effects on the fracture toughness values. While the KIc value obtained from gyratory compaction method is higher than the sample made of marshal method, opposite trends are seen for the shear type fracture modes (i.e. KIIc and KIIIc). The tensile mode over shear type mode fracture toughness ratios (KIIc/ KIc and KIIIc/KIc) as well as the effective fracture toughness and effective work of fracture values for the tested HMA mixtures are also presented and analyzed.

Shear strength of reinforced concrete deep beams containing recycled concrete aggregate and recycled asphalt pavement

In this study, the behavior of deep beams containing natural coarse aggregates (NCA), recycled concrete aggregates (RCA), and recycled asphalt pavements (RAP) is studied. Ten deep concrete beams with two length-to-depth ratios of 1.6 (group G1.6) and 2.7 (group G2.7) were constructed. In each group, one specimen was built with NCA concrete, two specimens were built with 50% of RCA and RAP replacement without mix design modification, and two specimens were built with 100% of RCA and RAP replacement with modifying the mix design to obtain the target compressive strength. The load–deflection curves, shear capacity of deep beams, absorbed energy, failure mode, cracking patterns, and strain in reinforcement bars were studied. The results showed by replacing NCA with 50% of RCA and RAP, the shear capacity of deep beams is reduced by 9 and 11.7% in G1.6 group and 4.66 and 7.52% in G2.7 group, respectively. Using 100% replacement of NCA with RCA and RAP and using the modified mix design to achieve the target compressive strength, the shear capacity of deep beams was nearly equal. The absorbed energy in deep beams containing RAP was higher than other specimens. Also, RAP deep beams had the highest and, RCA deep beams had the least reserved strength, showing the ductility of RAP and brittleness of RCA compared with NCA deep beams. The cracking patterns analysis showed that the number of flexural and diagonal cracks is reduced in RCA and increased in RAP specimens. The width of flexural and diagonal cracks was higher in RCA and less in RAP specimens than NCA specimens.

Limitations on the Use of Recycled Asphalt Pavement in Structural Concrete

Recycled materials from construction and demolition waste, such as recycled concrete aggregate, recycled brick aggregate, or recycled asphalt coming from the milling of road/motorway surfaces, are the key for a sustainable production of concrete. This paper reviews in particular the use of recycled asphalt pavement (RAP) aggregates in the production of concrete for structural uses. An overview is initially presented to describe the different areas of use of RAP, its definition and the limitations imposed by codes and standards. Relatively to the experimental data provided by the literature, a comparison with the Italian minimum requirements is also provided. Lastly, the influence of RAP on the characteristics of concrete such as compressive strength, flexural strength, Young’s Modulus and a study of durability are presented to define the possible applications of RAP in structural concrete in relation to the current allowable percentage of substitution.

PHStat testing and geochemical modeling of inorganic compounds in recycled asphalt pavement used in highway shoulders

Recycled asphalt pavement (RAP) has increasingly been used as a highway construction material due to its favorable physical properties. As with many industrial by-products, however, there are concerns about the impact of RAP on surface and groundwater caused by leaching of heavy metals present in the material. To determine the potential risks posed by heavy metals leaching from RAP, pHstat leaching tests were performed on seven Maryland-sourced RAPs, and were compared with two local topsoils. The pHstat leaching tests showed As leaching from RAPs between 0.3 and 68 mg/L at pHs below 9, which is above the US EPA maximum concentration limits for drinking waters (0.01 mg/L). Other analytes were largely detected below their respective EPA WQL in the drinking water pH range of 6.5–9. The topsoils leached lower concentrations for all analytes except for barium and aluminum. The geochemical model run to understand the nature and source of heavy metals leaching in the RAP samples indicated that leached metals were solubility controlled. The model results also showed Al and Fe leaching to be controlled by oxide/ hydroxide minerals, and Ba, Ca and Mg to be controlled by carbonate and/or sulfate minerals.

Systematic evaluation of effects of recycled materials and mix design parameters on the rutting and cracking performance of asphalt mixes

Problems associated with the rutting and cracking of asphalt mixes call for the use of balanced mix design and thus have received close attention from researchers and practitioners. The increased use of recycled materials, such as recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS), further complicates the performance of asphalt mixes. Most studies of RAP and RAS have focused on the inclusion of these recycled materials in asphalt mixes designed for research purposes, which could differ from mixes designed by contractors for practical use. Therefore, a systematic review is needed of the effects of recycled materials and mix design parameters on the rutting and cracking performance of mixes designed by contractors. In addition, contractors need guidance in developing asphalt mixes that meet specifications that require rutting and cracking tests instead of simply relying on trial and error. To address these needs, in this study, rutting and cracking tests of forty contractors’ asphalt mix designs were conducted and the most effective design parameters on the performance of asphalt mixes were presented and discussed. These mixes included different percentages of RAP or RAP/RAS, performance grades of binders, design gyration numbers, aggregate gradations, and other volumetric properties. The provided results and discussions can be used as guidance for contractors to improve their mix designs to meet specifications.

Asphalt Concrete for Binder Courses with Different Jute Fibre Content

Since the beginning of modern road construction, there have been effort to make durable, long life pavements. But no one pavement can fulfil designed purpose forever. On the other hand, some natural resources are limited, so it is important to maximize use of renewable resources. In recent years, there is a visible pursuit of this trend, in road construction represented mostly by use of waste materials, such as industrial by-products or recycled asphalt pavement itself. Within the effort, fibrous additives were established on the market to prolong life of pavement layers. Some commercial ones are synthetic polymer based, so it does not go well with the renewable part of pavement life cycle if we want to secure sustainable future. This paper describes use of fibres from natural renewable resource, specifically jute plant (Corchorus). Three asphalt mix variants with jute fibres were designed and further compared. Fibre content was 0.1 %, 0.2 % and 0.3 % by weight. Several tests were conducted to examine the effect of fibres on mixture properties, with aim on stiffness modulus (IT-CY) and crack propagation (SCB). Furthermore, indirect tensile strength ratio was calculated as a parameter showing performance of the mixture under the wet conditions. Control mixtures with paving grade and polymer modified bitumen were tested for better comparison and evaluation of the results.

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.

ANALYSIS ON OPTIMIZATION DECISION OF PAVEMENT MAINTENANCE MODE BASED ON ANALYTIC HIERARCHY PROCESS

With the rapid development of China's transportation and the improvement of people's living standards, China's highways have entered the peak maintenance period. According to the old road conditions and financial conditions, how to choose the appropriate maintenance technology to meet the technical and economic requirements of highway maintenance and construction projects has become a difficult problem faced by highway maintenance management departments. Therefore, based on the principle of index selection, this study comprehensively considered the impact of various factors on maintenance decision-making, determined four evaluation indexes, and systematically studied the compre-hensive decision-making system of asphalt pavement recycling maintenance. Based on the subjective-objective linkage and probability statistics method, the eigenvalue of the applicability of recycling mode was transformed to the same scale of 0 to 100, and the fuzzy scoring interval of the four bids was proposed. The calculation method of pavement quality recovery index (PQRI) and the analysis basis of economic benefits were clarified. Finally, the weight of each index was calculated by analytic hierarchy process, and the multi-index comprehensive decision-making method of pavement maintenance is constructed and used to theoretically verify and guide the actual road section. Results demonstrate that the proposed PQRI can realize the operability of quantifying the later operation of pavement. The weight of each index from big to small is PQRI > economic benefit > applicability of recycling mode. The recycled pavement quality recovery indices and applicability of the four recycling modes have small differences, and the proposed four bids interval makes the decision-making evaluation process more simple and explicit. The decision evaluation results of actual road section verify the rationality and practicability of the decision method. The conclusions are important for the maintenance and management of asphalt pavement recycling technology. Keywords: road engineering, recycling maintenance, intelligent decision-making, fuzzy evaluation

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.

Applicability of various mixing rules for hot asphalt recycled binders

In the mix design process of recycled asphalt pavement, the proportion of reclaimed asphalt pavement (RAP) binder and recycling agent (RA) are decided using mixing rules. However, the efficacy of mixing rules remains a concern due to the assumption of 100% blending between RAP binder and RA. This study revisits the applicability of different mixing rules viz. pure mixing rules, mixing rule with binary interaction parameter, and mixing rule with viscosity blending index (VBI). In this study, nineteen RAP-RA pairs were blended at multiple levels of RAP content. The difference between measured and modeled values was analysed using the chi-square test. The statistical analysis of the limited data set proved that the high performance grade (PG) temperature, softening point, Grunberg & Nissan, and phase angle mixing rules are satisfactory in predicting the property of recycled binders.

Characteristics and optimization of cement concrete mixes with recycled asphalt pavement aggregates

Characteristics and optimization of cement concrete mixes with recycled asphalt pavement aggregates

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.