Plasticity-Based Method for the Design and Analysis of Cold Recycled Pavement Layers

The usage of Reclaimed Asphalt Pavement (RAP) material is a highly resource-conservative, economical, and sustainable practice in flexible pavement construction. However, its usage in hot mix asphalt (HMA) is capped at 25% by the majority of state transportation agencies due to its aging levels, stiffness characteristics, and handling capabilities, which may result in early-age pavement distress. Though researchers suggest methodologies to increase RAP usage, higher RAP percentages in asphalt pavements require the support of state authorities. The main objective of this paper is to provide information on how different states design their mixtures with high RAP percentages. This study reviewed the current state of practice of fifty (50) state DOTs in the United States (US) with respect to RAP usage and the factors governing its regulations. It was observed that the limit of RAP content is mainly governed by traffic levels, gradation, binder content, and stiffness contributed by RAP and layer position in a pavement structure. The specifications also suggest that apart from volumetric and performance justification, blending charts, fractionation, and virgin binder grade selection would facilitate the use of higher RAP content in HMA. Controlled mixture design abiding by state specifications can increase the allowable RAP to 40–100%.

Reclaimed asphalt pavement (RAP) arises from the demolition of asphalt road layers. The Optimal Recycling of Reclaimed Asphalt Pavements Project concerns the cold recycling of 100 % RAP without binder addition in base and subbase layers of low-traffic roads. In this context, a test program was performed with Rhine region materials to evaluate the impact of the mastic coating of untreated RAP. A source of reclaimed asphalts with 4.4 % of bitumen is tested before (RAP) and after binder extraction (RAP-BE) and then is compared to an unbound granular material (UGM) with a similar particle-size distribution. Repeated load triaxial tests were conducted at several frequencies to study the permanent and resilient behaviors. The results show that the RAP before binder extraction and the UGM present similar permanent behaviors, while the aggregates without binder reveal low strains. Concerning the resilient phase, the RAP and the RAP-BE show similar levels of strains, but the resilient moduli of the UGM are significantly lower than those of the RAP. From the experimental results, the nonlinear elastic Boyce model was fitted and brings out a highly anisotropic mechanical behavior of the RAP. Finally, the RAP shows a frequency-sensitive viscous behavior because of the bitumen in the mastic, while the effect of the frequency is negligible for the RAP-BE.

For several years reclaimed asphalt pavement (RAP) material has been used as a construction material in hot-mix asphalt (HMA) to reduce material costs and stabilize pavements. Of the 45 million tons of RAP produced every year in the United States, only 33% is being used in HMA. Recent studies have demonstrated that RAP can be used effectively in base layers when it is blended with aggregate base materials and stabilized with cement or fly ash additives. This adoption in the pavement base layer helps maximize the reutilization of RAP material and minimize its disposal in landfills, thereby making it an environmentally friendly practice. However, studies reported so far addressed only the strength and stiffness characteristics of stabilized RAP in base layers in the short term, and not many studies have addressed its long-term behavior. In this study the long-term durability of untreated as well as stabilized specimens was tested by conducting standard durability testing to replicate the moisture fluctuations in the field from seasonal variations. In addition, leachate studies were conducted to examine the effect of rainfall infiltration on the leachability of the cement or fly ash stabilizer from stabilized RAP mixtures. Durability studies revealed a very low volumetric change and good retaining strength at the end of three, seven, and 14 cycles for RAP material from the El Paso, Texas, area, and leachate tests proved that the leaching of cement or fly ash stabilizer from RAP mixes cannot be considered to be a concern for long-term performance. However, approximately 2 years of field infiltration were replicated in the laboratory in this study. Of the several RAP mixtures studied, the mixture composed of 60% RAP and 40% base material with 2% cement was identified as an effective long-term-performing mixture.

The increased scarcity of natural quarry material has resulted in increases in the cost and burden on the environment. Pavement materials comprising asphalt coated aggregates that can be reused are called reclaimed asphalt pavement (RAP). RAP is crushed and screened, and then blended with one or more stabilization agents to produce a stabilized base or subbase aggregate. In the present study, the influences of fly ash dosage, lime dosage, and curing period on the strength, stiffness, and durability characteristics of RAP fly ash–lime (RFL) mixes were studied for utilization as a base layer material in flexible pavements. The dry density and moisture content relationship were determined by conducting a modified proctor test on all RFL mixes. Unconfined compression tests were conducted on specimens with different dry weight percentages of fly ash (10%–25%) and lime (5%–10%) content for different curing periods (0, 7, and 28 days). The optimum mix obtained as RFL2 had the proportions 70% RAP:22.5% fly ash:7.5% lime. A resilient modulus of 540 MPa at 28 days was observed for RFL2. The durability of RFL2 tested using the resistance index and a wet–dry cycle (weight loss) was observed to be 0.88% and 7.3%, respectively. Pavement analyses were performed for a pavement system with three layers using the KENLAYER program. The RFL2 mix as the base layer material was found to be superior to conventional wet mix macadam, hence the service life of an RFL2 pavement would be higher. Trial sections of the stabilized base and conventional pavement were constructed on a major district road. The falling weight deflectometer showed a better modulus (286 MPa) in RFL2. An RFL mix could therefore be used in a stabilized base layer to replace a conventional base layer.

This research provides useful insights into sustainable and cost-effective pavement rehabilitation by evaluating the combined effects of both Reclaimed Asphalt Pavement (RAP) and Crumb Rubber (CR) modification on flexible pavement performance using actual motorway sections. Pavement rehabilitation and maintenance can enhance the design and serviceable life of the pavement. Additionally, modification of asphalt with Crumb Rubber (CR) and Reclaimed Asphalt Pavement (RAP) not only proves to be economical but can also increase the resistance of flexible pavement concerning rutting, fatigue, and moisture damage. Four different pavement sections were selected, which were rehabilitated and modified with Reclaimed Asphalt Pavement (RAP), Crumb Rubber (CR), and a combination of both, along the Islamabad-Lahore motorway (M-2), Pakistan. The first pavement section consists of Asphalt Concrete Wearing Course (ACWC) with 60/70 grade bitumen as a binder (RAP 0%, CR 0%), the second pavement section was a mixture of asphalt concrete with crumb rubber modified bitumen as a binder (RAP0%, CR7%), the third pavement section was a blend of 15% RAP with 60/70 grade bitumen as a binder (RAP15%, CR 0%), the fourth section was a mixture of 15% RAP and 7% crumb rubber modified bitumen (RAP 15%, CR 7%). Pavement cores were extracted from the selected four pavement sections, which were experimentally explored in the laboratory to find the impact on the performance of highway pavement employing Reclaimed Asphalt Pavement (RAP) and Crumb Rubber (CR), partially replacing bituminous binder in the asphalt. The results show notable improvements in rutting resistance, tensile strength, and resilience. It was concluded that the performance of the section employing either RAP, CR or combined RAP and CR modified bitumen better enhanced the performance of pavement in terms of rut depth, indirect tensile strength and modulus of resilience. For instance, rutting depth was reduced by 41.35% and indirect tensile strength of pavement was increased by 17.93% by employing 15% RAP and 7% CR in modified bitumen binder for asphaltic mix. Likewise, the modulus of resilience was increased by 38.23% for the section employing 15% RAP and 7% CR in pavement.

The most important priority in the field of environmental protection is the implementation of the principle of closed - cycle materials management in construction. This problem also plays an important role in road construction. Due to the increasing traffic load of heavy vehicles and the impact of climatic factors, the road structure is subject to destructive processes that lead to the loss of its durability in time. Therefore, the roads periodically need to be modernized. Very often, it is necessary to carry out critical activities on the foundation to improve the load - bearing capacity of the pavement structure. As part of these works, large amounts of reclaimed asphalt and aggregate are obtained during milling of the lower structural layers of the surface. Applying the principle of closed - cycled material management, the most effective technology for using this material is its re - construction using deep cold recycling technology. This technology uses hydraulic binder and bituminous emulsion, and currently, more and more often, foamed bitumen. Due to the fact that the materials obtained from road structure layers are of very different quality, it is necessary to use a binder that will be dedicated specifically to the materials used (reclaimed asphalt pavement, reclaimed stone). In experiment Portland cement CEM I 32.5, hydrated lime and cement by - pass dust as a by - product obtained from cement plants were used. All components were mixed in various proportions controlled by experiment plan. The influence of a dedicated binder on absorption, dynamic modulus, phase angle in the specific temperature range and rutting resistance of a cold recycled mixture designed with reclaimed asphalt pavement, reclaimed aggregate and foamed asphalt was examined. The obtained test results were subjected to statistical analysis using the ANOVA test in order to determine the significance of the influence of individual components of the dedicated binder on the considered parameter of the cold recycled mixtures. It was determined that the dedicated binder used for the tested recycled asphalt mixture ensures its most favorable parameters when contains: 40% CEM I 35.2, 20% hydrated lime and 40% cement by - pass dust.

Quantifying the agglomeration effect of reclaimed asphalt pavement on performance of recycled hot mix asphalt

Nevertheless hot recycling process is nowadays a widespread technique, many doubts related to the in plant recycling process effects on the performance of recycled mixtures still exist and limit the maximum allowable amount of Reclaimed Asphalt Pavement (RAP). Therefore, the feasibility of an efficient production of plant hot recycled mixtures characterized by high RAP content and suitable performance should be properly addressed. To this aim, the overall performance of hot recycled asphalt mixtures produced in asphalt plant and containing high RAP content were assessed in this study. The mixtures were prepared with two different bitumens (high and low content of SBS polymer modifier) and 40 % of RAP only deriving from asphalt layers containing polymer modified bitumens. The aggregate grading curve was previously optimized through a specific laboratory study by applying the Bailey Method and using selected RAP. A third mixture, currently used for binder layers in motorway pavements, was also studied for comparative purposes. Compactability, stiffness, cracking and rutting resistance and fatigue behavior were investigated. Results of the mechanical tests suggest that mixtures containing 40 % RAP are suitable for the production of new asphalt pavements, especially when low modified bitumens are used. In fact, the performance of such mixtures were comparable or even higher than those of the reference mixture. In particular, the specific and accurate mix design allowed the potential drawbacks due to higher RAP content to be balanced.

Sustainable pavement design requires a balanced consideration of economic, environmental, and social impacts. In line with Federal Highway Administration (FHWA) guidelines for sustainable roadway infrastructure, incorporating recycled materials such as reclaimed asphalt pavement (RAP), recycled pavement material (RPM), recycled asphalt shingles (RASs), and warm-mix asphalt (WMA) has been shown to reduce natural resource depletion while promoting circular construction practices. This study investigates the structural performance of Portland cement concrete (PCC) pavements constructed on RAP and RPM base layers. A series of design scenarios was modeled using site-specific laboratory and field data—particularly subgrade soil properties and climatic conditions—from El Paso and San Antonio, Texas. The analysis incorporates unsaturated soil parameters and follows the performance thresholds set by the Mechanistic-Empirical Pavement Design Guide (MEPDG). Findings indicate that concrete mixture design, pavement structure, and local weather conditions are the primary drivers of distress in jointed plain concrete pavements (JPCPs). However, subsoil characteristics have a significant impact on joint faulting in JPCP and punchout occurrences in continuously reinforced concrete pavements (CRCPs), especially in thinner sections. Notably, the use of up to 50% recycled material in the base layer had minimal adverse effects on pavement performance, underscoring its viability as a sustainable design strategy for rigid pavements.

Rutting is a key factor affecting the safety, durability, and performance of asphalt pavements. Its effective control requires proper design, material selection, and construction practices. Reclaimed Asphalt Pavement (RAP) offers environmental and economic advantages by reducing the need for virgin materials and minimizing construction waste. Incorporating RAP and basalt fibers can further enhance rutting resistance, thereby improving pavement longevity and structural performance. This study investigates the development of reclaimed asphalt pavement (RAP) mixture using. The RAP content was set at 15%, 30%, and 45%, with the addition of 6 mm long and 3‰ basalt fibers. The Hamburg wheel tracking test was used to evaluate the mixture's resistance to permanent deformation. The results indicated a decrease in rut depth and surface peeling as the RAP content increased. Notably, asphalt mixtures with 0% RAP and 3‰ basalt fibers demonstrated lower rut depths compared to control samples. The experiments showed that RAP mixtures exhibit superior rutting resistance compared to hot mix pavements. Additionally, integrating recycled materials and basalt fibers significantly enhanced rutting resistance, as evidenced by the incorporation of 45% RAP and 3‰ basalt fiber, which resulted in nearly a 47% decrease in rutting depth. Future research may focus on evaluating the crack resistance of asphalt pavements reinforced with high tensile strength basalt fibers.

With the increasing importance of conserving natural resources and moving toward sustainable practices, the aging transportation infrastructure can benefit from these ideas by improving their existing recycling practices. When an asphalt pavement needs to be replaced, the existing pavement is removed and ground up. This ground material, known as reclaimed asphalt pavement (RAP), is then added into new asphalt roads. However, since RAP was exposed to years of ultraviolet degradation and environmental weathering, the material has aged and cannot be used as a direct substitute for aggregate and binder in new asphalt pavements. One material that holds potential for restoring the aged asphalt binder to a usable state is waste engine oil. This research aims to study the feasibility of using waste engine oil as a recycling agent to improve the recyclability of pavements containing RAP. Testing was conducted in three phases, asphalt binder testing, advanced asphalt binder testing, and laboratory mixture testing. Asphalt binder testing consisted of dynamic shear rheometer and rotational viscometer testing on both unaged and aged binders containing waste engine oil and reclaimed asphalt binder (RAB). Fourier Transform Infrared Spectroscopy (FTIR) testing was carried out to on the asphalt binders blended with RAB and waste engine oil compare the structural indices indicative of aging. Lastly, sample asphalt samples containing waste engine oil and RAP were subjected to rutting testing and tensile strength ratio testing. These tests lend evidence to support the claim that waste engine oil can be used as a rejuvenating agent to chemically restore asphalt pavements containing RAP. Waste engine oil can reduce the stiffness and improve the low temperature properties of asphalt binders blended with RAB. Waste engine oil can also soften asphalt pavements without having a detrimental effect on the moisture susceptibility.

High-modulus asphalt concrete (HMAC) has been widely used in the surface coating of high-grade pavement. Due to HMAC’s modulus being significantly higher than traditional asphalt concrete, the mechanical responses of a pavement structure using an HMAC coating must be notably different from those of a traditional asphalt pavement structure. Moreover, when asphalt surface coating is fixed, the selection of base-course combinations will determine the mechanical response of the whole pavement structure. However, previous studies usually analyzed the mechanical response of pavement structures at limited combinations of base-courses, resulting in difficulties comprehensively understanding the laws of mechanics and effectively optimizing the HMAC pavement structure. Hence, in this study, a total of 108 groups of numerical experiments under six working conditions of base-course combinations are carried out using orthogonal experimental design to investigate the mechanical response of pavement structures using HMAC coatings using the PR MODULE high-modulus additive. The effects of pavement thickness, material modulus, and structural combination on mechanical responses are analyzed for the 108 groups to determine the optimal pavement combinations based on the balance of mechanical response and economic efficiency. The results show the following: The effect of the base layer type on mechanical response is more significant than that of the subbase layer type. Surface and undersurface layer thickness for the granular material base layer; surface and base layer thickness for the asphalt mixture base layer; and base layer thickness, subbase layer modulus, and base layer modulus for the inorganic binder mixture base layer are the key factors for mechanical response. Finally, six recommended HMAC pavement structure configurations for various base-courses are proposed.

The recycling of existing asphalt pavement materials produces new pavements with considerable savings in material, money, and energy. Understanding the ability of an asphalt pavement containing reclaimed asphalt pavement (RAP) to resist fracture from repeated loads is essential for the design of hot mix asphalt (HMA) mixtures. However, reaching a better understanding of fatigue behaviors of these pavements continues to challenge researchers all over the world, particularly, as recycled materials with more complex properties are being used in HMA pavements. This study explores the utilization of the conventional fatigue analysis approach in investigating the fatigue life of asphalt mixtures containing RAP. The fatigue beams were made with two asphalt binders, two aggregate sources, four RAP contents (0 %, 15 %, 25 %, and 30 %), and tested at 5 and 20°C. A total of eight mixtures was evaluated and 64 fatigue beams were tested in this study. The test results indicated that the addition of RAP, as expected, increased the viscosity, G∗sinδ, and creep stiffness values while reducing the m-values. However, no obvious trends were found for stiffness and fatigue life of mixtures as the RAP content increased. Statistical analysis results indicated that for binders and mixtures containing 30 % RAP, the utilization of softer binder significantly decreased the viscosity, G∗sinδ, and creep stiffness values; however, there were no significant differences in the stiffness and fatigue life values of these mixtures.

Permeable Friction Course (PFC) is a hot-mix asphalt that contains interconnecting voids that provide improved pavement surface drainage during rainfall. The objective of this study was to determine if PFC mixtures which incorporate reclaimed asphalt pavement (RAP) will provide performances that are similar to PFC mixtures which only use virgin materials and whether binder type will affect performance. Utilizing current design specifications, PFCs were designed with RAP contents of 0%, 15%, and 25% and four asphalt binders. These mixtures were subject to a barrage of tests which measured their ability to resist draindown, abrasion, fatigue cracking, rutting, and moisture damage. Other testing determined permeability, porosity and workability. Rutting testing employed the industry standard asphalt pavement analyzer. Fatigue cracking and moisture susceptibility testing utilized the semicircular bending test. It was determined that it is possible to design a PFC incorporating RAP which will have good performance. However, this will only be achieved when the proper materials are used. The RAP must be properly fractionated and a modified binder such as asphalt rubber or a highly modified asphalt binder (HiMA) must be used. The mixture tests combined with Life Cycle Cost Analyses demonstrated that a PFC with up to 15% RAP combined with an asphalt rubber or HiMA can provide good performance and be cost effective. Furthermore, the use of 25% RAP in combination with these binders was only limited by the asphalt rubber not meeting the specification for permeability.

A comprehensive review on the plant-mixed cold recycling technology of emulsified asphalt: Raw materials and factors affecting performances