Recycled Asphalt Pavement Content Research Articles

Valorization of petroleum sludge as rejuvenator for recycled asphalt binder and mixture

The production of new pavements involving recycled asphalt pavement (RAP) is beneficial for preserving petroleum asphalt and natural aggregates. However, increasing the RAP content raises performance concerns in new pavement, thus necessitating the use of rejuvenators. This research examined the potential of using petroleum sludge (PS) as a rejuvenator for RAP recycling. Gas chromatography-mass spectrometry (GCMS) detected the PS hydrocarbons involved in rejuvenation. The dynamic shear rheometer (DSR) provided the rheological data of rejuvenated binders. The rheological data were subsequently processed using response surface methodology (RSM) to develop rutting and fatigue models. RSM was also employed to model the Marshall and volumetric properties of the asphalt mixture. Atomic force microscopy (AFM) of PS rejuvenated RAP binder revealed a new microstructure containing protrusions that resembled the morphology of lightweight bitumen fractions. These rejuvenating effects were attributed to lightweight hydrocarbons of PS, which supplement the maltenes fractions in aged asphalt. The multi-objective optimization provided the RAP and bitumen content of 90% and 4.79% to meet the required PWD specifications.

Enhancing high-content recycled asphalt pavement regeneration: A laboratory separation and treatment approach

The escalating costs of aggregates and stringent sustainable development policies have emphasized the significance of effective high-content recycled asphalt pavement (RAP) regeneration technology. This study aims to present a novel laboratory separation and treatment approach for RAP materials, ensuring optimal performance of high-content RAP recycled asphalt mixtures. The proposed method is compared against factory-separated RAP materials in terms of agglomeration evaluation and mixture performance comparison. High- and low-temperature performance of the recycled asphalt mixture were evaluated through wheel tracking and trabecular bending tests. Furthermore, the moisture sensitivity of the recycled mixture was studied through immersion Marshall and freeze-thaw splitting tests. The uniformity and fusion between aggregates and asphalt in the recycled asphalt mixtures were meticulously analyzed using advanced techniques such as Scanning Electron Microscope and industrial Computed Tomography scans. The laboratory separation method encompasses flexible separation for 5–10 mm RAP materials and rigid separation for 10–20 mm RAP materials. Notably, the laboratory separation methods proved more effective in removing aged asphalt from the surface of 10–20 mm RAP materials compared to factory separation, thereby enhancing the adhesion between aggregates and asphalt and ensuring a more uniform recycled mixture. Although the dynamic stability of recycled asphalt mixture was reduced using laboratory separation, it still meets the requirements of relevant specifications. Moreover, the low-temperature maximum flexural tensile strain of the recycled asphalt mixture increased by 16%, with the residual stability and tensile strength ratio rising by 1.33% and 2.69%, respectively. Compared with the factory separation method, the laboratory separation method reduces the porosity percentage of the recycled asphalt mixture cross-section by 3.47%. Overall, the laboratory separation method for RAP materials provides valuable insights for enhancing the factory processing of RAP materials, contributing to the successful application of high RAP content regeneration technology in the pursuit of sustainable and cost-effective road construction practices.

Asphalt pavement pothole repair with recycled material and preheating: Laboratory and field evaluation

Asphalt pavement pothole repair with hot-mix asphalt (HMA) is one of common maintenance activities for transportation agencies, which requires considerable energy use and generates greenhouse gas emission (GHG) for production of HMA. This study investigated mechanical performance and environmental impact of an innovative pothole repair method using recycled asphalt pavement (RAP) and preheating. According to the common failure modes of asphalt patch, comprehensive laboratory tests were conducted on the lab-made and field-cored specimens, including indirect (IDT) strength, interface bonding strength, and abrasion resistance at dry, freeze-thaw, and pore pressure conditions. Based on laboratory testing results of the HMA with 0%–50% RAP contents, HMA with 30% RAP was selected for pothole repair in the field test section because it can lead to satisfactory moisture resistance and comparable interface bonding and abrasion resistance with traditional HMA. After repair, field cores were collected for additional laboratory analysis. The results show that moisture resistance of the patching materials decreased with the increase of RAP content. The freezing thaw (FT) effect was found to cause more degradation in IDT and interface shear strength than dynamic pore water pressure simulated in moisture induced stress tester (MIST), while the pore water pressure caused more abrasion loss of patching material. On the other hand, preheating the pothole before repair was found to be effective in enhancing mechanical performance and durability of asphalt patch under various environmental conditions. With the application of preheating, asphalt patching repaired by HMA with 30% RAP can achieve comparable or better performance than that made with traditional HMA, while reducing energy consumption and carbon emission.

Dynamic mechanical response of hot central plant recycling asphalt pavement considering the rutting deformation of existing structure: pollution reduction and durability promotion.

In the pavement industry, there is a pressing need for the reuse of recycled asphalt pavement (RAP) materials. However, the rutting deformation in existing pavement structures is often overlooked in the design of recycled asphalt pavement, which hinders long-term performance prediction and durability assessment. This study examined the viscoelastic properties and fatigue performance of recycled asphalt mixtures. Different combinations of surface layers with varying RAP contents and binder layers with different rutting damage levels were designed. A 3D-Move Analysis model was used to analyze the dynamic mechanical response of these structures under moving loads. Results showed that the stiffness of recycled asphalt mixture increased with the RAP content, but the fatigue performance decreased by 39.4% when the RAP content reached 50%. Incorporating 50% RAP in the surface layer can reduce the compressive stress caused by vehicle loading, thus reducing the vertical compression strain and permanent deformation of the asphalt layers and the subgrade. However, the surface layer with higher RAP content is exposed to intense alternating tensile and compressive strains, leading to poor fatigue durability. The dynamic mechanical behavior of recycled asphalt pavement structures was found to be significantly impacted by the characteristics of the binder layer. The lower dynamic modulus of the binder layer (e.g., 18 mm rutting depth) can lead to more deformation and an increased risk of fatigue cracking. Moreover, the dynamic performance of mixtures with 0% and 50% RAP in the surface layer is even more affected by changes in the binder layer properties. It is recommended to consider the design of dynamic modulus combinations of existing binder layer materials and surface materials with higher RAP, in order to increase the utilization of RAP for high-grade highways and improve the stress distribution to enhance their durability.

Performance evaluation of WMA mixtures with RAP

Nowadays, asphalt industries are seeking for new methodologies in order to minimize global warming and emission of greenhouse gases. One of the solutions found out was the use of warm mix asphalt (WMA) technology which allows reduction in asphalt mixing, working and compaction temperature. WMA reduces the desired temperature in comparison with hot mix asphalt by 20–40°C. In addition to this issue, the lack of superior quality natural aggregate resources everywhere around the world, it is essential to use the available natural resources efficiently along with the available construction and demolition waste such as recycled asphalt pavement (RAP) if possible, without compromising in the performance of the mixtures. In this study, reclaimed asphalt pavement was used as partial replacement for conventional aggregates and binder. The RAP contents of 0%, 25% and 50% were considered. Zycotherm was used as warm mix additive which improves the pavement moisture resistance by serving as an anti-stripping agent. The mixtures were prepared with HMA @ 130°C, HMA @ 160°C, WMA @ 130°C and all these three mixtures with partial replacement with RAP. The RAP material with 0, 25 and 50% replacement was adopted for both HMA and WMA for DBM grade 2 course. Zycotherm was added by 0.1% by weight of binder in both HMA and WMA mixes. The prepared test specimens were tested for Marshall and indirect tensile strength (ITS) test. The test results indicated that the WMA blend prepared using 0.1% by the weight of binder content showed good results compared to the hot mix asphalt @ 130°C. The indirect tensile strength ratio (TSR) of mixes containing RAP is found to be higher when compared to the mixes without RAP indicating lower moisture susceptibility of the mixtures. This study demonstrated the possible use of RAP in WMA mixes with better performance than HMA.

Comparative cracking resistance‐cost study for the hot mix asphalt (HMA) mixtures made of natural and recycled asphaltic materials

AbstractCracking performance of control and RAPed hot mix asphalt (HMA) mixtures was studied under low and medium temperatures. The effects of recycled asphalt pavement (RAP) content (0 and 50%), compaction method, and temperature (−20, 0 and +20°C) on KIf and KIIf were investigated. Cracking resistances of both modes showed similar trends. The fracture toughness of RAPed mixture at +20°C was higher than the control mixture. However, at −20°C, KIf and KIIf obtained from the RAPed mixture were about 22% lower than control mixture. A cost analysis was performed to compare the manufacturing costs of both mixtures. Accordingly, the cost of HMA mixture containing 50% RAP was 26% less than the control mixture. The proposed life‐cost index in the RAPed mixture was 10, 25, and 100% greater than the control mixture at −20, 0, and +20°C, respectively. Temperature and RAP content had the most important impacts on fracture toughness and cost, respectively.

Effect of waste brick powder rich in SiO2 on the physical and mechanical properties of Portland cement concrete containing coarse recycled asphalt pavement aggregates (RAP)

Promoting sustainable development involves minimizing the consumption of natural resources, including aggregates, without compromising the performance of concrete. In Algeria, the rapid expansion of road projects results in substantial quantities of Recycled Asphalt Pavement (RAP) generated through milling and excavation of existing bituminous roads. To enhance the reuse of RAP aggregates in concrete, it is well-established that incorporating cement with silica-rich mineral additives can reduce energy consumption and enhance concrete efficiency and performance. This study focuses on investigating the potential use of waste brick powder (WBP) as supplementary cementitious materials (SCMs) to enhance the physical and mechanical properties of concrete containing coarse RAP aggregates. The substitution levels of WBP were set at 0%, 5%, and 15%, respectively, in blends comprising 0%, 25%, 50%, 75%, and 100% RAP aggregates. Various tests were conducted, including slump tests, compression strength analysis, ultrasonic velocity measurements, dynamic elastic modulus assessments, water permeability evaluations, and examination through Scanning Electron Microscope (SEM). The results indicate that blends containing 5% WBP demonstrate improved mechanical and physical properties compared to other blends. However, microstructural and elemental analyses reveal that the enhancement in Interfacial Transition Zone (ITZ) properties is not significant. It was also observed that water absorption decreased with increasing RAP content. Generally, a coarse RAP content of up to 50% proves to be suitable for achieving satisfactory performance in concrete.

The Influence of Using Sustainable Materials on Paving Cost of AL-Kut-Maysan Highway Using Cost-Benefit Analysis

Paving is regarded as one of the essential layers in the construction of a road since it directly affects traffic loads and is subject to environmental factors. As a result, appropriate asphalt mixes that can support the designed traffic loads and environmental conditions must be developed. From an economic and environmental aspect, recycling the waste from the old pavement is a good step in this regard. This paper comprises detailed laboratory work that tested the impact of using different recycled asphalt pavement (RAP) content in addition to 3% crumb rubber (CR). The (CR) is used as fine aggregate. The tests were evaluated based on the response of hot asphalt mixes (HMA). The objectives of this study are to analyze the volumetric or weight change in hot mix asphalt of the different percentages and then analyse the costs of Kut-Maysan Road as a case study in case of using the different percentages of RAP and CR. The results show that the cost analysis of using RAP reduces the cost of a produced ton of HMA. On the other hand, the use of CR increases the cost of producing HMA. Using 10% RAP reduces the cost of one ton of HMA by 0.64 $ while using 20% RAP reduces the cost by 1.10 $, and the cost is reduced by 1.41 $ when using 30% RAP. On the other hand, the use of 3% CR with 10% RAP increased the production cost of one-ton HMA by 1.47 $. While decreased by 0.82 $ with 20% RAP content and by 0.28 $ with 30% RAP.

Recycled asphalt mixture's discrete element model-based composite structure and mesoscale-mechanical properties

To investigate the composite structure and mesoscale-mechanical properties of recycled asphalt mixture, this paper has established discrete element models of recycled asphalt mixture with distinct characteristics of new aggregates, recycled asphalt pavement, new asphalt, and old asphalt according to the coarse aggregate contour characteristic parameters obtained by three-dimensional scanning. The composite skeleton and micro-crack development characteristics of recycled asphalt mixture were also studied. Finally, a method for determining the recycled asphalt pavement content was proposed considering the balance between rutting and crack resistance. The results show that the recycled asphalt pavement content has a negligible impact on the number of contact points of the composite skeleton, and this component primarily impacts the interfacial mechanical properties and contact of asphalt mortar. When the recycled asphalt pavement contents were 0 %, 15 %, 30 %, 45 %, and 60 %, the bottom stresses of the rutting specimens were approximately 0.6, 0.55, 0.5, 0.48, and 0.44 times of the bearing plate stress, respectively. In the composite skeleton, there were compressive, tensile, and tensile–compressive stresses at the contact point of coarse aggregates, the proportions of which were generally 70–80 %, 15–20 %, and 5–10 %, respectively. Shear cracks mainly occurred in the recycled asphalt pavement contact interface area, while tensile cracks occurred at the aggregate–aggregate contact interface, as well as in the asphalt mortar. The number of shear cracks was 50–80 % that of the tensile cracks. The maximum micro-crack length is 8–12 mm, and its minimum length is approximately 0.3 mm with micro-crack generally in the asphalt mortar. The results can provide a reference for the recycled asphalt mixture design to improve road performance.

An improved regression model to predict fatigue life of asphalt mixes incorporating low to moderate RAP contents

The research on the fatigue performance of recycled asphalt mixture and the establishment of its fatigue life prediction model is the key to its large-scale engineering application. The four-point bending fatigue tests of the fresh and recycled asphalt mixtures under the strain control of cyclic loading were conducted to investigate influencing factors on their fatigue performance and establish a new fatigue prediction model for RAP (recycled asphalt pavement). The hot recycled asphalt mixture samples of AC-16C were prepared by a uniform test design method, with the RAP content of 0%, 20%, 30%, and 40%. Through the fatigue test data of 20 groups of fresh asphalt mixture with 0% RAP and 40 groups of recycled asphalt mixtures with the contents of 20%, 30%, and 40% RAP, the simplified applicability of the fatigue prediction model in the current Chinese specifications for the design of highway asphalt pavement (JTG D50-2017, JTG model) and its parameters modification were studied, thereby an improved regression fatigue prediction model of recycled asphalt mixture is established on consideration of strain level, asphalt content, void ratio, and RAP mixing amount. This fatigue prediction model for recycled asphalt mixtures was proposed by modifying the parameters of the fatigue equation for new asphalt mixtures in the Chinese Highway Asphalt Pavement Design Code. (JTG D50-2017) and comparing the fatigue test data of the recycled asphalt mixture. The research results show that: The simplified JTG fatigue prediction model can effectively predict the fatigue life of fresh asphalt mixture with the content of 0% RAP, and the model parameter a is a constant of the order of 1016; The correction coefficients α and β of the initial bending stiffness modulus S0 and the Voids Filled with Asphalt (VFA) in the improved JTG model of the hot recycled asphalt mixture considering the RAP content are 0.006 and 0.0136, respectively; The model can accurately predict the fatigue life of recycled asphalt mixtures with the range of RAP content of 0–40%, with an average deviation of only 0.106, and has higher prediction accuracy for fatigue life measured close to or higher than 106 times. The average deviation of the predicted life of 20%, 30%, and 40 %RAP fatigue is only 0.057, 0.079, and 0.125. This paper’s indoor fatigue prediction model has higher accuracy for recycled asphalt mixture than the well-known traditional models.

Rice husk ash as an alternative soluble silica source for alkali-activated metakaolin systems applied to recycled asphalt pavement stabilization

Alkali-activated binders have been shown as a viable alternative do ordinary Portland cement. However, the development of lower carbon emission activators for this process is still a research-gap. The goal of this research was to analyze the stabilization of recycled asphalt pavement (RAP) mixtures with a metakaolin-based binder, alkali-activated by rice husk ash synthetized sodium silicate. Compaction, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were conducted in stabilized RAP mixtures, submitted to different curing periods and temperatures. Also, results were correlated with the porosity/binder content index. Compaction results showed a reduction in dry unit weight as the RAP content increased for non-stabilized mixtures and a non-linear behavior for stabilized ones. For the UCS tests, the increase in binder content led to an increase in strength for all mixtures. High curing temperatures prevented the efflorescence phenomenon, however reduced strength due to crack formation. XRD analyzes showed the formation of minerals rich in silica and alumina, indicating the formation of geopolymerization products. Finally, the porosity/binder index was shown to be a viable dosage method to predict the strength of stabilized RAP mixtures.

Effects of Filler Types and High RAP Content on the Ability of HMA to Withstand Moisture Damage

Using hot mix asphalt (HMA) and recycled asphalt pavement (RAP) simultaneously has many technological benefits. At all service temperatures, moisture damage is a hazard with these mixes. Thus, moisture's effects on mixtures' effectiveness were studied using experimental techniques, such as the tensile strength ratio (TSR). Four different ratios of RAP for the surface layer (20, 30, 40, and 50%)) were added to the asphalt mixture (HMA) to study as well as find the content Optimal RAP for both layers RAP through Marshall stability and hygroscopic resistance of asphalt mixtures through moisture damage is examined. The ratio (TSR) of the optimal RAP content mixture is compared with the asphalt mixture without RAP for three fillers and for both layers. The findings revealed a slight reduction in tensile strength of the (HMA) that does not contain RAP in contrast to the asphalt control mix containing the reclaimed pavement, where it was found that the percentages were slightly more and still higher than 80%. The results indicate that, in general, "Hot asphalt mixtures" containing RAP can be recommended for areas that experience moisture damage without worrying about environmental and natural resource restrictions.

Investigation of Waste Electrical Power Plant Oil as a Rejuvenating Agent for Reclaimed Asphalt Binders and Mixtures.

One of the main difficulties with employing recycled asphalt pavement (RAP) in hot mix asphalt (HMA) is bitumen aging; hence, the percentage of RAP in the HMA is limited. This research evaluates the rheological properties of the RAP binder and the performance of HMA containing high RAP content using waste engine oil (WEO) from an Electrical Power Plant as a rejuvenator. The rheological and microstructural properties of the RAP binder and rejuvenated RAP binder were determined in the laboratory. Both the recycled and rejuvenated recycled mixes were tested for Marshall stability, indirect tensile strength, dynamic modulus (E*), and flow number tests. The RAP binder was recovered using two different processes: rotavapor distillation followed by centrifugation (RCRD) and column distillation without centrifugation (RNCCD). The optimal WEO percentages for the RCRD and RNCCD recovery procedures were 0.5% and 3%, respectively. The Marshall test results revealed that adding WEO to the recycled mix enhanced its stability and flow compared to the control mix. The rejuvenated mix containing recovered binder from the RCRD recovery process was found to be better than the rejuvenated mix containing recovered binder from the RNCCD recovery process. The rejuvenated recycled mixes outperformed the recycled mix in terms of moisture resistance, which was evidenced by tensile strength ratio values of 0.88, 0.90, and 0.91 for the control and 0.5% and 3% WEO modified mixes, respectively. Finally, the results of dynamic modulus and flow number testing revealed that the rejuvenated mixes had a modest drop in both the dynamic modulus and flow number compared to the non-rejuvenated mix.

Influence of mobilized RAP content on the effective binder quality and performance of 100% hot in-place recycled asphalt mixtures

Hot in-place recycling (HIR) is a promising technique to consume 100% recycled asphalt pavement (RAP) for pavement surface rehabilitation. When RAP aggregates are incorporated in asphalt mixtures, a proportion of the RAP binder can be mobilized by the virgin binder or additive and achieve a homogenous binder blend, named “the effective binder blend.” There exist two major concerns of using 100% RAP in HIR mixes: 1. How much of the RAP binder can be mobilized to coat aggregates? 2. What are the contributions of the mobilized RAP binder to the performance of HIR mixes? This study firstly developed an approach to quantify the mobilized RAP content in HIR mixes. Afterward, the effective binder blends were prepared in the laboratory, based on the mobilized RAP and virgin asphalt percentage. Finally, the dynamic shear rheometer test and sessile drop method were adopted to characterize the effective binder qualities, while AMPT and Ideal-CT tests were utilized for mixture performance evaluation. Results showed that the mobilized RAP binder altered the binder qualities of the effective binder blends and also the effective asphalt content in HIR mixes. The binder qualities, including rheological properties and surface free energy, contributed to the different stiffness and cohesion of the effective binder blends in HIR mixes. However, the effective asphalt content proved to dominate the cracking resistance of HIR mixes.

Evaluating effect of rejuvenators on high RAP mixtures through laboratory performance tests and construction of field test sections

Although thirty-one US states utilize 20% recycled asphalt pavement (RAP) or greater in asphalt pavements, Iowa limits the usage of RAP to 20%, and 30% with a softer binder in the surface layer. Because high RAP mixtures can cause asphalt mixtures to stiffen due to the hardening effect of the aged binder, rejuvenators should be used to improve the cracking resistance of high RAP mixtures. Due to increasing demand for sustainable, and environmentally materials, two bio-based rejuvenators, Invigorate and Tufftreck, were considered for this study. To evaluate effect of rejuvenators on high RAP mixtures, field test sections were constructed in Cerro Gordo County, Iowa, 2020. The field test consists of six different sections with two rejuvenators and three different RAP contents of 22%, 34% and 45%. Performance grading (PG) of asphalt with rejuvenators adopted for the field test sections lowered both high and low temperatures of the virgin asphalt. Based on the eight cores for each test section, all six test sections with or without rejuvenators exhibited field densities between 93.6% and 95.2%, exceeding the minimum requirement of 93%. First, loose field samples were compacted at the laboratory for Hamburg wheel tracking test, semi-circular bending test, and disc-shaped compact tension test. Second, the laboratory test results were analyzed to determine if rejuvenators were effective in mitigating rutting, moisture damage and cracking. Based on the analysis of limited laboratory test results, Tufftrek was effective in lowering rutting and moisture damage whereas, for minimizing cracking, using a soft binder was most effective. Third, a condition survey on test sections was performed in one year after construction. Based on a condition survey of six test sections, no rutting was observed from all test sections, but some low-severity cracks were observed in sections without rejuvenators. Based on the limited condition survey results, it can be concluded that rejuvenators were effective in delaying the initiation of cracking.

Mechanical Properties of Cold Mix Asphalt (CMA) Mixed with Recycled Asphalt Pavement

From the perspective of sustainability and environmental concerns, the use of cold-mix asphalt (CMA) and recycled asphalt pavement (RAP) is more advantageous than the use of hot mix asphalt (HMA) and warm mix asphalt (WMA). Some researchers used a mixture of CMA and RAP to improve the mechanical properties of pavement and made it more economical. However, only a few studies have focused on using a high content of RAP—particularly 100% RAP—as the virgin aggregate. Therefore, this study aims to analyse cold-mix asphalt (CMA) using 100% recycled asphalt pavement (RAP) instead of virgin aggregate raw materials and to determine the best mixture for the production of environmentally friendly asphalt. It is necessary to investigate the performance of CMA mixed with RAP in terms of the resilient modulus, indirect tensile strength, fatigue and rutting resistance. In this study, the percentage of bitumen emulsions added is 2%, 2.5%, 3%, 3.5%, and 4%, along with 100% RAP material. The results indicate that the fatigue life of the RAP mixture increased by 49.34% with the addition of bitumen emulsion (BE) from 2% to 4%, while the wheel tracking test experienced a decrease in rutting depth along with an increase in BE dose of 4%, which was 9 mm. The mixture containing 4% asphalt emulsion has the best performance. The results suggested that increasing the BE dosage increases the resistance against rutting and fatigue.

Effect of RAP content on fatigue performance of hot-mixed recycled asphalt mixture

Although it was widely recognized that the addition of recycled asphalt pavement (RAP) would affect the fatigue performance of hot-mix recycled asphalt mixture (HRAM), a quantitative analysis of how it affected the fatigue performance so far still lacking. The purpose of this study was to identify the effect of RAP content on the fatigue performance of HRAM. For this, the self-developed rejuvenator was used to prepare specimens, then the pavement performance test and the four-point bending test were performed on the specimens to measure the fatigue performance of HRAM. In which, the specimens were prepared with RAP content of 0%, 30%, 40%, and 50% respectively, and the dosage of rejuvenator was 5%. Results suggested that with the addition of RAP, the dynamic stability of HRAM increased by 4.8% ∼ 34.5%, and the rutting deformation decreased by 5.22% ∼ 19.22%. The flexure-tension failure strength of HRAM decreased by 12.39% ∼ 35.66%, and the maximum failure strain decreased by 9.31% ∼ 27.02%. The splitting strength of HRAM decreased by 6.73% ∼ 17.45%, and the TSR decreased by 3.57% ∼ 4.36%. This indicated that the high-temperature performance of HRAM had a positive correlation with the content of RAP, while the low-temperature performance and water stability showed a decreasing trend. The principal component analysis model was established to quantify the influence of RAP content on pavement performance through related performance indexes. From the fatigue performance test, the fatigue life of HRAM was increased with the addition of RAP. The variance analysis under the interaction of multiple factors showed that the p-values for temperature and strain level were 8.14E-4 and 1.418E-20 respectively. The temperature and strain level had a significant effect on the fatigue performance of HRAM, and the strain level was the main factor affecting the fatigue performance, then the fatigue equation and fatigue limit equation based on the temperature factor was established. The effect of different factors on fatigue performance of HRAM was quantified by establishing the back propagation (BP) neural network model, it was found that the prediction value was very close to the test results, and the R2 was 0.98819, which indicated that the established model has good fitting accuracy. The effect of RAP content on pavement failure characteristics was studied by establishing the three-dimensional finite element model, it was found that the deformation depth in each direction had a good linear relationship with the RAP content, and the fitting accuracy was close to 1. A comparison study indicated that the fatigue equation and fatigue limit equation based on temperature factor can better describe the coupling effect between RAP content and fatigue performance, the principal component analysis model can better describe the correlation degree between RAP content and pavement performance, the finite element model can better describe the correlation degree between RAP content and pavement structure deformation.

Determining the maximum permissible content of recycled asphalt pavement stockpile in plant hot-mix recycled asphalt mixtures considering homogeneity: A case study in China

In engineering practice, recycled asphalt pavement (RAP) is often obtained from various sources and is mixed and stockpiled in a disorderly manner, which is defined as a hybrid RAP. Thus, the material component of hybrid RAP shows great variability, possibly preventing the plant hot-mix recycled asphalt mixture (RHMA) from achieving stable quality. To address this problem, the German TL Asphalt-StB 07 guideline introduced an approach for evaluating the variability of RAP stockpile characteristics and subsequently determined the maximum permissible content of RAP in RHMA for different pavement layers based on the variability of the RAP stockpile. This study adopted this method in the Fuzhou–Yinchuan expressway maintenance project, Jiangxi Province, and reported a homogenization treatment measure for hybrid RAP. The results show that the material composition of hybrid RAP is characterized by significant heterogeneity in gradation and asphalt content, effectively reducing the heterogeneity of hybrid RAP, and the maximum permissible content of RAP in the binder layer can be increased by approximately 10% in the mass of RHMA. The homogenization treatment scale should comprehensively consider indices such as efficiency, cost, and expected dosage. The results of this study can serve as a reference value for determining a reasonable content of hybrid RAP in RHMA and ensuring stable RHMA quality.

Investigation on the Effects of RAP Proportions on the Pavement Performance of Recycled Asphalt Mixtures

In-plant hot mix recycling technology has been widely used in maintenance and reconstruction due to its good recycling performance. However, the utilization rate of recycled asphalt pavement (RAP) is still only 10–25%, resulting in excessive accumulation and landfilling of RAP materials, which fails to promote the sustainable value of RAP in recycling. Therefore, this paper comprehensively explores the pavement performance of AC-20 ordinary asphalt recycled mixture and AC-13 modified asphalt recycled mixture with different proportions of RAP. The pavement performance test includes the dynamic modulus, rutting, dynamic creep, semicircular bending, and freeze-thaw splitting tests. The results show that, with the increase of RAP content, the mechanical properties and high-temperature properties of the two types of recycled asphalt mixtures are improved, the low temperature properties and moisture susceptibility properties are enhanced first and then weakened, and the best performance is reached when RAP content is 20 and 40%, respectively. According to the entire pavement performance test results, the influence of RAP content on AC-13 recycled modified asphalt mixtures is relatively smaller than that of AC-20 normal recycled asphalt mixtures. The addition of rejuvenator can improve the low-temperature performance and moisture susceptibility of recycled asphalt mixtures to a certain extent, especially for AC-20 ordinary recycled asphalt mixture. Consequently, it is suggested to use AC-13 recycled modified asphalt mixture in the upper layer of road; the RAP content can reach 20%, and rejuvenator can be used to improve its moisture susceptibility and low-temperature performance. AC-20 ordinary recycled asphalt mixture can be used in the middle surface layer, and the RAP content can reach 40%, or using AC-13 recycled modified asphalt mixture, the RAP content can reach 50%.

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.