Recycled Asphalt Pavement Materials Research Articles

Investigation of Recycled Asphalt Pavement Materials Treated by Refined Crushing and Screening Process: Comparison with Conventional Methods

Investigation of Recycled Asphalt Pavement Materials Treated by Refined Crushing and Screening Process: Comparison with Conventional Methods

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.

Effect of Mechanical Properties on Performance of Cold Mix Asphalt with Recycled Aggregates Incorporating Filler Additives

The utilization of recycled asphalt pavement in the construction and maintenance of flexible pavement with asphalt emulsion is advantageous and environmentally friendly. It saves energy due to zero heat loss during the mixing and laying of pavement compared to hot mix asphalt. Recycled asphalt pavement (RAP) is a sustainable material in place of virgin aggregates in road construction. The focus of this study is (i) virgin aggregate production, (ii) the utilization of waste material (additive), (iii) reducing the production temperature, and (iv) recycled RAP material in the pavement. This paper attempts to create a venue for using RAP greater than 50% during pavement construction. Cold mix asphalt (CMA) containing 0%, 50%, and 100% RAP materials with different dosages of cement, fly ash, and Stabil-road at 1%, 2%, and 3% of dry aggregate weight were used for ascertaining the mechanical and volumetric properties of mixtures. The mechanical properties for CMA samples, such as stability, tensile strength, moisture susceptibility, stiffness modulus, and the abrasion loss of CMA samples, were evaluated with and without RAP incorporation. Present laboratory studies revealed that a cold mix containing 50% RAP materials produced a higher stability value than the control mix, irrespective of the types of additives in its contents. All the additives can potentially resist moisture damage in the mix. Also, a significant improvement in the resilient modulus was considered for RAP-incorporated mixtures with the additives.

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.

The influence of recycled asphalt pavement materials on low and intermediate fracture behavior of asphalt concrete (AC) after exposing to different thawing and freezing periods

The effects of compaction process, mixture type and environmental conditions on mode I cracking resistance of asphalt concrete (AC) materials was investigated experimentally. To do that, a large number of edge notched disc bend specimens containing 0, 25 and 50% recycled asphalt mixture (RAP) material and exposed to different numbers of thawing and freezing cycles (0 to 10 cycles) were fractured. The critical values of stress intensity factor and fracture energy indexes were obtained for the AC mixtures at three test temperatures of −25, 0 and + 25 °C. Based on the results, the fracture resistance capacity of the AC mixture was decreased by increasing the RAP content, number of thawing/freezing cycles and decreasing the test temperature. The effect of thawing/freezing cycles on decreasing the cracking resistance was more pronounced for the first cycles and the variations of fracture toughness and fracture energy values with the numbers of thawing/freezing cycles showed a plateau form for higher numbers of cycles. The fracture curves of the tested samples manufactured using the Gyratory compaction method was upper than the related curves of samples made by Marshall compaction method. The sensitivity of fracture results (i.e., gradient of reduction in the fracture resistance versus freeze/thaw cycles) became low by increasing the test temperature.

Effect of Temperature on Interface Characteristics between Compacted Recycled Asphalt Pavement and Geogrid

This study presents an experimental investigation of the interface behaviors of recycled asphalt pavement (RAP) reinforced with biaxial geogrid. A series of direct shear tests were conducted on compacted RAP specimens with or without geogrid under different normal stresses (50, 75, and 100 kPa) and test temperatures (0, 20, and 35°C) using an improved temperature-controlled direct shear apparatus. The effect of test temperature on interface shear strength and strength parameters was systematically examined. Test results showed that shear stress versus shear displacement curves of RAP specimens with or without geogrid show strain-softening characteristics. Under the same normal stress, the curve of the reinforced RAP sample with a high temperature is always below that with a low temperature, which indicates the test temperature has an adverse effect on the strength of the reinforced RAP sample. The shear strength consistently increases linearly with the increase of applied normal stress for all RAP samples. The shear strength with geogrid is greater than pure RAP under a given test temperature and normal stress. The shear strength of RAP samples at lower test temperatures is higher than that at a higher temperature. Both apparent adhesion intercept of RAP-geogrid and cohesion of RAP show a decreasing trend with the increase of the test temperature and tend to be stable with increasing temperature. Both the interface friction angle of RAP-geogrid and the internal friction angle of RAP slightly decrease with the increase of test temperature. For RAP-geogrid, the value of the apparent adhesion intercept is higher than that for sand and gravel with geosynthetics. The interface friction angle is close to that of sand and gravel with geosynthetics. Therefore, RAP material can be well used as alternative backfill materials in lieu of natural aggregates such as gravel and sand in geotechnical applications.

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.

Characterization of Recycled Asphalt Pavement Materials for Use in Hot-Mix Asphalt Mixes

Abstract The use of recycled asphalt pavements (RAPs) has been a common practice in recent times owing to the sustainability aspect as well as the cost savings. Characterization of RAP is a challenging task because of the high variability in RAP, which can be associated with several factors such as the source, milling method, and processing techniques. RAP material characterization requires a sophisticated material testing facility and is time-intensive. A round-robin test organized by the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM) Technical Committee 237-SIB has resulted in a new characterization protocol that is primarily intended for new construction, rehabilitation, and maintenance requirements of pavements utilizing RAP. The current study has adopted the RILEM recommendations to categorize RAP from various sources using basic tests: gradation and cohesion. RAPs obtained from seven sources, including artificially aged RAP, were investigated in the current study, and the tests were carried out on 100 % RAP. The allowable proportion of RAP that could be used for the hot-mix asphalt mix design was computed for all seven RAP sources using the blending charts. Furthermore, significant correlations were obtained between the allowable RAP content and the cohesion indices. The observations from this study suggest that basic tests, such as cohesion tests, can reduce the need for complicated test procedures to some extent and can be very advantageous for extensive field projects using RAP.

Quantifying the Degree of Binder Availability in Recycled Asphalt Mix Design Using White and Black Rock Mixes

Quantifying recycled asphalt binder availability in recycled asphalt pavement (RAP) mix design is very essential, as the widely adopted 100% RAP binder availability assumption in RAP mix design never holds correct. Depending on the mix production condition, recycled binder stiffness, and virgin binder properties, the degree of binder availability in the mix is always partial. The present study proposes a simple procedure to estimate the degree of recycled binder availability in RAP mix design. In the proposed methodology, the designer needs to compare optimum binder content of bituminous mixes prepared using white rock aggregate gradation and virgin aggregates, along with mixes designed by blending black rock gradation and virgin aggregates blended in proportion to achieve the target white rock gradation. The binder content in the RAP fraction used in the blending exercise was determined using ignition oven method. RAP mix designs were performed for RAP material collected from two different sources, and design was performed for three mixing durations in a laboratory pug mill—60, 120, and 180s. The mixes were prepared with 50% RAP incorporation level. RAP material was conditioned at 110°C for 2 h, whereas virgin aggregates were superheated to 175°C. Using the methodology proposed, RAP binder availability was found to vary between 92.5% and 96.6% for softer RAP material, 75.9% to 91.5% for mixes incorporating stiffer RAP. With increasing mixing time, even though the total active binder content did not change significantly, a mixture performance test quantified the implication of increased RAP binder availability in mixes. A higher degree of binder activation resulted in mixes being rut resistant, while the same mixes exhibited relatively higher cracking susceptibility.

Structural model performance and reinforced pavement technology in unstable location in the south of the Republic of Benin (West Africa)

The main cities in West Africa have been characterized by the development of infrastructure in past decade. This paper examined the performance of the soil and of pavement in Benin (West Africa). In this research, four objectives have been adopted in-depth on the performance characteristics of West African soil and aim to (i) accessing characteristics of soil types in the region; (ii) assessing the performance of these soils with 3% of lime, with the combination of 3% lime and 3% cement; (iii) using geogrid to evaluate the performance of pavement on clayey soil; (iv) proposing a new pavement model strategy considering economic aspects of construction. The methods used to examine these objectives are experimental tests according to standard French test. Design of flexible pavement is largely based on empirical methods according to the transport research laboratory (TRL) Note 31 with WinJulea software and compared with a designed and evaluated pavement structure adopting the center experimental of building and public works (CEBTP) method. In addition, the research quantified the percentage of biaxial geogrid impacting the performance of pavement in a diminishing perspective. Flexible pavements (with and without geogrids) were built and subjected to 127.49 ​kN load applications. This paper firstly reveals the unstable and stable areas in southern Benin (West Africa) with the presence of clay soil, and secondly reveals that the use of 3% lime and the combination of 3% lime and 3% cement are limited in subgrade. In addition, the TRL Note 31 with WinJulea software is more economical while the one of CEBTP highly performs. More so, the paper confirms that the use of biaxial geogrid reinforcement in pavement structures highly reduces the construction cost. As conclusion, firstly, the pavement made from the recycled asphalt pavement materials with biaxial geogrid in subgrade is the best in the clayey area.

Effect of recycled aggregate gradation on the degree of blending and performance of recycled hot-mix asphalt (HMA)

The application of recycled asphalt pavement (RAP) could bring huge economic and environmental benefits. Until now, the role of RAP gradations has not been fully considered in the design. Therefore, this study attempted to investigate the effect of recycled aggregate gradation on the degree of blending and performance of recycled HMAs. Six groups were designed, including the three experimental groups mixing with different particle sizes of RAP, designed as “partial blending groups”, a control group designed as “full blending group”, and two further groups designed as “no blending groups”. Then, the volumetric parameters, degree of blending, water stability, high and low temperature performance of each group were evaluated. It can be found that with the addition of finer particles of RAP materials, more RAP binder was activated, and the DoB in recycled HMAs increased. However, despite the DoB increased, the water stability and thermal cracking performance of recycled HMAs containing fine particles of RAP were still worse than that of recycled HMAs containing coarse particles of RAP, which may be due to the unfavorable distribution of RAP binder in these mixtures. Especially, the low temperature performance of recycled HMAs containing 32% 0–5# RAP was only 1.638 MPa, even close to that of the “no blending group”. In addition, the high temperature performance showed the opposite trend. The shear strength of recycled HMAs increased with the addition of finer particles of RAP. Overall, the fine particles of RAP were recommended to avoid use in the cold and rainy regions.

Effect of saw dust ash (SDA) and recycled asphalt pavement (RAP) in the bituminous concrete

The present study deals with the effect of saw dust ash (SDA) as an alternative filler and recycled asphalt pavement (RAP) material in bituminous concrete (BC). Several physical and chemical experiments were performed to characterize the SDA and RAP material according to the standard specifications. To execute such study, virgin aggregate and RAP were blended as 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 25 :75, 0 :100% and 8% SDA was used as filler to prepare the BC mix. In this study, 2% ordinary Portland cement (OPC-43) was utilized to prepare the control mix. However, to quantify the performance of RAP and 8% SDA in the BC mix, several Marshall properties, and the performances criterion against various distress (rutting, cracking, and moisture susceptibility) were conducted. The experimental results reveal that 60% RAP-8%SDA enriched BC mix shows superior rutting, cracking, and moisture resistance potency with the highest structural integrity of 82.10%. Since the dominant percent of calcium oxide mineral present in that filler reacts with the dipolar carboxylic acid which already exists in an aged binder and thus the adhesive property of the binder in the BC is improved significantly.

Maximizing the Application of RAP in Asphalt Concrete Pavements and Its Long-Term Performance: A Review.

The use of recycled asphalt pavement (RAP) materials in asphalt concrete pavements (ACP) brings significant cost and environmental benefits. In practice, however, the amount of RAP readily available far exceeds the amount being utilized in ACPs, which still leaves the problem of excess RAP in the environment partially solved. Additionally, ACPs containing RAP materials (i.e., RAP-ACPs) can still be landfilled after they have reached the end of their useful life, which may restore the original environmental waste problem. To address these, researchers have demonstrated different ways to maximize the application of RAP in ACPs. Among them, the use of RAP in pavement preventive maintenance (PPM) treatments and the repeated recycling of RAP-ACPs (i.e., RnAP) are specifically discussed in this review. It is envisaged that, by promoting these two practices, the application and benefits of RAP can be further maximized to improve sustainability. This review also discusses the long-term behavior of RAP-ACP, which is crucial to inspire confidence in the wider application of RAP in ACP. Studies on RAP-PPM have shown that virgin PPM treatments can successfully accommodate RAP materials by adjusting their mix design. So far, research on RnAP has been limited to how multiple-recycling affects the performance properties of the blends, showing improvements in rutting resistance and moisture susceptibility but little effect on linear viscoelasticity and cracking. Overall, the lack of sufficient research is considered to be the biggest challenge in facilitating the implementation of these two sustainable RAP technologies. Little or nothing is known about the bonding mechanisms between RAP and fresh PPM binders, the molecular and chemical changes in RnAP binders, or the functional performance characteristics, actual pavement performance, and long-term performance of both RAP-PPM and RnAP blends. An understanding of these aspects is very relevant to maximize and continue the beneficial reuse of RAP in ACPs while safeguarding human and environmental health.

Geri Dönüştürülmüş Asfalt Kaplama Malzemesinin Betonda Kullanımı Üzerine Bir Araştırma

Doğal kaynaklarımızın giderek yok olması, agrega temini için yeni kaynakların araştırılması ve bitüm malzemesi konusunda dışa bağımlı olunması, yıpranmış asfalt kaplamaların yeniden kullanımı konusunda teşvik edici olmaktadır. Ayrıca asfalt kaplamaların ekonomik açıdan yüksek değere sahip olması da kaplamaların yeniden kullanılabilirliği üzerinde çalışılması gerektiği düşüncesini doğurmaktadır.
 Bu çalışmada; yol inşasında kullanılan asfalt kaplamanın geri dönüştürülmesi ve geri dönüşüm yöntemlerinin incelenmesi amaçlanmıştır. Ayrıca geri kazanılmış asfalt kaplama malzemesi üzerine yapılan bilimsel çalışmalar incelenmiştir. Çalışma sonucunda; geri dönüştürülmüş asfalt kaplama agregalarının betonun basınç dayanımı ve akışkanlık değerlerinde azalma, tuza ve dona karşı dayanımlarında ise artış meydana geldiği görülmüştür. Bunun yanı sıra atık asfalt kaplamaların ekonomiklik, sürdürülebilirlik ve enerji tasarrufu yönünden oldukça değerli bir atık olduğu tespit edilmiştir. Ayrıca yıpranmış, bozulmuş eski asfalt kaplamaların yeniden kullanımı çevre korunumu açısından oldukça önem arz ettiği anlaşılmıştır.

Experimental Study on Characterization of Bituminous Mixes Containing Recycled Asphalt Pavement Materials for the Construction of Surface Course in Flexible Pavements.

Abstract: In India majority of the road network has a bituminous top surface made of naturally accessible road materials and bitumen. This process has resulted in a faster depletion of road aggregates as well as an increase in gas emissions into the atmosphere, resulting in pollution. The most promising approach for achieving sustainability in road building will be to use low emission bitumen, re-use aggregates obtained from milling, and material reclaimed from the old distressed pavement to create or rehabilitate new roads. In this regard, the current study seeks to evaluate and compare the physical and engineering features of bituminous mixes including RAP material in various percentages for the construction of the surface course in flexible pavements through thorough laboratory investigations. According to the results of laboratory experimental tests, a bituminous mix containing recycled asphaltic pavement (RAP) material exhibits better Marshall Properties, performance properties, and volumetric properties, and meets all of the requirements of the bituminous concrete (BC) layer as per standard specifications. According to the findings of the study, it is possible to create an acceptable grade bituminous mix with a high RAP component that meets the needed volumetric characteristics and performance parameters for the construction of flexible pavements under current traffic and environmental circumstances. Keywords: RAP, Sustainable roads, Volumetric properties, Marshall Properties, ITS.

Evaluation of Engineering Properties of Recycled Aggregates and Preliminary Performance of Recycled Aggregate Base Layers

Although there have been several studies about using recycled aggregates to construct recycled aggregate base (RAB) layers, there is a lack of information about the effects of gradation of recycled concrete aggregate (RCA) materials on the performance of such layers. There is also limited information available regarding the use of RCA and recycled asphalt pavement (RAP) materials together in RAB layers. In this study, three test cells were constructed with RAB layers using two different RCA materials with different gradations and a blend of RCA and RAP materials, and another cell was constructed with a natural aggregate base layer. Physical characteristics of the base layer aggregates were determined, and resilient modulus (MR) tests were performed. A series of falling weight deflectometer (FWD) tests were performed in the field, and changes in air and soil temperatures over time were monitored. This paper contains detailed information about the evaluation of the engineering properties of recycled aggregates and the preliminary performance of the constructed RAB layers.

Evaluation of the Effect of RAP and Lime on Geotechnical Properties of Clayey Soil

Abstract: Road network plays a large role in the rapid development of the economy of a country, providing connectivity to remote areas for various transportation activities. India ranks second in the world in terms of length of road network after the United States. The major road network in the urban locality consists of bituminous pavements periodically resurfaced during maintenance. From the milling process, reclaimed asphalt pavement (RAP) is obtained. Additionally, RAP can be used for the utilization of recycled asphalt pavement (RAP) materials in subgrade soil. Reclaimed Asphalt Pavement (RAP) is being used in this case study to stabilize the subgrade soil collected from Crop Research Center (CRC), Govind Ballabh Pant University, Tanda Range, Uttarakhand (29°01'09.7"N, 79°28'55.9"E). To conduct the experimental program, a variable amount of RAP percentages viz., 5, 10, 15, and 20%, and different percentages of lime i.e., 2, 4, 6, and 8% were mixed with natural soil. Based on gradation, Standard Proctor Test (SPT), Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and Specific gravity, the characteristics of RAP-soils with added lime were evaluated. For soil mixture including 10% RAP and 4% lime, a maximum MDD of 19.04 and a percentage increase in compaction of 11.93% was observed. OMC value was observed as 11.35%, which further decreased as RAP content increased. Due to RAP containing coarse aggregate, a higher CBR value was obtained due to the harder sample surface. For all soil mixers of 15% RAP and 4% lime, unsoaked CBR and soaked CBR values were found to be 31.39% and 18.69% respectively. Percentage increases in their respective CBR values were 868.83% and 662.86%. for every percentage of lime variation, maximum CBR was obtained at 15% RAP, and maximum CBR value for soaked CBR was obtained for soil with 15% RAP and 2% lime, whereas for unsoaked CBR, it was obtained for soil with 15% RAP and 4% lime. Maximum UCS values of 412.45 kN/m2 , 606.81 kN/m2 and 857.62 kN/m2 were observed on 3rd, 7th and 14th days for soil mix with 15% RAP and 4% lime, with percentage increase of 291.17%, 249.40% and 387.78% respectively. Based on the results of the study, RAP materials can be effectively used in the soil subgrade, sub-base, and base of flexible pavements, reducing the cost of construction. Keywords: Reclaimed Asphalt Pavement (RAP), Lime, CBR, SPT, UCS, OMC, MDD.

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.

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%.

A comparative life cycle assessment study with uncertainty analysis of cement treated base (CTB) pavement layers containing recycled asphalt pavement (RAP) materials

Cement Treated Base (CTB) is a mixture of aggregates, Portland cement and water that hardens through curing to create a strong and durable material that is widely used as a base course in road pavement construction. This layer can be used in either flexible or rigid pavements, and the range of possible materials used in CTB has been recently expanded to include Reclaimed Asphalt Pavement (RAP). Despite the considerable use of CTB in road pavements, there is only limited information regarding its environmental performance, especially when RAP is added. This paper presents a comparative assessment of the environmental performance of sixteen CTB mixtures, with and without RAP, with different cement percentages, different production methods and different recycling procedures. The thickness of the pavement layers required for a given purpose was calculated for each CTB mixture using a pavement design tool (KENPAVE®) and data obtained from laboratory tests (both primary and secondary data). The environmental sustainability assessment used the Life Cycle Assessment (LCA) methodology combined with uncertainty analysis. The functional unit (FU) consisted of a road pavement structure corresponding to a 1 km stretch of 22 m wide major urban road including a CTB layer that would enable a specified volume of traffic to drive safely over a 20-year lifespan. A cradle-to-gate system boundary was adopted. The characterisation modelling to quantify the potential environmental impacts of each pavement structure was carried out using the CML v. 4.4 2015 impact assessment method at midpoint level. The analysis shows that having higher percentages of cement in the CTB mixture allows a thinner base-course layer, thereby compensating for the increased environmental burdens related to the production of cement and transport. The uncertainty analysis shows that including RAP in the mixture leads to greater spread in the LCA results. Further, the results of a real case study show, regardless of the CTB composition, that mixed-in-place production substantially reduces the environmental impacts compared to central-plant-mixed production. Overall, this research increases the knowledge on the environmental performance of CTB layers containing high percentages of recycled materials and produced using alternative construction methods.