Proportions Of Reclaimed Asphalt Pavement Research Articles

The Effect of Refined Separation on the Properties of Reclaimed Asphalt Pavement Materials

Refined separation not only controls the variability of reclaimed asphalt pavement (RAP), but also improves the mixing ratio of RAP and the quality of recycled asphalt mixtures. This study examines RAP treated with various refined separation frequency parameters, analyzes the variation rules and the variability of RAP aggregate gradation, asphalt content, asphalt properties, and aggregate properties, and calculates the maximum mixing percentage of coarse RAP material by using the gradation variability control method and the asphalt content variability control method. The results show that the variability of gradation and asphalt content of coarsely separated RAP is considerable, and a refined separation process significantly reduces the variability of gradation and asphalt content of RAP; the agglomeration of RAP decreases with an increase in the refined separation frequency; and the RAP agglomeration of three kinds of RAPs (E1, E2, and E3) under a refined separation frequency of 55 Hz reduces by 6.40%, 4.30%, and 4.30%, respectively, as compared with that of coarsely separated RAPs. The asphalt content of the refined separation RAP gradually decreases with an increase in frequency, and the asphalt content of E1 and E2 (55 Hz) was only 0.95% and 1.10%, respectively. The maximum percentage of RAP in recycled asphalt mixtures was calculated using the gradation variability control method and the asphalt content variability control method, respectively. The maximum proportions of RAP were 45% and 33% for A1 (0 Hz), respectively, and the maximum proportions of RAP for E1 (55 Hz) were all 100%. The results of the two methods show that the process of refined separation can increase the maximum proportion of blended RAP materials. They also demonstrate that the refined separation process can increase the maximum blending ratio of coarse RAP materials, thereby improving the quality of the RAP, increasing the proportion of RAP blending, and ensuring the quality of the recycled asphalt mixture. In conclusion, the refined separation process holds promise for maximizing the potential value of RAP and optimizing its recycling, environmental, and economic benefits.

Rheological characterisation of bituminous binder blends for the design of asphalt mixes containing high recycled asphalt content

Reclaimed asphalt pavement (RAP) is gained from road reconstructions; however, its usage is less optimised in Hungary and neighbouring regions, since on the project level the proportion of RAP in the asphalt mixes is only 10-15%. This is less than the recommended level in other EU countries. The higher usage of RAP provides economic and environmental advantages, decreasing the need for new materials, the transport cost, and the carbon footprint. The composition of the resultant bituminous binder blend is a critical element in the asphalt mix design with high RA content. This paper discusses the design of the resultant bituminous binder blend to provide performance and compliance characterisation. This paper also presents the complex rheological analysis of the base bitumen, the bitumen extracted from the RA and the bituminous binder blend, applying the dynamic shear rheometer (DSR) device. It was shown that for paving grade bitumen (B), polymer modified bitumen (PmB) and rubber modified bitumen (GmB), the addition of higher proportions of RA content is possible without compromising on the performance of the binder blend. With a carefully chosen paving grade bitumen it is possible to utilise up to 40% RA content. For the polymer modified bitumen, the limit of the RA content is 20%. For the rubber modified bitumen, the various proportions of RA contents showed no or negligible changes in the characteristics of the bitumen and the RA content can reach 30% in this case.

Characterization Of Soil For Road Shoulders Mixed With Reclaimed Asphalt Pavement Waste

The use of recovered asphalt pavement can reduce the amount of new bitumen and aggregates used in pavement construction and rehabilitation (RAP). RAP is a waste product that results from the removal of an old or damaged pavement surface. Although it has been used since the 1970s, and numerous recommendations for using RAP in the new mixture have been made, there are only a few research available. Because the materials used are recycled, it is also cost-effective and environmentally friendly. The purpose of this study is to characterize soil that has been blended with reclaimed asphalt pavement (RAP) for use on the local road shoulder. RAP is one of the rehabilitation procedures used to repair a deteriorated surface by removing the upper pavement and replacing it with new pavement. According to earlier study, mixing dirt with different materials improves the finding. The goals of this study are to establish the material qualities of soil and RAP, determine the optimum moisture content of material and degree of compaction for road shoulders, and determine the appropriate mix proportion of soil and RAP for road shoulders using the California Bearing Ratio (CBR) test. The Atterberg limit, liquid limit, and plastic limit for soil were evaluated on a sample of soil and RAP. For soil and RAP, a sieve analysis was performed. Compaction tests for soil and RAP were carried out with a mixture of 10S, 2S8RAP, 4S6RAP, 6S4RAP, 8S2RAP, and 10RAP, as well as CBR tests for soil and RAP. . According to the results of the laboratory test, 20% of RAP (8S2RAP) had a better-mixed proportion for the road shoulder. As a result, repurposed materials like RAP can be used as road shoulder material. 
 Keywords: reclaimed asphalt, reuse of Asphalt,

Research on failure strength master curve and fatigue performance of asphalt mixture containing high-proportion reclaimed asphalt pavement

Reclaimed Asphalt Pavement (RAP) is a cleaner production widely used in road engineering. In order to investigate the failure strength and long-term performance of high-proportion RAP asphalt mixture, this research prepared two high-content RAP recycled asphalt mixtures (50% and 60% RAP-RAM) with the gradation of AC-20 based on Styreneic Methyl Copolymer (SMC) regenerant. Firstly, indirect tensile (IDT) strength tests were implemented on 50% and 60% RAP-RAM at four temperatures and six loading rates. Secondly, IDT fatigue tests at six stress levels were carried out. The relationships of strength and temperature, strength and loading rate were obtained based on strength test results. The master curve model of indirect tensile strength and loading rate of high-proportion RAP recycled asphalt mixture was established by linear and Sigmoidal functions. On the basis of the Sigmoidal strength master curve equation, the fatigue stress ratio was calculated. Finally, this paper established the fatigue equation of the high-content RAP recycled asphalt mixture based on the fatigue stress ratio. The analysis results show that 50% and 60% RAP-RAM based on SMC regenerant show favorable strength and fatigue properties. In addition, increasing the proportion of RAP improves the strength of the mix while reducing the loading rate sensitivity of strength. However, the fatigue performance of the mix reduces by increasing RAP content. The fatigue equation based on the fatigue stress ratio takes the factors of temperature and loading rate into account, reflecting the mix's fatigue performance more realistically. The strength and fatigue performance results verify the reliability of the high-content RAP recycled asphalt mixture based on SMC regenerant and provide a reference for the effective utilization of RAP which can generate environmental benefits of saving aggregate and asphalt and reducing energy consumption and carbon emissions.

A High Proportion Reuse of RAP in Plant-Mixed Cold Recycling Technology and Its Benefits Analysis

The concept of the “no-waste city” has focused increasing attention on the recycling of solid waste. One such waste is reclaimed asphalt pavement (RAP), which is generated during road maintenance. The potential to reuse this resource has attracted extensive attention in recent years. This paper explores this concept via a case study of the reconstruction of two sections of the Beijing-Taipei Expressway (from Bengbu to Hefei, sections K69–K69 + 500 and K69 + 500–K69 + 900). The upper base layer of one section was paved with a novel mixture of emulsified asphalt, mixed with a high proportion of RAP made using plant-mixed cold recycling technology (EAPM-HPRAP). For comparison, the upper base layer of the other section was paved with a conventional large-stone porous asphalt mix (LSPM). The proportions of the components of EAPM-HPRAP were optimized via laboratory-based proportioning design followed by proportioning verification. The results showed that the high-temperature stability, water damage resistance and pavement strength of the EAPM-HPRAP met the specifications of relevant engineering standards. Next, the economic and environmental benefits of this novel approach were estimated. The approach was estimated to save CNY (China Yuan) 1.5–1.8 million in engineering costs per km of road (roadbed width = 27.5 m) and CNY 158–189 million for the whole project (105 km in length). It was also estimated to reduce energy consumption equivalent to 67.41 tons of standard coal per km. Further calculations showed that every km of pavement could reduce CO2 emissions by 176.6 tons, SO2 emissions by 0.6 tons, NOX emissions by 0.5 tons, ash emissions by 17.6 tons and soot emissions by 1.0 tons compared with conventional methods. For the whole road section, this is equivalent to reducing CO2 emissions by 18,543 tons, SO2 emissions by 60.2 tons, NOX emissions by 52.5 tons, ash emissions by 1848 tons, and soot emissions by nearly 105 tons. In summary, it is feasible for EAPM-HPRAP to be used as the upper base layer in highway renovation projects. It reduces the need to mine new ores and allocate land to RAP storage, which is associated with soil and water pollution due to chemical leaching from aged asphalt. This approach provides great economic and environmental benefits compared with the use of conventional pavement technology.

Laboratory investigation of bituminous concrete using Reclaimed asphalt pavement and waste Engine oil

The conventional method of preparing bituminous mixes incorporating bitumen and virgin aggregates requires a huge amount of energy to produce along with environmental concerns. In pavement industry, the usage of Reclaimed Asphalt Pavement (RAP) material is growingup dueto financial considerations and the necessity of environmental conservatism. The effective utilisation of reclaimed asphalt pavement waste in bituminous pavement can overcome its disposal issue as well as it is cost effective too. Whereas replacing RAP with virgin aggregates have some drawbacks related to workability and overall quality of the pavement. Reclaimed Asphalt Pavement is subjected to environmental degradation hence affected due to aging. Long term aging effect is very prominent in reclaimed asphalt pavement materials. Hence, it becomes stiff and difficult to employ. To make it workable and its efficacious usage rejuvenators are needed. The addition of oil-containing additives can be useful as rejuvenators. For the present study, Waste Engine Oil (WEO) has been used as a rejuvenating agent. The main objective of this research is to evaluate the effect of RAP with or without rejuvenator in the Hot Mix Asphalt (HMA) mixtures. To assess the performance of the bituminous mixes Marshall properties, Tensile Strength Ratio (TSR) and Indirect Tensile Strength (ITS) for moisture susceptibility were performed. The HMA mixture with 20%, 30%, 40%, 50%, 60%, and 70% of RAP content were prepared and subsequently 1.5% of waste engine oil (by the weight of RAP content) was added to other HMA mixes containing the same RAP proportion. Corresponding result indicates that with the addition of RAP to the HMA mixes showed improved Marshall Properties, Tensile Strength and resistance against moisture susceptibility. Whereas, addition of WEO improves the Marshall Properties but decrement in Tensile Strength was observed.

Correction to: Laboratory Study on the use of Reclaimed Asphalt Pavement and Copper Slag in Warm Mix Asphalt Pavements using Waste Engine Oil as a Rejuvenator

This study aims to evaluate the effect of waste engine oil (WEO) on warm asphalt mixes incorporated with waste materials. Copper slag (CS) and reclaimed asphalt pavement (RAP), both considered waste materials were used in asphalt mixes. Seven types of mixes were prepared with different proportions of copper slag (0–15%) and RAP (0–30%) at 5%, 7.5%, and 10% WEO dosages. Marshall stability test, indirect tensile test, resilient modulus, and flow number test was carried to check the performance of these mixes. Also, a cracking test was used for evaluating the fracture energy of asphalt mixtures. It was found that asphalt mixes incorporated with CS (15%) and RAP (30%) performed similar to control mixes up to 7.5% rejuvenator dosages. The incorporation of copper slag (5%) improved the Marshall stability and tensile strength due to more angularity (multi-faced) and frictional angle (53°) of CS, resulting in excellent stability and load capacity. The resilient modulus in Mix 6 (30%RAP-5% CS) was observed to be maximum (3310.3 MPa). The use of waste engine oil softened the aged RAP bitumen, which leads to a decrease in stability, resilient modulus, rutting resistance, and increase in fracture energy. The RAP incorporated mixes showed lesser fracture energy due to the presence of stiff RAP bitumen. However, with the addition of WEO, the fracture energy increased which indicates that the cracking resistance of these mixes improved due softening action of WEO. Marshall quotient, which represents stiffness, decreased with an increase in CS content at all rejuvenator dosages.

Performance evaluation and sustainability assessment of precast concrete paver blocks containing coarse and fine RAP fractions: A comprehensive comparative study

Concrete paver blocks have recently developed as the most attractive and economically viable option for extensively recycling wastes. This deescalates the environmental concerns related to waste disposal, encourages conservation of natural resources, and contributes to a sustainable production process. In the present study, laboratory performance of concrete paver blocks using coarse and fine fractions of non-beneficiated reclaimed asphalt pavement (RAP) materials, derived as a waste residue from demolished asphalt pavement, was comprehensively and comparatively investigated. A two-factor analysis of variance and multiple comparisons test was performed to investigate the influence of RAP proportion and moist curing age. The laboratory findings revealed that the produced concrete blocks containing RAP have a great potential to be used for medium, heavy, and very-heavy traffic applications. The dosage of RAP as a natural aggregate replacement as well as the durability of RAP concrete can be increased using a staged mixing approach and a time-controlled dual-source compaction technique, which involves synchronized impact pressure and vibratory compaction energy. Moreover, assessing economic and environmental benefits highlighted the potentially sustainable aspects of recycling RAP fractions into precast concrete paver blocks.

Effect of copper slag and reclaimed asphalt pavement on the skid resistance of asphalt mixes

ABSTRACT This study describes the findings of an experimental work conducted on asphalt mixtures incorporated with copper slag (CS) and reclaimed asphalt pavement (RAP). CS and RAP are considered waste materials and these waste materials create enormous environmental issues. Their use in the highway construction sector will resolve the landfill problems associated with them. In this study, nine types of asphalt mixtures were prepared with different proportions of CS (0–15%) and RAP (0–30%). These mixes were tested for frictional characteristics under various conditions. The incorporation of CS improved Marshall stability and skid resistance of asphalt pavements. Mix 3 (0%RAP, 15%CS) showed the maximum skid resistance in dry conditions. The increase in skid resistance may be attributed to the high angularity, density, and friction angle of CS particles. However, the incorporation of RAP decreased skid resistance. The CS-RAP mixes also contribute to green technology as waste materials reduce the need for virgin aggregates in the road construction sector. The statistical analysis performed showed that the results are highly significant except in icy conditions where results obtained are insignificant.

Sustainable materials in the production of pavement base and subbase courses

The use of sustainable materials in construction is the need of the hour amidst the depletion of natural resources at a rapid rate. The significance of green roads is increasing day by day and green approach for road construction can be only achieved by the use of sustainable construction materials. In the present study, an effort has been made to make base and subbase courses sustainable using Reclaimed Asphalt Pavement (RAP) and Ground Granulated Blast Furnace Slag (GGBS) along with a very less quantity of cement. RAP used in the present study was obtained from the in situ milling of NH-16 at Srikakulam. To meet the gradation requirements as per IRC Ground Granulated Blast Furnace Slag (GGBS) was used along with RAP. Upon initial trial tests, it was concluded that unbound specimens made with RAP and GGBS have failed to meet the minimum unconfined compressive strength(UCS) requirements as per IRC: SP-89:2010 due to which cement by weight of 2% of total mix was added to meet the UCS requirement of 4.5 MPa at seven days. The optimum proportion of RAP that can be used to replace virgin aggregate (VA) was found to be 30% based on UCS test results. The durability studies of GGBS stabilized RAP/VA mixes were found to be satisfactory. The retained strength of the samples after durability studies is 91.43% which is greater than 80% as specified by IRC: SP-89:2010.

Fatigue and Healing Characteristics of RAP Mixtures

The healing properties of bituminous mixes prepared using reclaimed asphalt pavement (RAP) material are different from those of virgin mixes because the chemical characteristics of RAP binder blends are different (depending on the extent of aging) compared to virgin binders. Very limited research work has been reported in the literature on the healing potential of RAP mixtures. The current study aims to examine the fatigue and healing characteristics of RAP mixtures with varying rest periods between loads. To this end, different blends of RAP and virgin binders (VG30) were prepared at varying proportions (0%, 15%, 25%, 35%, and 45%) of RAP material in mix. The fatigue lives of different RAP mixes were evaluated by varying the rest period (400, 650, 900, and 1,400 ms) between load pulses. The healing potential of the mixes was evaluated in terms of the slopes of the lines drawn between fatigue life and rest period. The fatigue life of a mix increased with increases in the proportion of RAP in the mix. The degree of healing indicated by the slope of log (fatigue life) versus log (rest period) line was found to depend on RAP content and rest period. Mix time lag (between the peaks of stress and strain), a viscoelastic property of the mixes, was determined from the stiffness modulus test. Different rheological and chemical characteristics of the binder blends and the time lag values of the mixes were correlated with the fatigue lives and healing indexes of the mixes. The Superpave binder fatigue parameter (G*sinδ) and the mix time lag were observed to have good correlation with the fatigue life of RAP mixes. Surface free energy and different aging indexes of the binders (ICO and ICH) showed good correlation with the healing index of the mixes. Flow (consistency) parameters, such as softening point and viscosity at 60°C, correlated well with the healing index. These correlations are expected to improve understanding of the fatigue and healing behavior of RAP mixes.

MIX RATIO OPTIMIZATION DESIGN METHOD FOR HOT IN-PLACE RECYCLED ASPHALT MIXTURES

The mix design for hot in-place recycled mixtures is the key that determines the regeneration performance of asphalt pavement. However, existing design methods have numerous problems, such as the involvement of numerous influential factors and levels and poor adaptation to the composition features of hot in-place recycled mixtures. To establish a mix design method for hot in-place recycled mixtures, the mode of action of rejuvenator was analyzed in this study, and the mix design method for mixtures was optimized by introducing an orthogonal test. The regeneration mechanism of rejuvenators in reclaimed asphalt pavement (RAP) was analyzed, and the optimal working conditions of rejuvenators were determined preliminarily through physical performance, chemical composition, and dynamic shearing rheological tests. In addition, the influences of the dosage of rejuvenator, RAP, and new asphalt on the high-temperature and low-temperature performance and water stability of the recycled asphalt mixture were analyzed through an orthogonal design method by combining trabecular bending rheological, wheel rutting, and freeze-thaw splitting tests. The optimal mix design of the recycled mixture was determined on this basis. According to test results, the rejuvenator and RAP can influence the pavement performance of the recycled mixture more than new asphalt. When the dosage of the rejuvenator is 5% of the total asphalt mass, the proportion of RAP and new asphalt are 80% and 0%, respectively, and the recycling effect of the asphalt mixture is the best. The proposed method is economical and environmentally friendly and has been well applied in ordinary trunk highway maintenance engineering in Hanzhong City, Shaanxi Province, China, since 2017. Research conclusions can provide references for the hot in-place recycling engineering of asphalt pavement. Keywords: Hot in-place recycling, Rejuvenator dosage, RAP, Dynamic shear rheological test, Orthogonal test

Laboratory study on the use of copper slag and RAP in WMA pavements

This paper presents the results of an experimental investigation carried out on warm mix asphalt (WMA) incorporated with copper slag (CS) and reclaimed asphalt pavement (RAP) material. Both CS and RAP are considered as waste materials and cause a lot of environmental problems. Their use in asphalt pavements will solve the landfill problems associated with them. Also, to save energy and reduce carbon emissions, WMA technology was adopted in this study. A total of nine combinations of warm mixes were prepared with varying proportions of CS (0–15%) and RAP (0–30%). The use of CS improved Marshall stability, indirect tensile strength, and tensile strength ratio. The introduction of CS and RAP produced a balanced mix as CS improved mechanical properties due to high angularity, density, and lime content. In contrast, RAP decreased these properties except the Marshall quotient and resilient modulus. All the RAP–CS WMA mixes satisfied the minimum value of stability (9 kN) as required for dense bituminous macadam. Furthermore, it was concluded that the mechanical properties of RAP–CS WMA mixes decreased with each freeze–thaw (F–T) cycle. The CS-incorporated mixes showed better resistance against F–T cycles.

Effects of recycled aggregate composition on the mechanical characteristics and material design of cement stabilized cold recycling mixtures using road milling materials

Road milling materials, including the reclaimed asphalt pavement (RAP) and the reclaimed cement stabilized base-course (RAI), have been widely used as the recycled aggregates (RA) to prepare cement stabilized cold recycling mixtures (CSCRM) used in highway rehabilitation. However, there are few studies on the effect of RA composition (RAP and RAI proportion in RA) on the pavement performance of CSCRM. In this study, therefore, a total of forty-two groups of CSCRM are prepared in the case of different RA contents, RA compositions and cement contents. The investigation of mechanical characteristics (unconfined compressive strength, splitting strength and uniaxial compression modulus) of CSCRM reveals the effect of RA content, RA composition and cement content. The RA content, RA composition and cement content play an important role in the mechanical properties of CSCRM. The strength mechanisms of CSCRM are revealed via the micro-interface characteristics for based on SEM-image. Finally, the recommended material compositions of CSCRM are put forward and verified via durability tests (fatigue tests, dry-shrinkage tests and water-erosion tests). Results show that the recommended CSCRMs present a better overall performance.

Asphalt Recycling Technologies: A Review on Limitations and Benefits

Recycling of asphalt pavements gained popularity in 1970s due to the rapidly increasing cost and reducing supply of oil and hence - bitumen. However, presently there are other reasons to develop this technology, the main being the ability to utilize non-renewable resources. Sustainability of asphalt pavement construction can only be ensured if we are able to utilize the available reclaimed asphalt pavement (RAP) material completely in the new construction. Another potential advantage is the mutual benefit of using RAP in conjunction with warm mix asphalt (WMA). This is due to compensation of hardened binder from RAP with softer binder of WMA. For such mixes, significant energy savings can be realized due to the lower mixing and compaction temperature as well as due to lesser efforts required for compaction. This paper summarises several approaches that can be adopted to maximize the amount of RAP material in asphalt mixtures. In addition, the current recycling practices implemented in the industry are discussed to identify the main reason behind the lacking confidence in using high RAP content in mixes. The environmental and economical benefits of high rate of recycling are also discussed. Finally, the possible research directions that will allow to incorporate high proportion of RAP without compromising the performance of pavement are discussed.

Utilization of industrial and agricultural wastes for productions of sustainable roller compacted concrete pavement mixes containing reclaimed asphalt pavement aggregates

Asphalt pavement recycling has become a common practice across the globe and has been successfully employed in construction of new pavements. While several studies considered utilization of reclaimed asphalt pavement (RAP) aggregates for flexible and rigid pavements, very few attempted its possibility for roller compacted concrete pavements (RCCP). Additionally, studies on the possibility of enhancing the proportion of RAP for RCCP are very scanty. The present study is an attempt to increase the potential of RCCP mixes containing 50% RAP (dust contaminated & stiffened asphalt coated: 50RAP via including various industrial and agricultural wastes such as Silica Fume, Fly ash, and Sugarcane ash as partial replacement of conventional cement. It was observed that the inclusion of the stated admixtures had an insignificant effect on the density of the fresh RCCP mixes, however, increased the moisture demand considerably. In fact, the results firmly indicated the potential of silica fume for RAP-RCCP blends, as, it not only enhanced the physical and mechanical properties, but found to improve the durability of RCCP mixes considerably. Also, utilization of silica fume was found to be economical & environmentally friendly amongst all wastes: with reduced initial construction cost & CO2 emissions by up to 8.4% & 9.7%. As far as the other industrial wastes are concerned, 15% fly ash could also be utilized for producing sustainable RCCP mixes, whereas, higher dosage of fly ash (30%) and sugarcane ash (10 & 15%) may be employed as base layer material of conventional concrete pavements.

A study to compare virgin and target asphalt binder obtained from various RAP blending charts

Use of reclaimed asphalt pavement (RAP) material in mixes is on the rise. Currently, RAP proportion to reach the target binder grade is determined by absolute viscosity and performance grade (PG) methods. However, it is necessary to compare the RAP proportion recommended by the two methods. Further, it is essential to ascertain whether the RAP blended target binder is equivalent to virgin target binder based on various rheological and chemical properties. In this study different percentages (i.e. 0%, 15%, 25%, 40% and 50% by weight of binder) of RAP binder was blended with base binder (AC10). RAP proportion to achieve target grade (AC30) was determined based on absolute viscosity, PG, LAS and MSCR tests. Absolute viscosity and PG methods recommended the RAP proportion of 48% and 32% respectively. Thereafter, average of the two RAP proportions was blended with AC10 binder to obtain target grade of AC30 (AC30_RAP). AC30_RAP was observed to have a higher fatigue life than AC30 binder at lower strains and the trend reversed at higher strain. Higher recovery (R) and lower non-recoverable creep compliance value (Jnr) was exhibited by AC30. FTIR spectroscopy indicated that AC30_RAP had higher sulphoxide and carbonyl content. LAS and MSCR tests recommended the RAP proportion of 35% and 48% based on fatigue and rutting performance respectively.

Laboratory Investigation on the Fresh, Mechanical, and Durability Properties of Roller Compacted Concrete Pavement Containing Reclaimed Asphalt Pavement Aggregates

The present study evaluates the potential and suitability of different fractions of reclaimed asphalt pavement (RAP) for roller compacted concrete pavement (RCCP) mixes. Natural coarse and fine aggregates were replaced, partially and in combination, by coarse RAP, fine RAP, and combined RAP for preparation of RCCP mixes. The considered properties to determine the optimum RAP fraction and its proportion for RCCP were fresh density and water demand, compressive strength, flexural strength, split tensile strength, porosity, water absorption, abrasion resistance, and performance in aggressive environments of chloride- and sulfate-rich ions. It was observed that inclusions of all the fractions of RAP considered could reduce the strength related properties of RCCP mixes significantly at all curing ages. However, fine RAP mixes were found to exhibit better strength properties than coarse RAP and combined RAP mixes. It was also observed that none of the RAP mixes could achieve the recommended compressive strength criterion of 27.6 MPa, however, they exhibited enough flexural strength to replace a fraction of conventional aggregates, individually or in combination, for construction using RCCP. In fact, 50% coarse and 50% fine RAP mixes had higher flexural strength than the target laboratory mean strength of 4.3 MPa. Similarly, these mixes were found to have sufficient abrasion resistance and could be included in RCCP (surface course) to be constructed in areas having high concentrations of chloride and sulfate ions. Additionally, the results also indicated that higher proportions of fine RAP may be suggested for RCCP mixes to be laid in sulfatic environments.

Effect of Mixing Time and Temperature on the Homogeneity of Asphalt Mixtures Containing Reclaimed Asphalt Pavement Material

Laboratory-produced reclaimed asphalt pavement (RAP) material, new aggregate, and tinted new binder were mixed (RAP proportion: 40%) with 12 different combinations of mixing temperatures and times, based on which circular specimens of various thicknesses were fabricated and then subjected to multi-direction indirect tensile stiffness modulus (ITSM) testing and color image analysis. Statistical calculations including average value, coefficient of variation, standard deviation, and range were carried out to investigate the effects of different mixing conditions on the homogeneity of asphalt mixtures containing RAP. The results show that the deterioration of homogeneity of asphalt mixtures containing RAP was mainly caused by the asynchronous breaking of clusters. The mixing temperature was decisive in determining the resistance of clusters to breaking, and for mixing conditions chosen in this study, the resistance increases with the increase of mixing temperature. Short mixing time might lead to a phenomenon of “momentary homogeneity,” in which clusters were not broken and the blending degree between aged and new binder was low.

Mixture design consideration for foamed asphalt using RAP materials

The use of reclaimed asphalt pavement (RAP) in cold foamed asphalt mixture can decrease the need of fresh aggregate and bitumen, reduce fuel consumption and CO2 production. A cold foamed asphalt using RAP material is a unique asphalt mixture. Performance of these materials will be affected by mix design process. This paper discusses about mix design consideration for these mixture especially to set the aggregate and foamed bitumen properties properly. The method used to propose mix design consideration in this paper is by analyzing results of the long research work about foamed asphalt and RAP materials in laboratory. It is found that the optimum value of foamed bitumen properties is affected by bitumen grade, foam characteristic, water content at foaming, and temperature of bitumen. The best aggregate properties should consider the plasticity index, aggregate gradation, and the percentage of RAP proportion. The percentage of RAP proportion influence specific gravity, mixture density, volumetric characteristic, and mixture performance.