Feasibility analysis of recycled asphalt pavement and recycled concrete aggregate in emulsified asphalt-treated bases

Zheng K., Yang Q., Qiu X., Xu W., Liu H., Chen Z.

The interfacial bonding capacity between cement emulsified asphalt composite binder (CEACB) and reclaimed asphalt pavement (RAP) plays a critical role in improving the pavement performance of cold recycled asphalt emulsion mixtures (CRAEMs). This study aims to investigate the formation and development of the interfacial bonding capacity between CEACB and RAP. First, the dynamic wettability and the spreading behaviors of CEACB on RAP surfaces were explored according to the surface free energy theory. Second, digital image processing (DIP) technology was employed to recognize interfacial failure patterns. Lastly, the influence of internal and external factors on the interfacial bonding capacity between CEACB and RAP during the curing process was analyzed via grey relational analysis (GRA). The results indicate that a moderate cement content with a mass ratio of asphalt to cement equivalent to 1.0 can significantly enhance the wettability of CEACB on RAP surfaces. By appropriately prolonging the curing time and controlling the curing temperature, it is possible to increase the bonding strength between CEACB and RAP. Additionally, a strong correlation exists between initial wettability and ultimate bonding capacity during the bonding strength curing process. The good wettability that developed in the initial stage of interfacial strength formation relates to the decreased spalling rate of CEACB on the RAP surface. This study is not only devoted to understanding the mechanisms that can enhance CRAEM performance but also provides important guidance for practical engineering applications of cold recycled asphalt pavements.

Gangu S.K., Shankar S.

Sanei S., Modarres A.

In recent years, extensive research has been conducted on the use of second-hand or waste materials in the road pavement construction layers. Most of these studies evaluated the mechanical properties of materials and emphasized the environmental benefits of using waste materials for use in road construction projects, regardless of the environmental consequences. The present study intends to compare the life cycle of waste materials with standard materials and determine the optimal conditions for the selection of waste materials based on environmental criteria by considering life cycle assessment (LCA) and several environmental indicators. The analysis considered emulsified cold recycled asphalt with different types of activator fillers including cement, coal waste+lime and coal waste ash+lime. Also, the recycled pavement was compared with that of conventional asphalt pavement in this environmental assessment. The LCA analysis was performed for pavements with design traffic of 0.1 to 100 million equivalent single axle loads (ESALs). In order to design the pavements structure, 96 resilient modulus tests were done for 32 recycled mixes. Environmental indicators under study included energy consumption, abiotic depletion potential (ADP), global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP). The collected data for the studied functional unit was undergone an environmental analysis in SimaPro software. Apart from a standard case, parametric study was accomplished to analyze the effect of activator additive content. Accordingly, it was concluded that for the standard case, the traffic level or in other words the highway grade is of the main importance criterion in choosing the rehabilitation method based on environmental indicators. Emulsified cold recycled pavement with waste additives can be environmentally justified only in projects with low to medium traffic levels of less than 5-10 ESALs. For projects with medium to high traffic levels, only the ordinary recycling method with cement was comparable to conventional reconstruction.

Ma F., Dong W., Fu Z., Wang R., Huang Y., Liu J.

Timely maintenance is crucial to ensure the long-term performance of asphalt pavements. Due to the large amount of greenhouse gases (GHG) emitted during construction, it is important to evaluate the environmental impacts of various maintenance technologies, so that the whole life impacts of asphalt pavements can be understood and reduced. This paper estimated the GHG emissions of 16 maintenance technologies in the four categories of surface seal or coating system, thin overlay system, hot recycling system and cold recycling system by using life cycle assessment (LCA), and identified the technologies and the combination of them that have the least GHG emissions. In order to compare the maintenance technologies on a level-playing basis, this study designed maintenance scenarios for the entire life cycle of the pavement, and established a system boundary where all maintenance scenarios are compared transparently for a defined functional unit. Results show that, among the preventive maintenance technologies, micro-surface and fog seal have the lowest GHG emissions. In order to meet the same performance requirements of highway pavement, cold recycling with extra overlay will generate more than twice GHG emissions that of hot recycling. Increasing the frequency of preventive maintenance, and reducing the occurrence of corrective maintenance can reduce GHGs emissions by 30%–45% in pavement life. Reasonably designed maintenance plan for the entire life cycle can significantly reduce the GHG emissions of asphalt pavements.

Offenbacker D., Saidi A., Ali A., Mehta Y., Decarlo C.J., Lein W.

AbstractThe purpose of this study is to evaluate and quantify the construction costs, energy costs, and environmental benefits of using cold in-place recycling (CIR) as a pavement rehabilitation te...

Goli H., Latifi M.

The Warm Mix Asphalt (WMA) mixture containing Recycled Asphalt Pavements (RAP) has the advantages of the WMA technology and the RAP simultaneously. Also, moisture damage is a concern in these mixtures in all service temperatures which has not been investigated comprehensively for all service temperatures in one study. Therefore, performance of this mixture against moisture in all service temperatures, and was considered as the target of this research study. In this way, effects of moisture on performance of the mixtures were investigated using experimental methods including Resilient Modulus, Indirect Tensile Strength (ITS), Indirect Tensile (IDT) fatigue failure, Semi-circular Bending (SCB), and Dynamic Creep tests. The results generally indicated that although the WMA mixtures containing RAP have hydrophilic and moisture sensitive aggregates and aged binder, they had an appropriate performance against the effect of moisture. Therefore, this mixture can be recommended for the regions with moisture damage, environmental, and natural resources limitations concern.

Chen T., Luan Y., Ma T., Zhu J., Huang X., Ma S.

Cold recycling technique is an effective strategy of cost reduction, resource conservation and energy consumption in pavement maintenance and rehabilitation. However, the mechanical mechanism of cold recycled mixture is not clear in the process of strength formation. The research was to put forward practical suggestions for mechanical property improvement of cold recycled mixture and generalize the application more efficiently to reach an ultimate purpose of energy and resource conservation. Various mixing orders were designed to construct different interfacial features and reflect on mechanical properties, and two-phase “aggregate-binder” interfaces were considered as the main interface forms to respectively reveal the mechanical and microstructural characteristics of cold recycled mixture. The mechanical properties of different mixing orders were compared and analyzed by the indirect tensile tests and dynamic modulus tests. Besides, the microstructure was observed by scanning electron microscope and the backscattered images were captured to extract microvoid parameters. Results indicated that different mixing orders and interface forms had a great influence on the mechanical properties of cold recycled mixture. Within the range of binder content applied in cold recycled mixture, the strength of the interface involving the recycled asphalt particles was larger than that of the interface involving the new aggregates. The indirect tensile strength of the interface involving asphalt emulsion was larger than that of the interface involving cement, while the microvoidage was just on the contrary. In conclusion, mixing cement before adding asphalt emulsion is not conducive to the improvement of mechanical properties. It is suggested that cement and asphalt emulsion should be fully mixed before the contact between aggregate and mortar in order to realize the optimal performance of cold recycled mixture; otherwise, mineral aggregates mixed with asphalt emulsion first can also be a better alternative.

Visintin P., Xie T., Bennett B.

In an attempt to limit the environmental impact of cement and concrete manufacture, much research has been devoted to the potential use of concrete waste as recycled aggregate. While this research has shown technical feasibility, a limited amount of research has been devoted to quantifying the environmental impact of recycled aggregate concrete production. In this work, to quantify the CO2 equivalent emissions and embodied energy of a broad range of mixes, life-cycle assessment is undertaken on 624 recycled aggregate concrete mix designs collated from 61 individual studies. The study includes: consideration of an expanded functional unit that accounts for the potential need to increase cement content to allow for the loss of strength and durability associated with recycled aggregate inclusion, the impact of the allocation of emissions from the recycling process, and the uptake of CO2 during the primary and secondary life as a result of carbonation. Based on the large-scale life-cycle assessment, emission factors for recycled aggregate concrete are defined, and it is shown that considering an expanded functional unit incorporating volume, strength and durability yields similar mean emission factors to a simple volumetric functional unit but with a significantly larger range. Further it is shown that due to the high carbonation rate, in many instances the crushing of concrete to aggregate size and use as fill may be preferable in comparison to use in concrete.

Daryaee D., Ameri M., Mansourkhaki A.

Rejuvenating agents have been used to restore physical-rheological properties of reclaimed asphalt binder (RAB) and improve cracking resistance of asphalt mixtures containing the reclaimed asphalt pavement (RAP). Softer bitumen and polymer modified bitumen have also been successfully used to improve performance of the RAP-containing mixtures. Because the use of polymers as bitumen modifier is economically costly, possibility of using waste polymer as a cost effective and environmental-friendly material in hot asphalt recycling was evaluated in this study. The objective of this research study was to evaluate the effect of combination of waste polymer, soft bitumen and rejuvenator simultaneously on the performance of high RAP asphalt mixtures (50%RAP). In this paper the fatigue resistance, moisture susceptibility and rutting resistance of the asphalt mixture were evaluated. The four-point beam fatigue test, resilient modulus test, indirect tensile strength test and dynamic creep test were utilized for this purpose. Moreover, using the dynamic shear rheometer test, the fatigue and rutting resistance of the different asphalt binders were evaluated. The Results showed that use of rejuvenator, waste polymer and soft bitumen simultaneously in 50%RAP mixture, can dramatically enhance fatigue, rutting and moisture resistance of the mixture. Furthermore, waste polymer modified bitumen in combination with rejuvenator had softening effect in RAB-containing asphalt binders at intermediate temperatures while did not have a significant negative effect on rutting resistance of the RAB-containing asphalt binders at high temperatures.

Chakravarthi S., Boyina A., Singh A.K., Shankar S.

Cement stabilization is the most frequently used technique to enhance the mechanical properties of recycled materials. Reclaimed Asphalt Pavement (RAP) and Recycled Concrete Aggregate (RCA) are abundantly available recycled materials and utilization of these materials in road construction is a sustainable and eco-friendly process. However, the advantage of cement stabilization of RCA over RAP and blending with Conventional aggregates (VA) as a base and subbase course material at different stabilization levels is unknown. In the current study the same is investigated by stabilizing mixes with cement contents varying from 2 to 6% and blending with VA compared in terms of physical properties, compaction characteristics, and the performance tests like Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS), and Modulus of Elasticity (E) at 7 days of curing period. From the results, it is observed that recycled aggregate blends need higher cement contents to satisfy the specifications as base layer for high volume roads and the stabilization of RCA is more pronounced compared with RAP. Significant improvement in strength is observed when blended with VA at all cement contents. However, RCA mixes achieved maximum strength at equal proportions of RCA and VA. No particular trend is observed in Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) for RCA blends due to the non-homogeneous distribution of mortar. The Elastic modulus of the RCA mixes declines with RCA content at higher cement content due to brittle nature. Summarily, 25% RAP, 25% RCA and 50% RCA blends at 6% cement performed well.

Severis R.M., Simioni F.J., Moreira J.M., Alvarenga R.A.

The shift toward the adoption of sustainable lifestyles may be achieved with the support of environmental indicators, such as those obtained from Life Cycle Assessment (LCA). The aim of this paper was to perform a Consumer LCA of the potential environmental impacts of mobility habits of a generic consumer. This study also proposed a methodology for analyzing life cycle impact assessment (LCIA) results called Marginal Variation on Impact Assessment (MVIA). Mobility habits in lifestyles were modeled considering transportation to short and long-distance travels. The mobility alternatives considered were travel on foot, by bicycle, car (private and shared), bus, and airplane. Linear regression was applied to identify the marginal variation in aggregated single score results of transportation habits. Mobility with a private car had the highest environmental impact, whereas the use of a bus, bicycle and walking were the most sustainable alternatives. The results exhibited sensitivity to car-sharing. Taking flights for long-distance travels resulted in higher environmental impacts than other alternatives. Marginal Variation on Impact Assessment indicated that the consumer may find the greatest potential to change behavior and reduce impacts in mobility habits related to short-distance travels as well as by reducing the frequency of long-distance travels. The proposed MVIA methodology fits as a tool to support environmental life cycle impact assessment. • We analyzed different mobility options through a Consumer LCA. • For daily transport habits, high variations were observed. • For long-distance travels, frequency significantly influenced results. • Marginal Variation on Impact Assessment methodology is suitable for LCA studies.

Flores G., Gallego J., Miranda L., Marcobal J.R.

At present there is no consensus on the most suitable methodology for the design of cold recycled mixtures with emulsion, due to its complexity. Therefore, design is generally based on compliance with one or more volumetric or mechanical parameters established in the highway regulations, which does not guarantee the optimization of the mixture. The present work proposes a design methodology for cold recycled mixtures with emulsion, in which 6 parameters are evaluated: Air voids, Indirect Tensile Stress, Indirect Tensile Strength Ratio, Wheel Tracking, Stiffness Modulus and Fatigue life. Performance indexes were established to evaluate the values obtained from the tests according to behavior graphs with the maximum value of 1. These graphs evaluate the results of the tests, considering as a maximum value the most favorable results for the optimal performance of the mixture. Finally, for the analysis of the mixtures the authors propose a Global Performance Index (GPI) that shows the average of the 6 parameters measured. The result is a number that represents each job mix formula, which is sensitive to changes in the values of the properties and is obtained using a systematic methodology. Therefore, the choice is based on technical criteria and according with the GPI; the influence of the materials or the formulas used for each mixture can be ranked.

Gandi A., Cardenas A., Sow D., Carter A., Perraton D.

In most countries, there is a low temperature limit to lay down hot asphalt mixes because if it is too cold, it becomes impossible to get proper compaction. For cold recycled bituminous mixture (CRM), there is little information on the effect of the low temperature on their behavior. The goal of this study is to evaluate, in laboratory, the impact of the compaction and curing temperature on the behavior of CRM. To do so, CRM containing 50% reclaimed asphalt pavement (RAP) and 50% natural aggregates treated with foamed asphalt or bituminous emulsion were mixed and cured at different temperature between 0 °C and 23 °C for up to 10 days before being tested in indirect tension. The results show that for all mixes, a cure at lower temperature means lower tensile strength, but the decrease is more noticeable for emulsion treated materials than for foamed treated mixes. The trend is not as obvious for Marshall stability results. A second cure at ambient temperature was also done, and the analysis of the results showed that the decrease in mechanical performance remains important even after a second cure at higher temperature for all mixes treated with bituminous emulsion, but there is some mechanical gain for mixes treated with foamed asphalt. • Cold temperature curing reduces ITS of CRM treated with foam or emulsion. • CRM treated with emulsion are more sensitive to cure temperature than CRM treated with foamed asphalt. • A secondary cure at room temperature has limited impact on ITS for emulsion treated CRM that were first cured at 0 °C.

Zhu C., Zhang H., Guo H., Wu C., Wei C.

The influence of different gradations on the final and long-term performance of cold recycled mixture with asphalt emulsion (CRME) was investigated. The weight ratio of recycled asphalt pavement (RAP) to virgin aggregate and mineral powder remained 4:1 unchanged, three gradations were selected in a modified grading range which was determined based on the engineering practices of Hunan province and the Chinese specification for cold recycling (JTG F41-2008). The tested performance included mechanical property, moisture susceptibility, high-temperature stability, low-temperature cracking resistance and long-term performance. The long-term performance was simulated using a laboratory accelerated aging test. The results show that CRMEs with the selected three gradations have good above-mentioned performance, manifesting that the modified grading range for guiding the CRME engineering practices is feasible to some extent. As the aging time goes on, the indirect tensile strength (ITS) and freeze-thaw ITS ratio of all CRMEs firstly increase quickly and then increase slowly or even decrease, and the aging of asphalt in CRME becomes more and more serious. Compared with three gradations, the CRME with finer gradation has the better final and long-term performance. Moreover, after long term service, the effect of gradation on mechanical property of CRME becomes more significant.

Thives L.P., Ghisi E.

The objective of this paper is to assess carbon dioxide emissions and energy consumption for the production of road pavements by means of a literature review. The construction of the main types of pavements requires energy and generates greenhouse gas emissions that impact the environment. Different types of asphalt mixtures such as cold mixtures, warm mixtures, asphalt rubber mixtures and mixtures with reclaimed asphalt pavement were assessed. The fuel used in the burners that heat and dry the aggregates is the main source of emissions. Also, the aggregates moisture content is an important parameter that influences the energy consumption. On the other hand, the energy consumption and emissions to produce Portland cement mixtures are related to the process of cement production. For both asphalt and Portland cement mixtures, the extraction, manufacturing and placement were also evaluated. Moreover, the energy consumption of the pavements structures was evaluated. Pavements composed of Portland cement concrete consume more energy than hot mix asphalt. But, warm mix asphalt technologies can save 20–70% of the energy consumption when compared to hot mix asphalt, mainly due to the temperature reduction in the warm mix processes. In addition, the emissions caused by different fuels used to produce pavement mixtures were compared. Asphalt mixtures and their alternative technologies consumed less energy and emitted fewer gases than Portland cement mixtures. Carbon dioxide emissions for hot mix asphalt and asphalt rubber mixtures can be 70% lower than emissions for Portland cement concrete. Some alternatives to reduce energy consumption and greenhouse gas emissions in asphalt mixtures production are the decrease of aggregates moisture content, reduction of the asphalt mixtures production temperature and use of waste materials in pavement construction. Switching from hot mix to warm mix technologies would reduce the carbon footprint generated by the asphalt industry.