Cold Recycling Research Articles

Cold In-Place Recycling Moisture-Related Design and Construction Considerations for Single or Multiple Component Binder Systems

In recent years, cold in-place recycling (CIR) has gained momentum because of its economic, performance, and sustainability characteristics; as a result CIR markets are likely to expand into, for example, higher traffic routes. To further understand how to continue improving CIR for existing applications as well as future applications, better techniques are needed with regard to interfacing design and construction. Moisture is one key area in which design and construction are often disconnected. This study’s objective, therefore, was to evaluate the moisture (and associated early-age strength and stability) aspects of CIR, particularly within a framework that could consider hydraulic cement, bituminous emulsion, or combinations of both binders. A universal design framework that accommodates any binder or combination thereof while representing early-age field conditions has advantages for agencies, not only in its reasonable characterization of construction processes, but also in its facilitation of competition and creativity in the process of selecting materials and proportions. This study was organized in three phases. Phase 1 documented moisture instrumentation of a cement CIR project. Data were successfully obtained throughout compaction and curing and were used in Phases 2 and 3 alongside supplemental field and laboratory testing. Phase 2 evaluated moisture’s role in compaction; Phase 3 evaluated moisture–strength and moisture–stability relationships for various curing protocols. Phase 2 concluded that high (>6%) moisture content, typical of Proctor compaction, is generally unnecessary. Thus, Proctor compaction is discouraged in favor of a fixed design moisture content. Phase 3 concluded that humid (35% to 50% humidity) and dry 40°C oven curing protocols are candidates for universal CIR design.

Dynamic Modulus of Recycled Pavement Mixtures

Pavement recycling techniques have been shown to be effective for rehabilitating pavements by reducing environmental impacts, construction costs, and time. For various reasons, many highway agencies have not widely embraced these processes despite the demonstrated advantages. One such reason is that the mechanical properties of these materials have not been widely studied, resulting in a lack of consensus on proper design values, which causes concern for highway agencies. This study sought to determine the dynamic modulus of field-produced and field-cured recycled pavement materials from 24 projects constructed in the United States and Canada. The dynamic modulus is one of the primary material parameters for mechanistic–empirical pavement design and performance prediction. On the basis of a statistical test and observation of the constructed master curves, this study found that the three pavement recycling processes studied (cold central-plant recycling, cold in-place recycling, and full-depth reclamation) had a similar range of dynamic modulus values. In addition, cold central-plant recycling and cold in-place recycling showed greater stiffness temperature dependency than that of full-depth reclamation, suggesting that the binder from the existing reclaimed asphalt pavement may play a role in their stiffness properties. The master curves also showed that the use of chemical additives generally increased the stiffness and reduced the temperature dependency of the recycled materials. The master curves showed that dynamic modulus values were similar when emulsified asphalt and foamed asphalt were used as the stabilizing and recycling agents.

Life Cycle Assessment of Aluminium Recycling Process: Case of Shredder Cables

Life cycle impact of European generic primary and secondary aluminium are well defined. However specific recycling processes are not available in literature. In this study, the environmental assessment of cable recycling processing is examined. The data come from a recycling plant (MTB Recycling) in France. MTB process relies only on mechanical separation and optical sorting processes on shredder cables. On the one hand, the study demonstrates huge environmental benefits for aluminium recycled in comparison with primary aluminium. On the other hand, the results show the harmful environmental influence of the heat refining by comparison with cold recycling process.

The Application of Asphalt Cold Recycling Technology in Lower Yellow River Flood Control Project

Asphalt cold recycling technology has many advantages, such as rapid construction, energy saving, and environmental protection. In this article, the works based on the flood control dike road repair of lower Yellow River flood control project and cold asphalt recycling technology. Combined with the current flood control dike road in Liaocheng, the old pavement rehabilitation program was designed and the program was successfully implemented. It provided a successful reference cases for application of asphalt cold recycling technology for flood control dike road repair in the lower Yellow River flood control project.

Selection of asphalt–concrete mixed compositions in cold recycling of road surfaces

This article reviews the main causes of damage to road asphalt–concrete surfaces and their consequences. The peculiarities of the design of new road mixtures in different recycling nonwaste technologies of repair of damaged road sections are shown. The basic composition of the components and characteristics of their interaction are determined.

Influence of Cement on Rheology and Stability of Rosin Emulsified Anionic Bitumen Emulsion

AbstractOrdinary portland cement (OPC) has been extensively used in cold recycling asphalt and cold-mix asphalt as an additive in order to improve the early age performances of these mixtures. The main purpose of its application is that cement hydration benefits the strength development by consuming water and by accelerating the bitumen emulsion breaking. The aim of this study is to investigate the influence of cement on the rheology and stability of rosin-emulsified anionic bitumen emulsions. With this purpose, an anionic bitumen emulsion blended with various amounts of cement and limestone filler was studied by means of a Brookfield viscometer. Optical microscopy was used to investigate the breaking process of the bitumen emulsion and the morphology of bitumen droplets in the presence of cement and filler. In addition, the stability of anionic bitumen emulsions was studied in dependence of the pH and the calcium ion concentration. The results indicate that, unlike limestone filler, which has no signific...

Specification development for cold in-situ recycling of asphalt

In-situ cold recycling provides a valuable means to reduce the environmental impact of road construction. The reduced energy requirements relative to traditional hot mix recycling can lead to significant reductions in cost and associated CO2 emissions. Worldwide, in-situ cold recycling has been found to be particularly useful in the rehabilitation of rural roads where site locations are far from asphalt plants. However, practical issues remain due to the evolving nature of cold bituminous materials. Unlike hot-mix asphalts which gain strength quickly as they cool, cold-mix bituminous materials gain strength slowly over time. This is particularly an issue in countries with cooler, wetter climates, such as Ireland. Consequently the specification of cold materials poses a number of challenges relating to curing and testing protocols.This paper reports on the development of a specification for cold recycled materials and the application to a case study in Ireland. This work was conducted as part of the CEDR funded project CoRePaSol which focused on the development of harmonised design procedures for cold recycled mixes. In collaboration with the Irish National Roads Authority a 2.5km site on a national road was identified for a recycling trial. The existing guidance for Low Energy Pavements was used to classify the road with respect to traffic levels and a testing programme was implemented which sought to reflect best practice across Europe. A series of recycling options were assessed and four different mix designs were proposed. These included variation in the binder type (foam mix or emulsion, with or without cement), binder content and recycling depth, reflecting the wide array of options available to engineers seeking to promote cold recycling. Due to the lack of harmonised guidelines across the Europe on design and evaluation of cold mixtures a specific focus is given in this paper to the mix evaluation procedure where alternative laboratory test specimen curing and testing procedures are investigated and recommendations are given.

Evaluation of fatigue behavior in cold recycled mixture using digital image correlation method

Cold recycling (CR) is a reconstruction technique that produces a rehabilitated asphalt pavement without heating materials during the recycling process. It has been widely practiced in recent years, but the fatigue properties of CR mixtures are not fully understood. The objective of this study is to evaluate the laboratory fatigue behavior of CR mixtures with the application of digital image correlation (DIC) technique. The semicircular bending (SCB) and indirect tensile (IDT) fatigue tests were utilized to compare the resistance of CR and hot mix asphalt (HMA) mixtures to crack propagation in the stress-controlled mode of loading. According to the results of this study, the addition of cement to the CR mixture improves the overall fatigue performance; however it decreases the fatigue life of CR mixture under the same stress level. The SCB and IDT fatigue tests are in agreement with each other in ranking the fatigue resistance of different mixtures. The CR mixture has longer fatigue life and larger tensile strain at the failure point than the HMA mixture at lower stress levels. In addition, the contour plots of the horizontal tensile strain of CR specimen demonstrate the cracking path and the three stages of fatigue process. From the full-field strain results of the fatigue test, the two transition points in the fatigue curve are verified as the initial cracking point and fatigue failure point, respectively. Overall, this study provides a better understanding of the fatigue behavior of CR mixtures to improve the mix design and field performance.

Study on the Physical Properties of Recycled Cold Asphalt Using Cementless Binders

In this study, the optimal mixing conditions for recycled cold asphalt, which recycled waste asphalt and used cementless binders, was assessed through verification of the performance. The cementless binder mixing ratio of 6% desulfurization gypsum substitution rate for blast furnace slag was found to have the most outstanding properties. For the Marshall stability, 4% filler mixing brought about a 1.92 times strength increase effect compared to OPC. The flow value testing showed that an increase in the use of asphalt emulsion resulted in an increased flow value while it decreased with the increase in filler substitution rate. The optimal mixing condition that satisfied mechanical performance and durability among the test conditions assessed in this study was found to be 4% filler mixed.

Experimental Assessment of Fly-Ash Stabilized and Recycled Mixes

Abstract The use of fly-ash stabilizers, materials from fluidized combustion fly-ash, and other solid coal-burning residues, which are called coal combustion by-products (CCB), have good potential for application in subgrade structures and roadbed materials of roads as well as in the structural pavement layers. One of the many factors limiting the application of some CCB sorts is the relatively low resistance in repetitive contact with water, volumetric changes, and the risk of partly unsatisfactory hygienic and environmental parameters. With respect to the aforementioned negative characteristics of CCB, which occurred primarily under the repetitive impact of water and freezing, the experimental examination focused on improving CCB resistance to frost and water, verification of volumetric changes, and improvement of pozzolana characteristics of CCB by increasing the percentage of fine particles in the original material (e.g., by means of mechanical and/or chemical activation, including combination of both types). At the same time, the road construction industry strives to find a suitable substitute for the traditionally applied hydraulic binders as well as expand the existing base of the binders applied. The experience with using CCB as a binder or binder component has not been as extensive so far as to allow any generalisation of conclusions. Therefore, the possibilities of applying alternative additives as a replacement for the binders traditionally applied have been researched. Another application of the coal combustion by-products tested was in cold recycling mixes. In this case, the fly-ash from fluidized combustion is used as a substitute for the hydraulic binder. The fly-ash tested was subjected to mechanical activation, while the parameters of the mix under scrutiny reflected the impact on the strength and deformation parameters of the mix; last but not least, the water susceptibility indicator was also monitored. From the environmental perspective of practical applicability of the mixes a chemical analysis and leaching tests have been done.

Development of Holding Strategies for Deteriorated Low-Volume Roads

Heavily deteriorated low-volume roads in the United States often face the plight of insufficient maintenance funding. Funding priority is usually given to roads that are part of the National Highway System (NHS). Rural highways that have the geometry and speed limits intended for lower traffic volume are not included in the NHS and may be managed by state highway authorities, counties, or townships. Low-volume roads provide access to areas that are less populated and typically have traffic counts of less than 1,500 average daily traffic. To improve such roadways, highway agencies are interested in holding strategies that are more aggressive than preventive maintenance but not as extensive as rehabilitation. The Iowa Department of Transportation constructed test sections with 10 holding strategy treatments to aid in the development of appropriate guidelines. Holding strategy treatments use various combinations of thin surfacing technologies and base recycling and strengthening treatments for flexible pavement rehabilitation and preservation, including single- and multiple-layer chip seals, thin and ultra-thin asphalt overlays, cold in-place recycling, and full-depth reclamation. This paper summarizes the construction of the test sections and recent observations of the performance and maintenance of the treatments. On the basis of the construction costs and treatment life expectations from the literature, a draft decision table is proposed for the selection of holding strategy treatments. The decision table recommends the most cost-effective holding strategy treatment among the 10 treatments that were constructed for a specified holding period. The decision table will be validated in the future with further performance observations.

Performance Evaluation of Semiplastic Recycled Cold Asphalt Using Noncement Binders

The optimal mixing conditions for semiplastic recycled cold asphalt, which recycled waste asphalt and used noncement binders (NCB), were assessed through verification of the performance. The NCB of 6% desulfurization gypsum mixing was found to have the most outstanding properties. For the Marshall stability, 4% (NCB) filler mixing brought about a 1.92-time strength increase effect compared to OPC (2%) and was improved when using modified asphalt and SBR. The flow test results showed that although an increase dosage of filler and SBR decreased the flow value of the semiplastic recycled cold asphalt, an increase dosage of asphalt emulsion improved the flow value. The indirect tensile strength and liquid immersion residual stability for the condition with greatest Marshall stability were most outstanding with 0.95 MPa and 83.6%, respectively. Evaluation of the recycled cold asphalt abrasion durability revealed that for the case of mixing more than 4% NCB the mass loss rate was lower than 20%. The abrasion durability was found to improve when using modified emulsified asphalt and SBR substitution. From the test results, it was found that the optimal mixing proportion of semiplastic recycled cold asphalt satisfied mechanical properties and durability is NCB with 4%, emulsified asphalt with 3%, and SBR substitution with 20%.

Characteristics of the fatigue life (IT-FT) of the recycled base course at the controlled stresses state

The paper presents the results of the base coarse made in the cold deep recycling technology with the emulsion in aspect of its durability for a different tensile stress level. The recycled base design simulated a deep recycling process with materials from existing crushed bituminous pavement layers("in-situ" technology). While assessing the quality of the designed MCE mixture, the following physical and mechanical parameters were considered: void contents Vm, indirect tensile strength ITSDRY at 25oC, tensile strength ratio TSR, stiffness modulus Sm. Additionally, the evaluation of fatigue was done at three stress cases: 250 Pa, 400 Pa, 500 Pa. The impact of the vehicle axle load on the stress state in the base course was simulated. For the purpose of determining the pavement durability, one of the method of fatigue life test was used. The tests were done according to IT-FT, based on an indirect tensile test (ITT). This method was choosen because it exhibits good equivalence to the real road pavement behaviour.

Field validation of recycled cold mixes viscoelastic properties

Visco-elastic properties of recycled cold mixes are analyzed in this paper by tests carried out in laboratory; the aim of the paper is to evaluate how reliable are these properties to be used for the prediction of visco-elastic response of pavement layers containing recycled cold mixes.The paper focuses on both bitumen emulsion and foam bitumen recycled cold mixes; two different mixtures were designed in laboratory to achieve specific mechanical properties and used to build two instrumented test sections. Visco-elastic properties and fatigue resistance of these mixtures were determined on cores extracted from the test sections and compared with those determined on a conventional hot asphalt mixture for base layer. This comparison allowed to highlight the reduced thermo-sensitive and time-dependant behavior of these mixtures.Visco-elastic properties of the recycled cold mixtures determined in laboratory, then were used to predict strains in the base layer of the test pavements by using the ViscoRoute 2.0 software. The comparison between measured and predicted strain pulses allowed to evaluate the reliability of visco-elastic parameters determined in laboratory to predict response of layers composed of recycled cold mixes. The obtained results show that visco-elastic parameters of bitumen emulsion recycled cold layers exhibit a satisfactorily capacity to accurately reproduce the pavement response; the same reliability cannot be found for foam bitumen recycled cold layers, whose behavior diverges significantly from that of a continuum.

Comparing the mechanical properties of cold recycled mixture containing coal waste additive and ordinary Portland cement

Pavement cold recycling is considered as an efficient rehabilitation method, especially in severely distressed roads. Modifier additives have been used for improving the performance of cold recycled mixture (CRM), especially at initial days of curing. In this study, coal waste taken from coal washing plant and its ash produced through the incineration process were used as pozzolanic additives in CRM with bitumen emulsion. To assess the effects of using these additives on mechanical properties of CRM, Marshall stability, indirect tensile strength (ITS), resilient modulus, dynamic creep and fatigue tests were applied. Furthermore, the effect of using these additives on CRM moisture sensitivity was evaluated. Application of coal waste powder improved the mechanical properties of CRM, but it could not exert a positive effect on CRM moisture sensitivity. Thus, coal waste can be used as CRM additive in conditions that moisture damage does not significantly affect the pavement performance. Unlike the coal waste powder using the coal waste ash not only increased the durability of CRM, but also it showed upgrading the mechanical properties. In continue, the mechanical properties of the CRM containing coal waste and its ash were compared with the mix that stabilised with 1% and 2% ordinary Portland cement (OPC). Based on the comparisons, coal waste powder and its ash had comparable effects to OPC. For example, the results of fatigue tests revealed that at higher strain levels of 200 μϵ the fatigue life of the CRM mix containing 7% coal waste and coal waste ash was higher than that of containing 1% and 2% cement. Finally, apart from the several environmental advantages it was concluded that the use of coal waste powder and its ash had technical benefits in cold recycling with bitumen emulsion.

The theoretical analysis of the RAP aged asphalt influence on the performance of asphalt emulsion cold recycled mixes

Traditionally, reclaimed asphalt pavement (RAP) was commonly recognized as “black rock” in cold recycling mixes, so that aging of the asphalt in the RAP normally was not taken into account during the cold recycling mix design. The objective of this research was to evaluate the influence of aged asphalt in the RAP on the performance of asphalt emulsion cold mixes. Firstly, the RAP material was simulated in the laboratory using the asphalt long-term aging procedure. Secondly, the properties of the four different mixes were evaluated based on Marshall stability, indirect tensile strength, dynamic modulus and fatigue life which associate with aged asphalt and cement. Finally, a finite element model for cold recycled mix was established with the aim to theoretically evaluate the effect of the aged asphalt in the RAP. The results indicated that the existence of the aged asphalt and cement in the RAP could improve the indirect tensile strength, high temperature stability, moisture resistance and fatigue performance of asphalt emulsion cold recycled mixes. Furthermore, the analysis by finite element method (FEM) showed that the simulation in terms of the effect of the aged asphalt was basically consistent with the laboratory results. Essentially, the existence of the aged asphalt in the RAP could reduce the stress and strain concentration in the interphase between the aggregate and virgin asphalt. Therefore, RAP should be not considered as “black rock” in cold recycled mixes based on this research.

Crumb Rubber in cold recycled bituminous mixes: Comparison between Traditional Crumb Rubber and Cryogenic Crumb Rubber

Today recycling is one of the most innovative and interesting techniques for the rehabilitation of destressed road pavements. In recent years the increased interest in this process, has led to the development of various alternative methods for the recovery and the reuse of road bituminous materials. Cold recycling is, among the recycling techniques, certainly the most studied and developed: it allows the recovering of bituminous material from an existing pavement without the addition of heat, whilst ensuring the creation of high quality bound base layers. A wide range of materials have been tested together with Reclaimed Asphalt Pavement (RAP) and, consequently, there is a large number of variables that can be considered in the mix-design process of new eco-friendly Cold Recycled Mixes. In particular, the present research involves the use of Crumb Rubber within a mixture containing 100% Reclaimed Asphalt Pavement, cold recycled with bitumen emulsion and cement. Two different Crumb Rubbers were adopted: one from the ambient production method, and one produced with the cryogenic process. The goal of this research project was to analyze and evaluate the different physical and mechanical characteristics induced by the shared use of two different types of Crumb Rubber in the Cold Recycled Mixes.

Study of the Bulk Index Measuring Methods on Foamed Asphalt Cold Recycling Specimens

For the foamed asphalt cold recycling mixture,we mould the specimens under two different gradation using Marshall compaction method.Then we measure the bulk specific density using the volumetrical method, the corelock method, the wax-sealing method and the saturated surface dry method, calculate the porosity and compare the results.The conclusion is that the results are almost the same under the corelock method, the wax-sealing method and the saturated surface dry method, we can choose the saturated surface dry method to gain the porosity in practical use.

High-temperature performance of multilayer pavement with cold in-place recycling mixtures

The cold in-place recycling (CIR) technique has been gradually accepted and applied in multiple areas of China as the lower layer of highway pavement. The overall pavement typically shows satisfactory resistance to permanent deformations. The objective of this research is to evaluate the high-temperature performance of a typical China pavement structure with CIR. Since the conventional creep test cannot adequately simulate the field conditions, an Advanced Cyclic Creep Test, which can replicate in the laboratory stresses and temperatures encountered in the field was developed and utilised to study the resistance of the CIR pavement to high-temperature deformations. Creep curves following three-stage creep models best fits were obtained to study the effects of cement contents (1.5%, 2.0%, 2.5%) in CIR mixtures and anti-rutting agent in the middle layer on the high-temperature performance of the composite specimens under different testing conditions. In the process of specimen preparation, the impact of the middle-layer compaction on the CIR mixtures was also quantified. According to the results of this research, 6 days of curing time is recommended to restrict the effect of paving and rolling of the hot mix asphalt (HMA) on top of the CIR layer. Adding 0.3% anti-rutting agent to the HMA in the middle layer can enhance the resistance of the composite specimen to high-temperature deformations. An increase in cement content of the CIR mixtures from 1.5% to 2.0% can improve the high-temperature performance of the CIR pavement. Comparing with newly constructed pavement, it is verified that the typical China highways pavement structure including CIR shows satisfactory high-temperature performance.

The effect of Cryogenic Crumb Rubber in cold recycled mixes for road pavements

Over recent years, the necessity of reducing the environmental impact of building new infrastructures has increasingly directed research toward developing innovative manufacturing methods and materials that can satisfy these objectives. Cold recycling, widely used in renovating road pavements in Italy, is also moving in this direction, lowering the manufacturing temperatures of bituminous mixes and reducing or ultimately eliminating the use of virgin raw materials. Currently, a wide range of materials are used and, consequently, the number of variables to be considered in the mix-design process of cold recycled mixes for road bases is considerable. Furthermore, new products are continuously being introduced or developed for recycling purposes. The objective of this research project was to test the effects, both mechanically and environmentally, of crumb rubber included in 100% Reclaimed Asphalt Pavement cold mixes for road bases, bound with bitumen emulsion and cement. The crumb rubber is produced cryogenically with granulometric selection, which together with the bitumen, the cement and the fine fractions of the mix forms a resilient mastic capable of imparting significant fatigue resistance properties to the conglomerate.