Cold In-place Recycling Research Articles

Three-dimensional fracture simulation of cold in-place recycling mixture using cohesive zone model

Cold in-place recycling (CIR) shows a good performance in the resistance to cracks in the field and a newly developed Arcan configuration has been used to investigate the Mixed-Mode cracking behaviour of CIR mixture. In this research, a three-dimensional (3D) heterogeneous fracture modeling method was presented to simulate complex cracking development in CIR mixture. The X-ray computed tomography (CT) technique and digital image processing (DIP) method were employed to create 3D heterogeneous numerical model of CIR mixture. In the modeling, a cohesive zone model (CZM) was utilized to estimate the crack resistance of the interface based on laboratory fracture test. The coalescence of micro-cracks and the inception and propagation of macro-cracks in CIR mixture were carefully studied under fracture Mode I and Mode II, respectively. The fracture process zone was also investigated. Three types of displacements, including the Load-Line Displacement (LLD), Crack Mouth Opening Displacement (CMOD), and Crack Tip Opening Displacement (CTOD) were utilized to plot load-displacement curves and the corresponding fracture energies were calculated. The analyzing results of virtual numerical test are proved to be quite consistent with the actual experimental test. The validity of numerical model is verified.

Rational Mix-Design Procedure for Cold In-Place Recycling Asphalt Mixtures and Performance Prediction

AbstractA new volumetric mix-design procedure utilizing the Superpave gyratory compactor (SGC) was developed for cold in-place recycling (CIR) asphalt mixtures with assistance from the Federal Highway Administration (FHWA). It was developed for partial-depth CIR using asphalt emulsions as the recycling additive. This procedure was calibrated using materials from five geographically varied locations in North America: Connecticut, Kansas, Ontario, Arizona, and New Mexico. It required that specimens be prepared at densities similar to those found in the field. The performance of CIR mixtures prepared in accordance with the new mix-design procedure was evaluated in the laboratory with mechanistic-empirical pavement design guide (MEPDG) models as well as in the field. Creep compliance and strength of the mixtures were determined at 0, −10, and −20°C using the Superpave indirect tensile tester (IDT) with satisfactory results. A field test section also had been established with CIR mixtures in Arizona using this...

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.

Cost and Eco-Effective Cold In-Place Recycled Mixtures with Foamed Bitumen During the Reconstruction of a Road Section Under Variable Load Bearing Capacity of the Subgrade

The development of vehicle transport, causing increased numbers of vehicles and road users as well as increased loads acting on the pavement, has a negative impact on its durability within the intended life cycle. A major part of Polish road network has severely deteriorated and requires that immediate measures be undertaken to improve the safety and comfort of users. Cold In-place Recycling with Foamed Bitumen (CIR-FB) technology uses 100% of reclaimed material by converting distressed layers into new materials for the stabilization of the subgrade and/or base courses without the need to demolish, haul and manage them. This paper presents a proposal of the reconstruction of the pavement of a road section localized in central Poland (świętokrzyskie province) using traditional and alternative materials. Cost effectiveness and ecological effectiveness of proposed technologies were compared taking into account variable load bearing capacity of the subgrade (frequent in linear construction projects), resulting from its non-uniformity. In the case analysed, due to the presence of various sands (including sand dust and same uniformly graded sand of poor compactibility), the pavement durability was estimated based on the assumption of 50MPa and 80MPa subgrade bearing capacity. It was demonstrated that, considering economy and ecology, the replacement of standard solutions based on new materials by the CIR-FB materials is the most effective way of road reconstruction with its long service life maintained.

Comparative life cycle assessment of asphalt pavements using reclaimed asphalt, warm mix technology and cold in-place recycling

In this work the environmental sustainability of asphalt pavement is analyzed, from material production and maintenance strategy point of view. The work consists of an analysis of the life cycle of 1km of road pavement and includes all stages of the life cycle: from extraction of virgin materials to end of life. Three types of pavements are compared, among which one produced with virgin materials and traditional technologies in plant, which is used as a reference, and two in which the use of Reclaimed Asphalt Pavement (RAP) and Warm Mix Asphalt (WMA) technology are combined. Also the implementation of the practice of Cold In-Place Recycling (CIR) at the end of life is considered from an environmental point of view: after the first 15 years of life the comparison is made between traditional recycling in plant and CIR. The impacts are evaluated using different methods. Decrease in environmental impacts are found for the options that combine the use of RAP and WMA reaching up to a percentage of reduction of 12% for CO2eq, 15% for energy consumptions, 15% for water used during the lifecycle, and 10–15% for the three macro-categories of damage evaluated in the ReCiPe endpoint method. Additional reductions could be achieved by applying also CIR technology especially for greenhouse gas emissions (−9%).

Characterization of air voids in cold in-place recycling mixtures using X-ray computed tomography

With the increasing application of cold in-place recycling (CIR) techniques, many performance studies have been done, but they rarely focus on the internal structure of CIR mixture. The objective of this study is to investigate the characteristics of air voids in CIR mixtures with the X-ray computed tomography (CT) and digital image processing (DIP) methods. The volume, size, and number of air voids in CIR specimens were statistically analyzed considering different aggregate gradations and compaction methods. The two-parameter Weibull function was used to model the air void gradation of CIR mixtures. Especially, the differences in air voids between CIR and hot mix asphalt (HMA) mixtures were fully quantified. According to the results of this study, with coarser aggregate gradation, the CIR mixture tends to have larger size and less number of air voids. Comparing with the Superpave gyratory compactor (SGC) method, the Static Load compaction produces relatively small air voids. The distributions of air void number in specimen depths for the three compaction methods are different. The scale and shape parameters in Weibull function are both sensitive to the changes in aggregate gradation and compaction method. The substantial difference of air voids between CIR and HMA mixtures is in the aspect of the air void number rather than the air void size. Overall, this study provides a solid foundation for future research in exploring the internal structure and mix design of CIR mixtures.

Initial Performance of Virginia's Interstate 81 In-Place Pavement Recycling Project

Rehabilitating or reconstructing existing asphalt pavements by applying in-place pavement recycling techniques has been shown to be more cost-effective and more environmentally friendly than with traditional techniques. However, the scanty information in the literature documenting the structural and functional performance of these processes for high-volume roadways, leads to a perception by pavement engineers that the techniques are suitable only for lower-volume roads. This paper presents performance data for the 3.66-mi section of Interstate 81 in Virginia that was rehabilitated through the use of full-depth reclamation, cold central-plant recycling, and cold in-place recycling during the 2011 construction season. The performance data used to document the pavement condition included the structural capacity obtained by a falling-weight deflectometer and rut depth and ride quality measurements collected by an inertial profiler. The structural layer coefficients for the recycled materials were at the upper range of values reported in the literature. The pavement sections continued to perform well in regard to their functional and structural condition after the application of approximately 6 million equivalent single-axle loads and nearly 3 years of service. Two sections with different overlay thicknesses in the right lane also performed well after nearly 3 years of service.

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.

Laboratory and Field Investigation of Mechanistic Properties of Foamed Asphalt Recycled Base Course Materials for High Volume Pavements in India

The quality of cold in-place recycling (CIR) is strongly dependent on the capability of proper laboratory investigation and design, and quality control during construction. The objective of this study was to evaluate the quality of the first major foamed asphalt CIR recycled layer in India, laid on a national highway in India. A nonnuclear density gauge (NNDG) and a portable seismic properties analyzer (PSPA) were utilized to determine the density and stiffness of the foamed asphalt recycled layer. In addition, cores and material samples from the recycled layer were also tested in the laboratory for density and stiffness using dynamic modulus tests and the seismic method. The results of tests were related to material properties and critical factors influencing the performance-related properties were identified. Comparisons between laboratory and field sample data were made. Foaming temperature and gradation control of crusher dust were identified as parameters requiring tight control to achieve the required quality. The detrimental effects of excess blending of cement were also revealed. The NNDG and the PSPA were found to be capable of identifying poor quality areas both in midsections and at joints, and to be capable of monitoring the quality of recycled layer.

Laboratory Investigation of Cement-Treated Reclaimed Asphalt Pavement Material

Cold in-place recycling is considered as a pavement rehabilitation technique that is more environmentally friendly than the common practice of simply constructing a new hot-mix asphalt (HMA) overlay on the existing wearing surface. This paper describes a laboratory experimental study for the formulation and mechanical characterization of cement-treated reclaimed asphalt pavement (RAP) material to be used as a base layer during the rehabilitation of pavements. RAP content was varied between 0 and 100% in order to study the effects of this parameter on the mechanical properties. Portland cement content was kept constant at 6% by weight of dry constituents. Results have shown that an increase in RAP content results in a decrease in compressive strength, flexural strength, indirect tensile strength, and elastic modulus. However, for any RAP content of 60% or less, acceptable mechanical properties for a pavement base layer were achieved. Unrestrained shrinkage testing showed statistically insignificant change in shrinkage strain with RAP content.

Cold In-Place Recycling as a Sustainable Pavement Practice

Pavement rehabilitation and reconstruction methods with CIR (cold in-place recycling) are alternatives that can effectively reduce the high stresses and waste produced by conventional pavement strategies. An attempt was made to predict the performance, particularly low-temperature cracking resistance characteristics of CIR mixtures. These were prepared with the mix design procedure developed at the URI (University of Rhode Island) for the FHW A (Federal Highway Administration) to reduce wide variations in the application ofCIR mixtures production. This standard was applied to RAP (reclaimed asphalt pavement) to produce CIR mixtures with CSS-lh asphalt emulsion as the additive. By adjusting the number of gyrations of the SGC (Superpave gyratory compactor) for compaction, the field density of 130 pcf was represented accurately. To secure a base line, HMA (hot mix asphalt) samples were produced according to the Superpave volumetric mix design procedure. The specimens were tested using the IDT (indirect tensile) tester according to the procedure of AASHTO T 322 procedure at temperatures of -20, -10 and 0 °C ( -4, 14, and 32 Gp, respectively). The obtained results for the creep compliance and tensile strength were used as input data for the MEPDG (mechanistic empirical pavement design gnide ). The analysis results indicated that no thermal or low-temperature cracking is expected over the entire analysis period of 20 years for both HMA and CIR mixtures. Thus, it appears that CIR is a sustainable rehabilitation technique which is also suitable for colder climates, and it is reconunended to conduct further investigation ofload-related distresses such as rotting and fatigue cracking.

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.

Mixed-Mode cracking behavior of cold recycled mixes with emulsion using Arcan configuration

Cold In-place Recycling (CIR) has gained popularity in recent years and it shows a good resistance to reflective cracking from underlying concrete pavement. The objective of this research is to investigate the Mixed-Mode cracking behavior of CIR mixtures, as there are indications that reflective cracks do not form in a 100% Mode I fashion. A newly developed Arcan configuration was utilized to simulate five levels of Mixed-Mode cracking. The peak load, crack angle, and three types of fracture energies were obtained to compare the Mixed-Mode cracking characteristics of CIR mixture. Utilizing Digital Image Correlation (DIC) allowed for full-field displacement/strain fields to be captured, along with the more traditional readings from attached gauges. The accuracy of DIC was verified and the effect of rigid displacement in Arcan test was eliminated. The results of this study indicates that crack initiation in 100% Mode II cracking produces the highest peak load, but it propagates rapidly once the crack is initiated. The peak load is more sensitive than fracture energy to temperatures. A strong correlation was found between crack angle and the level of Mixed-Mode cracking: it increases as the percentage of Mode II increases. A common feature of the five strain maps for Mixed-Mode cracking is that the strains near crack tip are higher than other strains, which results in the crack initiation. However, the crack path formed along higher strains changes significantly with five levels of Mixed-Mode cracking. Overall, this research provides a solid foundation for future research in exploring reflective cracking characteristics of CIR mixtures.

Field investigation of pavement rehabilitation utilizing cold in-place recycling

Despite the widespread field and laboratory research works there are still a lot of unknown aspects about the cold in-place recycling. This paper presents the outcomes of a five year evaluation of a major highway in Iran which had been rehabilitated by cold in-place recycling. Before starting the rehabilitation process, a comprehensive field survey was performed. During the pavement surveying, type, severity and reason of distresses were investigated and PCI parameter was calculated. Furthermore, both destructive and nondestructive tests were carried out to evaluate the pavement condition and estimate the remaining life. On the basis of these investigations studied highway was divided to six design sections. Based on technical analysis four sections were recycled whereas two other sections were rehabilitated with the conventional cold milling and overlay method. Afterwards, the pavement performance was monitored during the next 5 years. After about six months of monitoring, structural failures were detected in about 10% of recycled areas. Based on field surveying, low compaction and load bearing of subgrade materials and lack of high quality unbound pavement layers accompanied by some shortcomings in recycled layer resulted in undesirable results in these areas. Based on obtained results and performed analysis a practical flowchart was presented which could be used as a project selection guideline.

Cold In-Place Recycling in Nevada

The Nevada Department of Transportation has long used CMS-2S emulsion for cold in-place recycling (CIR) projects and has recently introduced solvent-free (Reflex) emulsion and polymerized asphalt surface sealer (PASS) emulsion. An observed difference in CIR performance with changing emulsion technology prompted the assessment of long-term performance of CIR pavements throughout Nevada. The evaluated CIR projects were divided on the basis of rehabilitation type and then subdivided on the basis of emulsion technology. The study revealed that CIR followed by a hot-mix asphalt (HMA) overlay and a surface treatment performed much better on high-volume roads than did CIR with surface treatment on low-volume roads. Transverse and longitudinal cracking were the major types of distresses in CIR pavements. Approximately 50% of pavements constructed with HMA overlay and surface treatment and 95% of pavements constructed with only surface treatment experienced transverse cracking during service life. About 30% of pavements constructed with HMA overlay and surface treatment and 70% of pavements constructed with only surface treatment experienced longitudinal cracking. The CIR technology with HMA overlay and surface treatment significantly improved rutting resistance and pavement roughness. Climatic condition, CIR layer thickness, and surface treatment types were found not to affect performance of roads with CIR. The CMS-2S projects constructed with surface treatment and 1.5- to 2.5-in. HMA overlay were predicted to reach a pavement condition index value of 60 for rehabilitation in 15 years. The CMS-2S projects constructed with 3 to 4 in. of HMA overlay performed excellently up to 9 years and were expected to last more than 20 years before rehabilitation. The CIR with CMS-2S and PASS emulsions constructed with surface treatment were predicted to reach the index value of 60 after 15 and 19 years, respectively. However, Reflex emulsion was predicted to need rehabilitation after only 6 years.

Vacuum Sealing–Based Volumetric Density Measurement Approach for Cold In-Place Recycling

Recent economic limitations have fostered increased use of pavement rehabilitation methods such as cold in-place recycling (CIR). CIR could be more appealing to departments of transportation provided variability were lower and performance were more predictable. Because of the nature of the materials and construction processes, CIR is likely to be more variable than plant-mixed asphalt, and it is believed that the performance variability of CIR can be reduced through enhanced density control. The many density control methods described in the literature for CIR are often vague. This study used ASTM D6857 vacuum sealing to obtain the maximum theoretical specific gravity ( Gmm) of reclaimed asphalt pavement (RAP) and a gravity-proportioning equation to estimate CIR Gmm (specific gravity after cement, emulsion, or a combination is mixed with RAP). Vacuum sealing was also used to obtain the bulk specific gravity ( Gmb) of compacted CIR (AASHTO T 331). In all, 240 Gmm and 156 Gmb tests were conducted. D6857 and AASHTO T 209 detect differences between RAP and hot-mix asphalt Gmm, but the differences led to manageable errors for CIR density control that should still allow for some improvements over many current practices. The equation developed in the study estimated CIR Gmm with reasonable error, and T 331 suitably characterized CIR Gmb at the often high air void levels that were observed. The findings show that CIR Gmm and Gmb, as determined by vacuum sealing and the gravity-proportioning equation, constitute a reliable, convenient, and implementable approach to controlling density and likely reducing performance variability.

Cold asphalt recycling with 100% reclaimed asphalt pavement and vegetable oil-based rejuvenators

Cold in-place recycling methods are used to different extents but are often not very suitable for small construction sites. Therefore, a new process was developed using vegetable oil-based rejuvenators to reactivate the old binder of the reclaimed asphalt pavement (RAP) material. Briefly summarised, RAP is produced on-site from the old pavement, then sprayed with water and rejuvenator before it is mixed thoroughly and immediately compacted. Process parameters have been optimised in laboratory tests with gyratory compacted specimens. It turned out that rejuvenators with used cooking oil did give comparable results to virgin rapeseed and linseed oil. Only the outcome of the water sensitivity tests was not satisfactory, as the wet specimens showed a considerable loss of tensile strength. However, the damage was only temporary and the stability recovered to the original value after drying of the water-saturated specimens. In a second step, four cold mixtures with different rejuvenator compositions were compared in a trial field section with conventional hot mix asphalt concrete. In situ testing with the mobile load simulator MMLS3 showed good performance for three of four cold mixture pavements, which was comparable to the rutting behaviour of hot mix asphalt. Several wearing courses but also surface layers for small secondary roads have been constructed during the last three years. No significant damage has been reported for these cold mixture pavements so far. Particularly, the use of used cooking oil as a rejuvenator is promising due to its low price. Since only recycling products are used and no transport of the cold mixture is necessary for in situ recycling, this new cold recycling system is highly ecological as well.

Cement-fly ash stabilization of cold in-place recycled (CIR) asphalt pavement mixtures for road bases or subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement (RAP) aggregate and stabilized soil (S) for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent (MA) on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy(SEM) images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

Evaluation of Cold In-Place and Cold Central-Plant Recycling Methods Using Laboratory Testing of Field-Cored Specimens

AbstractDuring the 2011 construction season, the Virginia Department of Transportation (VDOT) completed a major pavement recycling project that marked the first time full-depth reclamation (FDR), cold in-place recycling (CIR), and cold central-plant recycling (CCPR) were used together on a single project on the US interstate system. The CIR and CCPR mixtures were produced by using foamed asphalt and hydraulic cement as the stabilizing agents. After completing the pavement rehabilitation project, engineering properties of the CIR and CCPR mixtures were determined in the laboratory from field-cored specimens. VDOT conducted this study because the agency was considering using a single set of construction specifications for both CIR and CCPR materials if the engineering properties of the two processes were found to be similar. This project offered a unique opportunity to evaluate the two recycling methods by using materials from the same location. Laboratory tests included gradation, binder content, density m...