Cold In-place Recycling Research Articles

Development of a Simulation-Based Approach for Cold In-Place Recycled Pavement Moisture-Content Prediction Using Ground-Penetrating Radar

Ground-penetrating radar (GPR) recently has been used for quality control and quality assurance of the asphalt concrete (AC) pavement-construction process. The objective of this study was to investigate the feasibility of estimating, by using GPR, the moisture content in AC pavement. This application is particularly important for emulsion-stabilized cold in-place recycling (CIR) and cold central-plant recycling (CCPR), where monitoring the moisture content is necessary for deciding the timing of opening the road to traffic, overlay placement, or both. Four field tests were performed using GPR on CIR- or CCPR-treated AC pavement. A numerical simulation model of AC pavement with internal moisture was generated using the information from mix design, and virtual GPR tests were performed using the finite-difference time-domain (FDTD) method. After calibration, a moisture-prediction formula derived from the simulation model was used to correlate the dielectric constant predicted by GPR to the moisture content within cold recycled layers. The GPR signal was “denoised” by improving its stability and mitigating the measured-height mismatch. The in-situ moisture content was predicted using the proposed method and compared with field-collected samples. Results showed that the proposed method is effective in estimating CIR- and CCPR-layer moisture content. The variation of dielectric constants in field tests is also discussed. A testing protocol for predicting moisture content using GPR is suggested for CIR and CCPR pavement.

Numerical simulation of the stiffness evolution with curing of pavement sections rehabilitated using cold in-place recycling technology

Cold in-place recycling (CIR) technologies are becoming one of the main bets in the road sector to promote the reduction of greenhouse gas emissions. This technique also contributes to the circular economy, reusing 100% of the RAP from worn roads. In this research, numerical simulations of CIR sections are presented. The nonlinear behaviour of the CIR-base material is modelled using three predictive models based on triaxial test results. Variations in the performance depending on the type of subbase, the curing of the CIR-base material and its thickness, and the effect of the wearing-course were analysed. The response of the sections with unbound granular subbase proved to be very sensitive to variations in the parameters studied, and the increase in CIR base thickness was beneficial, while the opposite occurred with a cement-treated subbase.

Performance evaluation of cold in-place recycling materials through a simple semi-circular bending test

Cold in-place recycling (CIR) is a method of recycling existing Hot Mix Asphalt (HMA) pavements. In this study, a new performance-based test method, called Fracture Index Value for Energy (FIVE), is developed to capture the fracture energy of the CIR materials. Furthermore, various stabilisation agents were used including engineered emulsion (EE), high float asphalt emulsion (HFMS-2s), commodity asphalt emulsion (CSS-1) and foamed asphalt. The FIVE test was first validated using disk-shaped compact tension (DCT) test and then was implemented on the study mixtures at their optimum stabilisation agent contents. The ranking of the mixtures and reproducibility of the FIVE test was proved to be true through inter-lab comparisons of the test results between two independent testing laboratories. The statistical testing results postulate that the FIVE test is a simple test method that is capable of characterising the cracking performance of the CIR mixtures.

Laboratory Investigation of Factors Affecting the Evolution of Curing in Cold In-Place Recycled Materials

Most cold in-place recycling (CIR) construction uses asphalt emulsion or foamed asphalt as stabilizing agent, which requires placing and compacting at optimum moisture or fluid content in the field. To ensure the CIR layer gains appreciable mechanical capacity to support traffic (including that of construction vehicles), the CIR layer must cure. Curing is typically expressed in relation to moisture content in the CIR layer; however, there is need to explore if a direct link exists between the amount of moisture in CIR and the mechanical properties of CIR. Presently, to ensure sufficient curing, construction specifications recommend time estimates with minimal consideration of how various factors such as material variations, climatic inputs, and construction process differences may affect the curing evolution. The objective of this study was to investigate and identify the critical factors that affect the curing evolution of CIR materials. Curing was evaluated in relation to moisture loss (using gravimetric measurements) and gain in mechanical properties (using indirect tensile strength and resilient modulus tests). The results show that there is further gain in mechanical properties after the CIR mixtures have reached an equilibrium moisture condition. Additionally, the following factors were identified to most significantly affect the curing evolution of CIR materials: stabilizer type and amount, active filler type and amount, initial moisture content, curing temperature (when active filler is present), and moisture reintroduction through external sources (e.g., rainfall). On the other hand, density and curing temperature (in the absence of active filler) did not seem to affect the rate of curing.

Development of a Performance-Based Approach to Asphalt Emulsion Selection for Cold In-Place Recycling Applications

Asphalt emulsions are currently selected based on material classification. These properties do not predict performance and provide the same classification to emulsions that behave quite differently in the field. Therefore, this research developed a performance-based approach to asphalt emulsion selection for cold in-place recycling (CIR) applications. The performance period was broken down into three categories: workability, compactibiltiy, and cohesion gain. Superpave Gyratory Compactor (SGC) metrics, the loose triaxial-, raveling-, direct shear-, and compacted triaxial tests were used to quantify the behavior of three CSS-1h asphalt emulsions. It was found that the final density and the CIR workability engergy index SGC compaction metrics showed the most promise, whereas the Dongre workability test was found to have potential. The loose triaxial test was able to distinguish the performance of the three asphalt emulsion at 100 and 200 kPa confining pressures, but the results were not consistent with viscosity measurements. The raveling test showed high levels of variability, whereas the direct shear- and compacted triaxial tests showed similar trends and were able to distinguish between the three emulsions. Finally, for all tests, curing samples at 10°C is recommended.

Evaluation of the shear and permanent deformation properties of cold in-place recycled mixtures with bitumen emulsion using triaxial tests

The cold in-place recycling (CIR) technique is a road rehabilitation method suitable for a circular economy. Triaxial tests have proven to be suitable for studying the mechanical behaviour of cold mixtures. In this study, CIR specimens were prepared using a gyratory compactor with different proportions of bitumen emulsion. The Mohr–Coulomb diagrams and shear parameters were obtained by conducting monotonic triaxial tests at different confining pressures. The binder content provided adequate cohesion; however, an excess of binder reduced internal friction. Subsequently, repeated load permanent deformation triaxial tests were performed. Accordingly, critical stress ratios between 20% and 30% were obtained, and the mix with a 2.50% binder exhibited the best response. Lastly, two permanent deformation prediction models were fitted to the measured results. For high deformations, the Paute model underestimated the deformations, whereas the Huurman model demonstrated the best fit.

Evaluating the Potential Environmental Benefits of Cold Recycling-Based Methods for Flexible Pavement Rehabilitation in Virginia

This paper describes a study conducted to quantify the potential environmental benefits of recycled asphalt pavement projects completed in Virginia. Three restorative maintenance projects were evaluated: (i) a 5-in. hot-mix asphalt (HMA) over 5-in. cold in-place recycling (CIR) with foamed asphalt stabilization; (ii) a 3.5-in. HMA over 5-in. CIR with emulsion stabilization; and (iii) one non-recycling structural overlay (5-in. HMA over an existing pavement). In addition, the following reconstruction projects—the first three constructed on primary roads and the last two constructed on interstates—were assessed: (i) a 2.5-in. HMA over 9.6-in. full depth reclamation (FDR) with asphalt stabilization; (ii) a 3.5-in. HMA over 9.0-in. cement stabilized FDR; (iii) a non-recycling reconstruction project (7-in. HMA over 12-in. aggregate base and subbase); (iv) a 6-in. HMA over 6-in. asphalt-stabilized cold central plant recycled layer over a 12-in. lime-stabilized FDR base; and (v) a non-recycling reconstruction project (8-in. HMA over 18-in. aggregate base and subbase). When considering exclusively cradle-to-laid system boundaries, the results show that pavement recycling projects used for interstate reconstruction and primary route restorative maintenance yielded lower global warming (GW) than non-recycling approaches. When considering the entire life cycle, the study found that approximately 98% of the total GW came from pavement–vehicle interaction that takes place during the use stage. Finally, to reduce GW, the Virginia Department of Transportation could encourage (or even incentivize) practices that improve the initial pavement smoothness for recycling projects and use structural designs that are expected to have a low annual deterioration rate.

Experimental investigation of reclaimed asphalt foamed bituminous mix: a cold mix technique

PurposeNatural good-quality sources of aggregates are depleting, whereas large amount of reclaimed asphalt pavement (RAP) is produced annually. Safe disposal and use of RAP in the cold in-place recycling (CIR) using foamed bitumen could be sustainable approach where milling and mixing operations are accomplished simultaneously. This will not only help in minimizing contamination (probability) and transportation cost but also reduces the carbon footprints. Therefore, this study aims to investigate the scope of RAP utilization up to 100% and further its effect on the behavior of reclaimed asphalt foamed bituminous mix.Design/methodology/approachReclaimed asphalt foamed bituminous mix (FBM) is still a new technique. The evidence of performance of 100% recycled pavement (CIR) is only anecdotal and lacks in systematic guidelines and literatures. Foam binder coating around the aggregates is also a concern. Therefore, this study is mainly emphasized to investigate the scope of RAP use in the FBM up to 100%. RAP content is varied in each trial, i.e. 70, 85, 100 and 0% (only fresh aggregates), to make the FBM. RAP use and its effect on the behavior of FBM in terms of resilient modulus, variation in resilient modulus with curing, rutting performance and the potential of resistance against the moisture damage are addressed.FindingsConsidering the laboratory studies, it can be accomplished that mechanistic properties and performance of FBM are largely influenced by RAP material and portray less susceptible characteristics against the moisture damage. FBM containing 70% RAP content exhibits maximum resilient modulus. However, use of RAP up to 100% in FBM is satisfying the minimum required specification.Originality/valueOverall, the study may be helpful to highway professionals and could generate another possible option of 100% RAP replacing fresh aggregates in the flexible pavements.

Short-term resilient behaviour and its evolution with curing in cold in-place recycled asphalt mixtures

This study evaluates the short-term resilient behaviour of cold in-place recycled (CIR) asphalt mixtures with bitumen emulsion when they are more similar to non-cohesive granular materials than to conventional hot mixtures. Gyratory compacted CIR specimens were manufactured using different proportions of bituminous emulsion and water, and dynamic triaxial tests were conducted at different curing times. The resilient moduli were obtained experimentally and fitted using three numerical models. Characteristic nonlinear elastic behaviour and an increase in stiffness with curing time were observed. Water loss during curing and stiffness increase were found to be related. Mixtures with 2.50% residual bitumen and 2.75% added water showed the best short-term stiffness evolution.

Sustainability Evaluation of Cold In-Place Recycling and Hot Mix Asphalt Pavements: A Case of Qassim, Saudi Arabia

The construction of conventional hot mix asphalt (HMA) pavements results in a number of economic and environmental issues, such as the cost of new overlays and associated impacts on natural resources. Although the cold recycling with an emulsified asphalt-recycling agent holds certain benefits over the HMA, its implementation on different road types, ranging from farm-to-market roads to expressways, is yet contentious due to the need for sophisticated equipment and trained workforce. The present research developed a methodology to evaluate all the three dimensions of sustainability, including economic (construction cost), environmental (natural resource depletion), and social (need for advanced equipment and skilled labor) of various scenarios of RAP and conventional asphalt pavements. The present study evaluated an equivalent thickness of the Cold In-place Recycling (CIR) pavement, which behaves similar to HMA pavement under the influence of different traffic loads. Fifty CIR and HMA scenarios for different traffic volumes and pavement layers thicknesses were developed. Finally, the sustainability of all the scenarios was evaluated for traffic designation in Saudi Arabia using fuzzy-based multicriteria analysis. Ranking of scenarios found CIR as a more sustainable overlay option for the feeders, collectors, main urban streets, expressways, and heavily trafficked highways in industrial areas where ESALs (Equivalent Single Axle Loads) range between 2,000,000 and >31,000,000. Considering the limited availability of advanced equipment and skilled labor for CIR pavements, HMA was found be a more sustainable option for farm-to-market roads with the “very light” traffic class. The methodology will help the pavement managers in decision making regarding the selection of sustainable pavement technologies for different road types in Saudi Arabia and the rest of the world.

Cold in-place recycling of aged and deteriorated asphalt and concrete pavements

This study focuses on implementing two distinct recycling methods, the reclaimed asphalt pavement and the reclaimed concrete material, on classical road pavements, by totally replacing the surface or base courses with ones made with recovered materials. The majority of the road networks in the eastern European countries were built between 1950 and 1980 and are, nowadays, aged and degraded. Within this frame, the cold in-place recycling methods were developed, which can be applied to both asphalt and concrete pavements. During the cold in-place recycling process, the reclaimed asphalt or concrete materials do not leave the construction site at all, but they are processed on the spot and reused immediately. Thus, the material is granulated to the desired depth, mixed with the binding agent and water and then repaved and compacted in a new layer. One of the most significant benefits of the cold in-place recycling process is that the material is simultaneously recycled and mixed with the binding agent, enabling the road pavement to be strengthened without the need to import expensive virgin aggregates. This work describes the manufacturing technology and the equipment train used to cold recycle aged and deteriorated asphalt and concrete pavements.

Performance Characteristics of Cold In-Place Recycling Mixtures

AbstractCold in-place recycling (CIR) of asphalt pavements is a process that has successfully been used for many years. The use of CIR for rehabilitation offers many advantages over reconstruction....

CALCULATION OF GRADING OF COLD RECYCLED MIXTURES USING NEW AGGREGATES ACCORDING TO THE DESIGNED THICKNESS OF A REHABILITATED LAYER

Technologies of cold recycling of asphalt concrete using various types of binders have been widely implemented in road building industry in Ukraine. Technologies of cold recycling allow to eliminate some types of deformations or destructions and also to enhance bearing capacity of flexible road pavements. If required, process of cold recycling assumes application of new aggregates to achieve standard grading of a recycled mixture. As the standard requirement does not state any restrictions on relative content of new aggregates, these can be applied to achieve the designed thickness of a rehabilitated layer. This article presents a method for calculation of grading of cold recycled mixtures according to the designed thickness of a rehabilitated layer assuming the amount of reclaimed asphalt pavement (RAP) equals to the amount of asphalt concrete in a milled layer. The proposed method is based on calculation of grading of a mixture of new aggregates that should be rather individual for each recycled mixture. The input data for calculation should be obtained from results of a field testing of “old” road pavement construction and also from laboratory investigation of “old” asphalt concrete cores. The article gives also some examples of calculation which are performed on base of mean values of standard grading of recycled mixtures. Nevertheless, the proposed method of calculation could be applied on the base of any values selected within the standard limits. The proposed method assures precise modeling of composition and properties of a recycled mixture and could be implemented when planning projects on rehabilitation of flexible road pavements either by cold in-plant or cold in-place recycling.

Structural Contribution of Cold In-Place Recycling Base Layer

Cold in-place recycling (CIR) of asphalt pavements is a process that has successfully been used for many years. The use of CIR for rehabilitation offers many advantages over traditional overlays due to its excellent resistance to reflective cracking and its environmentally friendly impacts. Despite the good performance and positive sustainability aspects of CIR, the structural contribution of the CIR base layer has not been well defined. In this research, CIR mixtures were designed with different asphalt emulsions. The mixtures were then subjected to dynamic modulus, repeated load triaxial, and flexural beam fatigue testing over a range of temperature and loading conditions. The performance test data generated were then used to develop CIR rutting and fatigue performance models used in the mechanistic analysis of flexible pavements. The technique used to develop the performance models leveraged the fact that the rutting and fatigue models for individual CIR mixtures were all within the 95 percent confidence interval of each other. A mechanistic analysis was conducted using the 3D-Move Mechanistic Analysis model. With the laboratory-developed performance models, the structural layer coefficient for the CIR base layer were developed for use in the 1993 AASHTO Guide for the Design of Pavement Structures. This analysis led to the determination of an average structural coefficient of the CIR base layer of 0.25.

Ruggedness Evaluation and Precision Estimates for Newly Developed Test Methods for Asphalt-Treated Cold Recycled Pavements

Asphalt-treated cold recycled pavements, including cold in place recycling, full depth reclamation, and cold central plant recycling, are becoming popular rehabilitation options because they are economical, sustainable, and provide good performance. Because asphalt-treated cold recycled pavements use foamed or emulsified binder, they require a curing period post-construction before being opened to traffic or surfaced. Uniform guidelines on when an asphalt-treated cold recycled roadway can be opened to traffic or surfaced are not widely established, many are based on time or moisture content, and extreme ranges exist among agency specifications. Mixture designs also vary widely among agencies with regard to active filler use and asphalt recycling agents, further complicating the determination of necessary curing time. NCHRP Project 09-62 investigated a variety of test methods for determining when a recycled roadway could be opened to traffic or surfaced. This included extensive laboratory and field evaluations. New shear strength and raveling test methods were developed. For each test method a ruggedness study and inter-laboratory study were performed. The ruggedness study revealed critical test fixture and operation parameters. Six asphalt-treated cold recycled pavement process/material combinations were tested by three entities to develop precision estimates and statements (i.e., repeatability and reproducibility) for the new test methods. Tools and information from this study provide a rational basis for establishing specifications, which will help reduce pavement damage from early traffic and minimize roadway closures and delays.

Development of Warm In-Place Recycling Technique as an Eco-Friendly Asphalt Rehabilitation Method

Cold In-place Recycling (CIR) has been widely used in the world since it is easy to apply it in the field at a low cost. However, it is not normally used as a surface layer as a result of its inconsistent quality due to an excessive amount of fine aggregates pulverized during the milling process. Hot In-place Recycling (HIR) can retain the original shape of the aggregates, but it often produces a large amount of Volatile Organic Compounds (VOCs). Therefore, a third in-place recycling technique is introduced in this paper: Warm In-place Recycling (WIR). The WIR technique overcomes the limitations of both CIR and HIR techniques by lowering a heating temperature while adding a Tetraethylenepentamine (TEPA)/Soybean/SBS additive. To identify the effect of the additive on the RTFO-aged binder, viscosity and dynamic modulus values were measured at different temperatures. Based on Hamburg Wheel Tracking (HWT) and Disc-Shaped Compact Tension (DCT) tests, the additive improved the moisture susceptibility and low temperature cracking resistance. The indirect infrared heating equipment reduced the emission by lowering the pavement surface heating temperature by 20 °C from 140 to 120 °C. Compared with the heating at 140 °C, the LPG usage for heating at 140 °C was lowered by 21%. The proposed WIR equipment with an additive would revolutionize the in-place recycling practices.

Long-Term Performance of Pavement Structures with Cold In-Place Recycled Base Course

Properly designed and maintained asphalt pavements operate for ten to twenty-five years and have to be rehabilitated after that period. Cold in-place recycling has priority over all other rehabilitation methods since it is done without preheating and transportation of reclaimed asphalt pavement. Multiple researches on the performance of cold recycled mixtures have been done; however, it is unclear how the entire pavement structure (cold recycled asphalt pavement overlaid with asphalt mixture) performs depending on binding agents. The main objective of this research was to evaluate the performance of cold in-place recycled asphalt pavements considering binding agents (foamed bitumen in combination with cement or only cement) and figure out which binder leads to the best pavement performance. Three road sections rehabilitated in 2000, 2003, and 2005 were analysed. The performance of the entire pavement structure was evaluated in terms of the International Roughness Index, rut depth, and pavement surface distress in 2013 and 2017.

Functional characterization of a Cold-In place-Recycled pavement at different stages of the curing process

Cold-In place-Recycled (CIR) pavements are an environmentally friendly option for road rehabilitation operations on aged pavements. These pavements are generally employed as base layers, and a surface treatment is performed on them. However, the design of new additives and enhancements in the technique for constructing CIR pavements have enabled such pavements to be used as wearing courses in some cases. In this context, research on the functional characteristics of CIR pavements is required for characterizing their performance and, therefore, broaden their knowledge and use as a noise mitigation measure. The aim of this study is to analyze some of these functional characteristics: tire/pavement sound levels, texture, and dynamic stiffness. An experimental test track section was evaluated during the pavement curing process (very short term) by means of laboratory and field auscultation. Different measurement campaigns were conducted at different stages of the pavement curing process. According to our results, the changes in the pavement during curing lead to higher tire/pavement sound levels due to the evolution of the dynamic stiffness of the pavement. The increase in tire/pavement noise levels is mainly located at the peak frequencies (800–1250 Hz) of the sound spectra, with values from 76.2 dB(A) to 81.5 dB(A) at 800 Hz. The differences among the mean values of the macrotexture (Mean Profile Depth — MPD) do not explain the different overall tire/pavement noise levels measured at the different stages of curing. However, the texture spectrum undergoes an evolution. The initial texture levels, with wavelengths between 100 mm and 500 mm decrease during the curing process.

Compaction and volumetric analysis of cold in-place recycled asphalt mixtures prepared using gyratory, static, and impact procedures

Compaction is one of the most important factors to be considered while manufacturing laboratory samples of cold in-place recycled (CIR) mixtures.In this study, the effect of three laboratory compaction procedures (static, gyratory, and impact) on the volumetric performance of CIR mixtures was investigated. CIR specimens were manufactured with the same proportion of added water and bitumen emulsion, and using several levels of compaction, varying the number of gyrations and blows. The volumetric properties were evaluated by different procedures, both before and after curing. A comparison between the laboratory results of the different tests, the design target values, and actual in-field values was performed. It was observed that gyratory compaction proved to be the most versatile and one that best represented the real compaction. The bulk density procedure by dimensions was useful for laboratory design; however, it overestimated the sizes of the air void content by more than 10% compared to the field values.

Unconfined Compressive Strength of Rehabilitated Road Base via Polymer-Modified Cold In-Place Recycling (CIPR)

Cold In-Place Recycling (CIPR) is a road maintenance technology, which chemically stabilize, recycle and improve existing asphalt concrete together with road base underneath. Cement is the most common chemical for CIPR adopted in Malaysia. However, shrinkage crack remains as unresolved technical drawback of cement stabilization, road practitioners are always seeking alternative materials to replace cement in CIPR. A proprietary product, Polymer Modified Cementitious (PMC) chemical binder was identified as the research object to verify the suitability in CIPR application and to study the strength-gain over time, through laboratory testing. To replicate CIPR process, Crusher run (CR) and Recycled Asphalt Pavement (RAP) were mixed at various ratio to study the effect of CR to RAP ratio on strength gained; with PMC added in dosage between 2-4% per dry weight of the materials to compare strength gain at different dosage. Samples were compacted and cured for 7 days then subjected to Unconfined Compressive Test where the strength UCS (qu7) was recorded. Strength-gain over time from 1 day to 28 days, for a specific CR-RAP ratio at fixed PMC dosage was also studied. It was found that UCS was directly proportionate to PMC dosage and amount of CR component in the mixture. This study concluded that at various combination of CR-RAP ratio, with varying PMC dosage, minimum requirement of UCS (7-day) of 2 MPa for road base application specified by local authority is achievable. The correlation between strength and curing duration obtained serves as guideline to extrapolate long-term strength from short-term strength.