In-place Recycling Research Articles

Economic and Environmental Cost Analysis of Cold In-Place Recycling

The 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 technique. For this study, the costs of using CIR mixes prepared using either asphalt emulsion (CIR-E) or foamed asphalt (CIR-F) were compared with conventional 5.1-cm (2-in.) hot-mix asphalt (HMA) mill and overlays. Three different costs were considered for the production of each pavement rehabilitation technique: (1) construction, (2) energy, and (3) environmental costs. To facilitate the cost comparisons, an equivalent pavement structural analysis was conducted between each pavement rehabilitation technique using a standard design method. The results of the study showed that initial construction costs of using CIR are less than the conventional HMA mill and overlay. The energy and environmental costs were also found to be much lower for CIR mixtures compared with the HMA mill and overlay, with energy savings of up to 63%. Overall, when considering all costs, the use of CIR has lower costs compared with traditional HMA overlays. Cost savings of approximately $34,000–$39,000 were observed when using CIR with HMA overlays, with a total cost savings between 41% and 47% over traditional HMA mill and overlays. This study gives an overall procedure for assessing the economic and environmental costs of different pavement rehabilitation techniques and provides further evidence of the cost benefits associated with CIR to practitioners.

Field observations and laboratory evaluations of asphalt pavement maintenance using hot in-place recycling

To evaluate the short- and long-term effectiveness of hot in-place recycling (HIR), the field measurements and laboratory tests were performed. Results indicate the HIR with favorable construction quality is positively effective in restoring high-temperature stability and is acceptable in maintaining low-temperature performance and moisture susceptibility. The findings highlight the rejuvenator application to reconstitute the rheological properties of aged asphalt and the construction control to ensure the uniformity of recycled layer and the degree of compaction. In addition, longer monitoring of pavement deteriorations is promising to determine the practically extended service life from HIR and optimize the follow-up maintenance decision-making, especially in maintenance timing.

Numerical simulation analysis on multi-layer low-temperature heating method of asphalt pavement in hot in-place recycling

Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling (HIR). To improve the heating speed of asphalt pavement in HIR, based on the numerical analysis model of asphalt mixture heating process, a new multi-layer low-temperature heating method (MLHM) was proposed. Considering input heat flux, the thermal capacity and thermal resistance of asphalt mixture, the heat transfer model was established based on energy conservation law. By heating the asphalt mixture in layers, it changes the situation that the heat energy can only be input from the upper surface of the asphalt mixture pavement. Through the simulation of the heating method of asphalt mixture in the existing technology, the result shows that the existing heating methods lead to serious aging or charring of the asphalt mixture. By MLHM, the upper and the bottom of the asphalt mixture are heated at the same time, and the heating temperature is lower than other heat methods, which not only reduces the heating thickness and increases the heating area of the asphalt mixture pavement, but also improves the heating speed, saves the energy resource and ensures the heating quality. Especially, by MLHM, the heating uniformity is better and speed is faster.

Performance and Impact Analysis of Key Structural Parameters of Hot In-place Recycling Equipments Using on Hot-air Circulated Asphalt Road

Performance and Impact Analysis of Key Structural Parameters of Hot In-place Recycling Equipments Using on Hot-air Circulated Asphalt Road

Study of the Incorporation of Ladle Furnace Slag in the Manufacture of Cold In-Place Recycling with Bitumen Emulsion.

Cold in-place recycling with bitumen emulsion is a good environmental option for road conservation. The technique produces lower CO2 emissions because the product is manufactured and spread in the same location as the previous infrastructure, and its mixing with bitumen emulsion occurs at room temperature. Adding materials with cementitious characteristics gives the final mixture greater resistance and durability, and incorporating an industrial by-product such as ladle furnace slag (of which cementitious characteristics have been corroborated by various authors) enables the creation of sustainable, resistant pavement. This paper describes the incorporation of ladle furnace slag in reclaimed asphalt pavements (RAP) to execute in-place asphalt pavement recycling with bitumen emulsion. Various test groups of samples with increasing percentages of emulsion were created to study both the density of the mixtures obtained, and their dry and post-immersion compressive strength. To determine these characteristics, the physical and chemical properties of the ladle furnace slag and the reclaimed asphalt pavements were analyzed, as well as compatibility with the bitumen emulsion. The aforementioned tests define an optimal combination of RAP (90%), ladle furnace slag (10%), water (2.6%), and emulsion (3.3%), which demonstrated maximum values for compressive strength of the dry and post-immersion bituminous mixture. These tests therefore demonstrate the suitability of ladle furnace slag for cold in-place recycling with bitumen emulsion.

Performance evaluation of temperature effect on hot in-place recycling asphalt mixtures

Hot in-place recycling (HIR) is a novel technique to rehabilitate the surface layer of the pavements, in which recycling agents are commonly utilized to restore the binder rheological properties of reclaimed asphalt pavements (RAP). Considering the energy consumption and smoke issue, the heating temperatures for HIR containing 100% RAP mix are usually controlled around 110 °C, which is significantly lower than that for the traditional hot mix asphalt (HMA). . To evaluate the effect of temperature on the performance of 100% recycled asphalt mixtures after the HIR process, the materials obtained from an HIR project were remixed and compacted at different temperatures (110 °C, 120 °C, and 130 °C). The asphalt mixture performance tester, asphalt pavement analyzer test, Superpave indirect tension tests, and moisture susceptibility tests were conducted to evaluate the performances of the HIR mix. The staged extraction tests were used to identify the mobilized RAP binders under different temperatures. It was revealed that mixtures heated with a higher temperature exhibit better cracking and moisture resistance performances. It was also found that a larger proportion of the RAP binders can be activated to coat the aggregates at a higher mixing temperature, which may increase the rutting potential.

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

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

Review of Agency Pavement Recycling Construction Specifications

Cold in-place recycling, cold central plant recycling, and full depth reclamation are cost-effective, environmentally conscious pavement rehabilitation or reconstruction techniques. Although these techniques are not new, they have not been widely adopted among state agencies. There has, however, been a recent resurgence in interest in these techniques. To date there are no national specification guidelines for these processes to assist in their widespread implementation, and those specifications that do exist often have a wide range of requirements. This paper presents the results of a review of state and local agency specifications for pavement recycling techniques and offers suggestions to help agencies achieve a better and longer-lasting product when specifying pavement recycling techniques.

Field and laboratory evaluations of maintenance treatments for semi-rigid base asphalt pavement

To evaluate the effectiveness of maintenance treatments for asphalt pavement, four types of treatments, including the hot in-place recycling (HIR), milling and resurfacing (M&F), thin HMA overlay (THO) and microsurfacing (MS), were analyzed. 8 highway segments, in total 491.74 km, in Jiangsu Province in China, were investigated and the data of rutting depth (RD) in their maintenance history was collected. Based on the data of RD, the effectiveness of four treatments was quantitatively compared by three indicators, namely, performance jump (PJ), deterioration rate reduction (DRR) and average deterioration reduction rate (ADRR). Moreover, the applicability of the proposed effectiveness analyses was assessed by laboratory rutting tests with field cylindrical samples. Results indicate that the HIR is the most effective treatment, followed by M&F and THO. While the MS is the least effective treatment, whose service life is only three or four years. The findings highlight the significance of the proper traffic opening time after maintenance to avoid the weakened rutting resistance caused by high-temperature mixtures, the effect of the RD before maintenance on maintenance decision-making, and the application of high-quality RAP in the timely maintenance activities. Therefore, the performance-based maintenance strategy should be establish to improve pavement performance and extend pavement service life. Further research on the pavement performance after RAP application is necessary.

Quantifying effects of laboratory curing conditions on workability, compactability, and cohesion gain of cold in-place recycling

Cold in-place recycling (CIR) is a pavement rehabilitation treatment which has shown promise in terms of environmental benefits, cost savings, and successful performance. Current procedures for asphalt emulsion CIR mix design, AASHTO PP86 and AASHTO MP31, address mixture proportion selection and final performance prediction but do not consider performance of the material during the construction process. This research proposed the addition of three intermediate stages into asphalt emulsion CIR mix design: workability, compactability, and cohesion gain. Equipment commonly available in asphalt laboratories was evaluated for ability to quantify workability, compactability, and cohesion gain by measuring differences in performance due to changes in curing conditions. Cure temperature generally had a more significant influence on test results than cure time. Superpave Gyratory Compaction (SGC) metrics were recommended for quantifying workability and compactability. The direct shear test showed promise for quantifying cohesion gain moving forward based on agreement with the triaxial test.

Research of temperature change of pavement heating in the process of hot in-place recycling of asphalt concrete

The object of research is the technology of hot asphalt concrete regeneration by the in-place method. Temperature regimes for heating asphalt concrete pavement are one of the key technological parameters that affect the quality of the output regenerated asphalt concrete. In order to establish the dependence of the temperature of the pavement heating at different depths on the heating time, field studies are carried out directly when performing work on the hot regeneration of asphalt concrete using the Reshape method. The work is carried out at an ambient temperature of 25–30 °C and calm weather. The regenerated hot asphalt mix, which is used when conducting studies on the grain composition and bitumen content, corresponded to a hot, fine-grained mixture, dense asphalt concrete, type A, continuous granulometry, grade II, in accordance with DSTU B V.2.7-119:2011. Content of residual bitumen loosened asphalt crumb is 6.0 %. During the research, measurements are carried out at different speeds (1.8 m/min and 2.1 m/min) of the thermal installation for heating the Wirtgen HM 4500 asphalt concrete pavement (country of origin is Germany). The obtained graphical dependencies and mathematical models make it possible to determine that the most optimal pavement heating mode is gradual heating. This mode will allow avoiding the burning of bitumen and provide pavement heating at the level of the base of the regenerated layer, which is very important when determining the temperature of mixing the mixture. Analysis of graphs and mathematical models suggests that a decrease in the temperature of the pavement heating by at least 10–20 °C will lead to an increase in the performance of the thermal device. In this case, the increase in productivity can be from 20 % to 25 %, which will reduce the gas consumption and, accordingly, the cost of work. Thus, the obtained dependencies can be used to optimize the process of hot asphalt concrete regeneration by the in-place method.

Development and Assessment of Rapid Tests for Construction of Asphalt-Treated Cold Recycled Pavements

Pavement recycling techniques, including full depth reclamation, cold in-place recycling, and cold central plant recycling, are effective at rehabilitating existing pavements and constructing new pavements while reducing construction costs, environmental impacts, and construction time. Despite these benefits, these techniques are not used as often as they could be, in part because agencies are unable to assess rapidly the quality of the recycled material or to determine when a recycled pavement has sufficient structural capacity to handle traffic or construction equipment for surfacing, or both, without causing damage, especially at early ages. To describe better the time-critical properties of recycled materials, a series of tests was conducted to assess the stiffness, penetration resistance, and shear and raveling properties of laboratory-produced recycled mixtures sampled from field projects. These tests were conducted to evaluate their potential to discriminate among various factors affecting the behavior of the materials in the laboratory. The study found that penetration resistance tests were most sensitive to the factors assessed, followed by stiffness and then torque values from shear and raveling tests. These tests will be further validated using additional mixture types in the laboratory, and their performance in the field will be studied.

Assessment of Permanent Deformation Properties of In-Place Recycled Pavement Mixtures

Cold in-place recycling (CIR), cold central plant recycling (CCPR), and full depth reclamation (FDR) are techniques that can be used to rehabilitate deteriorated pavements or used in new pavement construction projects. Use of these techniques has been found to be both fiscally and environmentally beneficial. However, there is a lack of literature that examines the mechanistic behavior of these mixtures, particularly when it comes to asphalt mixture-related test methods. This paper presents a comprehensive analysis of data from repeated load permanent deformation (RLPD) testing, a laboratory test that describes a mixture’s rutting behavior, conducted on bituminously stabilized CIR, CCPR, and FDR mixtures. The mixtures were collected as a part of NCHRP 9-51, Material Properties of Cold In-Place Recycling and Full-Depth Reclamation Asphalt Concrete for Pavement Design. The permanent deformation behavior of specimens from 23 projects sampled between 12 and 24 months after construction is presented. The impact of stabilizing or recycling agent as well as the presence of chemical additives on the permanent deformation behavior was considered. Density, one of the most prevalent factors in field-based quality control and acceptance of cold recycled mixes was also examined with respect to its impact on permanent deformation behavior.

Homogeneity evaluation of hot in-place recycling asphalt mixture using digital image processing technique

Hot in-place recycling (HIR) allows 100% reuse of reclaimed asphalt pavement (RAP) directly on a construction site. However, the homogeneity of the HIR is difficult to be evaluated due to the complexity of the material composition and construction process. In this study, in view of the homogeneity of the HIR can be reflected by the mixing quality of virgin and RAP aggregates, the homogeneity of virgin and RAP aggregates was investigated. Firstly, the Marshall test specimens of an HIR asphalt mixture were prepared and saw-cut, and the microstructure of each cross section was extracted using digital image processing (DIP) technique, including image enhancement, iterative threshold segmentation and maximum between-class variance (OTSU threshold), retention of the green channel, and image morphology. Then, each cross section of the specimen was divided into 36 regions of equal area by an annular segmentation with sector segmentation. Based on the coefficient of variation in the area ratio of the virgin aggregate to RAP aggregate, a homogeneity coefficient of HIR asphalt mixture was proposed. Another nine groups of Marshall specimens were prepared and cut, and the homogeneity coefficient of each group was calculated. The results showed that the virgin and RAP aggregates in the cross section could be effectively identified due to different gray values by retaining the green channel. The characteristics of the virgin and RAP aggregates could be comprehensively described using annular segmentation combined with sector segmentation. The related macro qualitative test showed that the aggregate in the asphalt mixture could be accurately extracted by the threshold segmentation method based on annular segmentation combined with the OTSU method. The homogeneity could be accurately and quantitatively evaluated by a homogeneity coefficient based on the area ratio of the virgin and RAP aggregates in each cross section. An improvement in the homogeneity of the virgin and RAP aggregates was achieved with an increase in the heating temperature of RAP and mixing time. However, no further improvement was noticed as the heating temperature and mixing time increased. In short, the quantitative homogeneity evaluation index of virgin and RAP aggregates presented in this study, reflecting the homogeneity of HIR asphalt mixture, is helpful for controlling the quality of the HIR asphalt pavement.

Study on impact of variables to pavement preheating operation in HIR by using FEM

Hot In-place Recycling (HIR) is an innovative pavement maintenance and rehabilitation technology that can reuse up to 100% of the material from an existing pavement as Reclaimed Asphalt Pavement (RAP). Pre-heating the pavement is the first step in the HIR process and uniformly heating distressed pavement is crucial to the quality of the recycled mixture in terms of rejuvenator diffusion, required adhesion between virgin and old material, and achieving an efficient asphalt ratio in RAP materials. The low thermal conductivity of asphalt concrete makes the transmission of heat from the top of the pavement to the scarification depth difficult. This study analyzed the impact of seven different operational parameters of recycling heating equipment on the heating efficacy by using the finite element method (FEM). The parameters include the height of heating board, equipment speed, output power, construction temperature, heating repetition, gap distance between two heaters, and area of heating board. The impact of variations in each parameter was statistically analyzed through fractional factorial experiment design. The heating board’s area and heating repetitions were found to be the two dominant factors affecting pavement surface preheating, and construction temperature is the most significant factor for pavement heating at a depth of 4 cm. Finally, three reasonable combinations of equipment operational parameters were provided to guide field construction practices.

Life cycle assessment of asphalt pavement maintenance and rehabilitation techniques: a study for the City of St. John’s

Although pavement maintenance and rehabilitation (M&R) techniques are usually examined in economic terms, there is a growing need to address their environmental footprints. The objective of this study is to assess the environmental impacts of M&R techniques. Life cycle assessment (LCA) can help in the decision-making process of selecting suitable maintenance techniques based on their environmental impacts. This study investigates: patching, rout & sealing, hot in-place recycling, and cold in-place recycling. Global warming potential (GWP), acidification potential, human health particulate, eutrophication potential, ozone depletion potential, and smog potential are estimated as environmental impacts for each maintenance activity. Materials, equipment use (for construction and M&R), and transportation were the main elements considered. A sensitivity test is performed to identify the significant factors for the LCA. The study concluded that GWP was the most important impact category. Rout & sealing and cold in-place recycling produced the lowest GWP emissions. Notably, pavement patching and hot in-place recycling showed significant detrimental environmental impacts.

Heating process monitoring and evaluation of hot in-place recycling of asphalt pavement using infrared thermal imaging

The original asphalt pavement heating plays a key role in the entire construction procedure of hot in-place recycling (HIR). At present, the temperature of heating process in HIR is monitored by infrared temperature gun with single or multiple test points which cannot fully understand real heating situation. Moreover, there are no evaluation indices for quantifying heating quality. To objectively perceive and evaluate the heating quality, the infrared thermal imaging (ITI) system was used to monitor heating process of HIR and the combination of digital image processing (DIP) and artificial neural network (ANN) was applied to extract and correct the distorted thermal image to restore pavement surface temperature. Based on corrected thermal images, the heating quality of HIR was firstly quantitatively evaluated using three proposed indices: transverse uniformity Tu for evaluating the temperature uniformity, represent temperature RT for assessing the heating effect and proportion of temperature above 200 °C PTA200 for judging the overheating. Furthermore, on-site heating quality of three heating systems: respectively flame, infrared radiation and recycled hot-wind system, was analyzed and compared based on the above three indices. The results indicate that the superiority of the flame system and the infrared heating system is strong heating effect to realize the higher pavement surface temperature, but the temperature uniformity is poor, even some areas are overheated. On the contrary, the recycled hot-wind heating system provides the better temperature uniformity and avoids overheating, but the heating effect is poor. In addition, a comprehensive analysis reveals that high RT and poor Tu are mainly cause of overheating and the better Tu is required to match the increasing pavement surface temperature for high level of the heating quality. Finally, when using 200 °C as the high temperature boundary, the evaluation indices Tu and RT preferably satisfy the following relationship RT + RT × Tu < 190 °C to avoid occurrence of overheating in HIR.

Experimental study to investigate the performance of cold in-place recycling asphalt mixes

This research work was performed to study the impact of steel slag and limestone virgin aggregates as a substitution for recycled asphalt pavement (RAP) in cold in-place recycling (CIR) asphalt mixes. An anionic slow-setting (SS-1) emulsion was used to fabricate the specimens. Marshall stability and flow test, dynamic creep test and moisture susceptibility test were performed to evaluate the mechanical performance of the CIR mixes. The results of this research showed that the presence of modifier aggregates leads to an increase of Marshall stability, and a decrease in permanent deformation and moisture susceptibility. Furthermore, the additional aggregate contents have a significant impact on the moisture and rutting resistance of CIR mixes. Limestone-modified mixes were more resistant to moisture damage. However, steel slag-modified mixes showed better performance against rutting distress.

Strength prediction of adhesively bonded ferrite pillar–tin bronze plate under axial shear loading

With the fast development of electronic, automotive and aerospace engineering in recent years, ferrite material has been widely used in devices including inductor, voltage transformer, filter and choke coil, etc. The proper characterisation on the mechanical capacity of the connection between ferrite and traditional metals has become a key issue for both industrial and academic fields. This work focused on the mechanical performance as well as fracture behaviour of adhesively bonded ferrite–tin bronze plate (FTBP), subjected to axial shear loading through experimental and numerical approaches. In the process, a new set of Arcan testing methods was developed for mechanical parameter determination of high flow epoxy adhesives. The material parameters of the epoxy adhesive connecting the ferrite pillar and bronze were experimentally determined. Curing mould was designed for the manufacture of the selected adhesive with high flowability in dumbbell tensile testing and Arcan testing under 0° and 90° loading directions. Quasi-static shear loading test was then conducted on bonded FTBP with a specially designed jig, and the failure surface was studied through optical microscopy and scanning electron microscopy (SEM) observations. Finite element (FE) modelling was carried out to simulate the loading process up to failure, where the crack propagation in the adhesive layer was modelled using cohesive zone model (CZM) with a bilinear traction-separation response. The experimentally measured and numerically simulated results of the adhesively bonded FTBP were compared with each other, proving the validity of the strength prediction approach developed in this work.Abbreviation: FTBP: Ferrite - Tin Bronze Plate; SEM: Scanning Electron Microscope; FE: Finite Element; CZM: Cohesive Zone Model; CIR: Cold In-place Recycling; DIC: Digital Image Correlation; DCB: Double Cantilever Beam; ENF: End-notched Flexure; PTFE: Polytetrafluoroethylene; CTOD: Crack Tip Opening Displacement; SDEG: Scalar Stiffness Degradation Variable; DOF: Degree of Freedom.

Optimizing the asphalt pavement cold in-place recycling process containing waste pozzolans based on economic-environmental-technical criteria

Abstract In this research, it was tried to determine an optimized procedure in CIR process regarding the stabilizer additive type used to accelerate the setting of bitumen emulsion and executive thicknesses by considering the technical, environmental and economic criteria. Three stabilizers were studied including type II Portland cement (cement) as conventional stabilizer, coal combustion ash (CCA) and lime activated coal waste ash (LA-CWA) at rate of 2, 8 and 8% by weight of recycled asphalt pavement, respectively. In economic-environmental analysis the reconstruction method with unbound base and hot mix asphalt overlay was also analyzed as a conventional rehabilitation method. Four different thicknesses were considered for CIR layer including 10, 15, 20 and 25 cm. Furthermore, four equivalent single axle loads from 1 to 50 million were considered in designing the pavement structures. Based the results, by considering the total energy usage and CO2 emissions, implementing CIR layer with thicknesses lower than 20 cm is a sustainable rehabilitation technique, while the executive costs encouraged higher thicknesses than 20 cm. Among the pozzolanic additives, the use of LA-CWA resulted in more variable results in comparison to CCA. Therefore, considering the risk of construction processes, CCA can be recommended as a more reliable replacement of cement than LA-CWA.