Cold In-place Recycling Research Articles

Cold In-Place Recycling Asphalt Mixtures: Laboratory Performance and Preliminary M-E Design Analysis.

Cold in-place recycling (CIR) asphalt mixtures are an attractive eco-friendly method for rehabilitating asphalt pavement. However, the on-site CIR asphalt mixture generally has a high air void because of the moisture content during construction, and the moisture susceptibility is vital for estimating the road service life. Therefore, the main purpose of this research is to characterize the effect of moisture on the high-temperature and low-temperature performance of a CIR asphalt mixture to predict CIR pavement distress based on a mechanistic–empirical (M-E) pavement design. Moisture conditioning was simulated by the moisture-induced stress tester (MIST). The moisture susceptibility performance of the CIR asphalt mixture (pre-mist and post-mist) was estimated by a dynamic modulus test and a disk-shaped compact tension (DCT) test. In addition, the standard solvent extraction test was used to obtain the reclaimed asphalt pavement (RAP) and CIR asphalt. Asphalt binder performance, including higher temperature and medium temperature performance, was evaluated by dynamic shear rheometer (DSR) equipment and low-temperature properties were estimated by the asphalt binder cracking device (ABCD). Then the predicted pavement distresses were estimated based on the pavement M-E design method. The experimental results revealed that (1) DCT and dynamic modulus tests are sensitive to moisture conditioning. The dynamic modulus decreased by 13% to 43% at various temperatures and frequencies, and the low-temperature cracking energy decreased by 20%. (2) RAP asphalt incorporated with asphalt emulsion decreased the high-temperature rutting resistance but improved the low-temperature anti-cracking and the fatigue life. The M-E design results showed that the RAP incorporated with asphalt emulsion reduced the international roughness index (IRI) and AC bottom-up fatigue predictions, while increasing the total rutting and AC rutting predictions. The moisture damage in the CIR pavement layer also did not significantly affect the predicted distress with low traffic volume. In summary, the implementation of CIR technology in the project improved low-temperature cracking and fatigue performance in the asphalt pavement. Meanwhile, the moisture damage of the CIR asphalt mixture accelerated high-temperature rutting and low-temperature cracking, but it may be acceptable when used for low-volume roads.

Development of Cold In-Place Recycling with Bitumen Emulsion and Biomass Bottom Ash

Power generation from biomass is one of the most promising energy sources available today. However, this industry has a series of wastes derived from its activity, mainly biomass fly ash and biomass bottom ash. Biomass bottom ash is a waste that has no current use and, in most cases, is deposited in landfills. In turn, road construction is one of the activities that produces the most pollution, as it requires huge amounts of raw materials. Therefore, this research proposes the use of biomass bottom ashes, in an unaltered form, for the formation of cold in-place recycling with bitumen emulsion. This type of mixture, which is highly sustainable owing to the use of a high percentage of waste, was made with reclaimed asphalt pavement, biomass bottom ash, water, and bitumen emulsion. To this end, the grading curve of the materials was analyzed, different bituminous mixtures were made with varying percentages of emulsion and water, and the mechanical properties of the mixtures were analyzed. At the same time, the same type of mix was made with reclaimed asphalt pavement and commercial limestone aggregate, in order to compare the results. The tests showed a better mechanical behavior of the bituminous mixes made with biomass bottom ash, maintaining physical properties similar to those of conventional mixes. In short, it was confirmed that the production of this type of mix with biomass bottom ash was feasible, creating sustainable materials that reuse currently unused waste and avoid landfill disposal.

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.

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.

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.

Dynamic stiffness of road pavements: Construction characteristics-based model and influence on tire/road noise

Tire/pavement noise is produced by the interaction between a tire and the road surface. Complex noise generation mechanisms are involved in this process. Dynamic stiffness (or mechanical impedance) is considered as a related reduction/amplification mechanism. Despite its potential importance, in conventional hot bituminous mixtures this mechanism has little influence on tire/pavement noise. This is because the dynamic stiffness of tire treads is significantly lower than that of the hot bituminous mixes (conventional road surfaces). This paper presents a field assessment of the dynamic stiffness of five experimental sections with different characteristics: from the environmentally friendly mixes such as the Cold-In place-Recycled (CIR) pavement to the gap graded hot bituminous mixtures with crumb rubber (CR) from end of life tires (ELTs). The obtained dynamic stiffness spectra are fitted using a Boltzmann Sigmoid function. The relationships between the fitting coefficients and a few pavement construction characteristics are assessed in order to model the pavement dynamic stiffness as a function of these characteristics. In addition to dynamic stiffness, several surface characteristics such as the Close ProXimity (CPX) sound levels from the tire/pavement interaction, macrotexture in terms of the Mean Profile Depth (MPD), unevenness in terms of the International Roughness Index (IRI), and acoustic absorption are studied. According to our results, lower dynamic stiffness values are related to lower noise levels at high frequencies. No relationship was observed between the low dynamic stiffness values and noise attenuation at medium frequencies in this research work.

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.

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.

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.

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.

Finding an equivalent Hot-Mix Asphalt for Cold-in-Place recycled asphalt using laboratory testing and numerical analysis

Cold-in-Place Recycling (CIR) asphalt material is gaining increased popularity due to its innovative properties, performance and recycling values. However, detailed material properties of this material are required to design pavement using the CIR materials. This study finds out an equivalent conventional Hot-Mix Asphalt (HMA) which behaves very similar to the CIR material. As a first step, detailed properties of the CIR materials used in Colorado has been measured in the laboratory. Then, the performances of ten pavements which are built using the CIR are predicted using the AASHTOWare Pavement Mechanistic-Empirical (ME) Design (PMED) software. Then, different HMA mixes are used to run the PMED software and are compared with the performance of the CIR material. Results show that the PMED software analysis showed the PMED-predicted IRI and rutting values are close to the values measured in the field. However, the PMED-predicted fatigue cracking values are less than values measured in the field. CIR material behaves very similar to the HMA SX (75) PG 58-28 mix and thus may be used in place of CIR while analyzing a pavement using the PMED software.

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.

Practical method for in-place density measurement of cold in-place recycling mixtures

Cold in-place recycling (CIR) has been used for the past two decades as an effective rehabilitation technique for deteriorated asphalt concrete (AC) pavements. The CIR process consists of milling the top portion of the deteriorated AC layer, mix the reclaimed asphalt pavement (RAP) with asphalt emulsion and additive such as lime or portland cement, and compact. The generated CIR layer serves as a good base under the new AC overlay. The most critical property of the CIR layer is its excellent resistance to reflective cracking which makes it a highly effective rehabilitation treatment for cracked AC pavements. Other rehabilitation alternatives such as straight AC overlay would suffer from reflective cracking at the rate of 25 mm per service year.There are five parts of the CIR process; 1) milling, 2) mixing, 3) laydown, 4) compaction, and 5) overlay. Parts 1, 2, 3, and 5 have been well established while part 4 is still requires major improvements. Up to this date, the measurement of the in-place density of the compacted CIR layer is un-achievable. In the case of the AC layer, the in-place density during compaction is measured through a nuclear density gauge that has been calibrated against cores cut from the compacted mat. The application of the same process for the CIR layer faces major limitations: a) in-ability of the nuclear gauge to measure density due to excess water and b) cores cannot be cut from the CIR mat until the 14 days curing has occurred. This paper describes a new method to measure the in-place density of the CIR layer during the compaction process. The new method uses the Sand Cone apparatus to measure the bulk density of the compacted CIR layer. The proposed method has been validated through laboratory testing and field evaluation.

Preparation and characterisation of modified reclaimed asphalt using nanoemulsion acrylate terpolymer

PurposeThis paper aims to investigate the best methods of utilisation of reclaimed asphalt pavements (RAP) in Egypt, to determine the effect of using 100% RAP instead of using virgin aggregates and asphalt; investigate the effect of thermoplastic elastomer polymer as asphalt modifier; and also improve the mechanical and physical characteristics and consequently improving the quality of asphalt paving, increasing service life of asphalt-paving and reducing costs.Design/methodology/approachNano acrylate terpolymers were prepared with different % (Wt.) of and were characterised by Fourier transforms infrared (FTIR), for molecular weight (Mw), by thermo gravimetric analysis (TGA) and by transmission electron microscopy (TEM). A 4% (Wt.) of the prepared nanoemulsion terpolymer was mixed with virgin asphalt as a polymer modifier, to improve and reuse of the RAP. The modified binder was tested. The tests conducted include penetration, kinematic viscosity, softening point and specific gravity. Application of Marshall mix design types; hot mix asphalt (HMA), warm mix asphalt (WMA) and cold in place recycled (CIR). Four different mix designs used; control mix contained virgin asphalt by HMA, and the other three mix designs were polymermodified asphalt sample by HMA, WMA and CIR.FindingsThe research results showed that using 4 Wt.% of the prepared nanoemulsion terpolymer to produce hot mix asphalt (HMA) and warm mix asphalt (WMA) achieved higher stability compared to the control mix and cold in place recycled (CIR).Research limitations/implicationsThis paper discusses the preparation and the characterisation of nanoemulsion and its application in RAPs to enhance and improve the RAP quality.Practical implicationsNano-acrylate terpolymer can be used as a new polymer to modify asphalt to achieve the required specifications for RAP.Originality/valueAccording to the most recent surveys, Europe produced 265 tonnes of asphalt for road applications in 2014, while the amount of available RAP was more than 50 tonnes. The use of RAP in new blended mixes reduces the need of neat asphalt, making RAP recycling economically attractive.

The experimental study of mineral-cement-emulsion mixtures with rubber powder addition

The article describes properties of mineral-cement-emulsion (MCE) mixtures with addition of rubber powder. The mixtures were created with the use of reclaimed asphalt pavement (RAP) in the amount of 45%, consisting of old bitumen binder in the amount of B = 5,8% (m/m), virgin aggregate with grading distribution of 0/31,5 mm 44 ÷ 47%, rubber powder of 0/1 mm RP = 2 ÷ 5% (m/m), bitumen emulsion BE = 2% (m/m) and cement CEM 4% and 6% (m/m). The optimum moisture content of the mixtures determined in Proctor compaction test was approximately 6%.Production of the mineral-cement-emulsion mixtures was assumed as the Cold In-place Recycling (CIR). Laboratory studies of indirect tensile strength, stiffness modulus at the temperature of 5 °C, fatigue life at the constant set strain using four point bending beam method at the temperature of 10 °C and frequency of 10 Hz were performed and analysed.So far, mixtures with RAP, bitumen emulsion (2%) and a relatively large amount of cement (4% and 6%) with addition of rubber powder have not been used in cold-in-place recycling. Those mixtures are used for construction of road bases or reinforcement of pavements of local roads as flexible layers. The addition of rubber powder contributes to the decrease of the stiffness modulus and increase the fatigue life, which results in the possibility of reduction of the amount of added bitumen emulsion.

Establishment and implementation of an asphalt pavement recycling decision system based on the analytic hierarchy process

Asphalt pavement recycling technology is widely used in China and other countries due to its economic and environmental benefits. Pavement recycling methods can generally be divided into central plant hot recycling, hot in-place recycling, central plant cold recycling, and cold in-place recycling. However, no quantitative evaluation method and calculation program for selecting an optimal recycling method are available for existing asphalt pavements. In this study, a quantitative evaluation approach for recycling method selection was proposed in consideration of pavement performance and construction cost. An asphalt pavement recycling decision system was established, and a corresponding calculation program was developed based on the. Net platform. Case study showed that the asphalt pavement recycling decision system developed based on the analytic hierarchy process in this study is feasible and reasonable. The system can help pavement managers make efficient maintenance decisions in practical projects.

Use of bending beam rheometer test for rheological analysis of asphalt emulsion-cement mastics in cold in-place recycling

This paper focused on exploiting the potential of the bending beam rheometer (BBR) test for analyzing asphalt emulsion-cement (AEC) mastics tailored for cold in-place recycling applications in the first weeks of curing, i.e. phase which implies the coexistence of viscoelastic and brittle materials. A consistent modified BBR testing protocol, which includes the experimental solutions devised for the practical execution of these unconventional rheometric measurements (sample preparation and test procedure), was proposed. The authors suggested to introduce glass microspheres, acting as “inert solid skeleton”, in the production of AEC mastics for BBR prismatic beams, to study the interaction between asphalt emulsion and cement in thin film and to limit the specimens’ shrinkage and warpage during the curing period. Finally, a feasibility study for validating the new modified experimental setup was presented, highlighting, with an explanatory overview of the types of results that can be expected, the macroscopic behaviors of some AEC mastics as a function of different parameters (asphalt binder to cement ratio, curing time and temperature).

Enhancement of curing properties of cold in-place recycling asphalt mixtures by induction heating

ABSTRACT In this study, samples of cold in-place recycling mix (CIR) with steel fibres were manufactured and heated by electromagnetic induction. Heating was conducted to accelerate the curing process and make the CIR mixtures more competitive against other less-sustainable road materials. Heating can also be applied after years of service life to reduce the viscosity of the binder and make it flow through cracks, healing damage. Cylindrical Marshall samples were heated by induction for different durations immediately after production and their mechanical performance was assessed over different curing periods. In addition, 3-point bending healing tests were carried out on cured semicircular samples. The results showed that the remaining water content in samples heated for 180 s was lower than in control samples (not heated) after 21 days. The Marshall stability and flow after compaction increased by 147% and 144%, respectively, when heating was applied for 240 s. Healing tests produced encouraging results with strength recoveries higher than 50%.