Cold Recycling Research Articles

Laboratory evaluation on performance of emulsified asphalt modified by reclaimed ion exchange resin

The cold recycling technology using emulsified asphalt (EA) as the binder reduces the high pollution and high energy consumption of hot mix asphalt (HMA) pavement. However, the poor bonding ability and high temperature deformation resistance of EA limit its application. To improve the performance of EA and reduce the pollution of waste ion resin to the environment, this study used reclaimed ion exchanged resin (RIER) to modify EA and analyzed its performance through laboratory tests. Firstly, the ionic characteristics and basic properties of reclaimed ionic resin-modified emulsified asphalt (RIEA) were tested. In addition, the rheological properties of evaporation residues of reclaimed ionic resin-modified emulsified asphalt (RIEA) were tested by Dynamic Shear Rheometer (DSR). The interaction effect of RIER and evaporation residue of EA were analyzed by PalierneC model. After that, the adhesive properties and tensile properties of RIEA mixtures were characterized by boiling test and splitting test. Finally, the microscopic physical and chemical properties of RIEA evaporation residue were tested by Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrometer (FTIR). The results showed that RIER improved the stability of RIEA. The conductivity of EA increased by 294 % and the Zeta potential increased by 36 % when the RIER content was 30 %. Meanwhile, the penetration degree and ductility of RIEA evaporation residue were decreased, the softening point of that were increased. The Brookfield viscosity of EA with 30 % RIER content increased by 181 %, the dynamic viscosity increased, and the adhesion performance was improved. In addition, the complex shear modulus (G*) and rutting coefficient (G*/sinδ) of RIEA evaporation residue increased, while its phase angle (δ)decreased. The PalierneC interaction model exhibited that the interaction of EA and RIER showed different temperature responses with the change of loading frequency. The indirect tensile strength (ITS) of RIEA mixture was improved by adding RIER, and its value reaches the maximum value when the amount of RIER added is 30 %. RIER and EA are tightly bound in microstructure, and they interweave to form a glue-linked structure. FTIR results show that, the RIEA evaporation residue exhibited new absorption peaks at 1793.4 cm−1, 1302.1 cm−1, 876.0 cm−1, 806.1 cm−1 wavenumbers indicating a chemical reaction between them.

Optimum Fluid Content in Pavement Cold In-Place Recycling Containing Waste Materials

The planning of road infrastructure undergoes major changes, especially in terms of sustainable development. Recycling of pavement structures involves the reuse of materials from existing pavement structures due to its timesaving and environmental benefits, as well as cost reduction. According to the recycling temperature, recycling can be hot and cold. This paper deals with cold in-place recycling and the determination of the optimum fluid content for by-product materials in mixtures compared with one containing natural zeolite. The content of bitumen emulsion and cement—which are the most used materials so far in cold recycling along with foam bitumen—was replaced with fly ash, slag or natural zeolite, and bakelite, respectively, while recycled asphalt pavement from Serbia (Žabalj) was used. Six different mixtures were made. The mixture with the addition of fly ash had the highest optimum fluid content (7.6%) compared with all test mixtures. Mixtures with slag, natural zeolite, and bakelite were in the range of a mixture containing 2% cement. Furthermore, the mixture with 3% cement had the lowest optimum fluid content (5.7%) in comparison to all the mixtures that were tested.

Rejuvenate the aged asphalt with functional oil emulsion

The cold recycling technology of asphalt pavement has great economic benefits, is friendly to the environment and has a good development prospect. But the reclaimed asphalt pavement (RAP) is used as the "black aggregate," and the aged asphalt has not been fully utilized. Therefore, activating and reusing the aged asphalt in RAP is one of the key problems to be solved. By using artificially aged asphalt instead of naturally aged asphalt, this work reports a new technique for activating asphalt of RAP by functional oil emulsion. The functional oil emulsion was prepared by phase inversion method, and the asphalt regeneration effects were studied in detail. The optimum results showed that the solid content of the functional oil emulsion was 50% and the average particle size was 2.17 μm. The storage stability of 1 day and 5 days were 2.2% and 4.8% respectively, and the demulsification time at 20 °C and 40 °C were 2 hours and 1 hour respectively. By studying the penetration, ductility and softening point of recycled asphalt under different dosages of functional oil emulsion, it is found that the parameters of the recycled asphalt recover to more than 94% at 12% content of functional oil emulsion.

Numerical and Experimental Analysis of the Raise-Temperature Effect of Quicklime in Cold Recycled Mixtures

This study focuses on the development of a thermodynamic model to individuate the increment of temperature generated by the addition of quicklime as an active filler in cold recycled mixtures (CRMs). CRMs are increasingly popular mixtures primarily composed of reclaimed asphalt pavement (RAP) and produced at low temperatures. CRMs are composed of RAP aggregates, an asphalt stabilizing agent (emulsified or foamed asphalt), fillers and active fillers (traditionally cement or hydrated lime), and water. One of the main limitations of CRMs consists of their workability that requires high air temperature. For this reason, the construction season for the application of cold recycling technologies is usually limited to summertime, especially in colder areas. A solution to this limitation is the use of quicklime as an active filler in the mixture. As shown by previous research, calcium oxide causes an exothermic reaction with water generating heat and increasing the temperature (20°C–25°C) of the entire mixture. This paper presents a thermodynamic model to identify the temperature increase and its evolution during preparation and transportation to the site of CRMs. The scope is to individuate the correct procedure to identify the most suitable application rate of quicklime in the mix design in order to reach the desired CRM temperature and workability.

A High Proportion Reuse of RAP in Plant-Mixed Cold Recycling Technology and Its Benefits Analysis

The concept of the “no-waste city” has focused increasing attention on the recycling of solid waste. One such waste is reclaimed asphalt pavement (RAP), which is generated during road maintenance. The potential to reuse this resource has attracted extensive attention in recent years. This paper explores this concept via a case study of the reconstruction of two sections of the Beijing-Taipei Expressway (from Bengbu to Hefei, sections K69–K69 + 500 and K69 + 500–K69 + 900). The upper base layer of one section was paved with a novel mixture of emulsified asphalt, mixed with a high proportion of RAP made using plant-mixed cold recycling technology (EAPM-HPRAP). For comparison, the upper base layer of the other section was paved with a conventional large-stone porous asphalt mix (LSPM). The proportions of the components of EAPM-HPRAP were optimized via laboratory-based proportioning design followed by proportioning verification. The results showed that the high-temperature stability, water damage resistance and pavement strength of the EAPM-HPRAP met the specifications of relevant engineering standards. Next, the economic and environmental benefits of this novel approach were estimated. The approach was estimated to save CNY (China Yuan) 1.5–1.8 million in engineering costs per km of road (roadbed width = 27.5 m) and CNY 158–189 million for the whole project (105 km in length). It was also estimated to reduce energy consumption equivalent to 67.41 tons of standard coal per km. Further calculations showed that every km of pavement could reduce CO2 emissions by 176.6 tons, SO2 emissions by 0.6 tons, NOX emissions by 0.5 tons, ash emissions by 17.6 tons and soot emissions by 1.0 tons compared with conventional methods. For the whole road section, this is equivalent to reducing CO2 emissions by 18,543 tons, SO2 emissions by 60.2 tons, NOX emissions by 52.5 tons, ash emissions by 1848 tons, and soot emissions by nearly 105 tons. In summary, it is feasible for EAPM-HPRAP to be used as the upper base layer in highway renovation projects. It reduces the need to mine new ores and allocate land to RAP storage, which is associated with soil and water pollution due to chemical leaching from aged asphalt. This approach provides great economic and environmental benefits compared with the use of conventional pavement technology.

Complex modulus of cement-bitumen treated materials produced with different reclaimed asphalt gradations

The increasing attention over cold recycling technologies as sustainable paving solutions requires a proper characterisation in terms of complex modulus for supporting the pavement design. Among cold recycled materials, cement bitumen treated materials (CBTM) benefit from the presence of both bituminous and cementitious binders. This research aims at characterising the complex modulus of CBTM mixtures produced with three different gradations, modified bitumen emulsion and two types of cement. The complex modulus measurements were modelled considering the usual viscous dissipation behaviour, linked to the bituminous component of the mixtures, along with a time- and temperature-independent dissipation component. The results showed that both the aggregate skeleton and the composition of the fine aggregate matrix affected the rheological behaviour. Furthermore, the role played by the aged binder contained in the reclaimed asphalt aggregate was highlighted by the parameters of the rheological model.

Using Reclaimed Cement Concrete in Pavement Base Mixes with Foamed Bitumen Produced in Cold Recycling Technology.

The paper presents the results of exploratory research on the use of reclaimed cement concrete in cold-recycled mixes with foamed bitumen. Because reclaimed cement concrete, unlike natural aggregates, is expected to have a residue of the non-hydrated cement covering the aggregate grains, which may result in a secondary cementation process after its application in a road base, this avenue was explored by tracking the time evolution of the compressive strength of the final material. The tests were performed using two mixtures, i.e., a reference mixture and a mixture containing 25% reclaimed cement concrete. The mixtures containing reclaimed cement concrete were characterized by increased uniaxial compressive strengths after each curing period (3, 4, 7, 14 and 28 days)—by 11.5 kPa on average and e.g., 498 kPa vs. 506 kPa after 28 days. The obtained differences between the mixtures were not found to be statistically significant. The small effects of the incorporation of reclaimed cement concrete were attributed to the time passed typically between the demolition and new pavement construction and to the presence of a second binding material—bitumen.

Study on an Integrated LCA-LCC Model for Assessment of Highway Engineering Technical Schemes

This paper proposes an integrated life cycle assessment-life cycle cost (LCA-LCC) model of environmental and economic factors for highway engineering technical schemes to problems such as the limitations of single-dimensional assessment, their narrow scope, the difficulty in tracing sources, and the conflicts of various dimensions in existing integrated assessment methods. The latest documents issued by the Ministry of Ecology and Environment and the Ministry of Transport of China used as an integrated assessment database. Air pollution, water pollution, solid waste pollution, noise pollution, energy consumption, pre-project cost, project construction cost, project operation cost, and post-project cost were used to construct the integrated assessment index system of environmental and economic factors. An improved entropy method was adopted in the LCA-LCC model to overcome the problems of ambiguous results of the previous entropy due to too few assessment schemes, the inoperability of the method when it encounters a negative value or zero value, and unbalanced multi-angle assessments. This model was applied to the assessment of two asphalt pavement maintenance schemes of Highway US280 in Alabama and two improvement schemes of high liquid limit soil subgrade of Highway G360 in Hainan. The results show that the LCA-LCC model overcomes the limitations and imbalances of a single LCA or LCC. The gravel improved scheme and the cold recycling scheme were identified through quantitative assessment as more sustainable. This paper can provide a reference for the comprehensive quantitative assessment of environmental and economic benefits of highway engineering technical schemes.

Structural Performance of an Asphalt Pavement Containing Cold Central Plant Recycling and Full-Depth Reclamation

Pavement recycling techniques are often perceived as only applicable to lower traffic volume roadways. However, recent studies have shown their potential for long service lives in higher traffic volume applications. This study documented the response of an asphalt pavement section, constructed using full-depth reclamation (FDR) and cold central plant recycling (CCPR), on a portion of I-64 in Virginia reconstructed between 2016 and 2019. The pavement section was instrumented and the response was compared with a similarly instrumented pavement section (Section S12) placed at the National Center for Asphalt Technology (NCAT) Test Track in 2012. Previous studies have shown that Section S12 is a long-life pavement and it carried 30 million equivalent single axle loads (ESALs) while showing no evidence of deterioration at the pavement surface or from installed instrumentation. The results from the I-64 Segment II project showed that it had much lower horizontal strain values at the bottom of the asphalt layers but slightly higher vertical pressure values on top of the subgrade when compared with NCAT Section S12. Despite the slightly higher values (about 1 pounds per square inch [psi] difference), the vertical pressure on top of the subgrade was very low for both pavement sections. The study confirmed that a recycled pavement section could be constructed and result in low strain and pressure values and is expected to have a long service life in a high traffic volume environment.

Characterization of Cold Bituminous Mastics Prepared with Different Active Fillers at High and Intermediate Temperature

Cold recycling of asphalt mixes is becoming a usual pavement rehabilitation technique. The use of active fillers in conjunction with bituminous emulsion changes the properties of the mixes, mainly on the mastic characteristics. The use of active filler can make the mastic more brittle, but limited data are available on this aspect. In this study, emulsion-active filler mastics were prepared with two different mixing methods. Two different active fillers, ordinary Portland cement and fly ash, were used at four different contents with a single emulsion and an inert filler. Once cured, the mastics were tested with a dynamic shear rheometer (DSR) to get the viscoelastic properties at high temperature and with the double-edge-notched tension (DENT) test to look at the cracking potential at intermediate temperature. The results show that the order that the materials are incorporated during the mixing of the mastics does have a significant effect on the properties. Also, in terms of stiffness, the optimum amount of active filler is different for the cement than for the fly ash. For the cracking resistance, the results have shown that the addition of both active fillers does have an impact on the cracking resistance, but in the amount tested, no brittle fracture was observed. The results have shown that the type and quantity of active filler are important since it changes the fracture performance and the viscoelastic properties of bituminous mastic.

Pavement Recycling in Cold Climates: Laboratory and Field Performance of the MnROAD Cold Recycling and Full Depth Reclamation Experiment

In 2019 a series of test sections were constructed on 70th Street in Albertville/Otsego, MN. The existing roadway was badly deteriorated with an international roughness index value above 300 in./mi, which places it in a “poor” performance category. A combination of treatments including cold in-place recycling (CIR), cold central plant recycling (CCPR), and full depth reclamation (FDR) stabilized with foamed or emulsified asphalt were used to evaluate performance in cold regions. Sections including a typical hot mix asphalt (HMA) mill and fill were also evaluated. All sections contained a 1-in. HMA thinlay as the wearing surface. This paper presents the laboratory testing data for the mixtures, including application of HMA tests not typically applied to CIR, CCPR, and FDR, the field performance to date, and a new approach to connecting laboratory data to field performance.

Aggregate packing characterisation of cold recycled mixtures

ABSTRACT Despite its significant role in cold recycling mix design and construction process, the effect of reclaimed asphalt pavement aggregates’ gradation and physical properties are relatively less understood. The ambiguities associated with the gradation effect led to challenges in determining the best practices in gradation control and stockpile management and blending in both cold-in-place and central plant recycling operations. Therefore, the main goal of this paper is to quantify the impact of gradation changes and proportioning of reclaimed asphalt pavement aggregates on the packing characteristics and performance of cold recycled mixtures. Binary blends consisting of fine and coarse reclaimed asphalt pavement stockpiles were combined to obtain fourteen gradations using a volumetric aggregate proportioning technique. The compatibility of five of the most prominent binary aggregate packing models was evaluated in cold recycling application. The modified Toufar model was able to accurately predict the blend of fine and coarse aggregates that offers the optimum packing prediction. Complex modulus tests showed linear viscoelastic characteristics of the cold recycled mixtures as well as the sensitivity to the packing states. In essence, this research shows the effectiveness of applying volumetric packing principles and aggregate proportioning techniques to achieve improvements in cold recycled mixtures’ volumetric and mechanical performance.

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.

Effects of aging on rheological, chemical, and micromechanical properties of waterborne epoxy resin modified bitumen emulsion

ABSTRACT Bitumen emulsion, which is widely used for surface treatment and cold recycling in pavement engineering, has the advantage of not requiring heating during construction. But it has the disadvantage of low mechanical strength, especially at higher temperatures. Various studies have proved that waterborne epoxy can effectively improve the mechanical properties of bitumen emulsion. However, how aging affects the performance of waterborne epoxy resin-modified bitumen emulsion is still unclear. This study aims to fill this knowledge gap through combined rheological and microscopic characterisation. Fourier transform infra-red spectroscopy (FTIR) was first applied to characterise the oxidative reaction during the pressure aging vessel (PAV) test. The rheological behaviours before and after PAV aging were evaluated through dynamic shear rheometer (DSR) tests. The peak force tapping quantitative nanomechanical (PFT QNM) test was further conducted to measure the micromechanical performance of the waterborne epoxy bitumen emulsion residues. The results indicated that waterborne epoxy resin could improve the resistance to oxidative aging of the emulsion residues. In addition, it was found that the complex moduli generally increased while the phase angle decreased after PAV aging, and the aging process would lead to higher micromechanical modulus and lower adhesion.

Effect of Fine Aggregate Gradation on Macro and Micro Properties of Cold Recycling Mixture Using Emulsified Asphalt

In order to explore the influence of fine aggregate on the macro and micro properties of cold recycling mixture using emulsified asphalt (CRME), mechanical and microscopic property tests were carried out. The indirect tensile strength (ITS), unconfined compressive strength (UCS) and triaxial shear strength of different fine aggregate gradation was measured for analyzing the effects of fine aggregate on the mechanical strength, triaxial shear resistance and fracture energy of CRME. Meanwhile, the surface morphologies and air voids distribution of different CRME were observed by scanning electron microscopy (SEM) and X-ray computed tomography (X-ray CT). The results show that fine aggregate has a significant effect on the mechanical strength and shear resistance of CRME. With the same water and asphalt content, the fracture energy and failure strain of the mixture with less fine aggregate (G3-2) decreased by 16.2% and 18.2%, respectively. The less content of powder there was, the fewer cement hydration products there were due to some cement being coated by emulsified asphalt and the “cement hydration products fiber” length being shorter. Approximately 70% of the AFt hydration products in the G3-2 mixture were in the range of 1–4 μm, while those in the G1 mixture were in the range of 4–8 μm. With the increase in filler content, the number of air voids in the volume range of 0.5 mm3 ≤ V < 5 mm3 in CRME decreased, and the number of air voids in the volume range of V < 0.5 mm3 significantly increased, while the equivalent radius of air voids decreased slightly with the increase in filler content.

Assessing the Field Curing Behavior of Cold Recycled Asphalt Mixtures

Cold recycling techniques in road construction have been of rising interest because of huge environmental benefits in terms of energy saving, emission reduction, and preservation of natural resources. The improvement on selection and quality of the raw materials and binders as well as the enhancement of the knowledge on mixture performance are leading to the intensive use of cold recycling techniques in place of traditional ones. One of the main differences between cold and hot techniques is the evolutive development of performance, generally identified as curing process, due to the presence of water and hydraulic binders in the cold mixtures. Environmental-related factors such as temperature, humidity, wind, and rainfall significantly influence the curing process and, as consequence, the mixture properties over time. Several laboratory curing protocols have been developed by universities, research centers, and agencies, but a clear relationship between simulative procedures in laboratory and the field is still an open challenge. This paper aims at characterizing the short-term and midterm curing behavior of a cold recycled material (CRM) mixture. A CRM mixture was selected and characterized in laboratory, and the in-plant production procedure was validated. The CRM mixture was used to build the binder course of an instrumented pavement in the Republic of San Marino. Volumetric and mechanical testing on laboratory-produced specimens and cores were analyzed considering the temperature and moisture sensor measurements in field. Results address to a new insight for laboratory procedures and prediction models matching laboratory conditions and the real curing condition in field.

Application of Wasted and Recycled Materials for Production of Stabilized Layers of Road Structures

The construction industry, as one of the most complex sectors, depends on using wasted and recycled materials, timely decision-making, and adequate execution of all activities in supply chains. This paper presents tests of mixtures for cold in-place recycling where existing material is used. In this research, we used cement and bitumen emulsion as well as fly ash, zeolite, slag, and Bakelite. A total of seven mixtures were tested in order to increase sustainability. It was tested the indirect tensile strength and dynamic modulus of elasticity after seven and 28 days for dry specimens, after 28 days for water-saturated specimens and for specimens exposed to frost. After completing the tests using the MEREC (MEthod based on the Removal Effects of Criteria) and CoCoSo (Combined Compromise Solution) multi-criteria model, mixtures were evaluated and ranked in terms of mechanical properties, price, and environmental protection. Considering the ranking of mixtures using the CoCoSo method, the highest quality mixtures, for most combinations of weight factors, are mixtures with slag, mixtures with fly ash, and mixtures with 2% of cement and 2% of bitumen emulsion. Sensitivity analysis was also performed with new simulated values of the criteria in order to determine the individual influence of the criteria on the ranking of mixtures. The conclusions are as follows: the use of bitumen emulsion, cement, waste materials, and other materials in cold recycling would reduce the cost of recycling pavement structures, increase environmental protection, while the mechanical properties of the pavement structures are within acceptable limits.

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.

Characterization of fatigue performance of cold mix recycled asphalt mixtures through uniaxial tension–compression testing

Cold recycling of pavements utilizes nearly 100% of the reclaimed asphalt pavement (RAP) for pavement rehabilitation. Due to the large amount of RAP, the cold recycled mixes would become prone to fatigue cracking, and hence evaluation of their fatigue performance becomes highly important. In this study, three cold recycled asphalt mixes were prepared using a regular cationic slow setting asphalt emulsions with hard base asphalt binder (CSS-1h) with and without Portland cement stabilization, and a polymer modified emulsion (CSS-1hp). The optimum emulsion and pre-mix water contents were determined using Superpave Gyratory compacted specimens through the mix design process by studying the air void levels and meeting minimum strength requirements. Fatigue properties of these three groups of mixes were then evaluated through a series of uniaxial cyclic tension–compression tests. The results were compared in terms of the modulus degradation, dissipated energy capacity, changes in phase angle, and number of cycles to failure, to determine the fatigue lives of the different mixes. The results indicated that adding 1% Portland cement to the cold recycled specimens significantly improved their fatigue performance as compared to the control scenario specimens prepared with regular CSS-1h emulsion. Using the polymer modified emulsion also led to a slightly improved fatigue resistance of the cold mix specimens as compared to the mixes prepared with regular emulsion. Furthermore, Multiple Stress Creep Recovery (MSCR) testing of the two residual emulsion binders indicated potential of improving the rutting resistance for the mixes prepared with the polymer modified emulsion.

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.