Cold Recycled Mixtures Research Articles

Performance of Hot and Cold Recycled Mixtures with High Reclaimed Asphalt Pavement Content

Florida Department of Transportation yearly maintenance and rehabilitation activities include milling and resurfacing of approximately 2,000 lane miles of roadway, with an average resurfacing depth of about 2.1 in. (55 mm). These activities result in the generation and accumulation of roughly 1.8 million tons of reclaimed asphalt pavement (RAP) each year. The use of elevated quantities of RAP in asphalt pavement provides an environmentally responsible solution to the accumulated RAP surplus in some urban areas, while at the same time offering an economical pavement maintenance and rehabilitation option to local agencies facing budget constraints. The objective of this project was to compare the performance of mixtures with 60% RAP content to be used primarily on low volume roads (average daily traffic <750 vehicles) and suggest adequate test methods within the context of a balanced mix design approach. To accomplish this objective, three types of mixtures were considered: hot, cold with emulsion, and cold with foamed binder. Performance testing included intermediate temperature cracking, rutting, moisture susceptibility, and durability. The hot recycled mixtures showed good moisture susceptibility and cracking resistance, especially when rejuvenators were incorporated. The cold recycled mixtures showed poor moisture susceptibility and durability characteristics, which were alleviated when hydrated lime or Portland cement was incorporated in the emulsified and foamed mixtures, respectively. Most hot recycled mixtures, and all the cold recycled mixtures, exhibited poor rutting behavior, likely because of the harsh conditions of the test. A life-cycle cost analysis demonstrated more favorable savings when cold recycled mixtures were used.

Cold asphalt mix with emulsion and 100% rap: Compaction energy and influence of emulsion and cement content

The present work aims at determining the conditions for the compaction of cold recycled mixtures with emulsion and 100% RAP. Additionally, the influence of the emulsion and cement on the final properties of the recycled mixtures has been investigated. To achieve these purposes, reclaimed asphalt material coming from the milling of a distressed pavement was mixed with different proportions of water, asphalt emulsion and cement. The mixtures were compacted by a gyratory compactor. As a result of the investigation, it is recommended to apply a compaction energy level of 100 gyrations for specimens 100 mm diameter and 60 mm height, and an energy of 200 gyrations for specimens 100 mm diameter and 100 mm height. As for the mechanical properties of the mixtures, the laboratory tests showed that the presence of cement contributes to improving the sensitivity to water attack, the resistance to permanent deformations, the stiffness modulus and the fatigue life of the mixtures.

Performance and viscoelastic assessment of high-recycle rate cold foamed bitumen mixtures produced with different penetration binders for rehabilitation of deteriorated pavements

The paper investigates the influence of the binder penetration grade on the volumetric, mechanical and viscoelastic properties of cold recycled mixes with foamed bitumen. Cold recycled mixtures produced with foamed bitumen differ significantly from other bituminous paving materials (e.g. hot mix asphalt) in terms of aggregate coating and bonding with the bituminous binder. What is more, hydraulic binders usually contribute to the strength of those mixtures. These factors result in a decreased viscoelastic response of cold recycled mixtures, which may impact the sensitivity of these mixtures to the type of binder used, which has not been thoroughly studied yet. The main body of the conducted experiments included complex stiffness moduli measurements under cyclic uniaxial compressive loading, supplemented by assessment of air void content, indirect tensile strength, resistance to moisture damage, indirect tensile stiffness and static creep modulus. The composition of investigated mixtures with high rate of recycled materials was designed to reflect a common scenario in rehabilitation of deteriorated pavements subjected to low and medium traffic loads. The three utilized binders were graded as 35/50, 50/70 and 70/100 penetration road paving bitumen, and were added as foamed bitumen in 2.5% amounts to the cold mix. The recycled mixes contained 50% of reclaimed asphalt pavement material, 30% of reclaimed crushed stone base and 20% of virgin aggregates. A hydraulic binder in form of Portland cement was used as a binding agent in amounts of 2%. Each of the investigated mixtures exhibited significantly distinct results in terms of air void content, indirect tensile strength and creep stiffness modulus. The performance of mixtures with 50/70 and 70/100 binders was similar in indirect tensile stiffness moduli and complex stiffness moduli. It was found, that the binder type had significant effects on the compactability of investigated mixtures, which resulted in different mechanical performance. At the same time the influence of the binder type on the viscoelastic properties of the cold mixtures was attenuated. It was concluded that the limited influence of the binder used was caused by the significant amount of reclaimed asphalt material in the evaluated mixtures and the effects of cementitious binding of the Portland cement. The results showed that a wide range of penetration grade bitumen can be used for producing cold recycled mixtures with foamed bitumen with only minor effects on their performance and viscoelastic properties.

Effects of recycled aggregate composition on the mechanical characteristics and material design of cement stabilized cold recycling mixtures using road milling materials

Road milling materials, including the reclaimed asphalt pavement (RAP) and the reclaimed cement stabilized base-course (RAI), have been widely used as the recycled aggregates (RA) to prepare cement stabilized cold recycling mixtures (CSCRM) used in highway rehabilitation. However, there are few studies on the effect of RA composition (RAP and RAI proportion in RA) on the pavement performance of CSCRM. In this study, therefore, a total of forty-two groups of CSCRM are prepared in the case of different RA contents, RA compositions and cement contents. The investigation of mechanical characteristics (unconfined compressive strength, splitting strength and uniaxial compression modulus) of CSCRM reveals the effect of RA content, RA composition and cement content. The RA content, RA composition and cement content play an important role in the mechanical properties of CSCRM. The strength mechanisms of CSCRM are revealed via the micro-interface characteristics for based on SEM-image. Finally, the recommended material compositions of CSCRM are put forward and verified via durability tests (fatigue tests, dry-shrinkage tests and water-erosion tests). Results show that the recommended CSCRMs present a better overall performance.

Complex Modulus Testing and Rheological Modeling of Cold-Recycled Mixtures

Abstract This research compares the rheological behavior of different cold-recycled mixtures (CRMs) produced in-place through full-depth reclamation. Reclaimed asphalt pavement (RAP) obtained from the milling of the old asphalt layers was blended with reclaimed unbound aggregate from the existing subgrade. Asphalt emulsion, foamed asphalt, and portland cement were employed as stabilizing agents. The complex modulus was measured on cylindrical cores, applying a sinusoidal strain with an amplitude of 30 microstrain at testing temperatures ranging from 0°C to 50°C and frequencies ranging from 0.1 to 20 Hz. The Huet-Sayegh (HS) rheological model was applied to simulate the experimental data. The results showed that the behavior of CRM is thermo- and frequency-dependent and that the time-temperature superposition principle can be applied. The HS model provides an excellent fitting of the dynamic modulus data, whereas fitting of the loss angle data was improved, introducing a temperature- and frequency-independent correction. The RAP influences the rheological behavior, but viscous dissipation is mainly due to the asphalt-stabilizing agents (emulsion residue or foamed asphalt).

The influence of combination of binding agents on fatigue properties of deep cold in-place recycled mixtures in Indirect Tensile Fatigue Test (ITFT)

The publication presents fatigue properties of cold recycled mixtures for eight combinations of binding agents (cement and bituminous emulsion). Cold recycled mixtures were evaluated in Indirect Tensile Fatigue Test (ITFT) at the temperature of 20 °C in controlled stress mode. As a function of horizontal stress, fatigue life is strongly influenced by combination of the binding agents. When fatigue life is analyzed as a function of initial horizontal strain, the difference between different combinations decreases. In all cases, the influence of a specific binding agent is more visible for combinations with lower total amounts of the two agents.

The Influence of a Polymer Powder on the Properties of a Cold-Recycled Mixture with Foamed Bitumen.

The paper investigates the influence of redispersible polymer powder (RPP) on the physical and mechanical properties of a cold-recycled mixture with foamed bitumen (CRM-FB). Four types of RPP with a varied chemical base were used: VA-VeoVA, VA-VeoVa-Ac, EVA and VA/VV/E/Ac. The polymer powder-modified cold recycled mixture with foamed bitumen, (P)CRM-FB, was composed of 45.8% reclaimed asphalt pavement (RAP), 45.8% natural aggregate (VA), 3.0% Portland cement CEM I 42,5R, 3.0% foamed bitumen 50/70 and 3.0% RPP, all dosed by weight. The reference mixture, (R)CRM-FB, served as a reference point for comparison. It was found that RPP improved the workability of the CRM-FB mixture. This results in a reduced number of compaction cycles and lower energy needed to obtain the air void content as in the reference mixture. In addition, the RPP modifier markedly increased the CRM-FB mixture cohesion (ITSDRY) and strength, by approximately 40–70%, depending on the RPP used. These findings are particularly important for CRM-FB mixtures designed for road bases. The present investigations confirmed the improvement of the CRM-FB mixture parameters after the modification with RPP, regardless of the powder type used.

Influência da velocidade de carregamento e temperatura no comportamento mecânico de misturas recicladas a frio com emulsão asfáltica e espuma de asfalto

A reciclagem a frio de pavimentos é uma alternativa sustentável para a redução do consumo de materiais virgens e do descarte inadequado de resíduos gerados em obras de restauração. Entretanto, ainda não há um consenso sobre as propriedades mecânicas das misturas recicladas a frio, principalmente em relação ao comportamento viscoelástico. Por meio de simulações computacionais usando o software 3D-Move Analysis, avaliou-se a influência que a velocidade dos veículos e a temperatura de trabalho têm sobre as propriedades mecânicas de um pavimento cujas camadas de base são constituídas por misturas recicladas a frio estabilizadas com emulsão asfáltica (AEM) ou com espuma de asfalto (FAM). Com o objetivo de estudar como variam as deformações longitudinais para um ponto localizado no fundo do revestimento asfáltico, observou-se que os materiais reciclados a frio apresentam comportamento viscoelástico, pois diferentes combinações de velocidade e de temperatura resultam em diferentes distribuições de tensão e deformação na camada de revestimento. Dessa forma, observou-se que a não consideração da presença de viscoelasticidade linear para estes materiais pode vir a subestimar a capacidade de suporte da estrutura.

Influence of low production temperatures on compactability and mechanical properties of cold recycled mixtures

In cold regions, the production of Cement-Bitumen Treated Materials (CBTM) represents an issue in terms of annual time available for production. The objective of this research is to study the influence of different combinations of production temperatures for mixing, compacting and curing (developed in two steps) on the mechanical properties of CBTM produced with two sources of bitumen emulsion. Workability, compactability, indirect strength and other additional tests were involved in the analysis. Findings highlighted the critical effect of transportation and compaction temperatures on CBTM workability. Moreover, the emulsion source significantly affects the mixture strength when produced at low temperatures.

Preliminary assessment of the secondary setting of Portland cement in recycled crushed concrete incorporated in cold recycled road base mixes with foamed bitumen

The recycled crushed concrete (RCC) unlike the natural aggregates, has a residue of the unhydrated Portland cement (PC) covering the aggregate grains, which may result in a secondary cementation process after its application in a road base. The paper presents the results of exploratory research on the phenomenon of the secondary setting of Portland cement in recycled crushed concrete aggregates in cold-recycled mixes with foamed bitumen (FB). The tests were performed using two mixtures, i.e. Mix-FBREF reference mixture without the addition of RCC, and Mix-FBRCC research mix containing 25% of RCC. The composition of mineral mixtures with foamed bitumen was designed using typical recycled materials, used as a part of the road repair works of pavements, i.e. Reclaimed Asphalt Pavement (RAP), Reclaimed Aggregates (RA) and new aggregates (NA). All mineral materials used in the tests met the requirements in terms of suitability for the foamed bitumen cold-recycled mixtures, intended for basecourse. The total amount of the bituminous binder in the Mix-FB mix was 5.5%. To assess the phenomenon of the secondary setting of Portland cement contained in the recycled concrete, tests were conducted to evaluate the increase of the unconfined compressive strength (UCS) in time of the material. The strength of UCS samples of Mix-FBREF and MixFBRCC mixtures was determined after 3, 4, 7, 14 and 28 days of conditioning. The tests showed that the value of the analysed parameter in the reference mixture increased by about 180 kPa with time, whereas for the mixture containing the concrete recycled aggregate the difference was virtually unnoticeable (only by 6 kPa). The obtained test results were subjected to the statistical analysis, which showed that for each of the considered sample conditioning periods, no statistically significant differences between the strength values of unconfined compression of the tested mixtures were found. The presence of bituminous binder in basecourse cold-recycled mixtures, (old, with RAP and new, in foamed form) yields the bituminous binding dominant over the effects of PC binding, therefore minimizing the effects of the secondary Portland cement setting.

Influence of Binder Property and Mortar Thickness on High-Temperature Performance of Cold Recycled Mixtures with Asphalt Emulsion.

Four kinds of cold recycling (CR) mixtures with different asphalt emulsions were studied for their high-temperature performance in both binder properties and internal structures aspects. Digital image processing was introduced to determine the thickness spectrum for the asphalt mortar of the CR mixtures from a mesoscopic perspective. The time–temperature sweep (TTS) test was conducted to obtain the rheological parameters of each corresponding emulsified residue and the permanent deformation performance of each CR mixture was measured by dynamic creep test. A principle component analysis (PCA) was used to compare the typical performance parameters of the CR mixtures and find the factors controlling the rutting resistance of CR mixtures. The results show that the high-temperature performance of the CR mixtures with a modified emulsified asphalt showed improvements relative to the nominal case. Including Marshall stability, several parameters from the rheological properties of binder (G*/sinδ, flow number) and mortar thickness (max, range proportion 0–10 mm) could significantly influence the high-temperature performance and rutting resistance of the CR mixtures.

Composition Design and Performance Evaluation of Emulsified Asphalt Cold Recycled Mixtures.

Based on an analysis of the cold regeneration mechanism of emulsified asphalt, the emulsified asphalt binders and cement were applied to prepare the cold recycled mixtures, and the main technical performances of the designed mixtures were evaluated, including high-temperature stability, water stability, and fatigue characteristics. A high content of 65% recycled asphalt pavement (RAP) material was used with some new aggregates and mineral powders, and the optimal emulsified asphalt binder and cement dosages were determined as 2.9% and 1.5% respectively. The technical performance test results show that: (1) The well-designed emulsified asphalt cold recycled mixtures have good high-temperature stability and water stability, and can meet the requirements of the road base layer and the lower layer. (2) When the stress level is lower, the fatigue performance of mixtures with lower emulsified asphalt binder dosage and lower cement content is better, but when the stress level is higher, the high dosage of emulsified asphalt binder is more favorable, while the cement content has little effect on the fatigue property. (3) The emulsified asphalt cold recycled mixtures have relatively poor fatigue resistance, and their fatigue life is significantly lower than that of the hot mixed asphalt mixtures.

Performance Evaluation of Recycled Asphalt Pavement Materials and Cold Recycling Mixtures Designed with Vibratory Compaction Method

In this paper, the basic composition and performance evaluation of the recycled asphalt pavement (RAP) materials were firstly analyzed, and two methods were proposed to evaluate strength characteristics of RAP materials, including a triaxial method for the residual strength and the mortar cementing method for the strength of RAP lump. Then, the cold recycling technology was applied on RAP materials with emulsified asphalt by using vibratory compaction and heavy-duty compaction methods (Proctor compaction method), and the results showed that the maximum dry density obtained by heavy-duty compaction was closer to the actual situation. Finally, the effects of wetting water, emulsified asphalt dosage and curing conditions on the performance of the specimens were investigated. It was found that when the emulsified asphalt was mixed uniformly, whether or not to add the wetting water have almost no effect on the strength of the molded specimens. When the matrix asphalt content of the emulsified asphalt was 30%~60%, the water could be directly added to the cold recycling mixture. The intensity of accelerated curing for two days at 40 °C was approximately equal to that of natural curing for three days, while that of accelerated curing for three days at 40 °C was approximately equal to that of natural curing for seven days, which provided a basis for the short-term laboratory test.

Effect of gradation on volumetric and mechanical properties of cold recycled mixtures (CRM)

In recent times, recycling using cold bituminous mixtures has become one of the most interesting techniques in pavement engineering from sustainability aspect. This study focuses on the clarification of the steps concerned with the cold mixture mix design to determine the initial aggregate gradation of the mixture. The study has been developed involving procedures followed in Canada and Italy. In both the cases, three different gradations, normally employed in the production of traditional bituminous mixtures, were compared. The effect conferred by the gradation type has been studied in terms of workability, compactability and mechanical properties. Results show that in both the procedures the gradation influenced the workability and the compaction behaviour of the mixtures studied. At the same time, in terms of mechanical properties, the gradation influenced the strength of the final mixture in only one of the procedures applied.

Experimental characterization of the 3D linear viscoelastic behavior of cold recycled bitumen emulsion mixtures

Cold mixtures with bitumen emulsion are produced at ambient temperature, leading to substantial reductions of energy consumption and atmospheric emissions. In cold recycling applications, cement is normally used to improve the mixture performance. Thus, the rheological behavior of cold recycled mixtures is different from that of conventional hot mixtures because it is due to the interaction of fresh bitumen, aged bitumen and cementitious bonds. In this study, we investigated the three-dimensional (3D) linear viscoelastic (LVE) behavior of a cement-bitumen treated material (CBTM) mixture fabricated using bitumen emulsion and cement. For comparison, we also investigated the 3D LVE behavior of hot-mix asphalt containing 25% of reclaimed asphalt and fabricated using polymer-modified binder. Sinusoidal axial tests on cylindrical specimens, were carried out at various temperatures (from 0 °C to 50 °C) and frequencies (from 0.1 to 12 Hz). The complex Young's modulus E ∗ and the complex Poisson's ratio v ∗ were determined through the measurement of axial and transverse strain. We show that when considering E ∗ , CBTM mixtures may be considered thermo-rheologically simple and the Huet-Sayegh model can be used to simulate the frequency–temperature dependence. On the other hand, when considering v ∗ the behavior of CBTM mixtures is very different from that of hot mix asphalt. In particular, its absolute value is almost constant and very close to 0.15. • The 3D LVE behavior of HMA with 25% RAP can be simulated using the 2S2P1D model. • At high reduced frequencies, HMA is stiffer than cold-recycled mixture. • At low reduced frequencies, cold-recycled mixture is stiffer than HMA. • E ∗ of cold-recycled mixture can be simulated using the Huet-Sayegh model. • v ∗ of cold-recycled mixture is almost constant and equal to 0.15.

Evaluation of Laboratory Performance and Structural Contribution of Cold Recycled Versus Hot Mixed Intermediate and Base Course Asphalt Layers in New Hampshire

Depending on the local conditions and structural design of the pavement, multiple asphalt concrete layers including base, intermediate, and wearing courses are used. Typically, the base and intermediate layers have larger aggregate sizes and lower total asphalt binder contents as compared with the wearing course. Recently, cold recycled (CR) asphalt mixtures have gained attention as an alternative to the typical base, and to some extent intermediate courses, because of economic and environmental advantages. Challenges with CR include the potential high variability of recycled asphalt pavement (RAP) and lack of knowledge in relation to structural contribution and long-term performance of such layers. This study investigates four different types of CR and four hot mixed plant-produced asphalt mixtures (three intermediate courses and one base course) that are typical mixtures used in New Hampshire. The laboratory performance evaluation is conducted through the resilient modulus (Mr), complex modulus (E*), semi-circular bend and direct tension cyclic fatigue (S-VECD) tests. Pavement performance prediction is carried out using the results from S-VECD approach in the FlexPAVETM software. The test results indicate that the performance of CR is highly affected by the amount of oil distillate percentage in the emulsion as well as the amount of recovered binder in the RAP. While having a relatively lower rutting resistance capability, the CR mixtures maintained an acceptable fatigue performance. As compared with CR mixtures, hot mixed intermediate and base course mixtures indicated better rutting performance while having lower resistance to cracking.

Effect of cement on the strength and microcosmic characteristics of cold recycled mixtures using foamed asphalt

This paper investigates the influence of cement on the strength and microcosmic properties of cold recycled mixtures using foamed asphalt (CRMF). An indirect tensile strength (ITS) test and simple triaxial test (STT) were used to evaluate mixtures properties with and without cement. A repeated loading deformation-strength test (RLDST) was conducted to discern the difference of resistance to permanent deformation between the two kinds of mixture. An X-ray computed tomography (CT) test and scanning electron microscope (SEM) test were used to identify the air voids distribution and micromorphology characteristics of CRMF. Strength formation mechanism was revealed by analyze the micro-structure and air voids distribution of CRMF. Test results indicated that cement had a significant influence on ITS and resistance to moisture damage. Moreover, micro-structure and air voids distribution was obviously changed due to the addition of cement, as shown by SEM and CT test. STT results showed that internal friction increased significantly, while cohesion had little difference with addition of cement. The fracture energy of the mixture increased remarkably, but failure strain decreased obviously with the addition of cement. Thus, the brittleness of CRMF was enhanced, therefore flexibility was reduced. Results of RLDST indicated that resistance to permanent deformation was distinctly improved with addition of cement. The X-ray CT test indicated that the weak interface was destroyed as the freeze-thawing process continued, which resulted in several voids connecting to form a large voids. Consequently, air void distribution varied after freeze-thaw processes.

Design methodology for in situ cold recycled mixtures with emulsion and 100% rap

At present there is no consensus on the most suitable methodology for the design of cold recycled mixtures with emulsion, due to its complexity. Therefore, design is generally based on compliance with one or more volumetric or mechanical parameters established in the highway regulations, which does not guarantee the optimization of the mixture. The present work proposes a design methodology for cold recycled mixtures with emulsion, in which 6 parameters are evaluated: Air voids, Indirect Tensile Stress, Indirect Tensile Strength Ratio, Wheel Tracking, Stiffness Modulus and Fatigue life. Performance indexes were established to evaluate the values obtained from the tests according to behavior graphs with the maximum value of 1. These graphs evaluate the results of the tests, considering as a maximum value the most favorable results for the optimal performance of the mixture. Finally, for the analysis of the mixtures the authors propose a Global Performance Index (GPI) that shows the average of the 6 parameters measured. The result is a number that represents each job mix formula, which is sensitive to changes in the values of the properties and is obtained using a systematic methodology. Therefore, the choice is based on technical criteria and according with the GPI; the influence of the materials or the formulas used for each mixture can be ranked.

Stiffness and Fatigue Behavior of Emulsified Cold Recycled Mixture Containing Waste Powder Additives: Mechanical and Microstructural Analysis

AbstractIn recent years, due to economic and environmental considerations, the use of waste additives has been highly regarded in pavements. In the case of emulsified cold recycled mixtures (ECRMs)...

Laboratory mechanical characterisation of cold recycled mixtures produced with different RAP sources

Cold Recycled Mixtures (CRM) are composed of high amounts of Reclaimed Asphalt Pavement (RAP) together with bitumen emulsion. As additional binder, some ordinary cement is normally employed. Since RAP aggregates represents almost the entire solid structure, it is important to fully characterise Cement-Bitumen Treated Materials (CBTM) produced with different RAP materials. This work focuses the characterisation at small strain level, investigating the stiffness modulus at three testing temperatures; at the failure point, measuring the Indirect Tensile Strength; and studying the fracture behaviour, in Semi-Circular Bending Test configuration. From the results, it is possible to confirm the influence of different RAP materials, also characterised by different aggregates Nominal Maximum Size. As a consequence, a reliable RAP classification can allow a better prediction of the final CBTM mechanical properties.