Properties Of Cold Recycled Mixtures Research Articles

Evaluation of mixture grading and binder composition effects on the characteristics of cold-recycled mixtures with foamed bitumen

The investigation was carried out to evaluate the effects of the hydraulic binder's composition on the properties of cold recycled mixtures with foamed bitumen of different gradations. The evaluated hydraulic binders were composed of Portland cement, hydrated lime and cement by-pass dusts. The ratios of these three components simultaneously varied from 20 to 60% in relation to the mass of the resultant hydraulic binder. The mixtures were composed of reclaimed asphalt from a road base (coarse or fine RAP), natural aggregates (0/2 and 0/31.5 mm) in different ratios, hydraulic binder and 70/100 foamed paving grade bitumen. It was shown that the fine and coarse mixtures responded differently to the changes in the composition of the hydraulic binder. It was found that the optimum performance of the fine and coarse graded mixtures required different binder compositions.

Long-term effects of RAP on the mechanical properties of cold recycled mixtures

ABSTRACT This paper investigates the long-term influence of aged asphalt in reclaimed asphalt pavement (RAP) on the mechanical properties of the cold recycled mixture (CRM) with emulsified asphalt. Firstly, RAP was simulated by the long-term aging method. On this basis, indirect tensile strength tests were conducted to discern the long-term strength with different aged asphalt dosages (0%, 2%, and 4%) and aging degrees (0, 4, 8, and 15 h) of RAP. After accelerated curing, the indirect tensile strength (ITS) and fracture energy () were measured and the area ratio of uncoated aggregates of the fractured surface (Ra ) was established by image processing to reflect the long-term growth mechanism of strength. Considering the unfavourable states, interfacial drawing and shear tests were executed with different aging degree, load, interfacial contact and thickness of aged asphalt films. Results indicated that the strength increased with aged asphalt dosages of RAP, whereas aging degree had the opposite effect. Moreover, aging degrees, clean surface and external load are all salutary to the long-term adhesion of CRM, obviously. Therefore, it is proved that RAP makes contributions to the long-term growth in mechanical properties of CRM, which is also significant to sustainable asphalt pavement maintenance.

Effect of polymer modified bitumen emulsion production method on the durability of recycled asphalt mixture in the presence of deicing agents

This study investigated the effects of polymer modified bitumen emulsion production methods on the microstructural properties of modified binders and the mechanical properties of cold recycled mixtures with a more emphasis on durability. Modified bitumen emulsions containing styrene butadiene rubber (SBR) produced using three methods, including soap pre-batching, post-blending and co-milling. Surface free energy (SFE) and atomic force microscopy (AFM) tests have been used to inquire into the fundamental and microstructure properties of samples. Indirect tensile strength and dynamic modulus tests were used to investigate the mechanical properties of cold recycled mixtures. Mechanical properties of mixtures were investigated in dry state, after saturation and placement in the freeze-thaw (F-T) cycles with and without deicing agents including calcium magnesium acetate (CMA) and calcium chloride (CaCl2). Accordingly, the soap pre-batching method had the most suitable performance in terms of dynamic modulus at high temperatures and superior durability under F-T cycles. The samples made by soap pre-batching method showed the lowest surface roughness, maximum adhesion and the highest cohesive energy and surface free energy based on the results of AFM and SFE tests, which were effective in improving the mixture performance. Overall, the post-blending and co-milling methods can be rated as the second and third ranks in terms of both mechanical and nano-mechanical properties, respectively. Finally, in comparison with CaCl2, CMA salt significantly reduced the destructive effects of F-T cycles on the mechanical properties of recycled mixture.

Use of calcium oxide as active filler for bituminous stabilised materials

With the increasing usage of cold recycling techniques on maintenance of flexible pavements, increases also the need to better characterise the properties of cold recycled mixtures, usually composed of aggregates, reclaimed asphalt – RAP, active filler and bitumen. Understanding the mechanical behaviour of cold recycling mixtures is necessary to set the design process on a performance based approach. This study was designed to evaluate evolution of mechanical behaviour related with the use of quicklime (calcium oxide) as active filler in a BSM mixture; the quicklime was added on different contents up to 5%, considering that its chemical reaction with water can be very convenient to deal with environmental limitations on the construction of a BSM layer. Alongside, this study also compares in a qualitative way the changes in mechanical properties when lime or cement are used as active filler. Indirect tension tests and monotonic triaxial tests were run on BSM mixtures produced with either quicklime or cement added in different amounts. The results show that the use of quicklime may bring various advantages to cold recycling operations, with negligible performance variation even when added in higher amounts. Results also indicate that mixtures designed with cement are more susceptible to mechanical behaviour changes when compared to the ones designed with lime, which suggests that mixtures designed with cement need a more precise mix design and specially a more accurate mixing control in field operations.

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.

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.

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.

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.

Investigation of early-stage strength for cold recycled asphalt mixture using foamed asphalt

This papers aims at investigating the strength properties of cold recycled mixtures using foamed asphalt (CRMF) at its early-stage of curing. Indirect tensile strength (ITS) and deformation-strength test were used to figure out the early-stage strength development law of the CRMF. Through image processing and analysis the fracture interface characteristics of CRMF were identified. Statistical methods were used to analyze the amounts of air voids in the CRMF specimens and a two-parameter Weibull model was used to describe the distribution of air voids in the CRMF using X-ray computed tomography (CT) technique. The results indicated that moisture content had a significant effect on the strength of CRMF. Moreover, cement only affected the early strength while the foamed asphalt affected the long-term strength of CRMF. The fracture path was developed along the weak interface where there was moisture membrane especially at 0–3days curing. The asphalt mastic may be broken off forming the fracture path as the curing continuing after 3days of curing. The X-ray CT test indicated that a weak hydration products interface was destroyed and two voids were interconnected to become one large void. However, variations of the voids amounts had almost no significant effect to the Weibull distribution of air voids in CRMF. The findings helps us to understand well to the development mechanism of early-stage strength of CRMF and lead us to new approaches to improve the early-stage strength.

An Experimental Study on Pavement Performance and Dynamic Mechanical Properties of Cold Recycled Mixtures Consisted of Modified Asphalt Emulsion-Cement Binders

The objective of this study is to evaluate pavement performance and dynamic mechanical properties of cold recycled mixtures consisted of modified asphalt emulsion-cement binder (CRMC). A cold recycled mixture design procedure that includes original material selection and gradation design has been applied. Then pavement performance of CRMC has been comparatively analyzed with the recycled mixtures without cement by theoretical and experimental methods. In addition, the tests for dynamic mechanical properties of CRMC have been conducted. The overall performance tests results indicate that CRMC has good strength, moisture stability, high temperature stability, low temperature stability, anti-shrinkage and fatigue resistance properties compared to the cold recycled mixtures without cement; Dynamic mechanical properties confirm that CRMC are similar to the hot mixtures asphalt (HMA), although a certain amount of cement is added.