1,720,963 research outputs found
Fatigue and healing properties of rubberised asphalt binders produced with pre-treated recycled rubber
No full textIn this paper, the fatigue and healing properties of Recycled Tyre Rubber Modified Bitumens (RTR-MBs) produced with pre-treated recycled rubber were investigated. Using the pre-treated rubber has resulted in a considerable decrease in the High Temperature Viscosity (HTV) compared to none-pre-treated rubber which is important for better handling and workability. Fatigue cracking is considered the main distress mode of asphalt pavement at intermediate temperatures, as pavement is subjected to a considerable number of repetitive traffic loads. Thus, selecting an appropriate test method and parameters is crucial to realistically rate the binder contribution to fatigue damage resistance. Utilising the dynamic shear rheometer (DSR), time sweep tests were conducted by applying repeated cycling of stress or strain loading at selected temperatures and loading frequency. The healing potential of binders was evaluated by introducing short rest periods (RPs) after a certain number of load pulses. The unique energy parameter known as the Plateau Value (PV), which is obtained using the Ratio of Dissipated Energy Change (RDEC) approach, was applied to evaluate the fatigue binder damage and healing phenomenon. The results showed that both rubberised bitumens produced by activated recycled rubber are better fatigue and healing performers than the straight-run bitumen
Rubberised stone mastic asphalt mixtures: a performance-related evaluation
No full textThe binder content of rubberised asphalt mixtures is usually increased compared to that used in conventional asphalt. This increase is deemed important to compensate for the reduction in the actual bitumen due to the existence of rubber particles. This study presents the results of performance evaluation conducted on different rubberised Stone Mastic Asphalt (SMA) mixtures produced using different types and contents of rubberised bitumen. The energy ratio (ER) computed from Superpave Indirect Tensile (IDT) tests was used to evaluate the cracking resistance of asphalt mixtures while the rutting behaviour was evaluated using the Repeated Load Axial Test (RLAT). The indirect tensile stiffness and strength were used to evaluate the moisture susceptibility. Using the same binder content for rubberised SMA mixtures as used in the conventional mixtures can still give superior performance properties. Adding crumb rubber to softer base bitumen can produce asphalt mixtures with superior cracking and rutting resistance
Rubberised bitumen manufacturing assisted by rheological measurements
Full text linkThis paper investigates the effect of processing temperature and time on the rheological properties of recycled tyre rubber-modified bitumens (RTR-MBs) produced using two different base binders and an ambient ground crumb rubber modifier (CRM). The production of the RTR-MBs was accomplished by means of a standard Brookfield rotational viscometer together with a modified impeller, dual helical impeller, to allow mixing as well as real-time viscosity measurements of the produced RTR-MBs. The rheological properties of the final RTR-MBs were determined by means of standard dynamic mechanical analysis oscillatory and multiple stress creep recovery testing using a dynamic shear rheometer. The results indicate that the low processing conditions (160°C and 60 min) are not appropriate for developing RTR-MBs with enhanced physical and rheological properties. However, allowing the crumb rubber to interact with the base binder for longer mixing times (140 min) led to the development of an enhanced rubber (polymer) network structure within the blend (i.e. swelling of the CRM particles) and superior rheological properties. At the other extreme, using high-processing conditions (200°C and 140 min) led to RTR-MBs in which the rubber network had been subjected to devulcanisation and depolymerisation with a subsequent reduction in modification
An investigation on using pre-treated tyre rubber as a replacement of synthetic polymers for bitumen modification
Full text linkRubberized bitumen obtained through a swelling process, has widely proven to be a successful technology for asphalt pavement applications and a solution to reduce the dismantling of tyre rubber on landfills. However, this technology presents two main operative issues which needs the adoption of costly special equipment. Firstly, significant high value of High Temperature Viscosity (HTV) which imposes mixing and compaction difficulties and leads to increased energy consumption and emissions. Furthermore, during the hot storage period, phase separation between rubber particles and the base bitumen could occur. Developing Recycled Tyre Rubber Modified Bitumen (RTR-MBs) with improved storage stability and reduced values of HTV could allow using this technology in standard asphalt plants, resulting in an environmental-friendly and cost-effective option of standard Polymer Modified Bitumen (PMBs). In this study, two different pre-treated and one straight ambient recycled rubbers were used to produce RTR-MBs. The first RTR was pre-treated by special oil and Warm Mix Additives (WMA) and the second was partly devulcanised. Also, two base binders were selected with large differences in mechanical properties in order to identify the effect of base binder. The high temperature viscosity was successfully reduced by using pre-treated RTR. The use of RTR together with Fischer–Tropsch wax (Sasobit®) in bitumen technology offered superior high in-service temperature properties and reduced value of HTV, and thus can be preferred option over styrene–butadiene–styrene (SBS) modification
An investigation of the mechanical properties of rubber modified asphalt mixtures using a modified dry process
No full textIncorporating recycling tyres into asphalt mixtures contributes to solving a serious environmental problem as well as the potential of improving the mechanical performance of asphalt mixtures. The recycled tyre rubber is added by two technologies known as the dry process (when rubber particles are treated as an aggregate modifier) and the wet process (when rubber particles are treated as a binder modifier). Although, the dry process is easier and requires minimal or no modification in the asphalt plant, the inconsistency in field performance makes the dry process not widely used. The main reason for this is believed to be the lack of interaction between the rubber particles and binder. In order to overcome this issue fine rubber particles were used to enhance the interaction with the binder and reduce the springy nature of rubber particles that poses difficulties during the compaction process of mixtures. The mechanical performance-based properties for the control mixture (without adding rubber) and other different rubber asphalt mixtures were evaluated and characterised in terms of their fatigue resistance using the Indirect Tensile Fatigue Test (ITFT), rutting resistance using the Repeated Load Axial Test (RLAT). The stiffness modulus for the different mixtures was also measured by the means of Indirect Tensile Stiffness Test (ITSM). The results have shown that asphalt mixtures produced with the addition of crumb rubber using fine crumb rubber are able to reduce the permanent deformation rate as well as produce improvements in the fatigue cracking at lower strains levels
Evaluation of the fracture performance of different rubberised bitumens based on the essential work of fracture
Full text linkThe fracture performance of rubberised bitumen in addition to one pre-treated with a Warm Mix Additive (Sasobit®) was investigated using different test methods measuring different damage mechanisms. Two Recycled Tyre Rubber (RTR) modifiers together with two base binders were blended in the laboratory to produce various combinations of Recycled Tyre Rubber Modified Bitumens (RTR-MBs). The first RTR is a standard recycled polymer derived from discarded truck and passenger car tyres by ambient grinding. The second RTR consists of 100% recycled truck tyres derived by cryogenic grinding and pre-treated with special oil and WMA to allow further decrease of asphalt mixture production temperatures. A fracture mechanics testing approach was used for evaluating the binder fatigue resistance; consisting of the double-edge-notched tension (DENT) test. The critical tip opening displacement (CTOD) obtained from the DENT test was used for fracture characterization of the binders within the ductile failure region. The study applied the partitioning concept of the total energy of bituminous binders to have a more reliable parameter that could be independent of the stress state of the ligament. The results show that generally the addition of RTR improves the fracture properties of binders indicating better fatigue performance. Pre-treatment with Sasobit® makes the materials more brittle and hence more susceptible to fracture
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
On the Assessment and Optimisation of the Processing Conditions of Tyre-Rubber Modified Bitumen
No full textThe current study aims at understanding the effect of the variables associated with manufacturing rubberised bitumens in order to develop rubberised bitumen with superior mechanical properties and identify optimised processing conditions for its production. The experimental work covered extensive laboratory testing of several rubberised bitumen blends. The rubberised bitumen was manufactured using four paving grade bitumens (180/240, 160/220, 70/100, 80/100), three tyre rubber types (mechanical ground, waterjet powder, ambient ground powder), and various processing conditions (shear levels, temperatures, processing times). Characterisation of the manufactured blends included rotational viscosity, softening point, and Fraass breaking point. The findings derived from the experimental programme relate to optimised processing conditions for the tyre rubber blends. Overall, this research showed that simple, relatively quick, and inexpensive test methods can be used for comprehensive characterisation of recycled tyre rubber blends. Similarly, it was found that the properties of rubberised bitumen were highly factor dependent, including effects of the: source of base bitumen (physicochemical properties), source of rubber particles, and processing conditions (shear mixing, temperature, and time). The impact of rubber pre-treatment on the performance was found to be negligible for the studied combinations. Clear bitumen-specific effects were observed from the soft and hard bitumen types considered. Furthermore, temperature and shear processing conditions had the paramount effects on the level of bitumen modification. Optimised conditions for rubberised bitumen production suggested a range of temperature of 180–210 °C, up to 180 min for high shear, and up to 30 min for ultra-high shear
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