1,720,952 research outputs found
Effects of different aging methods on chemical and rheological properties of bitumen
No full textBitumen undergoes ageing, which leads to changes in its chemical and rheological properties, causing it to become harder and more brittle with time. This study aims to compare the effects of different laboratory ageing methods on the chemistry and rheology of three bitumen types: a Pen 40=60, a Pen 70=100, and a polymer-modified bitumen (PmB). Four ageing protocols were applied: ageing at room temperature, oven ageing, pressure ageing vessel (PAV), and rolling thin-film oven test (RTFOT) combined with PAVageing. The effects of temperature, pressure, and ageing time were studied using dynamic shear tests and infrared spectroscopy. The results highlight the relationship between chemistry and rheology of bitumen. Bitumen hardening, which was revealed by an increase in complex modulus and a decrease in phase angle, was reflected in the growth of specific chemical functional groups. Among all materials, soft bitumen showed the greater tendency to oxidize. Different behavior was observed for PmB, which presented the highest resistance against oxidation among the studied bitumens, even though the reaction with oxygen caused the deterioration of the added polymer modifiers.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement Engineerin
Framework for replacing steel with aluminum fibers in bituminous mixes
No full textThis research explores the incentives for replacing steel fibers with aluminum fibers in fiber modified bituminous mixes. In this work the focus is on fiber modified bituminous mixes especially designed for induction heating. Inductive fibers are heated up because eddy currents are generated - according to Joule’s law - when alternating magnetic field is applied by electro-magnetic induction coil. Aluminum fiber-type particles are proposed as an alternative solution for developing corrosion resistant and lightweight bituminous mixes capable to be induced by electro-magnetic fields. In another publication (Pavlatos et al., Inductive bituminous mortar with steel and aluminum fibers, Advances in Materials and Pavement Performance Prediction, Submitted, 2018), a finite element three-dimensional model is developed in order to determine the effective electrical conductivity of steel and aluminum fiber modified bituminous mortar, as well as to show the potential utilization of alternative particles for developing multi-functional paving materials with improved properties.Pavement Engineerin
Ageing effect on the relaxation properties of bitumen
No full textThe ageing of bitumen has a significant impact on the mechanical behavior of asphalt concrete. In this study, Dynamic Shear Rheometer (DSR) tests were utilized to investigate the effect of ageing on the relaxation properties of bituminous materials. PEN 70/100 bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the bitumen films. Three evaluation indices, explicitly the shear stress at 0 s and 100 s, the ratio of shear stress at 0 s and 100 s and the time that shear stress reduces to 50% and 25% of the initial value, were used to determine the evolution of the relaxation properties of bitumen. The results show that, in comparison to fresh bitumen, aged samples show higher residual shear stresses after relaxation and are more susceptible to stress accumulation thus cracking. In addition, temperature, followed by pressure and ageing time, was found to have the stronger impact on bitumen ageing.Pavement Engineerin
Modelling of membrane bonding response: Part 2 finite element simulations of membrane adhesion tests
No full textThe adhesive bonding strength of the membrane layers between the asphalt concrete surface layers and the decks of steel bridges has a strong influence on the fatigue life of orthotropic steel deck bridges (OSDBs). The interfacial properties between the membrane and the layers bonded to it have not been extensively studied in the current orthotropic steel deck bridge system. For the adequate characterisation of the adhesive-bonding strength of various membranes and surrounding materials on OSDBs and for the collection of the necessary parameters for finite element model, details of the membrane adhesion test (MAT) are introduced and simulated by using the adhesive traction-separation interface element which was developed in a companion paper to this contribution (Liu, X., Kasbergen, C., Li, J., & Scarpas, A. (2019). Modelling of membrane bonding response: part 1 development of an adhesive contact interface element. International Journal of Pavement Engineering). Parametric studies of the adhesive contact element utilised for modelling the membrane bonding layer in the MAT test have been performed on the basis of the combination of different critical strain energy release rates and the characteristic opening length in the constitutive model. Comparison of membrane deformation profiles and the in-time debonding force distribution between experimental observations and finite element simulations have been presented.Pavement EngineeringSanitary Engineerin
Computational Modelling of Compaction in Asphaltic Mixtures and Geomaterials
No full textAsphaltic mixtures are heterogeneous composite materials consisting of aggregates coated and bound by asphalt binder. The long term performance of asphaltic pavements is highly dependent on the mechanical behaviour of the asphaltic mixture during construction (mixing and compaction) and operation; inadequate mixture compaction leads to faster moisture and oxygen diffusion, ravelling, rutting and poor fatigue life
Moisture damage susceptibility of asphalt mixtures: Experimental characterization and modelling
No full textA well-functioning, long-lasting and safe highway infrastructure network ensures the mobility of people and facilitates the transport of goods, promoting thus environmental, economic, and social sustainability. The development of sustainable highway infrastructure requires, among other activities, the construction of pavement systems with enhanced durability. Moisture damage in asphalt pavements is associated with inferior performance, unexpected failures and reduced service life. All of these contribute to the increase of operational and maintenance costs in order to fulfill the intended service life of the pavement system. Moreover, global warming and climate change events such as temperature extremes, high mean precipitation and rainfall intensity may further increase the probability and rate of pavement deterioration. This dissertation aims to obtain an advanced understanding of the influence of moisture on pavement durability by developing a set of tools, i.e. experimental methods and computational models, which will provide insight into the fundamental moisture damage processes and on their impact on pavement systems. Based on this knowledge, researchers and practitioners will be able not only to design pavements with increased resiliency, thereby providing reliable services to road users, but also to minimize the risks in the face of changing climate conditions.Moisture diffusion is well-known to degrade the mechanical properties of asphalt mortars, namely bitumen, filler and sand, thus increasing the propensity of pavements to cracking. To determine the changes in the cohesion properties of the mortar, uniaxial tension tests were performed. Mortar samples were prepared and then subjected to five combinations of moisture and thermal conditioning, in an attempt to reproduce the various conditioning states that pavements undergo in the field, before being tested. Tensile strength and fracture energy were used to evaluate the changes in mechanical properties due to the various conditioning protocols. To post-process the experimental data, a new data analysis procedure was suggested in order to obtain a more accurate calculation of fracture energy. The procedure uses nonlinear finite element analysis to specify the unloading response outside the fracture zone, and then utilizes this information to compute the fracture energy of the binders. This methodology yields a framework for the calculation of fracture energy when only force-displacement data are available and therefore the estimation of the true stress-strain curve is not feasible.The experimental investigation revealed the deteriorating impact of moisture on the fracture characteristics of asphalt mortars, especially as regards to their low temperature properties. These effects were not reversible upon drying. On the contrary, the application of a drying cycle caused embrittlement of the mortars and indicated that continuous wet and drying cycles in the field may result in materials with poor performance characteristics. Also, the application of freeze-thaw cycles was shown to increase the susceptibility of mortars to low temperature cracking. Nevertheless, on the whole, the effect of freeze-thaw on fracture properties was observed to depend on the conditioning state (dry or wet) and composition of the mortars. The use of additives, such as hydrated lime filler and SBS modifiers, were found to improve the wet strength and fracture energy of the mortars. On the basis of moisture uptake measurements, it was confirmed that the chemical composition influences significantly the diffusivity characteristics of the mortars. Also, the maximum moisture uptake was found to be the main parameter that dictates the intensity of mortar damage. In addition, moisture susceptibility was studied at mixture level. At this level, besides moisture diffusion, excess pore pressure can contribute to the degradation of mixture performance depending on the mixture type, the traffic loading and the environmental conditions. Hence, a moisture conditioning protocol that comprises two conditioning types, namely bath immersion and pore pressure application, was proposed for evaluating susceptibility of asphalt mixtures to moisture. Also, evidence was collected of the effect that dynamic pore pressure has on mixture degradation by means of X-ray computed tomography and image analysis techniques. The two damage mechanisms were found to be relatively independent from each other, suggesting that an asphalt mixture can be more prone to one damage mode than the other, depending on its composition. The proposed protocol captures both processes that occur when water interacts with a pavement and can provide more reliable conclusions with regard to mixture sensitivity.In order to improve our perception of the influence of material microstructures on moisture sensitivity of the asphalt composite, an energy-based elasto-visco-plastic model with softening was implemented to model damage due to the coupled effects of moisture diffusion and mechanical loading. The model consists of a generalized Maxwell model, with hyperelastic springs and viscous time-dependent components, in series with an inelastic component that accounts for the irreversible processes within the microstructure of the material. Then, a computational scheme was proposed by means of a staggered approach: first a three-dimensional diffusion model was applied to obtain information on the accumulation of moisture within the mixtures and then the elasto-visco-plastic model was used to quantify mortar damage due to moisture diffusion. This method was successfully applied to study the influence of mixture morphology on moisture sensitivity. The results demonstrated that moisture content in a mixture strongly depends on its morphology, whereas the interconnectivity of the voids network controls the rate of damage development. Also, the analysis revealed the positive effect of using binders with high resistivity against moisture and quantified the benefits that would arise due to this choice, especially when designing porous mixtures that have an intrinsic sensitivity to moisture due to their morphological characteristics.More broadly, frost damage can be classified as part of the moisture damage related mechanisms. In the field, frost damage can be mainly attributed to the expansion of water accumulated in the pores of the pavement at sub-zero temperatures that causes additional stresses to the pavement structure. A numerical scheme to simulate frost damage was proposed. This scheme comprises a model that simulates the volume expansion of water during the water-to-ice phase-change, a thermal conduction model to simulate temperature distribution in the pavement, and the elasto-visco-plastic model to determine critical areas with a propensity to cracking on the basis of the pavement stresses.In conclusion, this thesis contributes to establishing a relationship of the physico-mechanical properties of the constituent materials and mixture morphology with the moisture susceptibility of pavement structures. The proposed experimental methods and computational models can serve as tools to investigate a great variety of parameters before a pavement structure is actually built. This allows for new materials and mixture designs to be investigated and the risks involved with their use to be minimized.<br/
Aging of Asphalt Symposium: Delft, the Netherlands September 17th 2014
No full textTechnical specifications for the asphalt concrete properties are developed to be able to specify mixtures that will perform well in pavement applications. Being able to identify and determine properties related to pavement performance in practice is crucial for both road authorities and contractors, since it allows for design and risk management by determining design life times and reliability. However, the properties of Asphalt Concrete (AC) change over its lifetime and since most pavement layers last for a decade or more these changes are crucial in determining the performance in practice.For many of the standard materials the effect of aging is implicitly dealt with in the safety factors that also account for other effects such as the variation rest periods/healing and variations in traffic and weather in the design methods and specifications. Rapid changes in the materials used (increasing percentages reclaimed asphalt, bio‐bitumen, rejuvenators, waste materials) and in theproduction of both bitumen (new refining methods resulting in different composition of bitumen) and asphalt concrete itself (warm mix asphalt, porous asphalt concrete, rubber asphalt mixtures) lead to increased uncertainty in the effects of aging. As a result, the uncertainties in pavement performance increase, which means the prediction of maintenance and the necessary budgets is getting more inaccurate.In order to maintain the ability to reliably design and maintain pavements and determine the most cost‐effective solutions for a given situation, a better understanding of the aging processes and objective methods to take into account aging effects on material properties is needed. This need is widely recognized, in the USA the Mechanical Empirical Design Guide takes aging into account through aging tests on the bitumen used and in Europe CEN TC227 works on establishing a method to assess the aging sensitivity of asphalt mixtures. This symposium aimed at combining the existing information and insights from ongoing research into recommendations that will allow thedevelopment of methods to determine aging sensitivity and the impact on pavement performance, facilitate the exchange of obtained data and stimulate further developments The resulting recommendations are: Do make long term aging sensitivity of binders part of the bitumen standards and take the results from the aging sensitivity of binders into consideration when assessing AC properties.Be aware that RTFOT testing only gives an indication of the sensitivity of a penetration grade binder to aging during hot mix production and construction, it doesn’t work for hard grades, PMB’s or warm mixes. Because of the many variables involved, developing one test method to characterise aging sensitivity seems improbable. However, PAV aging is both practical and, if tests at various conditions are carried out, able to give kinematic properties. A PAV protocol for testing at two temperatures and time intervals could provide practical characterisation information forthe short term and enable model development and validation on the long term. RCAT and other aging procedures could also be used in this sense, but considering the availability of equipment and the wide spread experience, PAV is the best candidate to allow the rapid development of international experience with the approach.Based on the current standards and the work presented during the symposium, PAV tests at 90 and 100 degrees Celsius and 20 and 40 hours, respectively, are suggested. The low values for temperature and duration are based on the current standards and fit both the USA and CEN procedure, while research shows that after 40 hours at 100 degrees the chemical (FTIR) and rheological (DSR) properties of laboratory aged and field samples were similar (Section6.5 and 8.5). At 100oC the temperature is low enough so that the effect of secondary reactions is negligible. As such, these conditions are appropriate for kinetic expressions for in service pavement performance. For high temperature processes and possibly also for repeated recycling (very long term) more sophisticated methods are needed. Set‐up and maintain field monitoring of temperature and UV radiation in various climate zones, as well as regular sampling over time and height to keep checking the predicted changes (from both tests and models), versus the actual changes in properties order to ensure reliability of the data as well as the applicability for pavement performance prediction. In setting up field tests, it is important to get both the composition of the virgin bitumen and the composition after mixing, transport and placement in the pavement. Thesecompositions provide the starting points from both the material and pavement structure point of view and can be used to assess the development of aging products over time. There is a lot of discussion about the impact of binder recovery methods on the observed composition, so until it is proven that this does not have an influence, for comparisons the same recovery method should be used. Set up a coordination and support action on AC‐Aging to continue to exchange information and experiences, both in research and in construction projects. develop an IR testing protocol, to facilitate the exchange of results and information. Compare the bitumen composition that is found through various recovery methods toestablish if there is an effect and if so, develop a procedure to address this. To further understanding of aging, a Round Robin test on the differences in test conditions between US and EU, allowing better access to each other’s data and knowledge would be seful. When developing aging tests for AC, it would be useful to look at the US experience. As long as there is no fundamentally correct method for assessing the aging, it would be preferable to standardize it as much as possible in order to allow cooperation and exchange of data.Pavement Engineerin
Study of Influence of Operating Parameters on Braking Distance
No full textStopping distance includes driver thinking distance and braking distance. Braking distance is one of the basic standards for road design and maintenance practices. Adequate tire–pavement skid resistance plays a significant role in reducing braking distance and consequently enhancing road safety. With technology such as the antilock braking system, the friction force is maximized by applying the brakes repeatedly, in an on-and-off pattern, such that the braking distance is shortened. Several studies have shown the effect that some parameters, such as water film thickness, tire inflation pressure, and wheel load, have on braking distance. Less discussed is the effect of slip ratio, temperature, and pavement surface characteristics. Measuring the braking distance in the field is energy-consuming and time-consuming, and there are uncertainties in the environmental conditions as well. General approaches to calculating braking distance are based on basic mechanics principles. To the authors’ knowledge, a model that can simulate the whole braking process is not available. The presented study proposes a way to predict braking distance by means of finite element modeling only. A model that can include the effect of parameters such as temperature, slip ratio, and pavement surface characteristics on the braking distance is introduced.Accepted Author ManuscriptPavement Engineerin
Numerical study of sorption of asphalt binders on minerals
No full textDuring the production of asphalt mixes, specific functional groups of asphalt binder interact chemically with certain reactive sites on the surface of minerals forming compounds that enhance the material resistance to environmental effects. The thermodynamics of surface phenomena between various combinations of functional groups of minerals and asphalt binders has been studied for quite a long time but it remains extremely difficult to control the desired material properties in practice. In this study, the chemical thermodynamics that determine the sorption phenomena and subsequently the relative affinity of asphalt binders onto mineral particles were analysed numerically and discussed. A two-step sorption configuration is studied in a multi-physics tool including reaction-driven mass transport of free species (i.e., carboxylic acid diluted in binder) onto a reactive surface (i.e., calcium functionalized mineral). Based on this configuration, the mechanism of asphalt-mineral interaction was determined at different surface temperatures and reactivity characteristics (i.e., activation energy and reaction kinetics of adsorption). The sorption model is applicable for various scenarios of asphalt-mineral interactions, especially for functionalized surfaces, in which the reaction-driven distribution of concentrations of asphalt adsorbates on minerals can provide useful information once the energetic parameters are known.Pavement Engineerin
Experimental Investigation of Rubber Swelling in Bitumen
No full textRubber swelling in bitumen, which is a diffusion-induced volume expansion process, plays a dominant role in the design of crumb rubber modified bitumen binders and their properties development. This study aims to investigate the kinetics of bitumen diffusion into truck tire rubber, the equilibrium swelling characteristics of rubber, and the mechanical properties of rubber before and after swelling at different high temperatures. Fourier transform infrared spectroscopy results indicate that no rubber dissolution happens during the interaction in the temperature range from 160°C to 200°C. Aliphatic compounds from bitumen preferentially diffused into rubber during the swelling process. The diffusion coefficients of bitumen into rubber were determined by the sorption test using the gravimetric method. The diffusion coefficient increases with the increase of temperature in an Arrhenius form. The volume expansion of rubber during swelling was captured by the X-ray computed tomography scan images. Rubber swells faster at the earlier stages, then the expansion rate slows down. The swelling ratio of rubber increased from 1.97 at 160°C to 3.03 at 200°C after 36 h interaction. Mechanical tests by dynamic shear rheometer reveal that swollen rubber becomes softer compared with the dry rubber and exhibits obvious viscoelastic behaviors. With the increase of temperature, the softening and viscous effect are more significant. The obtained parameters can be implemented to swelling and micromechanical models to better predict the binder properties.Accepted Author ManuscriptPavement Engineerin
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