1,720,996 research outputs found
Experimental characterization of asphalt for an elasto-visco-plastic constitutive model.
Full text linkThis paper describes a range of uniaxial creep tests that have been undertaken for a
proprietary polymer modified asphalt, the procedure used to determine the parameters
required for an elasto-visco-plastic constitutive model.
Uniaxial compressive creep testing and creep recovery testing have been undertaken
over a range of temperatures and stress conditions. Procedures used to determine the
model parameters from the test data are detailed and parametric equations are developed
to describe the model parameters as functions of the test conditions. Particular attention
is given to the determination of the parameters related to visco-plastic flow and damage
accumulation at high strain levels. The model has been implemented in to the CAPA-
3D Finite Element (FE) program and preliminary verification has been undertaken
Friction in Asphalt Concrete Mixes: Experimental and Computational Issues
No full textPavement EngineeringCivil Engineering and Geoscience
Numerical Simulation of Tire-Pavement Interaction
No full textGood skid resistance of a pavement surface is essential for road safety. Loss of skid resistance can lead to property damage and loss of lives. Ever increasing need of driver safety poses challenges to the highway authorities to evaluate pavement conditions even more precisely under different conditions. Environmental variables like temperature, water, snow etc. can have a significant effect on the skid resistance apart from the vehicle and pavement related factors. The temperature increase in the tire-pavement contact region results in a complex relationship between the temperature and the friction and constitutes one of the main sources of uncertainty in interpreting the data of continuous field measurements. Likewise, very low friction coefficients can be observed between the tire and pavement surface under wet conditions. Nevertheless, the phenomena have not been adequately quantified yet within the skid resistance evaluation engineering community. The road agencies use correlation factors to estimate frictional characteristics of the road. These correlation factors are based on the experience and field test measurements which have a very limited scope in terms of reliability and transferability. It is the aim of this research is to study the effect of temperature and water on the frictional performance of the asphalt surface, when a pneumatic tire is traversing at given operating conditions. The tire operating temperature is a very important concern to the tire manufacturers, highway agencies and users due to its major influence on the traction performance of a tire. Tire rubber hysteresis is considered to play a major role in countering skidding of a vehicle travelling at high speed. Past studies showed that the contribution from the hysteresis component in comparison to adhesion has a larger influence on the friction measurements. This research aims to develop a sequentially coupled thermo-mechanical model in the finite element (FE) framework to determine the progressive temperature development in a pneumatic tire rolling over a simulated asphalt pavement surface mesh and its eventual effect on the hysteretic friction. This research also studies the hysteretic frictional behavior of a test tire under different surrounding temperature conditions. In this methodology, first, the tire is tested under static loading conditions to obtain its overall deformation characteristics and in particular the relation tire load - inflation pressure – foot print. In the second step, rubber material tests are performed to determine the rheological characteristics of the tire tread rubber. The test results are used for the determination of rheological parameters of a tire rubber material in the form of Prony’s coefficients. The Prony’s coefficients are later utilized in the development of a 3D FE test tire. In the third step, the tire is modelled in the FE framework, accounting for the different components of a tire like tread, side wall, carcass, belts, plies, inner liner, rim etc. The FE simulation results corresponding to the footprint and the deformation are compared with the measurements of static load deflection tests. The FE mesh of a given asphalt pavement surface is developed based on scanned asphalt surface data obtained by a Laser Profilometer and an X-ray tomographer. A dynamic analysis of a tire rolling at a definite slip ratio over a simulated asphalt pavement surface is performed. The results obtained from this analysis are used in the subsequent energy dissipation analysis to determine the heat fluxes. These heat fluxes are the input of a heat transfer analysis to determine the temperature development in the body of a tire. Many past experimental studies showed that the tire-pavement friction values are related to the tire surrounding conditions such as pavement temperature, ambient temperature, contained air temperature and surface characteristic of pavement. Therefore, in this research, the effect of pavement temperature, ambient temperature and contained air temperature on friction measurements is studied. By using the developed FE model, practical test conditions of fully and partially skidding tires traversing over different asphalt pavement surfaces, namely, Porous Asphalt, Ultra-Thin Surface and Stone Mastic Asphalt and AC-10 are analysed. Emphasis is placed on the determination of tire tread temperature as a critical combination of pavement temperature and ambient temperature. An attempt has also been made to determine the time required for different regions of a rolling tire to reach an effective temperature equilibrated state. Such kind of analysis gives insight into the effect of thermal behaviour of different components of tire on the tire hysteresis which eventually decides its frictional performance. This research also deals with the cornering frictional behaviour of a pneumatic tire. By utilizing the developed FE model, the cornering friction was computed for inflation pressure, wheel load, vehicle speed, side-slip angle, surface texture and mix design. Good pavement macrotexture has a direct influence on the vehicle safety during wet weather conditions by improving its traction/braking ability. Apart from the macrotexture, there are several factors that affect the wet friction, such as, environmental, tire and pavement related characteristics. In recent years, development of powerful finite element tools made it possible to simulate complex wet tire-pavement interaction as close as possible to the actual field conditions. However, to the best of the author’s knowledge, none of the past analytical/numerical studies were able to include the asphalt pavement surface texture in their analysis. In the next part of this thesis, the loss of friction under wet/flooded pavement conditions is studied. This research presents an FE approach to study the effect of surface morphology of asphalt pavements on the wet friction coefficient. The wet friction performance of different asphalt surface morphologies of open-graded mix to close-graded mix are studied by using the developed FE model. The tire-wet asphalt surface interaction FE model is duly calibrated with the field investigations conducted by using the state-of-art field equipment. The extreme loss of wet friction which ultimately leads to risk of hydroplaning is also studied. The FE simulations are performed on different water film thicknesses, tread pattern and different tire slip ratios and yaw angles. The results from the current study can be used as safety indicators of in-service asphalt pavements under wet/flooded conditions.Structural EngineeringCivil Engineering and Geoscience
Cement Stabilized Materials with Use of RoadCem Additive
No full textStructural EngineeringCivil Engineering and Geoscience
Mechanistic procedure for parameter determination of multiplicative decomposition based constitutive models
No full textBy exploiting the Clausius–Planck local energy dissipation inequality, a large strain, three-dimensional constitutive model has been developed for the monotonic and cyclic response prediction of various asphaltic materials. The model consists of a Zener non-linear, visco-elastic component acting in series with a stress dependent viscous component. A novel computational scheme has been developed for solution of the coupled system of equations expressing the interdependent response of these two in series components. An explicit, mechanistic, parameter determination procedure is presented for the laboratory determination of all necessary model parameters. Examples of model parameter determination and utilisation for prediction of the response of a recycled asphalt mix and a stone mastic asphalt mix are presented
A Mechanics based Computational Platform for Pavement Engineering
No full textCivil Engineering and Geoscience
Integral pavement/soil-wall structures: A numerical study
No full textCivil Engineering and Geoscience
Optimum Design of Multilayer Asphalt Surfacing Systems for Orthotropic Steel Deck Bridges
No full textOrthotropic steel decks are widely utilized in long span bridges, movable bridges and shorter span road and rail bridges due to their favourable properties. These properties are low deadweight, large plastic reserves in case of overload and aesthetic advantages. Nowadays, more than 1000 orthotropic steel deck bridges (OSDBs) have been built in Europe, out of which 86 are in The Netherlands. Asphalt concrete surfacing structures have distinct advantages when compared to alternative surfacing structures: fast installation, good driving comfort, low noise levels, and relatively cheap construction costs. In the Netherlands, an asphaltic surfacing structure mostly consists of two structural layers. The upper layer consists of porous asphalt for noise reduction. For the lower layer guss asphalt is used. In the last three decades, several problems were reported in relation to asphalt surfacing materials on OSDBs such as rutting, cracking, loss of bond between the surfacing system and the steel deck. The severity of the problems is enhanced by the considerable increase in traffic in terms of number of trucks, heavier wheel loads, wide-base tires etc. Over the years, the Ministry of Transport, Public Works and Water Management (RWS) in the Netherlands is facing a growing challenge in maintaining network capacity. Even though the combined length of OSDBs in the primary road network is limited, the consequences of repairs of the steel deck plate or the overlaying surfacing structure to network capacity are dramatic. Unfortunately the service life of asphaltic surfacing structures on OSDBs is limited to an average of 5 years. Thus, improvements of the performance of asphaltic surfacing structures on OSDBs are of the utmost importance. Preliminary investigations have shown that the adhesive strength of the membrane between the surfacing layers and the decks of steel bridges has a strong influence on the structural response of OSDBs. The most important requirement for the application of membrane materials in OSDBs is that the membrane adhesive layer shall be able sufficiently bond the surrounding materials to each other, thus ensuring the structural integrity of the deck. This research project aimed at evaluating the performance of multilayer surfacing systems on steel deck bridges and prolonging the service life. Focus was on membrane performance and the effects hereof on the structure as a whole. The methodology used in this research was a multi-phase approach, which consisted of three study phases at different scales: 1) material scale, 2?section scale and 3) bridge scale. In Phase 1 of this study, a Membrane Adhesion Test (MAT) device was developed at Delft University of Technology for the characterization of the adhesive bonding strength of membranes with the surrounding materials on OSDBs. An adhesive contact interface element developed within the FE package CAPA-3D was utilized for simulating the process of debonding or delamination of membranes from the surrounding materials. A methodology of evaluating membrane products on various substrates by computational and experimental investigations was set up. Several qualified membrane products were chosen for further investigations in Phase 2 and 3. In Phase 2 of the project, four typical Dutch multilayer surfacing systems constructed with the five selected membrane products from Phase 1 were studied by means of five-point bending (5PB) beam tests and FE simulations. The findings of the 5PB beam tests will help for the verification and calibration of the finite element predictions and for the further ranking of the best performance of the multilayer surfacing systems for Dutch OSDBs. In order to study the influence of the geometrical and structural parameters on the performance of the multilayer surfacing system, finite element simulations of 5PB beam tests were performed. Parametric studies were performed by means of the finite element system CAPA-3D. The contributions to the overall system response of the mechanical properties of all the surfacing layers were studied. In the last stage of the work, Phase 3, finite element (FE) simulations of the Merwede Bridge subjected to dual wheel stationary and moving loads are presented. Three cases of load locations have been investigated. All cases were simulated under and respectively. Four different surfacing structures as utilized in the 5PB beam tests were chosen for the FE simulations. The results of the simulations provide a useful guidance regarding the expected maximum strains in the four surfacing structures for two different temperatures. Through those three research stages, a systematic and effective bottom-to-top design approach of multilayer surfacing systems for OSDBs has been established.Structural EngineeringCivil Engineering and Geoscience
Experimental and Numerical Investigation of Induction Heating in Asphalt Mixes
No full textConsidering the importance of the need of mitigating the energy consumption and the corresponding emission of CO2, the construction industry is focusing to develop novel materials with enhanced durability and new functionalities. State-of-the-art techniques have been adopted from the infrastructure industry in order to transform construction and maintenance processes to sustainable and eco-friendly. Asphalt mixture is a material widely used in the construction industry mainly for transportation infrastructure. During hot summers and long resting periods, asphalt mixtures can partially recover their mechanical properties such as strength and stiffness. This inherent property of asphalt mixtures is termed self-healing and has important impact on the service life of asphalt pavements. If the healing process could be sped up, pavements with longer lifespan could be built. The last few years, a lot of effort has been spent to develop innovative techniques in order to trigger the healing capability of asphalt mixtures. Induction heating is a technique via which asphalt pavements can be heated locally and mechanical properties can be recovered. The approach of using the induction heating technique to speed up the healing process is named induction healing. Induction healing approach requires the development of asphalt mixtures with electrically conductive additives and an electromagnetic source in order to increase the temperature of material. This thesis is aimed at developing insight into the induction heating technique and how the asphalt mixes at different levels are influenced from the additives. Control of the rheological, electrical, thermal and mechanical properties of asphalt mastic and mortar are among the key research objectives. For this, experimental and numerical methods have been used.Road and Railroad EngineeringStructural EngineeringCivil Engineering and Geoscience
Phase-Separation Characteristics of Bitumen and their Relation to Damage-Healing
No full textDuring the service life of flexible asphalt pavements, asphalt concrete degrades due to traffic loading and environmental conditions like temperature, rain, oxidation, ultraviolet-radiation from the sun. All these environmental factors have adverse effects on the performance of bitumen, which is the binder of asphalt concrete. They are known to cause ageing and eventually lead to hardening of bitumen. As a result, ravelling (i.e. release of stones from asphalt concrete) and cracking are observed as main distress mechanisms in asphalt concrete. These distress phenomena reduce the life span of the asphalt pavement, necessitate frequent maintenance and eventually complete replacement of the asphalt. Innovative solutions with a focus on better binder properties can improve this situation. Bituminous materials with improved properties can make the rate of deterioration slower and may offer fast, efficient and cost effective repair methods. Self-healing is a desirable property in this respect, which can improve the service life as well as reduce the maintenance cost of the roads. Bitumen is self-healing by nature. Micro-cracks that occur in bitumen during service may heal at rest and the early stages of cracking are self-repairable. But the knowledge on the mechanism of damage, healing and also the fundamental properties of bitumen is inadequate. The aim of the thesis is to understand the phase-separation characteristics of bitumen at the microstructural level and their relation to damage and healing processes within the material. Atomic Force Microscopy (AFM) has been used to investigate the bitumen morphology, phase-separation and mechanical response properties at nano to micro meter length scale. From the AFM investigation, microstructure is found to be a unique fingerprint of the bitumen type. Typical bitumen microstructure possesses a two-phase morphology: the domains (i.e. bee-structures) and the matrix phase. Chemical composition of bitumen is the key parameter which influences the microstructure properties, while wax and asphaltene fractions are responsible for most of the structuring observed. The wax component has been found to induce the phase separation of bituminous materials. Temperature during construction of asphalt and its change during the service life influence the properties of bitumen to a great extent. Thus, the influence of environmental conditions like temperature, thermal history and humidity on bitumen microstructure have been investigated. From the temperature and thermal history study, hysteresis in microstructure properties of bitumens between heating and cooling cycles has been observed. The rate of cooling of the material influenced the microstructure properties. Besides, high humidity conditions can be detrimental to bitumen performance as it can introduce regions of heterogeneous properties within the material. The mechanical response properties of bitumen at the fundamental length scale have been investigated. The mechanical property maps of modulus and AFM probe-sample adhesion force of the individual phases of bitumen at the microstructural level are obtained using a special mode of AFM. The domains are found stiffer than the matrix phase, whereas the matrix phase has shown greater adhesion property. These individual phase properties have been used and a mechanics based approach has been followed to derive the composite modulus property of bitumen. With the change of temperature, changes in the mechanical properties of the individual phases and the subsequent composite response of the material are observed. Microstructural change at the onset of crack formation in bitumen has been probed during mechanical loading. After application of tensile load, micro-cracks or crazes tend to originate at the interface between the phases and localize in the domain phase- leading to a significant microstructural change. By allowing rest periods or moderate thermal changes, re-arrangement of the microstructures are observed; resulting in disappearance of cracks. The extent of blending between reclaimed binder and the fresh bitumen in the case of recycling of asphalt has been investigated. It is proposed that the degree of interaction between the binders depends on the temperature and the mixing time of the materials in the recycling process. During the process of ageing, bitumen is hardened and the adhesion property deteriorates. For service life extension of asphalt pavement, additives (i.e. rejuvenators) are used to improve the adhesion of the aged bitumen and to decrease the viscosity of the binder. This process of rejuvenation has been probed at the microstructural level. The addition of rejuvenators to the aged bitumen has shown property restoring performance from both the rheological data and microstructural properties of the binders. Understanding the micro-scale material properties can help to understand the long term macro-scale material response properties. The research presented in this thesis will guide to a better understanding of the material response in relation to both environmental and mechanical changes at microstructural level. The microscale assessment of bitumens is a step forward towards associating the observed structures with the material's mechanical response properties.Structural EngineeringCivil Engineering and Geoscience
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