1,720,973 research outputs found
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
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
Crumb rubber modified bitumen: Experimental characterization and modelling
No full textA sustainable pavement, which can minimize environmental impacts through the reduction of energy consumption, natural resources and associated emissions while meeting all performance conditions and standards, is in urgent need to combat the climate change. The current scenario of depleting crude oil, reduced quarry zones, and stringent environmental regulations has driven the use of waste materials and by-products in pavement applications. The utilization of crumb rubber from scrap tires for bitumen modification has become a common engineering practice since last century...Pavement Engineerin
Parameter identification of layered systems using moving loads
No full textAn elegant approach to evaluate the quality of engineering structures is the Non- Destructive Testing (NDT). In the field of pavement engineering, a promising NDT method for pavement structural evaluation at network level is the Traffic Speed Deflectometer (TSD) test, which can continuously measure the surface response of pavements caused by moving loads at normal driving speeds. However, the wide application of the TSD test has been hindered by the lack of a commonly accepted parameter identification technique to process TSD measurements. To tackle this problem, this dissertation aims to formulate a mechanically correct, numerically accurate, and computationally efficient parameter identification technique specifically for the TSD test of pavements. The developed parameter identification technique is the combination of a theoretical model of the TSD test and a minimisation algorithm. The unknown parameters can be identified by minimising the differences between modelled and measured response of pavements..
Experimental Investigation of Membrane Materials used in Multilayer Surfacing Systems for Orthotropic Steel Deck Bridges
No full textIn the Netherlands asphaltic surfacings on orthotropic steel deck bridges (OSDB) mostly consist of two structural layers. The upper layer consists of what is known as very open porous asphalt (ZOAB) for noise reduction. For the lower layer Guss Asphalt (GA) is used. Earlier investigations have shown that the bonding characteristics of membrane layers to the surrounding materials have a very strong influence on the overall response of the steel bridge decks. Rijkswaterstaat, an agency of the Dutch Ministry of Infrastructure and the Environment, has commissioned Delft University of Technology to investigate and rank the performance of various commercially available membranes. In order to obtain insight into the response of membranes and their interaction with the surrounding materials on orthotropic steel decks, a project of evaluation of the performance of modern surfacing systems on OSDBs has been undertaken. Currently, there are various kinds of membranes provided by various companies. Thereby it was necessary to examine the bonding strength of these membrane products and to develop a ranking methodology. The research project focused on membrane performance and the effects hereof on the bridge deck as a whole. The methodology used was a multi-phase approach, which consisted of three main phases. In Phase 1, 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 on the basis of a fundamentally sound, mechanistic methodology. Several membrane products were tested monotonically in this phase. In Phase 2, the MAT device was utilised for investigation of the fatigue response of the various membrane products on various substrates and under two different temperature conditions and three different cyclic load levels. A ranking methodology consisting of a combination of experimental (via MAT) and computational investigations was also developed and utilized for the ranking of the various membrane products. In Phase 3 of the project, four typical Dutch multilayer surfacing systems, constructed with five selected membrane products from Phase 1 and 2, were studied by means of five-point bending (5PB) beam tests and FE simulations. The findings of the 5PB beam tests were used for calibration and validation of the finite element predictions and for further ranking of the performance of the various membranes in Dutch OSDBs. On the basis of the project results, the top two ranking membranes were selected for subsequent testing by means of the LINTRACK facility available at Delft University of Technology
Ageing of bituminous materials: Experimental and numerical characterization
No full textResearch of the ageing mechanisms in the Netherlands is crucial to deal with ageing infrastructure and the growing pressure on and lack of natural resources. The use of porous asphalt incurs the additional costs because of the shorter service life and the more expensive maintenance required. On the other hand, the Dutch road engineering community has made significant efforts in recycling of pavements after the end of their service life. Currently, 90% of the asphalt is demolished and used in new asphalt pavement. Ideally, it would be nice to keep recycling asphalt concrete indefinitely, but this should be done without loss of functionality or environmental risks.This thesis aims to acquire an advanced understanding of the fundamental thermal ageing processes of bituminous materials, by conducting a series of experiments and developing a set of computational models. A greater understanding of the bitumen ageing mechanisms and how they change physico-chemical properties of bitumen can help to accurately predict the service life of an asphalt pavement and develop high performance bituminous products that are less sensitive to ageing...Pavement Engineerin
Micromechanical Modelling of Porous Asphalt Mixtures
No full textWith the attempt to reduce traffic noise, porous asphalt (PA) mixture is widely used as a wearing course on the highways in the Netherlands. However, due to the open structure, PA mix pavement easily suffers from the loss of individual aggregates from its surface, which is named as ravelling. After the initial ravelling, the damage can rapidly develop into potholes which can significantly reduce the driving safety of the pavement....Pavement Engineerin
Direct Tensile Test to Assess Healing in Asphalt
No full textAsphalt concrete has the advantageous ability to heal. During restperiods, damage present In the material is restored to a certain extent.Healing of the material can be observed in iis regaining of strengthand stiffness after rest periods. In this paper, a new test method is presented.It was developed to increase the understanding of the healingphenomenon. The test method focused on asphalt as it v/ss assumed tobe the driver of the healing performance. The test method assessedthe heaUng performance of asphalt In stiffness and strength by testingthe bond strength In tensile mode of two pieces of asphalt that wereassembled under controlled temperature and stress conditions. Withthe test method, healing tests ^yere performed on one type of binder;the load level during healing and the healing tune were varied. The tesiresults showed that after a short healing time of only 6 min, a significantamount of healing could be detected. That finding indicates the importanceof adhesion between two crack surfaces v/hen the healing capacityis assessed. It v/as also found that the maximum tensile stress reached aplateau value after 24 h of healing; the finding indicates thatfull healingcan be realized in short time periods for pure, unaged, soft binders. Itv/as also shov/n that the load level perpendicular to the damage duringheaUng had a significant effect on the observed healing
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