A Mechanics based Computational Platform for Pavement Engineering

Civil Engineering and Geoscience

Probing Trace-elements in Bitumen by Neutron Activation Analysis

Trace elements and their concentrations play an important role in both chemical and physical properties of bitumen. Instrumental Neutron Activation Analysis (INAA) has been applied to determine the concentration of trace elements in bitumen. This method requires irradiation of the material with neutrons that transform the elements into radioactive isotopes. By analyzing the activity of the individual nuclides, the concentration of each detectable trace element can be determined with high precision. In this work, we perform trace elemental analyses of 13 distinct bitumens, including 2 modified and 3 bitumens from the material library of Strategic Highway Research Program (SHRP. Three elements, vanadium, nickel and cobalt are found to be present in all bitumens. Vanadium and nickel are found to be the most abundant among all the elements detected. Next to vanadium and nickel, significant concentrations of iron are found in 11 bitumens. The total number of trace elements identified varied from 17 to 28 for the bitumens studied. For modified bitumens, the concentration of trace elements is used as a parameter to measure the extent of modification. The sum of most abundant trace elements (vanadium and nickel) correlates well with the sulphur and asphaltene contents of the same bitumen. Moreover, the concentration of the latter metals are known to be an indicator for the aging characteristics of bitumen. Thus, INAA provides the content of trace elements in bitumen, where the concentrations vary (ppm to ppb) depending on the crude origin of the material. Thus, INAA can be used to trace back the crude origin of the material, which may have applications in the field of asphalt recycling (RAP and RAS).Pavement Engineerin

HighRAC workshop

With the increasing drain on natural resources and resulting aim to reduce the environmental impact of road engineering, the use of reclaimed asphalt in fresh asphalt becomes more and more important. Despite the experience in using RAC, there are still many questions regarding the effect of RAC on the technical and environmental performance of mixes, especially with high RAC content. For the true impact of RAC to be quantified, a methodology is needed for the evaluation of the possible environmental and other benefits of asphaltic mixes containing high percentages of RAC (HighRAC). For such a methodology to be precise, it will require reliable data about the durability of pavements constructed with these new types of mixtures. The HighRAC Workshop aimed to serve as a venue for a gathering of a select group of national and international experts to exchange knowledge, ideas and experience on : (i) appraisal of the long-term performance characteristics of HighRAC mixtures (ii) enhancement of the engineering properties of HighRAC mixtures by constituent material selection and/or modification at various length scales (iii) comparison and validation of current mix design procedures for mixtures containing HighRAC (iv) a holistic Life Cycle Assessment based approach for evaluation of long term pavement life including environmental and sustainability considerationsStructural EngineeringCivil Engineering and Geoscience

On the combined effect of moisture diffusion and cyclic pore pressure generation in asphalt concrete

In this paper, a new moisture conditioning protocol which attempts to distinguish the contributions of long- and short-term moisture damage, i.e. moisture diffusion and cyclic pore pressure generation, in asphalt mixtures is presented. The capability of the proposed protocol to rank various asphalt mixtures of known field performance for their short- and long-term sensitivity to moisture is evaluated on the basis of the Tensile Strength Ratio. Asphalt specimens with different types of aggregates and asphalt binders were conditioned by various combinations of water bath immersion and cyclic pore pressures by means of the Moisture Induced Sensitivity Tester. The results show that the proposed conditioning protocol can be used to evaluate the moisture susceptibility of asphalt mixtures and distinguish among mixtures with different moisture damage characteristics. In addition, it is shown that the use of cyclic pore pressures has a significant effect and can be used as an accelerated moisture conditioning procedure.Structural EngineeringCivil Engineering and Geoscience

Het healingmechanisme van bitumen nader verklaard

Asfalt heeft de aantrekkelijke eigenschap dat het zichzelf kan herstellen na schade. Er is echter tot op heden geen betrouwbare methode om de healingcapaciteit van een asfaltmengsel te bepalen. Bij het healingproces van een discrete scheur spelen twee processen een rol, namelijk het in contact komen van de oppervlakken van de scheur; het zogenaamde bevochtigen, en het vermogen van deze oppervlakken in contact om kracht over te dragen; de intrinsieke healing. In dit artikel wordt een testmethode gepresenteerd welke in staat is om de verschillende parameters die een rol spelen gedurende de healing te variëren om zo het belang van de processen in healing bloot te leggen. Met behulp van deze testmethode is de mate van healing van bitumen in de tijd onderzocht en de invloed van normaalkracht gedurende healing. Op basis van de gepresenteerde resultaten kan worden geconcludeerd dat bevochtiging van het scheuroppervlak tenminste 50% van de macroscopisch geobserveerde healing bepaalt voor pure bitumen. Dit inzicht kan worden gebruikt om een materiaalmodel voor healing van asfalt te formuleren, op basis waarvan een relatief eenvoudige healingtest kan worden ontworpen waarmee de healingcapaciteit van asfaltmaterialen onderling kan worden vergeleken.Pavement Engineerin

Finite elements simulation of reflective cracking in asphaltic overlays

Overlaying is one of the most popular and cost effective techniques of rehabilitation of cracked pavements. The placing of reinforcement between the overlay and the top layer of the cracked pavement is currently being utilised as a possible technique for delaying the development of cracks into the overlay. In order to assist the road designer with his attempt to determine the factors leading to the development of cracks into the overlay and in order to enable him to quantify the contribution of reinforcement in carrying tensile forces across cracks in overlayed pavements, CAPA, a user-friendly, PC based, finite elements system has been developed. A variety of options enable the simulation of discrete cracks in the pavement and their interaction with the surrounding materials. Starting from an initial crack length in the pavement, the system can automatically propagate the crack all the way to the surface computing at the same time the relevant fracture mechanics parameters at successive crack tip positions. A user friendly graphical screen input facility, together with a fully fledged mesh generator and extensive pre- and post-processing graphic facilities allow the designer to quickly evaluate the efficiency of various overlay techniques. By means of an example of an actual Dutch pavement profile it is shown that adequately bonded reinforcement can reduce the speed of crack propagation into the overlay and hence prolong the economic life of the structure.Structural MechanicsCivil Engineering and Geoscience

Finite element of multilayer surfacing systems on orthotropic steel bridges

Light weight orthotropic steel bridge decks have been widely utilized for bridges in seismic zones, movable bridges and long span bridges. In the last three decades, severe problems were reported in relation to asphaltic surfacing materials on orthotropic steel deck bridges. Earlier investigations have shown that the bonding strength of membrane layers to the surrounding materials has a strong influence on the structural response of orthotropic steel bridge decks. The most important requirement for the application of membrane materials on orthotropic steel bridge decks is that the membrane adhesive layer shall be able to provide sufficient bond to the surrounding materials. The research aims on developing a FE tool to simulate and understand the performance of asphaltic surfacing structures, so as to improve the design of surfacings and increase their service life. In this paper, Finite Element (FE) simulations of Merwedebrug bridge with two membrane layers system are presented. The finite element system CAPA-3D developed at the Section of Structural Mechanics of TU Delft has been utilized as the numerical platform for this study. Due to the multilayer of the surfacing materials and geometrical complexity of the steel bridge, the FE model shows the in time development of strains and stresses inside the surfacing materials depends highly on the wheel loading frequency, wheel position, membrane bonding strength as well as thicknesses and characteristics of the surfacing layers. Emphasis is placed on the distribution of strains and the evolution of damage in surfacing layers of different cases. Recommendations of surfacing structures design on orthotropic steel bridges are given.Structural EngineeringCivil Engineering and Geoscience

Towards an understanding of the self-healing capacity of asphaltic mixtures

The self-restoring or healing capacity of asphalt has been known for quite some time. Yet, to this date, there is no consensus of the fundamental mechanism underlying this phenomenon. In this paper a multi-scale model is presented which focuses on the healing phenomenon from a thermodynamic point of view. In the model, healing of bituminous material is simulated at the micro scale via a phase field model, utilizing a modified version of the Cahn Hilliard and Flory-Huggins equations. This model is then connected to a more general elasto-visco-plastic constitutive framework for the simulation of asphalt mixtures. The paper presents the developed hypothesis, the experimental evidence and summarizes some of the theoretical background. The model has been implemented in the 3D finite element system CAPA-3D and preliminary results are shown

Advanced numerical study of the response of orthotropic steel deck bridge with two membrane layers system

In the Netherlands an asphaltic surfacing structure for orthotropic steel bridge decks mostly consists of two structural layers. The upper layer consists of Porous Asphalt (PA) because of reasons related to noise hindrance. For the lower layer a choice between Mastic Asphalt (MA) or Guss Asphalt (GA), can be made. In this paper, a typical Dutch steel bridge deck surfacing system is simulated by means of the three-dimensional fmite element system CAPA 3D. Special attention is given to the structural distress phenomena and the parameters that influenced them. The FE model shows the distribution of strains and stresses inside the surfacing materials depends highly on the wheel load level, wheel load frequency, wheel position, membrane bonding strength as well as the thicknesses and the characteristics of the surfacing layers.Structural EngineeringCivil Engineering and Geoscience

Microstructural self-healing of bituminous materials: Combined experimental and numerical study

Bituminous materials form a class of materials that possess the intrinsic ability to selfheal. This self-healing capability is evidenced by the observation that the service life of these materials ‘in the field’ exceeds the service life as predicted by standard mechanical laboratory tests. This mismatch between laboratory prediction and field service life is usually accounted for by applying a shift or healing factor. In this contribution we demonstrate a model that is based on the observation that bitumen possesses a microstructure on the micrometre length scale, as can be observed by atomic force microscopy (AFM). On this scale bitumen can be regarded as a two-phase material, where the phases have a distinct stiffness. . One of the phases has a very typical appearance and is often referred to as ‘bee-phase’ [1-3]. The interface between the phases can be regarded as a manifold that is defined by stiffness gradient in the material. From mechanical considerations damage will initiate within this manifold. Modest variations in thermodynamic conditions (thus without melting the material) will already lead to rearrangement of phases, and a new damage initiation manifold, meanwhile the accumulated damage is erased. Starting from two experimental microstructural arrangements, one before and one after phase rearrangement, a finite element mesh is produced. For both phases a viscoelastic constitutive model is implemented. The interface manifold is treated equally, but is allowed to acquire damage, as are the other phases, to a lesser extent. In this way, using experimental observations as a starting point, it is demonstrated that the effect of healing in bituminous materials can be treated micromechanically, and leads to quantitative results. This opens the way to quantify the healing potential of a bituminous material upon its microstructure. Optimal manifolds to accommodate the healing behaviour can then be derived. The experimental challenge will be to engineer the interface manifold in accordance with the desired healing potential of the material.Structural EngineeringCivil Engineering and Geoscience