The impact of self healing materials on telecommunication: Towards a concrete aircraft?

The use of a material for a specific application is governed by considerations on the expected conditions during its lifetime. For aerospace applications for instance, lightness, reliability and thermal stability ofthe material are of major importance. No material will ever possess all the desired properties at the same time. Therefore the engineer is left with optimising the materials and minimise the impact of the ever-present 'disadvantageous' properties. By introducing the potential of 'Self Healing' in a material, the lifetime and reliability could be significantly improved. Introduction of safety factors in the design could be minimised, leading to leaner structures. Making an aircraft from concrete may seem far-fetched, but isn't that not what Aerospace Engineering is all about? Jules Verne is now our reality.Structural EngineeringCivil Engineering and Geoscience

Self Healing: An emerging property for new materials

Structural EngineeringCivil Engineering and Geoscience

Comment on ‘‘Zero Sound Mode in Normal Liquid ³He’’

Design and ConstructionCivil Engineering and Geoscience

Vulkanisme en water op Mars?

In januari 2004 werd Mars bezocht door de tweeling robotverkenners Spirit en Opportunity. Zij werden erop uitgestuurd om eindelijk het definitieve antwoord te geven op de vraag of er leven op Mars is geweest. Alles wijst er inmiddels op dat er op Mars ooit vloeibaar water stroomde. Of daarmee een bewijs geleverd is over het bestaan van leven op Mars blijft echter een open vraag.Structural EngineeringCivil 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

Temperature induced healing in strained bituminous materials observed by atomic force microscopy

Bitumen is the binder in the composite material named asphalt concrete. Under cyclic mechanical loading of traffic passing over the pavement, eventually damage will initiate in the pavement, leading to eventual structural failure. This damaging process is accelerated by time dependent change of the mechanical properties of asphalt concrete due to ageing mechanisms like oxidation. Bitumen displays spatial heterogeneity at the micrometer scale, which has been observed by atomic force microscopy (AFM). The mechanical properties of the elliptical, microstructural domains of bitumen are distinct from those of the continuous phase. This introduces stiffness discontinuities in the material, which under mechanical loading will concentrate stresses at the interfaces, and thus the locations where early stages of damage will develop. This work aims at in situ probing of the crack healing of bituminous materials as a function of moderate temperature changes. The bitumen was prepared on a flexible substrate which was mechanically strained to induce damage. AFM measurements of the strained bitumen specimen provides evidence of the crack initiation at the interface and the predominant propagation of cracks through the elliptical domain phases. Healing of these cracks was observed after applying modest amounts of heat to the material. Meanwhile the process was monitored in situ with AFM. With increase of temperature one of the phases starts softening, while the material as a whole remains solid. This allows the phases to rearrange and meanwhile eliminating micro cracks at the interface

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

Microstructural Changes in Bitumen at the onset of Damage-healing

Self-healing of bitumen is a property that positively contributes to the sustainability, maintenance requirements and cost effectiveness of asphalt pavements. Ideally one would like to design an asphalt mix with a well-defined healing potential. Although substantial research efforts have been dedicated to the healing mechanism in bitumen, complete understanding of the fundamental mechanisms that govern the property of healing is still lacking. Here we investigate the manifestation of damage and healing of bitumen at the microstructural level. Three distinct bitumen grades are subjected to mechanical loading conditions, and the damage is investigated at the microstructural level by atomic force microscopy combined with finite element simulations. One of the bituminous phases appears to display visible signs of cracks, which are found to (partly) disappear at moderate temperature changes. Simulations of mechanical loading of experimentally derived finite element meshes are corresponding well with these experimental observations. Moreover, the simulations provide a measure of mechanical response, i.e. stiffness, of the material as a function of strain level. From this it is found that the microstructural cracks lead to diminished structural response properties, whereas after healing these properties are partly recovered. The experimental observations, together with the simulations, support earlier ideas that relate the phenomenon of self-healing in bitumen to their rheological property of thixotropy. Moreover, the work presented hints that the property of self-healing is governed by processes at the microstructural length scale.Pavement Engineerin

BresDefender: A potential emergency measure to prevent or postpone a dike breach

Dikes are designed to withstand a load, with a certain finite probability of occurrence. In case of crises regarding to flood safety, the military is expected to prevent low-laying areas against flooding. Historical attempts show that the effectiveness of emergency measures and strategies are mainly successful caused by the adequate acts of the local people in charge. Based on a literature analysis of breach development, the available time for the application of emergency measures is estimated. This paper introduces the BresDefender strategy, an emergency response strategy, used by the military, to prevent or postpone dike failure. The current BresDefender strategy is a floating pontoon, which can placed on a weakened dike section. It is expected that it can be applied during two scenario’s. In the first scenario, the BresDefender is applied during the early stages of breach formation. In the second scenario, it restores the original crest height, where overflow is expected in the near future e.g. in case of macro instability. The BresDefender is expected to stabilize the weakened dike section.Hydraulic Structures and Flood Ris

Vergelijkend AFM Onderzoek: Microstructuur van bitumen in relatie tot healing

In this report we present the background, the scientific and experimental approach and the results of AFM experiments performed on two different batches of bitumen. The specific bitumen researched in this project has also been studied in the context of the InfraQuest project ‘Pragmatisch Healing Onderzoek’. It has been known for quite some time already that bitumen posessess a microstructure at the typical length scale of micrometers. This can be shown experimentally by imaging the bitumen surface with Atomic Force Microscopy (AFM). As is the case for many other engineering materials (e.g. steel), the microstructure will manifest itself by the macroscopic mechanical response of the material; thus on the typical length scales where it performs its load bearing function in pavement structures. Together with the hitherto not precisely specified properties of the many available bitumen grades, this justifies further research into the origin and properties of this microstructure. Here we also anticipate that a better understanding about the origin and properties of the bitumen microstructure will lead to improved bitumen grades (material appraisal) and possibly to better criteria for selecting a bitumen for a specific application. In the context of this research first the objectivity of the AFM imaging technique has to be established. Therefore two independent laboratories (TNO and CiTG, TU Delft) have prepared and conditioned bitumen samples for the AFM. All samples have been prepared from the same batch of bitumen. Then each laboratory has imaged its ‘home made ‘samples’ as well as the samples prepared at the other lab. The results appear to be qualitatively identical. Thus one may conclude that the microstructure of bitumen is a reproducible quantity. It was also found that the (thermal) conditioning of the bitumen (prior to imaging) has a significant impact on the microstructure observed. One may conclude from this that the sample conditioning procedure is a very important aspect in the AFM imaging process. In other words: an AFM image of bitumen is meaningless, unless the conditioning procedure of the samples is reported extensively. The next step was to find the influence of temperature on the observed bitumen microstructure. Identical samples have been prepared by TU Delft and both laboratories have imaged the microstructure as a function of temperature. A similar observation as stated before has been made: the microstructures observed by both laboratories were very similar. Moreover, it has been observed that the microstructure gradually disappears when the temperature is raised. However, even at the highest (experimental) temperatures (70 °C) traces of the microstructure remain visible. Apparently the ordering process that governs the bitumen microstructure has an associated interaction energy in the order of 400 kB, i.e. 30-40 meV (kB, Boltzmann constant). It was also found that (chemically) reclaimed bitumen (from an asphalt test beam) does show a microstructure as well. Surprisingly however, it was found that the microstructure of harder bitumen grades disappears at lower temperatures compared to softer bitumen grades. This is against the intuition that in harder bitumen molecules are more tightly bound together than in softer grades, and that for harder bitumen the microstructure would ‘melt’ (disappear) at higher temperatures. The molecular mobility appears to be higher in harder bitumen grade, hence they are anticipated to be better ‘healers’. Macroscopic fatigue test have shown similar trends.Structural EngineeringCivil Engineering and Geoscience