Rheology and microstructure of MDI–PEG reactive prepolymer-modified bitumen

This paper deals with the use of a new bitumen modifier, a reactive prepolymer, based on the reaction of 4,4^′-diphenylmethane diisocyanate (MDI) and a low molecular weight polyethylene glycol (PEG). The rheological and thermal behaviours of modified bitumen containing a low MDI–PEG concentration, as well as its morphology, have been studied. A relatively low amount of MDI–PEG (0.5 to 1.5% wt.) yields a significant improvement in the modified bitumen rheological properties, mainly in the high in-service temperature region. In this range of temperature, the rheological properties are clearly affected by curing time at room temperature. These results indicate that chemical changes, due to the reaction of MDI isocyanate groups with the most polar groups (–OH; –NH) of asphaltenes and resins, are produced. Thus, new chemical structures, non-visible by optical microscopy, slowly develop in MDI–PEG modified bitumen when samples are cured at room temperature.     

Spectral characterization of tissues microstructure by ultrasounds: a stochastic approach

A model of the echo formation process from tissues is suggested, in order to relate microstructural features to ultrasonic spectral signatures. The tissue is modeled as a collection of ideal randomly distributed scatterers, filtered by a time-invariant system representing the measurement apparatus and the average properties of the scattering medium, to obtain the backscattered signal. The gamma distribution has been assumed to describe the process, because it offers a flexible approach to approximating the parametric regularity of the scatterers. According to the model the spectral characteristics of the backscattered signal are strictly correlated with the spatial architecture and can be related to the gamma distribution parameters, i.e. interdistance and order. The model has been tested by simulating practical situations, in order to prove its validity and to test the procedure for estimating model parameters from actual data. The correspondence of experimental results obtained from tissues of different degrees of regularity with the simulated results confirms the effectiveness of the model for tissue characterization studies.     

Analysis of styrene-butadiene-styrene polymer modified bitumen using fluorescent microscopy and conventional test methods

This paper presents a laboratory study of modified bitumen containing styrene-butadiene-styrene (SBS) copolymer. Polymer modified bitumen (PMB) samples have been produced by mixing a 50/70 penetration grade unmodified (base) bitumen with SBS Kraton D1101 copolymer at five different polymer contents. The fundamental characteristics of the SBS PMB samples have been determined using conventional methods. The morphology of the samples as well as the percent area (%) distribution of SBS polymers throughout the base bitumen have been characterized and determined by means of fluorescence microscopy and Qwin Plus image analysis program, respectively. The mechanical properties of the hot-mix asphalt (HMA) containing SBS PMBs have also been analyzed and compared with HMA incorporating base bitumen. The effect of polymer addition on the short and long term aging characteristics of HMA have been evaluated by indirect tensile strength (ITS) test. The results indicated that polymer modification improved the conventional properties (penetration, softening point, etc.) and the mechanical properties (Marshall, ITS, etc.) of the base bitumen. It was also concluded that at low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed. Moreover, it was found out that the polymer addition minimizes the short and long term aging of HMA.     

Impact of maltene and asphaltene fraction on mechanical behavior and microstructure of bitumen

As a widely accepted concept, bitumen consists of four fractions that can be distinguished by their polarity. Highly polar asphaltene micelles are dispersed in a viscous phase of saturates, aromatics and resins (maltene phase). Different concentrations of asphaltenes in the bitumen result in a range of mechanical response properties. In an interdisciplinary study the impact of the maltene phase and asphaltenes on the linear viscoelastic behavior and the microstructure of bitumen were analyzed by creep recovery testing in a DSR and by atomic force microscopy (AFM). Therefore, bitumen was separated into the maltene and asphaltene fractions and artificial bitumen samples with different, pre-defined asphaltene concentrations were produced and investigated. It was found that the artificially produced, precipitated bitumen samples can be regarded as a representative, bitumen-like material in terms of mechanical behavior and microstructure. Asphaltenes play an important role in the typical viscoelastic behavior of bitumen being mainly responsible for stiffness and elasticity. Also, their concentration appears to be correlated to the occurrence and shape of the bee-like inclusions which can be typically observed by AFM.     

Exchange-coupled nanocomposites with novel microstructure and enhanced remanence by a new approach

Exchange-coupled nanocomposites with hard/soft magnetic phases are promising for the next generation of permanent magnets.Chemical methods have an advantage in controlling the nanoscale size of both phases.The nanocomposites obtained by the chemical method generally consist of a hard phase core and a soft phase shell.However,the soft-phase shell is easily oxidized leading to small enhancement of remanence.Here,a novel microstructure of Fe@FePt nanocomposites with Fe soft phase core and FePt hard phase shell has been synthesized by replacement reaction,in which the size of core and shell can be controlled below 10 nm by adjusting the ratio of Fe nanoparticles to PtCl4.Excellent exchange-coupling(single-phase-like demagnetization curves) between soft-hard phases was observed due to the precise size control of both phases,and substantial enhancements both in remanence (32 ％) and saturation magnetization (81％) were obtained in optimal nanocompistes.This work provides an alternative routine to prepare heterostructure materials with various applications.     

Polymer modified bitumen: Optimization and selection

Polymer modification of bitumen has been commonly performed since the 1980s in order to decrease bitumen (and pavement) susceptibility to high and low temperatures, allowing reduction in common failure mechanisms as rutting and cracking. Bitumen modification has been commonly performed by addition of thermoplastic or elastomeric polymers. However, there are just a few studies on bitumen blends using multiple materials, seeking for specific advantages provided by addition of these modifiers. This work describes the results obtained after the preparation of multicomponent polymer-bitumen blends (MC) based on an 80/100 penetration grade bitumen with varying amounts of (i) Polyethylene wax (PW); (ii) Styrene–Butadiene–Styrene copolymer (SBS); and (iii) crumb rubber (CR). Ideal blends depending on the amount of polymer modifiers added were found by using an experimental design procedure. It was possible to propose charts allowing optimizing and selecting appropriate polymer modified bitumens (PMB) depending on target properties for a given application by following Ashby’s materials selection methodology.     

The microstructure of a ZnO varistor material

The microstructure of a ZnO varistor material has been investigated by a combination of X-ray diffractometry and analytical electron microscopy (SEM, TEM, STEM, EDX). The material was found to consist of: ZnO grains (doped with manganese, cobalt and nickel); smaller spinel grains which hinder the growth of ZnO grains during sintering; intergranular Bi-rich phases (namely -Bi₂O₃, pyrochlore and an amorphous phase); and a small proportion of ZnO-ZnO interfaces which did not have any intergranular film but to which bismuth had segregated. The intergranular microstructure is largely a result of processes which occur during liquid phase sintering and subsequent cooling to room temperature.     

The microstructure of a graphene-reinforced tennis racquet

The microstructure of a graphene-reinforced tennis racquet has been analysed using a combination of optical microscopy and Raman spectroscopy. It is shown that the main structural components in the racquet frame are high-strength carbon fibres in an epoxy resin matrix. It is also found that graphene-based nanoparticles are used to reinforce resin-rich regions in the shaft of the racquet at the discontinuity in the fibre tows, where the handle is joined to the racquet head. From a detailed analysis of the relative positions and intensities of the Raman G and 2D bands, it is demonstrated that the nanoparticles employed in the racquet are most probably graphite nanoplatelets which have been added to improve the mechanical properties of the resin-rich regions. The nomenclature used for describing graphene-based materials is also discussed in the context of this present study.     

The effect of air blowing on the properties and constitution of a natural bitumen

Air blowing of a natural and vacuum-reduced bitumen causes marked changes in the properties and constitution of the material. The products are harder and have higher softening points than the original material and the changes in physical properties appear to be related to the asphaltene content which increases with the temperature and duration of the blowing process. Analytical data indicate that conversion of the original resins to asphaltenes and the formation of new resins from the oils occur simultaneously; the data also provide feasible representations of the pathways of bitumen maturation and asphalt deterioration.     

The oxidation of bitumen witnessed in-situ by infrared spectroscopy

During the production and recycling of asphalt concrete, bitumen in contact with inorganic particles is exposed to air at high temperatures. As a result an oxidation of bitumen, also known as aging, occurs. The reaction between bitumen and air at 163 °C was studied insitu with and without the presence of inorganic impurities by means of fourier transform infrared spectroscopy in the attenuated reflectance mode. This oxidation was discovered to be a step-wise reaction facilitated by the oxidation of thiols and creation of peroxides within the system. The rate of reaction was demonstrated to depend on the type of impurity present, of which iron (III) chloride was the strongest catalyst. It was further demonstrated that the oxidation reaction is inhibited by the adsorption of thiol species present in the system on copper particles. Combining copper with the iron (III) chloride-containing system also resulted in the inhibition of signal increase in the sulfoxide region of the spectra. The results of this preliminary research on the bitumen oxidation reaction presented are proposed for further research regarding control of aging of asphalt concrete, especially during the recycling works.     

The facilities layout problem: a multi-goal approach

This paper presents a combined quantitative and qualitative (subjective) approach to the plant layout problem. The two objectives, which may be conflicting, are minimizing the material handling cost and maximizing a closeness rating measure. A heuristic algorithm is developed which results in a discrete efficient frontier set, including only 'efficient layouts’. By specifying the different weights, or range of weights, for these goals, the 'best’ solution (layout) is generated.     

Highly fluorescent silver nanoclusters stabilized by glutathione: a promising fluorescent label for bioimaging

A panel of silver nanoclusters (Ag NCs) protected by glutathione has been produced by collecting them on a plastic surface during an interfacial etching process. Blue-green, yellow and red emitting Ag NCs with size smaller than 2 nm exhibited distinct fluorescence properties (both emission and lifetime). In particular, the yellow emitting Ag NCs were found to reach a very high quantum yield of over 60% with a monoexponential fluorescence lifetime. These labels show no bleaching and high photostability over time and a high stability for a wide range of pH values. Cytotoxicity tests demonstrated the viability in the presence of of these luminescent probes even at high concentration (1 mg/mL). Cell studies confirmed the uptake of Ag NCs in epithelial lung cancer cells by an endocytotic process. These results show the high potential of fluorescent noble metal nanoclusters for biolabeling and imaging as alternatives to the standard fluorescent probes such as quantum dots or organic dyes.      

From virgin to recycled bitumen: A microstructural view

In the present work, soft and hard bitumens recovered from unaged, aged and recycled asphalt concrete (AC) mixtures, which in laboratory tests performed mechanically as well as an AC mixture produced with virgin materials, were investigated regarding rheological, thermal and surface microstructural aspects. For comparison purposes, bitumen containing 50 wt% of virgin bitumen and 50 wt% of bitumen recovered from reclaimed asphalt pavement (RAP) was studied. Some properties of the bitumens remained unchanged throughout the preparation of the AC mixture, aging and recycling: Soft and hard bitumens retained their general rheological properties significantly, and their thermal and surface microstructural properties partially. Soft bitumens presented larger “bee” structures and, therefore, higher surface roughness, while hard bitumens presented smaller “bee” structures and, thus, lower surface roughness. Furthermore, soft bitumens seemed to contain higher crystalline-like content than hard bitumens. For the soft cases, the unaged recovered bitumen did not show the same characteristics (rheological and surface microstructure) as the virgin bitumen. Similarly the recovered recycled bitumen did not show the same characteristics (surface microstructure) as the bitumen prepared from the mixture of virgin bitumen and RAP bitumen. Aging of the AC mixture changed the rheological properties of the soft bitumen by increasing the complex modulus and decreasing the phase angle. Similarly, recycling changed the rheological properties by increasing the complex modulus and decreasing the phase angle. Compositional changes occurred during AC mixture preparation (possibly also aging and recycling) for both soft and hard bitumens. Consequently, more “phases” were observed on the surface microstructure for the recovered bitumens as compared with the virgin bitumens. However, no significant trend was found for the surface microstructure characteristics between the unaged, aged and recycled recovered bitumens. Moreover, the nature of the virgin bitumen influenced the properties of the recycled recovered bitumen, e.g. the glass transition temperature.     

Modelling of the microstructure: From classical cellular automata approach to the frontal one

A frontal cellular automata (FCA) approach for modelling of the microstructure is described. The approach allows for computation time reduction. The developed model contains the following two parts, namely the deformation and the microstructure part. The cellular automata (CA) cells are deformed according to the deformation. The model of recrystallization includes both the nucleation and the new grain growth stage. These stages depend on the deformation parameters such as: temperature, strain, strain rate, dislocation density and crystallographic orientation. The results related to the simulation of the dynamic recrystallization are also presented in the paper.     

Surface wrinkling: the phenomenon causing bees in bitumen

The so called “bee phenomenon” in bitumen has been investigated by means of AFM quantitative nanomechanical property mapping. Bees are a phenomenon that can be observed by topography measurements using AFM. The characteristic “bee” appearance comes from regions with alternating higher and lower bands in the surface topography of bitumen, which are surrounded by a flat area. The proposed mechanism for bee formation is phase separation and differential contraction during cooling from melt temperatures leading to wrinkling due to differences in the elastic modulus of the material phases. Using a laminate wrinkling model, the thickness of the bee laminate was calculated from the wavelengths and Young’s moduli of the bee laminate and the matrix. It was found to vary between 70 and 140 nm for the five bitumen samples that contained significant amounts of wax.     

Lamina cribrosa thickening in early glaucoma predicted by a microstructure motivated growth and remodeling approach

Glaucoma is among the leading causes of blindness worldwide. The ocular disease is characterized by irreversible damage of the retinal ganglion cell axons at the level of the lamina cribrosa (LC). The LC is a porous, connective tissue structure whose function is believed to provide mechanical support to the axons as they exit the eye on their path from the retina to the brain. Early experimental glaucoma studies have shown that the LC remodels into a thicker, more posterior structure which incorporates more connective tissue after intraocular pressure (IOP) elevation. The process by which this occurs is unknown. Here we present a microstructure motivated growth and remodeling (G&R) formulation to explore a potential mechanism of these structural changes. We hypothesize that the mechanical strain experienced by the collagen fibrils in the LC stimulates the G&R response at the micro-scale. The proposed G&R algorithm controls collagen fibril synthesis/degradation and adapts the residual strains between collagen fibrils and the surrounding tissue to achieve biomechanical homeostasis. The G&R algorithm was applied to a generic finite element model of the human eye subjected to normal and elevated IOP. The G&R simulation underscores the biomechanical need for a LC at normal IOP. The numerical results suggest that IOP elevation leads to LC thickening due to an increase in collagen fibril mass, which is in good agreement with experimental observations in early glaucoma monkey eyes. This is the first study to demonstrate that a biomechanically-driven G&R mechanism can lead to the LC thickening observed in early experimental glaucoma.     

The creative aspects of CAD: a possible approach

Whilst it is common ground that CAD systems can help designers in many areas, what is not clear is the extent of assistance that can be provided in the creative aspects. A possible approach to creative designing with computers is that of ‘prototype modification’. It is possible to see all designing in terms of this approach. The distinction between innovative design and design by modification results only from the quality and nature of the prototypes and modifications involved.     

Viscoelastic properties of a bitumen under continuous and cyclic deformation

An investigation was conducted on viscoelastic properties of a bitumen at various amplitudes and frequencies of the stresses acting on it; it established the effect of the amplitude of the deformation rate on the absolute value of the complex and effective viscosity.