Effect of foaming technique and mixing temperature on the rheological characteristics of fine RAP-foamed bitumen mixtures

This paper evaluates and compares the differences in the rheological characteristics of the fine aggregate matrix (FAM) portion of plant produced Foamed Bitumen Mixtures (FBMs) by means of a mechanical foaming process, and by the incorporation of zeolites in combination with Reclaimed Asphalt Pavement (RAP) material. This evaluation explores, for the first time, the impact of plant production variations for half-warm, warm and hot processes (i.e. mixing temperatures around 90°C, 120°C and 160°C, respectively) on their rheological response. A fine Virgin-HMA, a fine HMA-RAP – no foaming technique -, and a 100% fine RAP mixture were also produced for comparison purposes. Dynamic Mechanical Analysis (DMA) tests were conducted on all evaluated FAM mixtures to determine their linear viscoelastic properties. Results indicate that the rheological response of the fine RAP-FBMs is influenced primarily by the contribution of the RAP binder in the total bitumen blend, and ageing of the fine RAP material, which were a function of the foaming technology and the production temperature of the materials

Evaluation of moisture sorption and diffusion characteristics of asphalt mastics using manual and automated gravimetric sorption techniques

One of the most important factors influencing the durability of asphalt mixtures is moisture-induced damage resulting from the presence and the transport of moisture in pavements. Moisture-induced damage is an extremely complicated phenomenon that is not completely understood but believed to be governed by the interaction of moisture with asphalt mix components (mastic and aggregates). The objective of this study was, therefore, to characterize the sorption and diffusion characteristics of asphalt mastic using gravimetric vapor sorption techniques. Moisture transport, in the hygroscopic region, in asphalt mastics was studied using both static and dynamic gravimetric vapor sorption techniques to determine equilibrium moisture uptake and diffusion coefficients as a function of aggregate and filler types. For the 25-mm diameter thin asphalt mastic films and the testing conditions (23°C and 85% relative humidity) considered, the kinetics of moisture uptake obtained were characteristic of Fickian diffusion with a concentration-dependent diffusion coefficient. Equilibrium moisture uptake and diffusion coefficient estimated from the static measurements were comparable and of the same order of magnitude as those from dynamic sorption techniques. Both measurement techniques ranked the mixes similarly, which suggest either method could be used to characterize moisture transport in asphalt mastics. Equilibrium moisture uptake was relatively higher in mixtures containing granite aggregates compared with limestone aggregate. In contrast, the diffusion coefficient of limestone aggregate mastics was higher than granite. Thus, an inversely proportional relationship exists between moisture uptake and diffusivity of the asphalt mastics studied. The results suggest moisture transport is a function of aggregate type and that both equilibrium moisture uptake and diffusion coefficient are useful in studying moisture susceptibility in asphalt mixtures. The effect of mineral filler type on diffusion coefficient was minimal in the mastics containing granite aggregate but relatively high in mastic samples containing limestone aggregates. Diffusion coefficient was found to increase with sample thickness, which was unexpected because diffusion coefficient (in an isotropic material) is considered an intrinsic property that is independent of sample size. The results suggested anisotropic diffusivity can occur in asphalt mastics and could be attributed to factors, including mineralogy, microstructure, air voids, and the tendency of the aggregates to settle at the bottom of asphalt mastic with time. In addition to characterizing moisture transport in asphalt mastics, the results presented in this paper will be useful as inputs for numerical simulation of moisture damage in asphalt mixtures

Laboratory evaluation of Rediset modified bitumen based on rheology and adhesion properties

Warm mix asphalt (WMA) could significantly reduce the production temperature of asphalt mixtures. Lower production temperature meaning reduced fossil fuel consumption and greenhouse gas emission which in turn avoid environmental pollution in the road construction process. This study aims to characterise the properties of bitumen with the addition of a type of WMA additive – Rediset. The influence of Rediset on bitumen surface energy was evaluated by using the Dynamic Contact Angle (DCA) test. Complex modulus and phase angle of bitumen were evaluated through frequency sweep test using Dynamic Shear Rheometer (DSR). The high-temperature viscosity of bitumen was measured using a corn and plate system which installed in the DSR equipment. Finally, the Pneumatic Adhesion Tensile Testing Instrument (PATTI) test was performed to measure the tensile strength and moisture susceptibility of aggregate-bitumen combinations. The results show that the Rediset reduces the surface energy of bitumen. Moreover, as seen in the DSR test, the complex modulus increased while the phase angle decreased at the low frequency range due to the addition of Rediset. The decreased bitumen viscosity because of the addition of Rediset demonstrating reduced mixing and compaction temperature of asphalt mixture. In addition, the addition of Rediset could improve the bonding strength of aggregate-bitumen combinations at medium and high service temperatures but has no influence at low temperature. Furthermore, the Rediset is able to increase the retained tensile strength which in turn reduces the moisture susceptibility of asphalt mixture

Investigation into the bond strength of bitumen-fibre mastic

The loss of bond strength in road pavement surfacing due to high traffic loads or moisture is a recurring problem, creating distresses such as ravelling, fatigue and rutting. It is, therefore, important to find a way to prevent or at least delay the loss of bond strength in asphalt mixtures. Such an improvement would lead to longer service life and a more comfortable drive for road users. This study describes how the pneumatic adhesion tensile testing instrument (PATTI) was used to examine the mechanism by which fibres influence the pull-off tensile strength of asphalt mastic. This study assesses the potential for chemical modification of the binder due to the presence of fibres, by means of work of cohesion and work of adhesion calculations, based on surface energy parameters and a binder drainage test. The study also evaluates the influence of different filler-bitumen ratios and fibre percentages on pull-off tensile strength. The test results indicate that the fibres enhance the pull-off tensile strength of the mastic, in addition to changing the failure mode from cohesive to hybrid, implying an improvement in the cohesive strength of the mastic

Evaluation of the degradation of fine asphalt-aggregate mixtures containing high reclaimed asphalt pavement contents

This paper evaluates the mechanical properties and performance of the fine aggregate matrix (FAM) existing within full reclaimed asphalt pavement (RAP) asphalt mixtures, in terms of their rheological and fatigue deterioration properties. The RAP material was produced in the laboratory to control its properties and to reduce the effects of variability associated with these materials. Four FAM mixtures were analysed, including a virgin hot mix asphalt, a 100%RAP, and two mixtures containing 50% RAP in combination with virgin materials using different penetration grade virgin binders. The analysis of the deterioration properties was based on the application of a fracture model that incorporates the viscoelastic properties of the material, the quality of the adhesive bonds developed between the aggregates and the corresponding bitumen present in each mixture, and the rate at which the material dissipates energy when subjected to cycling loading. The input parameters for this model include the results obtained from dynamic mechanical analysis and surface free energy tests. In general, the results showed that the incorporation of 50% RAP content increased the stiffness of the final mixtures, as expected. However, this hardening effect did not result in mixtures with inferior fatigue performance of the FAM present in the full mixtures, at the applied strain level

Topographic determinants of foot and mouth disease transmission in the UK 2001 epidemic

Background A key challenge for modelling infectious disease dynamics is to understand the spatial spread of infection in real landscapes. This ideally requires a parallel record of spatial epidemic spread and a detailed map of susceptible host density along with relevant transport links and geographical features. Results Here we analyse the most detailed such data to date arising from the UK 2001 foot and mouth epidemic. We show that Euclidean distance between infectious and susceptible premises is a better predictor of transmission risk than shortest and quickest routes via road, except where major geographical features intervene. Conclusion Thus, a simple spatial transmission kernel based on Euclidean distance suffices in most regions, probably reflecting the multiplicity of transmission routes during the epidemic

Influence of the thermophysical properties of pavement materials on the evolution of temperature depth profiles in different climatic regions

The paper summarizes the relative influence of different pavement thermo-physical properties on the thermal response of pavement cross-sections, and how their relative behaviour changes in different climatic regions. A simplified one-dimensional heat flow modelling tool was developed to achieve this using a finite difference solution method for studying the dynamic temperature profile within pavement constructions. This approach allows for a wide variety and daily varying climatic conditions to be applied, where limited or historic thermo-physical material properties are available, and permits the thermal behaviour of the pavement layers to be accurately modelled and modified. The model was used with available thermal pavement materials properties and with properties determined specifically for the study reported here. The pavement materials included in the study comprised both conventional bituminous and cementicious mixes as well as unconventional mixtures that allowed a wide range of densities, thermal conductivities, specific heat capacities and thermal diffusivities to be investigated. Initially, the model was validated against in-situ pavement data collected in the USA in five widely differing climatic regions. It was found to give results at least as good as others available from more computationally expensive approaches such as 2D and 3D FE commercial packages. Then the model was used to compute the response for the same locations had the thermal properties been changed by using some of the unconventional pavement materials been used. This revealed that reduction of temperature range by several degrees was easily possible (with implications for reduction of rutting, fatigue and the Urban Heat Island effect) and that depth of penetration of peak temperatures was also achievable (with implications for winter freeze-thaw). However, the results showed that there was little opportunity to displace the peak temperatures in time

Influence of fibres on rheological properties and toughness of bituminous binder

Many studies have been made to examine different ways to modify bitumen and asphalt mixtures in response to increasing performance requirements. One of these is the use of additive materials and in this study, the potential of cellulose and glass fibres to modify the rheological properties of bitumen has been investigated. To achieve this, mixtures of bitumen with different contents of fibre were prepared and the properties of the bitumen and resulting modified binders were tested (penetration, softening point, viscosity and double edge notch tension test along with rheological testing in the dynamic shear rheometer). The experimental results demonstrated that adding fibres improves the rheological properties of bitumen across a range of loading frequencies and temperatures. Adding fibre reduced the penetration and increased the softening point and viscosity of bitumen implying improved rutting resistance of asphalt mixtures using these mastics. Finally this investigation established that adding fibre to bitumen improved its toughness, which could lead to improvement in asphalt fatigue performance. However, there are some limitations that are also discussed

Microstructure and mechanical properties of fibre reinforced asphalt mixtures

Conventional asphalt mixtures can perform satisfactorily in most flexible pavement and airfield applications. However, during recent years the trend has been towards traffic growth, severe climate conditions, and heavier loads. This allied to durability and cost effectiveness issues, has raised the demand to improve the mechanical properties of conventional asphalt materials by means of modification. Fibres may have the potential to achieve such modification and, thereby, enhance the mechanical properties of asphalt mixtures. This paper examines the relative performance of asphalt mixture modified with different fibre types and contents against the main distress types experienced by flexible pavements. Also, fibre distribution and orientation in the asphalt mixture are explored in this paper. The scanning electronic microscope images show the difference in the microstructure among fibre types. X-ray computed tomography investigation results indicate that steel fibres are present throughout the asphalt mixture specimen. The test results show that fibres have a notable impact on the stiffness modulus and fracture toughness of asphalt mixtures at 20 °C test temperature. In addition, fibres provide slightly improved fatigue life of fibre reinforced asphalt mixtures, mainly at low strain values. Furthermore, results indicate that there is no detrimental impact of fibres on either the tensile strength or the moisture damage resistance of such mixtures

High turnover drives prolonged persistence of influenza in managed pig herds.

Pigs have long been hypothesized to play a central role in the emergence of novel human influenza A virus (IAV) strains, by serving as mixing vessels for mammalian and avian variants. However, the key issue of viral persistence in swine populations at different scales is ill understood. We address this gap using epidemiological models calibrated against seroprevalence data from Dutch finishing pigs to estimate the 'critical herd size' (CHS) for IAV persistence. We then examine the viral phylogenetic evidence for persistence by comparing human and swine IAV. Models suggest a CHS of approximately 3000 pigs above which influenza was likely to persist, i.e. orders of magnitude lower than persistence thresholds for IAV and other acute viruses in humans. At national and regional scales, we found much stronger empirical signatures of prolonged persistence of IAV in swine compared with human populations. These striking levels of persistence in small populations are driven by the high recruitment rate of susceptible piglets, and have significant implications for management of swine and for overall patterns of genetic diversity of IAV.This work was supported by the RAPIDD program of the Science and Technology Directorate, Department of Homeland Security, and the Fogarty International Center, National Institutes of Health (V.E.P., S.R., J.L.N.W. and B.T.G.) and the Bill & Melinda Gates Foundation (V.E.P. and B.T.G.). J.L.N.W. is also supported by the Alborada Trust, the European Union FP7 project ANTIGONE (contract no. 278976) and by Biotechnology and Biological Sciences Research Council sLOLA BB/L001330/1.This is the final version of the article. It first appeared from Royal Society Publishing via http://dx.doi.org/10.1098/rsif.2016.013