Thixotropic behaviour of paving grade bitumens under dynamic shear

A material exhibits a thixotropic behaviour if its apparent viscosity decreases in time under stress, and if it progressively recovers its initial viscosity when the stress is released. Methods for characterizing thixotropy for fluids are relatively well known, the situation is more difficult for viscoelastic materials. For bituminous binders, it corresponds to a decrease of material stiffness under cyclic loading by modification of its internal structure and to a recovery of this stiffness after rest. This property has been highlighted by simple shear tests, carried out using a controlled stress rheometer. An experimental procedure has been defined for studying the thixotropic behaviour of binders in dynamic mode. Then, it has allowed describing the corresponding curves of complex modulus versus the set stress and the rest period at different conditioning times of samples. This study has also permitted to demonstrate that stiffness variations are linked to re-arrangement of molecular structure and not to cracks formation and healing. Finally, based on specific indicators, it has been possible to compare different bituminous binders in order to estimate the ability of materials to restore their internal structures

Kinetic of biobased bitumen synthesis from microalgae biomass by hydrothermal liquefaction

The current worldwide consumption of bitumen is about 100 million tons. A remarkable combination of properties (adhesion, impermeability to water, specific thermo-rheological behavior) makes it a key material in road construction. Today’s bitumen is mostly obtained from petroleum refining, so bioabased alternatives have to be explored for the future. The ALGOROUTE project funded by the French National Agency for Research (ANR) focuses on the use of hydrothermal liquefaction (HTL) process for the production of bitumen mimicking binders from microalgae biomass. HTL applied to microalgae is inspired by the geological process of petroleum formation, but on a very short time scale: For conditions around 260 °C / 50 bar, bitumen like products have been obtained by our consortium for residence times of about 1 hour [1] [2]. Beside temperature and pressure, the key parameters are the reaction time, algae/water ratio and loading level of reactor. Please click Additional Files below to see the full abstract

Linear viscoelastic properties of high reclaimed asphalt content mixes with biobinders

The use of high Reclaimed Asphalt (RA) content mixtures together with binders produced from renewable resources (biobinders) is one of the current challenges in pavement engineering research. On one hand, RA has been used for decades but there are still some concerns about its performance, especially when high contents are used (>30%). On the other hand, biobinders are relatively new materials which have to be deeply characterised and studied in order to develop good-practices for their use. In this paper, linear viscoelastic properties of biobinders and bio-mixtures manufactured with high-RA content and biobinders are analysed and discussed. High-modulus mixtures with 50% RA were selected for the mix design. Binders and mixtures were tested over a wide range of asphalt service temperatures and frequencies by means of DSR and two-point bending tests respectively. Results show that biobinders have an important effect on mixtures behaviour. However, no direct links between their linear viscoelastic properties were found. Bio-asphalt mixtures still need further development for commercial exploitation; however the take-away fact of this investigation is that it is possible to manufacture asphalt-like mixtures with acceptable viscoelastic properties while being composed only of RA and non-petroleum based binders

Molecular structure evolution of asphaltite-modified bitumens during ageing; Comparisons with equivalent petroleum bitumens

This work focuses on the molecular structure evolution of asphaltite-modified paving bitumens during ageing. In order to quantify the effect of ageing on the molecular weight distribution (MWD) of bitumens, a new parameter, called hereafter the ageing molecular-distribution shift (AMDS), is introduced. The molecular evolutions of asphaltite-modified bitumens during aging are compared with the molecular evolutions of pure petroleum bitumens of equivalent grade. The results based on AMDS confirm previous research showing that the asphaltite attenuates the ageing and, compared to hard petroleum bitumens produced in refinery, the asphaltite-modified bitumens present a better ageing performance. The AMDS parameter reveals appropriate for the evaluation of evolutions due to ageing

Analyse de la rupture d'un film de bitume par la méthode des éléments finis

Afin de mieux comprendre les phénomènes d'initiation et de propagation d'une fissure dans un matériau bitumineux, nous avons développé un essai innovant simulant le comportement d'un film mince de bitume entre deux granulats dans un enrobé. L'étude expérimentale considère la température et la vitesse de déformation comme les paramètres qui définissent la fissuration ductile et fragile. La géométrie de l'éprouvette permet d'initier et de propager une fissure au cœur de l'éprouvette en lui appliquant une phase de traction. La rigidité initiale de l'éprouvette non fissurée est caractéristique de sa géométrie et des propriétés rhéologiques du matériau. Le comportement du matériau viscoélastique est pris en compte en utilisant des séries de Prony. On montrera que l'analyse des essais permet de cerner la transition mécanique de l'état fragile à l'état ductile

Hydrothermal conversion of micro-algae as new biomaterials for pavement

Bitumen is a non-renewable petroleum-derived product whose market is under pressure due to the fossil fuel depletion and the environmental pollution concerns. It is therefore important to anticipate the replacement of this material, heavy fraction of petroleum distillation, used mostly in road construction as a matrix of an aggregate composite material. In that context, it is necessary to look for alternatives or substitution products and find processes that can valorize new renewable biomasses. Please click Additional Files below to see the full abstract

Thermal Behavior of a Novel Solar Hybrid Road for Energy Harvesting

International audienceTransportation is undergoing a radical transformation toward a novel way of thinking about road pavement: a sustainable, multifunctional infrastructure able to satisfy mobility needs, ensuring high safety standards, low carbon impact, automated detection through smart sensors, and resilience against natural and anthropogenic hazards. In this scenario, the road could also play a role for energy harvesting, thanks to the exploitation of solar radiation. The latter can be directly converted into electricity by solar cells placed under a semitransparent layer, or it can be harvested through a calorific flowing fluid. The aim of this paper is to introduce the concept of “hybrid road,” which is able to exploit both approaches. The innovative pavement is a multilayered structure composed by a semitransparent top layer made of glass aggregates bonded together thanks to a semitransparent resin, an electrical layer containing the solar cells, a porous asphalt layer for the circulation of the calorific fluid, and finally, a base waterproof layer. The hybrid road can generate electricity, contrast the heat-island effect, exploit the harvested energy to run a heat pump for heating purposes, or facilitate road deicing during winter. The present paper details experimental data obtained through energetic tests performed with a laboratory-size prototype of the hybrid road. The results show that the prototype is able to harvest around 55.2 W through the heat-transfer fluid. Furthermore, the heat exchange between water and asphalt has a cooling effect on the entire prototype

Guidelines for the implementation of SMARTI: Sustainable Multifunctional Automated Resilient Transport Infrastructure

The World's transport infrastructures (TI) network is facing fast changes due to population growth, mobility, business trades and globalization. More challenges are coming from unforeseen natural and human-induced hazards, including climate change's effects. Meanwhile, technology development continues apace, and new solutions from multi-disciplinary sectors could help solve the main challenges faced by the TI industry. This work presents “SMARTI”, a vision that aims at engineering and implementing concepts such as Sustainability, Multifunctionality, Automation and Resilience within the design, construction and management of TI. As a result, the paper provides roadmaps for each of the above-mentioned pillars, identifying aims, current practices and stepping stones that infrastructure managers, policymakers and governors should consider toward more sustainable TI within 2030

Laboratory investigation of bitumen based on round robin DSC and AFM tests

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T g temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T g's obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called "Bee” structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content