Vincent Gaudefroy

Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures

The use of recycled asphalt (RA) materials in pavement rehabilitation processes is continuously increasing as recycling techniques, such as cold recycling (CR), are being utilised in increasing magnitude and greater awareness for use of recycled materials and consideration of sustainable practices is becoming common in the construction industry. The focus of this paper is on developing a state of the art and state of the practice summary of processes used for classification of RA as well as the curing and specimen preparation practices for cold-recycled asphalt mixtures. A variety of topics were explored through an exhaustive literature search, these include RA production methods, definition of RA materials, stockpiling practices, industrial operations, specimen curing and preparation practices and in-field evaluation of cold-recycled rehabilitation. This paper was developed through efforts of CR task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-237 SIB).

Source dependency of rheological and surface characteristics of bio-modified asphalts

Asphalt industry has been looking to reduce their dependence on petroleum-based binders and apply non-petroleum binders as partial or full replacement for asphalt binders. This motivated several attempts by researchers to produce bio-modified asphalts from various materials including woody biomass, waste cooking oil, and bio-oil from animal manure. Accordingly, attempts have been made to incorporate bio-oils/bio-binders (BBs) made from these feedstocks mainly as partial replacements for petroleum-based asphalt. However, this effort has been found to be challenging mainly due to the high variations, in both the feedstock sources and the resulting bioproducts. Accordingly, aforementioned bio-modified asphalts behave differently in terms of their physicochemical and morphological properties, making them to be highly different in terms of their performance as well as their susceptibility to thermal and oxidative ageing. While there have been several studies on the application of various biomass-derived alternative binders, their effects on the physicochemical characteristics of asphalt before and after oxidative ageing have not been studied thoroughly. Therefore, this paper investigates the effects of introduction of four different BBs made from Swine Manure, Miscanthus Pellet, Corn Stover, and Wood Pellet on the rheological and chemical properties of a selected asphalt binder (PG64-22) before and after oxidative ageing. To study the effect of oxidative ageing on the chemical structure of bio-modified asphalt binder, Infrared Attenuated Total Reflectance Spectroscopy (Fourier transform infrared) was utilised. In addition, a Drop Shape Analyser, Rotational Viscometer, and Dynamic Shear Rheometer were used to evaluate the surface properties and rheological behaviour of each bio-modified asphalt binder. Overall, bio-modifiers (bio-oil/BBs) were found to be significantly different in terms of their ageing characteristics. Accordingly, their surface and rheological properties were found to be ranked differently before and after ageing when compared to that of control asphalt binder. The results showed that the BB from swine manure is less susceptible to ageing compared to plant-based bio-oils. This can be further attributed to the chemical structure and the high lipid contents of the BB from swine manure, making it less affected by oxidative ageing.

Evaluation of the compactability of bituminous emulsion mixes: experimental device and methodology

Laboratory asphalt mix design methodologies are aimed at predicting behaviour and determining characteristics of mixes. The French laboratory methodology for bituminous mixes is partially devoted to a compactability assessment. Samples are characterised by tests using the gyratory compactor. In this test, loose material is submitted to simultaneous compressive and shear forces, which lead to an internal aggregate reorganisation. The current French experimental device, called ‘PCG3’, was devoted strictly to hot mix asphalt characterisation. At present however, compactability properties of emulsion-treated gravel also appear as critical information due to the growing interest in bituminous cold mixes within an environmentally friendly context. A research project has been conducted in order to adapt the current ‘PCG3’ to allow for the compaction of cold mixes by adding the functionality of collecting extruded water due to emulsion breaking. This article is intended to describe this new device and determine the influence from adjusting parametric sensitivity on gravel treated with emulsion and compactability behaviour.

Bitumen emulsions formulation and destabilisation process relationship: influence of salts addition

To simulate ionic species release from hydrolysis reactions when bitumen emulsions come into contact with gravel, electrolyte solutions have been added to cationic emulsions and their impact on emulsions stability has been tested. In order to understand how the different parameters (oils viscosity, oils and electrolytes nature) influence the emulsion destabilisation, which included a gelation process, different materials have been used: two bitumen from different origins as well as two silicone oils with different viscosities, acting as model oils to simplify the system. According to cationic emulsifier, a quaternary ammonium salt was used. The different emulsions have been studied. Macroscopic and microscopic observations as well as size distribution measurements have been performed to evaluate the emulsion destabilisation. Results obtained show relationships between emulsion formulation and destabilisation evolution (gelation process included) of the materials studied. Phenomena observed could be interpreted by well-known mechanisms such as flocculation and coalescence. Moreover, it will be discussed how the coalescence and relaxation shape kinetics, probably due to salt and emulsion formulation, affect the gelation phenomenon.

Use of Inverse Method for Bonding Quality Assessment Between Bitumen and Aggregates Under Asphalt Mixes Manufacturing Conditions

In roads building, classical asphalt mix manufacturing commonly requires the heating (at 160°C) and the complete drying of aggregates. The induced energy cost has opened the way to develop alternatives processes and materials with low energy/carbon materials such as Warm Mix Asphalt (WMA). In warm mixes processes, aggregates manufacturing temperatures are different and lower than the Hot Mix ones. However, manufacturing temperature reduction can locally lead to poor bonding between bitumen and aggregate during the mixing step, due to the bitumen viscosity increasing, although bonding quality measurement remained a challenge. The aim of our study was to presents two thermal inverse methods for bonding quality assessment. These methods are based on Thermal Contact Resistance (TCR) assessment between bitumen and aggregate, during asphalt mix manufacturing. The experimental test principle consisted of heating both bitumen and cylindrical aggregate to their manufacturing temperatures (over 100°C) and to put them into contact thanks to a special experimental device. According to initial samples temperatures, heat transfer occurs from the bitumen to the aggregate. Two variants of the sequential Beck’s method were used to solve the inverse heat conduction problem. The first one consisted of determining the TCR from heat flux and temperatures and the second one consisted of identifying directly the TCR. The TCR values were interpreted as bonding quality criteria.Results showed low sensitivity to temperature measurement noise in the second variant of the inverse method. Moreover our study showed that bonding quality depends on bitumen and aggregate temperatures. The higher the component’s temperatures, the lower the TCR values and better is the bonding quality.Copyright

Bitumen Emulsion Destabilization Kinetics: Importance of the Crystallized Wax Content

We study the kinetics of bitumen emulsion destabilization after the addition of sodium hydroxide (NaOH) using macroscopic observations and rheology. Destabilization occurs in a two-step process: first, emulsion flocculates, forming a percolated network of contacting drops, and then coalescence provokes the irreversible connection of bitumen drops, leading to a bitumen continuous network that further relaxes the shape. We show that the destabilization kinetics exhibits a rheological easily identifiable signature allowing reproducible and accurate measurement of the connection/coalescence time trc (which corresponds to the time, determined by rheology, required to form the network made of drops connected by nonrelaxed coalescence). Using this powerful tool, we show that, even if viscosity is thought to govern the shape relaxation of the connected network it does not determine the connection kinetics. Indeed, emulsions with similar rheological behaviors exhibit very different destabilization times. Instead, we evidence a good correlation between the bitumen crystallized wax content and trc. From these experimental results, we discuss the stabilizing effect against coalescence of crystals in bitumen emulsions.

A Mineralogical Approach of the Interactions Between Bitumen, Clay and Water in Hot Mix Asphalt (HMA)

Clay fines are known to reduce the water resistance of bitumen-aggregates binding and cause stripping in Asphalt Concrete (AC) mixtures. To address this phenomenon, a better understanding of the mineralogical composition of aggregates is needed as well as an assessment of the bitumen-clay-water interactions. This paper contributes to reach this goal from a mineralogical perspective. The most common clays in natural aggregates, kaolinite, illite and montmorillonite, were used to prepare thin clay films and artificial clay-rich aggregates. The bitumen-clay interaction was studied using the sessile drop and the Oliensis spot tests on those thin clay films, whereas Duriez tests allowed measuring the stripping potential of AC mixtures containing the clay-rich aggregates. The results show that the water-bitumen-clay interaction and water resistance of the AC mixture are specific to the clay mineralogy. Furthermore, they show that the bitumen-clay interaction may be captured upon determining the surface energy of bitumen, the chemical composition and pH value of the clay and the bitumen-clay compatibility. Hence, predicting the water resistance of clay rich AC mixtures from mineralogical properties of the bitumen-clay interaction seems feasible.

Bitumen-in-water emulsion: Destabilization by electrolyte solutions and rheological evaluation

The breaking process of the bitumen emulsion is initiated when put into contact with aggregates during the mixing step. It is due to interactions between the binder and the aggregates and also water loss (evaporation and gravity flow). Some mechanisms are supposed to play a role in the breaking process which highly rules the coating quality of the aggregates by the bitumen binder, the implementation step of the mixture on the pavement and the final mechanical properties of the mixture. However the bitumen emulsion breaking process is not fully understood. It remains difficult to know which parameters have a preponderant role on emulsion breaking and how the kinetics of the different involved phenomena impact the global destabilization. The first part of the presented paper aims to determine the influence of electrolyte solutions, used as emulsion destabilizing agents to simulate ionic species release in the aqueous phase of the emulsion by the aggregates, on concentrated oil-in-water bitumen emulsion stability. Secondly, the evolution of rheological properties of the emulsion during destabilization process, which have been put in evidence in the first part, will be presented and discussed The emulsion destabilization, which included a gelation process, has been evaluated by macroscopic and microscopic observations, as well as size distribution and rheological measurements. An interpretation of the destabilization processes will be drawn using rheology, the emulsion formulation and the electrolyte solutions.