The breaking and coalescence process in bitumen emulsions during their application strongly influences the resulting long-term mechanical performance of the cold mix asphalt. This phase separation ...

Cold mix asphalt (CMA) emulsion technology has been the subject of research for many decades due to its proven environmental and economic benefits. However, issues relating to its mechanical perfor ...

The performance of asphalt mixtures is strongly influenced by the physical and chemical properties of the minerals and binders used, at various micro to macro scales. In cold asphalt mixtures a process that particularly strongly influences adherence between the minerals and binders (and thus performance) is the wetting of bitumen on the minerals' surfaces. Their adhesion is influenced by numerous factors and parameters, such as surface free energies of both binders and aggregates in the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures including open porosity, nature of the minerals and their surface chemical composition, as well as additives present in the binder phase. However, the relationships involved are not fully understood. Thus, in this study the surface free energies of both minerals/aggregates and binders were characterized using two approaches, one based on contact angles and the other on vapor sorption methods. Precise specific surface areas of four aggregates and seven minerals were determined using BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces, and calculating amounts of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were also calculated, based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions. The adhesive bond strength for the binder with each mineral/aggregate combination in wet condition has been improved by using additives. The presented study has highlighted the need for accurate measurements of aggregates' and minerals' specific surface areas and (hence) requirements to develop new approaches to resolve problems associated with BET-based methods. (C) 2016 Elsevier Ltd. All rights reserved.

Cold mix asphalt (CMA) emulsion based technology is a potential option to replace traditional hot mix asphalt due to environmental benefits and less energy consumption of producing it. However, the ...

Cold mix bitumen emulsion technology is getting a lot of focus by the road industries since a few decades due to the diminished environmental impacts and reduced energy associated with it. The dura ...

Cold mix asphalt (CMA) emulsion technology could become an attractive alternative for the road industry due to low startup and equipment installation costs, diminished energy consumption and reduced environmental impact. The performance of cold asphalt mixtures produced from emulsions is strongly influenced by a good control of the breaking and coalescence process. The wetting of bitumen on the surface of the aggregates is hereby of major importance for the performance of the asphalt. Premature coalescence of the bitumen emulsions away from the surface, could lead to poor adhesion and decreased mechanical strength of the asphalt. Today, the breaking and coalescence mechanisms of bitumen emulsions are still not fully understood due to their complexities and the lack of fundamental experimental methods and existing models. However, in the past years efforts have been made in defining relationships for understanding the bitumen emulsions. In this paper, a new experimental method is presented to study coalescence of bitumen by using shape relaxation of bitumen droplets in an emulsion environment. The coalescence of spherical droplets of different bitumen have been correlated with neck growth, densification and surface area change during the coalescence process. The test protocol was designed in a controlled climate chamber, to study the coalescence process with varying environmental conditions. The kinetics of the relaxation process was influenced by the temperature as well as other parameters. The research showed that the developed test procedure is repeatable and able to study the coalescence process on a larger scale. However, the relationship between the measured parametric relationships at the larger scale and the bitumen emulsion scale still needs further investigation. (C) 2016 Elsevier B.V. All rights reserved.

The purpose of this study is to evaluate how different binders react with polyphosphoric acid (PPA), and to contribute to a better understanding of this interaction. A number of bituminous binders were characterized before and after adding PPA, using rheological and chemical test methods, including FT-IR, uv-vis spectroscopy, NMR and gel permeation chromatography. The interaction with PPA is quantified as the change in softening point after adding a specific percentage of PPA. Most bitumen show an increase in R&B. Also in rheology, the stiffness increases, while the phase angle decreases when adding PPA. These observations are well-known and have been reported frequently by other authors. However, for one of the binders, small amounts of PPA lead to a decrease in R&B and to an increase in penetration. Rheological tests on this binder confirmed that the complex modulus decreases after adding PPA. These effects could be attributed to a precipitation, induced by PPA. This is very clear when investigating a drop of the bitumen-PPA blend in an optical microscope, and is also confirmed by storage stability tests. In conclusion, the findings suggest that PPA interacts with conjugated aromatic compounds, and this can in some cases lead to a precipitation.

In the nineties research started with the aim to develop robust technologies, allowing production of asphalt at ambient temperature. Such technologies results in significantly lower energy consumption and carbon emissions during asphalt production. The technology investigated and discussed here is based on gentle addition of bitumen-emulsion to aggregates, followed by controlled breaking of the emulsion on the road. However, despite some early success with a number of roads installed using emulsion based cold mix asphalt the market development of such materials failed to progress. Interest was also lost due to a significant drop in energy costs in the end of the nineties. In 2012 the Swedish road authority started an industry project to improve the understanding of cold mix design, production and performance and demonstrate the benefits of the technology on heavily trafficked roads. A strong relationship was found between surface area, chemical composition of stone aggregates and breaking rate of emulsions. This understanding has the potential to significantly improve the ability to design asphalt mixes that will be easy to produce and lay. Heavily trafficked test roads have been produced in the last two years with cold mixture asphalt as the base course. Further, durability data from roads produced fifteen years ago will be presented. It can visually be seen that the roads have survived over the years without any significant signs of aging. Analysis of the binders confirms that age hardening over time is limited, indicating the bitumen ages slowly in the road despite of high void contents.

In the days of concern about high energy consumption and global warming, all sectors of our society are scrutinised for potential savings of energy. One potential area for energy saving in the road construction sector is to make asphalt without heating the aggregates which is the current practice when making hot mix asphalt. Bitumen emulsions have been used to make cold mix asphalt, but uncertainties about the quality of the constructions have limited a wider use. Twenty years ago, an extensive development took place to improve cold mix asphalt to make it more sustainable. In the current paper, the development of an improved technology for the manufacture of cold asphalts using emulsions is described. The technique was used to produce a number of test roads to demonstrate performance. Several of the roads have now been in service for more than 15 years. The roads have been evaluated by sampling and analysis. It is shown that the roads have sustained excellently throughout the years and an evaluation of binders recovered from the roads show remarkably little ageing in spite of high void content of the asphalt.

For environmental reasons, low installation cost and initial investment; low energy infrastructure materials are becoming of high interest. A potential option to replace current hot mix asphalts is emulsifications, where bitumen binder is dispersed in a water phase aided by emulsifier and shear forces, and mixed at ambient temperature with unheated stones. Long term performance must, however, be guaranteed, otherwise the application benefits will be significantly diminished. In this paper, the main issues of cold mix (emulsion based) asphalt, like wetting in the presence of moisture and dust, and coalescence issues are discussed. Since both bitumen droplets and mineral surfaces were upscaled, pure mineral surfaces were investigated as stone material consists of different minerals. As a measure of the interfacial bond strength, surface free energies of different mineral aggregates and bitumen have been investigated in this paper as a stepping stone for further analyses of emulsions. From the analyses it was found that bitumen has only dispersive forces whereas most of the minerals surfaces have polar nature. According to Fowke's additive nature of the forces, bitumen and water are roughly equally strongly adsorbed to plagioclase and calcite, whereas water will displace bitumen from quartz, gypsum, potassium feldspar and mica surface.

It has been recognized that Polymer Modified Bitumens (PMB) have more potential for use in asphalt paving and can clearly demonstrate the value of their initial higher cost. To further assess sustainable benefits on heavy trafficked roads, test sections using various PMBs were built on highway E6 in Sweden during 2003-2006. The main objective of this paper is to study the aging and rheological properties of the binders used. A large number of cores were drilled and characterized with respect to stiffness, fatigue and permanent deformation. The binders (original, lab aged and recovered) were investigated extensively with rheological and chemical methods. It was found that PMBs, particularly SBS modified, demonstrate better rheological properties as compared to unmodified bitumens, even after several years in the field. These include higher strain recovery and lower non-recoverable compliance at high temperatures, and lower stiffness at low temperatures. For the SBS modified binders, good aging resistance was observed. The high resistance to aging for the SBS modified binders was also evident in the stiffness measurement made on asphalt field cores. Although significant differences have not yet been seen between the test sections (all the sections are in good condition after six years of traffic), the observed improvements for the modified binders are expected to be confirmed by a longer follow-up of the test road.

The relation between the chemical composition of bitumen and the physical properties, such as viscosity or viscoelasticity is very important for the use of bitumen as an advanced construction material. In view of the limited understanding of the exact molecular structure of the millions of different molecules constituting bitumen, many different proposals for the structure of bitumen have been published over the last 100 years. In this paper we propose that interactions between the molecules are the main determinants for the physical properties of bitumen. We discuss different types of interactions, typical for hydrocarbons, such as dispersive London interactions, polar interactions and pi-pi interactions, and how the strength of the interactions may be estimated by different methods. We also discuss one class of molecules in bitumen, defined by non-solubility, the asphaltenes, and why they contribute strongly to the thickening effect of bitumen, but we also conclude that asphaltenes are not the only molecules contributing to viscosity. Finally we show how the use of molecular parameters like molecular weight and aromaticity can be used to give a good estimate of the viscosity of heavy hydrocarbons of different composition. (C) 2014 Elsevier Ltd. All rights reserved.

In this paper, experimental support is provided showing the importance of polyaromaticity on the elastic properties of bituminous binders. Especially the size of the polyaromatic structures seems to play a crucial role. The observations indicate that larger conjugated aromatic structures provide stronger interactions and relate to the elastic behaviour at longer loading times or up to higher temperatures, while smaller aromatic structures determine more the elastic behaviour at short loading times or at low temperatures. In addition to aromatic interactions, natural wax can, upon crystallization, also induce increased elastic effects, especially at low frequencies. A large variety of binders was investigated: bitumen from straight distillation, visbreaking, solvent deasphalting and oxidation were included in the sample set. Average levels of aromaticity were determined by Fourier transform infrared (FT-IR) spectroscopy and by refractive index measurements. Chromatography combined with UV-visible absorption spectroscopy was used as an indicator of the average size of the aromatic structures. Rheological properties were determined using a dynamic shear rheometer, in a temperature range from 0 up to 90 °C. Good relations were observed between the phase angle measurements, at specific test conditions of frequency and temperature, and UV-vis absorption levels at specific wavelengths.

Due to the toxicity of aniline, it is desirable to find a replacement for aniline in the aniline point method. Here correlations between the aniline point and the turbidity temperature for 1,2-dimethoxybenzene, o-anisaldehyde, and p-anisaldehyde are presented. 1,2-Dimethoxybenzene correlates well to the aniline point but with a significantly lower turbidity point compared to the aniline point. p-Anisaldehyde also correlates well to the aniline point, and both the aniline point and the turbidity temperature are very similar in magnitude, making it a very strong candidate for replacement of aniline in the aniline point analysis.

Aggregates and bitumen together form a composite called asphalt concrete pavement. Moisture damage to asphalt concrete pavement can occur as stripping, and is a common problem that can lead to costly repairs. There is therefore a need to understand which stone aggregates adhere best to bituminous binder and result in a minimum of stripping. Lifshitz used the refractive index to estimate the dispersive non-polar van der Waal’s interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker’s coefficient, which in turn can be related to stripping potential. Aggregates consist of minerals and minerals consist of different elements. The objective of this study was to investigate variation in the dispersive component of minerals via their refractive indices using data from mineral data sheets. The influence of the position of elements in the periodic table and chemical composition on refractive index of minerals was examined in order to classify mineral aggregates for asphalt road building with regard to dispersive adhesive properties and expected resistance to stripping. It is clear from this study that the elemental composition of a mineral will affect its refractive index and hence its dispersive adhesion to bitumen. Aggregates and minerals have been classified according to degree of stripping in the literature. In this study it was shown that aggregates and minerals that have a refractive index higher than approximately 1.6 are expected to be less susceptible to stripping. Also, minerals containing alkali metals are sensitive to stripping since they are partially soluble in water.

In sustainable asphalt road construction, proper selection of materials is of great importance. A durable material along with optimal mix and pavement design is crucial to a long lifetime of asphalt pavements. For bituminous binders, increased experience and knowledge has been seen on use of polymer modification. The main objective of this paper is to study the durability of polymer modified binders in terms of resistance to aging, rutting and cracking. Asphalt samples were taken from test roads where polymer modified binders were tested in different layers. Field samples were analysed with respect to binder contents and air void contents. In characterisation of recovered binders various tests were carried out, including time-temperature sweeps and multiple stress creep and recovery test (MSCR) using dynamic shear rheometer, gel permeation chromatography, Fourier transform infrared spectroscopy, fluorescence microscopy, as well as conventional tests such as penetration. The chemical and mechanical tests were also conducted on original binders and those aged at laboratory by RTFOT and PAV. It was found that the polymer modified binders demonstrate better rheological properties than unmodified pen bitumen, even after several years in asphalt pavements. These improvements include higher strain recovery and lower non-recoverable compliance (Jnr) at high temperatures, and lower stiffness at low temperatures. For the modified binders with styrene-butadiene-styrene (SBS) polymers, good aging resistance was also observed. The improved binder properties should be beneficial in terms of resistance to asphalt rutting and cracking. This is expected to be confirmed by a longer time of follow-up on the performance of the test road.

Long lasting asphalt pavements are particularly desirable to ensure the efficiency of road transport. To find out key factors that determine the lifetime of an asphalt pavement, an extensive study was carried out on a number of long lasting road sections with known construction data and performance track records. Asphalt cores were drilled from the selected road sections and investigated by means of mechanical tests and non-destructive X-ray computed tomography. The field samples were further examined with respect to mixture composition, and binder chemistry and rheology. The study showed that long lasting pavements consist of thick asphalt layers with higher binder contents and low air voids. In general, the lower asphalt layer was stiffer than the upper layer. Although small local cracks were seen inside some cores, there was no propagated cracking. In all the studied road sections, bitumen ageing was found to be slow, as assessed either by a stiffening effect or by chemical compositional changes. The slow rate of bitumen ageing had kept asphalt layers flexible enough to resist cracking, which has been confirmed by the analyses using HMA fracture mechanics, as well as field performance observation. It was also shown that a tight or dense upper layer may prevent bitumen ageing in the underlying pavement. The present study highlights the importance of binder durability (resistance to ageing) in achieving a long lifetime asphalt road.