The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing against its regular application. The bitumen emulsion formulation process and compositional optimization are subjected to a high number of degrees of freedom. Consequently, obtaining the desired product is mostly based on a series of random and tedious trials because of the enormous number of tests that are carried out to meet the required properties, such as emulsion stability, viscosity, droplet size (and distribution), and bitumen emulsion chemistry. Several pre-established formulation procedures have been presented in the literature. Some of them have technical limitations to be utilized for practical industrial application, whereas others are still not understood enough to be applied in bitumen emulsion formulation. Therefore, discussing some important issues in this field could be useful to offer a practical guide for bitumen emulsion manufacturers when trying to formulate a well-defined bitumen emulsion to best fit its use in pavement infrastructure rather than to simply to meet standard specifications. This review paper aims to enable the ultimate potential of bitumen emulsion by further reviewing the research progress of bitumen emulsion manufacturing and discussing the literature available up to now on this topic, in the realm of bitumen emulsion manufacturing and emulsion chemistry.

Cold Bitumen Emulsion (CBE) mixture technologies have been recently developed to lower pavement construction temperatures to reduce environmental costs and control gas emissions. Due to its poor early mechanical strength, active fillers (i.e., cement) have been used to obtain high early stiffness in order to have the potential for timely construction of the next layer. There is, however, a lack of understanding about the impact of active fillers on the viscoelastic behavior and fatigue damage resistance of CBE mastics. This study, therefore, aims to identify the influence of active fillers on the rheological properties and the resulting fatigue behavior of CBE mastic, supported by chemical analysis for the filler-bitumen emulsion. For this aim, bitumen emulsion was mixed separately with seven fillers/blended fillers to prepare the CBE mastics. Various experiments, including continuous pH monitoring tests (chemical reactivity of filler-bitumen emulsion), Strain Sweep (SS) tests, Temperature-Frequency Sweep (TFS) tests, Time Sweep (TS) tests, and Linear Amplitude Sweep (LAS) tests were conducted on the CBE binder and the prepared mastics. Results show that the rheological performance and the fatigue damage resistance depend not only on the filler inclusions but also on filler type and chemistry. On this basis, the rise in complex shear modulus and the decrease in the viscous component is associated with a significant enhancement in fatigue performance for specific fillers.

In this study, the effect of various laboratory procedures for compacting hot-mix asphalt to form test specimens is investigated. Based on the triaxial cyclic compression test (TCCT) according to the European specification EN 12697-25, the resistance to permanent deformation of the specimen obtained from different types of laboratory compaction is studied. The deformation behaviour of the laboratory-compacted specimens is always compared with the deformation properties stated in TCCT for the asphalt mix specimen taken from on-site roller-compacted road pavement. As a result, the effect of the choice of laboratory compaction procedure on the resulting deformation behaviour in TCCT is assessed.

A dominant failure mode in hot-mix asphalt (HMA) layers is material fatigue, occurring when the asphalt layer is repeatedly loaded by tensile stresses. The maximum stress arises at the bottom of the asphalt layer and, in consequence, crack development is initiated at the bottom. Various techniques are known that simulate bottom-up fatigue cracking in the laboratory. Fatigue failure is also observed on top of the pavement. Especially in cold climates, temperature-induced top-down cracking initiated at the pavement surface is a well-known failure mode. Usually, horizontal tensile stresses in the surface layer are smaller than stresses in the bottom layer. At cold temperatures and when temperature falls within a short period of time, the traffic-induced stress is superposed by temperature-induced stress, and the total stress may come up to the tensile strength of the material. In order to test the material's susceptibility to temperature-induced top-down fatigue cracking in the laboratory, the Uniaxial Cyclic Tensile Stress Test (UCTST) was established and recently introduced in European Standards (prEN 12697-46). In this test, a prismatic shaped HMA beam is subjected to a constant tensile load (representing the temperature-induced stress) which is superposed by a sinusoidal tensile load (representing the traffic load). This loading situation results in a visco-elastic strain response on the one hand, and in an accumulation of visco-plastic strain on the other. Different failure modes are observed in UCTST. In this paper, the failure modes occurring in UCTST, i.e. cracking of the specimen, stiffness decrease, and creep, are discussed based on the results from laboratory testing of nine different HMA and on variation of loading conditions.

The global increase of road infrastructure and its impact on the environment requires serious attention to develop sustainable and environmentally friendly road materials. One group of those materials is produced by using bitumen emulsion. However, there are still scientific and technical obstacles standing against its regular application. The bitumen emulsion formulation process and compositional optimization are subjected to a high number of degrees of freedom. Consequently, obtaining the desired product is mostly based on a series of random and tedious trials because of the enormous number of tests to be carried out. The current review of the physicochemical formulation may indeed be extensively used in helping to reduce the number of unnecessary experimentations as well as discuss the vital aspects in the bitumen emulsion production process. Among these, emulsion stability, viscosity, droplet size (and distribution), bitumen emulsion chemistry, the function of the emulsion components, surfactant type, acids or alkalis, and additives are all discussed and used to define the emulsion's physical properties and reactivity. Besides, current developments in the mechanisms of breaking and setting processes are also summarized. It is discussed how emulsions are graded based on their reactivity, particle charge, and physical features. Two emulsification techniques are outlined namely the colloid mill method and the High Internal Phase Ratio (HIPR) method. Furthermore, some emulsion formulation tools/theories were identified and are explained. In that way, optimized formulations can be used to offer a practical guide for bitumen emulsion manufacturers when trying to formulate a well-defined bitumen emulsion for its use in pavement infrastructure rather than simply to meet standard specifications. This review paper aims to enable the ultimate potential of the bitumen emulsion in the field of cold recycling technology by further following up the research progress of bitumen emulsion manufacturing, therefore, this paper reviews and discusses the literature available up to now on this topic, in road engineering and emulsion chemistry.

This study examines the rejuvenation mechanisms in bituminous RAP mastics using Fourier transform infrared (FTIR) spectroscopy and multivariate discriminant analysis. The chemical interactions between RAP binders, virgin bitumen, warm mix additives, and two commercial rejuvenators (RJs) were evaluated to determine their effectiveness in restoring aged binders on the chemical level. A hybrid approach combining partial least squares regression and linear discriminant analysis (PLSR–LDA) was applied to extract latent variables, classify samples, and identify critical wavenumbers associated with rejuvenation. The findings indicate that Sylvaroad mitigates oxidation effects, particularly around ~ 1770–1725 cm ⁻¹ , while Storflux primarily influences methyl bending near 1370–1360 cm ⁻¹ . Despite these effects, irreversible oxidative aging remains evident in the 1300–1160 cm ⁻¹ range, linked to oxygen-containing compounds, suggesting that complete restoration of binder chemical alteration is unattainable. Additionally, mineral composition markers, particularly in the 489–446 cm ⁻¹ and 590–555 cm ⁻¹ ranges, persist as key indicators for distinguishing varying RAP contents after rejuvenation.