A literature review of the five main theories describing the interaction mechanisms in the bitumen/aggregate system was conducted: theory of weak boundary layers, mechanical theory, electrostatic theory, chemical bonding theory, and thermodynamic theory (adsorption theory). The adhesion assessment methods in the bitumen/aggregate system are described, which can be divided into three main groups: determination of adhesion forces for bitumen with different materials, determination of bitumen resistance to the exfoliating action of water with different materials, and determination of adhesion as a fundamental value (contact angle measurements, interfacial fracture energy, adsorption capacity and others). It is proposed to evaluate the quality of adhesive interaction in the bitumen/aggregate system in two stages. The authors recommend using the adhesion determination methods for these two stages from the second group of methods the determination of bitumen resistance to the exfoliating action of water with different materials. In the first stage, the adhesion in the bitumen/aggregate system is determined by an accelerated technique in which the used bitumen binder and mineral material are considered as test materials. After the first stage, there are positive results in the second tests on compacted mixtures (indirect tensile strength test, Modified Lottman indirect tension test, immersion-compression test, and Hamburg wheel tracking test).

With the continuing growth of waste sulfur production from the petroleum industry processes, its utilization for the production of useful, low-cost, and environmentally beneficial materials is of primary interest. Elemental sulfur has a significant and established history in the modification of bitumen binders, while the sulfur-containing high-molecular compounds are limited in this field. Herein, we report a novel possibility to utilize the sulfur/organic copolymers obtained via the inverse vulcanization process as modifiers for bitumen binders. Synthesis and thermal characterization (TGA-DSC) of polysulfides derived from elemental sulfur (S₈) and unsaturated organic species (dicyclopentadiene, styrene, and limonene) have been carried out. The performance of modified bitumen binders has been studied by several mechanical measurements (softening point, ductility, penetration at 25 °C, frass breaking point, adhesion to glass and gravel) and compared to the unmodified bitumen from the perspective of normalized requirements concerning polymer-modified bitumen. The interaction of bitumen binder with sulfur/organic modifier has been studied by means of FTIR spectroscopy and DSC measurements. The impact of the modification on the performance properties of bitumen has been demonstrated. The bitumen binders modified with sulfur/organic copolymers are in general less sensitive to higher temperatures (higher softening point up to 7 °C), more resistant to permanent deformations (lower penetration depth), and more resistant to aging processes without intrusive deterioration of parameters at lower temperatures. What is more, the modification resulted in significantly higher adhesion of bitumen binders to both glass (from 25% up to 87%) and gravel surfaces in combination with a lower tendency to form permanent deformations (more elastic behavior of the modified materials).

The process of chemical modification of tar and oxidized bitumen with formalin (a 37% aqueous solution of formaldehyde) in a hermetic container was investigated and the effectiveness of the proposed process was proven. It is shown that the most effective raw material for the process is tar, not oxidized bitumen. The expediency and impact of using different types of solvents (toluene, p-xylene and petroleum solvent, and n-octane) in the modification process were studied. It was established that the solvent should be used in the modification of oxidized bitumens, not tars. The low efficiency of the process of tar modification with formaldehyde without the use of a catalyst was proven, and it was shown that the most active catalyst in the process is sulfuric acid. The influence and optimal values of the main factors controlling the process of chemical modification of tar with formaldehyde were established, namely temperature, duration, and content of the modifier—formaldehyde. On the basis of the found regularities and optimal conditions of the modification process, samples of binding materials (of different brands) with different operational characteristics were obtained, and their comprehensive research was carried out. With the help of FTIR spectroscopy, the chemical interaction of tar with formaldehyde in the presence of an acid catalyst was confirmed. The design of the compositions of asphalt concrete mixtures using formaldehyde-modified tar was carried out, from which cylindrical samples of stone mastic asphalt (SMA-15 brand) were obtained, which were tested according to the main indicators: average density, water-saturation, compression strength at 20 and 50 °C, compression strength after water-saturation (MPa) at 50 °C.