Bitumen Film Research Articles

Effects and Mechanism of Oil-Absorbing Organogel as a Novel Modifier on the Performance of Bitumen Mixture

The unstable thermochemical properties of conventional polymer bitumen modifiers lead to a gradual invalid of effects on the bitumen performance in real service environments. As a novel modifier, the oil-absorbing organogel has been shown to enhance the properties of bitumen due to its superior stability and ability to absorb bitumen components. However, its effects and mechanisms on the performance of bitumen mixtures remain unclear. In this study, the oil-absorbing organogel polystyrene-stearyl methacrylate (P(S-SMAL)) was synthesized and used to prepare modified bitumens and mixtures. Rheological tests on bitumen and mechanical tests on the bitumen mixture indicated that P(S-SMAL) could enhance the high-temperature properties of bitumen and the mechanical properties of the bitumen mixture, while maintaining the low-temperature performance of both. With 5% P(S-SMAL) added, the modified bitumen deformation resistance improved by 22.25%, permanent deformation reduced by 47.65%, and the anti-rutting properties of the modified bitumen mixture improved by 111.22%. The enhanced performance of the bitumen mixture is attributed to the improved properties of P(S-SMAL) modified bitumen, resulting from the "supporting" and "hardening" effects of P(S-SMAL), as well as the hydrophobic nature of the modified bitumen film within the aggregates, driven by the lipophilic characteristics of P(S-SMAL).

Experimental study of asphalt mixtures with recycled resources: Influence of electric arc furnace slag aggregate roughness and bitumen film thickness on fatigue performance

Electric arc furnace slag (EAFS) is a viable alternative in asphalt mixtures due to its favourable mechanical properties. This study examines the impact of EAFS content and bitumen film thickness (TF) on the fatigue performance of asphalt mixtures. Mixtures with varying levels of EAFS replacement were designed, and their mechanical properties were evaluated through indirect tensile strength and stiffness tests, followed by fatigue tests using the four-point bending method and EBADE (Strain Sweep Test). The results indicated that mixtures with EAFS exhibited increased stiffness, but fatigue performance decreased at high strain levels. At low strain levels, EAFS mixtures performed similarly or better than the control. HMA_GL had the highest TF (13.97 μm), followed by HMA_GS (13.60 μm), HMA_SL (12.66 μm), and HMA_SS (11.77 μm), showing that as the EAFS content increases, the TF decreases. This finding was verified through Digital Image Analysis. This decrease in TF is due to the high porosity and roughness of the EAFS, which in turn reduces the effective bitumen (Pbe) in the mixture. HMA_SL*, with a TF equal to the control, demonstrated a 22 % improvement in fatigue performance compared to HMA_SL. In the EBADE tests, HMA_GL achieved 44.69 MJ/m3 of dissipated energy, HMA_GS 31.55 MJ/m3, HMA_SL 34.45 MJ/m3, and HMA_SS 35.54 MJ/m3. The improved HMA_SL* recorded 42.15 MJ/m3, nearly matching the control. EBADE results confirmed that higher EAFS content increased initial stiffness, but the complex modulus (|E*|) decreased more rapidly as deformation increased. These results are consistent with the stiffness tests. These findings suggest that EAFS can successfully replace natural aggregates in asphalt mixtures, with a moderate increase in bitumen content recommended to improve fatigue performance.

Evaluation framework for bitumen-aggregate interfacial adhesion incorporating pull-off test and fluorescence tracing method

The interfacial adhesion between bitumen and aggregate is crucial to maintain the mechanical performance of asphalt pavement. Numerous indicators characterize the bonding ability of bitumen to aggregate; however, indicators based on limited conditions are used infrequently to effectively evaluate the interfacial adhesion between bitumen and aggregate. This study introduces a method to assess adhesion and moisture damage resistance at the bitumen-aggregate interface by combining the pull-off test with the fluorescence tracing method. The improved pull-off test considers different bitumen film thicknesses, ambient temperatures, material combinations, and moisture damage conditions, and the fluorescence tracing method and surface energy parameters are utilized to precisely detect the extent of bitumen adherence to the aggregate. The findings of this study are summarized as follows. (1) The bitumen stripping ratio characterizes the influence of ambient temperature and bitumen film thickness, and the pull-off strength/work quantifies the influence of ambient temperature and material combination. (2) The indicators derived from surface free energy theory exhibit lower sensitivity to material combinations compared with the pull-off performance indicators, with a coefficient of variation for both adhesion and stripping work of approximately 6 % compared to 14.29 %–70.13 % for the pull-off performance indicators. (3) The pull-off strength indicator dominates the pull-off performance evaluation, with the bitumen stripping ratio necessary at 0°C and pull-off work significant at 40°C to evaluate adhesive properties. In addition, the bitumen stripping ratio increment should be considered alongside pull-off strength loss ratio when estimating anti-moisture damage performance. (4) The fluorescence tracing method shows great potential in terms of enhancing the accuracy of bitumen stripping ratio detection in the pull-off test, with bitumen stripping ratio discrepancies at 0°C–40°C ranging from 0.98 % to 7.16 % for 70#-Limestone and 2.10–9.21 % for 70#-Granite. The methodology presented in this study represents a promising framework to determine the interfacial adhesive properties of asphalt mixtures with high accuracy.

Experimental and predictive study of self-compacting concrete containing reclaimed asphalt pavement

This work focuses on the reuse of reclaimed asphalt pavement (RAP) in the production of self-compacting concrete (SCC) for usage in the construction of rigid pavements. The article first describes an experimental study where five SCC mixtures incorporating 0%, 20%, 40%, 60% and 100% volumetric substitutions of natural aggregates by RAP were formulated. Several characterisation tests in the fresh and hardened states were then performed. The results of all performed tests showed that RAP has a slight negative effect on SCC performance in the fresh state. The most significant reduction observed does not exceed 18% for slump-flow and 10% for L-shaped box values when total substitution is applied. Furthermore, the mechanical properties noticeably decrease with an increase in RAP content, with reductions of up to 37% in 28-d compressive strength and 23% in 28-d indirect tensile (IDT) strength observed in the case of full replacement. However, it is possible to formulate SCC mixtures even with 100% RAP substitutions and meet specifications for rigid pavement construction. In addition, modelling of the various mechanical characteristics made it possible to find out the reason behind the reduction in these properties with RAP content. In fact, the thin bitumen film around RAP particles weakens their surface adhesion with the hydrated cement paste. With the intrinsic RAP properties found, the hardened-state characteristics of any other SCC mixture incorporating RAP could be predicted.

Influence of the Chemical Composition of Kulantau Vermiculite on the Structure of Modified Bitumen Compositions

The article presents the chemical composition of vermiculite ores from the Kulantau deposits and the atomic structure of vermiculite during dehydration, in 1-, 2- and 3-layer hydrated states. It has been shown that vermiculites from deposits in the Turkestan region have significant differences in mineralogical composition. Rational ways of using Kulantau vermiculite as an innovative modifying additive in bitumen compositions are considered, which are intended to improve the asphalt concrete mixture during its preparation. A slight increase in structuring resins is a result of the elevated content of high-molecular-weight asphaltenes in the modified bitumen, as indicated by the analysis of the provided spectra. In turn, the systematization or structuring of bitumen leads to an increase in the mixture density, accompanied by a simultaneous rise in internal friction coefficients, and resistance to loads (shear and impact), as well as an enhancement in compressive strength. The influence of the chemical composition of Kulantau vermiculite on the structure of bitumen compositions is characterized by high adsorption capacity and effectively absorbs products resulting from the oxidation of hydrocarbons. Vermiculite is characterized by high efficiency in the activation phase, large pore volume, and selectivity. The alteration of the bitumen’s group composition due to the selective diffusion of oils, as well as resins in the material, occurs as a result of the interaction between bitumen and a material characterized by a fine-porous structure and high specific surface area. This process modifies the properties of bituminous layers on the surface of particles and leads to the formation of robust bitumen films appearing on the grain surfaces. Thus, enhancing the longevity of coatings, improving the quality of binding bitumen, and reducing asphalt concrete coverings necessitate the use of vermiculite in creating modified bituminous compositions.

Using surface free energy and mechanical methods to investigate the effect of aging on the fatigue cracking potential of UHMWPE-modified HMA

Aging due to environmental conditions significantly affects the occurrence of fatigue cracking in hot-mix asphalt (HMA). Previous analyses showed that aging reduces mastic resistance and bitumen-aggregate adhesion, but these experiments were usually performed on HMA samples, and failure mechanisms were not reflected in the results. Accordingly, via the surface free energy (SFE) theory, this study examined the impact of aging on the fatigue cracking mechanism of HMA. Dynamic methods, including indirect tensile fatigue test (ITFT) and Pull-Off tensile strength (POTS), were applied to HMA samples at 5 and 20 ˚C to study the association between the results of SFE tests. Two performance-graded bitumens (PG 58–22 and PG 64–16), two aggregates with different mineralogical properties (limestone and siliceous), and a polymeric additive (ultra-high-molecular-weight polyethylene-UHMWPE) as a bitumen modifier were also used. Based on the results, aging decreased and increased the polar (28.6%) and non-polar (15.14%) properties of bitumens, respectively. A decline in polar properties lowered the bitumen-aggregate adhesion (8.11%), which was generally because of polar bonds. The rise in cohesion free energy (CFE) by up to 9.5% and non-polar properties due to aging decreased the failure probability in the bitumen film of the aged specimens. UHMWPE improved the non-polar properties of the asphalt (by up to 15.09%), providing greater resistance against aging and reduced adhesion with mineral aggregates. According to the POTS test results at the state of cohesive failure, aging enhanced the POTS of cohesion, especially in UHMWPE-modified bitumen-aggregate by up to 12.12%. POTS in the state of cohesive failure was independent of adhesion free energy (AFE), yet CFE influenced POTS at the state of adhesive failure. Based on the fatigue life of HMA, even though aging increased the CFE and stiffness of HMA, the decline in the AFE parameters and flexibility reduced the fatigue life of the aged HMA in comparison to similar non-aged specimens (by up to 5.17%). The polymer additive significantly improved the resistance of asphalt mixtures to cohesion (by up to 23.16%), adhesion (by up to 16.78%), and fatigue life (by up to 12.8%). Additionally, in aged samples, there was a noticeable reduction in the parameters of cohesion, adhesion, and fatigue life in the modified samples compared to the base samples.

A molecular dynamics analysis of the influence of iron corrosion products on the healing process of bitumen

Corrosion of iron materials in the asphalt concrete pavement occurs commonly when the bitumen film peels off, and the generation of corrosion products would affect the healing performance of bitumen. To identify the affection, this research focuses on the influence of iron corrosion products on the healing process of bitumen by molecular dynamics simulation. Firstly, bitumen model and iron corrosion products model were built. Then the healing systems of sandwich structure were constructed, and the simulated temperature were applied to reach equilibrium in the healing process with NVT ensemble (constant number of atoms, volume, and temperature). Dynamic movements of bitumen were characterized by appearance qualitatively. Healing rate of crack and healing rate of bitumen aggregation were held to evaluate the healing effect. Diffusion behaviors, internal force of motivation and interaction effect were also analyzed. The results indicate the duplicity of iron corrosion products in the healing process including the ease for bitumen climbing and the obstruction of bitumen movement. The comprehensive healing index demonstrated that iron corrosion products would reduce the healing degree, which was mainly caused by the obstruction effect and large internal stress generated by severe aggregation of bitumen in the limited space. From the perspective of crack closure and bitumen aggregation degree in the corrosion area, FeO healing systems were healed best, followed by Fe3O4, Fe2O3 and FeOOH. Furthermore, diffusion period of bitumen molecules on the surface of iron corrosion products during the healing process should be regarded as the important period affecting healing.

Comparative Analysis of Asphalt Forming Processes Based on Finely Dispersed Expanded Clay Powders

The features of the structure formation of an asphalt binder modified with a highly dispersed expanded clay powder are investigated. The viscosity of the modified asphalt binder and the formation of an adsorption layer of bitumen on the surface of the particles of the mineral component at various degrees of filling in the temperature range of 100–180oC have been studied. The effect of the impact of expanded clay powder on the adsorption activity of bitumen, the adhesive strength of bitumen with a mineral filler and on the adhesion of an asphalt binder with a mineral filler is analyzed. It was revealed that the interaction of bitumen with highly dispersed expanded clay powder significantly increases the viscosity of the asphalt binder and increases the thickness of the bitumen film on the surface of mineral particles at all process temperatures compared with standard limestone mineral powder, which is determined by the processes of selective diffusion of low-molecular hydrocarbons into the particles of expanded clay powder occurring when combined with the binder. Modification of the asphalt binder with expanded clay powder significantly increases its adsorption activity and adhesion of bitumen to mineral aggregate and adhesive strength at the interface of the «filler–bitumen» phases. This is due not only to physical interaction, but also to the presence of an increased number of active surface adsorption centers of Lewis and Brensted on the surface of expanded clay particles, which indicates the formation of chemical bonds.

Bitumen emulsion effect on properties of asphalt-concrete mix for non-rigid road pavements (Tambov) .

During major repairs of non-rigid road surfaces and reconstruction of automobile roads, it is necessary to remove old coating with road cutters. During cold milling of the old coating, the material acquires the form of granules with the surface covered with a bitumen film. Over time, the bitumen film loses its properties, and to reuse the material, it is necessary to restore the binder properties. The introduction of the bitumen emulsion in the composition of asphalt-concrete mix, allows to restore the binder properties affecting not only strength properties of the asphalt-concrete mix, but also deformability and stiffness of the mixture layer under the compressive load.Purpose: Evaluation of the influence of the binder content on deformability and stiffness of the asphalt-concrete mix.Methodology: Asphalt granulate fractions are used in proportions 8 to 16 and 18 to 36 mm with a residual bitumen content of 2%. The bitumen emulsion EBK-2 is used as a binder. The ultimate strength of the asphalt layer is measured according to GOST 12801. Deformation of the mixture layer is measured on a TP-1-1500 hydraulic press.Research findings: The bitumen emulsion effect is shown for deformation and stiffness of the asphalt-concrete mix for the pavement construction.Value: It is shown that the bitumen emulsion in regeneration of asphalt granulate affects deformability and stiffness of the layer subjected to compaction load. The development of deformation and stiffness of the mixture layer under the load with different binder content, particles size, and layer thickness are established. Analytical dependences are suggested for deformation and stiffness of the loaded layer, its thickness during paving, and percentage of bitumen emulsion in the mixture.

UV-induced gradient aging of bitumen films: A comprehensive study

The aging of bitumen materials under ultraviolet (UV) radiation is a highly intricate process involving volatilization of components and multiple photochemical reactions. To gain a comprehensive understanding of the mechanism and progression of UV aging in bitumen films within bitumen mixtures, this study investigates the formation and evolution of UV aging gradients in bitumen films from various perspectives, including morphology, composition, macro-, and micro-mechanical aspects. Initially, specific bitumen film specimens were subjected to aging, and a protocol for sample handing and testing was developed. Optical microscopy images, functional group indices, and component contents of the bitumen films were then measured and calculated to track the UV aging process from the surface to the interior. Additionally, profiling micro-mechanical tests and layer-by-layer dynamic mechanical tests were conducted to characterize the variations in mechanical properties induced by UV aging gradients within the bitumen films. The results indicate that UV radiation causes significant volatilization of light components on the film surface, resulting in wrinkling. Concurrently, photochromic reactions take place in both bitumen macromolecules (asphaltenes and resins) and small molecules (saturates and aromatic), while molecular photodegradation may also occur. Fluorescence imaging, infrared spectroscopy analysis, and component determination reveal that the degree of UV aging in the bitumen films increases with radiation time and gradually propagates towards the interior. C-S bonds are more sensitive to UV radiation than C = C bonds, leading to oxidation and the formation of sulfoxide groups. Due to the adsorption of light components by aggregates, the modulus values at the surface of aged bitumen films and the aggregate interface are higher, while the intermediate region exhibits lower values. Rheological indicators demonstrate that UV aging, to a certain extent, results in the decomposition of bitumen molecules, leading to a decrease in complex shear modulus and an increase in phase angle. This work significantly enhances our understanding of the mechanism of UV aging in bitumen films and holds important implications for the design and development of UV-blocking materials.

Interfacial bonding property and microscopic damage mechanism of bitumen-aggregate in salt-freeze-thawing environment

Deicing salt or snow-melting agent has a corrosive effect on the pavement, which reduces the durability of asphalt pavement. The interfacial bonding properties of bitumen-aggregate is one of the main factors affecting the durability of asphalt mixture. To evaluate the interfacial bonding properties of bitumen-aggregate and reveal the damage mechanism under salt-freeze-thaw coupling effect, the bitumen-aggregate samples with the same film thickness were formed by controlling the applied load. The corrosion of deicing salt on bitumen-aggregate and bitumen film samples was simulated by freeze-thaw cycles in 1 %, 3 % and 5 % NaCl solution. The pull-off test of SBS modified bitumen-aggregate after salt-freeze-thaw cycles was conducted. The Fourier transform infrared spectrometer (FTIR) test was carried out to qualitatively and quantitatively analyze the impact of salt-freeze-thaw coupling effect on bitumen functional groups. The surface morphology of bitumen samples treated in salt-freeze-thawing environment was also scanned by atomic force microscopy (AFM) in tapping mode. The results illustrate that the pull-off strength of bitumen-aggregate decreases sharply first and then the decrease rate slows down with the rise of salt-freeze-thaw coupling cycles. The carbonyl index and sulfoxide index of SBS modified bitumen increases, and the butadiene index decreases after freeze-thaw cycles in NaCl solution. The environment of salt erosion and freeze-thaw cycle accelerates the deterioration of SBS modifier and reduces the distinction of various phases in bitumen binder. Then the Ra and Rq of SBS modified bitumen decreases significantly in salt-freeze-thawing environment. The decrease of butadiene index and root mean square roughness leads to the weakening of adsorption between SBS modified bitumen and aggregate, which is the main reason for the damage of interfacial bonding performance of bitumen-aggregate. In summary, the salt-freeze-thawing environment damages the bonding performance of bitumen-aggregate. The damage law and deterioration mechanism of bonding properties of bitumen-aggregate presented in this paper provides some references for the optimal design of asphalt mixture in salt-freeze-thawing environment.

Interpretation of stripping at the bitumen–aggregate interface based on fluorescence tracing method

Asphalt pavement field performance largely depends on the stripping resistance at the bitumen–aggregate interface. However, the conventional stripping resistance evaluation method is unsuitable for direct and precise quantification of the retained bitumen film area on the aggregate surface that designates the stripping resistance between bitumen and aggregate phases under the action of vehicle wheels or moisture damage. This study proposed a novel fluorescence tracing method to quantify the exact area of aggregate coating loss in accordance with the bituminous-coated aggregate image processing technique. The fluorescence tracing image acquisition and analysis system for precisely calculating the bitumen stripping ratio of the bituminous-coated aggregate were established after the bitumen stripping test. The thresholding manner of the two-mode threshold algorithm was devised to segment the fluorescence-traced bituminous-coated aggregate image with high quality. The results demonstrated that the appropriate threshold value for segmenting the fluorescence-traced image mainly falls in the range of 60–70 for limestone, 90–110 for basalt, and 100–110 for both granites; the ability of aggregates based on their chemisorption capacity with bitumen is in the order of limestone, basalt, and granite; the fluorescence tracing method eliminated nearly 92.3% of the undesirable reflection on bitumen phase; the detected bitumen stripping ratio, raised by 65.87% on average and by 37.82% in the median value in contrast to the conventional visual detection manner. This research introduces a practical framework from an engineering perspective for visually quantifying the interpretation of the adhesive bond at the bitumen-aggregate interface with reasonable accuracy and confidence.

Multiscale modelling of bitumen-aggregate interfaces from molecular debonding to pull-off strength

Cohesive and adhesive debonding and their percentages determine an asphalt mixture's bond energy which controls the material damage process. This study aims to establish the link of the probability of cohesive debonding at the nanoscale and the percentage of cohesive cracking at the microscale. Using this link, this study also investigates the influence of external conditions on the debonding behavior of bitumen-aggregate interfaces, and proposes a modified bond theory to predict the tensile strength of the interfaces. The debonding process was investigated numerically using coarse-grained molecular dynamics (CGMD) simulations at nanoscale and experimentally by a novel pull-off test (POT) at microscale. Results show that the debonding behaviors show consistency between the simulations and the experiments under different conditions. Cohesive fracture increases with bitumen film thickness and reaches a plateau (∼80% and 100% at the nanoscale and microscale, respectively); They also increase with temperatures (rise from 72% to 81% at nanoscale and from 73% to 100% at microscale, respectively) while show no relationship with loading rates. The pull-off strength decreases with bitumen film thickness and temperatures, and increases with loading rates. The modified Kendall's model can effectively predict the debonding behavior and the pull-off strength at different conditions.

Effect of Cement and Bitumen Emulsion on the Drying and Film Formation of Bitumen Emulsion Paste

To obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, the effect of cement content, cement type, and emulsion type on the drying and film formation of bitumen emulsion paste was studied. The drying and film formation mechanism of emulsion was employed to study the drying curve of bitumen emulsion paste. Results indicate that the drying and film formation process of bitumen emulsion paste can be divided into three stages. The solid volume fraction of the beginning of the final stage (ϕ2) and the maximum particle volume fraction (ϕm) are proposed to evaluate the drying and film formation quality of bitumen emulsion paste. Higher values of ϕ2 and ϕm indicate a denser particle packing state and lower residual water content of the final stage, which are beneficial to the drying and film formation quality of bitumen emulsion paste. The ϕ2 and ϕm of bitumen emulsion paste differ slightly with the increasing content of ordinary portland cement. However, these quantitative indexes vary significantly with changing bitumen emulsions with different values of ϕ2 and ϕm. Compared with ordinary portland cement, sulfoaluminate cement can lead to a noticeable decrease in ϕ2 and ϕm; thus, its addition is harmful to the film structure of bitumen emulsion paste. Overall, to obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, a bitumen emulsion with good drying and film formation quality is recommended.

INVESTIGATION OF THE WETTING EFFECT OF SURFACTANTS OF VARIOUS NATURE IN THE BITUMEN COMPOSITION

Asphalt concrete coverings are short-lived and are destroyed under the influence of external factors. The insufficient degree of adhesion at the interface between the bituminous binder and the hard surface of the mineral material causes a low hydrophobicity of asphalt concrete coatings, which is the main cause of damage and premature wear of the roadway. Optimization of the bitumen composition by introducing a variety of modifying agents can intensify the processes of wetting the hard surface with bitumen and increase the hydrophobicity of the surface films formed by it. The purpose is to establish the influence of various modifiers on the processes of wetting the surface of crushed stone with a bituminous composition, as well as to study the regularities of the influence of modifiers on the hydrophobicity of bituminous films. The methodology of this work included experimental determination of the wetting contact angle θ of a solid surface by the lying drop method at T=298 K. Results. Increasing the AC-2K content in bitumen from 0 to 1% reduced the contact wetting angle by 11.31° (relative to the base version without the modifier) to 114.35°. The AC-2 modifier contributes less to improving the wettability of the surface of the basic crushed stone with bitumen; with Cm=1%, the contact wetting angle is reduced to 118.68°. When modifying bitumen, PPS recorded a significantly smaller decrease in wetting contact angle at a higher concentration (Cm=2%) – by 2.4° (from 125.66° to 123.26°). The amino derivative AC-2K (Cm=1%) has the greatest water-repellent effect among the studied modifiers, increasing the wetting edge angle to 99.07°. Conclusion. The water-repellent properties of bituminous compositions are enhanced (Δθ=4.02°) at a narrow range of concentrations of the modifier AC-2K (with Сm=1%). The ultrasonic cavitation-derived AC-2K can be recommended for use in asphalt concrete coatings as an adhesive additive that provides a good wetting effect of bitumen in relation to the surface of the mineral filler while also increasing the hydrophobicity of bitumen films.

Dependence of carbonyl, sulphoxide and hydroxyl functional group formation on oxygen concentration during the oxidation of roading bitumen

The aim of this study was to provide insights into the chemical mechanism by which, over the course of its lifetime, bitumen in road surfacings reacts with oxygen in the atmosphere. Oxidation was measured at 50 °C (a realistic in-service temperature) to determine the effect of oxygen concentration on the formation of key oxidation products. Experiments were conducted on thin films of bitumen (<0.03 mm) so that the effect of oxygen diffusion on the rate was negligible. The films were oxidised under air (oxygen partial pressure 22.23 kPa) and pure oxygen (101.33 kPa).The rate of formation of carbonyl, sulphoxide and hydroxyl group containing reaction products was measured by infrared spectroscopy. The reactions were carried out over a time-frame sufficient to cover both the “fast” and “slow” (linear) reaction rate regions and the results discussed in terms of the reaction mechanism. It was observed that the rate of formation of all three functional groups was dependent on oxygen concentration. The apparent reaction order with respect to oxygen concentration was about 0.5 in each case and did not change significantly as the reaction moved from the fast and into the linear rate regions. The non-zero rate dependence observed despite the relatively high oxygen partial pressures used, is significant in that it is inconsistent with a conventional free radical autoxidation chain mechanism and suggests a parallel oxidation process is occurring.

STUDY OF THE INFLUENCE OF MODIFIERS ON THE PROCESSES OF WETTING MINERAL FILLERS AND HYDROPHOBICITY OF BITUMEN FILMS

As you know, the quality of asphalt pavement often does not meet the stated standards. The low degree of adhesion between bitumen and mineral material is primarily due to the insufficient ability of bitumen to effectively wet the surface of crushed stone, especially of an acidic nature. The aim of the work is to establish the influence of various modifiers on the wetting processes of bitumen compositions. The methods of the work included the study of the wetting processes of mineral fillers of various nature depending on the quantitative polymer content in bitumen, as well as the study of the regularities of the effect of modifiers on the hydrophobicity of bitumen films. The wetting angle θof the surface was experimentally determined by the lying drop method. Results and discussion: as follows from the analysis of the data obtained, the introduction of AG-4I most effectively contributes to the reduction of the surface tension σlgat the interface of the phases "bitumen composition –gray crushed stone". This is evidenced by the maximum wetting ability of the composition. Conclusion: it was found that of the two polymer modifiers, the spent sealing liquid AG-4I has the maximum effect on the wetting processes of mineral fillers and the hydrophobicity of bitumen films. A narrow range of modifier concentrations (Cmodif= 0.5%) was revealed, at which the water-repellent properties of bitumen compositions are enhanced. A hydrophobic effect comparable to AG-4I provides the introduction of 0.25% calcium chloride into the bitumen composition.

Evaluation of Moisture Sensitivity Performance of Stone Mastic Asphalt Mixes with Additional Filler: A Laboratory Comparison of Dry and Wet Mixing Methods

Gap-graded mixtures are one of the areas of improving the permanent deformation strength of hot-mixed asphalt mixtures. Additional filler materials can be needed due to the high bitumen amount and the less fine aggregate amount in the mixture. In this study, the effects of filler additives on moisture susceptibility of the gap-graded hot-mixed asphalt mixtures and mixing methods are investigated. Filler additives such as class C and class F fly ashes and hydrated lime are used 0.5 %, 1.0 %, 2.0 %, and 4 % of the total weight of mixture instead of mineral filler. Design mixtures are prepared according to the Turkish Highway Technical Specifications (THTS). To determine the effect of mixing methods, dry and wet (slurry) methods are used to mix the filler materials. Modified Lottman method (AASHTO T283) are used to determine the moisture susceptibility. An indirect tensile strength test is the measurement of bitumen film thickness which is also conducted. Test results showed that class C fly ash is significantly improved the moisture susceptibility of mixtures. While the slurry method does not give the expected improvement on class C fly ash added mixtures, it shows a positive effect on class F fly ash and hydrated lime added mixtures.

Research on Design and Performance of Self-Compacting Cement Emulsified Bitumen Mixture (CEBM).

To meet the needs of the road industry for maintenance operations, a new cement emulsified bitumen mixture (CEBM) with early-strength, self-compacting, and room-temperature construction characteristics was designed. The strength formation mechanism of CEBM was revealed with a scanning electron microscope (SEM) and the surface free energy (SFE) theory. The mechanical properties and road performance of the CEBM were investigated extensively. The results show that before the demulsification of emulsified bitumen, the SFE of the bitumen–aggregate–water three-phase system was reduced due to the replacement of the bitumen–aggregate interface with water. The adhesion work between the emulsified bitumen and the aggregate is negative, which means the adhesion between the emulsified bitumen and the aggregate will not occur spontaneously due to the existence of water. The liquid emulsified bitumen improves the workability of the mixture and ensures that the mixture can be evenly mixed and self-compacted. After demulsification, the work of adhesion between the residual bitumen and the aggregate is positive, which means residual bitumen and aggregate can bond spontaneously. In addition, the hydration products of cement and aggregate form a skeleton, and the emulsified bitumen film wraps and bonds the cement and aggregate together, creating strength. The emulsified bitumen, cement content, and curing conditions have significant effects on the stability of CEBM. The recommended dosage of emulsified bitumen and cement is 8% and 8–10%, respectively. This material integrates the hardening effect of cement and the viscoelastic performance of bitumen and has good workability, mechanical properties, and road performance. Therefore, the CEBM is technically feasible for application to bitumen pavement.

Quantifying oxygen diffusion in bitumen films using molecular dynamics simulations

Bitumen in asphalt pavements reacts slowly with atmospheric oxygen, resulting in oxidative ageing. This oxidative reaction is strongly dependent on the physical diffusion of the oxygen into the bitumen. This study aims to use molecular dynamics (MD) simulation to investigate the oxygen diffusion into the bitumen film and analyse the effects of anti-ageing compounds (AACs) on the oxygen diffusion. The MD diffusion simulations using a Polymer Consistent Force Field (PCFF) were conducted on a bitumen-air bi-layer model at different temperatures. Fick’s second law was used to calculate the diffusion coefficient of the oxygen in the bitumen film. It is found that the oxygen diffusion coefficients ranged from 6.67 × 10−10 to 7.45 × 10−11 m2/s for the unmodified and AAC-modified bitumens at the simulating temperatures of 25, 50 and 100 °C. Irganox acid and DLTDP (Dilauryl thiodipropionate):furfural showed two different anti-aging mechanisms, i.e., reducing the oxygen physical diffusion and controlling the chemical oxidative reaction. Reducing the oxygen diffusivity by constructing a network in the bitumen to retard oxygen diffusion and increase the transport path is an efficient way to slow down the bitumen aging without the antioxidant consumption. This work proposed a MD-based computational approach, contributing to 1) determination of the oxygen diffusion coefficient of the existing bitumen that is extremely challenging for the experimental measurement and 2) instruction of developing new antioxidant.