Xiaobing Chen

A steel slag porous asphalt (SSPA) mixture, as the surfacing layer of permeable asphalt pavements, not only ensures the pavement surface drainage and noise reduction functions, but also improves the comprehensive utilization of steel slag resources and the inherent protection of the ecological environment. However, compared with ordinary asphalt mixtures, SSPA is more susceptible to water damage, such as scouring and frost swelling caused by external rainwater intrusion, resulting in the deterioration of the pavement performance. Therefore, it is of good practical imperative to study the water stability and moisture damage mechanism of SSPAs. In this study, the water stability of SSPA, that was subjected to a series of time–temperature H₂O-immersion schemes, was investigated using the pull-out and H₂O-immersion Marshall tests, whilst the microscopic mechanism of moisture damage was studied using the scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD) tests. The corresponding results showed that: (a) with the increase in the H₂O immersion time, the water stability of SSPA first increased and then decreased; and (b) the water stability of SSPA was strong under medium-temperature H₂O-immersion or short-term high-temperature H₂O-immersion. SEM, on the other hand, showed that the transition zone spacing was closely related to the chemical adhesion mechanism between the asphalt and steel slag aggregate. Additionally, the FTIR analysis further showed that the steel slag asphalt mastic spectra had new absorption peaks at 3200~3750 cm⁻¹, inherently indicating the existence of chemical bonding between the asphalt and steel slag, with the XRD results showing that CaSO₄·2H₂O had a beneficial effect on the water stability of SSPA.

To explore the applicability of steel slag porous asphalt mixture, the interaction capability and microscopic interfacial mechanism between asphalt-binder and steel slag aggregate-filler were investigated in this laboratory study. These objectives were accomplished by comparing and analyzing the differences between steel slag and basalt aggregates in interacting with the asphalt-binder. The study methodology involved preparing basalt and steel slag asphalt mortar to evaluate the penetration, ductility, softening point, toughness, and tenacity. Thereafter, the interaction capability between the asphalt-binder and aggregates was characterized using the interaction parameters of the asphalt mortar obtained from dynamic shear rheometer (DSR) testing. For studying the functional groups and chemical bonding of the asphalt mortar, the Fourier Transform infrared (FTIR) spectrometer was used, whilst the interfacial bonding between the asphalt-binder and aggregates was analyzed using the scanning electron microscope (SEM). The corresponding test results indicated that the physical and rheological properties of the two asphalt mortars were similar. However, whilst the FTIR analysis indicated domination through chemical reactions, the interaction capability and interfacial bonding between the asphalt-binder and steel slag aggregates exhibited superiority over that between the asphalt-binder and basalt aggregates, with pronounced adsorption peaks appearing in the steel slag asphalt mortar spectrum. On the other hand, the SEM test revealed that, compared with the basalt, the micro-interfacial phases between the steel slag and asphalt-binder were more continuous and uniform, which could potentially enhance the interfacial bond strength between the asphalt-binder and aggregates (filler).

Asphalt binder is a complex mixture of dark brown polymers composed of hydrocarbons with generally poor fire resistance. To improve its flame retardancy when used in tunnel asphalt pavements, a new inorganic flame-retardant filler (FR) containing magnesium hydroxide, aluminum hydroxide, inorganic phosphate, and melamine salt was explored. Thereafter, limiting oxygen index (LOI) and smoke suppression tests for the flame-retarded asphalt binder (FRA) mastics mixed with FR and styrene-butadiene-styrene (SBS) copolymer asphalt binder were conducted. Thermogravimetric (TG) and differential scanning calorimetry (DSC) curves for the FRA were correspondingly generated. Based on the TG data, the reaction function g(α), apparent activation energy E_a, and pre-exponential factor A were quantitatively evaluated using kinetic analysis. In addition, a Fourier transform infrared spectrometry (FTIR) test was utilized to assess the effects of the presence of FR on the chemical composition of the asphalt binder. Dynamic shear rheometer (DSR) tests were also performed to evaluate the rheological behavior of FRA. Results show that the presence of the FR significantly reduced the LOI and improved the smoke suppression during combustion of the asphalt binder mastics. The presence of FR was found to increase the E_a and the complexity of the combustion reaction, thereby improving the flame retardancy of the asphalt binder. FTIR analysis indicated that the presence of FR did not induce any strong chemical reactions to significantly impact or alter the functional groups of the asphalt binder. Furthermore, it was also observed that the rutting parameter and critical failure temperature of FRA increased with the addition of FR due to the stiffening effect of the solid FR particles.

To investigate the influence of multiple cycles of aging and rejuvenation on the rheological, chemical, and morphological properties of styrene–butadiene–styrene (SBS)-modified asphalt-binders, the asphalt-binders were aged using two laboratory simulation methods, namely a rolling thin film oven (RTFO) test for short-term aging and pressure aging vessel (PAV) for long-term aging. The asphalt-binders were then rejuvenated with three types of rejuvenators (Type I, II, and III) with different dosages (i.e., 6%, 10%, and 14% for the first, second, and third rejuvenation, respectively). A dynamic shear rheometer (DSR) was then used to analyze the effect of rejuvenators on the rheological properties of all the asphalt-binders. The changes in the functional groups and microscopic morphology in the process of multiple aging and rejuvenation cycles were studied using Fourier transform infrared (FTIR) and atomic force microscopy (AFM). The results indicated that the three rejuvenators could soften the stiffness and restore the microstructures of the aged asphalt-binders in the process of repeated aging and rejuvenation from DSR and AFM testing. Considering the rutting and fatigue properties, the Type I rejuvenator exhibited the potential to achieve the desired rejuvenation effects under multiple rejuvenation cycles. During the multiple aging and rejuvenation cycles, the aging resistance of SBSMA decreased gradually from the FTIR results. This inherently limited the number of repeated rejuvenation cycles. This research is conducive to promoting the application of repeated penetrating rejuvenation.

Aging has a detrimental impact on the interfacial interaction and bonding between asphalt-binder and aggregates, which influence ultimately on the performance of asphalt mixtures and pavements. Evaluation of the mechanical properties of the interface between the asphalt-binder and aggregates has thus become a hot research topic, particularly as a function of aging. In this study, the interfacial tensile strength, compressive strength, elastic modulus, and interfacial recovery energy were measured and quantified using molecular dynamic simulation. Whilst the free volume of the asphalt mixtures exhibited sensitivity to aging, the interfacial tensile strength decreased with an increase in the degree of aging. In general, the mechanical properties of the asphalt-binder-aggregate interface were found to be significantly dependent on the aggregate type. Furthermore, the study results indicated that interfacial recovery energy is a key characteristic property for characterizing the interfacial adhesive force within asphalt mixtures. Overall, the study of mechanical properties of the asphalt-binder and aggregate interface, as presented in this paper, contributes to quantifying the adhesive properties and improving the performance of asphalt mixtures.

To evaluate the physical and rheological properties of rejuvenated styrene‐butadiene‐styrene‐modified asphalt (SBSMA) binders designed for rapid in‐place pavement recycling, an aged SBSMA binder was rejuvenated with three rejuvenators (i.e., Types I, II, and III) in different dosages. The physical properties of rejuvenated SBSMA were obtained to determine the optimal type and dosage of rejuvenators for the first and second rejuvenation. Performance grade (PG) tests, multiple stress creep recovery (MSCR) tests, and linear amplitude sweep (LAS) tests were conducted to measure the rheological properties using the dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The results exhibited that the rejuvenators could soften the multiple aged binder and enhance its high‐ and low‐temperature performance. The rejuvenation effect of rejuvenator Type I with the optimal dosage of 6∼8% was the most appropriate for the first rejuvenation. The optimal dosage of the second rejuvenation was 10∼12%. The addition of rejuvenators decreased the rutting factor (G^∗/sin δ), creep stiffness (S), delta T_c (ΔT_c) parameter, recovery response (R), and yield stress of rejuvenated SBSMA. On the other hand, an increase in the rate of relaxation (m-value), nonrecoverable creep compliance (J_nr), and yield strain of rejuvenated SBSMA was recorded. Overall, the study findings indicated an improvement in the elastic properties of rejuvenated SBSMA, which contributes to improving the rutting, thermal, and fatigue cracking resistance of asphalt binder and ultimately the response of asphalt pavements.

Due to the relatively longer length of Continuously Reinforced Concrete Pavement (CRCP), CRCP can be regarded as a long slab on the elastic foundation. According to the slippage assumption of shearing stress and maximum principal stress theory, the analytical solutions of the displacement, tensile stress, and shearing stress in CRCP under thermal load are deduced in this study. The following results are acquired from the analysis. Maximum thermal displacement, thermal tensile stress, and shearing stress have relations with the temperature difference, resistance coefficient of friction between slab and base, the thickness, modulus and length of slab. And they are in proportion to temperature difference. The influence of resistance coefficient of friction is significant to maximum thermal displacement and stress. In conclusion, reducing the resistance coefficient of friction is a preferential choice to decrease the maximum thermal displacement and maximum thermal stress.