Excessive usage of non-renewable natural resources and massive construction wastes put pressure on the environment. Steel slags, the main waste material from the metal industry, are normally added in asphalt concrete to replace traditional aggregate. In addition, as a typical microwave absorber, steel slag has the potential to transfer microwave energy into heat, thus increasing the limited self-healing ability of asphalt mixture. This paper aims to investigate the microwave absorption potentials of steel slag and the effect of its addition on road performance. The magnetic parameters obtained from a microwave vector network analyzer were used to estimate the potential use of steel slag as microwave absorber to heal cracks. Meanwhile, the initial self-healing temperature was further discussed according to the frequency sweeping results. The obvious porous structure of steel slag observed using scanning electron microscopy (SEM) had important impacts on the road performance of asphalt mixtures. Steel slag presented a worse effect on low-temperature crack resistance and water stability, while high-temperature stability can be remarkably enhanced when the substitution of steel slag was 60% by volume with the particle size of 4.75–9.5 mm. Overall, the sustainability of asphalt mixtures incorporating steel slag can be promoted due to its excellent mechanical and microwave absorption properties.

To solve the problems of insufficient flexibility and low-temperature cracking resistance of epoxy asphalt binders in steel bridge deck-paving, a segmented linear polyurethane (PU) asphalt binder with thermoplasticity was synthesised via a chain extension reaction between a PU pre-polymer and chain extender in asphalt matrix. Successful synthesis was confirmed through Fourier transform infrared (FT-IR) spectroscopy. A series of tests were conducted to evaluate the properties of PU binders and determine an appropriate formulation. Asphalt binders with high PU contents (30–50%) perform significantly better than the base binder in terms of the high-temperature, low-temperature and mechanical properties. Further, the synthesised PU binder and other frequently used binders, e.g. epoxy and SBS-modified binders, in bridge deck asphalt pavements were compared. Results show that the synthesised PU binder has remarkably better flexibility and low-temperature property, but worse mechanical and high-temperature properties than an epoxy binder. However, the mechanical and high-temperature properties of the synthesised PU binder are substantially better than those of an SBS-modified binder. These results provide useful information for pavement engineers for selecting steel bridge deck-paving materials.

Asphalt binders have been modified with Crumb rubber (CR) as an effort to fulfil the demand for the development of eco-friendly and sustainable pavements. The objective of this study was to investigate the high temperature rheological behaviors and fatigue performance of crumb rubber modified asphalt (CRMA) binder activated using trans-polyoctenamer (TOR). Long-term and short-term aging tests were performed on samples by thin film oven test (TFOT) and pressure aging vessel (PAV). Rotational viscosity (RV), softening point, and dynamic shear rheometer (DSR) tests were conducted to characterize the rheological and physical performance. A linear amplitude sweep (LAS) test was employed to evaluate the fatigue performance. The results show that TOR-activated CRMA is more capable of hardening the matrix bitumen and improving its high-temperature viscoelastic properties after TFOT. The high temperature viscoelasticity is significantly better than styrene-butadiene-styrene block (SBS) modified asphalt (SBSMA) and CRMA. TOR-activated CRMA exhibits strong rutting resistance, but it is more likely to generate fatigue cracks under the violent advancement of complex modulus. Therefore, TOR active agent has a negative impact on the fatigue performance of CRMA. SBSMA exhibited superior fatigue resistance. The viscosity temperature index (VTS) of TOR-activated CRMA and CRMA was basically identical; the TOR did not significantly improve the temperature sensitivity of CRMA.

The structure of organic reagents has an effect on the properties of the OREC modified asphalt. This study selected dodecyl trimethyl ammonium chloride (1231), lauryl dimethyl benzyl ammonium chloride (1227) and stearyl trimethyl ammonium chloride (1831) to modify Na-rectorite (Na-REC) and then prepared OREC modified asphalts. The objective is to evaluate the effect of organic reagents on short-term aging resistance of the OREC modified asphalt. Physical properties, rheological properties and FTIR tests were conducted. Results indicate that the introduction of Na-REC and ORECs improves the short-term aging resistance of base asphalt, and organic modifications to Na-REC have better effect. 1831-reagent endows OREC with the strongest restriction on oxygen penetration and then leads to the best short-term aging resistance of OREC modified asphalt, followed by 1227-reagent, 1231-reagent. Aging sensitivities shown by various rheological indices were compared. The result demonstrates that the complex modulus aging index and RAI (rutting resistance factor aging index) are most sensitive to rolling thin film oven aging, followed by VAI (viscosity aging index), phase angle aging index. Moreover, the atomic force microscope (AFM) was employed to evaluate the microstructure of asphalt samples. The result demonstrates that there is some absorption of Na-REC and ORECs to asphaltene, and ORECs probably hinder the transformation of asphalt from some lightweight compounds to asphaltenes more effectively than Na-REC during RTFO aging.