Steel slag is a main form of solid waste. Using this component to replace part of the aggregate in an asphalt mixture is an effectively way of treating solid waste. To study the performance degradation of asphalt mixture with various content of steel slag under heavy loading, some large-sized basalt hot mixed asphalt mixture (BHMA) and steel slag hot mixed asphalt mixture (SHMA) in a form of specimens were prepared and a heavy loading wheel tracking test was conducted. The aggregate characteristics of basalt and steel slag were measured. The deformation and skid resistance of the asphalt mixture with different content of steel slag was tested and analyzed. Due to the particle characteristics of steel slag aggregate, it was found that a low content of steel slag can effectively improve the resistance to deformation and skid resistance of the asphalt mixture under heavy loading. The response of SHMA can still meet the pavement technical requirement after long-term heavy loading service. The main change in the mixture under heavy loading is the crushing of the 9.5–16 mm aggregate, and the content of this part also significantly affects the deformation. This study explains the mechanism of degradation of SHMA under heavy loading: the large aggregate is crushed and forms a new aggregate skeleton structure.

Steel slag has been used widely as an aggregate in road application, but it could pose a contamination risk for the environment due to considerable heavy metals (HMs). To explore the leaching behavior and contamination risk of HMs from steel slag and its asphalt mixture is of great significance. In this study, the physical-chemical features, batch leaching test and semi-dynamic test were conducted to determine the mobility capability and leaching characteristics of HMs. The results show that steel slag presents a low pollution risk in short-term leaching, whereas the cumulative release mass of Cd, Ni, As and Pb are more than or approach the limits, which indicates that steel slag exhibits environment impacts to a certain extent. Steel slag covered with asphalt binder results in As and Cu reduced by 3.64% and 4.83%. Diffusion is the main controlling mechanism of HMs in asphalt mixture and the mobility capability of most HMs were classed as “low mobility” (LI > 8). Asphalt stripping off can aggravate the release potential of HMs from asphalt mixture, but the pollution risk remains controllable.

The primary objective of this paper was to investigate the effect of replacing steel slag powder (SSP) with limestone filler (LF) with different contents as an inorganic anti-stripping agent on the moisture susceptibility of asphalt mixtures. Two traditional inorganic anti-stripping agents were selected for comparison, namely cement (CE) and slaked lime (SL). Apparent morphology, chemical compositions, and the particle size distribution of the four fillers were firstly studied. LF was replaced by SSP, CE, and SL with different contents, and then mixed with asphalt to prepare asphalt mortars. An 80 °C water immersion test was conducted to investigate the adhesion of asphalt mortar and aggregates, and an image analysis technique was utilized to evaluate the stripping of asphalt from the aggregates. A Marshall stability test and freeze-thaw split test were then conducted to analyze the effect of different fillers on the moisture susceptibility of asphalt mixtures. The results show that SSP contains a large amount of CaO, which indicates that SSP has a certain alkalinity. Compared with LF, SSP has a rougher surface texture and a finer particle size. Image analysis results show that the partially replacement of LF by SSP increases the asphalt coverage rate of aggregates, which means that SSP can improve the adhesion between asphalt mortar and aggregates. However, the excessive addition of SSP will result in a decrease in adhesion. The results of both the Marshall stability test and freeze-thaw split test demonstrate that CE, SL, and SSP can improve the moisture susceptibility of asphalt mixtures compared with the LF group, and that asphalt mixtures containing SSP have better moisture damage resistance than those with CE, but less such resistance than those with SL. With the increase of the amount of SSP replacing LF, the moisture susceptibility of the asphalt mixture decreases gradually. The optimum substitution amount of SSP was 25% of the total volume of fillers in this test.

When a fire occurs in a tunnel, the instantaneous high temperature and smoke cause great danger to people. Therefore, the asphalt pavement material in the tunnel must have sufficient fire resistance. In this study, the effects of aluminum hydroxide and layered double hydroxide on the fire resistance of styrene-butadiene-styrene (SBS) polymer-modified asphalt was investigated. The fire resistance of the asphalt was evaluated by using a limiting oxygen index (LOI). The impact of aluminum hydroxide (ATH), layered double hydroxide (LDHs), and mixed flame retardant (MFR) on LOI was studied. The synergistic fire resistance mechanism of ATH and LDHs in asphalt binder was analyzed by using an integrated thermal analyzer‒mass spectrometry combined system (TG-DSC-MS) and Fourier transform infrared spectrometer (FTIR). The experimental results indicated that the main active temperature range of these flame retardants was 221–483 °C. The main components of smoke were methane, hydroxyl, water, carbon monoxide, aldehyde, carbon dioxide, etc. The addition of flame retardants could inhibit the production of methane, carbon monoxide, and aldehyde. Moreover, due to the good synergistic effects of ATH and LDHs, 20 wt % MFR had the best fire resistance.

In order to examine the geometric characteristics of BOF (blast oxygen furnace) slag coarse aggregate, the aggregate image measurement system (AIMS) was used to analyze the sphericity, gradient angularity and micro texture. Both volumetric and mechanical properties were studied to evaluate the influence of geometric characteristics of BOF slag coarse aggregate on asphalt concrete. The experimental results show that the BOF slag coarse aggregate has the characteristics of high sphericity, good angular performance and rough surface texture. The geometric characteristics of BOF slag has obvious influence on the volume performance of asphalt concrete. the higher sphericity of BOF slag causes an increase of the air voids of asphalt mixture. BOF slag coarse aggregate can effectively improve the road performances of asphalt concrete. BOF slag’s higher sphericity and angularity improve the moisture damage resistance and rutting resistance of asphalt concrete. Results indicate that better angularity can slightly enhance the moisture resistance property of asphalt concrete, but excessively high angularity of BOF slag coarse aggregates reduces the anti-rutting properties of asphalt mixture.