Effect of Using Steel Slag Aggregate in Slurry Seal Mixtures Containing Iron Oxide Pigments

An efficient approach to road safety coupled with preventive maintenance of asphalt pavements is the application of colored slurry seal, as it improves the road visibility while enhancing the aesthetic aspects of the urban space. Around the globe, application of colored surface treatments on roads has witnessed a growth in recent years, especially in urban areas. This study aims at investigating the feasibility and effectiveness of using electric-arc furnace steel slag as an alternative to natural aggregates in the colored slurry seal mixture design followed by a performance assessment of the resultant mixture. For this purpose, first, characteristics of the aggregate and steel slag were investigated. Next, performance of the designed slurry seal mixture was assessed by testing five different mixtures containing the slag at 0, 10, 20, 30 and 40 wt.%. Evaluation and comparison of the asphalt specimens were performed by conducting 30- and 60-min wet cohesion tests, 60-min wet track abrasion test, loaded wheel-sand adhesion test, and loaded wheel-displacement test according to ASTM D3910. Based on the XRF results, the considered steel slag powder contained a significant amount of calcium oxide (~ 57% of natural aggregate). The high CaO/SiO2 ratio for the steel slag indicates its alkalinity, which suggests its improved adhesion to bitumen thanks to its rather acidic nature. According to FESEM results, the steel slag material was found to be composed of particles of angular geometry with a rougher surface and higher porosity than natural aggregates, further indicating better slag-bitumen adhesion. Performance assessments indicated superior performance of the steel slag-containing specimens of colored slurry seal. Among the studied mixtures, the one with 40 wt.% steel slag exhibited the best performance, as shown by 27.8 and 37.3% increase in the mixture cohesion upon 30- and 60-min wet cohesion tests, respectively, as compared to the control specimen. Furthermore, 47.7% lower moisture sensitivity and 50.8% and 40% smaller vertical and lateral displacements, respectively, were observed for the slag-containing mixture. The bleeding potential of the mixtures decreased with increasing the steel slag dosage from 0 to 40 wt.%, so that the mixture containing steel slag at 40 wt.% exhibited 23.7% lower bleeding potential. Trying to optimize the asphalt emulsion dosage, it was figured out that the optimal content of asphalt emulsion increases with the added content of steel slag to the mixture. Accordingly, the mixture containing steel slag at 40 wt.% required 1.9% more asphalt emulsion to achieve a given cohesion level within a certain time. Based on the results of this research, in order to improve performance characteristics of colored slurry seal mixtures while observing environmental obligations, it is recommended to use steel slag as an alternative to natural aggregates in this type of surface treatment. Therefore, according to the environmental issues and the limitations of natural resources, it is recommended that steel slag be replaced by natural aggregates up to 40% in the colored slurry mixture. By replacing steel slag, proper adhesion and cohesion between asphalt mixture materials is achieved and its resistance to moisture sensitivity, traffic loading and bleeding is improved.