Experimental investigation of effect of Nano TiO2/SiO2 modified bitumen on the rutting and fatigue performance of asphalt mixtures containing steel slag aggregates

• Uses of Nano TiO2/SiO2 additive improve the rheological properties of original bitumen.
• Titanium oxide and silica powder in Nano scale is added to the asphalt mixture.
• Nano modified bitumen is commonly more viscous than the unmodified binders and tends to show improved adhesive bonding for aggregating the particles. Also better interlock between aggregates and Nano modified bitumen reduces the amount of deformations and lead to improve the fatigue life of pavement.
• Complex modulus of Nano TiO2/SiO2 modified asphalt binder at lower temperatures, is higher than that of unmodified asphalt binder. The phase angle of Nano TiO2/SiO2 modified asphalt binder is low, which increases slightly with increasing temperature.
• Marshal stability of the mixtures containing Nano particles, results in higher values than those of the control mixtures.
• The samples contain steel slag are less sensitive against stress compared to conventional samples and this causes higher resistance against rutting (plastic deformation).

Nanotechnology has been widely used in recent years due to its unique properties in improving the characteristics of many different kinds of materials, including asphalt binders. As an economically efficient material, hot mix asphalt (HMA) has a long history of being used as pavement. However, as they are viscoelastic materials, HMA mixtures experience different modes of failure when they undergo different temperature profiles and loading stress through the time. In pavements made of HMA, three types of distress are commonly observed, which include rutting, fatigue cracking and thermal cracking. Such distresses result in poor service conditions as well as shortening its service life. In almost all climate conditions, rutting in asphalt pavements is regarded as the most important distress factor, specifically in high temperature regions where pavement flexibility becomes a major problem and negatively affects the performance. Premature deterioration and high costs of restoration are among the adverse consequences of rutting. In addition, to improve the characteristics of asphalt mixture, Steel slag is selected because of its good physical properties. This research aims to analyze the results of laboratory tests that was performed on modified steel slag asphalt mixture (SSAM) containing TiO2 and Nano SiO2 particles, the materials that are added to improve the rutting resistance of Nano modified asphalt mixtures. Different tests for asphalt binder properties including penetration grade, softening point, ductility, rotational viscosity (RV) and dynamic shear rheometer (DSR) were used in a basic study to investigate the rheological characteristics of modified bitumen. In addition, to determine the optimum bitumen content in conventional and modified asphalt mixture, Marshal Test was used; and then, to determine the resistance against rutting as well as fatigue life, two tests including repeated load axial (RLA) test and Fatigue Test on asphalt concrete mixtures containing steel slag were conducted. Test results showed that adding Nano TiO2 and Nano SiO2 boost the bitumen rheological characteristics and improve toughness and viscosity by an average of 30% and 109%, respectively, while reduce penetration grade. In addition, the asphalt’s rutting resistance and fatigue life was improved.