Air-blown bitumen using grafted silica

A method of treating a modified bitumen, the method comprising:

• contacting the modified bitumen with a flow of air, wherein the modified bitumen comprises:
• about 90 wt % to about 97 wt % bitumen;
• about 2 wt % to about 6 wt % silica particles;
• and
• about 0.2 wt % to about 2 wt % acid component,
• wherein each silica particle is coupled to the acid component, and
• a temperature of the air is 170° C.;
• and
• removing the flow of air when a penetration grade of the bitumen is in a range between 50 and 100.