While f/1.8 is a very wide aperture, 18-35mm is a relatively wide angle range of focal lengths. This means that creating a strong background blur with a mounted APS-C format (only) DSLR camera requires a close subject. You can see a mild background blur in this mid-distance 35mm example.
Note that I was using a 1/8000 shutter speed for this shot. Not all cameras have this extremely fast shutter speed available.