First, a question. Is this silica fume (a byproduct of silicon metal production) or fumed silica (produced by companies like Evonik, Wacker or Cabot)? Also, what quantity are you working with?
This was densified silica fume (i.e. by blowing air through a bed of silica fume). The best way to break it down is to preblend the silica fume with aggregate in a dry state for a certain amount of time to break it down. I have not had any problems with this approach.