Angle grinder, Belt sander?
Depending how permeable the drive under the cement is you may have
difficulties removing all traces because of the depth of penetration.
There also chemical means available but these attack the cement bonding the
sand/ gravel and will also attack any cementitious sub strata if it is
present if left on too long, or not properly washed off after use.
Really best method depends of precise circumstances - thickness, area,
Realise this may not be down to you but by far the best idea is to either
use a builders spot to avoid contamination in the first place, or to wash it
off before it sets using liberal quantities of water.
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