snip

I try to cut them on a straight line and it's hopeless. Can't use a
recipricating saw because of the concrete layer underneath. Tried a angle
grinder and there were so much dust I could not stand it. Any advise?

Buy the cheapest saber saw (or jig saw) that Harbor Freight has. Break
off or grind off a blade to the exact length that will cut the
thickness you want and have at it. Pros use this same trick for
removing just the layers of old underlayment, flooring and what have
you without tearing up the subfloor. HTH

Joe