I have a 1917 house with concrete floors with tile set in the mortar bed. This rests on the joists which are narrow at the top to hold in the mortar. We had the pipes replaced with cpvc and in one bathroom they went though the floor to do this, leaving a trench in the floor.

I would like to fill this trench at least temporarily right now, what should I use to fill it? Quick set concrete? Thinset? The trench has gravel in it right now.

Someday I would like to tile over the whole floor, but I am not interested in ripping the whole floor up as right now it is our only functioning bathroom.