Choosing type of concrete

[Patrik Hazard]

Hi!
I've dug a trench in the basement floor to lay down new vs for an upcoming extension.
The slab was thin and underneath it, there's sand and small stones.
The house is old, so there is no reinforcement or insulation.
When I have installed the pipes that I need there, the area needs to be cast again as well.
I plan to reuse the excavated materials to fill the trench, but what type of mortar should I use to patch the slab?
There are a few types to choose from.

 

[Mattias_Eson]

If you're just going to repair the hole, regular coarse concrete in a sack works excellently. Apply some primer on the old concrete first so that it adheres properly.
When the concrete has dried enough that it barely leaves footprints, you can start treating the surface to the desired finish (probably scrubbing and steel troweling it).