construction question ( cement)

[RGD.]

Cement is an ingredient (binder) in concrete. Sand, gravel (stone) and cement is what makes up concrete. Cement is really not meant to be used by itself.

Your best bet is to grab a few bags of fast set concrete (for a 2 1/2 foot square by 2 inches you would need 3 60# bags), build your form, wet the existing concrete and mix and pour. Will set up in a few hours and you can set your new water heater. I'd give it a day before filling up the tank though.

Ron