Raw cement with the finest grain size

Hello everyone,
for the renovation of thin joints 2-3 mm wide, I am looking for a cement which has a maximum grain size of 1mm and is at the same time swelling or does not shrink when setting.
Does anyone have an idea?

The only thing I have found so far was a swelling or tamping mortar with 2mm grain size.

A swelling grouting mortar is out of the question. The stuff should not flow away but stay in the joint.

Thank you

Can't you just use grout that is also used for tiles? It doesn't have large grains and is available for both indoor and outdoor use.

It is a head joint in the brick masonry that is to be repaired. I don't think joint mortar is the right thing here?!