So if you did a "real time" simulation, you would take 400 seconds to move 4 mm. You can probably speed that up 400 times to 1 second.

The Explicit Dynamics solver calculates what the minimum time step must be for a stable solution. It's best to leave time steps Program Controlled.

Remember my 2D example? There were about 5 elements along the side of the rib on the rebar.

You're going to need at least 5 elements along the side of rib on the rebar to have a fine enough detail to see the gradual failure of the concrete. Your current mesh has 1 element along the side of the rib on the rebar.

Unfortunately, in Explicit Dynamics, the minimum stable time step is a function of element size. The smaller the element, the smaller the time step, so multiply by at least a factor of 5 the time to solve for the reduced element size, not to mention all the extra elements that will be created. The simulation could take days to solve to a 1 second end time. That's the way Explicit Dynamics works.