They're represented as a force field saving throw against attacks that bypass their armor save, not as if the ceramite armor was physically self-repairing.
Here's an example build I have from live. Basic shield, 350 LP armor, rusty gob, armor, medkit. Basic axe with impact mod and penetration/damage mod. You can swap out the axe for a sword or mace as per your preference. It has 150 toughness (the maximum on a slugga boy), for around 20% damage reduction against 100 penetration weapons, and 385 total hit points. It regenerates armor a little slowly, but at least it's tough, can deal damage, and heal itself in a pinch (which I use the medkit almost every spawn and gladly resupply it whenever possible). As others have mentioned the shield actually sucks and doesn't work very consistently. You might be able to get closer to 400 hit points by using a pistol instead of the shield. The dakka slugga is my old standby pistol. Does around the same DPS as a boltgun at close range, for short bursts. Aim for the head. If you take a pistol you have to rely on flanking. Shield really does not give you much resilience at all. It breaks at the drop of a hat, shots sometimes go through the shield...ugh. It's also unreliable in close combat, and if you are moving towards something, chances are someone is just going to shoot you in the ass anyway.
No... That's a magic forcefield caused by Chaos magic. Not power armor. It works on demons and cultists too.
