Cement is highly alkaline. If wet cement comes in contact with your skin, it can cause third degree chemical burns. So don't write your name in wet cement like Bart Simpson.
The "degree" is based on the amount of damage done to flesh, bone, and skin. Each type of burn has different criteria, so yes, a third degree chemical burn will be different from a third degree flame burn, which will in turn be different than a third degree steam burn.
How about this - your position is that a chemical burn from concrete cannot reach third degree? That it doesn't happen fast enough to cause that damage?
Let's get down to brass tacks. In your vast medical knowledge, would you say the treatment for a hard radiation burn is the same treatment you'd use for a steam burn of similar degree?