,I am not very familiar with concrete materials since I haven't worked on it, but as far as my knowledge goes, concrete is strong in compression and not in tension. And the crack thing is most oftenly related to the materials in tension. I don't think the mechanism of crack propogation beginning at yield strength and causing a fracture past it, is eligible for the materials in compression (including concrete). I think a different mechanism causes a yielding and fracture for materials in compression, not the crack propogation and enlargening of the cracks. So I don't know why you related the concrete example (under compression) to the crack propogation and ultimate fracture.