Steel is used to shape and reinforce concrete. Steel is also used in cutting bones in surgery and repairing bone through use of steel pins and braces. So, the answer is most definitely steel. In answer to your watch question, the volume of concrete was greater than that of your watch. The question of large volume vs. small volume is an easy one. Ten tons of human bone would easily reduce a 1 lb block of concrete to powder. Likewise, ten tons of concrete would snap a steel bar like a toothpick. Your watch had much less volume than the concrete you dropped it on. Furthermore, with enough force, your watch would have made a hole in the concrete, but its acceleration was not enough to counter the impacting force of the solid concrete reinforced by the soil and clay below it.
I guess I would ask you to define strong then? For example: make a bed and line it with steel, then lie down in it and have someone poor concrete on you. Let it dry overnight and then try and get out. What will break first? Could be anyone of these. If you had a watch made out of bone or concrete and it fell off, it too would break. There you have it amigo, define strong!
Steel would smash a bone ,and concrete needs steel reinforcing.But of these only a bone can heal. Steel is the strongest .
Takfam is correct, but in the loooong run, concrete will exist for thousands of years after the steel oxidized, deteriorates, and disappears. The ancients compounded concrete even before the Romans (I can't recall but during the time of the Assyrians), and concrete is almost forever.
