Rubble: broken bits and pieces of anything
Nehemiah 2:17-18
Then I said to them, "You see the trouble we are in: Jerusalem lies in ruins, and its gates have been burned with fire. Come, let us rebuild the wall of Jerusalem, and we will no longer be in disgrace".  I also told them about the gracious hand of my God upon me and what the king had said to me. 
Nehemiah 4:10
Meanwhile the people in Judah said, "The strength of the laborers is giving out, and there is so much rubble that we cannot rebuild the wall".