This may not be art, but it's an interesting use of concrete. Or perhaps the art is unintentional?
The Enewetak Atoll in the Marshall Islands of the Pacific contains one small island called Runit. Between 1977 and 1980 the U.S. government buried almost 85,000 cubic meters of radioactive debri from earlier nuclear tests. The debri was dumped into a crater on Runit left over from a 1958 blast—mixed with Portland cement—then covered with the concrete dome shown in the photograph. The dome is about 18" thick and 350 feet wide.