In article , Andy Dingley
writes
On 09 Feb 2005 19:13:48 GMT, Ian Stirling
wrote:

IIRC, there are concretes made from lead-bearing minerals that are double
the weight of ordinary.
(used for radiation shielding)

Barium I think, rather then lead. Barytes makes the aggregate. Good
neutron absorber and also heavy.

The radiation shielding grouts we made just contained steel shot, we
have three density's, 4.3, 4.8 and 5.3.
--
David