Not sure exactly what you're looking for but the only concrete chamber/manhole covers I know of, were used in the Telecoms sector and they stopped using those a long time ago.
It may of course be some kind of home-made or improvised cover.
Manhole covers and frames are usually made from Ductile Iron and are rated for the type of traffic they could be exposed to - e.g. A15 B125 C250 D400 (all in kiloNewtons). A15 are the lighest and only used in pedestrian areas - they are also made in pressed steel or heavy plastic.
JD, April 2009
