Bitumen-sand as fill under storage tanks

[EsserDK]

Hello
I can see that bitumen-sand is a returning topic in this forum, therefore apologies for re-opening the subject.
Our national recommendations (Denmark) state that a concrete slab with a layer of bitumen-sand above it can be accepted as a secondary barrier for a steel-bottom tank.
But as far as I understand from my research on the internet, the bitumen-sand-layer isn't a impermeable barrier, and could might as well be substituted with sand-fill or equivalent?

My problem is that the recommendations dosn't mention pure sand-fill, and it dosn't mention reasons why it should be a bitumen-sand-layer. It refers only to EMMUA 183, which, as I see it, isn't dosn't explain it neither. And I do not want to deviate from the recommendations as long I don't understand the topic fully.
So can anybody point me in the direction of the source/reasons for the use of bitumen-sand under tanks, or maybe some litterature where pros and cons are explained?
I can see that one of the pros should be regarding corrosion of the steel-bottom, but in our case, the bottom is seperated from the fill by a layer of thermal-insulation.

Best regards,
Kasper

 

[BJI]

The only reason would be corrosion protection. What type of thermal insulation? If it is the brick type then you could still use a layer of bitumen sand over the top for leveling. If it is a thin thermal membrane/blanket of some sort, is it required under the tank? If the membrane is required and tank base is suitably protected from corrosion then I can't see why clean fill couldn't be used under the insulation.

 

[MJCronin]

Some related AST information on asphalt impregnated board, used specifically for this purpose, can be found here:

http://www.eng-tips.com/viewthread.cfm?qid=359944

http://www.ast-forum.com/ast_forum_tree.asp?master=14923

http://www.ast-forum.com/ast_forum_tree.asp?master=9806

http://www.buildingmaterials.co.uk/bitumen-impregnated-fibre-board.html

MJCronin
Sr. Process Engineer

 

[EsserDK]

Thanks to both of you!
Especially the first link at

http://www.ast-forum.com

was usefull.

Regarding thermal insulation, we are planning to use foamglas or equivalent, maybe substituted with brick type insulation where the plates are being welded.
We would like to avoid the bitumen-sand if possible.

Best regards,

 

[BJI]

The Foamglas website says for high temp tanks, single layer of high load bearing Foamglas insulation with layer of sand, oil-sand mix or sand asphalt mix as leveling and pressure distribution layer.