Some time ago, I have already mentioned in a post that for tank bottom thermal insulation, more expensive boards could be replaced by gravel and the famous GLAPOR RDS system. The cost of the thermal insulation of the tank bottom should be reduced by about 80% and the installation (time) also of the same order.
In this system, the ring (walls of the tank) are supported by the GLAPOR RDS-composite while the bottom of the tank is insulated with cellular glass gravel. Today, GLAPOR RDS is used in Germany, Austria, Switzerland, Italy and Belgium for private houses. In that case, the load bearing walls are put on the GLAPOR RDS composites, while the actual floor is insulated and supported by cellular glass gravel.
But today, this system is already also used for water tanks. Concrete walls are supported by the RDS-composites while the actual bottom of the tank rests on cellular glass gravel. The following pictures are clear. In case of a bitumen of an ammonium tank, the cellular glass gravel layer has just to to be thicker. The price of cellular glass gravel is less than 50€/m³ while boards for tanks costs easily up to 400€/m³. The installation time of gravel is very short compared to boards.