Usually, the manufacturer sets the requirements for the products produced, unless someone wants to pay the premium for the cost of using specific mixes, accepting the liability for performance and any testing that is required for use and acceptance.
The reason is quite simple - The manufacturer has invested a great deal in facilities, inventory, testing and obtaining product acceptance if the product is used as produced and recommended. Usually the manufacturers known far more about the performance of the product and what is needed to accept the liability.
The cost of using special materials can be costly and increase the cost of production and the downtime/clean-up/ idleness. In most countries, the hollow core business is based on standard products with known accepted performance and low prices. Special materials and processes will increase the cost. In the case of requiring different materials, anything that retards the strength gain (GGBS) changes the production cycle times(curing) and increases the cost because of the decreased production.
It takes a huge amount of area (hectares/square footage) to justify the increased cost.
