I heard that when calcium carbonate is heated, it decomposes into calcium oxide.
It probably would be better, if using the calcium carbonate shown in the links, to use carbonated water (club soda) in the mixture. The ground limestone noted in the links contains a great deal of calcium oxide already. Calcium oxide + water yields calcium hydroxide (not good) but calcium hydroxide + carbon dioxide (from the club soda) yields calcium carbonate (good). I'm not certain it would make that much of a difference but the chemistry works...