Cement has more specific heat capacity per mass, but not per volume. One cubic meter of iron can hold something like 3.5 MJ per kelvin, while the same volume of cement can hold something like 2.33 MJ per kelvin.
In addition I'm not sure cement can go above 800 degrees Celsius, while iron melts at 1500 degrees. So one cubic meter of cement at 800 degrees celsius above background can hold 800 x 2.33 MJ = 1.86 GJ. One cubic meter of iron at 1500 degrees can hold 5.25 GJ. Now take the 9.5 GJ that has been reported. With cement, you need 9.5e9/1.86e9 = 5.11 cubic meters. With iron, you need 9.5e9/5.25e9 = 1.81 cubic meters. Assume you have 50 modules of 70 cm x 30 cm x 45 cm. That makes 4.7 cubic meters. Not enough space for cement (unless you know of some special kind of cement.) Using iron, it would fit, but it would weight way too much, at 250 kg per module. -- Berke Durak
