I am building a block building for a slaughterhouse and I was thinking about filling the block with sand for insulation. My goal is to be able to keep the rooms as cool as possible was wondering if sand would be a good idea thanks.
Sand could be an acceptable material for heat storage but still not as good as water. Sand has heat capacity of 0.83 kJ/kgK, but with density of 1600 kg/m3. Water has heat capacity of 4.19 kJ/kgK, but with density of 1000 kg/m3. Thus, one liter of sand stores 1.32 kJ, but one liter of water stores 4.19 kJ (per Kelvin). One area where sand excels is if you have the ability to heat it to above the boiling point of water (such as by using power plant waste heat). If you can't then water would be more ideal for heat storage.
As for insulation, sand has heat conductivity of 0.25 W/mK. Polystyrene foam has 0.03 W/mK thermal conductivity. So you can see sand is nowhere close to real insulators.
My advice is to use water if you want to store heat, and use real insulators if you want to prevent heat transfer. If you want to use both, use both water for storage and real insulators for preventing heat transfer. Don't try to cheap out and use sand, because it's a very bad material for either use.