How much muriatic acid to dissolve cinder block?
Keep in mind that a cinder block is likely to contain silicates, these will not dissolve well in hydrochloric acid. The silicates will either not react or they will form silica.

If you want to dissolve silicates then you need to use something which will complex to the silicon such as fluoride (HF). I have seen methods for the digestion of soil samples to get the plutonium out. To obtain the plutonium from a soil sample it is often important to digest down the silicate minerals. To do this you must boil the soil sample to dryness many times with a mixture of hydrofluric acid and nitric acid. This will convert the silicate minerals into silicon tetraflouride which will boil out of the mixture.