Abstract: A process for the grain size reduction of a raw material in piece form, wherein: all or part of the material in piece form is subjected to a grinding operation, capable of enabling to be obtained at its output a material in grain form having a requisite grain size distribution, starting out from any given grain size of the material in piece form; downstream, the material in grain form obtained is directed exclusively towards a common container, whatever the size of the grains, so as to obtain, in a single run, in the said container, a mixture of material in grain form having the grain size distribution, for use as such.