A process for producing a supplementary cementitious material (SCM) 114, comprising the steps; providing a calciferous feedstock 101, determining, before and / or after
size reduction, the free
lime content of the calciferous feedstock, subjecting the calciferous feedstock to
size reduction 102 under
phase transition conditions effective to produce a first crude
particulate material, and thereby reducing the free
lime content of the calciferous feedstock, and if the free
lime content determined prior to
size reduction is greater than about 4 wt.%, optionally reacting the first crude
particulate material to produce a second crude
particulate material with a reduced free lime content of below about 4 wt.%, or if the free lime content determined after size reduction is greater than about 1 wt.%, optionally reacting the first crude particulate material to produce a second crude particulate material with a reduced free lime content of below about 1 wt.%, and
processing the first and / or second crude particulate material to give the supplementary cementitious material 114, wherein the calciferous feedstock 101 comprises
slag. The size reduction may be achieved by atomisation or
granulation. Further processes, as well as systems and products thereof, are also defined.