Method for manufacturing a supplementary cementitious material

A supplementary cementitious material, having

• an activity index according to EN 450-1 after 28 days of not less than 70%, and
• a water demand according to EN 450-1 Annex B of not more than 110%,
• as well as:
• a loss on ignition at according to EN 196-2 of not more than 7.0 wt.-%, and/or
• a volume stability according to EN 196-3 for a paste made from 30 wt. % of the supplementary cementitious material and 70 wt.-% of an ordinary Portland cement, measured with the expansion value, of no more than 10 mm,
• wherein the supplementary cementitious material is obtained by
• providing a starting material containing fly ash and raw clay or a mixture of fly ash and bottom ash and raw clay, wherein at least 70 wt.-% of the starting material are clay, fly ash and bottom ash, wherein the fly ash or the mixture of fly ash and bottom ash has a water demand determined according to EN 450-1 above 105% or an activity index determined according to EN 450-1 on a sample prepared with 70 wt.-% CEM I 42,4 R at 28 days below 70% or at 90 days below 85%, either before or after heat treatment at a temperature ranging from 700 to 1000° C.,
• homogenization of the starting material,
• thermal treatment of the homogenized starting material at a temperature ranging from 700 to 1000° C. to provide a heat treated material
• cooling the heat treated material to provide a cooled product, and
• grinding the cooled product to provide the supplementary cementitious material.