(57) Portland cement clinker that includes C3A and C4AF in total from 22 to 40 mass % calculated by Bogue’s formulas and has an iron modulus (I.M.) of 0.8 to 1.3 is produced. The burned raw materials are annealed at a cooling rate of 20 °C or lower at least to 1200 °C so that the lightness of the cement clinker is made high. When annealing till lower temperatures, the lightness value becomes generally higher, but the effect becomes negligible lower at 1000 °C. Therefore, the raw materials are quenched at 1000 °C and lower for improving the productiveness.
(71) Tokuyama Corporation Shunan-shi, Yamaguchi 745-8648 (JP)
(84) Designated Contracting States: AL AT BE BG CH CY CZ DE DK EE ES Fl FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR; Designated Extension States: BA ME; Designated Validation States: KH MA MD TN