Coloured Cement

• For manufacturing various colored cements, either white cement or grey Portland cement is used as a base.
• The use of white cement as a base is costly. With the use of grey cement, only red or brown cement can be produced.
• Coloured cement consists of Portland cement with 5-10% of pigment.
• The pigment cannot be satisfactorily distributed throughout the cement by mixing, and hence, it is usual to grind the cement & pigment together.
• Chromium oxide – green colour
• Cobalt – blue colour
• Iron oxide – brown colour
• The raw materials used for white cement are:
  
  1. High purity limestone (96% CaCO3 & less than 0.07% iron oxide)
  2. China clay (0.72-0.8% of iron oxide, silica sand, fluorspar as flux and selenite as retarder)
• Grey colour of OPC is due to the iron oxide present.