Portland cement clinker colour

Portland cement clinker emerges from a dry process kiln as rounded pellets, or from a wet process kiln as irregularly shaped lumps, in either case typically of 3-20 mm dimensions. Typical clinkers are greenish black, the colour being due to ferrite phase that contains Mg (Ml8) in the absence of Mg , they are buff. Reducing conditions in the kiln typically produce clinkers that are yellowish brown, especially in the centres of the lumps, where less reoxidation has occurred. Light colours can also arise from underburning. 

Fig.11 Portland cement clinker under-burned (porous) micrograph obtained with reflected light free lime black pocket belite light-coloured textured areas alite dark textured areas pores (here filled with resin) grey areas with grinding scratches...

The four clinker minerals mentioned have characteristic properties with regard to rate of heat development and rate of strength development during hydration subsequent concrete durability and colour. Therefore, the useful quahties of Portland cement depend, at least in part, on the quantitative proportions of these clinker minerals in the cement. 

Masonry cements These are used for preparing bricklaying mortars and stuccos, and must not be used in concrete. They are usually complex proprietary formulations containing Portland clinker and a number of other ingredients that may include limestone, hydrated lime, air entrainers, retarders, water proofers and colouring agents. 

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