Unground clinker

This chapter deals with chemical and physical properties other than ones for which the nature of the hydration products must be considered, which are treated in Chapters 5 to 8. In general, properties of the whole clinker or cement are alone considered, those of the constituent phases having been dealt with in Chapter 1, but factors affecting the reactivities of these phases are included as a link with the following chapters on hydration. 

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. 

The bulk density of a clinker, determined under standard conditions by rejecting material passing a 5-mm sieve, pouring the remainder into a conical container, and weighing, is called the litre weight. This quantity, which is typically 1.25-1.35 kg 1 gives some indication of the operating conditions. Its optimum value depends on the composition. 

The measured true density of clinker is typically 3150-3200 kg m the value calculated from the X-ray densities and typical proportions of the individual phases is about 3200kgm The difference is probably due mainly to the presence of pores inaccessible to the fluids used in the experimental determination. Using mercury porosimetry. Butt et al. (B35) determined pore size distributions and discussed their relations with burning and cooling conditions and grindability. 

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Clinker. (1) Hydraulic cement in the unground state as it issues from the rotary or shaft kiln in which it was made. 

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