Portland clinker

The primary phases all contain impurities. In fact these impurities stabilize the stmctures formed at high temperatures so that decomposition or transformations do not occur during cooling, as occurs with the pure compounds. For example, pure C S exists in at least six polymorphic forms each having a sharply defined temperature range of stability, whereas alite exists in three stabilized forms at room temperature depending on the impurities. Some properties of the more common phases in Portland clinkers are given in Table 2. 

Agarwal et al. (A24) examined two alinite clinkers and further studied the process of their formation. The compositional range (Table 10.5) shows that, compared with typical Portland clinkers, they are of low LSF and low AR. The microstructures resembled those of typical Portland clinkers. XRD... 

Zeolitic tuff is also utilised in the cement industry as pozzolanic addition (see Sub-sec. 5.2.2.) to portland cement. This application recalls the use of pozzolana, since the beginning of the 1900s, to obtain blended cements, able to fix the lime formed by the hydration of the calcium silicate components of the portland clinker. The utilisation of zeolitic tuff, as substitute of pozzolana, to obtain pozzolanic cements is based on both economic and technical considerations. On one hand, manufacturing blended cements allows a 40% fuel savings, without reducing the quality of the produced binder (it is to bear in mind that the mixture lime-pozzolana is itself a cement), on the other, it involves some advantages, e.g., the... 

Hydraulic cement is produced by pulverizing Portland cement clinker and usually contains CaS04 (<5%). Portland clinker is produced by heating a mixture of CaO, Si02, AI2O3, and Fe203 until partly molten. 

C3S is the essential constituent of Portland clinker C2S, C3A, and C2(A,F) will also be present. 

Chromy, S., "Process of Portland Clinker Formation, Reactivity, and Burnability of Cement Raw Materials Part I Mechanism of Portland Clinker Formation," Zement-Kalk-Gips, Vol. 35, No. 4, 1982, pp. 204-210. 

Maki, I. Morikoshi, H. and Takahashi, S., "Processing of Portland Clinker and Microscopic Textures of Alite," 14th International Conference on Silicate Industry and Science, Budapest, May 1985,6 pp. 

Odler, I., and Maula, Abdul S., "The Effect of Burning Conditions of the Structures of Portland Clinker and the Reactivity of the Resultant Cement," 8th International Congress on the Chemistry of Cement, Rio de Janeiro, Brazil, Theme 1, Vol. II, 1986, pp. 265-269. 

Rivera, M. Odler, L and Abdul-Maula, S., "Formation of Portland Clinker—Studies on Synthetic Raw Meals," Advances in Cement Research, 1987, Vol. 1, No. 1, pp. 52-57. 

Svinning, K., and Bremseth, S., "The Influence of Material and Process Parameters on Cr)retal Size Distribution of Alite in Portland Clinker," Proceedings of the 15th International Conference on Cement Microscopy, International Cement Microscopy Association, Dallas, Texas, 1993, pp. 233-249. 

Binders that contain latently hydraulic or pozzolanic or non-reactive constituents in combination with Portland clinker (and usually also with calcium sulfate) are called composite or blended cements. 

Tricalcium silicate is an essential constituent of all Portland clinkers. In its crystalline lattice it contains Ca cations in combination with 8104 and anions in a ratio of 3 1 1. Upon heating or cooling tricalcium silicate undergoes a series of reversible phase transitions ... 

Free MgO, also called periclase, is present in Portland clinkers only at high MgO contents in the raw meal (usually in the form of MgC03). It may be tolerated if present in amormts of only a few per cent, but may cause concrete damage if present in higher amormts (see also section 2.9). 

The following alkali sulfates may be present in Portland clinkers ... 

In ordinary Portland clinker (corresponding to ASTM type I Portland cement) tricalcimn silicate is the most abundant phase, present in amormts between about 50% and 70%. Dicalcium silicate usually constitutes 15-30% of the clinker. Typical amounts of tricalcium aluminate are 5-10%, and of the ferrite phase 5-15%. In special Portland clinkers the individual clinker pliases may be present in increased or reduced amounts, or may be absent entirely. Free lime, free MgO and alkali sulfates are minor constituents of Portland clinker that are present only in small amounts or may be absent entirely. Calcium sulfate is only rarely a constituent of Portland clinker, but is intergroimd in limited amounts with it, to obtain Portland cement. In Table 2.1 different types of Portland cement are compared. 

The composition of Portland cement raw meals and Portland clinkers can be characterized by the mutual ratio of the main oxides present. The following ratios are those most widely employed (all amounts of oxides are given in wt%) ... 

The various constituents of Portland clinker differ in their grindability. In general, the grindability declines in the order calcimn sulfate>alite> almninate>ferrite>belite. As a consequence, different cement particle size fractions may vary in their phase composition. 

Limited amounts of limestone, interground with Portland clinker and calcium sulfate, may beneficially affect some properties of the resultant cement. This effect is achieved mainly by physical action, as calcite (CaCOg)— Ihe main or sole constituent of limestone—participates only marginally in the hydration process. 

If ground together with Portland clinker, limestone will predominate in the fine fractions, as it is significantly softer than the clinker. In a fresh paste made from such a cement, the fine limestone particles will fill the spaces between the coarser particles of clinker, and consequently the amount of water needed to attain a given consistency will decline, up to an optimum limestone addition. This amount of limestone may vary in different cements, up to as much as 25 wt%. 

A limited substitution of Portland clinker by limestone may result in a moderate increase of strength of the resultant cement (at a constant consistency of the fresh mix). This is brought about mainly by the water-reducing effect of limestone. 

It has long been recognized that, even in the absence of calcium sulfate, flash setting of cement may be prevented and a cement suspension of flowing consistency obtained by combining finely groimd Portland clinker with an alkali metal carbonate or hydrogen... 

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