Portland cement composition 69 clinker

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

Calculate the overall Ca and Si contents (expressed as CaO and Si02) of a Portland cement clinker that has 55% alite, 30% belite, 5% alumi-nate phase, and 10% ferrite (assume ideal compositions for the latter two). Would you expect this to behave as a fast or a slow setting cement ... 

There are three fundamental stages in the process of manufacture of Portland cement, namely. (I) preparation of the raw mixture. (2) production of the clinker. (3) preparation of Ihe cement. Whether the process used is wet or dry. the raw materials are selected, analyzed, and mixed so dial, alter ireatmeni, Ihe product, or clinker, has a desired, narrowly specified composition A factory analysis of slurry, where the wet process is in use. is as follows calcium oxide 44%. aluminum oxide 3.5%. silicon oxide... 

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

Table 4 Potential phase composition of Portland cement clinker...

Alite is the most important constituent of all normal Portland cement clinkers, of which it constitutes 50-70%. It is tricalcium silicate (CajSiOj) modified in composition and crystal structure by incorporation of foreign ions, especially Mg ", AP and Fe. It reacts relatively quickly with water, and in normal Portland cements is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. 

The ferrite phase makes up 5 15% of normal Portland cement clinkers. It is tetracalcium aluminoferrile (CajAIFeOj) substantially modified in composition by variation in Al/Fe ratio and incorporation of foreign ions. The rale at which it reacts with water appears to be somewhat variable, perhaps due to differences in composition or other characteristics, but in general is high initially and intermediate between those of alite and belite at later ages. 

Table 1.2 Typical compositions of phases in Portland cement clinkers (weight per cent)... 

Table 1.3 Atomic ratios for phases in Portland cement clinkers, calculated from the typical compositions in Table 1.2... 

In many clinkers, the ferrite phase is closely mixed with aluminate due to a similarity in cell parameters, oriented intergrowth can occur (MIS). The close admixture often renders X-ray microanalysis difficult or unreliable. For ordinary Portland cement clinkers, the compositions found in dilferent laboratories are nevertheless remarkably consistent. Table 1.2 includes an average value based on the results of investigations using X-ray microanalysis (H8,K1,B2,U1,H3,B4) or chemical analysis of separated material (Yl). Table 1.3 includes suggested site occupancies corresponding to these data. 

A knowledge of the relevant high-temperature phase equilibria is necessary for understanding the factors that govern acceptable bulk compositions for Portland cement clinker, the conditions under which the latter can be manufactured, and the phase composition and microstructure of the resulting material. This chapter deals with these equilibria and with the phases to which they relate, with the exception of the major clinker phases, which were described in Chapter I. Some anhydrous phases primarily of interest in relation to other types of cement are also considered here. Principles underlying the preparation of anhydrous silicate, aluminate and other high-temperature phases are outlined. 

The potential uses of XRD powder diffraction in the study of clinker or anhydrous cement include the qualitative and quantitative (QXDA) determination of phase composition, and the determination of polymorphic modification, state of crystallinity and other features of individual phases. In principle, information on compositions of phases is obtainable through cell parameters, but, due to the lack of adequate reference data, XRD is generally less satisfactory for the clinker phases than X-ray microanalysis. Table 4.2 gives the pattern of a typical Portland cement, with indications of the assignments of peaks to phases. 

Any standard method of matrix inversion, such as the Gauss-Jordan method (N13), may be used to solve the equations. The coefficients in equations 4.11-4.14 may be used without serious error for most ordinary Portland cement clinkers in which the alite composition is not too different from that assumed here. As a byproduct of the calculation described in this section, and using the full compositions of the phases given in Table 1.2, one may calculate a mass balance table (Table 4.3) showing the distributions of all the oxide components among the phases. 

Uchikawa (UI7) reviewed the hydration chemistry of pfa and other composite cements. Pfa cements differ from pure Portland cements notably in (i) the hydration rates of the clinker phases, (ii) CH contents, which are lowered both by the dilution of the clinker by pfa and by the pozzolanic reaction, (iii) the compositions of the clinker hydration products and (iv) formation of hydration products from the pfa. The two last aspects cannot be wholly separated. 

The hydrated material has been analysed by X-ray microanalysis and analytical electron microscopy. In a 3-day old paste, that formed in situ from alite or belite did not differ significantly in composition from the corresponding product in pure Portland cement pastes (H4). but at later ages Ca/ Si is lower and Al/Ca higher (R25,R26,T44,U 17,U 18,R42). Ca/Si is typically about 1.55, but the value decreases with age and ratio of pfa to clinker. Uchikawa (U20,U17) reported a value of 1.01 for a 4-year-old paste with 40% replacement of cement by pfa. Several of the studies (R25,T44,U20,U 17) showed that the C-S-H was higher in alkalis if pfa was present, but one cannot tell to what extent potassium or sodium apparently present in the C-S-H has been deposited from the pore solution on drying. For material close to the pfa particles in a 10-year-old mortar. Sato and Furuhashi (S92) found a Ca/Si ratio of 1.1-1.2. 

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