Portland cement clinker content

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 ... 

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. 

Fig. 3.1 Schematic diagram showing the variations in typical contents of phases during the formation of Portland cement clinker. Loosely based on a figure by Wolter (W9).

Portland cement clinkers typically contain around 0.2% of P2O5 higher contents lead to decreased formation of alite, and if above about 2.5% to... 

Type S cements are Portland cements high in C3A and with suitable contents of calcium sulphate they have found little favour as they are too diHicLilt to control. The A1,0, has also been supplied in forms other than those mentioned above. Impure alunite [KAl3(S04),(0H)(,]. which occurs as a natural rock, has been used, either after calcination (V6) or uncalcined (W30). In the latter case it was mixed with Portland cement clinker, anhydrite and pfa or slag and was found to dissolve relatively slowly, thus suitably delaying the expansive reaction. 

Concentration of these ions in pore solution of concrete plays a decisive role in the formation of efflorescence. Pore solution, in the case of ordinary cements, is always satinated with calcium hydroxide— the basic somce of efflorescence. The concentration of potassium and sodium is important too the potassium content is always several times higher. These both components occm in pore solution in the form of hydroxides, as a result of reaction with calcimn ions. Particularly sodium is a very mobile ion and in the case of concrete produced from alkali activated slag cement, with sodimn compound addition and without Portland cement clinker, Na+ ions migrate to the smface and the white sodimn carbonate effloreseenee is formed. 

Raw meals for high-belite chnkers are relatively easy to bum, and the consumption of energy is reduced, mainly because of a reduced CaCOj content. Compared with ordinary Portland cement clinkers, it is possible to reduce the binning temperature by up to about 100 °C and along with it the NO emission. At the same time the grindability of the clinker is improved (Ludwig and Pohlman, 1986). 

In contrast with liquid phases with a high Si02 content, the lime-rich alumino-ferritic liquid in Portland cement clinker undergoes complete crystallization even when cooled rapidly. 

Figure IL8 Calculated changes using thermodynamic modelling as a function of metakaolin content. 70 wt.% portland cement +30 wt.% (metakaolin + limestone) based on the data from Steenberg et al. (2011) assuming complete reaction of metakaolin and A/S = 0.09 in C-S-H. (From Steenberg, M. et al., Composite cement based on portland cement clinker, limestone and calcined clay. Proceedings of the 13th International Congress on the Chemistry of Cement, Madrid, Spain, 97-104, 2011.)...

Liquid or pulverized solid fuels are blown into the kiln through a nozzle with primary air. Additional secondary air is drawn into the kiln through the clinker cooler. The flame in the rotary kiln must meet several requirements. The clinker must be correctly burned, so as to minimize its content of free lime, with the least expenditure of fuel. The ash from a solid fuel must be uniformly absorbed by the clinker. For normal Portland cements, the conditions must be sufficiently oxidizing that the iron is present as Fe however, for white cements, mildly reducing conditions may be preferable. Proper flame control also extends the life of the refractory lining of the kiln. Computer-aided or fully automated control of kiln operating conditions is increasingly used. 

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. 

A typical CH content in the pastes prodnced from Portland cement is in the range 18-25 % after 3 month of hardening. AFt is present only at early age. Using some assumptions and methods Taylor [27] proposed a mass balance for the paste prepared at w/c=0.5 and stored one year at 11%RH. The following volume ratios of particular phases were proposed clinker 0.05 CH 0.11 CaCOj 0.01 C-S-H... 

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