The stoichiometry of cement hydration

3 The stoichiometry of cement hydration Many attempts have been made to formulate the stoichiometry of cementj 

The essential input data are (a) the bulk chemical composition of the cement, (b) the quantitative phase composition of the cement and the chemical compositions of its individual phases, (c) the fraction of each phase that has reacted, (d) the w/c ratio, (e) the COj content of the paste and an estimate of how it is distributed among phases, and (0 the composition of each hydrated phase for the specified drying condition. If (b) is unknown, it may be estimated as described in Section 4.4, and if (c) is unknown, it may be estimated from the age as described by Parrott and Killoh (P30), or, more simply though less precisely, by using empirical equations (D12,T37). If the phase composition by volume and porosities are to be calculated, densities of phases are also required. 

For any selected drying condition, a table is now completed, similar to the previous one, but with the HjO and CO2 content of each phase included and the quantities of elements expressed as weight percentages of oxide components. Table 7.3 shows results for a typical, mature cement paste thus calculated. It was assumed that the C-S-H had Ca/Si = 1.7 and Al/Ca = 0.02, that the AFm and AFt phases each had Si/Ca = 0.05 and that the hydrogarnet-type phase had the composition Ca2.95Alo.1Fe1 7sTio jMn 05- 

Alite Belite Alum. Ferr. C-S-H CH AFm AFt FeHP Mg HP CaCOj Other Pores 

Water contents (pereentages on the ignited weight) Bound water 31.2% Non-evaporable water 21.9% 

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