Activated belite cement

Kuznetsova et al. (1992) produced activated belite cements by introducing into the raw meal industrial waste products containing phosphoras, chromium, and titaniiun, and by employing cooling rates of up to 5000 K/min, Such clinkers contained dicalcium silicate mainly in its form, but a and a modifications were also present. By adding carbon to the raw mix, regions with local temperatures above 2100 °C were obtained before the bulk of limestone present was decarbonated. This resulted in a non-stoi-chiometry of the produced clinker minerals and along with it an increase of reactivity. 

A typical activated belite cement meets the requirements of specifications for ordinary and low-heat Portland cements, and appears to be suitable for appUcations in which moderate early strength development may be acceptable. A white belite cement may be produced by lowering the Fc203 content in the raw meal to near-zero values (Mimtean et al, 1992). 

Cuberos, A. J. M., A. G. De la Torre, M. C. Martln-Sedeno, L. Moreno-Real, M. Merlini, L. M. Ordonez and M. A. G. Aranda (2009). Phase Development in Conventional and Active Belite Cement Pastes by Rietveld Analysis and Chemical Constraints . Cement and Concrete Research 39 (10) 833-842. 

Stalk et al. [141-143] studied the possibility of belite cement activity improvement by qnenehing. A great impact of the cooling rate on the strength of mortar was proved, of elinker lime saturation factor below 90% (Fig. 9.31). 

Activated belite (or belitic) cements differ from normal belite cements by the presence of a belite phase whose reactivity has been enhanced by specific measures. The main purpose of such activation is to improve the strength development of the resultant cement, especially at shorter hydration times. 

Fuhr, C., and Knofel D. (1992) Activated belite-rich cements—ready for practical use Investigation of pore fluids and durability, in Proceedings 9th ICCC, New Delhi, Vol. 

Rajczyk, K., and Mocun-Wczelik, W. (1992) Studies of belite cement from barium containing by-products, in Proceedings 9th ICCC, New Delhi, Vol. 2, pp. 250-254. Roy, D.M., and Silsbee, M.R. (1992) Alkali-activated materials an overview. Materials Research Society Symposium Proceedings 245, 153-164. 

Temperature has a large effect, especially in the earlier stages of hydration for example, from QXDA, Copeland and Kantro (C39) found that in a Portland cement paste of w/c = 0.57, the fraction of the alite hydrated at 2 days was 0.28 at 5°C, 0.63 at 25°C and 0.81 at 50°C. Apparent energies of activation calculated from such data were 41 kJ moC at a = 0.6 and 26 kJ mol " at a = 0.7 for belite, a value of 56 kJ mol at a = 0.4 was obtained. The decrease in the apparent energy of activation in the case of alite was attributed to a gradual change in rate control from a chemical process to diffusion. 

Dreizler and Schafer (1990) also stated that the concentration of less active quartz in the coarse fraction of the raw material decreases sinterability, increases energy requirements or free lime, and increases development of belite nests. A chemical method of evaluating the burnability of various particle-size fractions of the feed, involving the calculation of the "weighted mean of the lime saturation standard," along with microscopy of the feeds, was said to be a very cost-effective tool in control of energy consumption and cement quality. For this study, six raw feed size fractions, from <32 to >200 pm, were investigated. 

We reported earlier the first-principles study on the crystal structure and hydraulic activity of P- and y-form belites (Sakurada et al. 2009a, 2009b). In this chapter, we present our DFT simulation results on the study of hydraulic properties of cement phases. Ca-Ca, Ca-0, and Si-0 bond lengths are chosen as a yardstick for making reliable prediction on the hydraulic activity of p- and Y-C2S phases. Moreover, to find a change in crystal structure of P-C2S on substitution of the strontium atom or barium atom for a calcium atom, a periodic boundary condition has been applied on a large supercell (504 atoms, a x 3, b x 3, c x 2) to remove any spurious interactions. 

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