Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1997-07-18
1998-12-22
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106709, 106735, 106736, 106739, 106763, 106765, 106767, 106768, 106772, 106775, C04B 704, C04B 1100
Patent
active
058512829
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a Portland cement clinker, the use thereof and a Portland cement. Portland cement usually consists of a Portland cement clinker and a sulphate carrier, normally gypsum.
A Portland cement clinker is made from a mixture of raw materials containing mainly certain proportions of calcium oxide (CaO), silica (SiO.sub.2), alumina (Al.sub.2 O.sub.3) and iron oxide (Fe.sub.2 O.sub.3). New compounds, the so-called clinker phases, are formed therefrom by heating the mixture up to sintering. Their typical quantities, in percent by weight, may be given as follows:
The cement mixed with water and hardened has its strength due to the clinker phase C.sub.3 S.
Producing the cement clinker requires a considerable expenditure of energy. The latter consists partly of thermal losses in burning (particularly by radiation, exhaust gas losses and hot clinker outputted at the end of the furnace). Another portion of energy is consumed in endothermal reactions, especially in the decomposition of calcium carbonate (important CaO carrier) into calcium oxide.
Accordingly, one endeavors to decrease the energy costs.
First, it seemed to be logic that this goal could be achieved most simply by decreasing the proportion of CaO- rich clinker phases (C.sub.3 A, C.sub.3 S) and increasing the proportion of the content of the phases with less CaO (C.sub.2 S, C.sub.4 AF) accordingly.
However, the disadvantage would be that the corresponding cement would fall far behind the usual Portland cements in its development of strength, because the hydration of C.sub.2 S and C.sub.4 AF proceeds much more slowly than that of C.sub.3 S and C.sub.3 A.
In this context, it was attempted to replace the clinker phase C.sub.3 S by C.sub.4 A.sub.3 S (wherein S stands for SO.sub.3), because C.sub.4 A.sub.3 S hydrates relatively fast. In this case, a separate addition of a sulphate carrier into the mixture of raw materials is necessary, the largest part of the sulphate (expressed as SO.sub.3) becoming bound within the phase C.sub.4 A.sub.3 S.
With this known cement (clinker), it is disadvantageous that C.sub.3 S is not formed at all in the burning process, because the formation to C.sub.3 S is hindered or prevented by the presence of the sulphates (SO.sub.3). "Zement-Kalk-Gips, 4/1990, p. 199" already describes that the C.sub.3 S (alite) content decreases with an increasing SO.sub.3 content in the clinker. Additionally, at burning temperatures as low as about 1250.degree. to 1300.degree. centigrade required for the formation of C.sub.4 A.sub.3 S no C.sub.3 S is formed in the presence of the high SO.sub.3 proportions (3-10% by wt.) required for the formation of C.sub.4 A.sub.3 S. An increase of temperature is out of the question, because then C.sub.4 A.sub.3 S becomes unstable and cannot be formed any more.
The DE 42 04 227 C1 describes a Portland cement clinker having a SO.sub.3 content of 3-8% by wt. In addition to C.sub.4 A.sub.3 S it contains also 30-80% by wt. C.sub.3 S. The synthesis of this clinker is achieved by addition of a F.sup.- containing additive to the mixture of raw materials. In addition to thermal energy also electrical energy is required for the grinding of the clinker.
The object of the invention is to provide a Portland cement, the clinker of which is produceable at lower burning temperatures and grindable with decreased expenditure of energy than for a conventional Portland cement, the Portland cement formed therefrom showing, after mixing with water, a development of strength which at least equals that of a conventional Portland cement.
Surprisingly, it was found that such a Portland cement clinker is produceable with a C.sub.3 S content from 40 to 80% by wt. and can be burned at low temperatures of 1250.degree. to 1350.degree., if a SO.sub.3 containing additive is mixed into the mixture of raw materials, the SO.sub.3 content of the clinker having to be >1.0 to <3.0% by wt. The addition of an additive containing flourine (e.g. CaF.sub.2 or ZnO) for the acceleration of the burning process is not necessary but possib
REFERENCES:
patent: 4036657 (1977-07-01), Mehta
patent: 4042408 (1977-08-01), Murray et al.
patent: 5356472 (1994-10-01), Odler
Gimenez et al "Production of cement requiring low energy expenditure ", Zement-Kalk-Gips, pp. 12-15 Jan. 1991.
A. Earley John F.
A. Earley III John F.
Green Anthony
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