Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1998-12-08
2000-10-31
Marcantoni, Paul
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106776, 106782, C04B 1100
Patent
active
061396214
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
1. Background of the Invention
The invention relates to a process for producing sulfate cement or sulfate cement aggregates.
2. Description of the Related Art
It was discovered at the beginning of this century that granulated blast furnace slags may be stimulated to hydraulically set not solely by lime or portland cement, but that such slags are capable of solidifying also when combined with gypsum in amounts ranging from approximately 10 to 15% by weight. Despite such findings, the technological application of these findings remained limited. Gypsum being a representative of sulfates, bears the risk of inducing gypsum blowing. The space required locally gypsum blowing due to the reaction product being rich in crystalline water will create an explosive effect. This, above all, applies to those cases where, as with known sulfate slag cements, initial solidification could be triggered only by admixtures of portland cement clinker as a lime carrier. With known sulfate slag cements, blast furnace slag was ground together with 15% by weight of calcium sulfate in the form of crude gypsum and approximately 2% by weight of portland cement was added. The presence of lime hydrate in the first stage of solidification proved to be necessary because otherwise a dense gel layer would primarily form before sulfatic setting occurred.
It is important to note that the solidification mechanism of sulfate slag cements must not be compared to the alkaline excitation of the hydration process in case of portland cements. With slag cements, the presence of lime hydrate suffices to induce hydration, whereas in the case of known sulfate slag cements a true reaction must take place, in the course of which gypsum is converted into calcium sulfoaluminate. The sulfoaluminate causes the necessary solidification. The fact that gypsum blowing must be safely avoided has led to the requirement of observing a high grinding fineness amounting to at least 4000 to 6000 cm.sup.2 /g with known slag cements. In any event it turned out that the majority of blast furnace slags were unsuitable for the production of sulfate slag cement. This especially applies because common blast furnace slags, generally, have relatively low alumina contents such that the desired formation of sulfoaluminates is infeasible or only to an insufficient degree, thus not eliminating the risk of gypsum blowing. Finally, a high content of lime is required; however, lime is generally not found in blast furnace slags. For all the reasons mentioned above, sulfate slag cements have not gained any importance in construction practice.
DETAILED DESCRIPTION OF THE INVENTION
The invention aims at providing a process of the initially defined kind by which it is feasible to obtain cement or cement aggregates which exhibit excellent sulfate and sea water resistances and are capable of being used, for instance, as bore hole cements with the danger of gypsum blowing being safely avoided. To solve this object, the process according to the invention essentially resides in that hydraulically active synthetic slags having slag basicities CaO/SiO.sub.2 of between 1.35 and 1.6 such as, for instance, waste incineration slags and/or blast furnace slags mixed with steel slags upon reduction of metal oxides in the melt, and Al.sub.2 O.sub.3 contents of 10 to 20% by weight and iron oxide contents of below 2.5% by weight are mixed with 5 to 20% by weight, based on the overall mixture, of an alkaline earth sulfate such as, e.g., crude gypsum, waste gas gypsum, smoke gas desulfurization plant gypsum, gypsum or anhydrite in the ground or comminuted form. By using a hydraulically active synthetic slag instead of naturally occurring slags, which, generally, do not at all meet the required demands, it has become feasible to provide the prerequisites for completely eliminating gypsum blowing and produce a cement or cement aggregate that stands out for its enhanced seawater resistance and enhanced sulfate resistance. By using a synthetic slag, it is feasible in the synthesis of the
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"Sulfate-Slag Cement Production" vol. 7, pp. 6-7 V.V. Omelchado (Abstract Only), Karagard Tsem. Zavod, Karaganda USSR (1969).
"Holderbank" Financiere Glarus AG
Marcantoni Paul
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