Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-09-21
2001-06-05
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S739000, C106S757000
Reexamination Certificate
active
06241816
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of treating cement clinker and more specifically to a method of treating cement clinker in the process of grinding the same.
2. Description of the Related Art
The cement clinker to which the invention relates is preferably Portland cement clinker, although it is not restricted to Portland cement clinker, but can be applied with other cement clinkers.
The nearest prior art is described in European Patent Application EP 0 081 861 and in Publication WO 94/00403, which teach methods of grinding Portland cement clinker with mineral additives and an organic water reduction agent. According to the last-mentioned publication, water is also added to the last mill chamber with the intention of adjusting temperature.
As a result of the physical and chemical adsorption of molecules of water-reduction agent on the clinker particles, the resultant ground cement will have a reduced water requirement and also greater strength in comparison with standard Portland cement. One decisive drawback with this method is the difficulty in controlling the extent of the reaction between Portland clinker and water reduction agent, this reaction having a direct influence on the instability of the properties of the final cement.
The same reduction in water requirement can also be achieved by adding a water reduction agent directly to concrete with water, in accordance with conventional methods. No appreciable increase in the chemical reactivity of Portland clinker can be achieved with these methods.
SUMMARY OF THE INVENTION
The present invention relates to a method of treating cement clinker whilst grinding the clinker and adding different substances thereto, in order to enhance the strength properties of the cement produced.
The present invention thus relates to a method of treating cement clinker, by grinding the clinker in a tubular mill whilst adding water and gypsum and possibly also a water reduction agent, wherein the method is characterized by injecting water that has a pH of approximately 9-13 into the mill during grinding of the clinkers.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will now be described in more detail with reference to various embodiments thereof.
Cement clinker is normally processed by first heating the clinker or calcine in a kiln at a temperature of 900-1450° C., such as to form the compounds 3 CaO SiO
2
, 2 CaO SiO
2
, 3 CaO Al
2
O
3
and 4 CaO Al
2
O
3
SiO
2
. This treatment process results in normal Portland cement.
In a second stage, the clinker is ground together with gypsum to particle sizes of between 10-20 micrometers, in a tubular mill that includes steel balls. Water is added during this grinding process. The present invention relates to this second stage.
According to the present invention, the water has a pH of about 9-13 and is injected into the mill during grinding of the clinkers.
According to one very preferred embodiment of the invention, the water injected has been brought to this pH-value by means of electrolysis.
OH
−
-ions are thus injected into the mill. These ions constitute highly reactive radicals that fasten to the surfaces of the non-hydrated cement particles, and facilitate formation of the complex qCaO.mSiO
2
.nH
2
O. This complex is formed on the surfaces of the cement particles.
Grinding of the clinker in the tubular mill will thus result in a dry product that contains cement particles which have a diameter of 10-20 micrometers, these particles being prehydrated insomuch that their surfaces are covered, either completely or partially, with a prehydrated coating that includes said complex.
Because the particles are prehydrated, they are very reactive. Adsorption of OH
−
-radicals on the surfaces of the clinker particles results in said complex-building and activation by virtue of the formation of a film of hydrosilicates on the particles. This complex acts as a nucleant for subsequent reaction with water. In combination, this results in a significant improvement in the strength development of cement paste and a reduced porosity, as will be evident from the following examples.
According to one preferred embodiment, a microfill agent and/or a water-reduction agent is/are added during the grinding process.
According to one highly preferred embodiment of the invention, part of the microfill agent and/or the water-reduction agent are mixed with said water of high pH-value to form a slurry which is injected into the mill during the grinding process, while adding dry microfill agent and/or water-reduction agent during the grinding process.
It is preferred that the water-reduction agent is slurried and that this slurry is brought to said pH-value by electrolysis, prior to injecting the slurry into the mill.
The ratio between the dry substance/substances and the slurry will preferably lie in a range of between 95 weight %/5 weight % to 85 weight %/15 weight %.
The liquid phase of the slurry will preferably exceed 50% of the weight of the slurry.
According to another preferred embodiment, microfill agent in the form of SiO
2
-containing substances, such as blast furnace slag and limestone, are delivered to the tubular mill in a quantity of up to 80% of the combined weight of microfill agent, water-reduction agent and water delivered to the mill.
According to another preferred embodiment, water-reduction agent in the form of polymers, such as lignosulfonate-based polymers that contain naphthalene or melamine or combinations thereof, are delivered to the tubular mill in an amount of up to 5% of the combined weight of microfill agent, water-reduction agent and water delivered to the mill.
A number of examples will now be described. The Table that follows the examples sets forth the results obtained with respect to water requirement, compression strength and porosity.
REFERENCES:
patent: 3689294 (1972-09-01), Braunauer
patent: 4464201 (1984-08-01), Pairon
patent: 5125976 (1992-06-01), Skvara et al.
patent: 0081861A1 (1983-06-01), None
patent: 0081861B1 (1984-09-01), None
patent: WO 94/00403 (1994-01-01), None
Derwent Abstract No. 92-257352/31, week 9231, Abstract of SU 1675255 A1, Cement Milling Method, (Belgorod Constr Materials Techn), Sep. 7, 1991.
Mangels Alfred J.
Marcantoni Paul
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