Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2002-11-26
2004-10-19
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S691000
Reexamination Certificate
active
06805740
ABSTRACT:
The invention relates to a novel phosphomagnesium mortar, to a process for obtaining this mortar and to the hydraulic binder of use in obtaining the mortar.
Phosphomagnesium cements are hydraulic binders, that is to say binders which solidify in the presence of water. They are characterized by a binder based on phosphorus and magnesium derivatives.
The phosphomagnesium mortars obtained from these cements are particularly advantageous for their speed of setting and their good mechanical properties. In addition, they can be used in contact with aggressive media. However, this very rapid setting, which is advantageous in some applications, such as the repair of an airport runway or a road, limit the use of these phosphomagnesium mortars.
These mortars are provided in the form of a thick paste which renders them not very compatible with applications such as the manufacture of a floor slab or prefabricated components, unless large amounts of water or of fluidizing agents are added to them. When fluidizing agents are added, the setting time is generally affected detrimentally. When the amount of water is increased in order to render the mortar fluid, the mechanical properties generally deteriorate.
Furthermore, the articles obtained from phosphomagnesium mortars exhibit in particular a weak flexural strength. Phosphomagnesium mortars are generally brittle and lack flexibility. This is a disadvantage when, for example, the mortar is used to cover a support which, subjected to various stresses, moves and undergoes deformations. If the coating based on phosphomagnesium mortar lacks flexibility, it cracks or splits.
The aim of the present invention is to provide a novel family of fluid and selfleveling phosphomagnesium mortars which exhibit short setting times and which develop excellent mechanical properties over time.
These aims are achieved in the present invention, which relates to a fluid and selfleveling phosphomagnesium mortar which comprises a phosphomagnesium binder comprising a phosphorus compound and a magnesium compound, granular components and water, in which the W/B ratio is less than 0.38, W representing the amount of water and B the amount of phosphorus compounds and magnesium compound in the mortar, and the fluidity of the mortar is at least 150%.
Another subject matter of the invention is a process for the preparation of a fluid and selfleveling phosphomagnesium mortar which comprises the addition of water to a mixture comprising a phosphomagnesium binder, comprising a phosphorus compound and a magnesium compound, and granular components, the amount of water added being such that the W/B ratio is less than 0.38, and the kneading of the mixture to which water has been added under conditions such that the energy supplied to the mixture is sufficient to allow the liquefaction point of the paste to be passed to form a mortar which exhibits a fluidity of at least 150%.
Finally, a subject matter of the invention is articles obtained from the mortar according to the invention which exhibit a compressive mechanical strength at 24 hours of at least 30 MPa.
In the context of the invention, the fluidity is measured from a metal cylinder with a diameter (di) of 3 cm and with a height of 4.8 cm placed on a plastic film. In a first step, the cylinder is filled with the mortar for which it is desired to measure the fluidity, the cylinder is immediately removed and the diameter (df) of the cake obtained is measured 2 minutes after having removed the cylinder. The fluidity according to the invention is defined in % according to the formula (df/di)×100.
During the mixing of the phosphomagnesium binder, granular components and water under the conditions defined above, a nonfluid thick paste is formed first. It has been found, surprisingly, that, applying intensive kneeding to this paste, the paste converted into a mortar with a fluidity of at least 150%. The term “intensive kneading” is understood to mean kneading which is carried out with sufficient energy to allow the liquefaction point of the paste to be passed, that is to say the instantaneous change from a pasty state to a fluid state. The formation of a thick paste is first observed, which paste is instantaneously converted into a fluid mortar after passing the liquefaction point. This fluidity is obtained solely by the use of the kneading stage, without supplementary addition of water or of fluidizing agent.
The mortar of the present invention which exhibits a fluidity of at least 150% makes it possible to produce, for example, floor coatings. Because of its fluidity, it also makes it possible for the manufacture of prefabricated components by the use of suitable mold. It can also be pumped and sprayed without difficulty.
The fluid mortar of the present invention is obtained with low amounts of water which makes it possible to obtain articles exhibiting good mechanical properties, in particular a high compressive strength, at early ages.
Furthermore, this mortar, when it does not comprise set retarder, exhibits a very rapid setting time.
Conventionally, a phosphomagnesium binder comprises at least one phosphorus compound and at least one magnesium compound. As regards the phosphorus compound, any phosphorus-based compound can be used insofar as it comprises phosphorus pentoxide, available directly or in the form of a precursor.
Thus, mention may be made, as phosphorus compound, without the intention of being limiting, of phosphorus pentoxide, phosphoric acid or derivatives, such as orthophosphoric acid, pyrophosphoric acid or polyphosphoric acid, or the salts of such acids, such as aluminum, calcium, potassium, magnesium or ammonium phosphates, hydrogenphosphates, orthophosphates, pyrophosphates, polyphosphates, tripolyphosphates or tetrapolyphosphates, or their mixtures.
It should be noted that phosphorus-comprising waste from the fertilizer-manufacturing industries or from steelworks (pickling of steel, treatment to reduce corrosion) can be employed as phosphorus-based constituents.
According to a specific embodiment of the invention, the salts of the phosphorus-based acids mentioned above are used.
Preferably, potassium, magnesium or ammonium phosphates or hydrogenphosphates or their mixtures are used. In an even more preferred way, the phosphorus-based constituent is ammonium dihydrogenphosphate, optionally mixed with ammonium tripolyphosphate.
The phosphorus compound can be provided in a liquid form or, preferably, in a solid form.
According to a first alternative form, the phosphorus compound is in the form of particles with a particle size more particularly of at most 300 &mgr;m. It should be noted that this value is not critical and that, while it is possible to use constituents with a particle size of greater then 300 &mgr;m, milling before incorporation in the composition according to the invention may be desirable. This milling can improve the kinetics of dissolution of the phosphorus compound.
According to a second alternative form, the compound is used in a form adsorbed on a porous support. Mention may be made, as support, for example, of diatomaceous earths, clay, bentonite, silica or alumina. Adsorption is carried out in a way known per se. Thus, conventionally, the phosphorus compound, in solution or in suspension, is brought into contact with the support, with stirring, and then the resulting suspension is heated in order to evaporate off the excess liquid. This operation can likewise be carried out by impregnation of the support in a drum or on a rotating disk.
The phosphomagnesium binder also comprises at least one magnesium compound.
Any magnesium-based compound is suitable for the present invention insofar as it reacts with the phosphorus compound in the presence of water.
Mention may be made, by way of example, as suitable for the implementation of the invention, of the following magnesium compounds: magnesium oxide, magnesium hydroxide or magnesium carbonate.
Preferably, a compound based on magnesium oxide is used. “Dead burned” magnesia, usually obtained after calcination of magnesium carbonate, at
Canac Cyrille
Orange Gilles
Riche Nathalie
Green Anthony J.
Rhodia Chimie
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