ACID/BASE BINDER COMPRISING PHOSPHATE-BASED CEMENTS

Abstract

The invention describes a phosphate-based inorganic binder obtained by reaction between at least one basic constituent and an acidic phosphate salt, in the presence of a retarder which is an X.sup.+A.sup. salt, the solubility of which in an aqueous medium, measured at 25 C., is greater than that of the acidic phosphate salt, and in which: X.sup.+ is a cation chosen from alkali metals, alkaline earth metals, zinc, aluminium and the ammonium ion, and A.sup. is an acetate, formate, benzoate, tartrate, oleate, oxalate, bromide or iodide anion.

Claims

1. A phosphate-based inorganic binder obtained by reaction between at least one basic constituent and an acidic phosphate salt, in the presence of a retarder which is an X.sup.+ A.sup. salt, wherein the solubility of the retarder in an aqueous medium, measured at 25 C., is greater than that of the acidic phosphate salt, X.sup.+ is at least one cation selected from the group consisting of alkali metals, alkaline earth metals, zinc, aluminium, and an ammonium ion, and A.sup. is an acetate, formate, benzoate, tartrate, oleate, oxalate, bromide, or iodide anion.

2. The binder according to claim 1, wherein the basic constituent is at least one selected from the group consisting of metal oxides, metal hydroxides, and sulphates.

3. The binder according to claim 1, wherein the basic constituent is at least one selected from the group consisting of iron oxide, aluminium oxide, zinc oxide, magnesium oxide, calcium oxide, silicates, sources of calcium sulphate, and metallurgical slags.

4. The binder according to claim 1, obtained from a mixture of at least two basic constituents, comprising at least one selected from the group consisting of magnesium oxide, calcium hydroxide, magnesium hydroxide, wollastonite, alumina, metallurgical slags, and calcium sulphate.

5. The binder according to claim 4, wherein the mixture comprises at least one additional basic constituent selected from the group consisting of kaolin, metakaolin, calcined clays, fly ash, limestone, dolomite, mica, and talc.

6. The binder according to claim 1, wherein the acidic phosphate salt is at least one selected from the group consisting of potassium hydrogenphosphate, calcium hydrogenphosphate, magnesium hydrogenphosphate, aluminium hydrogenphosphate, sodium hydrogenphosphate, ammonium hydrogenphosphate, potassium dihydrogenphosphate, calcium dihydrogenphosphate, magnesium dihydrogenphosphate, aluminium dihydrogenphosphate, sodium dihydrogenphosphate, ammonium dihydrogenphosphate, potassium pyrophosphate, calcium pyrophosphate, magnesium pyrophosphate, aluminium pyrophosphate, sodium pyrophosphate, ammonium acid pyrophosphate, potassium polyphosphate, calcium polyphosphate, magnesium polyphosphate, aluminium polyphosphate, sodium polyphosphate, and ammonium acid polyphosphate, alone or as a mixture.

7. The binder according to claim 1, wherein the cation X.sup.+ of the retarder is at least one selected from the group consisting of potassium, calcium, magnesium, sodium, zinc, aluminium, and an ammonium ion.

8. The binder according to claim 6, wherein the cation X.sup.+ of the retarder is identical to the cation of the acidic phosphate salt.

9. The binder according to claim 1, wherein the anion A.sup. is an acetate ion or a formate ion.

10. The binder according to claim 1, wherein the retarder is a mixture of salts having anions selected from the group consisting of acetates, formats, and oxalates.

11. The binder according to claim 1, wherein a content of retarder is between 1 and 10% by weight of a total amount of constituents of the binder.

12. The binder according to claim 1, further comprising at least one other phosphate-comprising compound selected from the group consisting of orthophosphate salts, polyphosphate salts, and pyrophosphate salts, and wherein the at least one other phosphate-comprising compound comprises, as a cation, at least one selected from the group consisting of sodium, potassium, calcium, and an ammonium ion.

13. A mortar or concrete composition, comprising at least one of the binder according to claim 1.

14. A construction product, prepared on site or prefabricated, obtained from the mortar or concrete composition according to claim 13.

Description

EXAMPLE 1

[0035] A mixture consisting of 50% by weight of lightly calcined magnesium oxide (ISMAF) and 50% by weight of potassium dihydrogenphosphate KH.sub.2PO.sub.4 (Prayon) is prepared. The water is added to the pulverulent mixture thus obtained in an amount representing 20% by weight, with respect to the total amount of pulverulent constituents. The practical duration of use measured for the paste is 0.5 min. The same composition is prepared by adding 3% by weight of potassium acetate (from Sigma Aldrich) as retarder. The amount of water added is also 20% by weight. The practical duration of use measured for the paste comprising the retarder is then 7 min.

EXAMPLE 2

[0036] A mixture consisting of 50% by weight of wollastonite CaSiO.sub.3 (Nordkalk) and 50% by weight of calcium dihydrogenphosphate monohydrate Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O (Budenheim) is prepared. The water is added to the pulverulent mixture thus obtained in an amount representing 50% by weight, with respect to the total amount of pulverulent constituents. The practical duration of use measured for this paste is 0.2 min. The same composition is prepared by adding 3% by weight of calcium acetate (from Sigma Aldrich) as retarder. The amount of water added is also 50% by weight. The practical duration of use measured for the paste comprising the retarder is then 3 min.

EXAMPLE 3

[0037] Three different mixtures of magnesium oxide strongly calcined at high temperature (1500 C.) and sintered (Grecian Magnesite) and of potassium dihydrogenphosphate KH.sub.2PO.sub.4 (Prayon) are prepared while varying the MgO:MKP ratio by weight.

[0038] Composition 3-1 corresponds to 25% by weight of MgO and 75% by weight of MKP. The amount of water added is 20% by weight, with respect to the total sum of the pulverulent compounds.

[0039] Composition 3-2 corresponds to 50% by weight of MgO and 50% by weight of MKP. The amount of water added is 21% by weight, with respect to the total sum of the pulverulent compounds.

[0040] Composition 3-3 corresponds to 75% by weight of MgO and 25% by weight of MKP. The amount of water added is 22% by weight, with respect to the total sum of the pulverulent compounds.

[0041] The practical durations of application of these three pastes are measured and are respectively 17 min for the paste obtained from Composition 3-1, 5 min for the paste obtained from Composition 3-2 and 4 min for the paste obtained from Composition 3-3.

[0042] 3% by weight of potassium acetate (from Sigma Aldrich) is added to each of Compositions 3-1, 3-2 and 3-3, while maintaining the MgO:MKP ratios, which are respectively 25/75, 50/50 and 75/25. The mixing water is added in the same proportions. The practical durations of use of the pastes obtained from Compositions 3-1, 3-2 and 3-3 to which the retarder has been added were measured and respectively have the values of 80 min for the paste obtained from Composition 3-1, 50 min for the paste obtained from Composition 3-2 and 18 min for the paste obtained from Composition 3-3.

EXAMPLE 4

[0043] Several compositions with an MgO:MKP ratio by weight identical to that of Composition 3-3 are prepared from the same starting materials.

[0044] Composition 4-1 corresponds to 75% by weight of MgO strongly calcined at high temperature and 25% by weight of MKP.

[0045] Composition 4-2 comprises 37.5% by weight of MgO strongly calcined at high temperature, 12.5% by weight of MKP and 50% by weight of silica sand.

[0046] Compositions 4-3 comprise 72.8% by weight of MgO strongly calcined at high temperature, 24.2% by weight of MKP and 3% by weight of a retarder. Different retarders are tested: potassium acetate from Sigma Aldrich (Composition 4-3a), potassium formate from VWR (Composition 4-3b) and, by way of comparison, 99,8% pure boric acid from Panreac (Composition 4-3c). Some mixtures of retarders have also been tested : the composition 4-3d comprises a mixture of 2,40% by weight of potassium formate from VWR and of 0,6% by weight of potassium oxalate from VWR. The composition 4-3e comprises a mixture of 2,40% by weight of potassium acetate from Sigma Aldrich and of 0,6% by weight of potassium oxalate from VWR. Other retarders as zinc formate from Alfa Aesar (composition 4-3f) and sodium formate from VWR (composition 4-3g) are used, in an amount of 3% by weight. The amount of water added for the mixing is 22% by weight, with respect to the total sum of the pulverulent compounds.

[0047] The practical durations of use of the different compositions are measured and are given in Table 3 below:

TABLE-US-00003 TABLE 3 Practical duration of use (min) Composition 4-1 4 Composition 4-2 10 Composition 4-3a 18 3% by weight of potassium acetate Composition 4-3b 7 3% by weight of potassium formate Composition 4-3c 12 3% by weight of boric acid Composition 4-3d 8 2.4% by weight of potassium formate and 0.6% by weight of potassium oxalate Composition 4-3e 30 2.4% by weight of potassium acetate and 0.6% byweight of potassium oxalate Composition 4-3f 15 3% by weight of zinc formate Composition 4-3g 13 3% by weight of sodium formate

[0048] It is found that the silica sand participates in the retarding effect but less effectively than the retarders according to the present invention, which make it possible to obtain, for some, a greater effect than that which was obtained with retarders, such as borax, used in the prior art.

EXAMPLE 5

[0049] In the same way, different compositions comprising an MgO:MKP ratio of 25/75 are prepared as in Example 4.

[0050] Composition 5-1 corresponds to 25% by weight of MgO strongly calcined at high temperature and 75% by weight of MKP.

[0051] Composition 5-2 comprises 12.5% by weight of MgO strongly calcined at high temperature, 37.5% by weight of MKP and 50% by weight of silica sand.

[0052] Compositions 5-3 comprise 24.2% by weight of MgO strongly calcined at high temperature, 72.8% by weight of MKP and 3% by weight of a retarder. Different retarding agents are tested: potassium acetate from Sigma Aldrich (Composition 5-3a), potassium oxalate from VWR (Composition 5-3b) and, by way of comparison, 99,8% pure boric acid from Panreac (Composition 5-3c). The amount of water added for the mixing is 22% by weight, with respect to the total sum of the pulverulent compounds.

[0053] The practical durations of use of the different compositions are measured and are given in Table 4 below:

TABLE-US-00004 TABLE 4 Compo- Compo- Compo- Compo- Compo- sition sition sition sition sition 5-1 5-2 5-3a 5-3b 5-3c Practical 17 25 80 40 57 duration of use (min)

EXAMPLE 6

[0054] A mixture (Composition 6-1) is prepared which consists of: [0055] 15.8% by weight of magnesia strongly calcined at high temperature (1500 C.) and sintered (Grecian Magnesite) [0056] 3% by weight of wollastonite CaSiO.sub.3 (Nordkalk) [0057] 1% by weight of calcined alumina Al.sub.2O.sub.3 (RBH) [0058] 79.2% by weight of potassium dihydrogenphosphate KH.sub.2PO.sub.4 (Prayon) [0059] 1% by weight of an inorganic pigment (Oximed 12A Europigments) which makes it possible to colour the sample and to visually reveal the presence of efflorescence. The amount of water added is 17% by weight, with respect to the total sum of the pulverulent compounds.

[0060] The practical duration of application of this paste is 13 min.

[0061] The same paste composition is prepared while adding 3% by weight of potassium acetate from Sigma Aldrich (Composition 6-2). The practical duration of application of this paste is increased and has a value of 40 min.

[0062] FIGS. 1 and 2 represent the cured products obtained from these Compositions 6-1 and 6-2: the presence of white regions in FIG. 1, reflecting the efflorescence phenomena, is noticed. In the presence of potassium acetate, this efflorescence phenomenon is controlled, the colour of the sample being more uniform.

EXAMPLE 7

[0063] A mixture comprising 52.6% by weight of lightly calcined magnesium oxide (ISMAF), 42.1% by weight of potassium dihydrogenphosphate KH.sub.2PO.sub.4 (Prayon) and 5.3% by weight of retarder, of different types, some being not in accordance with the invention and thus given by way of comparison, is prepared. The amount of water added is 37% by weight, with respect to the total amount of the pulverulent constituents. The practical durations of use of the different pastes obtained are measured and are shown in Table 5 below:

TABLE-US-00005 TABLE 5 Practical duration of use Retarder (min) Potassium formate (VWR) 8 Dipotassium tartrate (Sigma Aldrich) 2 Potassium benzoate (Sigma Aldrich) 4 Potassium bromide (Panreac) 5 Potassium iodide (Panreac) 4 Potassium oleate (Panreac) 1 Calcium citrate (Sigma Aldrich) 0.5 99.8% pure Boric acid (Panreac) 11 Potassium acetate (Sigma Aldrich) 12

[0064] By way of comparison, the same formulation without any retarder has a practical duration of application of 0.3 min.

EXAMPLE 7

[0065] A mortar composition is prepared by mixing the following different constituents: [0066] 40% by weight of magnesia strongly calcined at high temperature (1500 C.) and sintered (Grecian Magnesite) [0067] 40% by weight of potassium dihydrogenphosphate KH.sub.2PO.sub.4 (Prayon) [0068] 20% by weight of silica sand.

[0069] The amount of water added is 20% by weight, with respect to the total sum of the pulverulent compounds.

[0070] The practical duration of application of this paste is 4.5 min.

[0071] The same paste composition is prepared while adding 3% by weight of potassium acetate (Sigma Aldrich). The practical duration of application of this paste is increased and has a value of 32 min.