THIOSULFATES FOR USE AS RETARDERS FOR MAGNESIUM PHOSPHATE CEMENT PASTES

Abstract

A use of a thiosulfate as a retarder for a cement paste comprising a magnesium phosphate cement.

Claims

1. A method for delaying a setting of a cement paste comprising a magnesium phosphate cement, comprising including a retarder in the cement paste, wherein the retarder is a thiosulfate.

2. The method of claim 1, wherein the thiosulfate is sodium thiosulfate, potassium thiosulfate, calcium thiosulfate or magnesium thiosulfate.

3. The method of claim 1, wherein the magnesium phosphate cement comprises a source of magnesium in oxidized state, the source of magnesium in oxidized state being magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium hydroxycarbonate, magnesium chloride, magnesium bromide, or a mixture thereof.

4. The method of claim 1, wherein the magnesium phosphate cement comprises a source of phosphate, the source of phosphate being sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, aluminium phosphate, aluminium monohydrogen phosphate, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, or a mixture thereof.

5. The method of claim 1, wherein the magnesium phosphate cement has a molar ratio magnesium/phosphorus ranging from 1 to 12.

6. The method of claim 1, wherein the cement paste has a mass ratio thiosulfate/magnesium phosphate cement ranging from 0.01 to 0.25.

7. The method of claim 1, wherein the cement paste further comprises at least one adjuvant, the adjuvant being a.

8. The method of claim 7, wherein the retarder other than a thiosulfate is hydrofluoric acid, sodium fluoride, citric acid, sodium citrate, boric acid or borax.

9. The method of claim 1, wherein the cement paste further comprises at least one aggregate, the aggregate being a filler, a sand or a fine gravel.

10. The method of claim 1, wherein the cement paste has a mass ratio water/magnesium phosphate cement ranging from 0.10 to 1.

11. The method of claim 2, wherein the thiosulfate is sodium thiosulfate or potassium thiosulfate.

12. The method of claim 3, wherein the source of magnesium in oxidized state is magnesium oxide.

13. The method of claim 4, wherein the source of phosphate is potassium dihydrogen phosphate.

14. The method of claim 6, wherein the mass ratio thiosulfate/magnesium phosphate cement ranges from 0.03 to 0.20.

15. The method of claim 10, wherein the mass ratio water/magnesium phosphate cement ranges from 0.20 to 0.60.

16. The method of claim 1, wherein including the thiosulfate in the cement paste comprises mixing the magnesium phosphate cement with a mixing solution comprising the thiosulfate.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0072] FIG. 1 illustrates the setting height, denoted H and expressed in mm, as a function of time, denoted t and expressed in minutes, as obtained for two pastes, respectively P1 and P2, of dead burned MgO magnesium phosphate cement and only differing from one another in that the paste P1 only comprises borax as a retarder whereas the paste P2 comprises both sodium thiosulfate and borax as retarders.

[0073] FIG. 2 illustrates the trend in the temperature, denoted T and expressed in ° C., as a function of time, denoted t and expressed in hours, as observed for the cement pastes P1 and P2.

[0074] FIG. 3 illustrates the compressive strength at 28 days, denoted R and expressed in MPa, as obtained for two materials resulting from the hardening of the cement pastes P1 and P2 respectively.

[0075] FIG. 4 illustrates the setting height, denoted H and expressed in mm, as a function of time, denoted t and expressed in minutes, as obtained for five pastes, respectively P3, P4, P5, P6 and P11, of dead burned MgO magnesium phosphate cement, differing from one another by the retarder comprised therein (borax for the paste P3; sodium thiosulfate, at different mass concentrations, for the pastes P4, P5 and P6; potassium thiosulfate for the paste P11) and also in that the pastes P3, P4, P5 and P11 are mortars whereas the paste P6 is free from aggregates.

[0076] FIG. 5 is a reworking of the data shown in FIG. 4 for the cement pastes P3 and P4 making it possible to better visualise the setting height of these pastes over the first 60 minutes of the x-axis in FIG. 4.

[0077] FIG. 6 illustrates the yield point, denoted τ.sub.0 and expressed in Pa, as a function of time, denoted t and expressed in minutes, as obtained for the cement pastes P3 and P4.

[0078] FIG. 7 illustrates the setting height, denoted H and expressed in mm, as a function of time, denoted t and expressed in minutes, as obtained for four pastes, respectively P7, P8, P9 and P10, of magnesium phosphate cement comprising an MgO comparable to a soft burned MgO, these pastes differing from one another in that the pastes P7 and P8 only comprise borax as a retarder, whereas the pastes P9 and P10 only comprise sodium thiosulfate, at different mass concentrations, as a retarder.

DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATIONS

[0079] In the following examples, all the cement pastes are magnesium phosphate cement pastes and were prepared using: [0080] as magnesium oxide: either a dead burned magnesium oxide—hereinafter denoted DB MgO—from Richard Baker Harrison Ltd (DBM90 200 mesh), of specific surface area equal to 0.75 m.sup.2/g, or a high-purity (>98%) magnesium oxide from ChemLab, of specific surface area equal to 64 m.sup.2/g and which is comparable to a soft burned magnesium oxide—hereinafter denoted SB MgO—according to Table I hereinabove; [0081] as phosphoric acid salt: potassium dihydrogen phosphate KH.sub.2PO.sub.4 from ChemLab; and [0082] as retarder(s): sodium thiosulfate pentahydrate Na.sub.2S.sub.2O.sub.3.5H.sub.2O from ChemLab, potassium thiosulfate K.sub.2S.sub.2O.sub.3 from Sigma-Aldrich and/or borax Na.sub.2B.sub.4O.sub.7.10H.sub.2O from ChemLab.

[0083] Some of these pastes comprise aggregates, in which case they comprise a quartz powder (C800 from Sibelco) and sand of grain size 0.315/1 mm (Sabliéres Palvadeau).

[0084] Moreover, all these cement pastes were prepared by following the same mixing sequence wherein: [0085] the solid constituents (MgO, KH.sub.2PO.sub.4 and, where applicable, borax and/or quartz and sand) were introduced into a mixing bowl and mixed together for 2 minutes to obtain a homogeneous mixture, then [0086] the mixing water containing a thiosulfate (in the case of a paste according to the invention) or not (in the case of a paste serving as a reference) was added to the mixture and the whole was mixed for 2 minutes.

[0087] The cement pastes were hardened at a temperature of 20° C.±2° C. and a relative humidity greater than 50%.

[0088] The setting times of the cement pastes were measured with Vicat needle tests as per the European standard NF EN 196-3: 2017 (Methods of testing cement. Part 3: Determination of setting times and soundness).

[0089] The temperatures of the cement pastes were measured by means of a Langavant semi-adiabatic calorimeter as per the standard NF EN 196-9: 2010 (Methods of testing cement. Part 9: Heat of hydration—Semi-adiabatic method).

[0090] The compressive strengths of the materials obtained from hardening the cement pastes were measured by means of a press on half-specimens (4 cm×4 cm×16 cm) of these materials as per the standard NF EN 196-1: 2016 (Methods of testing cement. Part 1: Determination of strength).

[0091] The yield points of the cement pastes were determined with flow table tests; these tests consist of slowly pouring, onto a wet glass slab, samples of the cement pastes contained in a beaker, after having left these pastes to rest in the mixer and then mixing them for 15 seconds just before performing the flow table tests; the flow radius of the samples is measured and the yield point, denoted τ.sub.0 and expressed in N/m.sup.2 or, more preferably, in Pa, is calculated by means of the Roussel and Coussot equation whereby:

[00001]${\tau }_0=\frac{225\rho g{V}^2}{128{\pi }^2{R}^5}$

[0092] ρ is the density of the cement paste in kg/m.sup.3

[0093] g is the gravitational acceleration in N/kg

[0094] V is the volume of the cement paste sample poured onto the slab in m.sup.3

[0095] R is the flow radius of the cement paste sample on the slab in m.

Example 1: Demonstration of the Beneficial Effects Associated with the Presence of Sodium Thiosulfate in a DB MgO Magnesium Phosphate Cement Paste Comprising Borax

[0096] Two pastes, respectively P1 and P2, of DB MgO magnesium phosphate cement are prepared, which only differ from one another in that the paste P1 (serving as a reference) only comprises borax as a retarder whereas the paste P2 comprises both sodium thiosulfate and borax as retarders.

[0097] The qualitative and quantitative composition of these pastes is shown in Table II hereinafter.

TABLE-US-00002 TABLE II Na DB MgO KH.sub.2PO.sub.4 Borax Quartz Sand Thiosulfate Water Pastes (g) (g) (g) (g) (g) (g) (g) P1 500 340 25.sup.a) 217 1489 — 252 P2 500 340 25.sup.a) 217 1489 44.sup.b) 252 .sup.a)representing a mass ratio of borax/(MgO + KH.sub.2PO.sub.4) of about 0.03 .sup.b)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.05

[0098] The pastes P1 and P2 are subjected to tests aimed at measuring their setting time as well as their temperature during setting, whereas the materials obtained by hardening these pastes are subjected to tests aimed at measuring the compressive strength thereof.

[0099] The results of the setting time measurements are shown in Table III hereinafter and in FIG. 1 whereas the results of the temperature measurements during setting and of the compressive strength measurements are illustrated in FIGS. 2 and 3.

TABLE-US-00003 TABLE III Setting start time Setting end time Pastes (min) (min) P1 21 24 P2 234 (i.e. 3 513 (i.e. 8 hours and 54 min) hours and 33 min)

[0100] Table III and FIG. 1 show that the presence of sodium thiosulfate in a DB MgO magnesium phosphate cement paste comprising borax makes it possible to dramatically delay and slow down the setting of this paste compared to that of a cement paste of the same composition but free from sodium thiosulfate since the presence of sodium thiosulfate makes it possible to multiply the setting start time by a factor of 11 and the setting end time by a factor of 21.

[0101] FIG. 2 shows that the presence of sodium thiosulfate in a DB MgO magnesium phosphate cement paste comprising borax also makes it possible to significantly reduce the temperature rise of this paste during setting and, therefore, the heat of hydration thereof compared to that of a cement paste of identical composition but free from sodium thiosulfate.

[0102] As regards FIG. 3, it shows that the presence of sodium thiosulfate in a DB MgO magnesium phosphate cement paste comprising borax does not negatively impact the compressive strength of the material resulting from hardening this paste.

[0103] It should be noted that the setting times obtained for the paste P2 are similar to those obtained for Portland cement pastes.

Example 2: Demonstration of the Beneficial Effects Associated with the Presence of Sodium or Potassium Thiosulfate in DB MgO Magnesium Phosphate Cement Pastes Free from Borax

[0104] Five DB MgO magnesium phosphate cement pastes, respectively P3, P4, P5, P6 and P11, are prepared.

[0105] The paste P3 (serving as a reference) only comprises borax as a retarder.

[0106] The pastes P4, P5 and P6 only comprise sodium thiosulfate, at different mass concentrations, as a retarder.

[0107] The paste P11 only comprises potassium thiosulfate as a retarder.

[0108] Furthermore, the paste P6 differs from the four others in that it does not comprise quartz or sand.

[0109] The qualitative and quantitative composition of these pastes is shown in Table IV hereinafter.

TABLE-US-00004 TABLE IV DB MgO KH.sub.2PO.sub.4 Borax Quartz Sand Na.sub.2S.sub.2O.sub.3 K.sub.2S.sub.2O.sub.3 Water Pastes (g) (g) (g) (g) (g) (g) (g) (g) P3 500 340 25.sup.a) 217 1489 — — 252 P4 500 340 — 217 1489 66.sup.b) — 252 P5 500 340 — 217 1489 88.sup.c) — 252 P6 500 340 — — — 100.sup.d)  — 252 P11 500 340 — 217 1489 — 76.71.sup.e) 288.3 .sup.a)representing a mass ratio of borax/(MgO + KH.sub.2PO.sub.4) of about 0.03 .sup.b)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.08 .sup.c)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.1 .sup.d)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.12 .sup.e)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.09

[0110] The pastes P3 to P6 and P11 are subjected to tests aimed at measuring the setting time thereof whereas the pastes P3 and P4 are furthermore subjected to tests aimed at measuring the yield point thereof.

[0111] The results of the setting time measurements are shown in Table V hereinafter and in FIGS. 4 and 5 whereas the results of the yield point measurements are illustrated in FIG. 6.

TABLE-US-00005 TABLE V Pastes Setting end time (min) P3 24 P4 47 P5 116 (i.e. 1 hour and 56 min).sup.  P6 127 (i.e. 2 hours and 7 min)  P11 236 (i.e. 3 hours and 56 min)

[0112] This table and FIG. 4 show that the presence of sodium thiosulfate in a DB MgO magnesium phosphate cement paste makes it possible, in the absence of borax, to delay the end of setting of this paste, in an especially pronounced way as the mass concentration of sodium thiosulfate of the paste increases.

[0113] They furthermore demonstrate that the presence of potassium thiosulfate in a DB MgO magnesium phosphate cement makes it possible to dramatically delay and slow down the setting of this paste.

[0114] A specificity of the presence of sodium thiosulfate in a cement paste is that of increasing the thixotropic nature of this paste. Left to rest, the cement paste starts structuring within the first 10 to 20 minutes. Even though, at this time, the initial setting has not yet been achieved, the solid structure of the cement paste starts to form. This phenomenon can be observed during the first setting height measurements which are different from 0 in the Vicat needle tests. FIG. 5 shows that it takes place for the paste P4 comprising sodium thiosulfate before taking place for the paste P3 comprising borax. However, under stress such as that induced by mixing, the cement paste can be destructured, which makes it possible to lower the viscosity thereof.

[0115] Thus, FIG. 6 which illustrates the results of the yield point measurements of the pastes P3 and P4 as obtained after having left these pastes to rest in the mixer and then mixing them for 15 seconds demonstrates that, on one hand, the yield point of the paste P4 remains low for longer than the yield point of the paste P3 and, on the other, the increase in the point has slower kinetics than the increase in the yield point of the paste P3. This means that a cement paste comprising sodium thiosulfate remains fluid for longer than a cement paste comprising borax, which is liable to facilitate the use thereof on an industrial scale.

Example 3: Demonstration of the Beneficial Effects Associated with the Presence of Sodium Thiosulfate in SB MgO Magnesium Phosphate Cement Pastes Free from Borax

[0116] Four pastes, respectively P7, P8, P9 and P10, of SB MgO magnesium phosphate cement are prepared, differing from one another in that the pastes P7 and P8 (serving as references) only comprise borax, at different mass concentrations, as a retarder whereas the pastes P9 and P10 only comprise sodium thiosulfate, at different mass concentrations, as a retarder.

[0117] All these pastes are free from quartz and sand.

[0118] The qualitative and quantitative composition thereof is shown in Table VI hereinafter.

TABLE-US-00006 TABLE VI SB MgO KH.sub.2PO.sub.4 Borax Na Thiosulfate Water Pastes (g) (g) (g) (g) (g) P7 100 338 32.sup.a) — 100 P8 100 338 80.sup.b) — 100 P9 100 338 — 65.sup.c) 100 P10 100 338 — 80.sup.d) 100 .sup.a)representing a mass ratio of borax/(MgO + KH.sub.2PO.sub.4) of about 0.07 .sup.b)representing a mass ratio of borax/(MgO + KH.sub.2PO.sub.4) of about 0.18 .sup.c)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.15 .sup.d)representing a mass ratio of thiosulfate/(MgO + KH.sub.2PO.sub.4) of about 0.18

[0119] The pastes P7 to P10 are subjected to tests aimed at measuring the setting time thereof.

[0120] The results of these tests are shown in Table VII hereinafter and illustrated in FIG. 7.

TABLE-US-00007 TABLE VII Setting start time Setting end time Pastes (min) (min) P7 6 6 P8 18 18 P9 63 198 (i.e. 3 hours and 18 min) P10 60 198 (i.e. 3 hours and 18 min)

[0121] This table and this figure show that, in the case of a SB MgO magnesium phosphate cement paste, borax appears to be ineffective in delaying the setting of this paste.

[0122] However, sodium thiosulfate makes it possible to very effectively delay and slow down the setting of such a cement paste since an initial setting is obtained, for the pastes P9 and P10, at around one hour whereas a final setting is obtained, for the same pastes, at around 3 hours and 20 min.

[0123] Such setting times are compatible with large-scale use of the magnesium phosphate cements and make it possible to avoid the use of a dead burned magnesium oxide.

REFERENCES CITED

[0124] [1] WO-A-2016/102868 [0125] [2] E. Soudee and J. Pera, Cement and Concrete Research 2002, 32, 153-157 [0126] [3] U.S. Pat. No. 6,133,498 [0127] [4] WO-A-2018/002540