Ultra-light mineral foam

Abstract

A process for the production of a mineral foam includes (i) separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry includes water and Portland cement; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; (iii) adding a magnesium salt source before, during or after step (ii); and (iv) casting the slurry of foamed cement and leave it to set.

Claims

1. A process for the production of a mineral foam comprising the following steps: (i) separately preparing a slurry of cement and an aqueous foam that does not contain a magnesium salt source as an accelerator, wherein the cement slurry comprises water and Portland cement; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; (iii) adding a magnesium salt source as an accelerator during or after step (ii); (iv) casting the slurry of foamed cement and leave it to set, wherein the mineral foam is substantially free of particles with a mean diameter D50<2 m, wherein magnesium chloride (MgCl.sub.2) and/or magnesium sulfate (MgSO.sub.4) and/or magnesium nitrate (Mg(NO.sub.3).sub.2) are used as said magnesium salt source.

2. The process according to claim 1, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.1-2.0 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

3. The process according to claim 1, wherein the D50 of bubbles of the aqueous foam prepared in step (i) is less than or equal to 400 m.

4. The process according to claim 1, wherein step (ii) comprises the introduction of the slurry of cement and the aqueous foam into a static mixer to obtain the slurry of foamed cement.

5. The process according to claim 1, wherein a water/cement ratio (wt/wt ratio) of 0.28-0.35, is used in step (i).

6. The process according to claim 1, wherein the Portland cement is a cement of the type CEM I, CEM II, CEM III, CEM IV or CEM V.

7. The process according to claim 1, wherein the Portland cement has a specific surface (Blaine) of 3000-10000 cm.sup.2/g.

8. The process according to claim 1, wherein the cement slurry comprises a water reducer.

9. The process according to claim 1, wherein the slurry of foamed cement comprises at least one supplementary mineral component.

10. The process according to claim 1, wherein magnesium chloride (MgCl.sub.2) is in the form of a magnesium chloride solution, and/or magnesium sulfate (MgSO.sub.4) is in the form of a magnesium sulfate solution and/or magnesium nitrate (Mg(NO.sub.3).sub.2) is in the form of a magnesium nitrate solution.

11. The process according to claim 1, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.1-1.0 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

12. The process according to claim 11, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.2-0.7 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

13. The process according to claim 7, wherein the Portland cement has a specific surface (Blaine) of 3500-6000 cm.sup.2/g.

14. The process according to claim 8, wherein the water reducer is a plasticiser or super-plasticiser.

15. The process according to claim 9, wherein the at least one supplementary mineral component is a supplementary cementitious material.

16. The process according to claim 9, wherein the at least one supplementary mineral component is selected from calcium carbonate, silica, ground glass, solid or hollow glass beads, glass granules, expanded glass powders, silica aerogels, silica fume, granulated blast furnace slags, ground sedimentary siliceous sands, fly ash or pozzolanic materials or mixtures thereof.

17. The process according to claim 1, wherein the slurry of cement prepared in step (i) is devoid of a magnesium salt source as an accelerator.

18. A method comprising utilizing a magnesium salt source for enhancing the mechanical stability and/or reducing the collapse of a slurry of foamed cement, the magnesium salt source being magnesium chloride and/or magnesium sulfate (MgSO.sub.4) and/or magnesium nitrate (Mg(NO.sub.3).sub.2), said slurry of foamed cement being obtained by (i) separately preparing a slurry of cement and an aqueous foam that does not contain an magnesium salt source as an accelerator, wherein the cement slurry comprises water and Portland cement; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement, and (iii) adding a magnesium salt source as an accelerator during or after step (ii).

19. The method according to claim 18, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.1-2.0 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

20. The method according to claim 18, wherein magnesium chloride (MgCl.sub.2) is in the form of a magnesium chloride solution, and/or magnesium sulfate (MgSO.sub.4) is in the form of a magnesium sulfate solution and/or magnesium nitrate (Mg(NO.sub.3).sub.2) is in the form of a magnesium nitrate solution.

21. The method according to claim 19, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.1-1 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

22. The method according to claim 21, wherein magnesium chloride is added in an amount so that the aqueous foam comprises 0.2-0.7 wt.-% of MgCl.sub.2 in dry of the aqueous foam, wherein the weight percentages are expressed by weight of water in the aqueous foam.

Description

EXAMPLES

(1) The method according to the invention was used in order to produce mineral foams B, C, E, F, H and J starting from cement slurries with the slurry formulations I, II and III and from aqueous foam 2, 3, 5, 6 and 8. Comparative examples have also been realized, namely the mineral foams A, D, G and I starting from the cement slurries with the slurry formulations I, II and III and aqueous foam 1, 4 and 7 in order to illustrate the advantageous aspects of the invention.

(2) Materials Used:

(3) The cements are Portland cements originating from different Lafarge cement productions sites, as indicated in Table 1. These cements are standard type cements. The letters R and N correspond to the definition given in the European NF EN 197-1 Standard, version April 2012.

(4) The plasticizer is a mixture comprising a polycarboxylate polyoxide (PCP) from the Chryso company under the brand name of Chrysolab EPB 530-017, which does not comprise an anti-foaming agent. The solids content of Chrysolab EPB 530-017 is 48 wt.-%

(5) The foaming agents used are the following derivative proteins of animal origin: Propump 26 obtained from the company Propump Engineering Ltd having a solids content of 26 wt.-%; MAPEAIR L/LA obtained for the company MAPEI, having a solids content of 26 wt.-%: Foamcem LT2 obtained from the company Laston Italiana spa.

(6) Water: tap water.

(7) Equipment Used:

(8) The Rayneri mixer: A Turbotest mixer (MEXP-101, model: Turbotest 33/300, Serial N: 123861) supplied by the company Rayneri, which is a mixer with a vertical axis.

(9) Pumps: A pump having an eccentric screw conveyer Seepex of the type MD 006-24, commission no. 244920. A pump having an eccentric screw conveyer Seepex of the type MD 006-24, commission no. 278702.

(10) Foamer: A foamer comprising a bed of glass beads of the type SB30 having a diameter of 0.8-1.4 mm filled up in a tube having a length of 100 mm and a diameter of 12 mm.

(11) Static mixer: A static mixer comprised of 32 helicoidal elements of the type Kenics having a diameter of 19 mm and referred to as 16La632 at ISOJET.

(12) In the following examples, 10 mineral foams were produced. Each cement slurry is referred to by the numbers I, II and III, each aqueous foam is referred to by the numbers 1, 2, 3, 4, 5, 6, 7 and 8. The cement foam (mineral foam) as obtained is a combination of one of the cement slurries with one of the aqueous foams.

(13) Preparation of Cement Slurry

(14) TABLE-US-00001 TABLE 1 Slurry formulations I II III Cement type CEM I 52.5N CEM I 52.5N CEM I 52.5N CE CP2 NF LHY-05420 Lafarge plant Le Havre Mannersdorf Saint Pierre La Cour Water/Cement ratio 0.29 0.33 0.29 (wt/wt) x (% Na2O eq soluble) Cement (dry wt %) 70.60 75.10 76.83 Calcium carbonate 6.86 (dry wt %) Water (wt %) 22.39 24.71 21.49 Super-plasticiser 0.17 0.20 0.20 (wt %)

(15) The chemical composition of the various cement slurries used for carrying out the invention are presented in Table 1. The cement slurries have been prepared by using the mixer Rayneri Turbotest 33/300, into which the liquid components (water, super-plasticiser) have first been introduced. While mixing at 1000 rpm, the solid components (cement and all pulverulent components) have progressively been added. The cement slurry was then mixed for two additional minutes.

(16) Preparation of the Aqueous Foam

(17) An aqueous solution containing the foaming agent and magnesium chloride has been introduced into a receptacle. The composition of this aqueous solution of foaming agent (in particular the concentration and the nature of the foaming agent and the magnesium chloride) is reported in Table 2. The aqueous solution of the foaming agent was pumped by means of a volumetric pump having an eccentric screw conveyor Seed TM MD-006-24 (commission no: 278702).

(18) This foaming agent solution was introduced into the foamer through the bed of beads by means of pressurized air (1-6 bar) and a T-junction. The aqueous foam was produced in a continuous way at a rate as indicated in Table 2.

(19) TABLE-US-00002 TABLE 2 Aqueous foam formulation 1 2 3 4 5 6 7 8 Foaming agent Propump Mape Foamcem Mape Mape Mape Foamcem Foamcem 26 AIR LT2 AIR AIR AIR LT2 LT2 L/LA L/LA L/LA L/LA Concentration 3.5 2.5 3.0 2.5 2.5 2.5 3.0 3.0 (% liquid/water) Concentration 0.91 0.65 0.84 0.65 0.65 0.65 0.84 0.84 (% dry/water) Concentration 0.2 0.4 0.4 0.6 0.6 MgCl.sub.2 (% dry/water) Air rate (L/min) 8 8 8 8 8 8 8 8 Foaming agent 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 rate (L/min)

(20) Preparation of a Slurry of Foamed Cement

(21) The cement slurries as previously obtained have been poured into the mixing receptacle while mixing (400 rpm). The cement slurry was pumped by means of a volumetric pump having an eccentric screw conveyer Seepex MD 006-24 (commission no: 244920) at a rate of 0.25 L/min.

(22) The pumped slurry and the aqueous foam, continuously prepared, have been brought into contact with each other in a static mixer and a slurry of foamed cement was obtained.

(23) Preparation of a Mineral Foam

(24) The slurry of foamed cement was poured into cubes of polystyrene having a dimension of 101010 cm and into cylindrical columns having a height of 2.50 m and a diameter of 20 cm. Three cubes have been realized for each slurry of foamed cement. The cubes have been demoulded after 1 day and stored 7 days at a relative humidity of 100% and a temperature of 20 C. The cubes have then been dried at a temperature of 45 C. until a constant mass is obtained. A column has been realized for certain slurries of foamed cement. The columns have been demoulded after 3 to 7 days and then cut in sections having a length of 25 cm. The sections have been dried until a constant mass is obtained.

(25) Analysis of the Mineral Foams

(26) The stability of the foams has been measured by visual inspection of the cubes before demoulding. A foam has been described as stable, if the cube kept its height of 10 cm after setting. A foam has been described as unstable, if the cube has collapsed during its setting. Each test was carried out on 3 cubes of 101010 cm. The results show a similar performance among the 3 cubes. As the case may be, the results are the mean value of 3 cubes.

(27) A column has been considered stable if the density between the lower section and the upper section does not differ by more than 5 kg/m.

(28) Water Drainage

(29) The amount of drained water is measured at 24 hours by weighing the amount of water that is released upon demolding the 101010 cubes. Water drainage is expressed in g.

(30) Thermal Conductivity of the Mineral Foams

(31) The thermal conductivity has been measured by means of an apparatus for measuring thermal conductivity: CT-meter supplied by the company Alphis-ERE (Resistance 5, sensor wire 50 mm. The measurements have been carried out on dry samples at a temperature of 45 C. until a constant mass is obtained. The sample is then cut in two equal pieces by means of a saw. The measuring sensor was placed between the two surfaces of the sample halves (on the side of the sawing). The heat was transferred from the source to the thermo element through the material that surrounds the sensor; the temperature raise of the thermo element was measured as a function of time, which allowed to calculate the thermal conductivity of the sample.

(32) Density of the Mineral Foams

(33) The humid density of the cement slurry was measured by weighing the cubes at the time of casting.

(34) The dry density of the samples was measured on dried samples at a temperature of 45 C. until a constant mass was obtained, while pressing the cubes.

(35) The Results

(36) The results are presented in Table 4.

(37) TABLE-US-00003 TABLE 4 Mineral foam A B C D E F G H I J Aqueous 1 2 3 4 5 6 7 8 4 6 foam Cement I I I II II II II II III III slurry Density of 120 120 120 105 110 107 108 107 110 105 humid mineral foam (g/L) Density of 73 72 74 69 66 63 62 dry mineral foam (g/L) Stability Stable Stable Stable Unstable Stable Stable Unstable Stable Unstable Stable (cube) Bubble x > 2 1 < x < 2 1 < x < 2 1 < x < 2 1 < x < 2 1 < x < 2 1 < x < 2 size (mm) Drainage 10 5 2 5 nm 6 6 at 24 h on cube (g water) Stability Stable Stable Stable Unstable Stable Stable Unstable Stable Unstable Stable (column 16*32) Lambda 0.041 0.040 0.041 0.041 nm nm 0.042 (W/K .Math. m) (measured with CT- meter) nm . . . not measured unstable means that the foam collapsed

(38) The results show that all foams containing magnesium chloride (B, C, E, F, H and J) are stable.

(39) Furthermore, these stable foams have a reduced average diameter of their air bubbles, which is known to be associated with increased stability of the foam and a lower water drainage.