Ultra-light mineral foam

Abstract

A process for the production of a mineral foam includes separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry includes water and Portland cement as well as calcium silicate hydrate crystallization seeds; contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; and 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, wherein the cement slurry comprises water and Portland cement as well as calcium silicate hydrate crystallization seeds; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; (iii) casting the slurry of foamed cement and leave it to set, wherein no fine particle addition having a D50<2 μm is introduced to obtain the mineral foam such that the mineral foam obtained is substantially free of fine particles, wherein the slurry of foamed cement is obtained without using a calcium aluminate cement.

2. The process according to claim 1, wherein the calcium silicate hydrate crystallization seeds comprise calcium silicate hydrate particles.

3. The process according to claim 1, wherein the calcium silicate hydrate crystallization seeds are present in the form of an aqueous suspension.

4. The process according to claim 1, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.5-7% in dry calcium silicate hydrate by weight of Portland cement.

5. 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 μm.

6. 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.

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

8. 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.

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

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

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

12. A method comprising utilizing calcium silicate hydrate crystallization seeds for enhancing the mechanical stability and/or reducing the collapse of a slurry of foamed cement, said slurry of foamed cement being obtained by (i) separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry comprises water and Portland cement as well as calcium silicate hydrate crystallization seeds; and (ii) contacting the slurry of cement with the aqueous foam to obtain the slurry of foamed cement, wherein no fine particle addition having a D50<2 μm is introduced to obtain the slurry of foamed cement such that the slurry of foamed cement obtained is substantially free of fine particles, wherein the slurry of foamed cement is obtained without using a calcium aluminate cement.

13. The method according to claim 12, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.5-7% in dry calcium silicate hydrate by weight of Portland cement.

14. The process according to claim 4, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.5-5% in dry calcium silicate hydrate by weight of Portland cement.

15. The process according to claim 14, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.7-3% in dry calcium silicate hydrate by weight of Portland cement.

16. The process according to claim 9, wherein the Portland cement has a specific surface (Blaine) of 3500-6000 cm.sup.2/g.

17. The process according to claim 10, wherein the water reducer is a plasticiser or super-plasticiser.

18. The process according to claim 11, wherein the at least one supplementary mineral component is a supplementary cementitious material.

19. The process according to claim 11, 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.

20. The method according to claim 13, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.5-5% in dry calcium silicate hydrate by weight of Portland cement.

21. The method according to claim 20, wherein the calcium silicate hydrate crystallisation seeds are present in an amount of 0.7-3% in dry calcium silicate hydrate by weight of Portland cement.

Description

EXAMPLES

(1) The method according to the invention was used in order to produce mineral foams B, C, E, F and H starting from cement slurries with the slurry formulations II, III, IV, VI and VIII and from aqueous foam 1 and 2. Comparative examples have also been realized, namely the mineral foams A, D and G starting from the cement slurries with the slurry formulations I, IV and VII, 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.-%.

(6) The different CSH seeds used in the examples are produced by following the protocols described above: CSH seed (solids content=20.5%) Sludge (solids content=19.5%) Hydrated paste (solids content=16.6%)
Water: Tap Water.
Equipment Used:
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.
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.
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.
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.

(7) In the following examples, 8 mineral foams were produced. Each cement slurry is referred to by the numbers I to VIII and each aqueous foam is referred to by the number 1 or 2. The cement foam (mineral foam) as obtained is a combination of one of the cement slurries with one of the aqueous foams.

(8) Preparation of Cement Slurry

(9) TABLE-US-00001 TABLE 1 Slurry formulations I II III IV V VI VII VIII Cemen type CEM I CEM I CEM I CEM I CEM I CEM I CEM I CEM I 52, 5N 52, 5N 52, 5N 52, 5N 52, 5N 52, 5N 52, 5N 52, 5N Lafarge plant Le Le Le Saint Saint Saint Val d' Val d' Havre Havre Havre Pierre Pierre Pierre Azergues Azergues La Cour La Cour La Cour Water/Cement 0.29 0.29 0.29 0.29 0.29 0.29 0.29 0.29 (w/w) X (% Na2O eq 0.22 0.22 0.22 0.66 0.66 0.66 0.40 0.40 soluble) Cement (dry 77.45 76.86 76.85 77.40 74.52 76.81 77.44 76.83 wt %) Ca Carbonate — — — — — — — — Water (wt %) 22.46 19.24 18.36 22.35 6.03 19.18 22.36 19.21 Super-plasticiser 0.17 0.13 0.17 0.26 0.25 0.24 0.20 0.19 (wt %) CSH (wt %) 3.77 — — — — 3.76 — 3.77 Sedimentation — — — — 19.2 — — — sludge (wt %) Hydrated — — 4.63 — — — — — paste (wt %) % CSH/cement 1.00 1.00 5.00 1.00 1.00
The chemical composition of the various cement slurries used for carrying out the invention are presented in Table 1. The cement slurries have ben prepared by using the mixer Rayneri Turbotest 33/300, into which the liquid components (water, super-plasticiser, CSH crystallization seeds) 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.
Preparation of the Aqueous Foam

(10) An aqueous solution containing the foaming agent 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) 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).

(11) 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.

(12) TABLE-US-00002 TABLE 2 1 2 Foaming agent Propump26 MapeAIR L/LA Concentration (% liquid/water) 3.5 2.5 Concentration (% dry/water) 0.91 0.65 Rate, Air (L/min) 8 8 Rate, Solution (L/min) 0.41 0.41
Preparation of a Slurry of Foamed Cement

(13) 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.

(14) 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.

(15) Preparation of a Mineral Foam

(16) The slurry of foamed cement was poured into cubes of polystyrene having a dimension of 10×10×10 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.

(17) Analysis of the Mineral Foams

(18) 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 collapseed during its setting. Each test was carried out on 3 cubes of 10×10×10 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.

(19) 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.

(20) Thermal Conductivity of the Mineral Foams

(21) The thermal conductivity has been measured by means of an apparatus for measuring thermal conductivity: CT-meter supplied by the company Alphis-ERE (Resistance 5Ω, 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.

(22) Density of the Mineral Foams

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

(24) 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.

(25) The Results

(26) The results are presented in Table 3.

(27) TABLE-US-00003 TABLE 3 Mineral foam A B C D E F G H Aqueous 2 2 2 2 2 2 1 1 foam Slurry I II III IV V VI VII VIII formulation Density of 110 114 113 106 113 109 110 110 mineral foam, humid (g/L) Density of 72 73 69 nm 65 64 — 68 mineral foam, dry (g/L) Stability Stable Stable Stable unstable Stable Stable unstable Stable (cube) Size of >2 1 < x < 2 1 < x < 2 — 1 < x < 3 1 < x < 2 — 1 < x < 2 bubbles (mm) Stability nm Stable nm — nm Stable — nm (column 16*32) Lambda 0.043 nm 0.041 — nm nm — nm (W/k .Math. m) nm not measured unstable means that the foam collapsed

(28) The results show that all foams made from cement slurries that contain CSH crystallization seeds (II, III, V, VI and VIII) are stable.

(29) 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.

(30) Furthermore, comparing foams D and E, and the foams G and H, made from slurries where the only variable is the presence of CSH seeds, shows their role to generating a stable mineral foam.