ULTRA-LIGHT MINERAL FOAM AND METHOD FOR PRODUCING SAME

Abstract

A method for producing a mineral foam includes: (i) independently preparing a cement slurry and an aqueous foam, the cement slurry being prepared by mixing water E and cement C, the cement C including a soluble equivalent quantity x of Na.sub.2O, x being expressed by weight for 100 parts cement, the slurry having a ratio x/(E/C) less than or equal to 1.75, E/C being expressed by weight, and the particles of cement C having a size distribution such that the particle size distribution ratio d.sub.max(h/2)/d.sub.min(h/2) is between 5 and 25; (ii) bringing the cement slurry into contact with the aqueous foam in order to obtain a foamed cement slurry; and (iii) shaping the foamed cement slurry obtained in step (ii) and allowing setting to take place.

Claims

1. A Method for producing a mineral foam comprising the following steps: (i) independently preparing a cement slurry and an aqueous foam, the cement slurry being prepared by mixing water W and cement C, the cement C comprising an amount x of soluble Na.sub.2O equivalent, x being expressed in weight per 100 parts of cement, said slurry having a ratio x/(W/C) less than or equal to 1.75, with W/C expressed by weight, and the particles of cement C have a particle size distribution such that the ratio d.sub.max(h/2)/d.sub.min(h/2) of the particle size distribution is between 5 and 25; (ii) contacting the cement slurry with the aqueous foam to obtain a slurry of foamed cement; and (iii) forming the slurry of foamed cement obtained at step (ii) and leaving to set.

2. The method according to claim 1, wherein the ratio x/(W/C) is less than or equal to 1.60.

3. The method according to claim 1, wherein the ratio d.sub.max(h/2)/d.sub.min(h/2) is from 6 to 14.

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

5. The method according to claim 1, wherein the cement has a Blaine specific surface area of 3 500 to 10 000 cm.sup.2/g.

6. The method according to claim 1, wherein the cement slurry comprises a water reducing agent of plasticizer or superplasticizer type.

7. The method according to claim 1, wherein the mineral foam comprises a mineral addition.

8. The method according to claim 1, wherein the mineral foam contains substantially no fine particles.

9. The method according to claim 1, wherein the W/C weight ratio of the cement slurry ranges from 0.23 to 2.0.

10. The method according to claim 1, wherein the aqueous foam comprises water and a foaming agent.

11. A mineral foam obtainable using the method according to claim 1.

12. The foam according to claim 11, having a dry density of 30 to 300 kg/m.sup.3.

13. The foam according to claim 11, having a thermal conductivity of 0.030 to 0.150 W/(m.Math.K).

14. A construction element comprising a mineral foam according to claim 11.

15. A method comprising utilizing the mineral foam according to claim 11 as insulating material.

16. The method according to claim 2, wherein the ratio x/(W/C) is less than or equal to 1.50.

17. The method according to claim 15, wherein the mineral foam is utilized as thermal or sound insulation.

Description

[0079] The invention will be better understood on reading the following examples and Figures that are not in any manner restrictive and in which:

[0080] FIG. 1 is a graphical illustration of the particle size distribution in a typical cement used to implement the invention.

[0081] The following measuring methods were used:

[0082] Laser Particle Size Measurement

The particle size curves of the different powders were obtained using a laser size analyser of Mastersizer 2000 type (year 2008, series MAL1020429) sold by Malvern.

[0083] Measurement is carried out in a suitable medium (e.g. an aqueous medium) to disperse the particles; the particle size must be between 1 m and 2 mm. The light source is a red HeNe laser (632 nm) and blue diode (466 nm). The optical mode is a Fraunhofer model with polydisperse particle sizing standard.

[0084] Measurement of background noise is first performed using a pump rate of 2000 rpm, an agitator speed of 800 rpm and noise measurement over 10 s, in the absence of ultrasound. It is first verified that the light intensity of the laser is at least 80%, and that a decreasing exponential curve is obtained for background noise. If this is not the case, the cell lenses must be cleaned.

[0085] A first measurement is taken on the sample with the following parameters: pump speed 2000 rpm, agitator speed 800 rpm, no ultrasound, obscuration limit between 10 and 20%. The sample is inserted to obtain obscuration slightly higher than 10%. After stabilisation of obscuration, measurement is conducted with a time between immersion and measurement set at 10 s. Measurement time is 30 s (30000 diffraction images analysed). In the size distribution graph obtained, consideration must be given to the fact that part of the powder population may be agglomerated.

[0086] A second measurement is then carried out (without emptying the vessel) with ultrasound. The pump rate is increased to 2500 rpm agitation to 1000 rpm, and with 100% ultrasound emission (30 watts). This regimen is maintained for 3 minutes, before returning to the initial parameters: pump rate 2000 rpm, agitator speed 800 rpm, no ultrasound. After 10 s (to evacuate any air bubbles), a 30 s measurement is performed (30000 images analysed). This second measurement corresponds to a powder de-agglomerated by ultrasonic dispersion.

[0087] Each measurement is repeated at least twice to verify the stability of the result. The apparatus is calibrated before each work session using a standard sample (C10 silica Sifraco) having a known particle size curve. All the measurements given in the description and the given ranges correspond to the values obtained with ultrasound.

[0088] Method for Measuring BLAINE Specific Surface Area

[0089] The specific surface area of the different materials was measured as follows:

[0090] The Blaine method at 20 C. with relative humidity not exceeding 65%, using Blaine Euromatest Sintco apparatus conforming to European standard EN 196-6.

[0091] Before measuring the specific surface area, the wet samples were dried to constant weight in an oven at a temperature of 50 to 150 C. (the dried product was then ground to obtain a powder having a maximum particle size of 80 m or less).

[0092] Method for Measuring Alkali Content:

[0093] The alkali contents (% K.sub.2O and % Na.sub.2O) of these cements were measured by atomic emission spectrometry, method known as ICP-AES (Inductively-Coupled Plasma-Atomic Emission Spectrometry). The model of the measuring apparatus was a Varian 720-ES, series EL06093608, 2006. To perform this measurement a sample of 2 g of cement was solubilised in 100 mL demineralised water for 15 minutes then filtered through two superimposed filter papers e.g. a first of MN640W type and a second of MN640DD type, in a 200 mL flask, then rinsed with demineralised water. 20 mL of hydrochloric acid were added at a concentration of 1/20 (volume/volume). The flask was completed up to the graduation line of 200 mL by adding demineralised water. This solution was analysed on the ICP-AES apparatus.

[0094] The content of soluble Na.sub.2O equivalent was calculated on the basis of the following formula:

((M.sub.Na2O/M.sub.K2O)*K.sub.2O+Na.sub.2O)=Na.sub.2O.sub.eq, M being the molar mass of the compounds in subscript.

EXAMPLES OF EMBODIMENT

[0095] The method of the invention was practically applied to prepare cement foams of formulas I, II, V, VII, VIII, IX, X and XI. Comparative examples III, IV and VI were also carried out to evidence the advantageous aspects of the method of the invention.

[0096] Materials:

[0097] The cements used were Portland cements originating from different Lafarge cement plants identified by the name of the place of their location as specified in Table (I). These cements are standard type cements. The letters R and N correspond to the definition of standard NF EN 197-1, version April 2012.

[0098] Micro A anhydrite is anhydrous calcium sulfate supplied by Anhydrite Minerale France.

[0099] The superplasticizers used were mixtures comprising a polycarboxylate polyoxide (PCP) produced by Chryso under the name Chrysolab EPB530-017 (Formulas III to X) and Chrysolab EPB530-026 (Formulas I and II). They are based on Premia180 products (for Chrysolab EPB530-017) and Optima203 (for Chrysolab EPB530-026) and do not contain any anti-foaming agent. The dry extract of Chrysolab EPB530-017 is 48 weight %. The dry extract of Chrysolab EPB530-026 is 58 weight %.

[0100] The foaming agents used were derived from animal proteins and were the following: [0101] Propump26 and Propump 40 produced by Propump, the dry extracts thereof being 26 and 34 weight % respectively; [0102] MAPEAIR L/LA produced by MAPE having a dry extract of 26 weight %; [0103] Foamcem produced by LASTON having a dry extract of 28 weight %; [0104] EFA 1500 produced by Edama, having a dry extract of 36 weight %.

[0105] The water used was tap water.

[0106] Equipment Used:

[0107] Rayneri Mixers: [0108] Mixer of R 602 EV (2003) model supplied by Rayneri. The mixer is composed of a chassis on which drums of 10 to 60 litres are positioned. The 10 L drum was used with a paddle of blade type adapted to the volume of the drum. This paddle rotates about itself accompanied by planetary movement around the drum shaft. [0109] Turbotest mixer (MEXP-101, model Turbotest 33/300, series N: 123861) supplied by Rayneri. It is a mixer with vertical shaft.

[0110] Pumps: [0111] Seepex eccentric screw pump of MD 006-24 type, commission N 244920. [0112] Seepex eccentric screw pump of MD 006-24 type commission N 278702.

[0113] Foamer: [0114] Foamer composed of a bed of glass beads of SB30 type having a diameter of between 0.8 and 1.4 mm, packed in a tube of length 100 mm and diameter 12 mm.

[0115] Static Mixer: [0116] A static mixer composed of 32 helical elements of Kenics type, diameter 19 mm, reference 16La632 by ISOJET

[0117] In the following examples mineral foams were prepared. Each cement slurry is referenced with a number from I to XI and each aqueous foam carries a number from 1 to 6. The cement foam obtained (or mineral foam of the invention) is a combination of one of these cement slurries with one of these aqueous foams.

I. Preparation of Mineral Foams

[0118] I.1 Preparation of a Cement Slurry

[0119] The chemical compositions of the different cement slurries used to carry out the invention are given in Table I. The slurries were prepared using the Rayneri R 602 EV mixer by previously loading the solid components (cement) then gradually adding water and the admixture. The slurry was then mixed for two additional minutes.

TABLE-US-00001 TABLE (I) Formulation of the cement slurries Formulas I II III IV V VI VII VIII IX type of cement CEM I CEM I CEM I CEM I CEM III/B CEM I CEM I CEM I CEM I 52.5 N 52.5 R 52.5 R 52.5 R 42.5 N 52.5 R 52.5 R 52.5 R 52.5 R Lafarge plant Le Havre Le Tell La Malle Port La La Malle Saint Saint Saint Val Nouvelle Pierre Pierre Pierre d'Azergue La Cour La Cour La Cour x (% soluble Na2O-eq) 0.22 0.14 0.78 0.54 0.43 0.66 0.66 0.66 0.4 cement (weight %) 78.80 77.54 77.30 77.44 77.99 76.87 68.87 66.56 66.18 water (weight %) 21.20 22.46 22.70 22.56 22.01 23.13 31.13 33.44 33.82 Superplasticizer 0.06 0.08 0.18 0.10 0.13 0.13 0.01 0.00 0.00 (weight %) W/C ratio (weight) 0.27 0.29 0.29 0.29 0.29 0.28 0.45 0.5 0.51 x/(W/C) 0.759 0.483 2.69 1.862 1.483 2.276 1.467 1.320 0.784 d.sub.max(h/2)/d.sub.min(h/2) 8.4 10.5 13.4 6.5 7.2 6.8 6.8 6.8 10.2 Formulas X XI type of cement CEM I 52.5 R (Blaine = 6340 cm2/g) CEM I 52.5 R (Blaine = 9000 cm2/g) Lafarge plant Saint Pierre La Cour Saint Pierre La Cour Cement (weight %) 16.33 16.15 Addition (weight %) 60.33 59.79 Micro A anhydrite 0.37 0.74 (weight %) Water (weight %) 22.85 23.15 SP superplasticizer 0.12 0.18 (weight %) W/C ratio (weight) 1.40 1.43 W/L ratio (weight) 0.30 0.30 x (% soluble Na2O-eq) 0.61 0.69 x/(W/C) 0.436 0.480 d.sub.max(h/2)/d.sub.min(h/2) 18.2 24.5

[0120] The values d.sub.max(h/2) and d.sub.min(h/2) were measured as described above, with reference to FIG. 1.

[0121] The results are generally visualised in graph form such as the graph given in FIG. 1 illustrating a typical particle distribution by volume. The height h is the height of the highest peak measured by laser particle size measurement (FIG. 1). Taking a height h/2 as reference, d.sub.max(h/2) and d.sub.min(h/2) are respectively defined as the size of the largest particles and the size of the smallest particles of distribution in a proportion equal to h/2.

[0122] I.2 Preparation of the Aqueous Foam

[0123] An aqueous solution containing the foaming agent was placed in a buffer vessel. The composition of his aqueous solution of foaming agent (in particular the concentration and type of foaming agent) is given in Table II. The solution of foaming agent was pumped through the volumetric eccentric screw pump Seepex MD 006-24 (commission N 278702).

[0124] This solution of foaming agent was passed through the bed of beads of the foamer together with pressurised air (range 1 to 6 bars) using a T junction. The aqueous foam was continuously generated at the flow rate indicated in Table II.

TABLE-US-00002 TABLE II formulation of aqueous foams and flow rate Aqueous foam number 1 2 3 4 5 6 Foaming agent Propump 26 Propump 40 MapeAIR L/LA Foamcem EFA1500 Propump26 Concentration 4.5 3 2.5 3 1.5 3.5 (% liq./water) Concentration 1.17 1.02 0.65 0.84 0.54 0.91 (% dry/water) Air flow rate 8 8 8 8 8 8 (L/min) Solution flow rate 0.41 0.418 0.41 0.41 0.418 0.418 (L/min)

[0125] I.3 Preparation of a Slurry of Foamed Cement:

[0126] The previously obtained cement slurry was poured into a buffer vessel held under agitation by means of a Turbotest Rayneri mixer (MEXP-101) comprising a deflocculating blade (blade adjustable from 1000 rpm to 400 rpm as a function of slurry volume). The slurry was pumped using a volumetric eccentric screw pump (Seepex MD 006-24, commission N: 244920).

[0127] The pumped slurry and the preceding, continuously generated aqueous foam were placed in contact in the static mixer paying heed to the flow rates specified in Table II. The volume of cement slurry used was about 33 L/m3 and the volume of aqueous foam about 967 L/m3. The slurry of foamed cement was thus generated.

[0128] I.4 Obtaining a Mineral Foam

[0129] The slurry of foamed cement was cast into polystyrene cubes having sides of 101010 cm and into cylindrical columns of height 2.50 m and diameter of 20 cm. Three cubes were prepared for each foamed slurry. The cubes were released from the could after 1 day and stored 7 days at 100% relative humidity and 20 C. The cubes were then dried to constant weight at 45 C. A column was formed with some of the foamed slurries. The columns were released from the mould between 3 and 7 days later and cut into sections of length 25 cm. The sections were dried at 45 C. to constant weight.

II. Analysis of the Mineral Foam

II.1 Stability of the Mineral Foam

[0130] The stability of the foams was simply measured by visual inspection of the generated cubes before mould release. A foam was described as being stable if the cube under consideration had maintained a height of 10 cm after setting. A foam was characterized as being unstable if the cube under consideration had collapsed when setting. Each test was performed on 3 cubes of 10*10*10 cm. The results show similar behaviour between the 3 cubes. When applicable, the results expressed are the mean of these 3 cubes.

[0131] A column was considered stable if the difference in density between the bottom section and the top section of the column did not exceed 5 kg/m.sup.3.

II.2 Thermal Conductivity of the Mineral Foams

[0132] Thermal conductivity was measured using thermal conductivity measuring apparatus: TC-meter supplied by Alphis-ERE (Resistance 5, wire probe 50 mm). Measurement was performed on samples dried at 45 C. to constant weight. The sample was then sawn into two pieces of equal size. The measuring probe was placed between the two planar surfaces of these two sample halves (sawn sides). Heat was transmitted from the source to the thermocouple through the material surrounding the probe. The temperature rise of the thermocouple was measured as a function of time and allowed calculation of the thermal conductivity of the sample.

II.3 Density of the Mineral Foams

[0133] The wet density of the slurries of foamed cement was measured by weighing the cubes at the time of casting.

[0134] The dry density of the samples was measured on the dry samples dried at 45 C. to constant weight, again by weighing of the cubes.

II.4 Results

[0135] The results are given in Tables III and IV below,

TABLE-US-00003 TABLE (III) Analyses of mineral foams with the Propump26 foaming agent Aqueous foam formula 1 1 1 1 1 1 1 1 1 1 1 Slurry formula I II III IV V VI VII VIII IX X XI Wet density of foamed 108 113 112 117 114 112 110 113 112 100 102 slurry (g/l) Dry density (g/l) 72 71 76 82 71 69 57 59 Stability (cube) Stable Stable Not Not Stable Not Stable Stable Stable Stable Stable stable stable stable Stability Stable Stable Not Not Not Not Stable Not Stable Stable Stable (column) stable stable Measured stable Measured Lambda (w/k .Math. m - TC 0.043 0.044 Not Not Not Not 0.041 Not meter measurement) Measured Measured Measured Measured Measured Not stable means that the foam collapsed.

TABLE-US-00004 TABLE (IV) Analyses of mineral foams with different foaming agents Aqueous foam formula 2 2 3 3 4 4 5 5 6 6 Slurry formula II VI II VI II VI II VI II VI Wet density of foamed slurry 112 118 105 109 104 112 117 111 106 109 (g/l) Dry density (g/l) 73 69 68 76 69 Stability (cube) Stable Not Stable Not Stable Not Stable Not Stable Not Stable stable stable stable stable Stability Stable Not Stable Not Stable Not Stable Not Stable Not (column) Stable stable stable stable stable Lambda (w/k .Math. m - TC meter 0.043 0.042 0.043 Not 0.043 measurement) Measured Not stable means that the foam collapsed.

II.5 Conclusions

[0136] These examples allow assessment of the role played by the soluble alkali equivalent in the stability of a cement foam. If the alkalinity content is held at a low level through the use of a low alkali cement, or if the ratio x/(W/C) is lower than 1.75, the foam is stable. When the alkali content increases, the foam becomes destabilised and collapses. It can be noted that the type of clinker used does not have any influence on the stability of the foam. For example, the clinker contained in the cement of slurry formula III (comparative) and V (of the invention) have the same origin. However, the soluble alkali equivalent of the cement used in formula V is strongly reduced through the addition of slag. This dilution allows obtaining of the desired stability.

[0137] The invention is not limited to the embodiments presented and other embodiments will be clearly apparent to persons skilled in the art.