FOAMED MINERAL BINDER COMPOSITIONS

Abstract

A method for producing a foamed mineral binder composition includes the steps of: a) separately providing: (i) an aqueous foam; and (ii) an aqueous slurry including a mineral binder and a dispersed polymer; (b) mixing the slurry of the mineral binder with the aqueous foam to obtain the foamed mineral binder composition; whereby during the production of the foamed mineral binder composition, carbon dioxide and/or a carbonate is provided such that it is incorporated in the foamed mineral binder composition.

Claims

1. Method for producing a foamed mineral binder composition, comprising the steps of: a) separately providing: (i) an aqueous foam; (ii) an aqueous slurry comprising a mineral binder and a dispersed polymer; b) mixing the slurry of the mineral binder with the aqueous foam to obtain the foamed mineral binder composition; whereby during the production of the foamed mineral binder composition, carbon dioxide and/or a carbonate is provided such that it is incorporated in the foamed mineral binder composition.

2. Method according to claim 1, whereby in step a) (i) an aqueous foam comprising dissolved carbon dioxide and/or carbonate is provided.

3. Method according to claim 1, whereby the aqueous foam is produced by dissolving a substance selected from carbon dioxide, a source of carbon dioxide, carbonate and/or a source of carbonate in water to obtain an aqueous mixture, and subsequently foaming the so obtained aqueous mixture with a gas.

4. Method according to claim 1, whereby the aqueous foam comprises carbon dioxide with a concentration of 150-30000 mg per liter of liquid water in the aqueous foam.

5. Method according to claim 1, whereby the aqueous foam is produced by adding a carbonate, whereby a weight proportion of carbonate ions (CO.sub.3.sup.2?) comprised in the substance is from 0.01-3 wt. %, with respect to the mineral binder.

6. Method according to claim 1, whereby the aqueous foam comprises a surfactant.

7. Method according to claim 1, whereby the surfactant is mixed with the water of the aqueous foam before foaming.

8. Method according to claim 1, whereby the mineral binder in the aqueous slurry comprises a hydraulic binder.

9. Method according to claim 1, whereby the dispersed polymer is selected from polyacrylates, polyvinyl esters, polyvinyl alcohols, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, styrene-butadiene copolymers, vinyl acetate-vinyl neodecanoate (VeoVa) copolymers, polyurethane polymers or mixtures thereof.

10. Method according to claim 1, whereby a proportion of the water dispersed polymer is from 1-25 wt. %, with respect to the weight of the mineral binder in the aqueous slurry.

11. Method according to claim 1, whereby the aqueous slurry comprises a plasticizer.

12. Method according to claim 1, whereby in step b) the aqueous foam and the slurry of the mineral binder are mixed together in a static mixer.

13. Method according to claim 1, whereby a density of the foamed mineral binder composition directly after preparation is <500 g per liter and/or a density of the foamed mineral binder composition after hardening for 16 hours is <500 g per liter.

14. Foamed mineral binder composition obtainable or obtained by a method according to claim 1.

15. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0116] The drawing used to explain the embodiments shows:

[0117] FIG. 1 calorimetric data recorded during the hardening process of differently produced foamed cement compositions.

EXEMPLARY EMBODIMENTS

1. General Method

[0118] For producing foamed mineral binder compositions, a device of type Foamed Concrete Laboratory MixerSBL from GERTEC Maschinen-und Anlagenbau GmbH (Germany) was used.

[0119] Thereby, an aqueous foam with a predetermined density was produced in a first container, and a cement slurry was produced in a second container. Subsequently, the aqueous foam and the cement slurry were driven by pressurized air through a static mixing unit of the device in order to obtain a foamed mineral binder composition, i.e. a foamed cement composition. Thereby, the target foam density of the foamed cement composition was adjusted by the air pressure.

2. Cement Foams Produced with Dissolved Carbon Dioxide

2.1 Preparation

[0120] Aqueous foams have been produced with the above described Gertec device by foaming 10 kg of a saturated solution of CO.sub.2 in water (approximately 1.7 g CO.sub.2 per liter) and 0.2 kg of an organic tenside (Sika? Lightcrete-400; available from Sika Deutschland GmbH). The foam density in the range of 100-150 g/liter has been adjusted by appropriate machine settings. Specific foam densities are given in tables shown below. These aqueous foams are referred to as carbonized foams CF1.

[0121] Aqueous foams have been produced with the above described Gertec device by foaming a solution of 0.2 kg of a protein based surfactant (Foamrock PFA available from FLP Konovalov D.S., Ukraine) in 10 kg of water with air containing 8 Vol % of CO.sub.2 (Vol % relative to air). The foam density of 100 g/liter has been adjusted by appropriate machine settings. Specific foam densities are given in tables shown below. These aqueous foams are referred to as carbonized foams CF2.

[0122] For comparative experiments, corresponding foams with pure water instead of a saturated solution of CO.sub.2 in water were produced as well. These aqueous foams are referred to as water based foams WF.

[0123] Aqueous cement slurries have been produced by mixing 25 kg of Portland cement (CEM I, 52.5 N; from Lafarge Holcim) with 0.05 kg of a polycarboxylate ether plasticizer, water (w/c=0.4) and a redispersible polymer (RDP) based on a hard copolymer of vinyl acetate and ethylene. Specific amounts of the RDP are given in tables shown below.

[0124] Subsequently, the aqueous foams and the cement slurries were pumped (2-5 bar above environmental air pressure) through the static mixing unit of the device in order to obtain the foamed cement composition.

2.2 Properties

[0125] In a first series of experiments A.1-A.7, for reasons of comparison, the effect of the redispersible polymer was evaluated with water based foams WF. Foam stability has been judged optically by eye. R1 is a control experiment without any RDP. Table 1 gives an overview of the results:

TABLE-US-00001 TABLE 1 Effect of the redispersible polymer (RDP) aqueous Density Appearance of Exp. foam type [g/liter] RDP [kg] foamed cement R1 WF 135 0 collapsed A.1 WF 135 0.5 collapsed A.2 WF 135 0.75 collapsed A.3 WF 135 1.25 partially collapsed A.4 WF 135 2.5 stable A.5 WF 80 2.5 collapsed A.6 WF 135 3.75 (unstable process)

[0126] It was observed that a stable foam could be obtained with 2.5 kg RDP per 25 kg cement (10%) (cf. A.4). However, when switching to a lower target density (100 g/liter; A.5), the foam collapsed. Increasing the RDP content further led to an unstable process, very likely due to viscosity increase (A.6), where no continuous foam could be produced.

[0127] In a second series of experiments B.1-B.3, the effect of carbon dioxide or CO.sub.2, respectively, was evaluated. Thereby, no RDP was used in the cement slurries. The results are shown in table 2.

[0128] R2 is a control experiment in which a water based foam WF (not carbonized) was produced and the aqueous foam/cement slurry mix was driven through the static mixing unit by pressurized CO.sub.2 instead of air. This results in a very high CO.sub.2 loading in the foamed cement composition.

TABLE-US-00002 TABLE 2 Effect of carbon dioxide aqueous Density Appearance of foamed Exp. foam type [g/liter] RDP [kg] cement/density [g/liter] R2 WF 80 0 collapsed/1800 B.1 CF1 80 0 partially stable/149 B.2 CF1 100 0 partially stable/152 B.3 CF2 100 0 stable/145

[0129] With experiment R2, a full carbonation of the cement has to be expected, however, this approach results in complete foam collapse already inside the foam generator. Although it is known that carbonation by slow diffusion increases the strength and decreases the density, we speculate that using a high CO.sub.2 loading in the foaming process leads to a fast carbonation reaction which destroys the foam structure. Surprisingly, introducing carbon dioxide through the aqueous foams, for example based on the carbonized water, is a convenient way for producing stable low density foams (cf. B.1, B.2, and B.3).

[0130] The negative effect of high CO.sub.2 loading during foaming of the mix has also been confirmed by a trial with only the aqueous foam (without mixing in the cement slurry). In this case, the foam stability has been judged by the foam height reduction of foam samples in beakers, observed over 60 min.

[0131] Using carbonated water with 2 wt. % tenside resulted in a foam height reduction of 5% (17 cm initial foam height.fwdarw.16 cm foam height after 60 min), while a variant using pure water with 2 wt. % tenside and pressurized CO.sub.2 instead of air for foam generation, resulted in a foam height reduction of 65% (17 cm initial foam height.fwdarw.6 cm foam height after 20 min, followed by a full collapse after 30 min). This shows that already the foam generation is compromised with high CO.sub.2 loadings, which might be due to a de-foaming in combination with the tenside.

[0132] In a third series of experiments, the combined effect of carbon dioxide in the aqueous foam and the RDP in the cement slurry was evaluated. R3 is a control experiment without carbon dioxide in the aqueous foam. Table 3 gives an overview about the results.

TABLE-US-00003 TABLE 3 Combined effect of carbon dioxide and RDP aqueous Density RDP Density of foamed ? Exp. foam type [g/liter] [kg] cement [g/liter] [mW/m .Math. K] R3 WF 80 2.5 184 (collapsed) 60 C.1 CF1 80 2.5 88 (stable) 42

[0133] Evidently, experiment C.1 shows a strong improvement of the foam stability and the density obtainable over the control experiment R3 without carbon dioxide in the aqueous foam. Especially, the very low density gives rise to a low thermal conductivity A well below 50 mW/m.Math.K.

3. Cement Foams Produced with Carbonate Salts

3.1 Preparation

[0134] Aqueous foams were produced as described above in chapter 2. However, instead of carbon dioxide, carbonate salts were added. The foam density in the range of 160-150 g/liter has been adjusted by appropriate machine settings. Specific salts and theirs proportions as well as foam densities are given in the tables shown below.

[0135] Aqueous cement slurries were produced as described above in chapter 2. Thereby, no RDP was added.

3.2 Properties

[0136] Several foamed cement compositions were prepared as shown in table 4. D.1 and D.3 are control experiments with CaCl.sub.2 instead of a carbonate salt and not according to the present invention.

TABLE-US-00004 TABLE 4 Effect of carbonate salts Proportion of Density of carbonate salt foamed cement Density of with respect to after foamed cement Carbonate dry cement preparation after 16 h Exp. salt [wt. %] [g/liter] [g/liter] D.1 CaCl.sub.2 1.3 160 406 D.2 NaHCO.sub.3 1.0 150 122 D.3 CaCl.sub.2 1.3 290 453 D.4 NaHCO.sub.3 1.0 300 317

[0137] Foamed cement compositions prepared with NaHCO.sub.3 did not collapse for fresh densities of 150 g/liter (D.2) and only slightly for fresh densities of 300 g/liter (D.4).

[0138] In contrast, with non-carbonate salts (CaCl.sub.2), the foamed cement compositions significantly collapsed as evident from the strong increase of the density over 16 h (D.1 and D.3).

[0139] Furthermore, calorimetric data have been recorded during the hardening process of experiments D.2 and D.3 with a device of type Calmetrix I-CAL 8000 HPC (available from Calmetrix Inc., USA). FIG. 1 shows the respective data. Evidently, the experiment with CaCl.sub.2 (D.3) shows a strong accelerating effect, whereas with NaHCO.sub.3 there is hardly any acceleration when compared with a reference without any additional salt (Ref).

[0140] Additionally, the flow table spreads (determined similar to DIN EN DIN EN 12350-5) were determined for different foamed cement compositions. Details and results are shown in table 5. D.5 is an example in which CO.sub.2 was used instead of a carbonate salt whereas D.6, D.7 and D.8 are examples with other salts. Examples D.2, D.5, D.6, and D.7 are according to the present invention while examples D.1, D.8, D.9, and D. 10 are comparative examples and not according to the present invention.

TABLE-US-00005 TABLE 5 flow table spread of foamed cement compositions Flow table spread of foamed Proportion of cement compositions directly after Exp. Salt salt [wt. %] preparation [cm] D.1 CaCl.sub.2 1.3 >35 D.2 NaHCO.sub.3 1.0 <12 D.5 CO.sub.2 1.6 g/liter <12 D.6 K.sub.2CO.sub.3 1.0 <12 D.7 Na.sub.2CO.sub.3 1.0 <12 D.8 CaCO.sub.3 1.0 >35 D.9 NaOH 0.5 >35 D.10 NaCl 0.7 >35

[0141] Thus, the rather small flow table spreads observed for the experiments with the water soluble carbonate based salts/CO.sub.2 (D.2, D.5, D.6, D.7) are indicative of a fast thickening of the foamed cements. In contrasts, the accelerating salts CaCl.sub.2 and CaCO.sub.3 (hardly water soluble) show much higher flow table spreads (D.1, D.8). Also the salts NaOH and NaCl lead to much higher flow table spread (D.9, D.10). It can therefore be concluded that it is not the accelerating effect of carbonate salt that leads to the improved foam stability. Rather it seems to be the thickening effect.

[0142] It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed implementations and embodiments are therefore considered in all respects to be illustrative and not restricted.

4. Cement Foams Produced with Varying Content of CO.SUB.2

4.1 Preparation

[0143] Aqueous foams were produced as described above for CF2 in chapter 2 but using surfactant Sika? Lightcrete-400. However, varying content of CO.sub.2 in the air for foaming was used (see table 6). The targeted foam density of 100 g/L has been adjusted by appropriate machine settings.

[0144] Aqueous cement slurries were produced as described above in chapter 2. However, 2.5 kg of RDP and 5 kg of a polyurethane dispersion with 40 w % solids content were added in all cases.

4.2 Properties

[0145] Several foamed cement compositions were prepared as shown in table 6. E.1 is a control experiment using synthetic air without CO.sub.2 and not according to the invention.

TABLE-US-00006 TABLE 6 Effect of varying CO.sub.2 concentration in air CO.sub.2 content Density of foamed cement Exp. in air [Vol %] after 16 h [g/liter] E.1 0 109 E.2 8 120 E.3 16 150 E.4 50 224 E.5 100 >1000

[0146] It can be seen from the above results that a concentration of CO.sub.2 of 8 Vol %, 16 Vol %, and 50 Vol % in the air used for foaming is suitable to obtain foamed cement without changes in process parameters. When pure CO.sub.2 gas is used (cf. E.5), the density of the foamed cement is strongly increased.

[0147] Without wishing to be bound by theory, it is believed that the density increase is due to the dissolution of CO.sub.2 in water with subsequent formation of carbonate and precipitation of calcium carbonate. This series of reaction leads to a volume reduction.

[0148] A CO2 content in the air of 4 Vol % is equivalent to a concentration of CO.sub.2 of appr. 2400 mg per liter of liquid water in the aqueous foam. A CO.sub.2 content in the air of 8 Vol % is equivalent to a concentration of CO.sub.2 of appr. 4500 mg per liter of liquid water in the aqueous foam. A CO.sub.2 content in the air of 16 Vol % is equivalent to a concentration of CO.sub.2 of appr. 9500 mg per liter of liquid water in the aqueous foam. A CO.sub.2 content in the air of 50 Vol % is equivalent to a concentration of CO.sub.2 of appr. 29700 mg per liter of liquid water in the aqueous foam. Pure CO.sub.2 (i.e. a content in the air of 100 Vol %) is equivalent to a concentration of CO.sub.2 of 60000 mg per liter of liquid water in the aqueous foam.

[0149] Additionally, mean pore diameters of dried foams produced as above were determined by measurement of optical microscope images. The dried foams were of different target densities which are stated in below table 7 and which were achieved by adjusting machine settings accordingly. Experiments E.6-E.8 are not according to the present invention.

TABLE-US-00007 TABLE 7 Effect of varying CO.sub.2 concentration in air Density of foamed CO.sub.2 content cement after 16 h Mean pore diameter Exp. in air [Vol %] [g/liter] [mm] E.6 0 112 0.73 E.7 0 141 0.50 E.8 0 215 0.35 E.9 16 128 0.27 E.10 16 151 0.27 E.11 16 225 0.29 n.m.: not measured

[0150] It can be seen from the results of above table 7 that the addition of CO.sub.2 leads to a stable mean pore diameter over various densities of the dried foam. On the contrary, where no CO.sub.2 is added, the mean pore diameter largely depends on the density of the dried foam.