VISCOSITY REDUCTION IN ALUMINUM SULFATE SUSPENSIONS USING ALKALI METAL COMPOUNDS

Abstract

A soluble alkali metal compound for adjusting, in particular reducing, the viscosity of an aluminum sulfate suspension, the alkali metal being selected from among sodium, potassium and/or lithium.

Claims

1. A method for adjusting the viscosity of an aluminum sulfate suspension comprising a step of mixing at least one soluble alkali metal compound, aluminium sulfate, and water, wherein the alkali metal is selected from sodium, potassium and/or lithium.

2. The method of claim 1, wherein the aluminum sulfate suspension is a solidification accelerator and/or hardening accelerator for a composition comprising a mineral binder, wherein the aluminum sulfate suspension is preferably a spray concrete accelerator.

3. The method of claim 1, wherein the alkali metal compound is an aluminate, oxide, hydroxide, carbonate, hydrogen carbonate, nitrate, sulfate, phosphate, halide, formate, citrate, thiocyanate, silicate and/or acetate.

4. The method of claim 1, wherein the alkali metal compound is selected from sodium aluminate, sodium carbonate, sodium bicarbonate, sodium oxide, sodium hydroxide, potassium aluminate, potassium carbonate, potassium bicarbonate, potassium oxide, potassium hydroxide, lithium aluminate, lithium carbonate, lithium bicarbonate, lithium oxide, lithium hydroxide or a mixture thereof.

5. The method of claim 1, wherein an amount of the at least one alkali metal compound is chosen such that the alkali metal atoms, based on the total weight of the aluminum sulfate suspension, have a proportion of 0.02-5% by weight.

6. The method of claim 1, wherein the aluminum sulfate suspension, based on the total weight of the aluminum sulfate suspension, has a proportion of sulfate (SO.sub.4.sup.?) of 19-40% by weight, and wherein the aluminum sulfate suspension, based on the total weight of the aluminum sulfate suspension, has a proportion of aluminum (Al) of 3.5-10% by weight.

7. The method of claim 1, wherein the aluminum sulfate suspension, based on the total weight of the aluminum sulfate suspension, contains 22-46% by weight of aluminum sulfate (Al.sub.2(SO.sub.4).sub.3).

8. The method of claim 1, wherein the aluminum sulfate suspension, based on the total weight of the aluminum sulfate suspension, contains 0.01-15% by weight of aluminum hydroxide.

9. The method of claim 1, wherein a molar ratio of aluminum to sulfate in the aluminum sulfate suspension is less than or equal to 0.9.

10. The method of claim 1, wherein the aluminum sulfate suspension additionally contains 0.1-15% by weight, based on the total weight of the aluminum sulfate suspension, of an alkanolamine, wherein the alkanolamine used is advantageously monoethanolamine, diethanolamine, triethanolamine and/or methyldiisopropanolamine.

11. The method of claim 1, wherein the alkali metal compound is added to the aluminum sulfate suspension or during the production of the aluminum sulfate suspension in powder form or as an aqueous solution.

12. The method of claim 1, wherein the alkali metal compound is used for reducing viscosity in combination with a calcium compound or a magnesium compound.

13. The method of claim 12, wherein the calcium compound or magnesium compound is an oxide, hydroxide, carbonate, nitrate, sulfate, phosphate, halide, formate, acetate and/or citrate.

14. The method of claim 12, wherein the calcium compound is calcium carbonate, calcium oxide and/or calcium hydroxide and the magnesium compound is magnesium carbonate, magnesium oxide and/or magnesium hydroxide.

15. The method of claim 12, wherein an amount of the calcium compound or magnesium compound is chosen such that the calcium atoms or magnesium atoms, based on the total weight of the aluminum sulfate suspension, have a proportion of 0.001-4% by weight.

16. A solidification accelerator and/or hardening accelerator for a composition comprising a mineral binder, wherein the solidification accelerator and/or hardening accelerator is a spray concrete accelerator, comprising: a) 22-46% by weight of aluminum sulfate (Al.sub.2(SO.sub.4).sub.3; b) optionally 0.01-15% by weight of aluminum hydroxide (Al(OH).sub.3); c) optionally 0.001-5% by weight of a calcium compound selected from calcium oxide and/or calcium hydroxide or of a magnesium compound selected from magnesium oxide and/or magnesium hydroxide; d) optionally 0.001-10% by weight of iron; e) optionally 0.001% to 5% by weight of silicon dioxide; f) at least one soluble alkali metal compound, the alkali metal being selected from sodium, potassium and/or lithium, in an amount such that the alkali metal atoms, based on the total weight of the aluminum sulfate suspension, have a proportion of 0.02-5% by weight; g) optionally 0.1-15% by weight of alkanolamine; h) optionally 0.01-10% by weight of fluoride; i) and water, where the proportion missing from 100% by weight is water.

17. A solidification accelerator and/or hardening accelerator as claimed in claim 16, wherein the alkali metal compound is selected from sodium aluminate, sodium carbonate, sodium bicarbonate, sodium oxide, sodium hydroxide, potassium aluminate, potassium carbonate, potassium bicarbonate, potassium oxide, potassium hydroxide, lithium aluminate, lithium carbonate, lithium bicarbonate, lithium oxide, lithium hydroxide or a mixture thereof.

Description

EXEMPLARY EMBODIMENTS

[0166] The following materials were used in the examples that follow:

TABLE-US-00001 Name Description Al.sub.2(SO.sub.4).sub.3approx. Aluminum sulfate containing 17-18% Al.sub.2O.sub.3, 14H.sub.2O in powder form Water Deionized water Na aluminate A Aqueous solution of sodium aluminate (contains 19% by weight of Na.sub.2O and 24% by weight of Al.sub.2O.sub.3) Na aluminate B Powder containing at least 39% Na.sub.2O and 53-55% Al.sub.2O.sub.3 NaOH Aqueous solution of NaOH (50% by weight) Na.sub.2CO.sub.3 Na.sub.2CO.sub.3H.sub.2O in powder form KOH KOH in powder form LiOH LiOH in powder form KHCO.sub.3 KHCO.sub.3 in powder form

[0167] In the values stated below for the proportion of Al.sub.2(SO.sub.4).sub.3.Math.approx. 14H2O, the water of crystallization is included. Al.sub.2(SO.sub.4).sub.3.Math.approx. 14H.sub.2O contains 57% by weight of Al.sub.2(SO.sub.4).sub.3. The water of crystallization is accordingly included in Na.sub.2CO.sub.3.Math.H.sub.2O too.

[0168] In the employed solutions of NaOH and sodium aluminate, the proportions of NaOH and NaAlO.sub.2 in the values stated below relate to the NaOH and sodium aluminate as such, without the water of the solution. The latter is included under H.sub.2O.

[0169] Viscosities were measured according to standard DIN EN ISO 2431:2011 using an ISO No. 6 cup at a temperature of 23? C. or an ISO No. 4 cup at a temperature of 23? C. n.d. in the tables below means that the viscosity could not be determined. The times listed in the tables below relate to the time t=0 that is the starting point at which all components of the mixture had been combined.

[0170] The components can generally be added to the mixture in powder form or as an aqueous solution. For example, material in powder form and an aqueous aluminum sulfate suspension are both suitable as starting material for the aluminum sulfate.

[0171] The aluminum sulfate suspensions produced according to the invention were found to be storage-stable over several months and have a viscosity suitable for practical applications as spray concrete accelerator in the region of <2000 mPa.Math.s.

Examples 1 to 4

Production of Aluminum Sulfate Suspensions Containing Sodium Aluminate

[0172] A beaker was initially charged with a defined amount of water. While stirring (mechanical propeller stirrer at 650 rpm), the Al.sub.2(SO.sub.4).sub.3.Math.approx. 14H.sub.2O and sodium aluminate (0% to 4% by weight) were then added portionwise in the order and proportions stated in Table 1 and the suspension was stirred at room temperature for 6 h.

TABLE-US-00002 TABLE 1 Aluminum sulfate suspensions produced Example Order Substance 1* 2 3 4 1 H.sub.2O [% by wt.] 40 39 38 36 2 Na aluminate A [% by wt.] 1 2 4 3 Al.sub.2(SO.sub.4).sub.3approx. 14H.sub.2O 60 60 60 60 [% by wt.] *Comparative example

[0173] The viscosity was measured after defined times. Table 2 gives an overview of the results.

TABLE-US-00003 TABLE 2 Dependence of viscosity on the proportion of sodium aluminate Example 1* 2 3 4 Proportion of Na aluminate A [% by wt.] 0 1 2 4 Viscosity [mPa .Math. s] after 1 h 669 385 200 n.d. after 2 h 404 303 183 132 after 3 h 323 228 189 113 after 4 h 260 212 183 119 after 5 h 233 184 189 125 after 6 h 194 172 155 119 after 24 h 136 155 137 113 after 48 h 57 79 79 72 after 16 days 87 89 85 91 *Comparative example

[0174] As can be seen from Table 2, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of sodium aluminate.

Examples 5 to 8

[0175] Production of aluminum sulfate suspensions containing sodium aluminate The experiments were carried out in the same way as examples 1 to 4 but with a change to the order of addition, as shown in Table 3.

TABLE-US-00004 TABLE 3 Aluminum sulfate suspensions produced Example Order Substance 5* 6 7 8 1 H.sub.2O [% by wt.] 40 39 38 36 2 Al.sub.2(SO.sub.4).sub.3approx. 14H.sub.2O 20 20 20 20 [% by wt.] 3 Na aluminate A [% by wt.] 1 2 4 4 Al.sub.2(SO.sub.4).sub.3approx. 14H.sub.2O 40 40 40 40 [% by wt.] *Comparative example

[0176] The viscosity was measured after defined times. Table 4 gives an overview of the results.

TABLE-US-00005 TABLE 4 Dependence of viscosity on the proportion of sodium aluminate Example 5* 6 7 8 Proportion of Na aluminate A [% by wt.] 0 1 2 4 Viscosity [mPa .Math. s] after 1 h 846 407 207 58 after 2 h 495 314 218 120 after 3 h 338 240 184 151 after 4 h 260 201 161 180 after 5 h 233 179 150 138 after 6 h 189 161 131 87 after 24 h 132 139 117 89 after 48 h 80 93 83 57 *Comparative example

[0177] As can be seen from Table 4, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of sodium aluminate.

Examples 9 to 14

Production of Aluminum Sulfate Suspensions Containing Sodium Aluminate

[0178] The experiments were carried out in the same way as examples 1 to 4 but with changes to the amount of sodium aluminate and to the order of addition, as shown in Table 5.

TABLE-US-00006 TABLE 5 Aluminum sulfate suspensions produced Example Order Substance 9 10 11 12 13 14 1 H.sub.2O [% by wt.] 32 32 32 32 32 32 2 Al.sub.2(SO.sub.4).sub.3approx. 10 20 30 40 50 14H.sub.2O [% by wt.] 3 Na aluminate A 8 8 8 8 8 8 [% by wt.] 4 Al.sub.2(SO.sub.4).sub.3approx. 60 50 40 30 20 10 14H.sub.2O [% by wt.]

[0179] The viscosity was measured after defined times. Table 6 gives an overview of the results.

TABLE-US-00007 TABLE 6 Dependence of viscosity on the split of the Al sulfate Example 9 10 11 12 13 14 Proportion of Na 8 8 8 8 8 8 aluminate A [% by wt.] Viscosity [mPa .Math. s] after 2 h 983 502 972 980 976 818 after 3 h 983 512 908 795 812 722 after 4 h 510 369 509 488 430 510 after 5 h 417 316 382 370 321 381 after 6 h 318 236 294 296 268 281 after 24 h 142 124 142 124 134 136 after 48 h 98 89 95 90 89 93

Examples 15 to 19

Production of Aluminum Sulfate Suspensions Containing Sodium Aluminate

[0180] The experiments were carried out in the same way as examples 1 to 4 but using a different sodium aluminate (Na aluminate B) and with a change to the order of addition, as shown in Table 7.

TABLE-US-00008 TABLE 7 Aluminum sulfate suspensions produced Example Order Substance 15* 16 17 18 19 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 20 20 20 20 20 14H.sub.2O [% by wt.] 3 Na aluminate B 0.5 1 2 3 [% by wt.] 4 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 40 40 40 40 40 14H.sub.2O [% by wt.] *Comparative example

[0181] The viscosity was measured after defined times. Table 8 gives an overview of the results.

TABLE-US-00009 TABLE 8 Dependence of viscosity on the sodium aluminate Example 15* 16 17 18 19 Proportion of Na aluminate B [% by wt.] 0 0.5 1 2 3 Viscosity [mPa .Math. s] after 1 h 686 371 250 93 43** after 2 h 438 324 283 185 139 after 3 h 357 277 256 219 151 after 4 h 264 212 196 213 139 after 5 h 243 212 190 208 133 after 6 h 216 195 190 173 107 after 24 h 127 133 127 89 87 after 48 h 87 125 97 78 103 *Comparative example. **Value inexact/measurement time too short for ISO No. 6

[0182] As can be seen from Table 8, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of sodium aluminate.

Examples 20 to 25

Production of Aluminum Sulfate Suspensions Containing Sodium Aluminate

[0183] The experiments were carried out in the same way as examples 1 to 4 but using a different sodium aluminate (Na aluminate B), as shown in Table 9.

TABLE-US-00010 TABLE 9 Aluminum sulfate suspensions produced Example Order Substance 20* 21 22 23 24 25 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 36 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] 3 Na aluminate B 0.5 1 2 3 4 [% by wt.] *Comparative example

[0184] The viscosity was measured after defined times. Table 10 gives an overview of the results.

TABLE-US-00011 TABLE 10 Dependence of viscosity on the amount of sodium aluminate Example 20* 21 22 23 24 25 Proportion of Na 0 0.5 1 2 3 4 aluminate A [% by wt.] Viscosity [mPa .Math. s] after 1 h 513 249 n.d. n.d. n.d. n.d. after 2 h 352 200 234 n.d. n.d. n.d. after 3 h 226 178 195 162 126 81 after 4 h 199 155 178 162 113 81 after 5 h 165 149 155 150 80 94 after 6 h 136 143 155 132 34* 94 after 24 h 102 115 126 74 52 98 after 48 h 70 110 84 63 60 105 **Value inexact

[0185] As can be seen from Table 10, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of sodium aluminate.

Examples 26 to 31

[0186] Production of aluminum sulfate suspensions containing sodium aluminate The experiments were carried out in the same way as examples 1 to 4 but using a different sodium aluminate (Na aluminate B) and with a change to the order of addition, as shown in Table 11. In addition, a higher aluminum sulfate concentration was used, with a dissolver disk used for stirring instead of the propeller stirrer. In all experiments a loss of water was registered, which was not compensated for.

TABLE-US-00012 TABLE 11 Aluminum sulfate suspensions produced Example Order Substance 26* 27 28 29 30 31 1 H.sub.2O [% by wt.] 35 34.5 34 33 32 31 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 30 30 30 30 30 30 14H.sub.2O [% by wt.] 3 Na aluminate B 0.5 1 2 3 4 [% by wt.] 4 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 35 35 35 35 35 35 14H.sub.2O [% by wt.] *Comparative example

[0187] The viscosity was measured after defined times. Table 12 gives an overview of the results.

TABLE-US-00013 TABLE 12 Dependence of viscosity on the amount of Na aluminate Example 26* 27 28 29 30 31 Proportion of Na 0 0.5 1 2 3 4 aluminate B [% by wt.] Viscosity [mPa .Math. s] after 4 h 1167 914 831 442 419 539 after 5 h 1076 843 770 453 392 512 after 6 h 1071 818 750 432 370 496 after 24 h 708 757 953 432 300 346 after 48 h 368 365 414 270 233 335 *Comparative example

[0188] As can be seen from Table 12, the viscosity of the aluminum sulfate suspension can, even at a very high aluminum sulfate content, be significantly reduced in the first hours by the addition of sodium aluminate.

Examples 32 to 37

Production of Aluminum Sulfate Suspensions Containing Sodium Hydroxide

[0189] The experiments were carried out in the same way as examples 1 to 4 but using sodium hydroxide solution (50%) as the alkali metal compound instead of sodium aluminate, as shown in Table 13.

TABLE-US-00014 TABLE 13 Aluminum sulfate suspensions produced Example Order Substance 32* 33 34 35 36 37 1 H.sub.2O [% by wt.] 40 39 38 36 34 32 2 NaOH [% by wt.] 1 2 4 6 8 3 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] *Comparative example

[0190] The viscosity was measured after defined times. Table 14 gives an overview of the results.

TABLE-US-00015 TABLE 14 Dependence of viscosity on the amount of NaOH Example 32* 33 34 35 36 37 Proportion of 0 1 2 4 6 8 NaOH [% by wt.] Viscosity [mPa .Math. s] after 1 h 966 447 201 72 49 53 after 2 h 660 432 234 101 61 52 after 3 h 410 293 212 147 162 68 after 4 h 390 277 207 135 169 70 after 5 h 328 228 179 103 169 70 after 6 h 313 190 184 98 168 72 after 24 h 145 130 127 74 101 57 after 48 h 87 130 95 68 85 56 *Comparative example

[0191] As can be seen from Table 14, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of NaOH.

Examples 38 to 43

Production of Aluminum Sulfate Suspensions Containing Sodium Carbonate

[0192] The experiments were carried out in the same way as examples 1 to 4 but using sodium carbonate as the alkali metal compound instead of sodium aluminate and with a change to the order of addition, as shown in Table 15.

TABLE-US-00016 TABLE 15 Aluminum sulfate suspensions produced Example Order Substance 38* 39 40 41 42 43 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 36 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] 3 Na.sub.2CO.sub.3 [% by wt.] 0.5 1 2 3 4 *Comparative example

[0193] The viscosity was measured after defined times. Table 16 gives an overview of the results.

TABLE-US-00017 TABLE 16 Dependence of viscosity on the amount of Na.sub.2CO.sub.3 Example 38* 39 40 41 42 43 Proportion of 0 0.5 1 2 3 4 Na.sub.2CO.sub.3 [% by wt.] Viscosity [mPa .Math. s] after 1 h 947 391 367 162 645** 50** after 2 h 903 386 372 174 594 50 after 3 h 370 228 245 185 774 n.d. after 4 h 354 206 235 174 814 n.d. after 5 h 318 228 272 156 624 442 after 6 h 313 217 262 168 629 437 after 24 h 158 132 161 134 83 87 after 48 h 100 139 115 98 73 77 *Comparative example. **Extrapolated

[0194] As can be seen from Table 16, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of Na.sub.2CO.sub.3.

Examples 44 to 49

Production of Aluminum Sulfate Suspensions Containing Potassium Hydroxide

[0195] The experiments were carried out in the same way as examples 1 to 4 but using potassium hydroxide as the alkali metal compound instead of sodium aluminate and with a change to the order of addition, as shown in Table 17.

TABLE-US-00018 TABLE 17 Aluminum sulfate suspensions produced Example Order Substance 44* 45 46 47 48 49 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 36 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] 3 KOH [% by wt.] 0.5 1 2 3 4 *Comparative example

[0196] The viscosity was measured after defined times. Table 18 gives an overview of the results.

TABLE-US-00019 TABLE 18 Dependence of viscosity on the amount of KOH Example 44* 45 46 47 48 49 Proportion of KOH 0 0.5 1 2 3 4 [% by wt.] Viscosity [mPa .Math. s] after 1 h 1385 731 n.d. 207 65** after 2 h 968 n.d. 360 218 80 42 after 3 h 657 n.d. 360 212 78 50 after 4 h 502 344 292 229 85 72 after 5 h 426 271 217 207 82 86** after 6 h 406 234 195 201 88 100 after 24 h 182 117 155 192 53 78 after 48 h 80 73 115 187 60 79 *Comparative example. **Extrapolated

[0197] As can be seen from Table 18, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of KOH.

Examples 50 to 55

Production of Aluminum Sulfate Suspensions Containing Lithium Hydroxide

[0198] The experiments were carried out in the same way as examples 1 to 4 but using lithium hydroxide as the alkali metal compound instead of sodium aluminate and with a change to the order of addition, as shown in Table 19.

TABLE-US-00020 TABLE 19 Aluminum sulfate suspensions produced Example Order Substance 50* 51 52 53 54 55 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 36 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] 3 LiOH [% by wt.] 0.5 1 2 3 4 *Comparative example

[0199] The viscosity was measured after defined times. Table 20 gives an overview of the results.

TABLE-US-00021 TABLE 20 Dependence of viscosity on the amount of LiOH Example 50* 51 52 53 54 55 Proportion of LiOH 0 0.5 1 2 3 4 [% by wt.] Viscosity [mPa .Math. s] after 1 h 767 345 93 *** *** *** after 2 h 767 365 184 *** *** 86 after 3 h 578 287 184 50** *** 178 after 4 h 412 228 173 79 65 99 after 5 h 376 137 161 99 65 119 after 6 h 324 178 161 93 72 99 after 24 h 133 101 105 81 71 86 after 48 h 95 157 77 72 72 90 *Comparative example. **Value inexact. ***Measurement time for ISO No. 6 too short (i.e. viscosity too low for measurement method)

[0200] As can be seen from Table 20, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of LiOH.

Examples 56 to 61

Production of Aluminum Sulfate Suspensions Containing Potassium Hydrogen Carbonate

[0201] The experiments were carried out in the same way as examples 1 to 4 but using potassium hydrogen carbonate as the alkali metal compound instead of sodium aluminate and with a change to the order of addition, as shown in Table 21.

TABLE-US-00022 TABLE 21 Aluminum sulfate suspensions produced Example Order Substance 56* 57 58 59 60 61 1 H.sub.2O [% by wt.] 40 39.5 39 38 37 36 2 Al.sub.2(SO.sub.4).sub.3 .Math. approx. 60 60 60 60 60 60 14H.sub.2O [% by wt.] 3 KHCO.sub.3 [% by wt.] 0.5 1 2 3 4 *Comparative example

[0202] The viscosity was measured after defined times. Table 22 gives an overview of the results.

TABLE-US-00023 TABLE 22 Dependence of viscosity on the amount of KHCO.sub.3 Example 50* 51 52 53 54 55 Proportion of 0 0.5 1 2 3 4 KHCO.sub.3 [% by wt.] Viscosity [mPa .Math. s] after 1 h 677 662 391 239 93 106 after 2 h 657 653 427 239 119 131 after 3 h 498 452 355 245 131 131 after 4 h 422 401 303 217 119 106 after 5 h 386 335 261 206 131 119 after 6 h 314 298 223 190 125 112 after 24 h 157 154 144 133 98 103 after 48 h 94 101 112 106 90 108 *Comparative example

[0203] As can be seen from Table 22, the viscosity of the aluminum sulfate suspension can, at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of potassium hydrogen carbonate.

Summary of the Results

[0204] As can be seen from the examples, the viscosity of the aluminum sulfate suspension can, even at a high aluminum sulfate content, be significantly reduced in the first hours by the addition of soluble alkali metal compounds. In particular, the spikes in viscosity that commonly occur at the start can be avoided.

[0205] Accordingly, a soluble alkali metal compound can be used to control the viscosity of an aluminum sulfate suspension. The order of addition and the split in the components play no important role.

[0206] All experiments were carried out at room temperature. As is known, a decrease in viscosity can generally be achieved by heating, but the time and energy required make this undesirable. The inventive use of soluble alkali metal compounds means that heating to a lower temperature is sufficient or allows heating to be avoided altogether.

[0207] In addition, it has been found that the viscosities of the aluminum sulfate suspension thus produced can be maintained over 3 months without significant change.

[0208] The above-described aluminum sulfate suspensions have been found to be excellent accelerators for spray concrete and spray mortar.

[0209] Although the above-described embodiments of the invention are preferred, it will be apparent that the invention is not limited to these embodiments and can be modified as desired within the scope of the disclosure.