GB1568123A - Additive for cementbased compositions method for preparing said additive and cement mortar or concrete slurry comprising said additive - Google Patents

Description

(54) ADDITIVE FOR CEMENT-BASED COMPOSITIONS, METHOD FOR PREPARING SAID ADDITIVE, AND CEMENT, MORTAR OR CONCRETE SLURRY COMPRISING SAID ADDICTIVE (71) We, COMPAGNIE DES CIMENTS BELGES (C.C.B.), Gaurain Rame-croix, Belgium, a company organized under the laws of Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an additive for cement-based compositions, notably for mortars and concretes.

It is known to mix with a green cement mixture, additives to make said mix more fluid and give it a better workability. Said additives, which are known as fluidizers, contain among other things either a melamine resin or a lignosulfonate.

Said known fluidizers based on melamine resin even if they cause a substantial improvement in the green cement mix consistency and if they are compatible with any cement and generate good mechanical performances at a later time, have however the drawback when they are used with some kinds of cements and aggregates, of lowering the mechanical strengths after 28 days. The additives based on lignosulfonate tend to cause too low an increase in the consistency and a substantial sweating of the cement mix while giving to the green cement mixes some delay in setting and hardening. They have moreover a different action according to the cement used.

An essential object of the invention thus lies in obviating the above drawbacks, in providing an additive for cement-based compositions, particularly for mortars and concretes, which gives both a very good workability and also an increase in the mechanical strength of the cement compositions. Moreover said additive substantially improves the homogeneity of the compositions which shows in a low sweating and the retaining of a good appearance for the hardened cement compositions.

According to the invention, there is provided an additive for cement-based compositions which comprises a mixture of at least one lignosulfonate selected from alkali metal and alkaline-earth metal lignosulfonates, an alkali metal salt of a hydroxy carboxylic acid, an ester defoaming agent, a melamine-formaldehyde condensate with sulfonic groups and an amine setting and hardening accelerator.

The term "alkali metal" as used herein includes ammonium.

In a particularly advantageous embodiment of the invention, said mixture comprises from 10 to 35 parts by weight of the lignosulfonate, from 3 to 15 parts by weight of the alkali metal salt of a hydroxy carboxylic acid, from 10 to 35 parts by weight of the ester defoaming agent, from 8 to 30 parts by weight of the melamineformaldehyde condensate ith sulfonic groups and from lOto 30 parts by weight of the amine setting and hardening accelerator.

In another advantageous embodiment of the invention. said mixture further comprises an emulsifier. Preferably, from 0.2 to 2 parts by weight of said emulsifier are used.

According to a further aspect of the invention. there is provided a method for making said additive as an aqueous phase emulsion, in which method an aqueous solution containing from 10 to 50% by weight of melamine-formaldehyde condensate is added to the other components of the additive so as to form an aqueous emulsion, and, if desired, the emulsion is diluted with the required amount of water to bring the concentration of water to 30 to 70% by weight of the emulsion.

The cements which pertain to this invention are "hydraulic cements". The hydraulic cements may comprise the Portland cements with or without additional components (slag, cinders and pozzolana), mixed metallurgical cements and clinker slag cements.

The additive of the present invention maximizes the workability of hydraulic cement based compositions and results in compositions which possess mechanical strengths from the first days on which are at least generally equal to those of cement compositions which do not contain additives or which contain known additives, while imparting thereto a high homogeneity and stability, which results in a low sweating and the retaining of a good appearance for the hardened mixes.

Even though it might be known to use mixtures of alkali metal lignosulfonates, salts of hydroxy carboxylic acids, alkali metal salts of alkylbenzene-sulfonic acids, water-soluble amines, or inorganic chlorides, as well as mixtures of sulfonated melamine resins and hydroxy carboxylic acids or alkali metal salts of such acids, for the purpose of increasing the mechanical strengths of mortars and concretes of recent date, it is not possible to obtain with the use of such additives all of the advantages resulting from the use of the additive according to the invention, as this will be particularly clear from the following tables.

According to the invention, the lignosulfonate which is either an alkali metal or alkaline-earth metal lignosulfonate or a mixture of alkali metal lignosulfonate and alkaline-earth metal lignosulfonate, and the alkali metal salt of hydroxy carboxylic acid, which is preferably selected from the gluconates and tartrates of sodium, potassium and ammonium, and mixtures thereof, as well as a sulfonated melamine-formaldehyde resin, are the fluidizers of the additive. The hydroxy carboxylic acid salt even if it improves actually the fluidifying action of the lignosulfonate which as already stated might prove insufficient, can further cause substantial delays in the setting and hardening. The lignosulfonate is preferably selected from the lignosulfonates of sodium, ammonium, magnesium and calcium, and mixtures of said various compounds, magnesium lignosulfonate being particularly suitable.Sodium gluconate has also proved of particular interest for this purpose. The introduction of the sulfonated melamine-formaldehyde condensate, which is also a well-known fluidizer as already stated, gives to the mixture of both mentioned fluidizers, that is the lignosulfonate and the salt of hydroxycarboxylic acid, the property of increasing even more the consistency caused by this mixture and simultaneously the homogeneity of the mortar and concrete slurries. According to the invention the melamine-formaldehyde condensate with sulfonic groups is preferably present as an aqueous solution containing from 10 to 50% by weight of solids.To prepare said melamineformaldehyde condensates as aqueous solutions, which is not however part of the invention, reference should be made to the literature and particularly to Belgian Patent 822,491 in the name of Siiddeutsche Kalkstickstoff-Werke AG.

The combined use of all three fluidizers has the drawback of causing air entrainment but this drawback is obviated according to the invention by adding to said fluidizers, an ester having a defoaming action. Said ester can be either an organic ester such as dibutyl phthalate, or an inorganic ester such as tributyl phosphate; or a mixture of both.

The additive according to the invention comprises moreover, besides the above-mentioned components: -an amine capable of acting as setting and hardening accelerator, which increases by a factor of from 2 to 3 the mechanical strengths of the cement mixes after 24 hours. Triethanolamine is particularly suitable for this purpose.

If desired, there can also be included as a component of the additive an emulsifier for emulsifying the water-insoluble organic compounds such as possibly the ester defoaming agent. The emulsifier can be selected from non-ionic or anionic agents. Among the non-ionic agents, the nonylphenol polyglycolic ethers are particularly suitable, while among the anionic emulsifiers, it is preferred to use salts of alkylarylsulfonic acids, sodium dodecyl benzene sulfonate being particularly suitable.

The additive of the present invention increases the consistency, the setting time and the strength of cements, mortars and concretes to which it has been added while decreasing their tendency to sweat.

The additive according to the invention preferably comprises from 10 to 35 parts by weight, more preferably from 18 to 26 parts by weight of lignosulfonate; from 3 to 15 parts by weight, more preferably from 6 to 10 parts by weight, of a hydroxy carboxylic acid alkali metal salt; from 10 to 35 parts by weight, more preferably from 18 to 26 parts by weight, of an ester defoaming agent; from 8 to 30 parts by weight, more preferably from 15 to 25 parts by weight, of a melamineformaldehyde condensate with sulfonic groups; and from 10 to 30 parts by weight, more preferably from 15 to 25 parts by weight, of an amine setting and hardening accelerator; and, if desired, 0.2 to 2 parts by weight, more preferably from 0.4 to 1 parts by weight, of an emulsifier.

To prepare fluid cement compositions according to the invention, use is advantageously made of 0.1 to 0.75% of the additive in dry condition relative to the weight of dry cement, and preferably from 0.18 to 0.45%, the water/cement weight ratio being from 0.35 to 0.60. It has however been noticed that better results are obtained by using the additive according to the invention as an aqueous-phase emulsion, at 370% by weight. For this purpose, the melamine-formaldehyde condensate with sulfonic groups is preferably added as an aqueous solution containing 10 to 50% by weight of the condensate to the other components, so as to form an aqueous emulsion and, if desired, the emulsion is diluted with the amount of water required to bring the concentration of water in the emulsion to 3070% by weight, preferably from 45 to 55% by weight.The emulsion thus obtained is then mixed with a cement composition. The better results obtained with the use of the additive according to the invention, are completely unexpected in the preparation of cement-based compositions, particularly for the preparation of mortars and concr < :tes, when referring to the state of the art.

The better properties of the green and hardened cement mixes incorporating the additive according to the invention are clearly shown in the following Examples. It will be noted from the results obtained in these examples, that a proportion of 0.30% of additive is usually better suited to Portland concretes and a proportion of 0.40% is somewhat better suited for slag cement concretes.

Example 1.

This example shows the characteristics of cement compositions to which the additive according to the invention is added, relative to the same compositions without additives. The compositions are Rilem Cembureau mortars (water/cement weight ratio = 0.50) according to the NBN B 12 standard.

TABLE I

Cement-based composition Cement 1 P400 Cement 2 P400 Cement 3 HK400 Dry additive, % by weight 0 0,20 0,40 0 0,20 0,40 0 0,20 0,40 relative to dry-cement weight Initial setting of the mortar 5h 05 6h 10 6h 30 5h 15 6h 05 6h 20 5h 15 5h 55 7h 05 Final setting of the mortar 5h 50 7h 45 9h 00 6h 55 7h 35 9h 40 6h 40 7h 45 11h 20 Consistency measured at 1.660 1.815 1.970 1.530 1.640 1.900 1.565 1.95 2.06 the laying Bending strength in kg/cm2, after 24h 44.2 43.1 32.2 18 19.6 19.3 27.3 25 22 3d 64 56 57.3 41.2 41.8 45.1 49.5 52.7 53.5 7d 74 68 71 54 60.5 62 72 67.5 69 28d 83.5 78 76.5 77 81.5 78 86.7 81.5 85 Crushing strength in kg/cm2, after 24h 146 125 136 74 69 63 100 87 74 3d 354 328 326 229 240 226 296 282 278 7d 413 398 414 373 369 378 433 419 416 28d 499 492 536 513 523 535 605 610 593 In the following Table II will be found the chemical composition of th cements used for this purpose.

TABLE II

Cements P400-1 P400-2 HK400 % SiO2 (total amount) 19.97 21.15 23.72 A1203 3.74 4.93 7.49 Be2O, 5.45 i 2.96 2.40 CaO (total amount) 62.20 65.00 58.12 MgO 2.16 1.16 | 3.01 SO, 2.51 3.13 3.83 Mn2O3 0.03 0.08 0.10 TiO2 0.21 0.27 0.25 K2O 1.12 0.80 0.97 P2 s 0.30 0.25 Undetermined components 0.69 Piring loss 1.82 2.76 | 2.71 The additive used in this example is supplied in the form of an aqueous-phase emulsion which comprises, besides the water, 25.5 parts by weight of Na lignosulfonate, 7.5 parts by weight of sodium gluconate, 25.5 parts by weight of dibutyl phthalate, 18 parts by weight of melamine-formaldehyde condensate and 23 parts by weight of triethanolamine, the melamine-formaldehyde condensate having been prepared as an aqueous solution containing 20% by weight of solids.The required amount of water is then added to form an aqueous emulsion at 49.8% by weight.

As it can be seen from the results given in Table I, the mechanical strengths after 28 days for the mortars according to the invention are generally somewhat better either with the proportion of 0.20% or with the proportion of 0.40% of additive, than the strengths of mortars without additive, while being quite good after 24 hours.

Example 2.

This example shows the increase in the spreading of the concretes made in the laboratory with the addition of different proportions of the additive according to the invention, relative to concretes without additive, which corresponds to a better workability in the young periods than the concretes without additive. There will also be noted from the following Table III that the concretes according to the invention retain a good homogeneity (low sweating) and have good mechanical characteristics at 28 days relative to the concretes without additive.

TABLE III

Cements 1 2 3 4 5 6 7 8 Cement-based compositions Portland Limestone 8/22, kg. 1250 1253 1255 1268 rolled grit 4/32, kg. 1087 1104 1106 1102 - - - Rhiue sand 755 767 768 767 671 673 674 681 P400, kg. 353 358 357 358 353 354 354 358 Mixing water, liters 171 173.8 174.1 173.5 177.4 177.8 178.1 180 Additive in dry condition. % by 0 0.20 0.30 0.40 0 0.20 0.30 0.40 weight relative to dry cement weight Consistency on the shaking table Before adding the additive 1.77 1.75 1.73 1.70 1.63 1.65 1.60 1.63 After adding the additive - 2.27 2.37 2.50 - 2.13 2.13 2.17 Volume mass of the hardened concrete, kg/m3 2351 2375 2400 2379 2430 2443 2432 2464 Crushing strength 24h 124 96 88 48 166 122 120 88 kg/cm2 3d 274 292 304 298 310 318 357 388 7d 330 376 386 379 372 410 404 409 28d 401 476 488 512 495 464 524 554 Sweating, g/dm2 - - 2.5 - - - 2.6 TABLE III (Continued)

Cements 9 10 11 12 13 14 15 16 Cement-based compositions Iron blast-fumaces Limestone 8/22, kg 1228 1218 1212 1227 rolled grit 4/32, kg. 1088 1087 1083 1079 - - - Rhine sand 0.5, kg. 756 755 712 749 659 654 651 654 HK400, kg. 353 352 351 350 347 344 342 346 Mixing water, liters 186.4 186.1 185.6 184.9 191.1 189.6 188.6 190.9 Additive in dry condition, % by 0 0.20 0.30 0.40 0 0.20 0.30 0.40 weight relative to dry cament weight Consistency on the shaking table Before adding the additive 1.70 1.70 1.73 1.77 1.73 1.67 1.67 1.65 After adding the additive - 2.07 2.40 2.70 - 2.37 2.47 2.50 Volume mass of the hardened concrete, kg/m3 2358 2360 2366 2341 2408 2366 2366 2404 Crushing strength 24h 64 60 54 36 76 70 70 40 kg/cm2 3d 210 245 261 232 226 218 245 228 7d 308 340 358 358 329 330 339 334 28d 454 454 486 520 444 466 498 508 Sweating, g/dm2 - - - 20 - - - The additive used is prepared as in Example 1, the components being the same and used in the same proportions as for Example 1, with the exception of the further addition of 0.4 parts by weight of sodium dodecyl benzene sulfonate and of the use of magnesium lignosulfonate instead of sodium lignosulfonate.

Example 3.

Table IV compares the characteristics of calcareous granulate concretes obtained with the known additives on the basis of melamine or lignosulfonate, with the characteristics of calcareous granulate concretes obtained with the additive according to the invention (refer to the preceding Tables I and III), relative to concretes without additive taken as reference. Tables I, III and IV show moreover the higher strengths as well as the lower sweating of the concretes according to the invention, relative to the concretes comprising the additives on the basis of melamine or lignosulfonate.

TABLE IV

Cement-based compositions Cements Cements sodium sodium Sulfonated lignosulfonate Sulfonated lignosulfonate melamine dibutyl melamine dibutyl Reference formaldehyde phthalate reference formaldehyde phthalate Portland Blast-fumace Limestone 8/22, kg. 1250 1253 1240 1228 1240 1225 Rhine sand 0/5, kg. 671 675 667 659 666 659 P400, kg. 353 354 350 347 350 346 Mixing water, liters 177.4 175.2 173.3 191.1 193 171.3 Additive in dry condition, % by - 0.35 0.70 - 0.35 0.70 weight relative to dry cement weight Consistency on the shaking table Before adding the additive 1.63 1.63 1.67 1.73 1.65 1.53 After adding the additive - 2.48 2.28 - 2.70 2.27 Volume mass of the hardened concrete, kg/m3 2430 2438 2414 2408 2415 2385 Crushing strength 24h 166 138 15 76 64 36 kg/cm2 3d 310 301 285 226 212 196 7d 372 363 352 329 322 383 28d 495 423 464 444 468 443 Sweating, g/dm2 - 2.9 10.3 - 6.3 10.1 Example 4.

This example relates to tests on work-place concretes. As it is clear from Table V below, the results obtained also show a substantial increase of the spreading (consistency on the shaking table) of the concretes comprising the additive according to the invention relative to concretes without additive.

TABLE V

Cements Cements 1 2 3 4 5 6 Cement-based compositions Portland Blast-fumace Limestone 2/3,kg. 265 265 Limestone 8/22, kg. 1200 1200 865 865 Rolled grit 4/32, kg. 1200 1216 Rhine sand 0/5. kg. 725 725 710 710 642 645 P400, kg, 300 300 325 325 HK400, kg. 375 375 Mixing water, liters 150 150 173 173 203 201 Additive in dry condition, % by weight Water relative to dry cement weight addition for consistency 0.3 nil 0.3 - 0.4 Consistency on the shaking table Before adding the additive 1.17 1.17 1.78 1.78 1.91 1.93 After adding the additive 1.73 1.73 - 2.18 - 2.65 Crushing strength in kg/cm2, after 24 hours 72.5 100 100 79 3 days 179 208.5 219 208 7 days 250 300 320 316 317 320 28 days 325 426 429 425 402 486 The additive used for these tests is an aqueous emulsion which contains besides the water, 22 parts by weight of calcium lignosulfonate, 9 parts by weight of potassium tartrate, 22 parts by weight of tributyl phosphate, 24 parts by weight of melamine-formaldehyde condensate with sulfonic groups, 21 parts by weight of triethanolamine, and 0.4 parts by weight of sodium dodecyl benzene sulfonate, the melamine-formaldehyde condensate being prepared in the form of an aqueous solution which contains 20% by weight of solids. The required amount of water is then added to form an aqueous emulsion at 48%.

Example 5.

This example shows the improvement in the consistency and the mechanical strengths (pressure strength) (Table VI) as well as the lowering of the sweating (Table VII) obtained with the additive according to the invention relative to a known additive comprised of 100 parts by weight of sulfonated melamine resin and 10 parts by weight of sodium gluconate, for Rilem Cembureau mortars (water/cement weight ratio = 0.5).

The additive according to the invention is formed by an aqueous emulsion at 52%, comprising 24 parts by weight of magnesium lignosulfonate, 7.4 parts by weight of sodium gluconate, 25 parts by weight of dibutyl phthalate, 20 parts by weight of melamine-formaldehyde condensate resin, 22 parts by weight of triethanolamine, and 0.6 parts by weight of sodium dodecyl benzene, the melamine-formaldehyde condensate being prepared as an aqueous solution containing 30% by weight of solids.

TABLE VI

Mechanical strengths Consistency 24 hours 3 days 7 days 28 days Dry Mel- Mel- Mel- Mel- Mel Concrete additive Inven- Gluc. Inven- Gluc. Inven- Gluc. Inven- Gluc. Inven- Gluc.

composition Cements amounts tion Na tion Na tion Na tion Na tion Na - 350 kg/cement HK-400-2 0 1.85 1.85 107 107 246 246 333 333 436 436 - 1250 kg/ 0.3 2.33 2.10 93 96 271 256 380 319 516 462 rolled grit 4/32 0 1.83 1.83 136 136 283 283 357 357 453 453 P-400-3 -630 kg/ sand 0.3 2.29 2.20 128 126 303 287 403 397 488 452 -168 liters water 0 1.90 1.90 100 100 209 209 285 285 420 420 P-400-4 0.3 2.50 2.33 94 91 242 228 321 331 463 460 0 1.90 1.90 209 209 325 325 367 367 473 473 P-400-5 0.3 2.20 2.20 179 209 326 343 385 387 492 509 Mean values of the parameters for concretes with additive 2.33 2.18 123.5 130.5 285.5 278.5 372.5 358.5 489.8 470.8 TABLE VII

Final sweating cm3/cm3 HK-400-2 P-400-3 P-400-4 P-400-5 Additive in dry condition. Mel- Mel- Mel- Melamounts Invent. Gluc. Na Invent. Gluc. Na Invent. Gluc. Na Invent Gluc. Na 0 0.0036 0.0036 0.0058 0.0058 0.0090 0.0090 0.0100 0.0100 0.3 0.0045 0.0044 0.0032 0.0046 0.0074 0.0096 0.0062 0.0094 0.4 0.0026 0.0062 0.0016 0.0024 0.0040 0.0080 0.0028 0.0066 The chemical composition of the cements used for this purpose will be found in the following Table VIII.

TABLE VIII

Cements HK 400-2 P 400-3 P 400-4 P 400-5 % SiO2 (total amount) 26.16 19.72 21.67 20.34 Algol 11.39 6.95 5.62 3.92 Foe203 2.44 3.13 2.76 5.08 CaO (total amount) 49.39 59.85 63.15 61.91 MgO 3.26 1.25 1.21 2.24 So, 3.23 2.68 1.94 2.44 Mn2O 0.13 0.22 0.09 0.03 TiO2 0.22 0.32 0.32 0.23 K2O 0.79 1.45 0.62 1.20 P2O5 0.17 0.23 0.21 0.11 Undetermined components - 0.60 0.35 0.22 Firing loss 2.82 3.60 2.06 2.28 WHAT WE CLAIM IS:- 1. Additive for cement-based compositions, particularly for mortars and concretes, which comprises a mixture of at least one lignosulfonate selected from alkali metal and alkaline-earth metal lignosulfonates, an alkali metal salt of a hydroxy carboxylic acid, an ester defoaming agent, a melamine-formaldehyde condensate with sulfonic groups and an amine setting and hardening accelerator.

2. Additive according to Claim 1, in which said mixture comprises from 10 to 35 parts by weight of the lignosulfonate, from 3 to 15 parts by weight of the alkali metal salt of a hydroxy carboxylic acid, from 10 to 35 parts by weight of the ester defoaming agent, from 8 to 30 parts by weight of the melamine-formaldehyde condensate with sulfonic groups and from 10 to 30 parts by weight of the amine setting and hardening accelerator.

3. Additive according to Claim 2, in which said mixture is comprised of 18 to 26 parts by weight of the lignosulfonate, 6 to 10 parts by weight of the alkali metal salt of a hydroxy carboxylic acid, 18 to 26 parts by weight of the ester defoaming agent, 15 to 25 parts by weight of the melamine-formaldehyde condensate, and 15 to 25 parts by weight of the amine setting and hardening accelerator.

4. Additive according to any one of Claims 1 to 3, in which said mixture further comprises an emulsifier.

5. Additive according to Claim 4, in which the mixture comprises 0.2 to 2 parts by weight of the emulsifier.

6. Additive according to Claim 5, in which the mixture comprises from 0.4 to l part by weight of the emulsifier.

7. Additive according to any one of Claims l to 6, in which the lignosulfonate is selected from sodium lignosulfonate, magnesium lignosulfonate, ammonium lignosulfonate, calcium lignosulfonate, and a mixture of said compounds.

8. Additive according to Claim 7, in which the lignosulfonate is the magnesium lignosulfonate.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (25)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE VIII Cements HK 400-2 P 400-3 P 400-4 P 400-5 % SiO2 (total amount) 26.16 19.72 21.67 20.34 Algol 11.39 6.95 5.62 3.92 Foe203 2.44 3.13 2.76 5.08 CaO (total amount) 49.39 59.85 63.15 61.91 MgO 3.26 1.25 1.21 2.24 So, 3.23 2.68 1.94 2.44 Mn2O 0.13 0.22 0.09 0.03 TiO2 0.22 0.32 0.32 0.23 K2O 0.79 1.45 0.62 1.20 P2O5 0.17 0.23 0.21 0.11 Undetermined components - 0.60 0.35 0.22 Firing loss 2.82 3.60 2.06 2.28 WHAT WE CLAIM IS:-

1. Additive for cement-based compositions, particularly for mortars and concretes, which comprises a mixture of at least one lignosulfonate selected from alkali metal and alkaline-earth metal lignosulfonates, an alkali metal salt of a hydroxy carboxylic acid, an ester defoaming agent, a melamine-formaldehyde condensate with sulfonic groups and an amine setting and hardening accelerator.

2. Additive according to Claim 1, in which said mixture comprises from 10 to 35 parts by weight of the lignosulfonate, from 3 to 15 parts by weight of the alkali metal salt of a hydroxy carboxylic acid, from 10 to 35 parts by weight of the ester defoaming agent, from 8 to 30 parts by weight of the melamine-formaldehyde condensate with sulfonic groups and from 10 to 30 parts by weight of the amine setting and hardening accelerator.

3. Additive according to Claim 2, in which said mixture is comprised of 18 to 26 parts by weight of the lignosulfonate, 6 to 10 parts by weight of the alkali metal salt of a hydroxy carboxylic acid, 18 to 26 parts by weight of the ester defoaming agent, 15 to 25 parts by weight of the melamine-formaldehyde condensate, and 15 to 25 parts by weight of the amine setting and hardening accelerator.

4. Additive according to any one of Claims 1 to 3, in which said mixture further comprises an emulsifier.

5. Additive according to Claim 4, in which the mixture comprises 0.2 to 2 parts by weight of the emulsifier.

6. Additive according to Claim 5, in which the mixture comprises from 0.4 to l part by weight of the emulsifier.

7. Additive according to any one of Claims l to 6, in which the lignosulfonate is selected from sodium lignosulfonate, magnesium lignosulfonate, ammonium lignosulfonate, calcium lignosulfonate, and a mixture of said compounds.

8. Additive according to Claim 7, in which the lignosulfonate is the magnesium lignosulfonate.

9. Additive according to any one of Claims 1 to 8, in which the hydroxy

carboxylic acid alkali metal salt is selected from the gluconates and tartrates of sodium, potassium and ammonium, and mixtures thereof.

10. Additive according to Claim 9, in which the hydroxy carboxylic acid alkali metal salt is sodium gluconate.

11. Additive according to any one of Claims 1 to 10, in which the ester defoaming agent is selected from dibutyl phthalate, tributyl phosphate, and mixtures thereof.

12. Additive according to Claim Il, in which the ester is dibutyl phthalate.

13. Additive according to any one of Claims 4 to 12, in which the emulsifier is a non-ionic agent.

14. Additive according to Claim 13, in which the emulsifier is a nonylphenol polyglycolic ether.

15. Additive according to any one of Claims 4 to 12, in which the emulsifier is an anionic agent.

16. Additive according to Claim 15, in which the emulsifier is sodium dodecyl benzene sulfonate.

17. Additive according to any one of Claims 1 to 16, in which the melamineformaldehyde condensate is present as an aqueous solution containing from 10 to 50% by weight of solids.

18. Additive according to any one of Claims l to 17, in which the amine hardening and setting accelerator is triethanolamine.

19. An additive according to Claim 1 substantially as described in any one of the foregoing Examples.

20. Cement, mortar or concrete slurry, formed from a mixture of hydraulic cement, aggregates (in the case of mortar or concrete slurry), water and an additive as defined in any one of Claims 1 to 19.

21. Cement, mortar or concrete slurry according to Claim 20, in which the proportion by weight of the additive in dry condition is from 0.1 to 0.75% relative to the weight of dry cement.

22. Cement, mortar or concrete slurry according to Claim 21, in which the proportion by weight of the additive is from 0.18 to 0.45% relative to the dry cement weight.

23. Cement, mortar or concrete slurry according to anyone of Claims 20 to 22, in which the water/cement weight ratio is from 0.35 to 0.60.

24. Method for preparing an additive as defined in any one of Claims 1 to 19, as an aqueous phase emulsion, in which an aqueous solution containing from 10 to 50% by weight of melamine-formaldehyde condensate is added to the other components of the additive so as to form an aqueous emulsion, and, if desired, the emulsion is diluted with the required amount of water to bring the concentration of water to 30 to 70% by weight of the emulsion.

25. Method according to Claim 24 substantially as described in any one of the foregoing Examples.