GB2092564A - Lowering the viscosity of or liquefying Portland cement mixes - Google Patents

Abstract

Portland cement mixes are liquefied and/or their viscosity lowered by addition of a lignosulfonate whose purity is at least 85 per cent, conventional additives, and an accelerator, the accelerator quantity being 0.2 to 2.0 times as high as the quantity of lignosulfonate.

Description

SPECIFICATION Method for lowering the viscosity of and liquefying Portland cement mixes by means of lignosulfonate The subject of the present invention is a method in accordance with the preamble of claim 1.

The strength of various cement products normally depends on the ratio of the quantity of water used for the mix to the quantity of cement, i.e. on the water-to-cement ratio of the product or mix. The reason for this is that, when being hydrated, the cement binds a certain maximum quantity of water, whereas the remainder-mostly the main partf the water produces cavities and porousity, so-called capillary porousity in the hardened product. When the working of the concrete mix is insufficient-especially in the case of viscous mixes-so-called macropores are additionally produced, which also contribute to a deterioration of the strength.

By means of such plasticizing additives that disperse cement particles as plasticize the concrete mix even as little doses, it is possible to reach a considerably improved workability with unchanged water-to-cement ratio or, also, a reduced requirement of water with unchanged workability. In both cases a lower overall porousity is achieved in the cement product, and thereby the strength is increased.

Plasticizing additives additionally act so that, owing to their surface activity, they disperse such agglomerations of finely-divided particles as are always present in cement. This yields a better and more homogeneous distribution of cement in the product and thereby a more efficient utilization of the binder agent, which results in higher strength.

Plasticizing additives have been known and in use for a very long time. More recent agents in the field of additives are plasticizers whose dispersive effect on cement particles is even stronger than that of the normal plasticizers that were used previously.

These additives that have a high surface activity towards cement particles comprise mainly sulfonated and polymerized condensation products of formaldehyde and melamine and of formaldehyde and naphtalene, respectively. Also, modified lignosulfonates, i.e. condensation products of lignosulfonate and other organic substances, are used, but their efficiency has not been of the same order as that of the substances mentioned above. The difference between plasticizing and liquefying substances is not sharp. By means of plasticizing additives it is usually possible to achieve a reduction of about 1 5 per cent in the quantity of water, whereas by means of liquefiers one often achieves a reduction of up to 30 per cent in the quantity of water and an increase of 40 to 50 per cent in strength.

It is characteristic of liquefiers that they include a great number of polar groups, a number of acid functional groups (COOT, SO3H or their corresponding salts), as well as that they have a high molecular weight. Their precise functional mechanism is not known, but it is known that they are adsorbed in a more or less non-reversible way onto the surface of the cement particles, whereby these particles cannot be reunited with each other. The various clinker components and their hydration products present in cement adsorb organic additives in different ways, for which reason different cement qualities and types behave in different ways, e.g., when liquefiers are dosed. This is why empiric experiments are always necessary in order that it should be possible to determine the effect of an additive on a certain cement mixture or concrete.

Even if liquefiers permit the solution of many concrete-technological problems, their use has not obtained the extension that had been expected. This is partly due to high cost of these synthetic additives, which means a considerable additional expense, and to certain workhygienic drawbacks, resulting from formaldehyde.

Moreover, the efficiency of sulfonated melamine and of naphtalene resin seems to be reduced rapidly as pozzuolanas are added. As slag, fly ash, and other pozzuolanas are to-day added to normal Portland cement in many countries in order to reduce the energy expenses, this means that the possibilities of use of liquefiers based on melamine and naphtalene are reduced.

The efficiency of liquefiers based on lignosulfonate normally seems to be lower than that of the substances mentioned above, anddespite the abundant availability of inexpensive lignosulfonate-their use has not been equally extensive.

Unmodified lignosulfonates as sodium (NaLS) and calcium salts (CaLS) have been used as plasticizers for a rather long time. It has not been possible to use lignosulfonates as so high doses that a liquefying effect could have been reached. This comes from the, in many cases, quite serious secondary effects that are accompanied by the dosage of lignosulfonates, i.e. from the sugars and saccharic acids contained in lignin products, the quantities of said sugars and saccharic acids varying significantly from one cellulose cooking batch to the other. Among such secondary effects could be mentioned the considerable retardation of the hardening even with dosages of 0.2% out of the weight of cement. This effect comes out clearly from the following Table 1 (V.S. Ramachandran, Thermochim. Acta 4 (1 972)).

Table 1 Effect of lignosulfonate on properties of Portland cement concrete (Lignin purity 60%) Compression Setting time (h) strength as com Reduction at resistance to pared to refer Additive of Water/ in quantity penetration pin ence sample (%) cement cement of water (% by weight) ratio (%) 0,5N/mm2 3,5N/mm2 24h 3d 7d 28d 0 0,630 3-1/4 5 100 100 100 100 0,07 0,599 5 4 5-3/4 101 104 103 102 0,13 0,599 5 4 6-1/4 95 108 111 101 0,18 0,580 8 4-3/4 7-1/2 100 110 107 109 0,26 0,580 8 5-1/4 8-1/4 107 115 112 115 By means of plasticizers based on lignosulfonates, it is easily possible to obtain a reduction of 5 to 10 per cent in the requirement of water, but at the expense of a hardening time of 30 to 60 per cent higher length.The retardation increases when the dosage is increased, and in combination with the use of a low-heat cement the retardation may be very extensive and totally abnormal.

The retarding effect of lignosulfonate dosage on maturing and hardening has been utilized, e.g., in the preparation of concrete used for oil drilling.

Lignosulfonates contain a number of functional groups which, on one hand, help the adsorption of the product onto the surface of the cement particle and, on the other hand, owing to their hydrophily, bind water to the same product. E.g., owing to OH-groups, the adsorption may be even completely irreversible, in which case it is called chemisorption.

The lignosulfonates seem to be adsorbed in the first place onto aluminate phases (C3A and C4AF) and onto their hydration products. It looks like the lignosulfonates were adsorbed very strongly onto those metamorphic calciumaluminate hydrates that are formed as intermediate products (C2AH8 and C4AH19, respectively) of hydration of aluminate minerals and prevented a conversion into a more stable cubic C3AH6 form, which is the final hydration product. The reaction mechanism is, however, not fully known, and contradictory study results are also encountered in many cases.

It has also been noticed that the morphological structure of these intermediates has been changed into a structure which is assumed to yield higher strength.

It is commonly known that a C3A component of cement also affects the hydration speed of a silicate phase in a decisive way.

Under these circumstances, the components of the lignosulfonate used that are adsorbed onto the aluminate phase and its hydration products indirectly control the entire hydration process of cement.

The object of the present invention is to eliminate the practical difficulties that have been typically related to the varying quality of impure lignosulfonates and to provide a concrete product that matures and hardens in a desired and reproducible way and in which as binder is typically used Portland cement or its known commercial variations.

Surprisingly it has come out that, if lignosulfonate is purified and treated in the way to be described below to a purity higher than 85 per cent, an efficient liquefier is obtained for Portland cement and for its variations, in whose use no variability occurs and who does not cause uncontrollable retardation of the maturing and hardening of concrete.

More specifically, the method in accordance with the invention is mainly characterized in what is stated in the characteristic part of claim 1.

By means of the invention, remarkable advantages are obtained. Thus, by addition of a little quantity of an accelerator in itself known and in the first place affecting the hydration of the aluminate phase, it is possible to control the setting time of a cement mix or concrete within wide limits. If necessary, the method can also be used for purposes of increasing the porousity.

On the other hand, if it is desirable to avoid an increase in porousity, the necessary compensation can be easily accompished by means of deaerating agents in themselves known.

In the present invention, an entirely new lignin quality has now started being used as a plasticizer of cement. By cement is in this connection understood the normal Portland cement and its typical commercial variations, such as sulfate-proof cement, low-heat cement, low-alkali cement or blast furnace Portland cement, various pozzuolana cements, etc.

It is commonly known that lignosulfonates can be purified to a very high purity, e.g., by using ultra-filtration, whereby a purity of up to 97 per cent by weight is reached in the purity of a lignin product. This means that among the lignin product there are very little quantities of inorganic salts and of sugars or polysaccharides of low molecular weight. Further it is known, e.g. from the Finnish Patent Application 791696 or from the U.S. Patent 3,251,820, that lignin can be purified by utilizing liquid extraction. When proceeding in accordance with the said Finnish patent application, lignin sulfonate purities of 99 to 100 per cent can be achieved.

The retarding properties of commercial lignin products in cement mostly result from free sugars or saccharic acid, which are always present in normal lignin. A typical purity of the lignin contained in the spent liquor from cellulose cooking is of the order of 40 to 60 per cent by weight, and with a corresponding fermented spont liquor, from which alcohol, yeast, "pekilo", or any other typical fermentation product has been prepared, a lignin content of 65 to 80 per cent in the sulfite spent liquor is obtained as calculated from the dry substance.

All of the known lignin plasticizers mentioned above had been prepared by using such impure lignin products as the starting material.

In the tests performed by us we have noticed that, when only such a lignin product, purified either by ultrafiltration or by liquid extraction, was used as a plasticizer of the concrete mix, i.e.

for dispersing the cement particles, only slight retardation in the hardening of the concrete was noticed. In such a case the retardation does not result from sugars present but from the OH- and OCH3-groups involved in the structure of lignin, which groups bind Ca- and Al-containing ions efficiently in the hardening cement paste, and thereby reduce the mobility of these ions. Such a retarding effect is hardly encountered with the known plasticizers of cement, which are, among other things, sulfonated naphtalene condensates and sulfonated melamine-formaldehyde condensates.When one starts improving such a substantially pure lignin product in respect of its dispersing properties, whereby typical procedures applied are, e.g., desulfonating oxygenation, alkali treatment, slight ozonization, etc. treatment which reduces the numbers of sulfone groups, no detrimental oxydation products are produced from the impurities either. In the known methods (e.g. U.S. Patent 4,088,640), in which very strong ozone treatment is applied, these detrimental impurities are oxydated into a harmless form. If this treatment is, however allowed to remain at a slight form, which would be enough for desulfonation of lignin, e.g., the sugars would remain saccharic acids, which would still be efficient retarders of the hardening of the concrete.

When substantially pure lignosulfonate products are used for dispersing cement, as a simultaneous effect a very slight retardation in the hardening of concrete is obtained. This property of slight retardation in itself can be compensated easily in known ways.

Since lignosulfonates are primarily adsorbed on the aluminate phase of cement and prevent any other reaction, it is to be expected that accelerators affecting the hydration of the aluminate phase are here efficient.

Soda (Na2CO3) as well as bicarbonate (NaHCO3) are well-known accelerators, which have, also when used together with the lignin preparation used, proved capable of compensating the retardation in the setting time. This comes out from Table 2.

Table 2 Plasticizing of rapid cement by means of lignosulfonate and sodium carbonate.

Immediate flow = Melam. Increase form. Water/ in cone LS 95% LS 99% sulfon. Na2CO3 cement diameter T(80-0) Density Test (%) (%) (%) (%) ratio (mm) (h.min) (kg/m3) 1. - - - - 0,50 33 4.13 2065 2. 0,5 - - 0,5 0,50 103 0.37 2224 3. 0,5 - - 0,3 0,50 95 3.12 2220 4. 1,0 - - 1,0 0,50 150 0.35 2216 5. - 0,5 - 0,3 0,50 100 0.40 2200 6. - 1,0 - 0,6 0,50 135 0.46 2156 7. - - 0,5 - 0,50 53 3.53 2143 8. - - 1,0 - 0,50 78 4.30 2113 9. 1,5 - - 2,0 0,50 81 3.56 2102 10. 0,5 - - - 0,50 105 6.32 2220 (NaHC03) 11. 1,0 - - 2,5 0,40 73 0.31 2214 (TEA) 12. 0,5 - - 0,5 0,50 130 0.07 2277 (TEA) 13. 0,5 - - 0,1 0,45 75 0.28 2195 (TEA) 14. 0,5 - - 0,05 0,38 85 0.44 2252 To the samples 2 to 9, 0.2% of Na-gluconate and 0.5% of tributylphosphate were added, as calculated from the quantity of cement.

As comes out from the tests, even a lignosulfonate addition of 0.3 to 0.5%, as calculated from the quantity of cement, produces good plasticization. A certain retardation in the setting time can be noticed when lignosulfonate alone is added, but this retardation can be compensated by means of a little addition of soda or bicarbonate.

By increasing the lignosulfonate addition from 0.5% to, e.g., 1.1% no improved workability is obtained, but instead the setting time becomes longer.

The reduction in the quantity of water, as compared with a mortar with no additives, is about 30%.

In the preceding table T(80-0) indicates the hardening time of cement mortar within which the flow of the cement mortar on the table is changed from 80 mm to O mm. In the table there are three columns for different liquefiers; the first two involve pure lignosulfonate products prepared in different ways, and the third column contains, as a reference, a common commercial melamine-formaldehyde condensate sulfonate.

From Table 2 it is noticed that, when pure lignosulfonate is used, a very little addition of alkali carbonate is sufficient to compensate the retardation of the hydration of cement produced by the lignin itself.

Further, the examination of the effect of lignosulfonates of different degrees of purity on the hardening of cement mortar was continued. Cement and sand were used at the ratio of 1:3, and the temperature continued to be 30'C.

Table 3 Immediate flow = Increase in cone LSA 100% LSA 95% LSA 91% LSA 80% Na2CO3 diameter T(80-0) Test (%) (%) (%) (%) (%) (mm) (h.min) 15. 0,5 - - - 0,5 101 0.43 16. - 0,5 - - 0,5 103 0.37 17. - - 0,5 - 0,5 95 1.37 18. - - - 0,5 0,5 82 3.11 19. - - - 0,75 1,1 102 5.04 In the preceding Table 3 the effect of the purity of LSA on the plasticity and retardation of cement mortar was examined. The product had been purified by ultrafiltration, by using membranes GR 6 produced by De Danske Sukkerfabrik, and the products had been taken from the same batch of spent liquor from cellulose cooking at different stages of purification.The 100% pure lignosulfonate product had been prepared by extraction in accordance with the Finnish Patent Application 85076, whereby the lignosulfonates are extracted by means of an amine into an organic phase and removed from the organic phase by means of NaOH-treatment.

All of the lignin products discussed above had been prepared from the spent liquor of Nabisulfite cook, wherein the sulfonation degree is 0.3. This relatively low sulfonation degree has been noticed to be favourable as compared, e.g., with a Ca-lignosulfonate prepared by means of ultrafiltration, wherein a typical sulfonation degree is, owing to the acidity of the cook, of the order of 0.45 to 0.5. Further, it has been noticed that from such cellulose cooks in which the sulfonation degree is very low, such as catalysed alkali-sulfite cooks, an even more advantageous lignin product is obtained to be used for dispersing cement (Finnish Pat. Appl. 793453).In such a spent liquor from alkali sulfite cellulose cooking the sulfonation degree of the lignin can be even as low as 0.1 5. The sulfonation degree means here the number of sulfone groups in the lignin structure per one aromatic ring.

Now it has been noticed further that, when lignosulfonates that have been purified either by extraction or by ultrafiltration are treated under slightly alkaline conditions with heat and/or when the sample has been at the same time oxygenated either with air or, e.g., with hydrogen peroxide, their sulfonation degree can be easily lowered to about 0.2 and even below this without lignin in itself still beginning to decompose and, in a known way, to form vanillin and other known decomposition products. When substantially sugar-free lignins are treated under slightly oxydating conditions, there is no risk of saccharic acids being formed under certain conditions nor of their further oxydation under other conditions. This means that, when oxygenation is continued further, pure lignosulfonates constantly obtain properties continuously changing in the same direction.

Table 4 Immediate flow = Increase LSA 95% LSA 95% LSA 95% in cone SA 0,30 SA 0,24 SA 0,21 Na2CO3 diameter T(80-0) Test (%) (%) (%) (%) (mm) (h.min) 20. 0,5 - - 0,5 102 0.47 21. - 0,5 - 0,5 125 0.42 22. - - 0,5 0,5 134 0.43 The LSA-products used in the tests 20, 21 and 22, which are here characterized by different sulfonation degrees (SA), were prepared by mixing appropriate quantities of hydrogen peroxide into an alkaline water solution of lignosulfonate and by heat-treating the product for certain periods of time.The conditions of the said procedure were the following: A 1 6 % N all 16% Na-lignosulfonate-water solution was prepared, to which 4% of NaOH and O to 1.5% of hydrogen peroxide, as calculated from the weight of lignin, and about 2% of lime milk, as calculated from the weight of lignin, were added. The reaction times used were 30 min., 40 min., and 55 min., whereby the given sulfonation degrees were reached at 100"C. The NaOH used was later converted into Na2CO3 by means of CO2. A corresponding desulfonation can be produced in a known way even without oxygenation by incubating the lignin under stirring and in the presence of Ca(OH)2. In such a case, however, reaction times of the order of 2 to 4 hours are obtained.

Example on desulfonation of LSA A solution was prepared that contained 1 6% of 100-percent lignosulfonate, to the solution was added 4% of NaOH and 2% of Ca(OH)2, and the solution was boiled for 2.5 hours. The boiling was continued as periods of 2.5 hours and samples were always taken between these periods. In the starting situation the sulfonation degree of the LSA was 0.30, and after 2.5 hours it had been lowered to 0.20, and the sulfonation degree was not lowered from this further even by subsequent treatments.

The same solution as above was in addition to mere incubation also treated with a quantity of 2% of hydrogen peroxide, and the same degree of sulfonation, 0.1 95, which was by cooking alone reached in 2.5 hours was now reached after a trreatment of 5 minutes.

The first test was repeated so that the incubation was continued for 1 hour only, whereby the degree of sulfonation was lowered to 0.24.

The determinations of sulfonation degree were performed from weil filtered iiquors by determining the total sulfur in the liquor.

Previously, in this connection, compensation of the retarding effect caused by pure lignosulfonate by means of soda has been discussed. The same compensation of retardation can be obtained by using soluble calcium salts (e.g., Ca-formiate, CaCI2, Ca(NO2)2 and Ca(NO3)2), among which the most advantageous one is calcium nitrite because of its other advantageous effects. It is well known that with lignosulfonate plasticizers usually, e.g., CaCI2 is used in order to compensate the retarded hydration caused by the said plasticizers. Then it is necessary to use large quantities of the calcium chloride product, which causes corrosion, because the lignin product used normally contains sugars and/or saccharic acids, whose retarding effect is remarkably high.

Table 5 LSA 95% Na2CO3 NaHCO3 CaC12 Ca(COOH)2 Ca(NO2)2 Strength(MPa) Test (%) (%) (%) (%) (%) (%) 1 d 2 d 3 d 23. 0,5 0,5 - - - - 22,2 43,4 45,8 24. 0,5 - 1,0 - - - 20,3 38,5 42,8 25. 0,5 - - 1,0 - - 18,5 24,0 36,0 26. 0,5 - - - 1,0 - 21,2 26,0 28,0 27. 0,5 - - - - 1,0 24,2 28,2 29,0 28. 0,5 - - - - - 19,5 24,9 25,4 The lignosulfonate used, whose purity was 95% and sulfonation degree 0.30, when compared with commercial liquefiers based on melamine and naphtalene, was noticed to give both better workability and higher strength, which comes out from the following Table 6.

Table 6 Concrete 8 mm, 300 kg RHC/m3 Volu- Air Water/ Strength (MN/m3) metric con cement weight tent Test Liquefier ratio 1 d 3d 7 d 28d (kg/1) (%) 29. - 0,60 16,2 30,5 36,1 2,309 3,9 30. M 0,57 15,8 32.1 36,8 2,309 3,9 31. N 0,57 17,3 32,4 38,1 2,350 3,0 32. P 0,56 14,2 33,4 40,4 2,312 4,0 33. LS 0,5% 0,50 22,2 43,4 45,8 2,369 3,0 34. LS 1,0% 0,50 - 18,4 30,6 2,351 2,4 The cement used was RHC of a fineness grading of 450 m2/kg. Workability (i.e. flow on a vibrator table as per DIN Standard) was in all cases 12 cm. The quantity of additive was in all cases 0.5% of the cement quantity. Out of the liquefiers indicated in the table, M = based on melamine N = based on naphtalene P = based on lignosulfonate, and LS = based on a lignosulfonate in accordance with the invention (purity 95%).

As is seen, the water/cement ratio can be reduced by about 17% without a change in the workability, whereby an increase of 37% in strength is obtained after 24 hours. An increase in the LSA quantity to 1 % causes a considerable retardation in the development of strength.

Table 7 Effect of pure (95%) lignosulfonate when fly ash (PFA) and ground blast furnace slag (MK) is used as an admixture for Portland cement (OPC) Water/ Na-glu Mix LSA 95% cement Na2CO3 conate TFB Flow Test ratio (%) ratio (%) (%) (%) (mm) 35. 100% OPC 0,5 0,37 0,3 0,08 0,05 80 36. 70% OPC 0,5 0,37 0,3 0,08 0,05 140 + 30% PFA 37. 70% OPC 0,5 0,37 0,3 0,08 0,05 135 + 30% MK (TBF = tributylphosphate, in Table 7) The viscosity lowering effect of the lignosulfonate can be stil improved by adding small amounts of NaOH to the additive, which appears from the test results below (Table 8).

In the tests a concrete was used which contained rapid cement in amount of 360 kg/m3. The maximum granule size was 14 mm and the mixture was 50 1 in a coercive mixer. The LSA content was 0.6% by weight of cement. The water-to-cement ratio was 0.42.

Table 8 The effect of NaOH addition on the viscosity lowering effect of lignosulfonate and on the strength of concrete Addition of Depression/ Depression/ Flow/O min Flow/15 min NaOH (g) 0 min (cm) 1 5 min (cm) (cm) (cm) 0 5.5 stiff 36 stiff 5 17 6.5 43 38 9 17 17 49 48 14 18 16 49 48 18 5 65 38 34 Compression strength at 50 C (10 cm cubes) al 4 (MN/m2) tJ7(MN/m2) a28(MN/m2) O ~ ~ 5 30 42 50 9 28 41 48 14 31 43 52 18 31 43 51 The addition of Na2CO3 does not influence on the viscosity lowering effect but on the increase in strength. The results appear from Table 9.

Table 9 The effect of Na2CO3 addition on the viscosity lowering effect of lignosulfonate and on the strength of concrete.

The concrete was the same as in the previous example. However, the water-tocement ratio was 0.46.

Addition of Depression/ Depression/ Flow/O min Flow/15 min Na2CO3 (9) 0 min (cm) 1 5 min (cm) (cm) (cm) 0 65 18 41 42 12 8 8 37 38 24 8 6 38 36 36 5 5 36 34 Compression strength at 50 C (1 0 cm cubes) awl 4 (MN/m2) a7 (MN/m2) a28 (MN/m2) 0 30 48 54 12 37 55 60 24 37 57 64 36 32 45 56 In pulping, different catalysts for accelerating the cook have been used for testing purposes.

This leads to a bigger gain as an exaggerated splitting of fibres and saccharides is avoided.

The lignin obtained from the cook has in its pure form proved to be an effective liquefier, the viscosity lowering effect of which is higher than that of pure lignin, which apprars from the test results below (Table 10).

Table 10 The effect of the quality and amount of lignosulfonate on the properties of mortar (The cement was 100% RHC) Quality and Water-toamount of cement Flow T80-0 Volumetric lignosulfonate ratio (cm) (h.min.) weight (kg/l) UF/0.2% 0.50 80 3.05 2.12 AK/0.2% 0.50 95 3.10 2.20 US/0.5% 0.40 90 2.40 2.15 AK/0.5% 0.40 100 2.05 2.05 UF/0.8% 0.35 70 2.15 2.20 AK/0.8% 0.35 98 2.30 2.20 To all test masses were added 0.3% Na2CO3 and 0.1% TBF by weight of cement.

UF denotes normal Na-lignosulfonate having a purity of 95%.

AK denotes purified lignosulfonate obtained from an antrachinon cook.

Table 11 Effect of an addition of lignosulfonate on the air centent of mortar Incr.

Volu- in NaLS Water/ metric quant.

95% cement Flow T(80-0) weight of air Test Cement (%) ratio (mm) (h.min.) (kg/l) (%) 38. 100% RHC 0,50 85 3.30 2,16 16 39. 100% RHC 0,15 0,48 70 2.26 2,05 5,2 40. 70% RHC - 0,50 93 4.23 2,17 17 + 30% MK 41. 70% RHC 0,15 0,50 95 4.35 2,03 6,5 + 30% MK 42. 70% RHC - 0,47 80 4.20 2,18 18 + 30% PFA 43. 70% RHC 0,15 0,42 83 3.07 2,10 3,5 + 30% PFA The tests 38 to 43 prove that even with a little increase in the quantity of lignosulfonate an extra content of air is achieved, whereby at the same time the setting becomes faster. The test was performed with a mortar whose mix ratio was 1:3. The specific surface area of the cement was 430 m2/kg.

Claims (14)

1. A method for lowering the viscosity of and liquefying a Portland cement mix, particularly a Portland cement concrete, by adding small amounts of additives to the mix, comprising the addition of: conventional additives, -a lignosulfonate having a purity of at least 85 per cent, and -an accelerator known per se in a quantity of 0.2 to 2.0 times the quantity of lignosulfonate.

2. A method as claimed in claim 2, wherein such a lignosulfonate is used whose purity is 90 to 99 per cent.

3. A method as claimed in claim 1 or 2, wherein such a lignosulfonate is used as has been purified by means of ultrafiltration to a purity of 90 to 97 per cent, preferably 92 to 96 per cent.

4. A method as claimed in claim 1, wherein such a lignosulfonate is used as has been purified by means of extraction to a purity of 90 to 99 per cent, preferably 96 to 98 per cent.

5. A method as claimed in claim 1, wherein such a lignosulfonate is used as has been obtained from a cook in which chinon, antrachinon or a similar catalyst has been used for activating the cook.

6. A method as claimed in claim 1, wherein as accelerator is used some alkali carbonate, such as soda, potash, or equivalent.

7. A method as claimed in claim 1, wherein as accelerator is used some alkali bicarbonate, such as sodium bicarbonate, potassium bicarbonate, or lithium bicarbonate.

8. A method as claimed in claim 1, wherein a hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide, or another strongly alkaline compound is added in order to increase the viscosity lowering effect of the lignosulfonate.

9. A method as claimed in claim 1, wherein as accelerator is used some calcium salt soluble in water, such as calcium chloride (CaC12), calcium nitrate (Ca(NO3)2), calcium nitrite (Ca(NO2)2), or calcium formiate.

1 0. A method as claimed in claim 1, wherein as accelerator of the setting of cement is used some small-molecule organic amine, e.g., triethanolamine.

11. A method as claimed in claim 1, wherein lignosulfonate is used in a quantity of 0.1 to 1.5 per cent by weight as calculated from the quantity of cement used.

1 2. A method as claimed in any of claims 1 and 4 to 7, wherein lignosulfonate is used in a quantity of 0.3 to 0.7 per cent by weight and the accelerator in a quantity of 0.3 to 0.7 per cent by weight as calculated from the quantity of cement used.

13. A method as claimed in claim 10, wherein about 0.5 per cent by weight of lignosulfonate and about 0.5 per cent by weight of accelerator are used.

14. A method as claimed in claim 1 or 3, wherein the sulfonation degree of lignosulfonate has been lowered to a level between 0.4 to 0.15.