CA1222530A - Cement dispersant - Google Patents

Abstract

Cement Dispersant Abstract of the Disclosure The cement dispersant comprises a macromolecular lignosulfonic acid or a salt thereof. It may be a composition which comprises (a) said macromolecular lignosulfonic acid or a salt thereof and (b) a condensate of beta-naphthalenesulfonic acid and formaldehyde or a salt thereof. It prevents the slump loss in the cement composition.

Description

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22S3~) Cement Dispersant This invention relates to a dispersant for cement. More particularly, the present invention relates to a water reducing agent and a slump loss preventing agent for use with cement paste, mortar and concrete as cement compositions.

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~ A wide variety of cement dispersants are known , . and typical examples include salt of ~-naphthalene : sulfonic acid/formaldehyde condensate (hereinafter referred to as "~--NSF"), salt of meraminsulfonic acld/formaldehyde condensate, and lignosulfonates . (hereinafter referred to as "LS"). These disper-sants are used in kneading a cement composition to reduce the quantity of water to be used and to : ~ , ~ , .

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improve workability. However, these heretofore known dispersants involve in common the problem that fluidity drops remarkably with the passage of time (hereinafter reerred to as "slump loss").
In hydraulic cement compositions in general, chemical and physical aggr,egation of cement par-ticles proceeds with the passage of time after kneading, fluidity drops gradually and the problem of workability arises. Especially in the case of concrete to which a high range water reduc-ing agent typified by ~-NSF is added, the water reduction ratio becomes higher and hence the slump loss becomes all the more remarkable than when no chemical admixtures for concrete is added or when the conventional admixtures such as AE agents, water reducting agents, and AE water reducing agents are used. If the slump loss thus occurs,,various pro-blems will occur such as a drastic increase of a pumping pressure and clogging of a pump when the p~mping of concrete is temporarily stopped because of a lunchtime break or some other troubles and is thereafter started once again in a precasted concrete product plant. The problem of non-packing will also occur when molding such as tamping is delayed fo:r some reason or other after the cement composition is poured into a mold.

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~003 ~222~i3 In ready mixed concrete, too, the slump loss occurs from time to time during the period in which the concrete is transported from a concrete production plant to the job sitej so that workability drops remarkably, the pump is clogged and non-packing occurs during molding. Though the reason for the slump loss is not yet fully clari-fied, it is believed that after the cement parti-cles in the cement paste come into contact with water, chemical aggregation due to the hydration reaction and(/or~ physical aggregation due to the attraction between the particles proceed so that the fluidity of the cement paste and hence that of the hydraulic cement composition, drop. Particu-larly when a water reducing agent for concrete (cement dispersant) such as ~-NSF or LS is added, it is adsorbed by the cement.particles and elevates the zeta potential of the cement particles. The cement particles are thus dispersed by the electric repellency and the fluidity of the hydraulic cement composition can be improved (see, e.g., Hattori, "Konkurito-Kogaku", Vol. 14, No. 3, p.p. 12-lg, March, 1976). However, the water reducing agent is gradually incorporated in the hydrated minerals of the cement with the passage of ~, .
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time and the electric repellency is no longer ex-pected so that the fluidity drops. Accordingly, if it is possible to somehow continue the supply of the water reducing agent for dispersing the cement particles, the cemefit particles could be dispersed while keeping the form of the primary particles and hence the slump loss of the hydraulic cement composition could be prevented.

The following methods are found to cope with the slump loss on the basis of the technical con-cept described above.
i) A concrete mixing agent is shaped in the form of powder or particles or is entrapped into a carrier so that the ef~ective ingredient is gradually released into the system to retain its ef~ect (see, e.g., Japanese Patent Laid-Open No. 139929/1979).
ii3 A concrete mixing agent is repeatedly added to a hydraulic cement composition by means of mechanical force Isee e.g., Japanese Patent Publication No. 15856/1976).
However, though the method Ii) provides a sufficient slump loss preventing effect, the cement dispersant remains locally in the cement blend even ~- .

2~;i3~) after the retention of slump is completed and causes adverse influences such as occurrence of bleeding and eventual drop of strength. The mekhod (ii) provides a slump loss preventing effect, too, but if the concrete discharged from a mixer is inside a pumping pipe or in a mold, it becomes difficult to add the conrete admixture. As a method of preventing the slump loss, a method of retarding the initial hydration reaction of cement by adding hydroxycarboxylates or lignosulfonates or using them in combination in order to restrict the chemical aggregation of the cement particles has been found (see, e.g., Japanese Patent Publication Nos. 24533/1977 and 13853/1977 and Japanese Patent Laid-Open No. 17918/1979). Though these methods can restrict the chemical aggregation of the cement particles to some extents, their effect is not entirely high. I the amount of the additives is increased to enhance the effect, the initial slump becomes so high that separation of aggregates will occur.
Thus, none of the methods described above are entirely satisfactory for practicaL use.

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The inventors of the inVention have made a research about the method (i) in which a concrete mixing agent is used in the normal liquid form and then the method (ii) in which no mechanical force is used and found that the invention can prevent the slump loss.
According to one aspect of the present invention there is provided a dispersant composition for a hydraulic cement composition which dispersant composition comprises (a) a macromo-lecular lignosulfonic acid or a salt thereof having a viscosity of 25 to 400 cps at 20C in a 20% by weight aqueous solution thereof, having been obtained from a reaction between lignosulfonic acid or a salt thereof and a water-soluble peroxide to generate an oxygen radical and (b) a condensate of beta-naphthalene-sulfonic acid and formaldehyde or a salt thereof, at a weight ratio of from ~0/20 to 20/80.
According to another aspect of the present invention there is provided a method of preparing hydraulic cement comprising admixing the above dispersant composition in :the ceme~nt.

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~ - 6 -~,~22S30 . The reason why the m.~cromolecular ligno-sulfonic acid-or its salt exhibits a particularly high effect of preventing the slump loss is not yet clarified. It is assumed, however, that lignin substances, saccharides, carboxylic acid substances and the like have been known as those which have a retarding property and, because the lignin itself yet leaves some ambiguity in its structure, the effect obtained by rendering the lignosulfonic acid macromolecular arises from the peculiarity of lignin.
The macromolecuiar lignosulfonic acid or its salt.used in the present invention is a macro-molecular reaction product obtained by reacting a water-soluble peroxide capable of generating an o~ygen radical with a lignosulfonate and has a viscosity of 25 to 400 cps (at 20C) in the form of its ~0~ solution.
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The macromolecular lignosulfonic acid or its ;

salt of the present invention can be obtained by reacting LS or its sal-t with a water-solubLe pero-xide in water of a pH of 9 or below and preferably 8 or below at a temperature in the range of 10 to 60C and preferably from 20 to 40C. The LS or its .

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0~08 salt as the starting material may be ordinary one obtained in wood pulping, but preferably the resid-ual saccharide content of LS must be reduced by ultrafiltration or the like to restrict the delay of hardening. Ammonium persulfate and potassium persulfate are preferred examples of the water-sol~ble peroxide and are used in an amount of 2 to 15 wt~ on the basis of the solid of LS. To obtain a macromolecular product, LS or its salt must be reacted to such an extent that the viscos-ity of its 20% solution becomes 25 to 400 cps (at 20C) and preferably, 50 to 200 cps (at 20C).
Examples of cations that can form the salt are Na, K r Ca, NH4, and alkanolamine When lignosulfonic acid (LS-l) is rendered macromolecular, the mortar flow value drops in comparison with the conventional lignosulfonic acid as illustrated by LS-APS-l in the Eollowing Table 1 but the sIump can be kept constant for an extended period of time as will be illustrated in the later Examples. However, the conventional lignosulfonic acid does not provide any slump loss preventing effect as will be illustrated in the later Comparative Example. The macromolecular lignosulfollic ~cid of the present invention , .

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exhibits a gel chromatography pattern which is entirely different from that of the conventional lignosulfonic acid as shown in Figure 1.

srief Description of the hereto attached Drawing Figure 1 is a diagram showing a gel chromato-graphy pattern of lignosulfonic acid and that of the macromolecular lignosulfonic acid of the present invention.

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1) 8 wt% of ammonium persulfa-te (hereinafter called "APS") was added to LS-1 (commercially available lignosulfonic acid) on the basis of the solid of the acid and was reacted at 30 to 40C for 4 hours. The pH was adjusted using acetic acid and sodium hydrogencarbonateO
2) 20% solid concentration; measured by a Brook-- field viscometer.

3) molar number per phenylpropane;
(measuring method) After APS was removed by dialysis, cation ex-change was effected and conductometric analysis was carried out using O.lN^NH4OH as a titrating agent.

4) 3 parts each of various LS's was dissolved in 270 parts of water and 600 parts of ordinary Portland cement and 1,200 parts of fine aggre-gate was added. The mixture was mixed by a mortar mixer to obtain a mortar and the mortar flow value was measured in accordance with JIS R-5201.
Recently, a slump loss preventing agent con-sisting of an LS salt containing at least 0.20 mol, per phenylpropane, of carboxyl group and at least 0~1"

~222~3 0.10 mol of sulfonyl group is disclosed Isee Japanese Patent Publication No. 40,106/19Bl). The reference describes that since the LS salt having such a structure can easily form a chelate with AQ in the cement, it inhibits hydration and prevents the slump loss. In contrast, the macromolecular LS or its salt in accordance with the present invention contains 0.17 mol of carboxyl group and 0.08 mole of sulfonyl group, and LS that is rendered macro-molecular by the peroxide is believed to exhibit the slump preventing effect irrespective of -the contents of these groups, as illustrated in Table 1.

As before mentloned, the invention further provides a new cement dispersant composition which comprises (a) the above defined macromolecular lignosulfonic acid or a salt thereof and lb) a condensate of beta-naphthalenesulfonic acid and formaldehyde or a salt thereof.

The condensate (b) to be used in the invention is disclosed in Japanese patent puhlication No.
11737/1966. The beta-naphthalenesulfonic acid, .
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a reactant for said condensate (b), may be placed by a co-condensate of naphthalenesulfonic acid and alkylnaphthalenesulfonic acid.

A ratio of the component (a) to the component (b) in the composition according to -the invention ranges from 80/20 to 20/80, pre-~erably from 70/30 to 30/70.

According to the invention, the macromolecular lignosulfonic acid or a salt thereof is used in an amount of from 0.1 to 1~5 percent by weight based on the solid content of the hydraulic cement composition. Then the dispersant composition comprising (a) and (b) is used in an amount of from 0.25 to 1.5 percent by weight based on the solid content of the hydraulic cement composition.
If the composition is used at less than 0.25 ~, t cannot provide the cement particles with the sufficient dlspersion effect. If it is used at more than 1.5 %, the dispersion of the cement particles becomes so excessive that bleeding and paste separation will occur.
According to the invention, the cement ::
dispersant is preferably added to the hydraulic :

cement composition in the form o:, an aqueous solution. It may be used in -the powdery or granular form in order to prevent the slump los5.
The addition of the cement dispersant when the blend is kneaded and dissolved in water. Otherwise, the dispersant is added to the kneaded hydraulic cement composition, or that ih the powder form is added to the cement. It is practically convenient -that each component of the dispersant . .
blend is mixed in advance, but each component may be added separately at an arbi-trary stage in the kneading process of the hydraulic cement composi-tion.

The cement dispersant according to the invention may further contain anotheridispersant such as a carboxylic acid type and a polycarboxylic acid type r a water-reducing~agent, a mixlng agent, a hardening retarder and a water-soluble polymer compound such as polyvinyl alcohol, polyethylene glycol anl polyalkylene glycol.

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~L2X;~S30 Hereinafter, the present invention wi l be described with reference to Examples thereof, which are, however, merely i:Llustrative but not limitative in any manner.
Referential Example The p~ of 300 g of a 25% solid aqueous solution of commercially available lignosulfonic acid (a product o~ Borregaard Co., hereina~ter called "LS-l") was adjusted to 6`using acetic and sodium hydrogencarbonate. 6 g of ammonium persulfate (APS) was dissolved in 60 g of water and the solu-tion was added dropwise to the solution described above at room temperature. Thereafter, the reac-ti~n was carried out at 30 to 40C ~or 4 hours to obtain a ~acromolecular reaction product (herein-after called "LS-APS-l"). The 20% solid viscosity was found to be 54.6 cps (at 20C). Components (a) obtained in the same way but changing the treating conditlon are shown in Table 2. KPS represents potassium persulfate.

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~;~2~30 Table 2 .
Treating condi.tion 3) (reaction condition with peroxide) Viscosity LS1) (cps) Peroxide Reaction Time p~2) t20C) (q'ty) temperature _ LS-APS-l APS(8) 30~40C: 4 hr 6 72.3 LS-APS-2 APS(12) .. 3 hr 3 180.L
Ls-APs-3 APS(3) ., 4 hr 6 54.6 LS-APS-4 APS(8) ., 4 hr 9 38.2 LS-KPS-l potassi~lm .. 4 hr 6 49.3 persulfate~8) . _ Note:
1) wt% on the basis of the solid of LS.
2) adjusted by acetic acid and sodium bicarbonate .
3) measured at 20% solid concentr~tion.
Examples and Comparative Exa_ple 1) Specified mixture and materials of concrete Table 3 _ Intended Intended . W/C S/a C W - S G air q 'ty slump : (%) (%) ~kg/m ) (%) _(cm) ~8 303 167 864 951 3.5 2 Note:
Cement (C): ordinary portland cement (Onoda Cement) 01~17 Fine aggregate (S): sand of Kinokawa (specific gravity 2.58, FM 2.91) Coarse aggregate (G): crushed stone of Takarazuka (spec:ific gravity 2.61, FM 6 98) Water (W) Rneading method of concrete Method 1: The cement dispersant was in advance dissolved in kneading water.
40 Q of the mixture was kneaded in a tilting mixer at 25C to obtain each concrete shown in Table 3. While the number of revolution was ]cept at 2 rpm, kneading was continued for a predeter-mined period of time to measure changes in the slump and air quantity with the passage of time.
; Measurement of the slump, air quantity and compressive strength as well as sampling of a strength test specimen were carried out in accord-ance with JIS.
Method 2: The procedures of Method 1 were followed except that the cement dispersant the added simultaneously with the kneading water.

00~8 ~2;:253 2) Test conditions and test results are illustrated in Table 4.
It can be seen clearly from Table 4 that it is difficult to retain slump by use of ordinary LS and the product of the present invention ex-hibits an extremely high effect in respect to the slump residual ratio.

It is understood from examples and comparative examples that the conventional lignosulfonic acid cannot provide the advantageous effect by itself and even in combination with the component (b~.

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O 0 2 0 L222~i30 The dispersant composition which comprises (a) and (b) according to the invention will be illustrated below in line with examples t:hereof.

Table 5 _ ~
Cement dispersant Example _ ~neading No. Co~ponent (a) component (~)l3 addition2) method LS-APS-l70/30 O~70 method 1 16 LS-APS-150/50 O.60 ..
17 LS-APS-l30/70 O.50 .
18 LS-APS-250/50 O.60 ..
: 19 LS-APS-350/50 O.60 ..
LS-APS-450/50 O.60 ..
21 LS-KPS-150/50 0.60 ..
. 22 LS-APS-L70/30 O.45 method 2 23 LS-APS-l 50/50 O.40 ..
~: 24 LS-aPS-2 50/50 O.40 .. .

Note:
1) "Mighty 50", a product of Kao Corporation was used as the component (b), weight ratio per solid content.
2) wt% of solid content on the basis of cement.

~ f ra~ lc~rk 0i~21 Table 6 eomparative examples 2 to 4 are listed.

Comparative Cement dispersant Kneading Example No. Amount of method ~ind additionl) ..

2 Mighty 150 0.45 method 1 3 LS-l/Mighty 150 (weight O.h5 ratio of solid contenlt~
_ Mighty 150 0.30 method 2 .

Note:
1~ wt% o~ solid content on the basis of cement.
3) Test results:
TPst results are ~hown in Table 7.

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Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a hydraulic cement composition which comprises admixing with a hydraulic cement composition a dispersant composition, said dispersant composition comprising (a) a macromolecular lignosulfonic acid or a salt thereof having a viscosity of 25 to 400 cps at 20°C in a 20% by weight aqueous solution thereof, having been obtained from a reaction between lignosulfonic acid or a salt thereof and a water-soluble peroxide to generate an oxygen radical and (b) a condensate of beta-naphthalene-sulfonic acid and formaldehyde or a salt thereof, at a weight ratio of from 80/20 to 20/80.

2. A method according to claim 1 wherein the macromolecular lignosulfonic acid or salt thereof is present in the cement composition in an amount of from 0.1 to 1.5 % by weight based on the solid content of the hydraulic cement composition.

3. A method according to claim 1 wherein the lignosulfonic acid is used as a salt formed with a cation selected from the group consisting of Na, K, Ca, NH4 and alkanolamines .

4. A method according to claims 1, 2 or 3 wherein the reaction between the lignosulfonic acid or salt thereof with the water soluble peroxide is effected at a pH of less than 9 at a temperature in the range of 10°C to 60°C.

5. A method according to claims 1, 2 or 3 wherein the reaction between the lignosulfonic acid or salt thereof with the water soluble peroxide is effected at a pH of less than 8 at a temperature in the range of 20°C to 40°C.

6. A method according to claims 1, 2 or 3 wherein the water soluble peroxide is present in an amount of 2 to 15 wt. % based on solid lignosulfonic acid or salt thereof.

7. A method according to claims 1, 2 or 3 wherein the vis-cosity of said lignosulfonic acid or salt thereof is 50 to 200 cps at 20°C.

8. A method according to claims 1, 2 or 3 wherein the weight ratio of (a) to (b) is 70/30 to 30/70.

9. A method according to claims 1, 2 or 3 wherein said dispersant composition further comprises an additional dispersant selected from the group consisting of a carboxylic acid, a poly-carboxylic acid, a water reducing agent, a mixing agent, a harden-ing retarder, a polyvinyl alcohol, a polyethylene glycol and a polyalkylene glycol.

10. A method according to claims 1, 2 or 3 wherein said water soluble peroxide is ammonium or potassium persulphate.

11. A dispersant composition for a hydraulic cement compo-sition, which dispersant composition comprises (a) a macromolecular lignosulfonic acid or a salt thereof having a viscosity of 25 to 400 cps at 20°C in a 20% by weight aqueous solution thereof, having been obtained from a reaction between lignosulfonic acid or a salt thereof and a water-soluble peroxide to generate an oxygen radical and (b) a condensate of beta-naphthalene-sulfonic acid and formal-dehyde or a salt thereof, at a weight ration of from 80/20 to 20/80.

12. A dispersant composition according to claim 11 wherein the macromolecular lignosulfonic acid or salt thereof is present in the cement composition in an amount of from 0.1 to 1.5 % by weight based on the solid content of the hydraulic cement compo-sition.

13. A dispersant composition according to claim 11 wherein the lignosulfonic acid is used as a salt formed with a cation selected from the group consisting of Na, K, Ca, NH4 and alkan-olamines.

14. A dispersant composition according to claims 11, 12 and 13 wherein the reaction between the lignosulfonic acid or salt thereof with the water soluble peroxide is effected at a pH of less than 9 at a temperature in the range of 10°C to 60°C.

15. A dispersant composition according to claims 11, 12 or 13 wherein the reaction between the lignosulfonic acid or salt thereof with the water soluble peroxide is effected at a pH of less than 8 at a temperature in the range of 20°C to 40°C.

16. A dispersant composition according to claims 11, 12 or 13 wherein the water soluble peroxide is present in an amount of 2 to 15 wt. % based on solid lignosulfonic acid or salt thereof.

17. A dispersant composition according to claims 11, 12 or 13 wherein the viscosity of said lignosulfonic acid or salt thereof is 50 to 200 cps at 20°C.

18. A dispersant composition according to claims 11, 12 or 13 wherein the weight ratio of (a) to (b) is 70/30 to 30/70.

19. A dispersant composition according to claims 11, 12 or 13 wherein said dispersant composition further comprises an additional dispersant selected from the group consisting of a carboxylic acid, a polycarboxylic acid, a water reducing agent, a mixing agent, a hardening retarder, a polyvinyl alcohol, a polyethylene glycol and a polyalkylene glycol.

20. A dispersant composition according to claims 11, 12 or 13 wherein said water soluble peroxide is ammonium or potassium persulphate.