JPH0465027B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to cement dispersants, more specifically,
The present invention relates to a water reducing agent and a slump loss inhibitor used in cement compositions such as cement paste, mortar, and concrete. Various types of cement dispersants are known, but a typical one is β-naphthalenesulfonic acid formaldehyde condensate (hereinafter referred to as β-naphthalene sulfonic acid formaldehyde condensate).
NSF) salt, melamine sulfonic acid formaldehyde condensate salt, lignin sulfonic acid (hereinafter referred to as
(abbreviated as LS) salt is known. These are used when kneading cement compositions, thereby reducing the amount of water used and improving workability. However, it is known that all of these known dispersants have a common drawback of a significant decrease in fluidity over time (hereinafter referred to as slump loss). In general, in a hydraulic cement composition, after kneading, chemical and physical aggregation of cement particles progresses over time, gradually losing fluidity and causing problems in workability during construction. Especially β-
Concrete added with a high-performance water reducer such as NSF has a higher water reduction than when no concrete admixture is used or when conventional admixtures such as AE agents, water reducers, and AE water reducers are used. Due to the high rate, slump loss is significant. When such slump loss occurs, for example, when pumping cement composition at a concrete secondary product factory, pumping is temporarily interrupted due to a lunch break or trouble, and then when pumping is resumed, the pumping pressure Accidents such as a sudden increase in the amount of cement or blockage of the pump may occur.Furthermore, if compaction or other forming is delayed for any reason after the cement composition is poured into the formwork, problems such as non-filling may occur. . With ready-mixed concrete, slump loss also occurs during the period from the concrete manufacturing plant to the pouring site, which can significantly reduce workability and cause problems such as pump blockage and unfilling during molding. The cause of such slump loss is not clear, but after the cement particles in the cement paste come into contact with water, they undergo coagulation due to a chemical hydration reaction and/or physical aggregation due to interparticle attraction. However, it is thought that this is because the fluidity of the cement paste and, by extension, the hydraulic cement composition decreases over time. Especially β-NSF and
When a concrete water reducing agent (cement dispersant) such as LS is added, the water reducing agent adsorbs to the cement particles, increases the zeta potential of the cement particles, and its electrical repulsion disperses the cement particles, causing hydraulic cement Although it is possible to improve the fluidity of the composition (Hattori, Concrete Engineering Vol. 14, No. 3, 12
(See pages 19 to 19, March 1976 issue), it is thought that over time, the water reducing agent is stored in the hydrated precipitated minerals of cement, and its electrical repulsion is no longer expected, leading to a decline in fluidity. Therefore, if a water reducing agent for dispersing cement particles can be continuously supplied in some way, the cement particles can always be dispersed in the form of primary particles, and slump loss of the hydraulic cement composition can be prevented. It is thought that it is possible to do so. The following methods have been discovered as countermeasures against slump loss based on this idea. In other words, (i) concrete admixtures are made into powder or granules, or encapsulated in a carrier, and the active ingredients are gradually released into the system to maintain its effect (for example, as disclosed in Japanese Patent Application Laid-Open No.
54-139929). (ii) A concrete admixture is repeatedly added to a water-curing cement composition by mechanical force (for example, Japanese Patent Publication No. 15856/1983). etc. However, in (i), although the effect of preventing slump loss is well recognized, the cement dispersant remains locally in the cement mixture even after the purpose of maintaining slump has ended, causing local bleeding. This can lead to adverse effects such as a decrease in strength and a decrease in strength. In (ii), the effect of preventing slump loss is also recognized, but if the concrete after being discharged from the mixer is in the pressure pipe or formwork, it will be difficult to add a concrete admixture. In addition, as a measure to prevent slump loss, in order to suppress chemical agglomeration of cement particles, substances such as oxycarboxylate or lignin sulfonate are added or used in combination to delay the initial hydration reaction of cement (for example, Kimiaki
52-24533, Japanese Patent Publication No. 52-13853, and Japanese Patent Publication No. 54-17918), this method suppresses the chemical coagulation of cement particles to some extent, but the effect is not sufficient. Not. If the amount added is increased in order to increase the effect, there is a risk that the initial slump will become too large and cause aggregate separation, which will increase the setting time and cause a major problem in breathing and initial strength. As described above, each method has its own drawbacks and poses practical problems. The present inventors discovered that the dispersant is not in a solid state such as powder or granules as in the method (i) above, and that the dispersant is not applied by mechanical force as in the method (ii), but is The present invention was completed by researching methods for preventing slump loss using admixtures. That is, the present invention involves an oxidation reaction of a formalin cocondensate of the following components (a) and (b) with one or more of oxygen or peroxides under acidic or neutral conditions,
Alternatively, it is obtained by polymerization by oxidation reaction with metal oxide under acidic or neutral conditions, has a viscosity of 20% solids concentration of 25 centipoise or more at a temperature of 20°C, and has a weight of component (a) and component (b). Ratio is 95/5 to 20/80
The object of the present invention is to provide a cement dispersant for preventing slump loss, which contains a polymerized reactant as an essential component. (a) One or more compounds selected from the following compounds (1), (2) and (3). (1) Naphthalene sulfonic acid or alkylnaphthalene sulfonic acid. (2) A formalin condensate or co-condensate of one or more of the above (1). (3) The salt of (1) or (2) above. (b) Lignosulfonic acid or its salt The naphthalene sulfonic acid and alkylnaphthalene sulfonic acid of the component (a) of the present invention include creosote oil, naphthalene oil, and pitch produced during the coking process of coal, which contain these components. Components such as or sulfonated products such as coal liquefied oil are also used. Further, a partially unsulfonated compound such as naphthalene sulfonic acid or alkylnaphthalene sulfonic acid may be included. Further, before co-condensing formalin with component (b), component (a) itself may be subjected to formalin condensation or formalin co-condensation in advance. As the lignin sulfonic acid, component (b) of the present invention, those commonly used as cement dispersants are used, and among them, those with low air entrainment and low setting retardation are preferred. For this reason, it is preferable to remove sugar content and low molecular weight components by ultrafiltration or the like. These lignin sulfonic acids include Chemical Admixtures for
Conorete (MRRIXOM, E&F.N.Spon Ltd)
Pure with properties close to the analysis values and molecular weight distribution as described on pages 5 to 9 of
A typical example is lignosulphonate acid. Moreover, those that have been partially improved such as desulfonation may also be used. A reaction similar to the formalin cocondensation reaction of components (a) and (b) of the present invention is described in Japanese Patent Publication No. 52-24533, and a cocondensate can be obtained by a similar method. However, in Japanese Patent Publication No. 52-24533, desulfonated ligninsulfonic acid obtained by subjecting ligninsulfonic acid to an alkaline treatment such as air oxidation is used as the component (b), but in the present invention, (b) The component lignosulfonic acid or lignosulfonate is used without limitation. Particularly when the ratio of component (b) is large, insoluble precipitates are likely to form, so to prevent this, component (b) is preferably one in which low molecular weight components have been removed by ultrafiltration or the like.
The reason for this is thought to be that the low molecular weight component has many reaction points for the formalin cocondensation reaction and is therefore three-dimensionally crosslinked to form an insoluble precipitate. The polymerized reaction product of the formalin cocondensation reaction product of component (a) and component (b) of the present invention can be obtained by a known method. For example, oxidation reactions with metal oxides such as permanganate under acidic or neutral conditions, oxidation with oxygen catalyzed by transition metals or metal salts or metal complexes such as vanadium compounds and palladium compounds, hydrogen peroxide or ammonium persulfate. There are polymerization reactions using water-soluble peroxides such as persulfates.
The structure of these polymerization reaction products is not clear, and various bonds are formed depending on the conditions of the polymerization reaction. The compound of the present invention exhibits an extremely significant slump loss prevention effect by being made into a polymer, so the molecular weight is extremely important. There are various methods for measuring molecular weight, such as viscosity measurement and gel permeation chromatography, but the measurement method using a B-type rotational viscometer determines the viscosity at a solid content of 20% at a temperature of 20°C.
It must be 25 centipoise or higher. The reason why the compound of the present invention is extremely effective as a cement dispersant for preventing slump loss is not clear, but it is thought to be as follows. That is, it is known that the formalin condensate or formalin cocondensate of component (a) of the compound of the present invention exhibits high dispersibility, but since the compound of the present invention is polymerized, it cannot be used in cement. It is thought that it effectively adsorbs to particles and prevents agglomeration of cement particles due to charge and steric repulsion. It is also thought that the polymerization suppresses charge storage and prevents slump loss. The ratio of component (a) to component (b) is 95/5 to 20/80, preferably 90/10 to 25/75. If this ratio is too large, the polymerization reaction rate will be low, and if this ratio is too small, retardation of coagulation will occur. Although the cement dispersant of the present invention can be used as an acid, it is generally preferable to use it in the form of a salt. Cations that form salts include Na, K,
Examples include Ca, _NH4 , alkanolamine, N-alkyl substituted polyamine, ethylenediamine, polyethylenepolyamine, polyethyleneimine, and alkylene oxide adducts thereof. The amount of the cement dispersant of the present invention added is based on the cement of the hydraulic cement composition in solids weight %.
A value of 0.25 to 2.5 is good. If it is less than 0.25%, sufficient dispersion effect and slump loss prevention effect on cement particles cannot be obtained. Moreover, if it exceeds 2.5%, it is economically disadvantageous, and the dispersion of cement particles becomes excessive, causing breathing and paste separation. The cement dispersant composition according to the present invention is most preferably added to the hydraulic cement composition in the form of an aqueous solution, but the slump loss prevention effect can also be obtained in the form of powder or granules. The addition timing can be determined by dissolving the compound in mixing water, adding it at the same time as mixing water, adding it to the kneaded water-curing cement composition, or adding it to the cement composition in powder form. It is. Furthermore, it is also possible to add the dispersant of the present invention in portions at each stage. In addition to the cement dispersant of the present invention, other cement dispersants, water-soluble polymer compounds, etc. can also be used in combination. Other cement dispersants include formalin condensates of naphthalenesulfonic acid, ligninsulfonic acid salts, formalin condensates of melaminesulfonic acid, and polycarboxylic acid salts. Among these, formalin condensates of naphthalenesulfonic acid,
Particularly preferred are ligninsulfonates. In addition, as lignin sulfonate, Chemical
Admixtures for Concrete (MRRIXOM, E&
The analytical values and molecular weight distribution as described on pages 5 to 9 of FNSpon Ltd.
Pure lignosulphonate is good. The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. The concrete formulations and materials used in the Examples and Comparative Examples are shown in Table 1 below.

【table】

[Table] The method for adding the cement dispersant and the method for mixing the concrete were either Method 1 or Method 2 below. Method 1: Knead the cement dispersant in advance, dissolve it in water, and use a tilting mixer at 25℃.
40 Mix and obtain the concrete shown in Table 1,
Further, kneading was continued at a rotation speed of 2 rpm for a predetermined period of time, and changes in slump and air amount over time were measured. Measurements of slump, air volume, compressive strength, and collection of strength specimens are all conducted using JIS standards.
This was done in accordance with the. Method 2: The procedure was the same as Method 1 except that the cement dispersant was added at the same time as the mixing water. Reference example Naphthalene sulfonic acid (208g), 98% concentrated sulfuric acid (75g) and water (45g) were heated to 80-90℃,
% formalin (135g) in a flask and heated to 80℃.
Warm to. Next, 37% formalin (140 g) was added dropwise over 0.5 hours at 80-90°C, followed by reaction at the same temperature for 1 hour, and then ultrafiltered to obtain ligninsulfonic acid (45 g) and 37% formalin. (85
The mixture of g) was added in 4 portions at 1 hour intervals, and the reaction was carried out with stirring at 95 to 100°C for 18 hours. In this way, the formalin cocondensate obtained was made into a solution of pH 2 with sodium hydroxide, and the pH was adjusted to 60-70.
Polymerization was carried out with 30% hydrogen peroxide solution (15 g) at ℃. Thereafter, the pH was adjusted to 7 with sodium hydroxide. The viscosity of the obtained product at 20% solids concentration is
It was 260 centipoise (20℃). Table 2 shows the composition and viscosity of the inventive product and comparative product obtained in the same manner.

[Table] Examples 1 to 8 and Comparative Examples 1 to 5 Mixing tests into concrete were conducted using the products of the present invention and comparative products obtained in the above reference examples as well as commercially available cement dispersants as dispersants. Test conditions are shown in Table 3.

[Table] Tables 4 and 5 show the results of mixing tests into concrete.

【table】

[Table] From the results in Tables 4 and 5, it is clear that the product of the present invention has an extremely excellent effect in terms of slump survival rate.

Claims (1)

[Scope of Claims] 1. An oxidation reaction of a formalin cocondensate of the following components (a) and (b) with one or more of oxygen or peroxides under acidic or neutral conditions, Alternatively, it is obtained by polymerization by oxidation reaction with metal oxide under acidic or neutral conditions, has a viscosity of 20% solids concentration of 25 centipoise or more at a temperature of 20°C, and has a weight of component (a) and component (b). A cement dispersant containing as an essential component a polymerized reactant having a ratio of 95/5 to 20/80. (a) One or more compounds selected from the following compounds (1), (2) and (3). (1) Naphthalene sulfonic acid or alkylnaphthalene sulfonic acid. (2) A formalin condensate or co-condensate of one or more of the above (1). (3) The salt of (1) or (2) above. (b) Lignosulfonic acid or its salt. 2. The cement dispersant according to claim 1, wherein the peroxide is hydrogen peroxide or a water-soluble peroxide.