JPS6319463B2 - - 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 hydraulic cement compositions, after mixing, 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 that disperses 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 can be done. 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.
(ii) A concrete admixture is repeatedly added to a hydraulic cement composition by mechanical force (for example, Japanese Patent Publication No. 51-15856). 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 is difficult to add a concrete admixture. In addition, as a measure to prevent slump loss, in order to suppress chemical coagulation 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 is obtained by oxidizing a formalin condensate or formalin cocondensate of naphthalene sulfonic acid and/or alkylnaphthalene sulfonic acid or a salt thereof by an oxidation reaction. The present invention provides a slump loss-preventing cement dispersant, which contains as an essential component a compound having 0.1 to 1.0 carboxyl groups per naphthalene ring. As naphrene sulfonic acid and alkylnaphthalene sulfonic acid of the present invention, creosote oil, naphthalene oil, components such as pitch produced in the process of coking coal, or sulfonated products such as coal liquefied oil containing these components can also be used. be done. Further, a partially unsulfonated compound may be included as naphthalene sulfonic acid or alkylnaphthalene sulfonic acid. Further, for the oxidation reaction, it is preferable to contain an alkylnaphthalene sulfonic acid such as methylnaphthalene sulfonic acid as a component. The oxidation reactant can be obtained by a known method. For example, oxidation reactions with metal oxides such as permanganates, oxidation with oxygen or air using transition metals such as vanadium compounds and palladium compounds, metal salts or metal complexes as catalysts, oxidation with oxygen or air using alkaline catalysts, Oxidation reactions include hydrogen oxide or water-soluble peroxides such as persulfates such as ammonium persulfate. The structure of these oxidation reaction products is not clear, and depending on the oxidation reaction conditions,
Various bonds are oxidized. Typical reaction formats among these reactions include oxidation of naphthalene rings, oxidation of methylol groups generated during formalin condensation, and oxidation of alkyl groups such as methyl groups bonded to naphthalene rings. Oxidation is carried out on an industrial scale to produce phthalic acid from naphthalene. Through these oxidation reactions, it is possible to obtain a compound having 0.1 to 1.0 carboxyl groups per naphthalene ring. If the amount of carboxyl groups is less than 0.1 per naphthalene ring, it is not effective in preventing slump loss, and if it is more than 1.0, setting delay becomes significant, which is not preferable. 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 formalin condensates or formalin cocondensates as constituent components of the compounds of the present invention exhibit high dispersibility, and the carboxyl groups contained in the compounds of the present invention are effectively adsorbed onto cement particles. It is thought that the sulfone groups present in the compound are arranged outward, increasing the charge on the cement particles and preventing slump loss due to charge storage due to the hydration reaction of the cement. 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. The cations formed 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 or the dispersion of cement particles becomes excessive, causing breathing and paste separation. Although it is most desirable to add the cement dispersant according to the present invention to a hydraulic cement composition in the form of an aqueous solution, the effect of preventing slump loss can be obtained even if the cement dispersant is added in the form of a powder or granules. Also, when adding it, mix the dispersant and dissolve it in water.
It can be added at the same time as mixing water, added to a worked-up hydraulic cement composition, or added to a cement composition in powder form. 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 condensate of naphthalene sulfonic acid, lignin sulfonate, formalin condensate of melamine sulfonic acid, and polycarboxylate, which is the trade name of Mighty 150 (manufactured by Kao Soap Co., Ltd.). , among these, formalin condensate of naphthalene sulfonic 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 1ignosulphonate 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 Examples and Comparative Examples are shown in Table 1 below.

[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 and dissolve it in water, mix for 40 minutes in a tilting mixer at 25°C to obtain the concrete shown in Table 1, and continue kneading at a rotation speed of 2 rpm for a predetermined period of time until slump. and measured changes in air volume over time. Measurements of slump, air content, compressive strength, and collection of strength specimens were all carried out in accordance with JIS. 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 Naphthalenesulfonic acid (208g), methylnaphthalenesulfonic acid (45g), 98% concentrated sulfuric acid (10g), and water (50g) were placed in a 500ml flask and heated to 80°C. Next, at 80-90℃, 37% formalin (140g)
was added dropwise over 0.5 hours, and then reacted at 90 to 100°C for 8 hours to obtain a cocondensate. Thereafter, the mixture was made slightly alkaline with sodium hydroxide, potassium permanganate (65 g) was added, and the mixture was reacted at 50° C. for 3 hours and filtered according to a conventional method to obtain a product of the present invention. The amount of carboxyl groups was 0.2 (per naphthalene ring). Table 2 shows the composition of the product of the present invention obtained in the same manner.

[Table] Examples 1 to 9 and Comparative Examples 1 to 4 Mixing tests into concrete were conducted using the products of the present invention obtained in the above reference examples and comparative products such as commercially available cement dispersants as dispersants. Test conditions are shown in Table 3. In addition, the results of mixing tests into concrete are shown in Tables 4 and 5.

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[Table] (Note) 2) Standard curing (Kg/cm ² )
From the results shown in Tables 4 and 5, it is clear that the products of the present invention have extremely excellent effects in terms of slump survival rate.

Claims (1)

[Claims] 1. 0.1 to 1.0 carboxyl groups per naphthalene ring, obtained by oxidizing a formalin condensate or formalin cocondensate of naphthalene sulfonic acid and/or alkylnaphthalene sulfonic acid, or a salt thereof by an oxidation reaction. A cement dispersant that prevents slump loss and contains as an essential component a compound that has 2. The slump loss preventing cement dispersant according to claim 1, wherein the oxidation reaction is a reaction using a metal oxide. 3. The slump loss preventing cement dispersant according to claim 1, wherein the oxidation reaction is a reaction using oxygen or air using a metal or a metal salt as a catalyst. 4. The slump loss preventing cement dispersant according to claim 1, wherein the oxidation reaction is a reaction using hydrogen peroxide or a water-soluble peroxide.