JPS62103B2 - - 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, chemical and physical aggregation of cement particles progresses over time after mixing, gradually losing fluidity and causing problems in workability during construction. In particular, concrete added with a high-performance water reducer such as β-NSF is difficult to use when concrete admixtures are not used or
Compared to the use of conventional admixtures such as additives, water reducing agents, and AE water reducing agents, the water reduction rate is high, resulting in significant slump loss. If such a slump loss occurs, for example, when pumping cement composition at a concrete secondary product factory, the pumping is temporarily interrupted due to a lunch break or trouble, and then when the pumping is restarted, the pumping pressure may drop. Accidents such as sudden increase in cement composition and blockage of the pump may occur.Furthermore, if compaction or other forming is delayed for some reason after pouring the cement composition 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 may coagulate due to chemical hydration reaction and/or physical aggregation due to interparticle attraction. It is thought that this is because the fluidity of the cement paste and thus the hydraulic cement composition decreases over time. In particular, when a concrete water reducing agent (cement dispersant) such as β-NSF is added, the water reducing agent adsorbs to the cement particles, increases the zeta potential of the cement particles, and uses its electrical repulsion to disperse the cement particles. Although it is possible to improve the fluidity of hydraulic cement compositions, (Hattori, Concrete Engineering Vol. 14, No. 3, 12-19
Page, 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, resulting in a decrease 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 present inventors researched a method using a conventional liquid admixture for concrete, and found that a cement dispersant containing polymerized lignin sulfonic acid or its salt as an essential component showed high molecular weight when viewed in terms of mortar flow value. Although it is somewhat inferior to those without, it has been found that the effect of preventing slump loss is extremely remarkable, and the present invention has been completed. Although it is not yet clear why polymerized ligninsulfonic acid or its salt has a remarkable effect on preventing slump loss, lignin-based substances, sugars, carboxylic acid-based substances, etc. have been known to have retard properties. However, the structure of lignin itself is unclear, and it is presumed that the effects of polymerization are based on the special characteristics of lignin. The polymerized ligninsulfonic acid or its salt used in the present invention is a polymer product obtained by reacting a water-soluble peroxide capable of generating oxygen radicals with a ligninsulfonate, and the viscosity of a 20% solution thereof is twenty five~
It is a polymerized lignin sulfonic acid or its salt with a yield of 400 cps (20°C). The polymerized lignin sulfonic acid or its salt of the present invention combines LS or its salt and a water-soluble peroxide with a pH
It can be obtained by reaction in water of 9 or less, preferably 8 or less, at 10 to 60°C, preferably 20 to 45°C. The LS or its salt used may be general LS obtained during wood pulping, but in order to suppress hardening delay, it is preferable to use one whose residual sugar content has been reduced by ultrafiltration or the like. As the water-soluble peroxide, ammonium persulfate and potassium persulfate are preferable, and 2 to 15% of the solid content of LS is used.
% by weight used. In this reaction, it is necessary that LS or its salt be polymerized to a 20% solution having a viscosity of 25 to 400 cps (at 20°C), preferably 50 to 200 cps (at 20°C). Examples of cations that form salts include Na, K, Ca, NH ₄ and alkanolamines. When lignin sulfonic acid (LS-1) is made into a polymer, the mortar flow value decreases compared to conventional lignin sulfonic acid, as exemplified as LS-APS-1 in Table 1 below. As shown, the slump can be kept constant for a long time.
However, as shown in the comparative example, conventional lignin sulfonic acid does not have the effect of preventing slump loss. The polymerized lignin sulfonic acid of the present invention is the first
As shown in the figure, its gel chromatography shows a completely different pattern from that of conventional ligninsulfonic acid.

【table】

[Table] Recently, a slump loss inhibitor using an LS salt having 0.20 mole or more of carboxyl group and 0.10 mole or more of sulfone group per phenylpropane has been disclosed (Japanese Patent Publication No. 40106/1983), It is explained that the LS salt having a chelate tends to form a chelate with Al in cement, which suppresses hydration and prevents slump loss. On the other hand, as shown in Table 1, the polymerized LS or its salt of the present invention contains 0.17 mol of carboxyl groups and 0.08 mol of sulfonic groups, and regardless of the content of these groups, It is thought that LS whose molecular weight has been increased by oxides exerts the effect of preventing slump loss. The amount of the cement dispersant of the present invention added is % solids by weight based on the cement of the hydraulic cement composition.
0.1 to 1.5 is good. The cement dispersant of the present invention is most preferably added to the hydraulic cement composition in the form of an aqueous solution. Further, the timing of its addition may be such that it is added to the kneaded hydraulic cement composition dissolved in mixing water, or it is added to the cement in the form of a powder. In addition, the cement dispersant of the present invention may contain other dispersants,
It is also possible to use a water reducing agent and other admixtures together. The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Reference example: Commercially available lignin sulfonic acid (manufactured by Volleyguard,
300 g of a 25% solid aqueous solution of LS-1 (hereinafter abbreviated as LS-1) was adjusted to pH 6 with acetic acid and sodium bicarbonate, and 6 g of ammonium persulfate (APS) was added to this solution.
Dissolved in 60g of water and added dropwise at room temperature.
After dropping, the mixture is reacted at 30 to 40°C for 4 hours to obtain a polymer reaction product (hereinafter abbreviated as LS-APS-1). The 20% solids concentration was 54.6 cps (20°C). Table 2 shows component (a) obtained in the same manner with different treatment conditions. KPS stands for potassium persulfate.

【table】 Examples and comparative examples (1) Concrete mix and materials used

[Table] How to mix concrete Method 1: Knead the cement dispersant in advance, dissolve it in water, and mix it at 25℃ in a tilting mixer to obtain the concrete shown in Table 3.
Kneading was continued at 2 rpm for a predetermined period of time, and changes in slump and air amount over time were measured. All measurements of slump, air volume, compressive strength, and collection of strength specimens are carried out.
This was done in accordance with JIS. Method 2: The same procedure as Method 1 was carried out except that the cement dispersant was added at the same time as the mixing water. (2) Test conditions and test results are shown in Table 4. From Table 4, it is clear that it is difficult to maintain slump with a simple LS, and that the product of the present invention has an extremely excellent effect in terms of slump survival rate.

【table】 [Brief explanation of the drawing]

FIG. 1 is a diagram showing gel chromatography of ligninsulfonic acid and polymerized ligninsulfonic acid used in the present invention.

Claims (1)

[Scope of Claims] 1. Polymerized lignin whose 20% solution has a viscosity of 25 to 400 cps (20°C) obtained by reacting a water-soluble peroxide capable of generating oxygen radicals with lignin sulfonic acid or its salt. A cement dispersant characterized by containing sulfonic acid or its salt as an essential component. 2. The cement dispersant according to claim 1, wherein the water-soluble peroxide is ammonium persulfate or potassium persulfate.