JPS62104B2 - - 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 reducing agent such as β-NSF can be used without using concrete admixtures or with AE
Compared to the use of conventional admixtures such as additives, water reducers, and AE water reducers, the water reduction rate is high, resulting in significant slump loss. 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.
54-139929). (ii) A concrete admixture is repeatedly added to a hydraulic 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 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. Furthermore, if the amount added is increased in order to increase the effect, the initial slump will become too large and there is a risk of causing aggregate separation. 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 it is not applied by mechanical force as in the method (ii), but that the dispersant is used in concrete in a normal form. The present invention was completed by researching methods for preventing slump loss using admixtures. That is, the present invention provides a cement dispersant containing the following components (a) and (b) as essential components. Component (a): Polymerized ligninsulfonic acid or its salt, preferably a polymeric product obtained by reacting a water-soluble peroxide capable of generating oxygen radicals with ligninsulfonic acid (LS) or its salt. and a polymerized ligninsulfonic acid or its salt whose viscosity of 20% solution is 25 to 400 (cps) (20°C). Component (b): β-naphthalenesulfonic acid formaldehyde condensate or a salt thereof. Component (a) of the present invention is LS or its salt and a water-soluble peroxide in water with a pH of 9 or lower, preferably 8 or lower, at a pH of 10 to 60%.
It can be obtained by reacting at ℃, preferably 20 to 45℃. 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.
~15% by weight used. Component (a) has a viscosity of 25 to 400 cps (at 20°C) in a 20% solution, preferably 50 to 200 cps.
(20℃).
As the component (b) of the present invention, a β-naphthalenesulfonic acid formaldehyde condensate or a salt thereof described in Japanese Patent Publication No. 41-11737 may be used, but instead of β-naphthalenesulfonic acid, naphthalenesulfonic acid and alkylnaphthalene A co-condensate of sulfonic acid may also be used. The ratio of component (a) to component (b) in the cement dispersant of the present invention is 80/20 to 20/80, preferably 70/30 by weight.
~30/70. Examples of cations that form salts of components (a) and (b) include Na, K, Ca, NH ₄ and alkanolamines. When ligninsulfonic acid is made into a polymer, the following first
As illustrated in the table as LS-APS-1, the mortar flow value is the same as that of conventional lignin sulfonic acid (LS-APS-1).
However, when component (b) is used in combination with this, the slump can be kept constant for a long time as shown in Examples (Table 6) to be described later. However(b)
As shown in Comparative Example 3, the effect of the present invention cannot be achieved when the component is used in combination with conventional ligninsulfonic acid. As shown in FIG. 1, the gel chromatography of component (a), polymerized ligninsulfonic acid, shows a completely different pattern from that of conventional ligninsulfonic acid.

[Manufacture of component (a)]

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】 Example (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 for a predetermined time at 2 rpm, and changes in slump and air amount over time were measured. Measurements of slump, air content, compressive strength, and collection of strength specimens were all carried out in accordance with JIS. Method 2: The same procedure as Method 1 was carried out except that the cement dispersant was kneaded and added at the same time as water. (2) Test conditions The concrete mixing conditions are shown in Tables 4 and 5.

【table】

【table】 (3) Test results The test results are shown in Table 6.

【table】

[Table] From Table 6, it is clear that it is difficult to maintain slump by simply using LS or a combination of LS and β-NSF, and that the product of the present invention has an extremely superior effect in terms of slump survival rate. It is.

[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 Contains the following components (a) and (b) as essential components, and the ratio of components (a) and (b) is from 80/20 to 80/20 by weight of solid content. A cement dispersant characterized by being 20/80. Component (a): The viscosity of a 20% solution obtained by reacting a water-soluble peroxide capable of generating oxygen radicals with ligninsulfonic acid or its salt is 25%.
~400 cps (20°C) polymerized lignin sulfonic acid or its salt. Component (b): β-naphthalenesulfonic acid formaldehyde condensate or a salt thereof. 2. The cement dispersant according to claim 1, wherein the water-soluble peroxide is ammonium persulfate or potassium persulfate.