JPH0613424B2 - Cement dispersant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cement dispersant, and more particularly to a water reducing agent and a slump loss preventive agent used for cement paste, mortar and concrete which are cement compositions.

Various types of cement dispersants are known, and typical examples thereof include β-naphthalenesulfonic acid formaldehyde condensate (hereinafter abbreviated as β-HFS) salt,
Melamine sulfonic acid formaldehyde condensate salt and lignin sulfonic acid (hereinafter abbreviated as LS) salt are known. These are used at the time of kneading a cement composition, and by doing so, the amount of water used is reduced and the workability is improved. However, all of these known dispersants have a common drawback that their fluidity decreases with time (hereinafter referred to as slump loss).
Is known to be significantly large.

Generally, in hydraulic cement compositions, chemical and physical agglomeration of cement particles progresses with the lapse of time after mixing, and fluidity is gradually lost, causing a problem in workability in construction. Concretes with high performance water reducing agents, such as β-NSF, are sometimes compared with those when using no admixture for concrete or when using conventional admixtures such as AE agent, water reducing agent, and AE water reducing agent. , Slump loss is remarkable due to the high water reduction rate. When such a slump loss occurs, for example, when pumping the cement composition in a concrete secondary product factory or the like, the pumping pressure is temporarily interrupted due to a lunch break or a trouble, and then the pumping pressure is restarted when the pumping is restarted. Will increase suddenly and will cause an accident such as a blockage of the pump, and if molding is delayed such as compaction for any reason after driving the cement composition into the mold, problems such as unfilling will occur. .

Also for ready-mixed concrete, slump loss occurs during the period from the concrete manufacturing plant to the pouring site, resulting in a significant decrease in workability, blockage of the pump,
This may cause problems such as unfilling during molding. The cause of such slump loss is not clear,
After the cement particles in the cement paste come into contact with water, coagulation due to a chemical hydration reaction and / or physical agglomeration due to attraction between particles progresses, and the fluidity of the cement paste and eventually the hydraulic cement composition changes with time. It is thought to be due to the decrease in In particular, when a water-reducing agent for cement (cement dispersant) such as β-NSF or LS is added, the water-reducing agent is adsorbed on the cement particles, raising the Zeta potential of the cement particles, and dispersing the cement particles by its electrical repulsive force. And improve the fluidity of the hydraulic cement composition (Hattori, Concrete Engineering Vol. 14, No. 3, 12
(See p. 19, March 1976), the water reducing agent is stored in the hydrated precipitated mineral of cement over time, and its electrical repulsive force cannot be expected and fluidity decreases. Therefore, if the water reducing agent that disperses the cement particles can be continuously supplied by some method, 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 considered possible.

The following methods have been found as a countermeasure against slump loss based on such an idea. That is, i) the admixture for concrete is made into powder or granules or enclosed in a carrier to gradually release the active ingredient into the system to maintain its effect (for example, JP-A-54-139929).

ii) The admixture for concrete is repeatedly added to the hydraulic cement composition by mechanical force (for example, JP-B-51-1).
5856).

And so on.

However, in i), although the slump loss preventing effect is sufficiently recognized, the cement dispersant remains locally in the cement composition even after the purpose of maintaining the slump is terminated, and local breathing may occur. It causes adverse effects such as occurrence and eventually strength reduction. Also in ii), the slump loss preventing effect is recognized, but it is difficult to add the admixture for concrete if the concrete after the mixer is discharged is in the pressure-feeding pipe or in the form. As a measure to prevent slump loss, a method of delaying the initial hydration reaction of cement by adding or using substances such as oxycarboxylate or lignin sulfonate in order to suppress the chemical setting of cement particles (for example, JP-A-52-24533, JP-B-52-13853, and JP-A-54-17918) have been found, but this method suppresses chemical coagulation of cement particles to some extent, but its effect is not enough. If the amount added is increased to enhance the effect, the initial slump becomes too large and there is a risk of causing aggregate separation.

As described above, each of the methods has its own drawbacks and is problematic in practical use.

The present inventors have found that the dispersant is not in a solid form such as powder or granules as in the method i) above, and is not based on mechanical force as in the method ii), but is in a conventional form of an admixture for concrete. Researched a method for preventing slump loss by using the above method and completed the present invention.

That is, the present invention is a polymerized lignin sulfonic acid or a salt thereof, which has a 20% aqueous solution viscosity of 400 cps.
The present invention provides a slump loss preventive cement dispersant containing as an essential component a compound having a viscosity of more than 200,000 cps or less (20 ° C.) and another cement water reducing agent.

The polymerized lignin sulfonic acid of the present invention (hereinafter referred to as LS
Or its salt is LS or its salt and water-soluble peroxide in water of pH 9 or less, preferably 8 or less, 10 to 60.
The reaction can be carried out at ℃, preferably 20 to 45 ℃. The LS or its salt to be used may be a general LS obtained during pulping of wood, but it is preferable to reduce the residual sugar content by an ultrafiltration method or the like in order to suppress retardation of setting.

Ammonium persulfate (hereinafter APS) as water-soluble oxide
Abbreviated), potassium persulfate (hereinafter abbreviated as KPS), and hydrogen peroxide are used.
Most preferred is PS or KPS. In the case of APS or KPS, 5 to 20% by weight is used based on the solid content of LS, and in the case of hydrogen peroxide, 2 to 10% by weight is used based on the solid content of LS to react at pH 3 to 8. 20% aqueous solution viscosity is 40
0 to 200,000 cps (20 ° C), preferably 1000 to 10
It is necessary to polymerize up to 10,000 cps (20 ° C).

Examples of other cement water reducing agents used as essential components in the present invention include the following.

That is, β-naphthalene sulfonic acid formaldehyde condensate (β-NSF), lignin sulfonic acid (LS), melamine resin sulfonic acid, polycarboxylic acid or salts thereof, among which β-NSF and LS Most preferred is salt.

When lignin sulfonic acid is polymerized, LS is shown in Table 1 below.
As illustrated as -APS-1, the mortar flow value is lower than that of the conventional lignin sulfonic acid (LS-1), but when other cement dispersant is used in combination with this, the examples described below (Tables 4 and 5). As shown in (), the slump can be kept constant for a long time. The polymerized lignin sulfonic acid used in the present invention has a gel chromatograph showing a completely different pattern from that of the conventional lignin sulfonic acid as shown in FIG.

Recently, an anti-slump loss agent using an LS salt having 0.20 or more carboxyl groups and 0.10 or more sulfonic acid per phenylpropane has been disclosed (Japanese Patent Publication No. 56-40106). With L
Since S salt easily forms a chelate with Al in cement,
It is described that hydration is suppressed and slump loss is prevented. On the other hand, the polymerized LS of the present invention or a salt thereof has, for example, as shown in Table 1, 0.16 mol of carboxyl groups and 0.07 mol of sulfone groups, regardless of the content of these groups. It is considered that LS having a high molecular weight due to peroxide exerts a slump loss preventing effect.

As for the amount of the dispersant of the present invention added, the amount of polymerized LS or a salt thereof is preferably 0.05 to 1.0 as a solid content weight% with respect to the cement of the cement composition. 0.05
% Or less, the time for the slump prevention effect becomes short,
Does not show sufficient effect. Also, it can be used at 1.0% or more, but it is economically meaningless. Further, the addition amount of the cement water reducing agent other than the polymerized LS is 0.1 to 0.1% by weight of the solid content relative to the cement of the cement composition.
0.5% is good, and the addition amount can be determined according to the required slump value.

The cement dispersant composition according to the present invention is most preferably added in the form of an aqueous solution to the hydraulic cement composition, but the slump loss preventing effect can be obtained even in the form of powder or granules. In addition, the time of addition may be such that the compound is dissolved in water mixed by kneading, added to a hydraulic cement composition that has been kneaded, and added to cement in the form of powder. Furthermore, it is practically convenient to mix the components of the formulation in advance, but it is also possible to add the components separately to any process of mixing the hydraulic cement composition.

Further, the cement dispersant of the present invention may be used in combination with a hardening retarder, or may be used in combination with a water-soluble polymer compound such as polyvinyl alcohol, polyethylene glycol or polyalkylene glycol.

The present invention will be described below with reference to examples of the present invention, but the present invention is not limited to these examples.

Reference Example (Production of Polymerized Lignin Sulfonate) Commercial Lignin Sulfonate (manufactured by Boregard Co., LS hereinafter)
(Abbreviated as -1) pH of the solution is adjusted to 5.4 with 300 g of a 20% solid content aqueous solution of acetic acid and sodium bicarbonate, and 9 g of ammonium persulfate (APS) dissolved in 60 g of water is added dropwise to the solution at room temperature. . After dropping, the reaction is performed at 30 to 50 ° C. for 8 hours to obtain a polymer reaction product (hereinafter abbreviated as LS-APS-1). When water and PH were adjusted to 20% solid content, the viscosity at pH 5.4 was 3600 cps (20 ° C)
It was. Table 2 shows polymerized lignin sulfonates obtained in the same manner by changing the treatment conditions. KPS indicates potassium persulfate.

Example 1) Concrete mix and materials used Mixing method of concrete Method 1: Mix the cement dispersant in water in advance and mix it in water at 25 ° C with a tilting mixer to obtain 40 concrete and mix it with the rotation speed of 2 rpm.
Was continuously kneaded for a predetermined time, and the slump and the change in the amount of air with time were measured. Measurements of slump, air volume, compressive strength and sampling of strength specimens were all conducted in accordance with JIB.

Method 2: The same as in Method 1 except that the cement dispersant was added after the concrete was kneaded.

2) Test conditions Table 4 shows the mixing conditions of concrete.

3) Test results Table 5 shows the test results.

[Brief description of drawings]

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

Claims (2)

[Claims] 1. A polymerized lignin sulfonic acid or a salt thereof and another cement water reducing agent are contained as essential components, and the polymerized lignin sulfonic acid or a salt thereof generates an oxygen radical from the lignin sulfonic acid or a salt thereof. Is a polymer reaction product obtained by reacting with a water-soluble peroxide capable of
A cement dispersant characterized in that the viscosity of a 20% aqueous solution at 20 ° C is in the range of more than 400 centipoise and less than 200,000 centipoise. 2. The cement dispersant according to claim 1, wherein the water-soluble peroxide is ammonium persulfate or potassium persulfate.