JP2001048625A - Production of cement composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process of a cement composition such as concrete or mortar, which is excellent in workability immediately after mixing. SOLUTION: This production process comprises: adding a high solubility calcium salt to a mixed base material containing at least cement, water and an aggregate, after mixing and further mixing them, wherein the post-addition of the high solubility calcium salt is performed after a lapse of 15-120 min from a time point at which the mixing of the base material containing at least the cement, water and aggregate is initiated; also, the amount of addition of the high solubility calcium salt is 0.15-1.5 pts.wt., expressed in terms of its anhydrate, on the basis of 100 pts.wt. of cement preferably containing 50-75 wt.% 3CaO.SiO2; and a high polymer compound having carboxyl groups is preferably further added as a chemical admixture to the base mixed material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cement composition capable of sufficiently securing workability up to construction, and more particularly to a method for producing an early-strength cement composition.

[0002] In general, for a cement composition such as mortar and concrete, acceleration of hardening and improvement of early strength have been studied in order to shorten and simplify a construction period and a product manufacturing period. Use of early-strength cement such as early-strength Portland cement or ultra-high-strength Portland cement as cement can provide concrete and mortar with excellent early-strength development, but as a means to develop sufficient early-strength. On the other hand, it is necessary to accelerate the hardening of the uncured cement kneaded material by kneading it with hot water at the time of construction, or curing it with steam or autoclave at the time of product production. However, such curing imposes restrictions on construction and manufacturing, leading to an increase in cost and construction period. It is conceivable to reduce the amount of water used for cement (water-cement ratio = water amount / cement amount) in order to obtain sufficient hardening acceleration and excellent strength development even with standard curing, but if the water-cement ratio is reduced, The fluidity is poor and the workability is significantly reduced. For this reason, it was necessary to introduce an admixture such as a water reducing agent and a fluidizing agent.

[0003]

However, in concrete or mortar having a composition intended for early strength, a kneaded material that has not been kneaded even if such an admixture is blended is particularly suitable for slumping during construction and product manufacturing. The workability could not be improved sufficiently because the rate of decline was rapid and the fluidity did not increase as expected.

[0004]

Means for Solving the Problems The present inventors have mainly proposed a substance having a hardening accelerating action and an early strength increasing action as disclosed in
As a result of repeated studies to solve the above-mentioned problems by using calcium salts having high solubility such as calcium nitrate and calcium nitrite shown in JP-A No. 22957 and JP-A-60-264352, the timing of the addition thereof Even cement composition intended for early strength by adjusting the, has a high fluidity for a certain period of time required for construction and product production immediately after kneading,
At the same time, the slump can be sufficiently suppressed from decreasing, and the workability has been drastically improved. Thus, the present invention has been completed.

That is, the present invention is a method for producing a cement composition represented by the following (1) to (6). (1) A method for producing a cement composition, characterized in that a highly soluble calcium salt is added afterwards to a base kneaded material containing at least cement, water and aggregate and further kneaded. (2) The production of the cement composition according to (1), wherein the post-addition of the calcium salt having high solubility is performed 15 to 120 minutes after the start of kneading of at least cement, water, and aggregate containing cement. Method. (3) The amount of the calcium salt having a high solubility is 0.1% in terms of anhydrate based on 100 parts by weight of cement.
The method for producing the cement composition according to the above (1) or (2), which is 15 to 1.5 parts by weight. (4) 50 cement a C ₃ S
(1) to (1), wherein
(3) The method for producing a cement composition according to any of (3). (5) The above-mentioned (1) to (1), wherein an admixture containing a polymer compound having a carboxyl group as a main component is added to the kneaded material.
(4) The method for producing a cement composition according to any of (4). (6) The method for producing a cement composition according to any one of the above (1) to (5), wherein the cement composition has a water cement ratio of 0.25 to 0.5.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION
The content of C ₃ S because of high effect of calcium salt of high solubility to facilitate the hydration of C ₃ S is good even at relatively high cement, cement containing C ₃ S 50 to 75% by weight. Cements having a C ₃ S content of less than 50% by weight are not preferred because the initial strength development is considerably poor.
If it exceeds 5% by weight, it is difficult to obtain high fluidity, so that it is not preferable.

[0007] The cement, water and aggregate are used as essential components, and the components are mixed and kneaded with a commercially available kneader to prepare a base kneaded product. The mixing ratio of the essential components at the time of kneading is a weight ratio, and is generally cement: water: aggregate = 1: 0.25-0.5:
1.5 to 5.3. The order of mixing among these three members may be arbitrary, and the kneading time is not particularly limited. The aggregate may be any known aggregate for concrete,
For example, in addition to natural aggregates such as gravel and crushed stone as coarse aggregate and sand (any of river sand, sea sand, and land sand) and crushed sand as fine aggregate, artificial lightweight aggregate and slag aggregate with adjusted particle size Etc. can also be used. In addition, here, as components other than the essential components, for example, a water reducing agent, a high-performance water reducing agent, an AE agent, a high-performance AE water reducing agent, a defoaming agent, a setting retarder, such as those generally used in the production of concrete and mortar, One or more known concrete or mortar admixtures (materials) such as a thickener, a shrinkage reducing agent, a rust preventive, a foaming material, and an expansive material may be used in combination and may be appropriately added.

Among such admixtures (materials), an admixture mainly containing a polymer compound having a carboxyl group as a main component is added to 100 parts by weight of cement or 100 parts by weight of cement and another admixture (material). , 0.03 ~
It is preferred to add 1.0 part by weight. Addition of less than 0.03 parts by weight is not preferable because the addition effect is hardly exhibited, and addition of more than 1.0 part by weight is not preferable because the kneaded material may cause material separation. The used amount of the admixture is adjusted and used while confirming the fluidity suitable for work such as construction. In addition, as a polymer compound having a carboxyl group, a compound containing 50% by weight or more as a polyoxyalkylene is particularly preferable. By the addition of this agent, a steric hindrance effect works when the polyoxyalkylene group in the polymer compound is adsorbed to the cement particles in the kneaded material,
Even with a kneaded material having a relatively low water-cement ratio, high fluidity can be imparted.

After the base kneaded product has been prepared, the base kneaded product is prepared, ie, about 1 hour after the first kneading is performed.
This is allowed to stand still or the kneading is almost stopped until 5 minutes to 2 hours have passed. After the elapse of the above-mentioned time, a calcium salt having a high solubility was added thereto in an amount of 0.15 in terms of anhydrate based on 100 parts by weight of the cement used for preparing the base kneaded material.
１．５1.5 parts by weight, more preferably 0.3-1.2 parts by weight, and kneading is performed again. The high-solubility calcium salt may be any calcium salt having a solubility in water at 0 ° C. of 5 g / 100 ml. For example, calcium nitrite, calcium nitrate, calcium chloride, calcium formate, calcium bromide, iodine Examples thereof include calcium iodide and calcium sulfamate, and hydrates thereof. Of these, calcium nitrite is particularly preferred because it has a relatively high solubility and also has a high rust preventive action. When adding such a calcium salt, it is preferable to add the calcium salt as an aqueous solution because it is easily dispersed uniformly in the base kneaded material. In this case, the higher the concentration of the aqueous solution, the more the increase in the amount of water can be suppressed, and generally, the higher the solubility of the salt, the more easily the concentration of the aqueous solution can be easily increased. Also,
By adding the calcium salt of high solubility at a certain time after the production of the base kneaded material, it is possible to maintain the high fluidity of the cement composition for a while after the kneading, and at the same time to reduce the slump. Can be suppressed sufficiently. It is considered that this is because Ca ²⁺ ions in the liquid phase of the re-kneaded product increase by the subsequent addition of a calcium salt having a high solubility, thereby promoting the adsorption of the remaining admixture molecules to the cement particles. If the amount of the calcium salt is less than 0.15 parts by weight, the effect of adding the calcium salt is hardly exhibited, and if it exceeds 5 parts by weight, the effect of promoting the hardening is strongly exhibited, and the fluidity of the re-kneaded material is rapidly lowered, which is preferable. Absent. The re-kneading time when adding the calcium salt is not particularly limited, but may be about 2 to 3 minutes as a guide. After the re-kneading, it can be used for a desired construction or a molded product, and a hardened concrete or mortar cured at room temperature can be obtained. In addition, when the heat curing or the steam curing is performed, the pre-curing time can be shortened, and the production efficiency can be further improved.

[0010]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. C ₃ S having the content (% by weight) shown in Table 1
Containing cement (other major constituents are C ₂ S, C ₃ A,
C ₄ AF), water, Ogasawara land sand (fine aggregate) and crushed stone from Iwase (coarse aggregate) were weighed so as to have the compounding amount shown in Table 1.
Further, an admixture (solution having a solid content of 25%) containing a polymer compound having a carboxyl group as a main component in the amount shown in Table 1 was kneaded at a high speed for 3 minutes by a tilting mixer. Thereafter, the mixer was rotated at a rotation speed of 2 times per minute, and the time (minutes) shown in Table 1 from the start of kneading of the mixture of the raw materials was started.
An aqueous solution of calcium nitrite adjusted to a concentration of 30% by weight was added to the passed one in an amount shown in Table 1 (aqueous solution amount).
The mixture was again high-speed kneaded for 2 minutes with the same mixer. After that, while the mixer is rotating at a low speed of about 2 revolutions per minute, the change with time of the slump value immediately after the end of the initial kneading, after 30 minutes, after 60 minutes and after 90 minutes from the end of the initial kneading is determined according to JIS A1.
It measured by the method according to 101. Further, the compressive strength of a cement composition cured material obtained by subjecting a specimen consisting of the kneaded material to standard curing at a material age of 12 hours and 24 hours was determined according to JIS A1128.
It measured by the method according to. Table 1 also shows the measurement results.

[0011]

[Table 1]

[0012]

According to the production method of the present invention, even with a relatively low water-cement ratio, it has high fluidity, remarkably low slump loss, and operability such as construction after kneading and product production. In addition, the resulting cement composition such as concrete or mortar can have sufficiently high early strength development and stable quality characteristics even under standard curing.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shuzo Nakamura 2-4-2 Daisaku, Sakura City, Chiba Pref. Pacific Term Cement Co., Ltd. Sakura Laboratory F-term (reference) 4G012 MB04 MB08 PB05 PB07 PB09

Claims (6)

[Claims] 1. A method for producing a cement composition, comprising adding a calcium salt having high solubility to a base kneaded product containing at least cement, water and aggregate, followed by further kneading. 2. The cement composition according to claim 1, wherein the post-addition of the calcium salt having high solubility is carried out 15 to 120 minutes after the start of kneading of at least one containing cement, water and aggregate. Manufacturing method. 3. An amount of the calcium salt having a high solubility of 0.15 to 100 parts by weight of cement in terms of anhydrate.
3. The method for producing a cement composition according to claim 1, wherein the amount is 1.5 parts by weight. 4. The method for producing a cement composition according to claim 1, wherein the cement contains 50 to 75% by weight of C ₃ S. 5. The method for producing a cement composition according to claim 1, wherein an admixture containing a polymer compound having a carboxyl group as a main component is added to the kneaded material. 6. The water-cement ratio of the cement composition is 0.2.
The method for producing a cement composition according to any one of claims 1 to 5, wherein the ratio is 5 to 0.5.