JP3491971B2 - Cement additive and cement composition - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cement additive and a cement composition, and more particularly to a cement additive and a cement composition which prevent bleeding of cement and separation of materials.

[0002]

[Prior art and its problems] When placing mortar or concrete, especially when the water-cement ratio is large, when the hydration reaction is delayed due to low temperature, and when the fine powder content in the fine aggregate is small, etc. In addition, so-called bleeding may occur in which mortar or concrete kneading water collects upward due to sedimentation of cement particles or aggregates.

This bleeding is a kind of material separation, in which a water film is formed on the lower surface of the coarse aggregate and on the lower side of the horizontal reinforcing bar.
The adhesion between reinforcing bars and concrete is weakened, and the voids created by water veins deteriorate the watertightness and durability of concrete, and the particles that float with bleeding water accumulate on the mortar and the concrete top surface, creating latances and causing It weakens the adhesion of the splice surface and occurs until the cement begins to set and the solid particles such as the cement, the fine aggregate, and the coarse aggregate stabilize.

Conventionally, in order to prevent bleeding and material separation, mortar and concrete with a small amount of water used have been used.

Chemical admixtures such as AE water reducing agents, high performance water reducing agents, and high performance AE water reducing agents are used to reduce the amount of water used in mortar and concrete.

[0006] It has been difficult to reduce the amount of water used by the AE water reducing agent to a large extent because the delaying property increases and the entrained air amount increases excessively.

[0007] When a high-performance water reducing agent or a high-performance AE water reducing agent is used, such problems are reduced and the amount of water used can be greatly reduced, but not only the cost is increased but also a small amount of water is used. There were issues such as large changes in liquidity due to fluctuations.

Further, in order to prevent bleeding and material separation, in addition to this, an aggregate having an appropriate particle size distribution is used, and the fine aggregate 0.15 to 1.2 mm is adjusted so as not to decrease. , Replenishing fine particles such as high quality fly ash and silica fume, increasing the fine aggregate ratio, and increasing the unit cement amount to add viscosity, but new equipment must be installed. In some cases, it may be difficult to obtain the material, or the handling may not be easy. Therefore, it is difficult to completely prevent bleeding and material separation.

[0009] Recently, crushed stone and crushed sand are often used instead of gravel and river sand due to regulation of aggregate collection from rivers and increased demand for aggregate, and the amount of water used tends to increase. It's hard to reduce.

On the other hand, there is known a method of preventing bleeding and material separation by mixing a polymer thickening agent and a separation reducing agent into mortar or concrete to impart viscosity until setting.

Cellulose such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose as a polymer thickener and a separation reducing agent,
Sodium polyacrylate, polyethylene oxide,
Synthetic products such as polyacrylamide and polyvinyl alcohol, starch products such as hydroxyethyl starch, carboxymethyl starch, and dialdehyde starch, curdlan,
Examples thereof include biopolymers such as bururan, dextran, and xanthan (JP-A-5-139806 and JP-A-5-186637).

However, when a necessary amount of a polymer thickener or the like is added in order to effectively prevent bleeding and material separation, there is a problem that the fluidity decreases as the viscosity increases. In addition, the difference in viscosity depending on the temperature in summer and winter, and when used in combination with an AE water reducing agent, a high-performance water reducing agent, and a high-performance AE water reducing agent, the condensation time becomes particularly long at low temperatures, and the amount of entrained air increases. There was such a problem.

Further, a high-fluidity concrete in which inorganic fine fibers are mixed with no separation has been proposed, but there is a problem such that the fluidity decreases in proportion to the addition rate (Japanese Patent Laid-Open No. 5-1170).
No. 04 bulletin).

The present inventor has conducted various studies in order to solve the above problems, and as a result, the above problems can be solved by using a specific cement additive, the fluidity is not deteriorated, and the setting time is delayed. The present invention has been completed based on the finding that a cement composition that does not have the above problems and that does not have the problem of increasing the amount of entrained air can be obtained.

[0015]

Means for Solving the Problems That is, the present invention has a error over Te <br/> le bond, the degree of swelling with calcium hydroxide saturated solution is contained 2-8 wt% of cross-linked starch And a cement composition containing the cement and the cement additive.

The present invention will be described in detail below.

The crosslinked starch used in the present invention is a starch derivative in which a polyfunctional group is bonded to hydroxyl groups at two or more positions, and the properties of the starch change greatly with a slight amount of crosslinking. There are many starch cross-linking agents, such as phosphorus oxychloride and sodium trimetaphosphate, but the phosphoric acid cross-linked starch using this is not preferable because it is hydrolyzed and dissolved by a strong alkali. In the present invention, it is preferable to use a crosslinked starch having an ether bond. Specifically, it is a methylol cross-linked starch or a hydroxyalkyl cross-linked starch using a cross-linking agent such as acrolein or epichlorhydrin, and the swelling degree and the solubility decrease in proportion to the cross-linking degree. Here, the degree of swelling is
The weight of water absorbed by 1 g of starch is shown. Further, the cross-linked starch hardly dissolves in a calcium hydroxide saturated solution similar to that in cement and gradually swells, and the degree of swelling is 2
~ 8% by weight. If it is less than 2% by weight, a sufficient effect cannot be obtained, and if it exceeds 8% by weight, the initial fluidity cannot be obtained and the change with time tends to be large. The degree of swelling varies depending on the starch raw material such as corn, wheat, potato, tapioca, and sweet potato, and changes depending on the type of ether crosslinking agent, the degree of etherification, the degree of crosslinking, and the like. The crosslinked starch having an ether bond is stable without being hydrolyzed or gelatinized even when mechanically stirring a saturated solution of calcium hydroxide in a high alkali at high temperature. The particle size of the cross-linked starch is preferably such that 90% or more of it passes through a 200 mesh screen. Outside this range, the cement additive of the present invention disperses between the cement and the aggregate and does not dissolve, so that there is a tendency that bleeding and material separation cannot be prevented until setting begins. The amount of crosslinked starch used is preferably 0.1 to 6 parts by weight, more preferably 0.2 to 3 parts by weight, based on 100 parts by weight of cement. If it is less than 0.1 part by weight, sufficient effect cannot be obtained, and if it exceeds 6 parts by weight, initial fluidity cannot be obtained, and it tends to be difficult to obtain an effect commensurate with the amount used.

As the cement used in the present invention, various portland cements such as ordinary portland cement and early-strength portland cement, various mixed cements of blast furnace cement, silica cement and fly ash cement, alumina cement, and super rapid hardening cement, etc. Is mentioned.

The cement additive of the present invention may be used in the form of powder or dispersed in an aqueous solution.

In the present invention, when dispersed in an aqueous solution, it is preferable to use a high-performance water reducing agent or the like as a dispersant and a polymer thickener or the like as a material for preventing bleeding or material separation. It is preferable from the viewpoint of facilitating dispersibility in cement.

In addition to the cement composition of the present invention, a polymer thickener, a separation reducing agent, an AE water reducing agent, a high-performance water reducing agent, a high-performance AE water reducing agent, a fluidizing agent, and an admixture such as a defoaming agent. It is also possible to use an expansive material, a rapid hardening material and the like together.

[0022]

EXAMPLES The present invention will be further described below based on examples.

Example 1 100 parts by weight of cement, 1 part by weight of a superplasticizer, and Table 1
0.6 parts by weight of various cross-linked starches shown in Fig. 2 are mixed in a powder form, and then 200 parts by weight of fine aggregate are mixed, and water / (cement + starch) is added.
The ratio is set to 48%, and the mixture is kneaded for 90 seconds at 20 ° C using a mortar mixer, and for 20 seconds during the kneading, kneading is performed,
Mortar was prepared. The fluidity, bleeding rate, separability, and strength of the prepared mortar were measured. The results are also shown in Table 1.

<Materials used> Cement: Ordinary Portland cement, Denki Kagaku Kogyo, Onoda, and Sumitomo 3 brands Equivalent mixture fine aggregate: Niigata prefecture Himekawa production sand, FM2.82, specific gravity 2.61,
5mm water reducing agent: Melamine sulfonic acid formalin condensate, powder

<Measurement method> Flow value: Measurement to evaluate fluidity, spread of mortar after measurement and kneading, and after pulling out flow cone for predetermined time Bleeding rate: According to JIS A 1104, inner diameter 14 × inner height 13
Calculated by (Bleeding water amount / Water amount in sample) × 100 using cm container Separability: φ5 × 10 cm mold is filled with mortar and molded, and aggregate is formed on the upper part of the molded body by material separation. After removing fine particles that have hardened in the absence of heat, the height of the molded product after removal is measured at four locations, and the average strength is measured: after the separability is measured, the molded product is capped and used as a test sample according to JIS A 1108. Measures compressive strength for 24 hours

[0026]

[Table 1]

Example 2 As in Example 1, except that a cross-linked starch having a swelling degree of 4% by weight and a commercially available thickener were used and the amount used was changed with respect to 100 parts by weight of cement, as shown in Table 2. went. The results are shown in Table 2.
Also described in.

<Materials used> Commercially available thickener: biopolysaccharide, product name "Viscon 100" manufactured by Yamamune Chemical Co., Ltd.

[0029]

[Table 2]

Example 3 Except that the kneading temperature was 30 ° C., 0.5 parts by weight of cross-linked starch having different swelling degrees was mixed with 100 parts by weight of cement as shown in Table 3, and the fluidity and strength were measured. Was performed in the same manner as in Example 1. The results are also shown in Table 3.

[0031]

[Table 3]

Example 4 The kneading temperature was 5 ° C. and the swelling degree was 4% by weight as shown in Table 4.
The same procedure as in Example 1 was performed except that the starch of Example 1 and various admixtures were added instead of the starch. The results are also shown in Table 4.

<Materials used> Admixture A: Hydroxypropylmethylcellulose, trade name "Metroses 65SH" manufactured by Shin-Etsu Chemical Co., Ltd. Admixture B: Super absorbent resin, trade name "B-13 manufactured by Sanyo Kasei Co., Ltd."
0 ”, fine powder admixture C of several hundred microns: Trade name“ Cerish K ”manufactured by Daicel Chemical Industries, Ltd.
Y-100S ", microfiber

[0034]

[Table 4]

Example 5 Cement having a unit cement amount of 460 kg / m ³ and a swelling degree of 4% by weight
The cross-linked starch of No. 1 was mixed as shown in Table 5 and the unit amount was further added.
The fine aggregate of 867 kg / m ³ was mixed, and the mortar was kneaded in a thermostatic chamber at 20 ° C using a pan mixer. Then coarse aggregate 79
0kg / m ³ and 160kg / m ^{3 of} water in which 1.6 parts by weight of high-performance AE water reducing agent is dissolved in 100 parts by weight of cement, and super-fluidity of water cement ratio 35%, fine aggregate ratio 53% Concrete was prepared, and the table flow, the amount of air, the bleeding rate, and the compressive strength of a predetermined age were measured. For comparison, an example in which crosslinked starch was not added was also performed in the same manner. The results are shown in Table 5.

<Materials used> Coarse aggregate: River gravel from Himekawa, Niigata, specific gravity 2.67, Gmax 25m
m Water-reducing agent: High-performance AE water-reducing agent, Denka Grace's trade name "Darlex Super 100 PHX", main component polycarboxylic acid type

<Measurement method> Slump flow: In accordance with JIS A 1191 "Concrete slump test method", the diameter of the spread of concrete is 0.5c in two directions, the direction recognized as the maximum and the direction perpendicular to it.
Measured up to m and its average compressive strength: Measured according to JIS A 1108 "Test method for compressive strength of concrete"

[0038]

[Table 5]

[0039]

EFFECT OF THE INVENTION The cement additive of the present invention prevents bleeding and material separation without lowering fluidity, delaying setting time at low temperature, and increasing entrained air. There is an effect such as being able to.

Claims (2)

(57) [Claims] 1. A cement additive comprising an ether bond and a crosslinked starch having a swelling degree in a saturated calcium hydroxide solution of 2 to 8% by weight. 2. A cement composition comprising a cement additive for cement as in claim 1 - Symbol placement.