JP5120651B2 - Shrinkage reducing agent for cement composition - Google Patents

Description

  The present invention relates to a shrinkage reducing agent for cements such as mortar and concrete. More specifically, the present invention relates to a shrinkage reducing agent for a cement composition having a shrinkage-reducing effect and freeze-thaw resistance, and a cement admixture containing the shrinkage-reducing agent, which can maintain the appearance of the hardened cement surface.

Hardened concrete is a hydraulic composition composed of a reaction between water and cement. During the hardening process, water loss occurs due to water evaporation or hydration, which leads to the occurrence of concrete shrinkage. The shrinkage of the hardened concrete causes distortion in the member, eventually leading to cracks on the member surface, promoting deterioration of the concrete structure due to water leakage and the like, and possibly resulting in structural defects.
In addition, the white flower phenomenon (eflorescence) that occurs on the surface of the hardened body due to moisture movement in the hardened cement body and moisture transpiration to the outside, etc. not only impairs the aesthetics of the concrete structure, Care must be taken because it may indicate the presence or absence of deformation such as cracking or neutralization.

The use of a shrinkage reducing agent has been proposed as a countermeasure against concrete shrinkage and the like in such a curing process. For example, Patent Document 1 describes that an alkylene oxide adduct of a lower alcohol having 1 to 4 carbon atoms is used as a shrinkage reducing agent for cement. Patent Document 2 describes that a shrinkage reducing agent having a more excellent shrinkage reducing effect can be obtained by optimizing the copolymerization ratio of ethylene oxide and propylene oxide of an alkylene oxide adduct of a lower alcohol. Yes. Furthermore, Patent Document 3 describes that the strength reduction of the cured body can be prevented by improving the dispersion state of the shrinkage reducing agent in the cement slurry and reducing the foaming property.
On the other hand, as a conventional means for improving the surface appearance of a hardened cement body, a surface aesthetics improving agent containing a polypropylene oxide adduct of polyethylene glycol and / or a polypropylene oxide adduct of ethylenediamine polyethylene oxide adduct (Patent Document 4) or A liquid efflorescence inhibitor using a fatty acid alkali metal salt (Patent Document 5) has been proposed.
Japanese Patent Publication No. 56-51148 JP 2001-163653 A JP 2003-171155 A JP-A-11-199290 JP 2000-128597 A

The proposed shrinkage reducing agent for cement has the main purpose of suppressing shrinkage reduction of the hardened cement body or decrease in strength of the hardened body as shown in the above-mentioned literature. Met.
In recent years, after concrete is actually placed and hardened, problems with the appearance of the surface of the hardened body that occur over time, such as cracks that occur in a mesh form on the concrete surface (running the surface of the hardened body in the form of grooves, (It is different from the conventional cracks), white flower generation, resistance to dirt, etc. have emerged as new problems.
In addition, freezing and thawing of the hardened concrete causes cracks in the form of meshes and turtle shells on the surface of the hardened body, and the subsequent freezing and thawing action increases the crack opening width. Finally, the strength of the entire hardened body Improvement in the resistance to freezing and thawing of concrete is also an important issue in cold districts because it leads to a decrease. However, some conventional cement shrinkage reducing agents, when mixed with concrete, reduce the freeze-thaw resistance of the concrete, and there has been a need for a cement shrinkage-reducing agent that does not adversely affect the freeze-thaw resistance. .

  Of course, the present invention has a conventional shrinkage reducing effect and is a novel product under the viewpoint of solving new problems of “maintaining a good surface appearance through use over time” and “improving freeze-thaw resistance”. Designed to improve the performance of cement shrinkage reducing agents, the surface appearance of hardened cement can be maintained well even after many years of use. It is an object of the present invention to provide a shrinkage reducing agent and a cement admixture containing the shrinkage reducing agent that can effectively suppress a decrease in freeze-thaw resistance.

  The present inventors examined the degree of expression of a plurality of performances of shrinkage reduction effect and maintenance of freeze-thaw resistance, and as a result of research, as a result of lower oxide alkylene oxide addition compounds, By limiting the number of added moles and further reducing the content of low boiling point compounds as a shrinkage reducing agent, concrete shrinkage at the time of curing, as well as use over time after curing Deterioration of surface properties such as mesh cracks on the surface can be effectively suppressed, and a hardened concrete body that can maintain an excellent appearance can be obtained. In addition, the occurrence of frost damage when used in cold regions is effective. I found that I can prevent it.

That is, the present invention includes at least one compound represented by the following general formula (1), and the content of the compound having a boiling point of 140 ° C. or less is 5% by mass based on the mass of the whole compound. It is related with the shrinkage reducing agent for cement compositions characterized by being less than.
RO- (AO) n-H (1)
(In the formula, R represents a methyl group or an ethyl group, (AO) n represents a polyoxyalkylene group constituted by polymerization of 1 to 7 mol of ethylene oxide and 0 to 1 mol of propylene oxide, and n represents 1 Represents an integer from 1 to 8. )

  Furthermore, the present invention relates to the shrinkage reducing agent for cement composition, high performance AE water reducing agent, high performance water reducing agent, AE water reducing agent, water reducing agent, AE agent, foaming agent, antifoaming agent, curing agent, water repellent. A cement admixture characterized by containing at least one other concrete additive selected from the group consisting of an agent, a setting accelerator and a setting retarder.

According to the present invention, it is possible to effectively reduce / suppress the occurrence of shrinkage and cracks in the curing process, and shrinkage defects on the surface of the cured body that progress through long-term use after concrete hardening and appearance deterioration such as cracks. A shrinkage reducing agent for physical objects can be provided.
Moreover, the shrinkage reducing agent for a cement composition of the present invention can effectively suppress a decrease in freeze-thaw resistance of a hardened concrete.
Moreover, the cement admixture of the present invention can suppress the deterioration of the appearance of the concrete over a long period of time and can significantly improve the freeze-thaw resistance of the cured body by mixing with the concrete, as well as a water reducing effect. The effect that it is possible can be demonstrated.

Hereinafter, the present invention will be described in more detail.
In the compound represented by the general formula (1), R represents a methyl group or an ethyl group.
The above (AO) n represents a polyoxyalkylene group constituted by polymerization of 1 to 7 mol of ethylene oxide and 0 to 1 mol of propylene oxide, and n is the number of polymerization of the oxyalkylene group, Represents the number of ~ 8 .

In the above compound, the polymerization form of ethylene oxide and propylene oxide is not particularly limited, and may be any form of a random copolymer, a block copolymer, or a random / block copolymer, but may be a block copolymer. preferable.
Preferred are polyethylene glycol polypropylene glycol monomethyl ether, polyethylene glycol monomethyl ether, polyethylene glycol polypropylene glycol monoethyl ether, and polyethylene glycol monoethyl ether.

The shrinkage reducing agent for cement composition according to the present invention is characterized in that the content of a compound having a boiling point of 140 ° C. or lower is less than 5% by mass, and preferably the content is 3% by mass. The following is desirable. Examples of such a compound having a boiling point of 140 ° C. or lower include an unreacted component or a component generated as a by-product when the compound represented by the general formula (1) is produced.
By setting the content of these compounds to less than 5% by mass, especially 3% by mass or less, the number of coarse air holes generated on the surface of the hardened concrete can be reduced, and shrinkage cracks can be reduced. This leads to improved surface properties of the cured product.

  Conventionally known methods can be used to reduce the content of the compound at 140 ° C. or lower. For example, by distilling the unpurified reaction solution after the production of the compound represented by the formula (1), The content ratio of the compound can be reduced.

Other components that can be blended in the shrinkage reducing agent for cement composition together with the compound represented by the general formula (1) include shrinkage reducing agents that are used for general purposes. For example, polyoxyalkylene monoalkyl ethers having an alkyl group or alkenyl group having 1 to 8 carbon atoms and an average addition mole number of alkylene oxide having 2 to 4 carbon atoms of 1 to 20 moles; A polyoxyalkylene glycol having an alkylene group or alkenyl group having from 8 to 8 carbon atoms and an average addition mole number of an alkylene oxide having 2 to 4 carbon atoms of 1 to 20 moles; or an alkyl group having 1 to 8 carbon atoms or Examples thereof include polyoxyalkylene dialkyl ethers having an alkenyl group and an alkylene oxide having 2 to 4 carbon atoms and an average addition mole number of 1 to 20 moles.
The compounding ratio of these compounds used in combination is a mass ratio with the compound of the general formula (1), the compound (mass) represented by the general formula (1): the compound (mass) used in combination = 50: 50 to 99: The ratio of 1 is preferably 70:30 to 99: 1.

The shrinkage reducing agent for a cement composition of the present invention is used by blending with cements. The cement is not particularly limited. For example, ordinary Portland cement, early-strength Portland cement, ultra-early-strength Portland cement, sulfate-resistant Portland cement, moderately hot Portland cement, white Portland cement, super-hard Portland cement, expanded cement, acidic cement Phosphate cement, self-hardening cement, lime slag cement, blast furnace cement, high sulfate slag cement, fly ash cement, keens cement, pozzolanic cement, alumina cement, roman cement, white cement, magnesia cement, starch syrup cement, calcium Examples include aluminate, silica cement, silica fume cement, jet cement, and gypsum.
Further, the shrinkage reducing agent of the present invention can be used for concrete (concrete product, ready-mixed concrete, lightweight concrete) or mortar in which sand, pebbles, lime or the like is blended with these cements.

The blending amount of the shrinkage reducing agent for cement composition according to the present invention varies depending on the design blend of concrete and the like, but is usually preferably 0.1 to 3% by mass with respect to the cement mass. However, the amount of addition of the shrinkage-reducing agent for concrete and the shrinkage-reducing agent composition of the present invention is not limited to this because it varies depending on the concrete material and blending conditions.

  The usage mode of the shrinkage reducing agent for a cement composition of the present invention is not particularly limited, and the usage mode is similar to that of a conventionally known shrinkage reducing agent, for example, an mode in which the shrinkage reducing agent is added to the kneading water of cement, or the cement is kneaded. While being added thereto, an aspect in which it is absorbed into an oil-absorbing powder such as silica to form a solid and added to cement, or an aspect in which it is applied and impregnated on the surface of a semi-cured cement cured body, etc. Applicable.

The shrinkage reducing agent for cement composition of the present invention can be mixed with other cement additives and used in the form of so-called cement admixture. Other cement additives that can be formulated include high-performance AE water reducing agents, high-performance water reducing agents, AE water reducing agents, water reducing agents, AE agents, foaming agents, antifoaming agents, curing agents, water repellents, and setting accelerators. Agents, setting retarders and the like.
In addition to these, various admixtures commonly used in cement compositions such as thickeners, expansion agents, rust inhibitors, organic fibers, inorganic fibers, organic polymers, and pigments can be used.

  Next, based on an Example, this invention is demonstrated in detail. The present invention is not limited to the following examples.

The compounds represented by the general formula (1) used in the following Examples and Comparative Examples are as shown in Table 1 below. In Table 1, “EO” represents an oxyethylene group, “PO” represents an oxypropylene group, and the numbers in the EO and PO columns represent the average number of moles added.
The “ratio (mass%) of a compound having a boiling point of 140 ° C. or lower” in the following table is a value measured by gas chromatography. The measurement conditions are shown below.
[Gas chromatography measurement conditions]
Model: Shimadzu Corporation GC-14A
Column: OV-17 manufactured by GL Sciences
Temperature rising program: 100 ° C. → 300 ° C. (10 ° C./1 minute), injection 330 ° C., detector 340 ° C.
Carrier gas: Nitrogen gas, 40 ml / min Injection volume: 1 μl

[Mortar test]
In accordance with JIS R 5201, mortar was prepared with the mortar formulation shown in Table 2 below, and subjected to a mortar test.
Specifically, a Hobart mixer was used for kneading the mortar. First, water and cement were kneaded at low speed for 30 seconds, then sand was added and kneaded at low speed for 30 seconds. In addition, the said compound added in the following Example and Comparative Example was added with kneading water with the addition amount of 2 mass% uniformly with respect to cement mass. Then, after kneading at high speed for 30 seconds, stirring was stopped and the mixture was allowed to stand for 90 seconds. The mortar adhering to the wall of the container was scraped off in 15 seconds from the start of standing, and after standing, kneading was performed at high speed for 60 seconds. Here, the amount of air in the mortar was appropriately adjusted with an AE agent and an antifoaming agent so as to be 7 to 9%.

<Mortar flow and air volume>
A JIS cone was used for the measurement of the mortar flow, the total mass method was adopted for the measurement of the air amount, the measurement was performed using a graduated cylinder, and the air amount was calculated by the following formula. The results are shown in Table 3.
Air amount (%) = [1- (Mortar mass) / (Mortar mass at 0% of air amount determined from formulation)] × 100

<Shrinkage reduction rate and dry mass reduction rate>
The shrinkage reduction rate was measured using a mortar specimen prepared by filling a 4 × 4 × 16 cm mold in accordance with JIS R 5201. The cured specimen was demolded after 24 hours, and then subjected to water curing (20 ° C.) for 1 week. After the underwater curing, the dimensions of the specimen were measured by the contact gauge method described in JIS A 1129-2, and this was used as a reference value. Thereafter, the specimen was stored under conditions of a temperature of 20 ° C. and a humidity of 60%, and the dimensions of the specimen were measured again on the age of 56 days, and the rate of change in length was calculated. Furthermore, in parallel with the measurement of the rate of change in length, the change in mass of the mortar specimen was also measured.

The value of the shrinkage reduction rate was calculated by the following formula using the above-mentioned rate of change of the mortar specimen and the rate of change of the mortar specimen that did not use the shrinkage reducing agent as a blank. The results are shown in Table 3. In addition, it means that shrinkage | contraction can be suppressed, so that the value of a shrinkage | contraction reduction rate is large.
Shrinkage reduction rate (%) = [1- (length change rate of examples and comparative examples) / (blank length change rate)] × 100

The dry mass reduction rate was calculated by the following formula using the mass of each specimen at the start of measurement and the value of the specimen mass after the test. The results are shown in Table 3. In addition, it means that the moisture dissipation in a test body has been suppressed, so that the dry mass reduction rate is small.
Dry mass reduction rate (%) = (mass change amount of test specimen) / (test specimen mass at start of test) × 100

<Freeze-thaw resistance (mass reduction rate before and after freeze-thaw)>
For the evaluation of the freeze-thaw resistance, the value of the mass reduction rate before and after the freeze-thaw test solution was used. A simple method referring to the JIS A 1148 A method (in-water frozen water thawing method) was employed for this measurement.
Specifically, first, a specimen was prepared by the same mold form and method as those for the measurement of the shrinkage reduction rate and the dry mass reduction rate, and was cured in water. Thereafter, water on the surface of the specimen was gently wiped off, and the mass of the specimen before freezing and thawing was measured. Thereafter, the temperature was raised and lowered in the temperature range of + 20 ° C. to −20 ° C., and the specimen was repeatedly frozen and thawed. One freeze and thaw was taken as one cycle, and a total of 60 cycles of freeze / thaw tests were performed. The freezing and thawing steps are as follows.
Freezing step: Decrease from + 20 ° C. to −20 ° C. over 1 hour and hold at −20 ° C. for 7 hours.
Melting process: Rise from −20 ° C. to + 20 ° C. over 1 hour and hold at + 20 ° C. for 3 hours.
The temperature miscalculation range shall be within ± 2 ° C.

After completion of the freeze-thaw test, the moisture on the surface of the specimen was wiped lightly, the mass was measured, and the mass reduction rate before the test was calculated from the following formula. The results are shown in Table 3. It can be evaluated that a specimen having a smaller mass reduction rate obtained here has higher resistance to freezing and thawing.
Mass reduction rate (%) = [(sample weight before test) − (sample weight after test)] / (sample weight before test) × 100

<Appearance change: generation of white flower and presence of air holes>
The appearance of the entire surface of the specimen was visually observed to confirm the occurrence of white flower. The results are shown in Table 4.
In addition, the number of coarse air holes having a diameter of 1 mm or more and minute air holes having a diameter of 1 mm or less were visually measured on two surfaces of the mold contact surface of the specimen, ie, two side surfaces and a bottom surface. The results are shown in Table 4. It can be evaluated that the appearance criterion in this air hole measurement is that the larger the number of coarse air holes and the smaller the number of minute air holes, the worse the surface appearance.

As shown in Tables 3 and 4, the mortar of Example 1 using the shrinkage reducing agent for cement composition of the present invention contains Comparative Example 1 not using the shrinkage reducing agent and a compound having a boiling point of 140 ° C. or lower. The results were obtained that the shrinkage reduction rate and the dry mass reduction rate were low even after 56 days of age, at the same level or higher than the mortars of Comparative Examples 2 to 3 using a shrinkage reducing agent having a high ratio. In addition, the results showed that there was little mass loss after freeze / thaw cycles and the resistance to freeze-thaw was high.
Moreover, the result that the mortar of Example 1 had many fine air holes compared with the number of air holes with a rough surface air hole was obtained, and it was confirmed that the concrete hardened | cured material excellent in surface property can be obtained.
That is, the shrinkage reducing agent for a cement composition according to the present invention can balance the shrinkage reducing effect and the effect of preventing the effect of freezing and thawing, and can exert both well, and the surface of the hardened concrete body through use over time. It was confirmed that the appearance can be maintained well.

Claims (2)

The content ratio of the compound having at least one compound represented by the following general formula (1) and having a boiling point of 140 ° C. or lower among the compounds is less than 5% by mass based on the mass of the whole compound. A shrinkage reducing agent for a cement composition, which is characterized.
RO- (AO) n-H (1)
(In the formula, R represents a methyl group or an ethyl group, (AO) n represents a polyoxyalkylene group constituted by polymerization of 1 to 7 mol of ethylene oxide and 0 to 1 mol of propylene oxide, and n represents 1 Represents an integer from 1 to 8. ) The shrinkage reducing agent for cement composition according to claim 1, and a high performance AE water reducing agent, a high performance water reducing agent, an AE water reducing agent, a water reducing agent, an AE agent, a foaming agent, an antifoaming agent, a curing agent, and a water repellent. A cement admixture comprising at least one other concrete additive selected from the group consisting of a setting accelerator and a setting retarder.