JP7820159B2 - concrete - Google Patents

Description

The present invention relates to concrete using a shrinkage-reducing agent.

It is generally known that hardened mortar and concrete containing cement undergo drying shrinkage due to a decrease in volume caused by drying. Drying shrinkage-reducing agents for cement have been proposed as a means of suppressing this drying shrinkage (see, for example, Patent Document 1). However, concrete using shrinkage-reducing agents has the problem of delayed setting time. While the delayed setting time can be avoided by reducing the amount of shrinkage-reducing agent, this increases drying shrinkage strain, which may lead to cracking due to drying shrinkage. Another method of reducing drying shrinkage strain is to use an expansive additive in combination with a shrinkage-reducing agent. However, this increases the expansion strain, causing the restrained expansion strain to exceed the standard value for shrinkage-compensated concrete (the restrained expansion strain of concrete at 7 days is 150 to 250 × 10 ⁻⁶ ). Furthermore, this tends to reduce compressive strength.

Japanese Patent Application Laid-Open No. 59-184753

The present invention provides concrete that can shorten the setting time even when a shrinkage-reducing agent is used, achieves restrained expansion strain within the standard values for shrinkage-compensating concrete, and also has small drying shrinkage strain.

That is, the present invention provides the following [1] to [3].
[1] Concrete containing a shrinkage-reducing agent and a cement admixture containing an expanding material and aluminum sulfate, characterized in that, per 100 parts by mass of the cement admixture, the expanding material is 80 to 99 parts by mass and the aluminum sulfate is 1 to 20 parts by mass, and the amount of the cement admixture is 20 to 30 kg/ ^m3 .
[2] The concrete of [1], wherein the aluminum sulfate has a 150 μm sieve residue of 10 to 100 mass%.
[3] The concrete of [1] or [2], wherein the amount of the shrinkage reducing agent added is 1.5 to 12 kg/m ³ .

This invention shortens the setting time, achieves restrained expansion strain within the standard values for shrinkage-compensating concrete, and produces concrete with small drying shrinkage strain.

The concrete of the present invention contains a shrinkage-reducing agent and a cement admixture containing an expansive material and aluminum sulfate, with 80 to 99 parts by mass of the expansive material and 1 to 20 parts by mass of aluminum sulfate per 100 parts by mass of the cement admixture, and the amount of the cement admixture in the concrete being 20 to 30 kg/ ^m3 . This will be explained in detail below.

The expansive agent in the cement admixture of the present invention can be any of those containing free quicklime (f-CaO) as the active ingredient, those containing calcium _{sulfoaluminate} such as _{3CaO.3Al2O3.CaSO4} ( _aouine ) as the active ingredient, and those containing both free quicklime and calcium sulfoaluminate as active ingredients. In particular, those that exhibit an expanding effect due to an increase in volume caused by hydration of the free quicklime are preferred. The free quicklime content in the expansive agent is preferably 30 to 80% by mass, more preferably 40 to 70% by mass.

In addition to the above components, the expansive additive of the present invention _may contain, as hydraulic compounds, calcium silicates such as _CaO.2SiO2 ( _C2S ) _{and CaO.3SiO2} ( _C3S ), calcium aluminates such as CaO.Al2O3 (CA ₎ , _12CaO.7Al2O3 ( _C12A7 ), _{and 3CaO.Al2O3 ( C3A} ), _and calcium aluminoferrites such as _{4CaO.Al2O3.Fe2O3} ( _C4AF ) and _{6CaO.2Al2O3.Fe2O3} ( _C6A2F ). The content of the hydraulic compounds in _the expansive additive is preferably 3 _{to 40} mass%, more preferably _{5 to} 30 mass _% .

The expansive agent may further contain gypsum. Examples of gypsum include gypsum hemihydrate, gypsum dihydrate, and anhydrous gypsum, with anhydrous gypsum being particularly preferred. The gypsum content in the expansive agent is preferably 2 to 30% by mass, and more preferably 3 to 25% by mass.

The fineness of the expanding agent is preferably 2000 to 7000 cm ² /g, more preferably 3000 to 6500 cm ² /g, and even more preferably 4000 to 6000 cm ² /g in terms of Blaine specific surface area.

Next, as the aluminum sulfate in the cement admixture of the present invention, commercially available powdered aluminum sulfate can be used. For example, powdered aluminum sulfate (aluminum sulfate) commercially available for use as a flocculant is in the form of a hydrate ( _Al2 ( _SO4 ) _3.xH2O ), but anhydrous or _amorphous aluminum sulfate can also be used. From the viewpoint of storage in powder form, aluminum sulfate containing octahydrate to octadecahydrate water of crystallization is preferred.

In terms of the slump properties of fresh concrete, the particle size of the aluminum sulfate is preferably such that the 150 μm sieve residue is 10 to 100% by mass, more preferably 20 to 90% by mass, and even more preferably 40 to 80% by mass.

The contents of the expanding agent and aluminum sulfate in the cement admixture are 80 to 99 parts by mass of the expanding agent and 1 to 20 parts by mass of aluminum sulfate per 100 parts by mass of the cement admixture. If the aluminum sulfate content is less than 1 part by mass, the setting time will be longer, while if the aluminum sulfate content exceeds 20 parts by mass, there is a risk that the restrained expansion performance will not be able to be ensured and the fresh properties will be reduced. The aluminum sulfate content is more preferably 3 to 18 parts by mass, and even more preferably 5 to 15 parts by mass. The expanding agent and aluminum sulfate are thoroughly mixed in a mixer to prepare the cement admixture.

In addition to the above-mentioned components, the cement admixture of the present invention may contain small amounts of various additives, provided that the advantages of the present invention are not impaired. Examples of such additives include air-entraining agents, water-reducing agents, foaming agents, foaming agents, setting modifiers, hardening accelerators, waterproofing agents, water-repellents, water-retaining agents, rust inhibitors, thickeners, pigments, and anti-efflorescence agents.

The amount of cement admixture in the concrete of the present invention is 20 to 30 kg/m ³ from the viewpoint of compensation for shrinkage of the concrete, and more preferably 25 to 30 kg/m ³ .

The shrinkage-reducing agent used in this invention is not particularly limited, as long as it is one that is commonly used in concrete. Examples of its components include alkylene oxide adducts of alcohol, polyethers, polyoxyalkylene alcohol ethers, glycol ether amino alcohol derivatives, and alkylene oxide copolymers, and it is preferable to use one or more selected from these.

The amount of shrinkage-reducing agent added to the concrete of the present invention is preferably 1.5 to 12 kg/ ^m3 , more preferably 2 to 9 kg/ ^m3 , and even more preferably 3 to 6 kg/ ^m3 , from the viewpoint of minimizing drying shrinkage strain.

In addition to the materials mentioned above, the concrete of the present invention also contains cement, aggregate, and water, but there are no particular limitations, and the cement, aggregate, and water used in ordinary concrete can be used. Note that the concrete of the present invention also includes mortar that uses only fine aggregate.

Examples of cement used in the concrete of the present invention include one or more types selected from ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, low-heat Portland cement, moderate-heat Portland cement, ecocement, and mixed cements obtained by mixing the above Portland cement with blast furnace slag powder, fly ash, silica powder, silica fume, limestone powder, etc. The unit cement amount is preferably 270 to 500 kg/ ^m3 , more preferably 300 to 500 kg/ ^m3 .

The aggregate used in the concrete of the present invention is not particularly limited as long as it is an aggregate generally used in mortar concrete. Specifically, the fine aggregate may be one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, lightweight fine aggregate, etc., and the coarse aggregate may be one or more selected from river gravel, mountain gravel, crushed stone, lightweight coarse aggregate, etc. Furthermore, the aggregate is not limited to natural aggregates; artificial aggregates such as slag aggregate and recycled aggregates can also be used. Furthermore, the unit amount of the fine aggregate and coarse aggregate is preferably 500 to 1100 kg/m ³ , more preferably 600 to 1000 kg/m ³ , from the viewpoint of good workability.

The water used in the concrete of the present invention is not particularly limited, and any water that does not affect the strength development or fluidity of the concrete can be used, such as tap water, treated sewage water, and supernatant water from ready-mixed concrete. From the viewpoint of good workability, the unit water content is preferably 100 to 200 kg/m ³ , more preferably 120 to 180 kg/m ³ .

Furthermore, the concrete of the present invention can contain admixtures used in ordinary concrete, such as air-entraining agents, water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, and high-performance air-entraining water-reducing agents. In addition to these admixtures, foaming agents, foaming agents, waterproofing agents, rust inhibitors, thickeners, water-retaining agents, pigments, water-repellents, anti-efflorescence agents, fibers, and re-emulsified powdered resins can also be used depending on the application of the concrete.

The present invention will be explained in detail below using examples, but the present invention is not limited to these examples in any way.

Example 1
First, an expansive agent and aluminum sulfate were mixed to prepare a cement admixture. The expansive agent used was a quicklime-based expansive agent (free quicklime content: 50% by mass, Blaine specific surface area: 5,130 ^cm2 /g). Furthermore, as the aluminum sulfate, commercially available aluminum sulfate (17% alumina) with its particle size adjusted (150 μm sieve residue: 60% by mass) was used. The expansive agent and aluminum sulfate were thoroughly mixed in a blend mixer to prepare a cement admixture.

Concrete was produced using the prepared cement admixture in a 20°C environment. The concrete mix is shown in Table 2. Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) was used as the cement, mountain sand from Kakegawa was used as the fine aggregate, and crushed stone from Sakuragawa was used as the coarse aggregate. Two types of shrinkage-reducing agents were used: shrinkage-reducing agent A (commercially available product: polyoxyethylene alkyl ether) and shrinkage-reducing agent B (commercially available product: alkylene oxide adduct of lower alcohol). 0.6% by mass of admixture (commercially available product: AE water-reducing agent) was added to the total amount of cement and cement admixture (symbol P).

<Evaluation test>
The concrete thus prepared was tested for slump, setting time, restrained expansion strain, drying shrinkage strain and compressive strength using the following test methods.
(1) Slump The test was carried out in accordance with "JIS A 1101 Slump Test for Concrete."
(2) Setting test: The test was conducted in accordance with "JIS A 1147 Test method for setting of concrete."
(3) Restrained Expansion Test: In accordance with "JIS A 6202 Expansive Additives for Concrete, Appendix B," the restrained expansion strain after 7 days of material age was measured.
(4) Drying shrinkage test: This test was conducted in accordance with JIS A 1129, "Method for measuring changes in length of mortar and concrete." The concrete was demolded after 24 hours, and after 7 days of water curing at 20°C, the base length was measured. The amount of strain after 6 months of age was measured, and the drying shrinkage was calculated. The concrete specimens were stored in a constant temperature room at 20°C and 60% humidity during the ageing period.
(5) Compressive strength test: The compressive strength of the concrete was tested at 28 days of age in accordance with JIS A 1108 "Testing method for compressive strength of concrete." The curing temperature was kept at 20°C until just before the test.

<Test Results>
The test results are shown in Table 3.
It was found that the concrete of the present invention can obtain a restrained expansion strain within the standard value for shrinkage-compensating concrete (150 to 250×10 ⁻⁶ ), and also has small drying shrinkage strain, resulting in concrete with good compressive strength.

Example 2
Next, the effect of particle size of aluminum sulfate used in cement admixture was evaluated.
Table 4 shows cement admixtures using particle-sized aluminum sulfate.

The prepared cement admixture was added, and concrete was prepared in the same manner as in Example 1, and each evaluation test was carried out. The concrete mix is shown in Table 5, and the test results are shown in Table 6.
When the 150 μm residual content of aluminum sulfate was 0 mass%, the slump tended to be smaller. Also, the restrained expansion strain at 7 days of age tended to be smaller, although it was within the standard value for shrinkage-compensated concrete.

Claims (2)

A concrete having a unit cement amount of 300 to 500 kg/ m3, comprising a shrinkage-reducing agent, and a cement admixture containing an expanding agent having free quicklime and/or calcium sulfoaluminate as active ingredients , and aluminum sulfate having a 150 μm sieve residue of 10 to 100% by mass, wherein, per 100 parts by ^mass of the cement admixture, the expanding agent having free quicklime and/or calcium sulfoaluminate as active ingredients is 82 to 97 parts by mass, and the aluminum sulfate having a 150 μm sieve residue of 10 to 100% by mass is 3 to 18 parts by mass, and the amount of the cement admixture is 20 to 30 kg/ ^m3 . 2. The concrete according to claim 1 , wherein the amount of the shrinkage reducing agent added is 1.5 to 12 kg/m ³ .