JP7141867B2 - Strength enhancer and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cement strength enhancer and a method for producing the same.

In the construction industry, the expansion of the use of precast products for labor saving and quality stabilization, the expansion of the use of mixed materials for low carbonization, and the spread of highly durable concrete pavement are being considered. For secondary concrete products such as precast products, there is a demand for early-strength cements or admixtures capable of early demolding in order to improve productivity. The same is true for concrete pavement, and early strength that can be cured in several hours is required for early opening. Furthermore, the lack of initial strength and deterioration of durability due to neutralization are problems with the use of mixtures with slow hydration kinetics.

In order to solve the above problems, hydration accelerators capable of accelerating the hardening of cement and concrete have been proposed. For example, Patent Document 1 discloses a cement additive for high-temperature curing, which is composed of amorphous silica having an average particle size of 10 nm to 500 nm and shortens the appearance time of hydration exothermic peak of alite. Patent Document 2 discloses a cement composition containing calcium silicate hydrate as a hardening accelerator. Patent Document 3 discloses a hardening accelerating composition using fine particles of hydrate discharged from ready-mixed concrete plants and concrete products.

JP 2012-41243 A JP 2015-120630 A JP-A-5-238794

Secondary concrete products such as early-strength precast products are required to further improve the strength enhancement effect under steam curing in order to improve productivity. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a strength enhancer capable of improving early strength development of a cement composition produced through steam curing, and a method for producing the same.

As a result of intensive studies to solve the above problems, the present inventors found that a material containing a specific cementitious hydrate has the effect of increasing the curing speed of cement/concrete under steam curing, and completed the present invention. came to.

The strength enhancer according to the present invention contains a cementitious hydrate, and the proportion of clinker minerals in the cementitious hydrate is less than 50% by mass. By incorporating this strength enhancer into the cement composition, the hydration reaction of cement is promoted, thereby improving the early strength development of the cement composition produced through steam curing. Ready-mixed concrete sludge is exemplified as a material that can be used as such a cementitious hydrate. Ready-mixed concrete sludge has conventionally been a waste product, and by using this as a raw material to produce a strength enhancer, the waste product can be effectively utilized.

The fact that the ratio of clinker minerals in the cementitious hydrate is less than 50% by mass means that the hydration reaction due to clinker minerals has progressed to some extent. The cement-based hydrate contained in the strength enhancer is a product of the hydration reaction of cement (e.g., calcium silicate hydrate _{( 1.7CaO.SiO2.2H2O} ), calcium hydroxide (Ca(OH) ₂ )) in an amount of 50% by mass or more. The present inventors presume that the hydration reaction proceeds more easily due to the seed crystal effect in which the products of the hydration reaction become seed crystals, thereby improving early strength development.
According to the studies of the present inventors, in the strength enhancer, when the ratio of clinker minerals in the cement-based hydrate is extremely low (for example, less than 0.5% by mass), compared to when it is about 9% by mass Therefore, the lower limit of the clinker mineral content is, for example, 1.0% by mass.

From the viewpoint of excellent early strength development, the above cementitious hydrate is preferably in powder form and preferably has a proportion of particles having a particle diameter of 1 μm or less of 10% by volume or more. Preferably, the cementitious hydrate does not substantially contain crystalline calcium silicate hydrate. Since the cementitious hydrate does not substantially contain crystalline calcium silicate hydrate, the temperature generally applied in steam curing (for example, about 50 to 70 ° C.) is sufficiently high in the early stage under curing conditions. Compressive strength can be achieved.

The method for producing a strength enhancer according to the present invention includes a cementitious hydrate producing step of mixing a cement composition and water to produce a cementitious hydrate, and a ratio of clinker minerals in the cementitious hydrate. and a curing step of curing until the content becomes less than 50% by mass. Through this curing step, a cementitious hydrate containing less than 50% by mass of clinker minerals can be obtained.

It is preferable that the method for producing a strength enhancer according to the present invention further includes a pulverization step of wet pulverizing the cementitious hydrate obtained through the curing step. In this pulverization step, it is preferable to pulverize the cement-based hydrate so that the ratio of particles having a particle diameter of 1 μm or less is 10% by volume or more. In the pulverization step, wet pulverization is preferably performed under the condition that the ratio (A/B) of the mass A of the cement-based hydrate to the mass B of water is 0.01 to 10.

INDUSTRIAL APPLICABILITY According to the present invention, a strength enhancer capable of improving early strength development of a cement composition produced through steam curing and a method for producing the same are provided.

FIG. 1 shows an X-ray diffraction chart of the strength enhancer. FIG. 2 is a graph showing mortar curing conditions.

Embodiments of the present invention will be described below. In addition, this invention is not limited to the following embodiment.

<Strength enhancer>
The strength enhancer according to this embodiment is for enhancing the hardening of cement. The strength enhancer contains a cementitious hydrate, and the proportion of clinker minerals in the cementitious hydrate is less than 50% by mass. For example, by replacing a part of the cement and using it, the strength of the cement is increased.

(cement-based hydrate)
As described above, the proportion of clinker minerals in the cementitious hydrate is less than 50% by mass. If this proportion exceeds 50% by mass, the early strength development of the cement composition becomes insufficient. The clinker minerals referred to here mean unhydrated minerals present in Portland cement, and specifically, alite (3CaO.SiO ₂ , hereinafter sometimes referred to as C ₃ S), belite (2CaO. _SiO2 , hereinafter sometimes referred to as C2S), aluminate phase _{( 3CaO.Al2O3 ,} hereinafter sometimes referred to as _C3A ), ferrite phase _{( 4CaO.Al2O3.Fe2O3 ,} hereinafter sometimes referred to as _C3A ) C ₄ AF). The percentage of clinker minerals in the cementitious hydrate as used herein means the sum of the contents (% by mass) of these four types of unhydrated clinker minerals. These clinker minerals in cementitious hydrates can be quantified by X-ray diffraction Rietveld analysis.

The proportion of clinker minerals in the cementitious hydrate is preferably less than 30% by mass, more preferably 20% by mass, still more preferably 1.0 to 15% by mass. If this ratio is less than 1.0% by mass, the early strength development of the cement composition tends to be insufficient due to the lack of unhydrated minerals.

From the viewpoint of early strength development, the C ₃ S content in the cementitious hydrate is preferably 0 to 30% by mass, and may be 0 to 15% by mass or 0.1 to 10% by mass. From the viewpoint of early strength development, the C ₂ S content in the cementitious hydrate is preferably 0 to 25% by mass, and may be 0 to 15% by mass or 0.5 to 12% by mass. From the viewpoint of early strength development, the amount of C ₃ A in the cementitious hydrate is preferably 0 to 12% by mass, and may be 0 to 10% by mass or 0.1 to 8% by mass. From the viewpoint of early strength development, the amount of C ₄ AF in the cementitious hydrate is preferably 0 to 15% by mass, and may be 0 to 10% by mass or 0.1 to 5% by mass.

From the viewpoint of excellent early strength development, the above cementitious hydrate is preferably in the form of powder. In the cementitious hydrate powder, the ratio of particles having a particle diameter of 1 μm or less is preferably 10% by volume or more, more preferably 20% by volume or more, and still more preferably 30% by volume or more. The particle size of the cementitious hydrate can be measured with a laser diffraction particle size distribution meter.

Any type of cementitious hydrate can be selected as long as the proportion of unhydrated clinker minerals is less than 50% by mass. For example, cement can be partially hydrated by reacting it with water. There are no particular restrictions on the type of cement, and Portland cement such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, and mixed cement in which Portland cement is mixed with blast-furnace slag, fly ash, and siliceous material. is available.

Ready-mixed concrete sludge generated in a ready-mixed concrete factory or the like (hereinafter sometimes referred to as ready-mixed concrete sludge) may be used as the cement-based hydrate. The ready-mixed concrete manufactured at the ready-mixed concrete factory is transported to the construction site by an agitator vehicle. The ready-mixed concrete remaining inside the agitator after unloading the ready-mixed concrete at the construction site is removed by washing the inside of the agitator after the agitator returns to the ready-mixed concrete factory. Fresh concrete sludge is fine particles separated by removing coarse aggregate and fine aggregate from the solid residue generated when the inside of the agitator vehicle is washed. Coarse aggregate and fine aggregate are usually reused, but raw concrete sludge is often disposed of as industrial waste after being dehydrated by a dehydrator such as a filter press. Fresh concrete sludge contains cement hydrate obtained by hydration reaction of cement. By using fresh concrete sludge as a strength enhancer, it is possible to reduce industrial waste.

The clinker mineral contained in the cement composition undergoes a hydration reaction upon contact with water. In the hydration reaction of the cement composition, many reactions are intricately intertwined to produce calcium silicate hydrate (CSH) and the like. This CSH is generally amorphous because the crystal arrangement is irregular. Therefore, the composition after the hydration reaction of the cement composition is often amorphous.

Preferably, the cementitious hydrate is substantially free of crystalline calcium silicate hydrate. In order to produce crystalline calcium silicate hydrate, high-temperature curing at 90° C. or higher is required, and the curing is costly. In addition, substantially free of crystalline calcium silicate hydrate means that the X-ray diffraction pattern of the cement-based hydrate has peaks of unhydrated clinker minerals or aluminates such as ettringite and monosulfate. and does not have a sharp peak indicative of a calcium silicate hydrate such as tobermorite.

(other ingredients)
The strength enhancer according to the present embodiment may further contain at least one of magnesium hydroxide and calcium hydroxide, in addition to the cement-based hydrate, from the viewpoint of further promoting the initial hydration reaction of cement. The total content of magnesium hydroxide and calcium hydroxide is, for example, 0 to 20 parts by mass, and may be 0.1 to 5 parts by mass, with respect to 100 parts by mass of the cementitious hydrate.

The strength enhancer according to the present embodiment can promote strength enhancement of steam-cured mortar/concrete products. The strength enhancer is preferably added to replace cement. The replacement amount of the strength enhancer is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, more preferably 1.0 to 6% by mass, relative to cement. preferable.

<Method for producing strength enhancer>
The method for producing a strength enhancer according to the present embodiment comprises a cementitious hydrate producing step of mixing a cement composition and water to produce a cementitious hydrate; and a curing step of curing until the ratio is less than 50% by mass. Through this curing step, the cementitious hydrate having a clinker mineral content of less than 50% by mass can be obtained.

(Hydrate formation step)
The hydrate-producing step is a step of mixing the cement composition and water to cause a hydration reaction of the cement composition. In this step, the ratio (C/W) of the mass C of the cement composition to the mass W of water (C/W) is preferably 0.01 to 10, more preferably 0.02 to 5, considering the handling of the cement paste. Yes, more preferably 0.1 to 1. A commercially available mixer can be used to mix the cement composition and water. When using ready-mixed concrete sludge as the cement-based hydrate, the step of kneading the ready-mixed concrete corresponds to this step.

(curing process)
The curing step is a step of curing so that the ratio of unhydrated clinker minerals in the cement-based hydrate becomes less than 50% by mass due to the hydration reaction of the cement composition. Unreacted clinker minerals decrease as the hydration reaction of the cement composition proceeds. The above cementitious hydrate can be obtained by carrying out the hydration reaction between the cement composition and water until the amount of unreacted clinker minerals is less than 50% by mass. Since the hydration reaction rate changes depending on the temperature, the hydration time may be appropriately adjusted depending on the temperature. The hydration reaction of the cement composition during the hydration reaction may be terminated when the unreacted clinker mineral content becomes less than 50% by mass. Methods for stopping hydration include the following.
(1) A method of allowing a paste or the like mixed with a cement composition and water to dry naturally (2) A method of evaporating water by heating (3) A method of controlling humidity by reducing humidity (4) Drying by reduced pressure Method (5) Method by solvent extraction to extract water with alcohol or acetone

When using fresh concrete sludge as a cement-based hydrate, in order to stop the hydration reaction of fresh concrete sludge, the fresh concrete sludge should be dehydrated by a method such as a filter press, belt press, or screw press, or dried naturally or by heating. You can do it.

(Pulverization process)
The method for producing a strength enhancer may further include a pulverizing step of wet pulverizing the cementitious hydrate obtained through the curing step. By pulverizing the cementitious hydrate, the strength enhancement effect can be enhanced, and by wet pulverizing, a slurry containing the pulverized cementitious hydrate (strength enhancer) can be obtained. The wet pulverization can be carried out with a ball mill or the like using water as a solvent. In this case, wet pulverization is preferably performed under the condition that the ratio (A/B) of the mass A of the cement-based hydrate to the mass B of water is 0.01 to 10. This ratio is more preferably between 0.02 and 5, more preferably between 0.1 and 1.

When a powdery strength enhancer is produced, a step of drying the slurry to obtain a powdery hydrothermal reaction product may be further included after the pulverizing step. When the slurry is used as it is without being dried, a cement composition may be prepared by mixing Portland cement to be increased in strength, the slurry, and kneading water.

Examples of the present invention are described in detail below. The invention is not limited to the following examples.

[Raw material for cementitious hydrate]
・Normal Portland Cement (NC): manufactured by Ube Industries, Ltd. ・High-early Strength Portland Cement (HC): manufactured by Ube Industries, Ltd. ・Moderate Heat Portland Cement (MC): manufactured by Ube Industries, Ltd. ・Fresh Consludge 1 (SL1): Kanto Ube Concrete Industry Co., Ltd. Toyosu Factory (collected in November 2017)
・ Fresh concrete sludge 2 (SL2): Ricorn sustainable cement

Table 1 shows the ignition loss (ig.loss) and chemical composition of the cementitious hydrate raw material. The ignition loss was measured according to JIS R 5201 "physical test method for cement", and the chemical composition was measured according to JIS R5204 "method for fluorescent X-ray analysis of cement" using a fluorescent X-ray diffractometer (manufactured by Rigaku, ZSX-100e ).

[Preparation of cement-based hydrate]
At a water/cement ratio of 0.5, knead for 2 minutes with a hyper mixer (manufactured by Maruto Seisakusho Co., Ltd., model number CB-34). A cured product was produced by curing for 72 hours in a constant temperature machine. Thereafter, the hardened body was pulverized, immersed in acetone to stop hydration, and the acetone contained in the hardened body was dried under reduced pressure. After hydration was stopped, the hardened body was pulverized for 90 seconds with a vibration mill (GY-RO P-6200, company name unknown) to obtain cementitious hydrates of various Portland cements.

[Preparation of fresh concrete sludge]
Ready-mixed concrete sludge is produced by separating coarse aggregate and fine aggregate by washing the returned ready-mixed concrete collected at the ready-mixed concrete plant, and removing the solid content in the suspended water (cement hydrate, unhydrated cement, some fine aggregates, etc.). (including fine particles, etc.) was dehydrated by a filter press dehydrator. In addition, a commercially available dry raw consulge sludge (SL2) was used. ig. of raw consludge (SL1, SL2) Loss and chemical components are shown in Table 1.

[Preparation of strength enhancer]
(Example 1)
Ordinary portland cement (NC) hydrate and water are mixed at a mass ratio of 2:8, put into a φ80mm pod made of alumina with a capacity of 500ml, and φ10mm zirconia balls are added to the pod made of alumina. A strength-enhancing slurry containing ground NC hydrate was prepared by ball milling the pods while rotating for 24 hours.

(Example 2)
A strength-enhanced product composed of pulverized HC hydrate in the same manner as in Example 1, except that high-early-strength Portland cement (HC) hydrate was used instead of ordinary Portland cement (NC) hydrate. A slurry containing the agent was prepared.

(Example 3)
Strength enhancement consisting of pulverized MC hydrate in the same manner as in Example 1, except that moderate heat Portland cement (MC) hydrate was used instead of ordinary Portland cement (NC) hydrate. A slurry containing the agent was prepared.

(Example 4)
A slurry containing a strength enhancer consisting of the pulverized material of SL1 was prepared in the same manner as in Example 1, except that fresh concrete sludge 1 (SL1) was used instead of ordinary portland cement (NC) hydrate. .

(Example 5)
A slurry containing a strength enhancer consisting of the pulverized material of SL2 was prepared in the same manner as in Example 1, except that fresh concrete sludge 2 (SL2) was used instead of ordinary portland cement (NC) hydrate. .

(Reference example)
As a reference example, a powder obtained by mixing 50.7% by mass of coal ash and 49.3% by mass of slaked lime was kneaded at a water/powder mass ratio of 2.0 in an autoclave at 180 ° C. and 10 atmospheres. A hydrothermally synthesized hydrate obtained by reacting for 24 hours was pulverized under the same conditions to prepare a slurry.

[Identification of minerals and percentage of clinker minerals]
The minerals constituting the strength enhancers according to the above examples and reference examples were identified and the ratio of clinker minerals was measured. Quantification of clinker minerals was performed by adding 10% by mass of Al ₂ O ₃ (corundum, manufactured by Wako Pure Chemical Industries, Ltd.) as a standard sample, adding acetone, and mixing with a mortar to obtain a measurement sample for X-ray diffraction. was prepared. Using an X-ray diffractometer (manufactured by Bruker AXS Co., Ltd., acceleration voltage: 30 kV, current: 10 mA, tube: Cu), hydrates of each cement and fresh concrete sludge (including Al ₂ O ₃ as a standard sample) obtained an X-ray diffraction pattern of The crystal phase was identified from the obtained X-ray diffraction pattern using X-ray diffraction software (DIFFRAC.EVA).

The X-ray pattern obtained by X-ray diffraction was subjected to Rietveld analysis with analysis software (Topas, manufactured by Bruker AXS Co., Ltd.), and various Portland cement cement-based hydrates and fresh concrete sludge (SL1, SL2). C ₃ S, C ₂ S, C ₃ A and C ₄ AF contained in the water were quantified, and the sum thereof was defined as the ratio of clinker minerals. Table 2 shows the results. FIG. 1 is an X-ray diffraction chart of strength enhancers according to Examples 1, 4, 5 and Reference Example. As shown in FIG. 1, the hydrothermally synthesized hydrate according to the reference example contains tobermorite and hydrogarnet-based hydrate (C ₃ ASH ₄ ).

[Measurement of particle size distribution of strength enhancer]
The strength enhancer according to the above Examples and Reference Examples was dispersed in ethanol, irradiated with ultrasonic waves for 10 minutes, and then measured for particle size distribution using a laser diffraction/scattering particle size distribution analyzer (Malvern, Mastersizer 3000). The ratio (unit: volume %) having a particle diameter of 1 μm or less was calculated. Table 2 shows the results.

In Table 2, "clinker mineral (% by mass)" is for the strength enhancer before wet pulverization, and "percentage of particles with a particle diameter of 1 μm or less (volume %)" is for strength enhancement after wet pulverization. It is intended to measure agents. Since the hydrothermally synthesized hydrate according to Reference Example is completely hydrated, the content of unhydrated clinker minerals is 0% by mass. For SL1 and SL2 according to Examples 4 and 5, no data on "proportion of particles having a particle diameter of 1 μm or less" is obtained.

[Compressive strength test of mortar containing strength enhancer]
Mortars containing the strength enhancers according to Examples and Reference Examples were prepared and subjected to a compressive strength test. The mortar test formulations are shown in Table 3. Ordinary Portland cement (OPC) manufactured by Ube Industries was used as cement, and standard sand for cement strength test (hereinafter referred to as "standard sand") was used as fine aggregate. A slurry containing 20% by mass of a strength enhancer after wet pulverization is added so that the strength enhancer replaces ordinary Portland cement by 2%, 3%, and 5% by mass, and a slurry containing a strength enhancer is added. was replaced with kneading water to adjust the formulation. For kneading, a mortar mixer (manufactured by Maruto Seisakusho Co., Ltd., model number CB-34) is used to mix ordinary Portland cement and standard sand at low speed for 30 seconds, and after mixing the strength enhancer slurry and kneading water at low speed for 30 seconds, A mortar was prepared by high speed mixing for 60 seconds.

After filling the prepared mortar into a cylindrical mold of φ50 mm×height of 100 mm, the mold was sealed with a polyethylene film and steam cured for 3 hours under the temperature conditions shown in FIG. After that, the formwork was removed and the mortar compressive strength was measured. Table 4 shows the results. In Table 4, the compressive strength ratio is based on the compressive strength of the hardened mortar according to Comparative Example 1. A hardened mortar according to Comparative Example 1 was prepared in the same manner as in Example 1, except that no strength enhancer was added.

As shown in Table 4, the mortars according to the examples have higher compressive strength than the mortars according to Comparative Example 1 containing no strength enhancer, and the strength enhancer of the present invention has a high strength enhancement effect. I found out.

The mortars according to Examples 4b, 4c and 5 had higher compressive strength than the mortars according to Reference Examples b and c using hydrothermally synthesized hydrate. A diffraction peak derived from crystalline tobermorite was confirmed in the X-ray diffraction pattern of the hydrothermally synthesized hydrate according to the reference example, while crystalline calcium silicate hydrate was not found in the strength enhancers of the examples. It was found that the hydrate of the strength enhancer was substantially amorphous (see Figure 1). From this, it was found that the strength enhancer preferably does not contain a crystalline hydrate. Furthermore, the strength enhancers according to Examples 4 and 5 are not only excellent in strength development, but also consist of fresh concrete sludge, which has conventionally been disposed of as waste. Therefore, according to the example using raw concrete sludge as a raw material, it is possible to effectively utilize the waste as well as being excellent in early strength development.

Claims (8)

A strength enhancer consisting only of a cementitious hydrate,
A strength enhancer, wherein the cementitious hydrate has a clinker mineral content of 1.0% by mass or more and less than 50% by mass. A strength enhancer consisting only of a cementitious hydrate and at least one of magnesium hydroxide and calcium hydroxide,
The ratio of clinker minerals in the cementitious hydrate is 1.0% by mass or more and less than 50% by mass,
A strength enhancer, wherein the total content of the magnesium hydroxide and the calcium hydroxide is 20 parts by mass or less with respect to 100 parts by mass of the cementitious hydrate. 3. The strength enhancer according to claim 1 or 2 , wherein said cementitious hydrate is powdery and has a proportion of particles having a particle diameter of 1 [mu]m or less of 10% by volume or more. The strength enhancer according to any one of claims 1 to 3, wherein said cementitious hydrate is substantially free of crystalline calcium silicate hydrate. The strength enhancer according to any one of claims 1 to 4 , wherein said cementitious hydrate is ready-mixed concrete sludge. a cementitious hydrate producing step of mixing the cement composition and water to produce a cementitious hydrate;
A curing step of curing until the ratio of clinker minerals in the cementitious hydrate reaches 1.0% by mass or more and less than 50% by mass;
A method of making a strength enhancer, comprising: Further comprising a pulverizing step of wet pulverizing the cementitious hydrate obtained through the curing step,
7. The method for producing a strength enhancer according to claim 6 , wherein in the pulverizing step, the cementitious hydrate is pulverized so that the proportion of particles with a particle size of 1 μm or less is 10% by volume or more. The strength enhancer according to claim 7 , wherein in the pulverization step, wet pulverization is performed under the condition that the ratio (A/B) of the mass A of the cement-based hydrate to the mass B of water is 0.01 to 10. manufacturing method.

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