JP7849541B2 - Polymer cement mortar composition and polymer cement mortar - Google Patents

Description

This invention relates to polymer cement mortar compositions and polymer cement mortar.

Cement mortar is frequently used for repairing concrete structures, and the application methods vary depending on the application and scale, with plastering and spraying being the most well-known methods.

One disclosed spraying method for dry mortar involves separately preparing a powder mixture consisting of cement, aggregate, expansive agent, and a non-aqueous shrinkage-reducing agent, along with a polymer dispersion-containing liquid for cement admixture, mixing them in front of the spraying nozzle, and then spraying the mixture (Patent Document 1).

Dry spraying methods offer advantages such as excellent long-distance pumping capabilities, high daily construction volume, and the ability to place mortar in locations far from mixing plants. Therefore, they are used in special work environments such as culverts, waterways, tunnels, and roads with traffic restrictions.

As a material used in dry spraying methods, for example, a dry spraying mortar material is known that comprises a powder mixture containing cement, fine aggregate, an expansive agent, and a non-aqueous liquid shrinkage reducing agent, and a polymer dispersion liquid, wherein at least the cement in the powder mixture is coated with the non-aqueous liquid shrinkage reducing agent, the powder mixture contains 1 to 10% by mass of fine aggregate with an average particle size of 1.2 to 3.6 mm and a maximum particle size of 5 mm or more, and the polymer solids/cement mass ratio is 1 to 15% by mass (Patent Document 2).

Japanese Patent Publication No. 2006-283335 Japanese Patent Publication No. 2011-207643

Dry spraying methods involve spraying large amounts of material with high-pressure air for long-distance transport or large-scale construction. This results in challenges such as material rebound (bouncing back) and loss, as well as the generation of significant dust, which negatively impacts the work environment.

Furthermore, in dry spray application methods, the applied surface is sometimes finished with a trowel after spraying. Therefore, the spray material used must be able to finish the surface with fewer coats and have good trowel-finishing properties, meaning it adheres minimally to the trowel.

Therefore, the present invention aims to provide a polymer cement mortar composition and polymer cement mortar that exhibit excellent spraying performance, such as reduced rebound rate and low dust generation during spraying, as well as excellent trowel finishing performance.

As a result of diligent research into the above-mentioned problems, the inventors of this invention have found that by incorporating fine aggregate with an adjusted particle size distribution, a polymer cement mortar composition and polymer cement mortar that achieve both spraying performance and trowel finishing performance can be obtained.

In other words, the present invention is represented by the following [1] to [7].
[1] comprising cement, pozzolanic substance, cement polymer, and fine aggregate,
A polymer cement mortar composition wherein the particle size of the fine aggregate is such that, with respect to the total mass of the fine aggregate, the mass percentage of aggregate particles with a particle size of less than 0.6 mm is 2 to 45% by mass, the mass percentage of aggregate particles with a particle size of 0.6 mm or more and less than 1.2 mm is 35 to 90% by mass, and the mass percentage of aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm is 2 to 55% by mass.
[2] The polymer cement mortar composition according to [1], wherein the mass ratio of aggregate particles having a particle size of 0.6 mm or more and less than 1.2 mm is greater than the total mass ratio of aggregate particles having a particle size of less than 0.6 mm and aggregate particles having a particle size of 1.2 mm or more and less than 2.5 mm.
[3] The polymer cement mortar composition according to [1] or [2], wherein the content of the fine aggregate is 100 to 300 parts by mass per 100 parts by mass of cement.
[4] The polymer cement mortar composition according to [1] or [2], further comprising fibers.
[5] A polymer cement mortar composition according to [1] or [2], which is for use as a dry spray material.
[6] [1] or [2] comprises a polymer cement mortar composition and water,
A polymer cement mortar in which the water content is 10 to 25 parts by mass per 100 parts by mass of the polymer cement mortar composition.
[7] The polymer cement mortar described in [6], wherein, during hardening, the compressive strength at 28 days of age, measured in a 20°C environment in accordance with JIS A 1108:2018 "Test method for compressive strength of concrete", is 45 N/ ^mm² or more.

According to the present invention, it is possible to provide a polymer cement mortar composition and polymer cement mortar that exhibit excellent spraying performance, such as reduced rebound rate and low dust generation during spraying, as well as excellent trowel finishing performance.

The following describes in detail one embodiment of the present invention. In this specification, the content of materials other than water is stated on a solids basis and anhydrous basis. If a material contains water, that water is included in the water content of the polymer cement mortar.

The polymer cement mortar composition of this embodiment comprises cement, a pozzolanic substance, a cement polymer, and fine aggregate.

Various types of cement can be used, including ordinary, rapid-hardening, ultra-rapid-hardening, low-heat, and moderate-heat Portland cements, filler cements mixed with blast furnace slow-cooled slag powder such as limestone powder, and environmentally friendly cements (eco-cements) manufactured primarily from various industrial wastes. One type of cement may be used alone, or two or more types may be used in combination. Ordinary Portland cement or rapid-hardening Portland cement is preferred from the viewpoint of further improving the compaction of the polymer cement mortar during spraying and further enhancing the initial strength development.

The cement content is preferably 20 to 50 parts by mass, more preferably 25 to 45 parts by mass, and even more preferably 30 to 40 parts by mass, per 100 parts by mass of the polymer cement mortar composition. When the cement content is within the above range, the strength development is even better.

Examples of pozzolanic materials include various types of fly ash described in JIS A 6201:2015, silica fume described in JIS A 6207:2016, blast furnace slag powder, amorphous aluminosilicate, etc. From the viewpoint of achieving even better long-term strength development, fly ash and blast furnace slag powder having a Blaine specific surface area of 2000 to 5000 ^cm² /g, and silica fume having a BET specific surface area of 5 to 30 ^m² /g are preferred as the pozzolanic material.

The pozzolanic substance content is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, even more preferably 7 to 20 parts by mass, and particularly preferably 8 to 18 parts by mass, per 100 parts by mass of cement. When the pozzolanic substance content is within the above range, the stability during spraying and dust reduction are further improved, the trowel finish after spraying is also good, and the strength development after hardening is even better.

For cement polymers, those specified in JIS A 6203:2015 "Polymer Dispersions and Re-emulsifiable Powdered Resins for Cement Admixture" are preferred. Examples of such cement polymers include polymer dispersions and re-emulsifiable powdered resins.
Examples of polymer dispersions include synthetic rubber-based materials such as styrene-butadiene rubber (SBR); natural rubber-based materials; rubber asphalt-based materials; ethylene vinyl acetate-based materials; acrylic acid ester-based materials; and resin asphalt-based materials. Among these, synthetic rubber-based materials, ethylene vinyl acetate-based materials, and acrylic acid ester-based materials are preferred, and specifically, synthetic rubber latex, polyacrylic acid ester, and ethylene vinyl acetate are more preferred.
Examples of re-emulsifiable powder resins include synthetic rubbers such as styrene-butadiene rubber; acrylic acid esters; ethylene vinyl acetate; vinyl acetate/versatile vinyl ester; vinyl acetate/versatile vinyl/acrylic acid ester, etc.
Among polymers for cement, acrylic acid ester-based re-emulsified powder resins are preferred from the viewpoint of having superior water resistance.
As the polymer for cement, a polymer dispersion may be used, a re-emulsifiable powder resin may be used, or both a polymer dispersion and a re-emulsifiable powder resin may be used in combination. When using a polymer dispersion, it can be added by methods such as adding a mixture with water. The polymer for cement may be used alone or two or more types may be used in combination.

The content of the cement polymer is preferably 1 to 18 parts by mass, more preferably 2 to 16 parts by mass, even more preferably 4 to 14 parts by mass, and particularly preferably 5.5 to 12 parts by mass, based on solid content, per 100 parts by mass of cement. When the cement polymer content is within the above range, the adhesion and thickness of the sprayed cement will be even better.

The fine aggregate is not particularly limited and examples include river sand, silica sand, crushed sand, granite, limestone sand, and slag aggregate. From among these, silica sand is preferred as the fine aggregate because it exhibits superior strength development during spraying. The fine aggregate may be used individually or in combination of two or more types.

The particle size distribution of the fine aggregate is such that, relative to the total mass of the fine aggregate, the mass percentage of aggregate particles with a particle size of less than 0.6 mm is 2 to 45% by mass, the mass percentage of aggregate particles with a particle size of 0.6 mm or more but less than 1.2 mm is 35 to 90% by mass, and the mass percentage of aggregate particles with a particle size of 1.2 mm or more but less than 2.5 mm is 2 to 55% by mass. If the particle size distribution of the fine aggregate is outside the above range, it becomes difficult to achieve both the properties required during spraying, such as reduced rebound rate and reduced dust, and the trowel finish required after spraying. Furthermore, if the particle size distribution of the fine aggregate is within the above range, excellent spraying stability and thickness during spraying are achieved, and the surface finish after spraying is good.

The mass percentage of aggregate particles with a particle size of less than 0.6 mm is preferably 5 to 40% by mass, more preferably 8 to 30% by mass, and even more preferably 10 to 20% by mass, relative to the total mass of fine aggregate.
The mass percentage of aggregate particles with a particle size of 0.6 mm or more and less than 1.2 mm is preferably 40 to 80% by mass, more preferably 45 to 70% by mass, and even more preferably 50 to 65% by mass, relative to the total mass of fine aggregate. The mass percentage of aggregate particles with a particle size of 0.6 mm or more and less than 1.2 mm is preferably greater than the mass percentages of aggregate particles with a particle size of less than 0.6 mm and aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm, respectively, and is more preferably greater than the combined mass percentage of aggregate particles with a particle size of less than 0.6 mm and aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm.
The mass percentage of aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm is preferably 10 to 45% by mass, more preferably 15 to 35% by mass, and even more preferably 20 to 30% by mass, relative to the total mass of fine aggregate. The mass percentage of aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm is preferably greater than the mass percentage of aggregate particles with a particle size of less than 0.6 mm.
With respect to aggregate particles with a particle size of 2.5 mm or larger, it is preferable that their amount be 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the total mass of the fine aggregate, from the viewpoint of further reducing the rebound rate. The fine aggregate does not have to contain aggregate particles with a particle size of 2.5 mm or larger.
If the particle size of the fine aggregate is within the above range, it is easier to achieve both the properties required during spraying and the properties required after spraying, and it also results in even better spraying stability and thickness during spraying, and a better surface finish after spraying.

In this specification, "particle size" refers to the size measured by sieving using the method described in JIS A 1102:2014 "Sieving Test Method for Aggregates." Specifically, aggregate particles with a particle size of less than 0.6 mm refer to those that pass through a sieve with a mesh size of 0.6 mm; aggregate particles with a particle size of 0.6 mm or more and less than 1.2 mm refer to those that pass through a sieve with a mesh size of 1.2 mm and remain on a sieve with a mesh size of 0.6 mm; aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm refer to those that pass through a sieve with a mesh size of 2.5 mm and remain on a sieve with a mesh size of 1.2 mm; and aggregate particles with a particle size of 2.5 mm or more refer to those that remain on a sieve with a mesh size of 2.5 mm.

The fine aggregate content is preferably 100 to 300 parts by mass, more preferably 110 to 250 parts by mass, even more preferably 120 to 220 parts by mass, particularly preferably 130 to 195 parts by mass, and most preferably 145 to 185 parts by mass, per 100 parts by mass of cement. If the fine aggregate content is within the above range, the rebound rate can be further reduced, and the trowel finishability after spraying is further improved.

The polymer cement mortar composition of the present invention preferably further contains fibers from the viewpoint of improving its thickness-spraying properties. Examples of fibers include organic fibers such as vinylon fibers, polypropylene fibers, and nylon fibers; steel fibers; and inorganic fibers such as glass fibers. From the viewpoint of better dispersibility, organic fibers are preferred, and vinylon fibers and polypropylene fibers are more preferred. The fibers may be used individually or in combination of two or more types.

The length of the fibers is preferably 2 to 15 mm, more preferably 3 to 14 mm, and most preferably 4 to 13 mm. Within this range of fiber length, sufficient thickness can be easily achieved while maintaining fluidity.

The fiber content is preferably 0.01 to 2 parts by mass, more preferably 0.1 to 1 part by mass, even more preferably 0.3 to 0.8 parts by mass, and particularly preferably 0.35 to 0.6 parts by mass, per 100 parts by mass of cement. When the fiber content is within the above range, sufficient thickness and strength development can be easily obtained while ensuring fluidity.

In addition to the materials described above, the polymer cement mortar composition of the present invention may contain various admixtures used in mortar and concrete, provided that these do not impair the effects of the present invention. Examples of admixtures include Glauber's salt, gypsum, stone powder, inorganic fillers, water-reducing agents, thickeners, defoaming agents, foaming agents, shrinkage-reducing agents, accelerators, and expansive agents. One type of admixture may be used alone, or two or more types may be used in combination.
When a water-reducing agent is added, from the viewpoint of reducing the unit water content and ensuring early hardening, it is preferable that the amount is 1 part by mass or less, more preferably 0.5 parts by mass or less, even more preferably 0.1 parts by mass or less, and still more preferably 0.01 parts by mass or less, per 100 parts by mass of cement. The polymer cement mortar composition of the present invention may substantially not contain a water-reducing agent.

The method for premixing the polymer cement mortar composition of the present invention is not particularly limited. For example, it can be mixed using a ribbon mixer, paddle mixer, or the like, which have relatively little shear action and primarily rely on dispersion and diffusion through scraping with paddles or blades.

The polymer cement mortar composition of the present invention exhibits excellent spraying performance, including a low rebound rate, stability during spraying, and low dust generation during spraying, as well as excellent trowel finishing performance. Therefore, it is suitably used as a dry spraying material for dry spraying methods. The dry spraying system, for example, includes a spraying machine that air-pressures the polymer cement mortar composition via an air compressor and a liquid pump that pressurizes water. The water pressurized from the liquid pump is injected and mixed through a shower ring installed midway along the air-pressure hose of the polymer cement mortar composition (approximately 1-2 m before the spraying nozzle). The polymer cement mortar is then discharged from the spraying nozzle and applied to the target object such as walls, ceilings, slopes, and repair areas. The amount of water injected and mixed through the shower ring is preferably 10-25 parts by mass, more preferably 12-20 parts by mass, and even more preferably 13-18 parts by mass, per 100 parts by mass of the polymer cement mortar composition.

The polymer cement mortar composition of the present invention can be prepared as polymer cement mortar by mixing it with water, and the water content can be appropriately adjusted depending on the application. The water content is preferably 10 to 25 parts by mass, more preferably 12 to 20 parts by mass, and even more preferably 13 to 18 parts by mass, per 100 parts by mass of the polymer cement mortar composition. When the water content is within the above range, rebound is easily suppressed, and sufficient compressive strength is easily obtained.

The polymer cement mortar of the present invention preferably has a compressive strength of 45 N/mm² or higher, more preferably 50 N/ ^mm² or higher, even more preferably 55 N/ ^mm² or higher, and particularly preferably 60 N/ ^mm² or higher, measured at 20°C in accordance with JIS A 1108:2018 "Method for Testing the Compressive Strength of Concrete," when cured, in accordance with JIS A 1108:2018 "Method for Testing the Compressive Strength of Concrete," at 28 days of age. The compressive strength at 28 days of age may be 80 N/ ^mm² or ^lower . If the compressive strength at 28 days of age is within the above range, the long-term strength development performance can be further enhanced.

The polymer cement mortar of the present invention exhibits excellent spraying performance, including a low rebound rate, stability during spraying, and low dust generation during spraying, as well as excellent trowel finishing performance. Therefore, the polymer cement mortar of the present invention can be used not only for the dry spraying method described above, but also as a wet spraying material for wet spraying methods, and can also be used as a repair and reinforcement material for concrete structures, steel-concrete composite structures, etc.
The method of using the polymer cement mortar of the present invention can be appropriately selected. For example, methods such as filling depressions with a trowel, leveling with a vibrator or the like after filling and then finishing with a trowel, or wet spraying onto the repair area can be selected.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. All examples were conducted under a 20°C environment.

[material]
Cement (abbreviation C): High-early-strength Portland cement Fine aggregate (abbreviation S): Silica sand (adjusted to the particle size shown in Table 1)
Pozzolane material 1 (abbreviation P1): Blast furnace slag fine powder (Blaine specific surface area 4000 ^cm² /g)
Pozzolanic substance 2 (abbreviation P2): Fly ash (Blaine specific surface area 2500 ^cm² /g)
Pozzolanic substance 3 (abbreviation P3): Silica fume (BET specific surface area 10.2 ^m² /g)
Fibers (abbreviation F): Vinylon fiber (fiber length 5 mm)
Cement polymer (abbreviation CP): Re-emulsifiable powder resin (acrylic ester copolymer)

[Preparation of polymer cement mortar composition]
A polymer cement mortar composition was obtained by mixing various materials according to the formulations shown in Table 1 in a ribbon mixer.

[Dry spraying]
Dry spraying was carried out using the following system.
A polymer cement mortar composition was compressed and pumped through a pressure-resistant hose using an Ariba 237 dry mortar spraying machine via an air compressor. Water was pumped using a single-screw eccentric pump and injected into the air-pumped hose containing the polymer cement mortar composition at a rate of 14 to 16 parts by mass per 100 parts by mass of the polymer cement mortar composition through a shower ring installed 1.5 m before the spray nozzle to create the spray material (polymer cement mortar). This was then sprayed from the nozzle end onto the experimental side wall and core box. A pressure-resistant hose with an inner diameter of 1.5 inches and a length of 45 m was used to pump the spray material.

[Evaluation Test]
Dry spraying was performed on each of the polymer cement mortar compositions of Examples 1 to 15 and Comparative Examples 1 to 4 shown in Table 1, and various evaluation tests were conducted. The evaluation test methods are described below. The results are shown in Table 2.

- Rebound Rate: In accordance with JSCE-F563-2005, a core box (formwork) was placed vertically to the ground, and the amount of rebound (polymer cement mortar that did not adhere to the formwork and fell) was measured when the spray material (polymer cement mortar) was dry-sprayed vertically onto the core box for 1 minute. The rebound rate was calculated from the theoretical mass of polymer cement mortar produced (theoretical amount) and the rebound amount using the following formula.
Rebound rate (mass %) = (rebound amount / theoretical amount) × 100

- Spraying Stability: Dry spraying was performed on the experimental side wall for 10 minutes. The stability of the sprayed material (polymer cement mortar) was checked using a pressure gauge and visually. A rating of ◎ indicated that there was little pulsation at the nozzle tip and that it was stable, ○ indicated that there was some pulsation at the nozzle tip but it was stable, △ indicated that there was a lot of pulsation at the nozzle tip but it was stable, and × indicated that it lacked stability due to material separation or pulsation of the spraying machine.

- Dust level Dry spraying of the spraying material (polymer cement mortar) was performed on the experimental side wall in a U-shaped spraying yard, and the dust level was visually checked. As an indicator of dust level, ◎ was used to indicate that there was almost no dust, ○ to indicate that there was some dust, △ to indicate that there was some dust but the spraying worker and the spraying situation could be seen, and × to indicate that the spraying worker was difficult to see and there was a lot of dust.

- Thickness of application: Dry spraying of the spray material (polymer cement mortar) was performed on the experimental side wall in a single pass, and the spray thickness was measured. As an evaluation index for thickness of application, ◎ was used for spray thicknesses of 20 cm or more, ○ for 15 cm or more but less than 20 cm, △ for 10 cm or more but less than 15 cm, and × for less than 10 cm.

- Trowel finishability Dry spraying of the spray material (polymer cement mortar) onto a formwork (30 cm x 30 cm x 2 cm) was performed, and the finishability by troweling was evaluated. A rating of ◎ was given to a surface that was finished with only a few trowel strokes and with little mortar adhering to the trowel, a rating of ○ was given to a surface that was finished with more trowel strokes than ◎ and with some mortar adhering to the trowel, a rating of △ was given to a surface that was finished with more trowel strokes than ○ and with some mortar adhering to the trowel, and a rating of × was given to a surface that was not finished even after troweling and with a lot of mortar adhering to the trowel.

- Compressive Strength: The sprayed material (polymer cement mortar) applied to the core box was cured in air at 20°C for 7 days, and core samples of φ10cm × 20cm were drilled using a core drill. The core samples were then cured in air in a laboratory at 20°C and RH 60% for 28 days. On the 28th day, the compressive strength of the samples was measured in accordance with JIS A 1108:2018.

The polymer cement mortar composition in the example exhibited a low rebound rate when dry-sprayed, stable pumping during application, minimal dust generation, and good thickness-spraying properties. Furthermore, the polymer cement mortar composition in the example allowed for good trowel finishing after spraying, and the hardened body exhibited excellent compressive strength. In contrast, the polymer cement mortar composition in the comparative example had problems with either a high rebound rate, excessive dust generation during dry-spraying, or insufficient trowel finishing after spraying.

Claims (5)

It comprises cement, pozzolanic material, cement polymer, and fine aggregate.
The particle size of the fine aggregate is such that, relative to the total mass of the fine aggregate, the mass percentage of aggregate particles with a particle size of less than 0.6 mm is 2 to 45% by mass, the mass percentage of aggregate particles with a particle size of 0.6 mm or more and less than 1.2 mm is 35 to 90% by mass, and the mass percentage of aggregate particles with a particle size of 1.2 mm or more and less than 2.5 mm is 2 to 55% by mass.
The content of the pozzolanic substance is 1 to 40 parts by mass per 100 parts by mass of the cement.
A polymer cement mortar composition in which, when a water-reducing agent is added, the amount of the water-reducing agent added is 0.1 parts by mass or less per 100 parts by mass of the cement. The polymer cement mortar composition according to claim 1, wherein the mass proportion of aggregate particles having a particle size of 0.6 mm or more and less than 1.2 mm is greater than the total mass proportion of aggregate particles having a particle size of less than 0.6 mm and aggregate particles having a particle size of 1.2 mm or more and less than 2.5 mm. The polymer cement mortar composition according to claim 1 or 2, wherein the content of the cement polymer is 1 to 18 parts by mass in terms of solid content, per 100 parts by mass of cement. The polymer cement mortar composition according to claim 1 or 2, further comprising 0.01 to 2 parts by mass of fibers per 100 parts by mass of cement. A polymer cement mortar composition according to claim 1 or 2, for use as a dry-type spraying material.