JP4762654B2 - Crack prevention method - Google Patents

Description

  The present invention relates to a method for preventing cracks on the surface of expanded concrete, which is concrete using an expandable material mainly used in the civil engineering and construction fields, and its hardened cement, particularly in the early age of the next day after the surface finish of expanded concrete. The present invention relates to a method for preventing cracks on the surface of expanded concrete and its hardened cement body.

Expansion concrete, the amount of expansion material, typically concrete 1 m ³ per in the order of 20-30 kg, walls, general building roof slabs, and floor materials, etc. and, hydraulic structures such as tanks and pools, In addition, it is used to prevent cracks in general structures and secondary products such as pavements, floor slabs, and box culverts.

  About 40 years have passed since the expansion material has been used in the cement field, and it has been used in various places. However, cracking of a hardened cement body using the expansion material may not be completely prevented.

The crack of the hardened cement body using the expansive material is also said to be a crack or a crack like the hardened cement body using no expansive material, and when large drying shrinkage is constrained to the hardened cement body of the expanded concrete, If the surface of the expanding concrete that is being cured shrinks due to temperature drop or wind, etc., if the settlement of the expanded concrete that has not yet solidified is hindered by reinforcing bars, etc. When remarkably heat of hydration occurs, rebar corrosion due to alkali-aggregate reaction, seawater scattering, neutralization, etc., significant expansion occurs, and rapid temperature drop after steam curing The present invention is intended for cracks due to self-shrinkage and cracks due to drying shrinkage.
The reason why the hardened cement body does not disappear is that the tensile strength of cement is as low as 1/10 of the compressive strength, and the deformability is small.

Cracks are the result of external tensile forces that are greater than the tensile strength of expanded concrete at that time, and are caused by abnormal condensation of the materials used in the concrete, heat of hydration, alkali-aggregate reaction, drying shrinkage, rebar This is because deformation due to oxidation reaction and temperature change is constrained to act as a tensile force.
And even if a normal use material was used and the proper construction was performed, cracks may occur due to self-shrinkage or drying shrinkage.

  In order to prevent cracking of hardened cement paste due to severe self-shrinkage and dry shrinkage, the combined use of shrinkage reducing agents has been studied as one of the countermeasures.

  Shrinkage reducing agents are used as materials for reducing drying shrinkage in hardened cementitious materials, and are also used in general buildings such as walls and floor slabs, general structures accompanying road widening, and cement products. It is used for applications such as prevention and compensation for cure shrinkage.

As a method of using the shrinkage reducing agent, a method of mixing with cement or a method of applying after the expansion of concrete is known, and a kneaded mixture of a hydraulic composition, water, and a shrinkage reducing agent is cured. A method is also proposed in which an evaporative suppression coating layer is formed on a concrete surface (see Non-Patent Document 1 and Patent Document 1).
Moreover, the sealing agent containing an ethylene-vinyl acetate copolymer emulsion which coat | covers the concrete surface by spraying or apply | coating to the concrete surface is proposed (refer patent document 2).

In the method of adding the shrinkage reducing agent to the cement, the amount of the shrinkage reducing agent used is increased, the cost is increased, the amount of entrained air is increased, and the strength may be reduced. In the method of coating, it took time to penetrate, and during that time, other work could not be performed or cracking occurred before curing.
In addition, in the method of forming an evaporation-inhibiting coating layer using a shrinkage reducing agent, when cracking occurs at the early stage of age before construction, or when cracking does not occur at the early stage of age, the time until construction is reached. If the length is too long, cracks may occur in the hardened concrete, and it is necessary to sufficiently cure the material at the early stage of age, which causes problems such as an increase in work process and material costs.
And, in some cases, cracking cannot be prevented by a method in which an ethylene-vinyl acetate copolymer emulsion is sprayed or applied to the concrete surface and coated with an emulsion coating.

JP 2002-193686 A Japanese Patent Publication No. 62-000116 Expansion material and shrinkage reducing agent, Concrete engineering, Vol.24, No.2, Feb 1986, pp.56-62

  The present invention has been made as a result of various studies to solve the above problems, and by applying a drying shrinkage reducing agent at a specific time in a specific method, and performing surface finishing work of expanded concrete such as ruler work. It was completed by knowing that drying shrinkage and curing shrinkage from surface finishing to hardening of expanded concrete are reduced, and high crack resistance is obtained.

That is, the present invention is to Da設the Rise Zhang concrete, AraHitoshi work, ruler shear working, and perform final finishing operation, the expansion concrete before curing was pouring when surface finish rulers shear before work及beauty before final finishing operations, drying shrinkage reducing agent was the crack prevention method for spraying before the expansion concrete is cured, dried shrinkage reducing agent, 10 to 300 g / m ² before rulers shear work in terms of active ingredient ,及beauty, final finishing operation before 5 to 150 g / m ² in terms of active ingredient, are the crack prevention method for spraying before the expansion concrete is hardened, the dilution ratio of water drying shrinkage-reducing agent at 10 times or less It is a certain crack prevention method.

  By using the method of the present invention, it has become possible to prevent cracks in the early age of the next day after the surface finish of the expanded concrete used in the civil engineering / architecture field.

Hereinafter, the present invention will be described in detail.
The expanded concrete referred to in the present invention is a generic term for cement paste, mortar, and concrete using an expanded material, and the cemented cured product is a generic term for a cured product of expanded concrete.
In the present invention, “part” and “%” are based on mass unless otherwise specified.

  The present invention relates to a method for preventing cracking from surface finishing to hardening of expanded concrete and a hardened cemented body thereof, in which a drying shrinkage reducing agent is sprayed on a setting surface of the expanded concrete before hardening.

  In the present invention, expanded concrete is placed and the surface finish is performed before the expanded concrete is cured.

  In the present invention, roughening work, ruler work, and final finishing work are performed as surface finishing methods for expanded concrete.

  In the present invention, as a method for reducing the drying shrinkage of the hardened cement, a drying shrinkage reducing agent is sprayed on the surface of the expanded concrete before the expanded concrete is cured.

The drying shrinkage reducing agent used in the present invention is used for general buildings such as walls and floor slabs, general structures accompanying road widening, and cement products, and for applications such as drying shrinkage prevention and hardening shrinkage compensation. This is a nonionic surfactant that is used, and is dissolved in water in the pores of the hardened cement, which is liquid or powder, and reduces the surface tension of water when it evaporates. There is work.
The basic structure of the drying shrinkage reducing agent has a polyoxyalkylene polymer, and a lower alcohol, phenol, and amino bond are added to the terminal.
Specifically, polypropylene glycol, ethylene oxide methanol adduct ethylene oxide / propylene oxide block polymer, ethylene oxide / propylene oxide random polymer, glycol cycloalkyl group adduct, glycol adducts with methyl groups added to both ends of glycol, glycol A phenyl group adduct, a block polymer obtained by adding a methylphenyl group to glycol, an adduct obtained by adding ethylene oxide methanol to both ends of glycol, an adduct obtained by adding dimethylamine to glycol, or the like can be used.

The spraying of the drying shrinkage reducing agent is carried out before the setting of the cast expanded concrete, before the rule work of the surface of the expanded concrete and / or before the final finishing operation.
The drying shrinkage reducing agent is 10 to 300 g / m ^{2 in} terms of active ingredient when sprayed before the ruler work, and 5 to 150 g / m ^{2 in} terms of active ingredient when sprayed before the final finishing work. It is preferable to spray. If the application rate before ruler work is less than 10 g / m ^{2 in} terms of active ingredient, the crack prevention effect may not be obtained. If it exceeds 300 g / m ^{2 in} terms of active ingredient, strength may be reduced.
Also, if the spraying amount before the final finishing work is less than 5 g / m ^{2 in} terms of active ingredient, finishing work may be difficult or the effect of preventing cracking may not be obtained, and it exceeds 150 g / m ^{2 in} terms of active ingredient. In some cases, a thin skin-like latency may occur on the surface.
When the drying shrinkage reducing agent is a liquid, the stock solution itself is an active ingredient, and when it is a powder, the active ingredient is usually 50 to 100%.

  The dilution ratio of water of the drying shrinkage reducing agent is preferably 10 times or less. If it exceeds 10 times, the crack prevention effect may not be obtained.

  The method of spraying the drying shrinkage reducing agent is not particularly limited as long as it is a method of uniformly dispersing on the surface of the expanded concrete. Depending on the construction area, in the case of liquid, a sprayer, a sprayer, a watering can, etc. In the case of the body, there are methods using a spreader or a sieve.

  As the cement used in the present invention, normal, early strength, very early strength, low heat, and moderate heat Portland cement, various mixed cements and eco-cements in which these Portland cements are mixed with blast furnace slag, fly ash, or silica are used. Portland cement mixed with pozzolanic reaction such as white cement, super-hard cement, silica fume, fly ash and silicate clay, blast furnace slag fine powder, etc., and filler cement mixed with limestone fine powder, etc. It is done.

  The aggregate used in the present invention is not particularly limited as long as it can be used for ordinary mortar and concrete, and fine aggregates such as river sand, land sand, crushed sand, and sea sand, river gravel, Examples include coarse aggregates such as crushed stones and artificial lightweight aggregates.

  In the present invention, it is further possible to use a water reducing agent.

The water reducing agent is used to improve the fluidity of concrete or reduce the unit water volume, and it is possible to obtain a concrete having high durability, high strength, and high fluidity. . Established in 1982 as a chemical admixture for concrete in JIS A 6204.
As the water reducing agent, an AE water reducing agent, a high performance water reducing agent, a high performance AE water reducing agent, or the like can be used. Specifically, examples of the AE water reducing agent include a lignin sulfonic acid compound, a modified lignin sulfonic acid compound, a polyol, and an oxycarboxylic acid compound. Examples of the high performance water reducing agent include a formalin condensate of naphthalene sulfonate, Examples include melamine sulfonic acid formalin condensate, and high performance AE water reducing agents include polystyrene sulfonate, hydroxypolyacrylate, αβ-unsaturated dicarboxylic acid and olefin copolymer, polyethylene glycol monoalkenyl ether and maleic. Examples include polycarboxylic acids such as acid monomers, copolymers derived from methacrylic acid monomers, and styrene-acrylic acid ester-maleic acid copolymers, which are partially polymerized by a crosslinking reaction. Including oriented polymers and highly modified polymers, one or two of these The above use is possible.
The amount of the water reducing agent used is preferably 0.01 to 4 parts, more preferably 0.05 to 2 parts in terms of solid content, with respect to a total of 100 parts of cement and expansion material. If it is less than 0.01 part, it may be difficult to obtain a predetermined fluidity. If it exceeds 4 parts, separation or strength delay may occur.

  The amount of water used for preparing the expanded concrete in the present invention varies depending on the material used in combination other than cement, so it is difficult to determine uniquely. Usually, it is preferably 20 to 50 parts with respect to 100 parts of cement. 25 to 35 parts is more preferable. If it is less than 20 parts, workability may not be obtained, and if it exceeds 50 parts, material may be separated or durability may be inferior.

  There are no particular limitations on the method of charging and mixing cement, expansion material, etc., as long as it can be uniformly dispersed and mixed.

  In the present invention, cement or the like is charged, mixed, cast, cured, and a hardened cement body is prepared.

  Mixing and placing are in accordance with the method specified in JASS5 “Reinforced concrete work”, and pumping is controlled and compacted so that cold joints and jumpers do not occur. It is necessary to pay attention to driving and to prevent plastic cracks that occur before curing.

  The types of surface finish of the expansive concrete that has been placed include the materials used, concrete direct finish such as concrete finish floor and special surface finish floor, ordinary mortar finish, colored mortar finish, and synthetic resin finish. It is done.

  Roughening work, ruler work, and final finishing work are performed as surface finishing methods for each type of surface finishing of expanded concrete.

  Roughing work is, for example, using a scoop or a dragonfly to roughly level the unevenness of the surface of the expansive concrete that has been placed, and ruler work is to determine the height of the concrete. Yes, it affects the finishing accuracy and when the expanded concrete surface hardens to a certain extent, for example, using a dragonfly or a wooden trowel to smooth the surface of the expanded concrete. The work is performed while observing the state of hardening after the ruler, and is a work for obtaining a predetermined dimensional accuracy using a mechanical iron such as Trowell, a wooden iron, or a gold iron. There are cases where unevenness of the finished surface is corrected using a trowel.

  The flatness of each operation varies depending on the position, shape, dimensions, frequency, measurement method, etc. of the member. For example, the minimum value is defined as the F number method by ASTM, and the unevenness difference by the 3 m straight ruler is The roughening work is 13 mm or less, the ruler work is 8 mm or less, and the final finishing work is 5 mm or less.

A surface finishing method for a basic concrete direct finish floor will be described as an example of the type of surface finish of the placed expanded concrete.
In the concrete placement on the general floor, a portion having a large cross section such as a wall, a pillar, and a beam is placed first to the bottom of the floor, and the concrete is placed on the floor after waiting for the concrete to settle down. Then, before the concrete placed is hardened, the surface of the concrete is roughened to roughly level the unevenness, followed by a ruler work, and finally a final finishing work.
In the present invention, the drying shrinkage reducing agent is sprayed before the ruler operation and / or before the final finishing operation.

  If necessary, it is possible to perform tamping by striking the surface of the expansive concrete that has been laid with a square bar or the like while observing the degree of concrete congealing.

  Tamping is effective in preventing plastic cracks, and it is desirable that the tamping is carried out while it is still soft after it has been pressed once to crush the cracks.

The compressive strength of the hardened cement body is preferably 36 to 90 N / mm ² . If it is less than 36 N / mm ^2, it may be difficult to obtain the effect of the method of the present invention, and exceeding 90 N / mm ² is not currently required on the floor, unlike columns and beams.

The present invention is to spray the drying shrinkage reducing agent before the ruler work and / or before the final finishing work of the expanded concrete to perform the ruler work and the final finishing work. 10 to 300 g / m ^{2 in} terms of active ingredient before and / or 5 to 150 g / m ^{2 in} terms of active ingredient before final finishing work, and 10 times the dilution factor of water for drying shrinkage reducing agent This is a hardened cement body produced by the crack prevention method, and is a floor slab having a strength of 36 to 90 N / mm ² .

  Hereinafter, the present invention will be described based on experimental examples.

Experimental example 1
95 parts of cement, 5 parts of expanded material, 157 parts of fine aggregate, and 180 parts of coarse aggregate are put into a biaxial mixer. After 15 seconds of kneading, 34 parts of water and a water reducing agent are solidified to 100 parts of cement. 0.40 parts in terms of minutes were added and mixed for 120 seconds to prepare concrete.
The concrete slump flow was 58 cm, the air volume was 4.1%, and the temperature was 20 ° C.
Place the prepared concrete in a 10cm x 10cm x 40cm formwork, compact it to 13mm below the top surface, perform roughening work, and then spray the amount of dry shrinkage reducing agent shown in Table 1 with a sprayer. Then, use a square bar, perform ruler work, add concrete and compact it, spray the amount of dry shrinkage reducing agent shown in Table 1 on the surface in the same way, and use a wooden or gold trowel. Finishing work was performed and specimens were created.
Using the prepared specimen, compressive strength and drying shrinkage were measured, and the surface state after curing was evaluated. The results are also shown in Table 1.

<Materials used>
Cement: Ordinary Portland cement, commercially available, density 3.16 g / cm ³
Expansion material: Ettlingite-lime-based expansion material, commercial product, density 3.05 g / cm ³
Water-reducing agent: High-performance AE water-reducing agent, commercially available fine aggregate mainly composed of polycarboxylic acid: Crushed sand, mountain sand mixture 5mm below, density 2.64g / cm ³
Coarse aggregate: crushed stone, under 20 mm, density 2.71 g / cm ³
Drying shrinkage reducing agent a: Commercial product comprising a copolymer of low molecular weight ethylene oxide and propylene oxide as a component Dry shrinkage reducing agent b: Commercial product comprising an alkylene adduct of a lower alcohol as a component

<Measurement method>
Compressive strength: In accordance with JIS R 5201, using a 15cm x 30cm summit can, surface finishing, demolding after 24 hours, standard curing, change in measurement length: JIS A 1129-1 mortar and concrete length In accordance with the change test method and the comparator method, using a polyethylene sheet, cut the adhesion of the 10cm x 10cm x 40cm formwork and concrete, put the prepared concrete, and after surface finishing, the base length Measured, measured at 20 ° C, 60% RH, dry on one surface. Surface condition: Visually observed for microcracks and surface peeling, good condition with no fine cracks or thin skin, no fine cracks, but thin skin A thin-skinned one was generated, and a fine one was generated when a fine crack was generated.

  From Table 1, it can be seen that when the method of the present invention is used, a cement hardened body that is stable at an early age and has high crack resistance is obtained.

Experimental example 2
The same operation as in Experimental Example 1 was performed except that the drying shrinkage reducing agent shown in Table 2 was used. The results are also shown in Table 2.

Experimental example 3
Assuming a floor slab, a 2 m × 2 m × 0.2 m deep plywood formwork incorporating reinforcing bars was prepared, and concrete was prepared in the same manner as in Experimental Example 1.
Dilute the drying shrinkage reducing agent a 5 times and spray 40g / m ^{2 in} terms of active ingredient (stock solution) before ruler work, perform ruler and spray 20g / m ² in stock solution before final finishing work. The final finishing work was performed. Thereafter, cracks were observed after 24 hours.
For comparison, when a drying shrinkage reducing agent was not used, the same operation was performed when 120 g / m ² of a double solution of a drying shrinkage reducing agent and an emulsion curing agent was applied after finishing the surface.
In the comparative example using no drying shrinkage reducing agent, cracks with a crack width of 0.15 mm and a total length of 1.5 m were formed on the surface, and it became meaningless to apply the drying shrinkage reducing agent after curing. A comparative example of a drying shrinkage reducing agent and an emulsion curing agent produced cracks with a crack width of 0.05 mm on the surface, a total length of 1 m and a crack width of 0.15 mm on the surface, and a total length of 0.5 m. In the example in which sapphire was sprayed, no cracks were generated.

<Materials used>
Emulsion curing agent: Fine particle type acrylic emulsion on the market

  The method of the present invention applies to general structures such as walls, roof slabs and floor slabs, hydraulic structures such as aquariums and pools, and general structures and secondary products such as pavements, floor slabs, and box culverts. Used to prevent cracks.

Claims (3)

  When expansive concrete is placed, roughening work, ruler work, and final finishing work are performed, when the hardened expansive concrete is hardened, it is dried before the ruler work and before the final finish work. A method for preventing cracks on the surface of expanded concrete, in which a shrinkage reducing agent is sprayed before the expanded concrete hardens. The drying shrinkage-reducing agent, 10 to 300 g / m ² before rulers shear work in terms of active ingredient, and the final finishing operation before 5 to 150 g / m ² in terms of active ingredient are sprayed before the expansion concrete is hardened claims Item 2. The crack prevention method according to Item 1 .   The method for preventing cracks according to claim 1 or 2, wherein the dilution rate of water of the drying shrinkage reducing agent is 10 times or less.