JP2017186796A - Placing method of high strength concrete having freezing damage resistance - Google Patents

Abstract

[PROBLEMS] To provide a concrete placing method capable of sufficiently improving the frost resistance of the concrete without impairing the strength of the concrete when high strength concrete using fly ash cement is used in a cold district or the like. To provide. A method of transporting and carrying a fresh concrete material 1 comprising a cement material containing fly ash, an aggregate, and water from a concrete manufacturing site S1 to a concrete placing site S2, and concrete casting after loading. In the installation site S2, a step of adding and kneading the mousse-like foam lump 2 containing fine bubbles to the fresh concrete material 1 to obtain the fresh concrete 3 for placement, and the placement of the fresh concrete 3 for placement in the concrete placement site S2 And a step of placing at the placement point SP1 of the concrete. [Selection] Figure 1

Description

  The present invention relates to a method for placing high-strength concrete having frost resistance (hereinafter also referred to as “frost-resistant high-strength concrete”). In this specification, high-strength concrete with frost damage resistance (frost-resistant high-strength concrete) achieves both high levels of strength improvement by adding fly ash and frost damage resistance by entrainment of fine bubbles. The concrete which can form the hardened concrete hardened body shall be said.

  Fly ash produced in large quantities as a by-product from a pulverized coal fired boiler at a thermal power plant, when used as a cement admixture, the concrete structure becomes dense and strength (especially long-term strength) increases, and the particle size is spherical. Therefore, the fresh properties are also improved by the ball bearing effect. For this reason, high-strength concrete using cement material containing fly ash (hereinafter also referred to as “fly ash cement”) is widely used in various concrete structures, especially in mass concrete structures such as dams and bridges. (See Patent Document 1).

  Here, for example, dams, which are representative examples of mass concrete structures, are often constructed in cold regions. In this case, the high-strength concrete is required to be a concrete having excellent frost damage resistance in addition to the high strength described above.

  Regarding the frost damage resistance of concrete, it is known that a concrete having excellent frost damage resistance can be obtained by forming fine bubbles with an appropriate particle diameter in the range of an appropriate amount of air in the concrete (non-freezing damage). Patent Document 1). Moreover, as a method for forming such bubbles in concrete, for example, a method of adjusting the diameter of fine bubbles in concrete to about 0.25 mm or less by mixing AE agent or AE water reducing agent into fresh concrete. It is disclosed (see Patent Document 2).

  However, when high-strength concrete using fly ash cement is used in cold regions, the fly ash adsorbs the AE agent or the AE water reducing agent, so that fine bubbles for improving the frost damage resistance can be obtained. It has been a problem that stable formation is inhibited. This is considered to be due to adsorption of unburned carbon contained in fly ash and AE agent. In this case, compared to the case where ordinary cement is used as the cement material, the equivalent frost resistance performance cannot be secured unless a large amount of AE agent is added. On the other hand, the addition of a large amount of AE agent is stable. As a result, there was a risk that the amount of air would become excessive and the strength of the concrete would be reduced in a state where it was difficult to form bubbles.

Japanese Patent Laid-Open No. 9-25143 JP-A-10-259050

Proceedings of Concrete Engineering Vol.23 No.1 Jan 2012 Consideration on the relationship between the bubble structure of concrete and frost resistance

  The present invention relates to a method for placing concrete capable of sufficiently improving the frost resistance of the concrete without impairing the strength of the concrete when high strength concrete using fly ash cement is used in a cold district or the like. It is an issue to provide.

  The present inventor changed the addition of AE agent and the like to fresh concrete containing fly ash cement to a method of premixing this in a concrete factory, and included mousse containing fine bubbles. It has been found that the frost damage resistance of the above high-strength concrete can be stably improved by performing a method of kneading and adding foam-like foam blocks to the fresh concrete immediately before placing it. The present invention has been completed. Specifically, the present invention provides the following methods.

  (1) A method of placing high-strength concrete having frost resistance, and a fresh concrete material containing fly ash-containing cement, aggregate, and water from a concrete production site to a concrete placement site A step of transporting and transporting to the concrete, and a step of adding and kneading a mousse-like foam lump containing fine bubbles to the fresh concrete material at the concrete placement site after the transport to obtain the fresh concrete for placement. A method for placing concrete, comprising: placing fresh concrete for installation at a placement point in the concrete placement site.

  According to the invention of (1), frost damage resistance can be stably improved while the strength of fresh concrete for high-strength concrete containing fly ash cement is reliably maintained. Thereby, the quality stability concerning the intensity | strength and frost damage resistance of the hardened concrete body which consists of high-strength concrete containing fly ash cement can be improved significantly.

  (2) The concrete placing method according to (1), wherein the aggregate is an aggregate having alkali aggregate reactivity.

  According to the invention of (2), due to the excellent alkali-resistant aggregate performance of fly ash, even in a cold region or the like, it is necessary to use an aggregate having an alkali-aggregate reaction. The effect of the invention of (1) can be enjoyed stably.

  (3) The concrete placement method according to (1) or (2), wherein the concrete production site is composed of a plurality of production plants that exist in different places.

  According to the invention of (3), even when fresh concrete is carried in from a plurality of manufacturing plants, the formation of fine bubbles in the fresh concrete immediately before final placement can be stably controlled. This creates a great deal of flexibility in the combination of concrete transport and carry-in routes connecting the fresh concrete production site and the concrete placement site. As a result, the geographical restriction between the production site of the fresh concrete and the concrete placement site in the implementation of the invention of (1) or (2) is eliminated, and the economics are more advantageous (1) Or the possibility that the invention of (2) can be enjoyed remarkably expands.

  (4) The concrete placement method according to any one of (1) to (3), wherein a transport distance of the fresh concrete material from the concrete production site to the concrete placement site is 5 km or more.

  According to the invention of (4), even if the transport distance from the concrete manufacturing site to the concrete placement site is a long distance of a certain value or more, the implementation of any of the inventions of (1) to (3) It is possible to eliminate the geographical restriction between the production site of fresh concrete and the concrete placement site, and enjoy the effect stably. In particular, it has an advantageous effect in construction in mountainous areas where it is difficult to secure a concrete production site near the concrete placement site.

  (5) The concrete placement method according to any one of (1) to (4), wherein the concrete placement site is a cold district having an annual minimum temperature of −5 ° C. or less.

  According to the invention of (5), it is possible to stably enjoy the effects of any of the inventions of (1) to (4) even in a construction site where the annual minimum temperature is a cold region having a predetermined temperature or less. it can. Thereby, especially advantageous effects can be enjoyed in the construction of a huge dam in a cold region.

  As described above, according to the present invention, when high-strength concrete using fly ash cement is used in a cold district or the like, the frost damage resistance of the concrete can be sufficiently improved without impairing the strength of the concrete. It is possible to provide a method for placing concrete that can be used.

It is a chart figure which shows the embodiment of the placement method of the frost-proof high-strength concrete of this invention. It is a graph which shows the test result which concerns on the frost damage resistance of the frost damage high strength concrete hardening body which can be formed with the placement method of the frost resistance high strength concrete of this invention. It is a graph which shows the test result which concerns on suppression of alkali-aggregate reaction in the frost-resistant high-strength concrete hardening body which can be formed with the placement method of the frost-proof high-strength concrete of this invention. It is a graph which shows the test result which concerns on the intensity | strength of the frost damage resistant high intensity | strength concrete hardening body which can be formed with the placement method of the frost damage resistant high intensity | strength concrete of this invention.

  Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiment.

<Frost-resistant high-strength concrete>
In this specification, a cement material containing fly ash (fly ash cement) is used as a binder, and the amount of fine bubbles having a diameter of 0.01 mm to 0.3 mm is 0.2 volume. % Of concrete hardened body is said to be “frost-resistant high-strength concrete hardened body”. Moreover, the fresh concrete which can form this frost-proof high-strength concrete hardening body shall be called "frost-proof high-strength concrete."

[Frost-resistant high-strength concrete]
The frost-resistant high-strength concrete in the present invention is a fresh concrete using fly ash cement, and the amount of fine bubbles forms a hardened concrete body with a volume of 0.2% by volume or more. The amount of air in the concrete is preferably 3.5% or more and 6.0% or less. In addition, about the method of measuring the volume ratio etc. of the bubble part in fresh concrete, conventionally well-known methods, such as the buoyancy method which analyzes from the time-dependent change of the buoyancy by the bubble which rose in water, are employable.

(Cement material)
Cement material containing fly ash (fly ash cement) is used as a binder in the frost-resistant high-strength concrete. Although content of the fly ash in a cement material is not specifically limited, It is preferable that they are 5 weight% or more and 30 weight% or less in the internal division of cement. The fly ash used in the present invention is preferably concrete fly ash type I, type II, type III, and type IV described in JIS A 6201, but there is no particular limitation. So-called general coal ash in a broad sense including fly ash including coarse particles and cinder ash can also be used. Blaine value of the fly ash is preferably ^{2,500~10,000cm 2 / g, 3,500~6,500cm 2 /} g is more preferable. If it is less than 2,500 cm ² / g, the initial strength of the concrete may be insufficient. If it exceeds 10,000 cm ² / g, the strength improvement rate will be poor, and the concrete will become viscous, resulting in impact. This is because it is disadvantageous in that the load required for pumping during installation is increased.

(aggregate)
Aggregates used in the present invention include ordinary aggregates such as sand, gravel and crushed stone used in ordinary concrete, and artificial aggregates mainly composed of fly ash, anti-fluorite, expanded shale, etc. It can be used without limitation. In particular, fly ash contained as an essential component in the binder has excellent alkali-resistant aggregate performance, so it is necessary to select an aggregate that causes an alkali-aggregate reaction such as andesite and chart in cold regions. Even under conditions that cannot be obtained, the above-described effects of the present invention can be enjoyed stably.

(Mousse foam lump)
A mousse-like foam lump containing fine bubbles can be produced by gas-liquid mixing a foaming agent solution and compressed air. The foaming agent solution contains at least an air entraining agent, a capsule base, and water, and may further contain a foam suppressant.

  The air entraining agent contained in the foaming agent solution includes (1) fatty acid soap, alkenyl succinic acid soap, alkyl sulfonate, alkylbenzene sulfonate, dialkyl sulfosuccinate salt, (poly) oxyalkylene alkyl ether sulfonate , (Poly) oxyalkylene alkyl benzene sulfonate, alkyl sulfate, salt of natural oil and fat sulfate, (poly) oxyalkylene alkyl ether sulfate, alkyl phosphate ester salt, (poly) oxyalkylene alkyl ether phosphate salt Anionic surfactants such as (2) polyoxyalkylene alkyl ether, polyoxyalkylene alkyl phenyl ether, polyoxyalkylene alkyl ester, polyoxyalkylene castor oil, polyoxyalkylene hydrogenated castor oil, polio Nonionic surfactants having polyoxyalkylene groups such as salkylenealkylaminoethers, (3) Polyionic alcohol partial ester type nonions such as sorbitan monolaurate, sorbitan trioleate, glycerin monolaurate, diglycerin dilaurate Surfactants, (4) amphoteric surfactants such as alkyldimethylbetaines and alkylimidazoline betaine compounds, (5) cationic surfactants such as alkyltrimethylammonium salts, alkyldimethylethylammonium salts, alkylimidazolinium salts, etc. Can be mentioned. Of these, alkylbenzene sulfonate, alkyl sulfate, and (poly) oxyalkylene alkyl ether sulfate are preferable.

  Capsule bases contained in the foaming agent solution include (1) synthetic polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, (2) natural polymers such as gelatin, casein, starch, guar gum, xanthan gum, 3) Semi-synthetic polymers such as methylcellulose, sodium carboxymethylcellulose, soluble starch, alginate and the like. Among these, polyvinyl alcohol and methyl cellulose are preferable.

  Antifoaming agents contained in the foaming agent solution include polyoxyalkylene alkyl ether antifoaming agents, polyoxyalkylene fatty acid ester antifoaming agents, polyoxyethylene polyoxypropylene glycol antifoaming agents, and silicone antifoaming agents. Etc. Among these, polyoxyalkylene fatty acid ester foam suppressors are preferable.

  A mousse-like foam having the desired properties by mixing the foaming agent solution in which the content of each of the above components (air entraining agent and capsule base, and optionally a foam suppressor) is adjusted with compressed air. A mass can be made.

(Mixing ratio)
As for the blending ratio of frost-resistant high-strength concrete, as long as it is a fresh concrete using fly ash cement as a binder and kneading the above mousse-like foam, it can blend fine bubbles. It is not particularly limited, and may be appropriately set in consideration of the use and quality required at the time of becoming a concrete hardened body. Specifically, the water cement ratio is 40 to 60%, the fine aggregate rate (s / a) is 20 to 60%, the unit water amount is 110 to 185 kg / m ³ , the unit cement material amount is 210 to 450 kg / m ³ , and the unit fine bone A range of a material amount of 450 to 1000 kg / m ³ can be exemplified as a preferable blending example of “fresh concrete material” blended at a concrete manufacturing site.

  However, in the frost-resistant high-strength concrete placing method of the present invention, the above-mentioned “mousse-like foam lump” is used, and this is transported from the concrete manufacturing site to the concrete placing site immediately before placing. "Fresh concrete for placement" is obtained by adding to the concrete material and kneading.

  Although it is possible to add additives for forming fine bubbles only at the concrete placement site, general AE agents, AE water reducing agents, high performance AE water reducing agents and other admixtures are used in the final stage. It is preferable to add an appropriate amount in advance in the fresh concrete stage in such a range that the amount of air immediately before placing is not excessive. In addition, just before placing, fine adjustment of the final air volume is made by adding “mouse-like lump containing fine bubbles” to avoid the risk of strength reduction due to excessive air volume. In addition, it is possible to improve the quality stability of the frost-resistant high-strength concrete hardened body. Further, since the effect of the present invention can be fully enjoyed while suppressing the amount of the relatively expensive “mouse-like foam lump containing fine bubbles” to a necessary minimum amount, this is also economical. It is more preferable to use such an embodiment.

[Frost-resistant high-strength concrete hardened body]
The frost damage resistant high-strength concrete cured body can be obtained by curing the above-mentioned fresh concrete. The frost-resistant high-strength concrete hardened body is so-called cellular concrete in which a large number of cellular parts are dispersedly formed in cement. In addition, it is preferable that the bubble space | interval coefficient of a hardened concrete body is 0.4 mm or less, More preferably, it is 0.2 mm or less. By setting the bubble spacing coefficient in the above range, the freeze-thaw resistance of the frost-resistant high-strength concrete hardened body can be further improved. About the method of measuring the volume ratio of the bubble part, the bubble interval coefficient, etc. in the frost damage resistant high-strength concrete hardened body, for example, according to “Method for measuring bubble parameters of ASTM C457 hardened concrete with a microscope” which is a known method Can do.

<Method of placing frost-resistant high-strength concrete>
The process from the preparation of a conventional general fresh concrete to the placement is as follows. First, fresh concrete is mixed mainly in a production plant such as a ready-mixed concrete factory, that is, a “concrete production site”. Then, the blended fresh concrete is transported to a “concrete placement site” by an agitator vehicle. Then, the prepared fresh concrete that has arrived at the “concrete placement site” is transported and placed to the “placement site” by some pumping means at the site. For high-strength fresh concrete containing fly ash, the process from blending to placing was conventionally performed by this method.

  On the other hand, the frost-resistant high-strength concrete placement method of the present invention is a part of the preparation of fresh concrete that has been conventionally performed at the “concrete manufacturing site”, specifically, it is necessary in the fresh concrete. It is characterized in that the process for entraining air is performed by a method of adding and kneading “mousse-like foam lump containing fine bubbles” immediately before placing in the “concrete placing site”. Hereinafter, with reference to FIG. 1, the embodiment of the frost damage resistant high-strength concrete placing method of the present invention and the details of each step will be described.

[Process of transporting (st1) and carrying in (st2) fresh concrete material 1 from concrete production site S1 to concrete placement site S2]
The transport (st1) and the carry-in (st2) of the fresh concrete material 1 from the concrete production site S1 to the concrete placing site S2 can be performed by an agitator vehicle that has been widely used conventionally. This agitator car is a freight car equipped with a mixing drum in the loading platform that can transport the ready-mixed concrete with agitation, and there is no big difference in its function. Yes, depending on the application.

  The method for placing frost-resistant high-strength concrete according to the present invention is a process in which the final blending of the fresh concrete 3 for placement is performed in the concrete placement site S2 instead of the concrete production site S1, and therefore the concrete production site S1. However, even if it consists of multiple manufacturing plants that are located in different locations, it is possible to eliminate the variation in the blending ratio of fresh concrete at multiple concrete manufacturing sites in the final blending stage immediately before placing. This is possible, and the quality stability of the fresh concrete 3 for placement can be maintained.

  In addition, the method of placing the frost-resistant high-strength concrete of the present invention is different from the case of transporting fresh concrete prepared in advance by mixing AE agent or the like at the concrete production site to the concrete placement site. There is no risk of the bubble content decreasing or disappearing. Therefore, it is a particularly advantageous method when long-distance transportation is required.

[In the concrete placement site S2, the mousse-like foam lump 2 containing fine bubbles is added to the fresh concrete material 1 and kneaded to obtain the fresh concrete 3 for placement]
Addition of mousse-like foam 2 (st3) to the fresh concrete material 1 (st2) carried into the concrete placement site S2 by transportation (st1), and kneading them (st4) It is possible to obtain a fresh concrete 3 for casting in which fine bubbles that exhibit an excellent effect are dispersed and formed. The mousse-like foam lump 2 is preferably mixed so as to have a ratio of 0.1 kg or more and 20 kg or less per 1 m ^{3 of} fresh concrete material 1, and more preferably mixed so as to be 1 kg or more and 5 kg or less.

[(Placing the pouring fresh concrete 3 at the placing spot SP1 in the concrete placing site S2]
In the concrete placement site S2, the fresh concrete 3 for placement obtained in the above process is transported to a placement point SP1 in the site by some transport means and placed (st5). The fresh concrete 3 for placing is cast (st5) to obtain a desired hardened concrete. Placing (st5) can be performed by a conventionally known method. For example, after placing in a mold previously coated with a release agent, a hardened concrete can be obtained by steam curing.

  The frost-resistant high-strength concrete placing method of the present invention is a high-strength concrete using fly ash cement, and can form a hardened concrete body that is also excellent in frost-proof resistance. Therefore, when the placement site S2 is a cold district where the annual minimum temperature is −5 ° C. or less (the Architectural Institute JASS5 standard), the construction site has a particularly advantageous effect in the construction of mass concrete structures. It is something that demonstrates.

  Hereinafter, the method for placing the frost damage resistant high strength fresh concrete of the present invention will be described in detail with reference to examples. In addition, this invention is not limited to the Example shown below.

(Composition of fresh concrete material for placement)
As the fresh concrete for placement in Examples and Comparative Examples, those prepared as shown in Table 1 below using each material described below were used. Regarding the amount of air, in Example and Comparative Example 1, 3.5% air was entrained by the AE agent, and after arrival at the site, 1.0% air by the mousse-like foam (Ad1). Was added afterwards. The slump value of each fresh concrete material was adjusted to 8 cm. In Table 1, the blending ratio of the mousse-like foam lump (Ad1) indicates the volume ratio (%) with respect to the whole fresh concrete material at the time of arrival of the concrete, and the AE water reducing agent (Ad2) and AE agent (Ad3). ) Indicates a volume ratio (%) to cement (cement material 1 or cement material 2 below).

Water (W): supernatant water, density: 1.00 g / cm ³
Cement material 1 (FB): fly ash cement type B, density: 2.85 g / cm ³
Cement material 2 (OPC): ordinary Portland cement, density: 3.16 g / cm ³
Fine aggregate (S): Crushed sand Surface dry density 2.65 g / cm ³ (2.5 mm or less), coarse particle ratio 2.67
Coarse aggregate (G): crushed stone 20 mm to 5 mm, surface dry density: 2.65 g / cm ³ , actual volume ratio: 60.0
Moose foam lump (Ad1): Preform type AE agent (MAC REIT, manufactured by Milcon)
AE water reducing agent (Ad2): (main components: lignin sulfonate and oxycarboxylate)
AE agent (Ad3): (main component: modified rosin acid compound anionic surfactant)

(Test on frost resistance)
In order to verify the performance related to the frost damage resistance of each of the fresh concretes for placement in Examples and Comparative Examples, a test on freeze-thaw resistance was performed according to the JIS A 1148-A method. The relationship between the freeze-thaw cycle and the relative dynamic elastic modulus is shown in FIG. Comparative Example 1 using ordinary Portland cement and post-added mousse foam has the highest resistance to freezing and thawing, Comparative Example 4 using ordinary AE agent for ordinary Portland cement, and mousse foam for fly ash cement The relative kinematic elastic modulus of the case of the example in which was added later was approximately the same. In ordinary Portland cement using a normal AE agent, the relative dynamic elastic modulus of 300 cycles was 65%. In the case where a normal AE agent was used for fly ash cement, the measurement of the relative kinematic modulus became impossible at the 240th cycle, and the predetermined freeze-thaw resistance was not satisfied.

(Test on suppression of alkali-aggregate reaction)
In order to verify the inhibitory effect on the alkali-aggregate reaction of each of the fresh concretes for placement in Examples and Comparative Examples, a test on alkali silica reactivity was performed according to a concrete method (JCI AAR-3 (1987)). The relationship between the promotion period and the expansion rate is shown in FIG. In Comparative Example 1 and Comparative Example 4 using ordinary Portland cement, the expansion rate was 0.1% or more, and it was judged as having antkari silica reactivity. About the Example using a fly ash cement, the comparative example 2, and the comparative example 3, all became 26% or less and the expansion rate became 0.1% or less, and it was determined that there is no problem as alkali silica reactivity.

(Test on compressive strength)
FIG. 4 shows the test results of the compressive strength at the age of 28 days for each of the fresh concrete for placement in Examples and Comparative Examples. In Comparative Example 3 in which the air amount was 6.5% with the AE agent, the strength was significantly reduced, and it was confirmed that the strength was reduced by about 10% compared to the other examples.

  Table 2 below shows the evaluation results regarding the above test results for each of the fresh concrete for placement in Examples and Comparative Examples. Items that can be judged as acceptable frost-resistant high-strength concrete for use in cold regions with an annual minimum temperature of -5 ° C or lower (Architectural Institute JASS5 standard) are marked with “○”. I wrote.

  From the above results, according to the present invention, when high-strength concrete using fly ash cement is used in a cold district or the like, the frost damage resistance of the concrete can be sufficiently improved without impairing the strength of the concrete. You can see that

DESCRIPTION OF SYMBOLS 1 Fresh concrete material 2 Moose foam lump 3 Fresh concrete for placement S1 Concrete production site S2 Concrete placement site

Claims (5)

A method of placing high-strength concrete having frost resistance,
A process of transporting and carrying a fresh concrete material comprising a cement material containing fly ash, an aggregate, and water from a concrete manufacturing site to a concrete placing site;
In the concrete placement site after carrying in, the fresh concrete material is added and kneaded with a mousse-like foam lump containing fine bubbles to obtain fresh concrete for placement;
Placing the fresh concrete for placement at a placement site in the concrete placement site, and placing concrete.   The concrete placing method according to claim 1, wherein the aggregate is an aggregate having alkali aggregate reactivity.   The method for placing concrete according to claim 1 or 2, comprising a plurality of production plants in which the concrete production sites are located at different locations.   The concrete placement method according to any one of claims 1 to 3, wherein a transport distance of the fresh concrete material from the concrete production site to the concrete placement site is 5 km or more.   The concrete placement method according to any one of claims 1 to 4, wherein the concrete placement site is a cold district having an annual minimum temperature of -5 ° C or lower.

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