JP2019048742A - High strength concrete and production method of high strength concrete - Google Patents

Abstract

To provide high strength concrete in which a form removing material age is short, and a production method of high strength concrete.SOLUTION: High strength concrete 1 of the present invention is the high strength concrete with design standard strength of 100 N/mmor more, and includes water W, a binder B made of cement C and admixture A, fine aggregates S, and coarse aggregates G, in which a water-binder ratio W/B is 30% or less; the cement C is high early strength portland cement; and the admixture A includes silica fume A1, blast furnace slag fine powder A2, and gypsum-based component A3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to high-strength concrete and a method for producing high-strength concrete.

Conventionally, there is a PC (prestressed concrete) girder bridge having a main girder formed by a high-strength fiber reinforced mortar having a design standard strength of 100 N / mm ² or more (see Patent Document 1).
The main girder formed by conventional high-strength fiber reinforced mortar is a precast segment that is manufactured in advance at factories, etc., and high-strength fiber reinforced mortar is mixed, and then high-strength fiber reinforced mortar is placed in the formwork. Thus, it was manufactured by removing the mold after curing until a predetermined strength was developed.
In addition, the main girder formed by conventional high-strength fiber reinforced mortar has a curing time for developing strength, that is, the unframed material age is 4-5 days, and the main girder is produced in one production line The standard speed was about one per week.

JP 2004-270382 A

However, the construction period of a project for constructing a structure is costly depending on the length of the construction period. The construction period at the site of the PC girder bridge is greatly affected by the delivery cycle of the main girder to the site, that is, the age of the main girder in the factory, which has the same cycle as the delivery cycle, so the aging time of the girder is shortened. It is a problem to do.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-strength concrete with a short frame-free material age and a method for producing the high-strength concrete.

In order to achieve the above object, the following configuration is used.
(1) The high-strength concrete of the present invention is a high-strength concrete having a design standard strength of 100 N / mm ² or more, and the high-strength concrete includes water, a binder composed of cement and an admixture, and a fine aggregate. And a coarse aggregate, the water binder ratio is 30% or less, the cement is an early-strength Portland cement, and the admixture comprises silica fume, blast furnace slag fine powder, and a gypsum-based component. Including.
(2) In the configuration of (1) above, the high-strength concrete used for the precast segment is provided with a reinforcing bar.
(3) In the configuration of (1) or (2) above, high-strength concrete used for a precast segment constituting a bridge girder of a prestressed concrete bridge, comprising reinforcing bars and PC steel material, A plurality of precast segments are arranged side by side, and prestress is introduced by the PC steel material.
(4) In the configuration of (3) above, the ratio of the span to the bridge girder height is 25 or more and 40 or less.
(5) The method for producing high-strength concrete having the structure according to any one of (1) to (4) above is a method for producing high-strength concrete used for a precast segment constituting a bridge girder of a prestressed concrete bridge. A production process for producing fresh concrete by mixing materials contained in concrete, a placing process for placing the fresh concrete inside a mold, a steam curing process for steam curing the fresh concrete, and the mold And a de-framed step of de-framed at 2 days of unframed material.
(6) In the steam curing step of the configuration of (5) above, the fresh concrete outside air is held at a reference temperature, then heated, held at the maximum temperature, and then cooled.
(7) In the steam curing step having the configuration of (6), a temperature drop rate that is a temperature drop per unit time in the temperature drop is smaller than a temperature rise rate that is a temperature rise per unit time in the temperature rise.
(8) In the steam curing step having the configuration of (6) or (7), the holding time at the maximum temperature is longer than the holding time at the reference temperature.
(9) In the steam curing step having the configuration of (5), the temperature of the outside air is controlled so that the temperature difference between the temperature of the fresh concrete and the temperature of the outside air is maintained at 20 ° C. or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of high strength concrete with a short unframed material age and high strength concrete can be provided.

It is the perspective view which looked up at the PC girder bridge using the high strength concrete which concerns on embodiment from the bottom. It is a figure which shows the relationship between the age (time) of fresh concrete (high-strength concrete) which passed through the steam curing process, and the temperature (degreeC) of external air. It is a figure which shows the relationship between the age (day) of concrete (high-strength concrete) which passed through the steam curing process, and compressive strength (N / mm < ² >).

(Embodiment)
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings. In addition, the same number or code | symbol is attached | subjected to the same element through the whole description of embodiment. In the following, fresh concrete means concrete that is in a state from immediately after mixing the materials until the setting starts.

  FIG. 1 is a perspective view of a PC girder bridge 100 using the high-strength concrete 1 according to the embodiment as viewed from below. In addition, in FIG. 1, illustration of the pier is abbreviate | omitted.

  The high-strength concrete 1 which concerns on embodiment can be used for the main girder 10 which comprises the PC girder bridge 100 of low girder height as shown in FIG. A plurality of the main girders 10 are arranged in a direction perpendicular to the bridge axis, and are arranged along the bridge axis direction. In addition, cast-in-place concrete 20 is placed between adjacent main girders 10. By cast-in-place concrete 20, adjacent main girders 10 are structurally integrated. A roadway pavement 30, a sidewalk pavement 31, and the like are laid on the plurality of main girders 10. In addition, in FIG. 1, although the cross section of the main girder 10 is substantially T-shaped, it is not restricted to this, A substantially I shape may be sufficient and a hollow shape may be sufficient.

  High-strength concrete 1 can be used for a precast segment. Moreover, the high strength concrete 1 is provided with a reinforcing bar. Therefore, a large structure can be constructed by assembling a high-strength precast segment, and the construction schedule can be shortened.

Moreover, the high-strength concrete 1 is used for the precast segment which comprises the main girder 10 used as the bridge girder of a prestressed concrete bridge. The high-strength concrete 1 includes reinforcing bars and PC steel, and the main girder 10 serving as a bridge girder is formed in a state where a plurality of precast segments are arranged, and prestress is introduced by the PC steel. Therefore, the high compressive force by prestress can be endured and the span (span length) of the PC girder bridge 100 can be lengthened.
And the ratio of the span with respect to the girder height of the main girder 10 serving as a bridge girder can be 25 or more and 40 or less. Thereby, the ratio of the span with respect to the girder height of the main girder 10 serving as a bridge girder is large, and the PC girder bridge 100 having a low girder height can be realized.

The high-strength concrete 1 has a design standard strength of 100 N / mm ² or more. The compounding strength is 120 N / mm ² and the coefficient of variation is 10%. Thus, since the high-strength concrete 1 is high-strength concrete, the main girder 10 having high bending rigidity can be formed without increasing the girder height. And it can apply to the low girder height PC bridge (prestressed concrete bridge whose girder height is 1/30 or less of a span) which can respond to the place where girder height is restricted by a construction limit.

  The slump flow of the high-strength concrete 1 is set to 65 cm ± 5 cm in order to ensure the self-filling property having both fluidity and material separation resistance.

  The amount of air is set to 2.0% ± 1.5% in consideration of strength development.

  The high-strength concrete 1 contains water W, a binder B made of cement C and an admixture A, a fine aggregate S, and a coarse aggregate G. In addition, it is not essential to mix a fiber. Thus, since the high intensity | strength of the high strength concrete 1 is realizable, without mixing a fiber, the increase in the cost resulting from mixing a fiber can be suppressed.

  Further, the water binder ratio W / B of the high-strength concrete 1, that is, the weight ratio of the water W and the binder B is 30% or less. Further, the water binder ratio W / B is desirably 20% to 25% in order to ensure higher compressive strength and durability. Thus, since the ratio B / B of water binder is low and the ratio of the cement C with respect to the water W is high, it can be set as the high strength concrete 1 which can express high intensity | strength.

  Cement C is an early-strength Portland cement. Further, the proportion of alite which is one of the clinker constituent compounds in the early strong Portland cement is preferably about 65%, and more preferably 50% or more.

  Here, a general high-strength concrete has a high heat of hydration due to a low water cement ratio or water binder ratio W / B, and therefore, such as temperature stress cracking due to excessively high temperature of fresh concrete. In order to reduce the occurrence of defects, low-temperature cement with a low proportion of alite (about 30%) is often used as a cement for general high-strength concrete. However, if low heat cement is used for high-strength concrete, the time of hydration heat generation and initial strength development are delayed. Therefore, the high-strength concrete 1 according to the present embodiment uses early strong Portland cement having a high proportion of alite as the cement C, and accelerates the time of hydration heat generation and initial strength development.

  Admixture A includes silica fume A1, blast furnace slag fine powder A2, and gypsum-based component A3. As described above, the high-strength concrete 1 includes the admixture A composed of a combination of special kinds of materials in the binder B, so that the early-strength Portland cement is used as the cement C used for the binder B of the high-strength concrete 1. Even if the use of a coolant is used, the viscosity at the time of freshness can be suppressed while ensuring high fluidity, self-shrinkage can be suppressed, and the peak temperature due to hydration heat generation can be reduced. Therefore, the high-strength concrete 1 is high-strength, has rapid strength development, has excellent workability at the time of freshness, and can suppress generation of cracks after curing and cracks due to temperature stress. The admixture A may be premixed in a state where silica fume A1, blast furnace slag fine powder A2, and gypsum-based component A3 are mixed in advance.

  Specifically, the admixture A contains 20 to 300 parts by weight of silica fume A1, 20 to 300 parts by weight of blast furnace slag fine powder A2, and 100 parts by weight of gypsum component A3. Is desirable. Furthermore, you may include an expansion material as needed. Thereby, even if an early-strength Portland cement is used for the high-strength concrete 1, the viscosity at the time of freshness can be suppressed, the rapid temperature rise by hydration heat_generation | fever can be suppressed, and self-shrinkage can be suppressed. Although the kind of silica fume A1 is not specified, what suits JIS A 6207 "silica fume for concrete" is preferable. The type and fineness of the blast furnace slag fine powder A2 are not specified, but those conforming to JIS A 6206 “Blast furnace slag fine powder for concrete” are preferable. A blast furnace slag fine powder having a small specific surface area of 3000 or 4000 is particularly preferred from the viewpoint of suppression of temperature rise due to hydration heat generation and self-shrinkage. The gypsum-based composition A3 is preferably anhydrous gypsum.

  The replacement ratio A / B of the admixture A to the binder B obtained by adding the admixture A to the cement C is preferably 10% to 25%. Further, the substitution rate A / B is desirably about 20%. The greater the substitution rate A / B, the lower the viscosity during freshness and the better the workability. However, if the substitution rate A / B exceeds 25%, there is a possibility that defects such as cracks may occur in the cured concrete. There is.

The high-strength concrete 1 preferably contains a shrinkage reducing agent. Thereby, the self-shrinkage of the high-strength concrete 1 resulting from the low water binder ratio W / B can be suppressed.
Moreover, it is preferable that the high strength concrete 1 contains a high performance water reducing agent. Thereby, the fluidity | liquidity at the time of fresh is securable. It is good also as a high performance AE water reducing agent instead of a high performance water reducing agent.

  By blending the high-strength concrete 1 as described above, the unframed material age can be shortened compared to the conventional unframed material age of 4 to 5 days. The age (de-frame time, steam curing period) can be set to 2 days, and the delivery cycle to the site can be shortened.

Next, the case where the manufacturing method of the high strength concrete 1 which concerns on this embodiment is used for the precast segment which comprises the bridge girder of a prestressed concrete bridge is demonstrated to an example.
The manufacturing method of the high-strength concrete 1 includes the above-described materials contained in the high-strength concrete 1, that is, at least the water W, the binder B composed of the cement C and the admixture A, the fine aggregate S, and the coarse aggregate. G is mixed to produce a fresh concrete, a casting process in which the fresh concrete is placed inside the mold, a steam curing process in which the fresh concrete is steam-cured, and the mold is unframed. And a de-framed process of de-framed at 2 days of age.
In this way, the unframed material age can be shortened by blending and manufacturing the high-strength concrete 1 as described above.

  In addition, in the steam curing process, the fresh concrete outside air is held (preliminary) at a reference temperature (20 ° C. or more and less than 35 ° C.), then heated (for example, 15 ° C./hour), and the maximum temperature (for example, 50 ° C.) and then the temperature is lowered (for example, 30 ° C./26 hours). Thus, in the steam curing process, the outside air is changed in temperature according to the temperature change caused by the hydration heat generation of the fresh concrete, so that the hardening by the hydration reaction can be promoted and the strength can be expressed early.

Here, the holding (preliminary) at the reference temperature is maintained at a room temperature until the setting is started to some extent, specifically, at the start of setting, that is, until the start of hydration heat generation. Therefore, it is possible to suppress adverse effects on strength development and durability caused by raising the outside air to a high temperature by steam curing with respect to fresh concrete just placed. In addition, it is preferable that the reference temperature at the time of the introduction is 20 ° C. or more and less than 35 ° C. The reason why the temperature is lower than 35 ° C. is that it is confirmed that there is no problem in strength development and durability if the concrete is lower than 35 ° C.
In addition, in the method of manufacturing the high-strength concrete 1 according to the present embodiment, the holding at the reference temperature (preliminary) is different from the normal case, and the holding at the reference temperature is long (about approximately) until the setting starts (at the start of hydration exotherm). 9 hours) (previous), and the temperature of the outside air in the steam curing is raised at the same time as the hydration of the concrete starts. In this way, since it is maintained at the reference temperature longer than usual (preliminary), it is possible to prevent the adverse effect of the setting delay caused by using a large amount of the high-performance water reducing agent in the high-strength concrete 1.

  In the steam curing step, it is preferable that the temperature decrease rate, which is the temperature drop per unit time in the temperature decrease, is smaller than the temperature increase rate, which is the temperature increase per unit time in the temperature increase. Thereby, while promoting the hardening by the hydration reaction of concrete, the bad influence by a temperature contraction can be suppressed and intensity | strength can be expressed early.

  In the steam curing process, the holding time at the maximum temperature is preferably longer than the holding time at the reference temperature. Thereby, while promoting the hardening by the hydration reaction of concrete, the bad influence by a temperature contraction can be suppressed more, and intensity | strength can be stably expressed early.

  Furthermore, in the steam curing process, it is preferable to control the temperature of the outside air so that the temperature difference between the concrete temperature and the outside air temperature is maintained at 20 ° C. or less. In addition, the temperature of concrete here may be a surface temperature. Further, it is desirable that the temperature change curve of the outside air is substantially similar to the temperature change curve of the concrete temperature. The temperature of the outside air may be set in advance based on the prediction of the temperature change of the concrete by temperature stress analysis, and based on the temperature difference between the concrete temperature and the temperature of the outside air, the temperature difference will be zero. The feedback control may be performed in real time. As a result, the temperature difference between the concrete temperature and the outside air temperature in the steam curing process can be minimized, adverse effects such as cracks generated according to the temperature difference can be suppressed, and the durability of the deframed high-strength concrete 1 Can be enhanced.

Next, the blending test and blending test result of the high-strength concrete 1 according to the present embodiment will be shown.
In the blending test of high-strength concrete 1, the design standard strength of high-strength concrete 1 was 100 N / mm ² (blending strength: 120 N / mm ² , coefficient of variation: 10%).
In the blending test, the materials used for the high-strength concrete 1 were as follows.
That is, water W is tap water, cement C is early strength Portland cement having a density of 3.14 g / cm ³ , admixture A is silica fume A1, blast furnace slag fine powder A2, and gypsum component A3. The density was 2.64 g / cm ³ inclusive.
The fine aggregate S was crushed sand (an andesite from Kurashiki City) with a surface dry density of 2.60 g / cm ³ and a water absorption rate of 1.38%. The coarse aggregate G was crushed with an absorption coefficient of 0.60% (an andesite from Kurashiki City) with a surface dry density of 2.62 g / cm ³ and a size classification according to JIS A5005 of 2010: 1505 = 1: 1. did.
Moreover, the polycarboxylic acid type high performance water reducing material and the lower alcohol type shrinkage reducing agent were used as the admixture.

In the blending test, the blending was as follows.
That is, the water binder ratio W / B was 24%, the slump flow was 65 cm ± 5 cm, and the air amount was 2.0% ± 1.5%. Here, the binder B is a combination of the cement C and the admixture A. Moreover, the water W contains a high performance water reducing material and a shrinkage reducing agent (6 kg / m ³ ).
Furthermore, the water W and 150 kg / ^{m 3,} the cement C and 500 kg / ^{m 3,} the admixture A was 125 kg / ^{m 3,} the fine aggregate and 790 kg / ^{m 3,} the coarse aggregate 838kg / ^{m 3,} the high The performance water reducing material binder ratio SP / B was set to 1.5%.

Subsequently, the materials used were blended as described above and kneaded as follows.
That is, using a mixer, the cement C, the admixture A and the fine aggregate S are mixed for 15 seconds, and then water W containing a high-performance water reducing material and a shrinkage reducing agent is added. The primary kneading was performed for 1 second, and then the coarse aggregate G was added and the second mixing was performed for 60 seconds.

Then, the mixed fresh concrete was placed on a mold, and steam curing was performed in a variable temperature and temperature chamber as follows.
First, the temperature change of the concrete (high-strength concrete 1 in the curing process) was predicted by temperature stress analysis, and the temperature difference between the actual member and the outside air was set to 20 ° C. or less in steam curing.
FIG. 2 is a diagram showing the relationship between the age (time) of concrete (high-strength concrete 1) subjected to a steam curing process and the temperature (° C.) of the outside air.
Specifically, as shown in FIG. 2, the outside air is held at 20 ° C. for 9 hours (preliminary), then the outside air is heated at a rate of 15 ° C./hour for 2 hours, and then the outside air is heated to a maximum temperature of 50 ° C. The temperature was kept at 11 ° C. for 11 hours, and finally the temperature was lowered over 26 hours until the outside air reached 20 ° C. The frame was removed after 48 hours from the placement of the fresh concrete. In the steam curing, the humidity in the variable temperature and constant temperature chamber was maintained in a saturated state, and the atmospheric pressure in the variable temperature and temperature constant temperature chamber was 1 atm (atmospheric pressure) or more.

The result of the blending test of the high-strength concrete 1 that has been steam-cured in this way is shown.
FIG. 3 is a diagram showing the relationship between the age (days) and the compressive strength (N / mm ² ) of fresh concrete (high-strength concrete 1) that has undergone a steam curing process.
As shown in FIG. 3, compressive strength, 116 N / mm ² at 2 days age of, 128N / mm ² at an age of 14 days, it was a 131N / mm ² at the age of 28. As described above, since the compressive strength at the age of 2 days exceeds 100 N / mm ² , it was confirmed that early deframement and introduction of prestress were possible. Further, the compressive strength at the age of 14 days exceeded 120 N / mm ² , which is a blending strength considering a variation coefficient of 10%, and it was confirmed that the design standard strength was satisfied at the age of 14 days.
The temperature of the outside air in the above blending test is set in advance based on the prediction of the temperature change of the concrete by the temperature stress analysis, but instead of this, the temperature difference between the temperature of the concrete and the temperature of the outside air Based on the above, the temperature of the outside air may be feedback controlled in real time so that this temperature difference becomes zero.

  As mentioned above, although preferable embodiment of this invention was explained in full detail, the manufacturing method of the high strength concrete 1 and high strength concrete 1 which concerns on this invention is not limited to embodiment mentioned above, It is described in a claim. Various modifications and changes can be made within the scope of the present invention.

According to the high-strength concrete 1 of the present invention, the design standard strength is high-strength concrete 1 having a strength of 100 N / mm ² or more, and the high-strength concrete 1 is a binder B composed of water W, cement C, and admixture A. And the fine aggregate S and the coarse aggregate G, the water binder ratio W / B is 30% or less, the cement C is early-strength Portland cement, and the admixture A is silica fume A1. Because it contains blast furnace slag fine powder A2 and gypsum component A3, it can be unframed as early as 2 days of age, can exhibit high strength, and has a good self-filling property when fresh, after curing Can also prevent cracking. As a result, it is possible to provide a high-strength concrete 1 with a short unframed material, so that it can be used for the precast segment constituting the bridge girder of the prestressed concrete bridge, the construction period can be shortened, and the PC girder bridge with low girder and long span. 100 can be realized with a short construction period and low cost.

  According to the manufacturing method of the high strength concrete 1 used for the precast segment which comprises the bridge girder of the prestressed concrete bridge of this invention, the production | generation process which mixes the material which the high strength concrete 1 contains and produces | generates fresh concrete, It includes a casting process for casting inside the formwork, a steam curing process for steam curing fresh concrete, and a deframing process for removing the formwork at 2 days of unframed material. In such a case, high strength can be expressed as early as possible, and prestress can be introduced at that time. Moreover, the fluidity | liquidity at the time of fresh and self-filling property are good, and the crack after hardening can also be suppressed. Furthermore, it is possible to achieve a high design standard strength and to suppress cracking. In this way, it is possible to provide high-strength concrete 1 with a short unframed material, so it can be used for precast segments that make up the bridge girder of prestressed concrete bridges. The bridge 100 can be realized with a short construction period and low cost.

1 High-strength concrete 10 Main girder 20 Cast-in-place concrete 30 Road pavement 31 Sidewalk pavement 100 PC girder bridge A Admixture A / B Replacement rate A1 Silica fume A2 Blast furnace slag fine powder A3 Gypsum component B Binder C Cement G Coarse aggregate S Fine Aggregate SP / B High Performance Water Reducing Material Binder Ratio W Water W / B Water Binder Ratio

Claims (9)

High strength concrete with a design standard strength of 100 N / mm ² or more,
The high-strength concrete is
Contains water, a binder composed of cement and admixture, fine aggregate, and coarse aggregate,
The water binder ratio is 30% or less,
The cement is an early-strength Portland cement,
The high-strength concrete, wherein the admixture contains silica fume, blast furnace slag fine powder, and a gypsum-based component. High-strength concrete used for precast segments,
The high-strength concrete according to claim 1, further comprising a reinforcing bar. High-strength concrete used for precast segments that make up the prestressed concrete bridge girder,
Reinforcing bars,
PC steel material,
The high-strength concrete according to claim 1 or 2, wherein the bridge girder is formed in a state where a plurality of the precast segments are arranged, and prestress is introduced by the PC steel material. The ratio of the span to the girder height of the bridge girder is 25 or more and 40 or less, The high-strength concrete according to claim 3. A method for producing high-strength concrete used for a precast segment constituting a bridge girder of a prestressed concrete bridge,
A production process for producing fresh concrete by mixing the materials contained in the high-strength concrete;
A placing step of placing the fresh concrete inside a mold,
A steam curing process for steam curing the fresh concrete;
The method for producing high-strength concrete according to any one of claims 1 to 4, further comprising: a frame removal step of removing the mold frame at a frame removal material age of 2 days. In the steam curing process,
The method for producing high-strength concrete according to claim 5, wherein the fresh air is kept at a reference temperature, then heated, held at a maximum temperature, and then cooled. In the steam curing process,
The method for producing high-strength concrete according to claim 6, wherein a temperature decrease rate that is a temperature drop per unit time in the temperature decrease is smaller than a temperature increase rate that is a temperature increase per unit time in the temperature increase. In the steam curing process,
The method for producing high-strength concrete according to claim 6 or 7, wherein a holding time at the maximum temperature is longer than a holding time at the reference temperature. In the steam curing process,
The method for producing high-strength concrete according to claim 5, wherein the temperature of the outside air is controlled so that a temperature difference between the temperature of the fresh concrete and the temperature of the outside air is maintained at 20 ° C. or less.

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