JP2002048690A - Cracking judgment method in premature age of member using high strength concrete and judging apparatus using the same and casting method of high strength concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a judgment method which enables accurate judgment of cracking in the premature age of member using high strength concrete, a cracking judging device and a casting method of the high strength concrete which accurately prevents cracking. SOLUTION: A self-contraction stress calculation means calculates the self- contraction distortion and the self-contraction stress of concrete based on the temperature and effective material age (S6, S8). The correctness of the self contraction stress obtained considering the temperature of the concrete enables accurate determination of tensile stress σa generated in the concrete of the concrete member (S10) and hence, it can be judged accurately whether cracking occurs in the concrete member (S12). As a result, the concrete member without cracking at any premature material age can be obtained by following a curing method and a curing period determined with the device adapted to determine the curing method and the curing period of the member using the high strength concrete.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for judging cracks of a member using high-strength concrete at a young age, a judging device using the same, and a method for casting high-strength concrete.

[0002]

^2. Description of the Related Art Conventionally, high-strength concrete having a compressive strength of 36 N / mm ² or more has been widely used in buildings such as high-rise RC (steel reinforced concrete) and SRC (steel reinforced concrete) structures. Such high-strength concrete uses a large amount of cement and a large amount of unit cement, and thus generates a large amount of heat due to a hydration reaction when it is cast and hardened. Therefore, in a member cast with high-strength concrete, the portion near the surface of the member emits the heat to the outside of the member, whereas the portion near the center of the member is hard to emit heat and accumulates. Therefore, a temperature difference occurs between the surface portion and the central portion of the member. However, since all parts of the concrete member harden almost simultaneously, expansion of the central part of the concrete member due to temperature rise is restricted. As a result, temperature strain occurs due to so-called internal restraint, and a tensile stress acts on the surface of the concrete member to cause cracking. In particular,
At the young age of about 2 days after concrete casting,
Cracks are likely to occur due to the above temperature strain. The mechanism by which the stress due to the temperature strain is generated has been clarified, and a number of methods for determining cracks in consideration of the stress due to the temperature strain have been proposed.

[0003]

However, the above-mentioned conventional method for judging cracks has a problem that it is inaccurate because only the temperature strain is considered. That is, since the high-strength concrete has a large unit cement amount, the amount of self-shrinkage accompanying the hydration reaction is large. Since this large amount of shrinkage is constrained by the reinforcing bar of the concrete member, a tensile stress is generated in the concrete portion of the concrete member, and cracks occur. In other words, in the case of high-strength concrete, the conventional method for judging cracking was inaccurate because only shrinkage was considered in spite of the fact that autogenous shrinkage was also a cause of cracking. It was known that the amount of the autogenous shrinkage varies depending on the type of cement and the mix of concrete, but the effect of the temperature of the concrete was not considered, and the exact amount of autogenous shrinkage was not predicted.

In such a situation, the present inventor has found that the amount of the auto-shrinkage strain changes with the temperature of the concrete, and has found a method of obtaining the stress due to the auto-shrinkage strain corresponding to the temperature of the concrete.

Accordingly, an object of the present invention is to provide a determination method capable of accurately determining cracks at a young age of high-strength concrete in consideration of the influence of concrete temperature, a crack determination apparatus using the determination method, and It is an object of the present invention to provide a method for placing high-strength concrete based on the determination result.

[0006]

In order to achieve the above object, a method for judging cracks of a member using high-strength concrete at a young age according to the first aspect of the present invention is based on the concrete temperature and effective age. Calculating the stress based on the self-shrinkage strain of the concrete, and calculating the stress from the self-shrinkage strain.Based on the temperature of the concrete, calculating the temperature strain due to the internal constraint of the concrete, and calculating the stress from the temperature strain. Step, the stress due to the self-shrinkage strain of the concrete, and the tensile stress generated in the concrete based on the stress due to the temperature strain due to the internal constraint, and having a step of comparing the tensile strength of the concrete. Features.

According to the method for judging cracking of a member using high-strength concrete at a young age according to the first aspect of the present invention, the stress due to the self-shrinkage strain is obtained based on the concrete temperature and the effective age. , This stress is accurate. The stress generated in the concrete is accurately determined in consideration of the stress caused by the accurate self-shrinkage strain and the stress caused by the temperature strain. This stress is compared with the tensile strength of the concrete, and when the stress is larger than the tensile strength, it is determined that the concrete is cracked. As a result, cracks at the young age of the member using the high-strength concrete are determined with higher accuracy than the conventional determination method.

According to a second aspect of the present invention, there is provided an apparatus for judging cracks of a member using high-strength concrete at a young age, comprising: a cross-sectional dimension and a reinforcing bar arrangement of a concrete member; a concrete material and preparation; Input means for inputting data relating to and the curing period;
Temperature calculating means for calculating the temperature of concrete based on the input data, effective age calculating means for calculating the effective age of concrete based on the temperature of the concrete, and the temperature and effective age of the concrete Based on the self-shrinkage strain of the concrete in the concrete member, based on the self-shrinkage stress calculation means to calculate the self-shrinkage stress generated in the concrete of the concrete member from the self-shrinkage strain, based on the temperature and effective age of the concrete, Temperature stress calculating means for calculating the temperature strain caused by the internal constraint of the concrete in the concrete member, calculating the temperature stress generated in the concrete of the concrete member from the temperature strain, and a tensile stress calculating the tensile strength of the concrete based on the effective age. Strength calculation means and And shrinkage stress and temperature stress and tensile occurring concrete of the concrete member obtained by adding the stress, by comparing the tensile strength of the concrete is characterized by having a determining means for cracking.

According to the apparatus for judging cracks of a member using high-strength concrete at a young age according to claim 2,
The dimensions and reinforcement of the cross section of the concrete member input by the input means, and the material and mix of the concrete,
The temperature history and the temperature distribution of the concrete are calculated by the temperature calculating means based on the data on the curing method and the curing period of the concrete member. The effective age calculating means calculates the effective age of the concrete using the temperature history of the concrete. The self-shrinkage stress calculating means accurately obtains the self-shrinkage stress generated in the concrete at a predetermined time based on the effective material age and the temperature history. Further, the temperature stress calculating means accurately obtains the temperature stress generated in the concrete due to the internal constraint of the concrete at a predetermined position and time of the concrete member based on the effective age, the temperature distribution and the temperature history. The tensile strength calculating means obtains a concrete tensile strength at a predetermined time based on the effective material age. Then, the determining means compares the stress generated in the concrete, which is accurately obtained by adding the self-shrinkage stress and the temperature stress due to the internal constraint, with the tensile strength of the concrete. At this time, in all concrete members and all time series,
By comparing the stress generated in the concrete with the tensile strength, if the stress generated in the concrete is larger than the tensile strength, the determination means determines that the concrete member is cracked. As a result, the crack determining device for the member using the high-strength concrete at the time of the young age can determine the crack in the concrete member more accurately than the conventional determining method.

According to a third aspect of the present invention, there is provided a method for curing a member using high-strength concrete and an apparatus for determining a curing period, wherein the device for judging cracks of a member using high-strength concrete at a young age is used. An apparatus for determining a curing method and a curing period of a member using high-strength concrete, wherein when the determining means determines that the concrete member is cracked, data on the curing method and the curing period are different data. A requesting means for requesting replacement is provided, and the above-described determination is repeated to determine the curing method and the curing period based on the data on the replaced curing method and the curing period.

According to the third aspect of the present invention, when the determining means determines that the concrete member is cracked, the member using the high strength concrete is cured. The device for determining the curing method and the curing period requests that the data on the curing method and the curing period be exchanged. That is, with respect to the concrete member, for example, the material of the form used when casting concrete, the method of keeping or cooling the concrete member after the concrete is poured, or the method of placing the concrete after casting the concrete. The data regarding the curing method and the curing period, such as the time until removal, is replaced, and the above determination is repeated based on the replaced data. As a result, data on a curing method and a curing period for which the determination means determines that the concrete member does not crack can be obtained.

[0012] The method of placing high-strength concrete according to the invention of claim 4 uses the curing method and the curing period determined by the device for curing a member using high-strength concrete according to claim 3 and an apparatus for determining the curing period. And curing a member using high-strength concrete.

According to the fourth aspect of the present invention, concrete is poured by using a curing method and a curing period in which it is determined that the concrete member is not cracked by the determining means. That is, it is determined that cracks do not occur in the concrete member.For example, the material of the form used when placing concrete, the method of keeping the concrete member warm or cooling after the concrete is placed, or the method of placing concrete Concrete is actually poured according to the time from when the mold is removed to the time when the form is removed, so that a member made of high-strength concrete without cracks at a young age can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is a flow chart showing a method of curing a member using high-strength concrete and a process executed in an apparatus for determining a curing period according to an embodiment of the present invention.

First, data relating to the dimensions / arrangement of the section of the member and the material / mixing of the concrete are inputted by the input means (S1). Next, a curing method and a period after the concrete of the material and the mixture are cast are input by the input means (S2). The temperature history of the concrete member is calculated by numerical analysis based on the data input by the input means (S3). This temperature history may be obtained by actually measuring the temperature of the concrete member. Subsequently, the temperature distribution of the cross section of the concrete member and the average temperature of the cross section of the member are analyzed from the temperature history (S).
4). The temperature distribution and the average temperature may also be obtained by actually measuring the concrete member. The effective age of the concrete is calculated from the temperature distribution and the average temperature based on the temperature history (S5). Then, based on the effective age of the concrete calculated in S5 and the average temperature obtained in S4, the amount of auto-shrinkage strain is calculated (S6). On the other hand, from the effective age, the tensile creep coefficient and the tensile Young's modulus of the concrete at the effective age are calculated (S
7). Based on the amount of the self-shrinkage strain, the self-shrinkage stress is calculated using the tensile creep coefficient and the tensile Young's modulus (S8). Further, based on the temperature distribution in the cross section of the member, the thermal stress due to the internal constraint is calculated using the tensile creep coefficient and the tensile Young's modulus (S9). The tensile stress σa generated in the concrete on the surface of the concrete member by adding the self-shrinkage stress and the temperature stress.
(S10). The tensile strength Ft of the concrete of this concrete member was determined from the effective age (S11).
Thereafter, the value of the tensile strength Ft is compared with the value of the tensile stress σa to determine whether the concrete member is cracked (S
12). That is, when the value of the tensile stress σa is larger than the value of the tensile strength Ft, it is determined that the concrete member is cracked, and when the value of the tensile stress σa is smaller than the value of the tensile strength Ft, it is determined that the concrete member is not cracked. I do. When it is determined that the concrete member is cracked, the operator is prompted to input data different from the data from which the result is derived with respect to the curing method and period (S1).
3). When new data on the curing method and period is input, the process returns to S3, and based on the new data, S3
To steps S12 are repeated. The above curing method
If it is determined that no crack occurs depending on the period, S1
Proceeding to 4, the curing method and period are determined, and the processing of the apparatus for determining the curing method and the curing period of the member using the high-strength concrete is completed.

In the present embodiment, the self-shrinkage strain of concrete in a concrete member is calculated in step S6 based on the average temperature of the concrete member and the effective age of the concrete. The calculation formula used at this time is derived from experiments described below.

In this experiment, a straight specimen made of high-strength concrete was used, and three kinds of temperatures, ie, curing temperatures, which were set after the concrete of the specimen was cast, were set, and each specimen hardened. Measure the amount of strain when performing. The relationship between the measured strain amount and the concrete temperature and effective age is approximated by a function.

The high-strength concrete forming the test specimen is composed of the materials shown in Table 1 below and the formulations shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2] As shown in Table 2, the water binder ratio (W / B) was set to 22%, and the fine aggregate ratio (s / a) was set to 38%. Silica fume (SF) is 10% based on the mass of cement (C).
Percentages were replaced by percentages. The target values for concrete kneading are slump flow 60 ± 10 cm and air volume 2 ± 1.
%.

[0022] The dimensions of the above-mentioned specimens are reported by the JCI (Japan Concrete Institute) Superfluid Concrete Research Committee report.
II “Self-shrinkage test method for high fluidity concrete (tentative name)”
In accordance with the above, a rectangular column of 100 × 100 × 400 mm was formed. An embedded strain gauge with a temperature measurement function was attached to this prismatic test body, and the temperature of the test body was measured simultaneously with the strain generated in the test body.

After the concrete was poured, the test piece was sealed in such a manner that there was no escape of water and no water absorption.
Curing for 3 hours at 20 ° C, 40 ° C and 6 ° C
Curing was performed for 28 days at three curing temperatures of 0 ° C. Hereinafter, the names of the above-mentioned test specimens will be referred to as T2 according to the curing temperature.
0, T40, T60.

The setting time of the test specimen was measured by a proctor penetration resistance test using a wet screening mortar subjected to the same curing as described above.

FIG. 2 shows the measurement results of the strain measured by the above-described strain gauge. The horizontal axis is the effective age from the time when the concrete starts to set, and the vertical axis is the strain. The test specimen has dimensions of 100 × 100 × 400 mm
Since it is relatively small, it is safe to assume that there is almost no difference in temperature between the central part and the surface part of the specimen due to heat due to the hydration reaction, and therefore, there is almost no temperature distortion due to internal restraint. You can think. That is, it can be said that almost all the strains shown in FIG. 2 are self-shrinkage strains. In order to compare test specimens having different curing temperatures from each other, the effective material age of the test specimen was determined based on the curing temperature by the following equation (1).

[0026]

(Equation 1) Here, t: effective age (days), Δt _i : number of days during which the temperature is T (° C.), T ₀ = 1 ° C.

As for the self-shrinkage strain, the strain at the beginning of the setting was set to zero. The effective age at the onset of setting is T20
0.38 days at T40, 0.35 days at T40, 0.36 days at T60
Days, almost the same age. The coefficient of linear expansion is 11.5 × 10 ⁻⁶ / ° C., which is a value obtained from the relationship between strain and temperature in that case, by changing the curing temperature of the T20 specimen in a short time after 91 days of material age. Using.

With respect to the measurement result of the self-shrinkage strain shown in FIG. 2, the following approximate expression (2) was derived.

[0029]

２ _as = 1 / {1 + α · exp (−β · t ′)} · ε _∞ · {1−exp (−A · t ′ ^B )} (2) where ε _as : Auto-shrinkage strain, ε _：: final value of auto-shrinkage strain, t ': effective age (days) from the start of setting, A, B: constant, α, β: constant.

The above ε _as , A, and β are determined from the curing temperature, that is, the concrete temperature, as described below.

[0031]

[Number 3] _{ε ∞ = -81.1 · (T +} 10) 0.506 ··· (3)

[0032]

A = 0.0015 · (T + 10) +0.332 (4)

[0033]

Β = −0.145 · (T + 10) +20.85 (5) where T: curing temperature In addition, B and α are the following in the mixing of the concrete of the present embodiment. The values are as shown in Table 3. The above ε
Table 3 also shows the values of _∞ , A and β corresponding to the curing temperature.

[0034]

[Table 3] FIG. 3 shows the measurement results T20, T40, T
60 is a diagram in which curves C20, C40, and C60 according to equation (2) obtained by substituting equations (3) to (5) into 60 are superimposed. As can be seen from the measurement results of the auto-shrinkage strain, the higher the curing temperature, the greater the rate of increase in the auto-shrinkage strain,
At an effective age of 50 days, the strain in T60 is about 1.7 times T20 and T40 is about 1.4 times T20.
On the other hand, curves C20, C40, and C60 according to equation (2) are:
The measurement results of the self-shrinkage strain substantially agree with T20, T40, and T60. That is, the self-shrinkage strain at the young material age can be accurately obtained based on the curing temperature T by the equation (2). Therefore, the method for curing the member using the high-strength concrete and the device for determining the curing period in the present embodiment accurately calculates the autogenous shrinkage strain in step S6, and as a result, the concrete member cracks in S12. It is possible to determine whether or not it is more accurate than the conventional determination method.

Hereinafter, the curing method and the curing period of the actual high-strength concrete member are determined by the apparatus for determining the curing method and the curing period of the high-strength concrete in the present embodiment.

This concrete member has a cross section as shown in FIG. That is, this concrete member 1
Is a square section having a side of 1000 mm, and D41
Are arranged in the vicinity of the outer periphery of the concrete member, and furthermore, at the center of the member, a reinforcing bar D3 of D41 extending parallel to the main bar is provided.
.. Are arranged. The operator inputs the dimensions of the member cross section, the diameter and the number of main bars via the input device of the device for determining the curing method and the curing period (S1).

As the high-strength concrete forming the concrete member, the same concrete as that used in the experiment when the approximate expression of the self-shrinkage strain based on the curing temperature was derived was used. With the same material as
This is the same formulation as in Table 2. The operator inputs the materials and formulations shown in Tables 1 and 2 to an apparatus for determining a curing method and a curing period via an input / output device (S1).

Next, a method of curing the concrete member after the concrete is cast and a curing period are input. The curing method of the concrete member uses a formwork made of plywood having a thickness of 12 mm, and does not adjust the curing temperature by cooling, heat retention, or the like. The curing period of the concrete member is one day at the material age from the time the concrete is cast to the time the mold is released (S2).

Based on the above data, the temperature history of the concrete is calculated by the temperature calculating means. In the present embodiment, the temperature history of the concrete was obtained by the temperature sensor actually installed on the concrete member 1.
In FIG. 1, the temperature sensor includes a center 5 of the member cross section, a corner 6 of the member cross section, and a 3 between the center and the corner of the member cross section.
It was arranged at a point (S3).

The temperature distribution and the average temperature in a predetermined section of the member are analyzed using the temperature history. In the present embodiment, the temperature distribution was detected at the temperature sensor positions 5, 6, and 7 in FIG. 1 on the assumption that the center of the concrete member is distributed at the highest and the surface of the concrete member is distributed at the lowest quadratic curve. The quadratic curve is approximated based on the temperature (S
4).

Next, the effective age of the concrete is calculated by the effective age calculating means based on the temperature history and the average temperature of the concrete member. The effective age calculating means performs the calculation using the above equation (1) (S5).

Then, using the equations (2) to (5) obtained by the above experiment, the self-shrinkage strain is obtained based on the effective material age and the curing temperature of the concrete (S6).

Subsequently, the self-shrinkage stress is calculated by the self-shrinkage stress calculating means using the above-mentioned self-shrinkage strain. Before that, the tensile creep coefficient and the tensile Young's modulus used for calculating the self-shrinkage stress are calculated. (S7).

The tensile creep coefficient is expressed by a function based on the effective age and is obtained by the following equation (6) (Shinji Hagiwara et al., "Regarding mechanical properties and compressive and tensile creep behavior of high-strength concrete at an early age." Experimental Research ", Journal of Concrete Engineering, January 2000).

[0045]

(6) φ (t, t ₀ ) = ε _cr / ε _e (6) where, ε _cr = ε _cr ^∞ · [1-exp {−α · (tt ₀ ) β}], ε (and ^{_{ε cr ∞> 0) cr ∞}} = -142.8 · R e +142.6, R e = E (t 0) / E 28, ε e = 1 / E 28, φ (t, t 0) : Creep coefficient at effective age t loaded at effective age t ₀ , ε _cr : unit creep strain (× 10 ⁻⁶ / N / mm ² ), ε _cr ^∞ : ultimate unit creep strain (× 10 ^{− 6} / N / mm ² ), t: effective age (day) of interest, t ₀ : effective age of loading (day), α, β: constants representing creep progress rate, α =
0.394, β = 0.581, E (t ₀ ): Young's modulus (N / mm ² ) of concrete at the effective loading age t ₀ , ε _e : Unit elastic strain (× 10 ⁻⁶ / N / mm ² ), E ₂₈ : Young's modulus (= 47.5 kN / mm ² ) of concrete with a standard curing material age of 28 days.

The tensile Young's modulus is also expressed by a function based on the effective age, and is calculated by the following equation (7) (Report of the Japan Society for Concrete Engineering, Research Committee on Autogenous Shrinkage, 199).
June 7).

[0047]

Equation 7] _{E (t) = E 28 ·} exp (S e {1 - ((28-tf s) / (t-tf s)) 0.5}) ··· (7) Here, E (t) : Young's modulus of concrete at effective age t (N / m
m ² ), E ₂₈ : Young's modulus of concrete with 28 days of standard curing age
(= 47.5 kN / mm ² ), S _e : a coefficient (= 0.09) indicating the speed of onset of the Young's modulus
5), t: effective material age (day), tf _s: is the first departure time of condensation (= 0 41 days)..

Then, the self-shrinkage stress is calculated by the self-shrinkage stress calculation means using the above-mentioned self-shrinkage strain, tensile creep coefficient and tensile Young's modulus (S8).

In the present embodiment, the calculation of the self-shrinkage stress is performed by successive calculation using a step-by-step method based on the principle of superposition of creep of concrete. The step-by-step method based on the concrete creep superposition principle specifically uses the following equations (8) to (11).

[0050]

(Equation 8)

[0051]

(Equation 9)

[0052]

(Equation 10)

[0053]

[Equation 11] Here, σ (t _{i + 1/2} ): Concrete stress at step t _{i + 1/2} (N / mm ² ), ε _c (t _{i + 1/2} ): step t _{i + 1/2} actual concrete strain (all strain generated in the _{member), ε cf (t i +} 1/2): step t _{i + 1 /} concrete free strain at _{2, φ (t i + 1} /2, t _i): creep coefficient at step t _i step is loading with _{t i + 1/2, E} (t i): Young's modulus of the concrete in step ^{_{t i (N / mm 2)}} , E 28: standard curing It is the Young's modulus (= 47.5 kN / mm ² ) of 28-day-old concrete.

When the self-shrinkage stress is sequentially calculated using the above equations (8) to (11), the equation (2) representing the self-shrinkage strain obtained by the above experiment is substituted for the free strain _εcf . Further, the self-shrinkage strain is restrained by the main bars 2 and 3 of the concrete member 1, so that the compressive force applied to the main bars 2 and 3 in a predetermined cross section of the concrete member 1 is balanced with the tensile force generated in the concrete, and It is assumed that the strain amounts of the main bars 2 and 3 and the concrete are the same. This condition is expressed by the following equation (1)
2) and (13) are executed in the sequential calculation.

[0055]

(Equation 12) ... (12)

[0056]

(Equation 13) Here, A _c : cross-sectional area of concrete (= 0.968 m ² ), A _s : total cross-sectional area of main bar (= 0.032 m ² ), E _s : Young's modulus of main bar (= 190 kN / mm ² ), ε _s (t _{i + 1/2} ): actual strain of the main muscle at step t _{i + 1/2} , ε _st (t _{i + 1/2} ): temperature strain of the main muscle at step t _{i + 1/2} .

Although the self-shrinkage strain is determined based on the curing temperature, the curing temperature, that is, the concrete temperature changes as the hydration reaction proceeds. Therefore, the equation (2) for determining the strain based on the curing temperature is as follows. Into the equation (14) to calculate the strain based on the curing temperature for each successive calculation step.

[0058]

[Equation 14] here, , Ε _as (t _i , T ′): strain at the concrete temperature T ′ in step t _i , T: curing temperature, that is, concrete temperature.

The self-shrinkage stress calculating means repeatedly executes the calculation of the self-shrinkage strain based on the effective age of the concrete and the curing temperature (S6) and the calculation of the self-shrinkage stress (S8) based on the successive calculation. The autogenous shrinkage strain obtained according to the concrete temperature using the equation (14) is a curve A as shown in FIG. The vertical axis in FIG. 5 shows the strain amount, and the horizontal axis shows the effective material age (days). FIG. 5 shows a curve B indicating the self-shrinkage strain obtained without considering the conventional curing temperature. As can be seen from FIG. 5, when the heat generated by the hydration reaction of the concrete is considered, the strain becomes larger than when the heat generation is not considered.

On the other hand, the temperature strain due to the internal constraint
From the temperature distribution approximated to the quadratic curve obtained in. Based on the temperature strain, the tensile creep coefficient and the tensile Young's modulus obtained in S7, the temperature stress due to the internal constraint is calculated by the temperature stress calculating means (S9).

The temperature stress due to the internal constraint is also determined by a step-by-step method based on the principle of creep of concrete and by successive calculations using the above equations (8) to (11). Expressions (8) to (11)
When the temperature stress is sequentially calculated by using the above _equation , the temperature strain is substituted as the free strain _εcf .

The stress generated in the concrete member 1 is obtained by adding the self-shrinkage stress obtained by the self-shrinkage stress calculation means and the temperature stress obtained by the temperature stress calculation means. FIG. 6 shows the stress generated in the concrete member 1 thus obtained.
Curve C indicates the stress generated on the surface of the concrete member 1, and curve D indicates the stress generated on the center of the concrete member 1. In FIG. 6, the vertical axis represents the generated stress (N / mm ² ).
The horizontal axis is the effective age (days). As shown by the curve C in FIG. 6, the maximum tensile stress σa occurs at the initial material age of about 1.5 days after the high-strength concrete is cast on the surface of the concrete member. This maximum tensile stress σa
However, if it is greater than the tensile strength Ft of the concrete at that time, cracks occur on the surface of the concrete member.

FIG. 6 is a graph showing a rebar restraining stress, which is a stress generated by restraining the self-shrinkage strain by the rebar, corresponding to the self-shrinkage stress calculated by the self-shrinkage stress calculating means of the present embodiment, Indicated by E. Curve F
Is a curve showing the calculation result of the reinforcing bar restraining stress without considering the conventional curing temperature, and the curve G is a curve showing the actually measured value which is the result of measuring the stress actually restrained by the reinforcing bar. Comparing the curves E and G shows that the auto-shrinkage stress calculating means of the present embodiment can calculate the auto-shrinkage stress actually generated in the high-strength concrete substantially accurately. In addition, since the conventional calculation of the self-shrinkage stress does not take the curing temperature into account, it can be seen that the calculation result is smaller than the actually generated self-shrinkage stress. If the conventional calculation result is used for the crack determination of the concrete member, there is a case where the dangerous side, that is, the determination that the crack does not occur although the crack may actually occur.

The tensile strength Ft of the concrete is obtained based on the effective age by the tensile strength calculating means (S1).
1).

First, the tensile strength calculating means obtains the compressive strength of concrete based on the effective material age by the following equation (15) (Concrete Engineering Association, Report on the Committee for Autogenous Shrinkage, June 1997).

[0066]

(Equation 15) (15) where, F _c (t): compressive strength at effective age t (N / mm ² ), f ₂₈ : compressive strength at standard curing age 28 days (N / m ² )
m ² ), S _f : Coefficient due to the type of cement, a _f : Coefficient (day) due to the effect of solidification time, t: Effective age (day).

Next, from the compressive strength of the concrete obtained by the equation (15) according to the following equation (16), the tensile strength F of the concrete at a predetermined effective material age is obtained.
Finding t (Shinji Hagiwara et al., "Experimental Study on Mechanical Properties and Compression and Tensile Creep Behavior of High Strength Concrete at Early Age", Journal of Concrete Engineering, 200
January, 0).

[0068]

Equation 16] ^{_{F t = γ · F c 0.5}} ··· (16) Here, Ft: tensile strength ^{(N / mm 2), Fc} : compressive strength ^{(N / mm 2), γ} : constant (= 0. 618).

Then, the judging means compares the tensile strength Ft of the concrete with the tensile stress σa generated on the concrete member surface obtained in S10 (S12).

FIG. 6 shows a superimposed curve H indicating the tensile strength Ft of the concrete obtained by the above equation (16). As shown in FIG. 6, when there is a portion (effective material age: about 1.5 days) where the tensile stress generated on the surface of the concrete member of the curve C exceeds the tensile strength Ft of the curve H, the determining means determines that the concrete member has cracks. Is determined to occur (S12).

When the determining means determines that the concrete member is cracked, the request means requests the operator to re-enter the curing method and the curing period (S13).

When the operator inputs data relating to a new curing method and a new curing period such as, for example, changing the material of the mold to a different material, or changing the effective material age for releasing the mold to a different number of days, the operator enters this data. The processing steps from S3 to S12 are repeated based on the data. When the determination result based on the data of the new curing method and the curing period indicates that no crack is generated, the process proceeds to S14, where the data is determined as the curing method and the curing period, and the member using the high-strength concrete is used. The processing of the apparatus for determining the curing method and the curing period is ended.

When the high-strength concrete is actually cast based on the curing method and the curing period determined by the device for determining the curing method and the curing period of the member using the high-strength concrete, cracks actually occur. A predetermined concrete member can be obtained without the need.

In the above embodiment, the apparatus for determining the curing method and the curing period of the member using the high-strength concrete includes request means for requesting input of a new curing method and a curing period in S13. Until a curing method and a curing period that do not cause cracks are required, S3 to S
Although the processing up to 12 has been repeated, it is also possible to simply check whether or not a predetermined concrete member cracks without providing the requesting means in S13.

[0075]

As is clear from the above, according to the method for judging cracks of a member using high-strength concrete according to the first aspect of the present invention at an early age, based on the concrete temperature and the effective age. , And the stress is calculated from the self-shrinkage strain, so that the stress can be accurately obtained. Since the stress caused by the accurate auto-shrinkage strain and the stress caused by the temperature strain are taken into account, the stress generated in the concrete of the member using the high-strength concrete at the young age can be accurately obtained, and this stress and the concrete By comparing the tensile strength of the high-strength concrete member, it is possible to determine the cracking of the high-strength concrete member more accurately than the conventional determination method.

According to the apparatus for judging cracks of a member using high-strength concrete according to the second aspect of the present invention at an early age, the effective age obtained by the effective age calculating means is:
Based on the temperature history obtained by the temperature calculation means and the self-shrinkage stress calculation means for obtaining the self-shrinkage stress generated in the concrete at a predetermined time, the self-shrinkage stress is accurately obtained. The stress generated in the concrete of the concrete member is accurately calculated from the precisely determined self-shrinkage stress and the temperature stress generated in the concrete due to the internal constraint of the concrete, and the stress is compared with the tensile strength of the concrete. Since the crack of the member is determined, the crack of the concrete member can be determined more accurately than the conventional determination method.

According to the curing method and the apparatus for determining the curing period according to the third aspect of the present invention, when the determining means determines that the concrete member is cracked, a request for exchanging data relating to the curing method and the curing period is made. Since the means is provided, a curing method and a curing period that do not cause cracks in the concrete member can be obtained with higher accuracy than before.

According to the high-strength concrete casting method of the fourth aspect of the present invention, concrete is cast using the curing method and the curing period determined by the curing method and the apparatus for determining the curing period of the third aspect. So, at a young age,
It is possible to obtain a member made of high-strength concrete in which cracks do not occur as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a schematic operation of a crack determination device for a member using high-strength concrete according to an embodiment of the present invention at a young age.

FIG. 2 is a diagram showing the strain generated in a test body when the test body of high-strength concrete is cured at different curing temperatures, together with the temperature of the test body.

FIG. 3 is a diagram showing the self-shrinkage strain generated in a test body cured at different curing temperatures and the calculation result of a calculation formula for calculating the self-shrinkage strain based on the curing temperature.

FIG. 4 is a diagram showing a cross section of a concrete member for which crack determination has been performed in one embodiment.

FIG. 5 is a diagram illustrating an example of a curing method and an apparatus for determining a curing period according to an embodiment. FIG. 5 is a diagram illustrating a self-shrinkage strain A calculated based on a curing temperature and a conventional self-shrinkage strain B calculated without considering a curing temperature. FIG.

FIG. 6 In the curing method and the apparatus for determining a curing period according to one embodiment, it is determined that the tensile stress C generated on the surface of the concrete member exceeds the tensile strength H of the concrete, and cracks are generated on the surface of the concrete member. FIG.

[Explanation of symbols]

S1 Step of inputting dimensions and reinforcing bars of the member cross section and concrete material / mixing by input means, S2 Step of inputting curing method and period by input means, S3 Step of calculating temperature history of concrete member by numerical analysis and the like S4, the step of analyzing the temperature distribution and the average temperature of the cross section of the concrete member; S5 the step of calculating the effective age of the concrete based on the temperature distribution and the average temperature of the concrete member; S6 the effective age of the concrete; Calculating the amount of autogenous shrinkage based on the average temperature obtained in step S7, calculating the tensile creep coefficient and the tensile Young's modulus of the concrete based on the effective age obtained in step S5, and calculating the self-shrinkage amount in step S8. S7 based on the amount of contraction strain
Calculating the self-shrinkage stress using the tensile creep coefficient and the tensile Young's modulus obtained in step S9; calculating the temperature stress due to internal restraint based on the temperature distribution in the cross section of the concrete member; and S10 determining the self-shrinkage stress in step S8. A step of obtaining the tensile stress σa generated on the surface of the concrete member by adding the shrinkage stress and the temperature stress obtained in S9; S11 a step of determining the tensile strength Ft of the concrete based on the effective material age; S12 a step of S10 Comparing the value of the tensile stress .sigma.a with the value of the tensile strength Ft determined in S11 to determine whether or not the concrete member is cracked. S13 It is determined that a crack is generated, and the data is again determined with respect to the curing method and the curing period. Inputting step, S14, it is determined that no crack is generated, The step in which the life period is determined.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Uenishi 2-2-2 Matsuzakicho, Abeno-ku, Osaka-shi, Osaka Prefecture Okumura Gumi Co., Ltd. (72) Inventor Shinji Hagiwara 4-5-6 Kasuga, Tsukuba-shi, Ibaraki F term (reference) 2E172 AA05 AA09 EA13 2G061 AC03 BA03 CA08 DA11 EA04

Claims (4)

[Claims] 1. A step of calculating a self-shrinkage strain of concrete based on a temperature and an effective age of the concrete, and calculating a stress from the self-shrinkage strain. Calculating the temperature strain, calculating the stress from the temperature strain, the stress due to the self-shrinkage strain of the concrete, the tensile stress generated in the concrete based on the stress due to the temperature strain due to the internal constraint, the above Comparing the tensile strength of the concrete with the tensile strength of the concrete. 2. Input means for inputting data relating to the dimensions and arrangement of the cross section of the concrete member, the material and mix of the concrete, the curing method and the curing period of the concrete member, and based on the input data. Temperature calculating means for calculating the temperature of concrete by calculating the effective age of concrete based on the temperature of the concrete; and concrete means for calculating the concrete age based on the temperature and effective age of the concrete. Means for calculating the self-shrinkage strain of the concrete, and calculating the self-shrinkage stress generated in the concrete of the concrete member from the self-shrinkage strain. The temperature strain due to Adding a temperature stress calculating means for calculating a thermal stress generated in the concrete of the concrete member from the strain, a tensile strength calculating means for calculating a tensile strength of the concrete based on the effective age, and the self-shrinkage stress and the temperature stress. A judging means for judging cracks by comparing the tensile stress generated in the concrete of the concrete member and the tensile strength of the concrete obtained together; Crack judgment device at the age of age. 3. An apparatus for determining a curing method and a curing period of a member using high-strength concrete, using the device for determining cracks of a member using high-strength concrete at a young age according to claim 2, When the determining means determines that the concrete member is cracked, the method further comprises requesting means for requesting that data relating to the curing method and the curing period be replaced with different data, and data relating to the replaced curing method and the curing period. An apparatus for determining a curing method and a curing period of a member using high-strength concrete, wherein the curing method and the curing period are determined by repeating the above-described determination based on the method. 4. A method of curing a member using high-strength concrete by using a method and a curing period determined by an apparatus for determining a curing period and a curing period using high-strength concrete according to claim 3. A method for placing high-strength concrete.