JP2008008753A - Early estimation method of concrete dry shrinkage factor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate highly accurately in a short-term material age, a concrete dry shrinkage factor in a long-term material age, in order to control concrete shrinkage crack caused by concrete dry shrinkage. <P>SOLUTION: In this method, a drying period calculation reference period required for reaching a concrete dry shrinkage factor which is a half of the final concrete dry shrinkage factor is set from a change-with-time characteristic coefficient determined by multiplying a factor exerting an influence on the concrete dry shrinkage as a coefficient. An extrapolation primary complementary coefficient is determined based on the drying period calculation reference period and one piece of short-term drying period measured data. The concrete dry shrinkage factor at an optional drying period-elapsed time after the drying period calculation reference period is estimated from the drying period calculation reference period and the extrapolation primary complementary coefficient. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an early estimation method of concrete drying shrinkage rate, and in particular, to control the shrinkage cracking of concrete caused by drying shrinkage of concrete, the drying shrinkage rate of concrete in long-term age, The present invention relates to an early estimation method for concrete drying shrinkage that can be estimated with high accuracy at an early stage.

  One of the causes of cracks generated in concrete structures is drying shrinkage of concrete. In order to control the shrinkage cracking of this concrete, the dry shrinkage amount (final dry shrinkage amount) or dry shrinkage rate (final dry shrinkage rate) that progresses over the long-term age (long-term drying period) is estimated and predicted. This is very important.

  By the way, in the length change test (JIS A 1129) for measuring the drying shrinkage rate (shrinkage strain) of ordinary concrete, it is generally dried after being cured under water until the age of 7 days, and usually measured for a period of about 6 months. Is required. In general concrete construction, it is difficult to confirm the quality of concrete more than six months ago, and it is not practical to apply the above test as it is for concrete construction. For this reason, various past studies are underway to estimate (predict) the amount of drying shrinkage at long-term ages from data on drying shrinkage obtained in a short period of time. Various concrete standards in Japan and other countries, The standard proposes estimation (prediction) formulas based on independent research and research results.

  In the Architectural Institute of Japan, in Non-Patent Document 1, based on past research results (Non-Patent Document 2), etc., the relationship between the drying shrinkage strain at the drying period of 4 weeks and 26 weeks (corresponding to the above 6 months) As an average value of the ratio of the two, 1.8 is exemplified, and a value obtained by accumulating about 1σ is recommended as a design value of the drying strain in consideration of other data.

  In Non-Patent Document 2, the ratio of the drying shrinkage at 26 weeks and the drying shrinkage at the short-term age (according to the rapid drying shrinkage test by high temperature and reduced pressure curing) is obtained based on laboratory experiment data, and the drying shrinkage at the short-term age A method for estimating the 26-week drying shrinkage rate by multiplying the measured value of the rate by this ratio has been proposed.

  Other standard recommended values include, for example, the CEB-FIP-1990 formula and the Japan Society of Civil Engineers formula. The CEB-FIP-1990 formula is a prediction formula that takes into account factors such as the curing conditions and age of the specimen as well as the cross-section of the member. The Japan Society of Civil Engineers formula is an experimental regression formula created based on a large number of experimental data. On the other hand, in the research results disclosed in Non-Patent Document 3, supplementation with short-term age data is performed by applying the civil engineering formula to the above-mentioned CEB-FIP-1990 formula. It has been clarified that the accuracy of the prediction formula has been improved.

Edited by Architectural Institute of Japan, “Shrinkage Crack Control Design / Construction Guidelines (Draft) / Commentary of Reinforced Concrete Buildings”, Architectural Institute of Japan, February 10, 2006, p. 120 The Architectural Institute of Japan, “Abstracts of Architectural Lectures of the Architectural Institute of Japan (Kinki)”, The Architectural Institute of Japan, September 2005, p. 601-p. 602 The Architectural Institute of Japan, “Abstracts of Architectural Lectures of the Architectural Institute of Japan (Tokai)”, The Architectural Institute of Japan, September 2003, p. 115-p. 116

However, with the prediction formulas and criteria proposed in Non-Patent Document 1 and Non-Patent Document 2,
(1) It is not practical to calculate the ratio of the drying shrinkage ratio between the drying period of 4 weeks and 26 weeks from the laboratory experiment data, since it is necessary to collect data on the age of 6 months as a reference.
(2) With actual concrete, the time-dependent change characteristics of drying shrinkage differ depending on the materials used and the mixing conditions. For this reason, when the ratio between the drying period of 4 weeks and 26 weeks is uniformly defined as 1.8, the estimation accuracy may be inferior.
(3) Short-term data can be used only for measurement data in the drying period (4 weeks) for which the relationship was obtained in advance, and the estimated drying shrinkage rate was also obtained in the drying period (26 weeks) for which the relationship was obtained in advance. Only things.

Also, in Non-Patent Document 3 and various proposal estimation (prediction) formulas based on past research, materials used for cement (cement type, aggregate type / quality, presence / absence of admixture) and mixing conditions (water cement ratio) It is not taken into consideration that the time-dependent change characteristics of drying shrinkage differ depending on each other, and the verification accuracy is not sufficiently verified.
Therefore, the object of the present invention is to solve the problems of the conventional techniques described above, and propose an estimation formula that takes into account the materials used and the factors of the mixing conditions that are considered to affect the drying shrinkage of the concrete as parameters. It is an object of the present invention to provide an early estimation method for a concrete drying shrinkage rate in which the drying shrinkage rate of concrete in a required age (drying period) is obtained from the short-term age by the estimation formula.

  In order to achieve the above object, the present invention provides a drying period calculation reference period that reaches a drying shrinkage ratio that is 1/2 of the ultimate drying shrinkage ratio from a time-varying characteristic coefficient obtained by multiplying a factor that affects the drying shrinkage of concrete as a coefficient. And calculating an extrapolation primary complementation coefficient based on the drying period calculation reference period and one short-term drying period measurement data, and from the drying period calculation reference period and the extrapolation primary complementation coefficient, It is characterized by estimating the drying shrinkage rate of concrete when an arbitrary drying period has elapsed after the drying period calculation reference period.

  A drying period calculation reference period that reaches a drying shrinkage ratio that is 1/2 of the ultimate drying shrinkage ratio is set from a time-varying characteristic coefficient that is multiplied by a factor that affects the drying shrinkage of the concrete, and the drying period calculation reference period Based on a plurality of short-term drying period measurement data, an extrapolation approximation formula that asymptotically approximates the ultimate drying shrinkage rate is obtained, and based on the extrapolation approximation formula, concrete at any time after the drying period calculation reference period It is characterized in that the drying shrinkage rate of is estimated.

  The extrapolation approximation formula is preferably obtained by a least square method based on the plurality of short-term drying period measurement data.

  It is preferable that the time-varying characteristic coefficient includes a coefficient defined by a linear expression according to a difference in water cement ratio and aggregate dry density.

  Furthermore, it is preferable that the time-varying characteristic coefficient includes a coefficient set according to the difference in aggregate type, cement type, and whether or not an expansion material is used.

  As described above, according to the present invention, the concrete drying shrinkage rate in a predetermined long drying period can be known with high accuracy from a small amount of measurement data obtained in a short drying period through a simple analysis. There is an effect that can be.

  Hereinafter, as the best mode for carrying out the method for early estimation of the concrete drying shrinkage rate of the present invention, two examples that can be selected depending on the difference in the number of measurement data will be described with reference to the accompanying drawings.

FIG. 1 is a flowchart of an estimation method in which the drying shrinkage rate in the long-term drying period t of the concrete to be measured is calculated by the early estimation method of the concrete drying shrinkage rate of the present invention. As shown in the figure, first, in the present invention, the influence on the drying shrinkage of concrete is increased by taking into account the factors of use materials and blending conditions that are considered to affect the fluctuation of the drying shrinkage rate as factors. It was evaluated as a coefficient or a reduction coefficient, and the coefficient obtained by multiplying these coefficients (hereinafter referred to as the time-varying characteristic coefficient) was multiplied by the basic drying period D (days) to take into consideration the materials used and the mixing conditions. , drying period calculation reference period (= 1/2 is reached dry period of the last drying shrinkage S _t (day): Nsa) is calculated.

  Here, the time-varying characteristic coefficient will be described with reference to FIG. In the present invention, what is considered as a factor in the existing estimation formula is adopted, but as shown in each figure of FIG. 2, the change in the coefficient Pα due to the difference in the water cement ratio X, the absolute dry density of the aggregate A coefficient obtained by a linear regression equation for the change in the coefficient Gα due to the difference in Dd is employed. In addition, as other factors, the coefficient Gβ due to the difference in aggregate type, the coefficient Cα due to the difference in cement type, and the like are taken into account, but when applying the coefficient Gβ, limestone is used as an aggregate. Is set to 0.9, and 1.0 for other aggregates. Further, when applying the coefficient Cα, the progress of drying shrinkage of each cement was taken into consideration for three types of cement (ordinary Portland cement, moderately heated cement, and blast furnace cement (Type B)). As a result, Cα was set to 1.0, 1.25, and 0.6, respectively, with the highest value for moderately heated cement with a slow drying shrinkage progression rate. Further, the coefficient Cβ in the case of using the expansion material was set to a coefficient of 1.1 with respect to the case of not using (1.0).

As shown in the following formula, a value obtained by multiplying the basic drying period D by a coefficient (time-varying characteristic coefficient) obtained by multiplying all the coefficients Pα, Gα, Gβ, Cα, and Cβ as described above is a drying period calculation standard. Calculated as the period Nsa (days).
Nsa = D × Pα × Gα × Gβ × Cα × Cβ (Formula 1)
Here, the basic drying period D was set based on the average value of the preparation based on the laboratory experiment for the present invention (D = 25 (days) in this example).

  It should be noted that the change in the relationship between the above-described coefficient effect that affects each time-dependent change characteristic and the drying period calculation reference period Nsa due to the passage of the drying period is shown by the relationship curve schematically shown in FIG. I can know.

  Next, in setting the estimation formula based on the dry period calculation reference period: Nsa, either of two estimation methods may be applied according to the number of measurement data in an arbitrary short-term drying period. Is possible.

[When there is one measurement data]
The drying shrinkage St of the concrete in an arbitrary drying period t (days) is extrapolated from the equation (2) using one measurement data Sts in the drying period calculation reference period Nsa and the short drying period ts (days). By obtaining the complementary coefficient k, it can be easily obtained as (Equation 3).

Ｓt＝ｋ・Ｓts …（式３）
ここで、
Ｓt：乾燥期間ｔ（日）における乾燥収縮率
ｋ：外挿１次補完係数
Ｓts：乾燥期間ts（日）における乾燥収縮率（実測値）
Ｎsa：乾燥期間算出基準期間（日）
ｔ：乾燥期間（日）
ts：短期測定時の乾燥期間（日）

St = k · Sts (Formula 3)
here,
St: Drying shrinkage ratio during the drying period t (days)
k: extrapolation first-order interpolation coefficient
Sts: Drying shrinkage rate during drying period ts (days) (actual measurement value)
Nsa: Drying period calculation reference period (days)
t: Drying period (days)
ts: Drying period for short-term measurement (days)

[Effect of Example 1]
FIG. 4A is a correlation diagram comparing the accuracy of the estimation method using Equation 1 and the estimation method of the prior art. The figure also shows the 95% confidence limit. The prior art shown in FIG. 4B estimates the 26-week dry shrinkage rate by multiplying the measured value of the 4-week dry shrinkage rate by a constant (1.8 times). On the other hand, in order to compare with this prior art, the estimation method of the present invention also showed the result of estimating the 26-week drying shrinkage rate by multiplying the measurement data of the dry material age of 4 weeks by k. The coefficient k at this time is a value that varies depending on Nsa. Specifically, it was obtained by substituting t = 182, ts = 28 and Nsa corresponding to each formulation into (Equation 2). Table 2 illustrates the relationship between Nsa and k when t = 182 and ts = 28.

In the test results shown in the correlation diagram of FIG. 4A, since Nsa is in the range of 10.4 to 32.5, the coefficient k is 1.30 to 1.83. Regarding the correlation accuracy, the determination coefficient R ² = 0.76 and 95% confidence interval ± 1.22 × 10 ⁻⁴ in the conventional technique, whereas in the estimation method of the present invention, the determination coefficient R ² = 0. .87, 95% confidence interval ± 0.88 × 10 ⁻⁴ . When compared under the same conditions, it was demonstrated that the estimation method of the present invention can estimate the drying shrinkage rate with higher accuracy than the prior art.

[When there are two or more measurement data]
In the case where there are a plurality of measurement data for a short drying period, the drying shrinkage rate of the concrete in an arbitrary drying period t (days) is the measurement data for the drying period calculation reference period Nsa and the short drying period (for example, t = 7). , 14, 21,...), A relational expression (extrapolation approximate expression) of data on the graph with the drying period t (day) as the horizontal axis and the drying shrinkage rate St as the vertical axis is calculated by the least square method. Calculate. As a result, a relational expression asymptotic to the ultimate dry shrinkage S∞ is obtained (FIG. 5). This relational expression can be expressed by the following expression.

St = S∞ · t / (Nsa + t) (Formula 4)
here,
St: Drying shrinkage during the drying period t (days)
S∞: Ultimate drying shrinkage
Nsa: Drying period calculation reference period (days)
t: Drying period (days)
Therefore, thereafter, the drying shrinkage rate St in the drying period t (days) can be obtained by substituting the predetermined drying period t into (Equation 4). The accuracy of the equation 4 can be improved by resetting the equation 4 when the number of measurement points of the short-term measurement data increases as the drying period elapses.

[Effect of Example 2]
FIG. 6 is a correlation diagram showing the accuracy of the estimation method using (Expression 4) for the same data as FIG. 4 (a). In order to compare with the estimation method of the prior art (FIG. 4B), in the estimation method of the present invention, a relational expression is obtained using measurement data up to a drying period of 3 weeks, and the results up to the 26-week drying shrinkage rate are estimated. Indicated. Regarding the correlation accuracy, in the estimation method of the present invention, the coefficient of determination R ² = 0.89, 95% confidence interval ± 0.79 × 10 ⁻⁴ . In the estimation method of the present invention, it was confirmed that it was possible to estimate the material age one week earlier than the prior art, and that the accuracy was estimated to be higher (dry shrinkage rate).

The flowchart which showed the work procedure in the Example of the early estimation method of the concrete dry shrinkage rate by this invention. The graph which showed the relational expression of the coefficient for calculating | requiring a time-dependent change characteristic coefficient. The relationship curve figure which showed typically the change by progress of the drying period of the influence of the magnitude of each coefficient, and the relationship with the drying period calculation reference period Nsa. The correlation diagram which compared the precision of the estimation method (Example 1) of this invention, and the estimation method of a prior art. The relationship curve figure which showed the Example which calculated | required the relational expression (extrapolation approximate expression) from the short-term measurement data by the least square method. The correlation diagram which showed the precision of the estimation method (Example 2) of this invention.

Claims (5)

  A drying period calculation reference period that reaches a drying shrinkage ratio that is 1/2 of the ultimate drying shrinkage ratio is set from a time-varying characteristic coefficient that is multiplied by a factor that affects the drying shrinkage of the concrete, and the drying period calculation reference period An extrapolation primary complementary coefficient is obtained based on one short-term drying period measurement data, and an arbitrary drying period after the drying period calculation reference period is determined from the drying period calculation reference period and the extrapolated primary interpolation coefficient. An early estimation method of concrete drying shrinkage characterized by estimating the drying shrinkage of concrete at the time.   A drying period calculation reference period that reaches a drying shrinkage ratio that is 1/2 of the ultimate drying shrinkage ratio is set from a time-varying characteristic coefficient that is multiplied by a factor that affects the drying shrinkage of the concrete, and the drying period calculation reference period Based on a plurality of short-term drying period measurement data, an extrapolation approximation formula that asymptotically approximates the ultimate drying shrinkage rate is obtained, and based on the extrapolation approximation formula, concrete at any time after the drying period calculation reference period A method for early estimation of dry shrinkage of concrete characterized by estimating dry shrinkage of concrete.   The method of early estimation of the concrete drying shrinkage rate according to claim 2, wherein the extrapolation approximation formula is obtained by a least square method based on the plurality of short-term drying period measurement data.   The method for early estimation of concrete drying shrinkage rate according to claim 1 or 2, wherein the time-varying characteristic coefficient includes a coefficient defined by a linear expression corresponding to a difference in water cement ratio and aggregate dry density, respectively. .   The method for early estimation of the concrete drying shrinkage rate according to claim 1 or 2, wherein the time-varying characteristic coefficient includes a coefficient set according to an aggregate type, a cement type difference, and whether or not an expansion material is used.

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