JP2013092445A - Early-stage evaluation method for concrete dry shrinkage strain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an early-stage evaluation method for dry shrinkage strain of concrete that can determine dry shrinkage strain of concrete from a short material age to a necessary long material age with an estimation expression for dry shrinkage strain of concrete.SOLUTION: An early-stage evaluation method for dry shrinkage strain of concrete includes: calculating respective differences (Δε, Δε) between respective final dry shrinkage strain values (ε, ε) of a plurality of pieces of concrete at a temperature of 20±2°C, at a humidity of 60±5%, and at a temperature of 80±3°C (humidity substantially 0%, although no special adjustment is made) and measured values (ε(35,7), ε(35,7)) in a drying period of 28 days, and utilizing a relational expression obtained by approximation of relation between Δεand Δεwith a linear expression or quadratic expression.

Description

  The present invention relates to a method for early evaluation of concrete drying shrinkage strain, and in particular to control cracks caused by concrete shrinkage, the rate of change in length due to drying shrinkage of concrete over a long period of time (hereinafter referred to as “drying shrinkage strain”). It is related with the early evaluation method of the concrete drying shrinkage distortion | strain which can be determined with high precision at an early stage by concrete of short-term age.

As concrete dries, its volume decreases, and this phenomenon is called drying shrinkage. When drying shrinkage is applied to a concrete structure, it causes cracking, so that drying shrinkage strain is regulated.
Shrinkage cracking due to drying shrinkage of concrete is one of the factors that greatly affect the decline in functionality and durability depending on the structure type of buildings and civil engineering structures, and the social demand for its control is increasing year by year. .

For example, in the concrete standard specifications of the Japan Society of Civil Engineers, the drying shrinkage strain of concrete to be considered in the design is indicated as 1200 × 10 ⁻⁶ . In other words, concrete having a drying shrinkage strain of 1200 × 10 ⁻⁶ is practically difficult to apply without taking any measures to a structure in which shrinkage is a problem. Based on the above, the response value of the structure is calculated and the flow to find the solution that passes the verification is recommended. On the other hand, JASS5 of the Architectural Institute of Japan defines the drying shrinkage strain of concrete according to the period of service, the long-term service class of about 100 years as the planned service period, and the ultra-long service of about 200 years as the planned service period In the class, it is 800 × 10 ⁻⁶ or less.

However, the drying shrinkage strain is developed over a long period of time, and it takes several years to complete the numerical value.
Therefore, in order to control the drying shrinkage strain of this concrete, it is important to estimate and predict the drying shrinkage strain that progresses over the long-term age, but in reality it is necessary to confirm long-term measurement data. Is a difficult situation.

In the length change test (JIS A 1129-2 Annex A) for measuring the drying shrinkage rate (dry shrinkage strain) of concrete, it is generally dried after being cured under water until the age of 7 days (182). Day) period 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, in order to estimate the drying shrinkage strain in the long-term age from the drying shrinkage data of the concrete obtained in a short period, various estimation formulas have been proposed, and the judgment for regulating the drying shrinkage strain is Estimates based on short-term data are being used.

  In the Architectural Institute of Japan “Shrinkage Crack Control Design and Construction Guidelines (Draft) of Reinforced Concrete Buildings” (Non-patent Document 1) and the Japan Society of Civil Engineers “Standard Specification for Concrete” (Non-patent Document 2), Due to the characteristic of asymptotically approaching the final value over a long period of time, it is estimated by approximating with functional expressions such as the following expressions (1) and (2).

Here, in the above formula, ε _sh (t, t ₀ ) is the drying shrinkage strain (× 10 ⁻⁶ ) from the drying start material age t ₀ day to the material age t day, and ε _{sh ∞} is the final value of the drying shrinkage strain ( × 10 ⁻⁶ ), α, β, γ, and δ are coefficients representing the degree of progress of drying.

For example, as in Equation (1) ', specific measurement data of drying shrinkage strain from the drying start ages t ₀ at any short ages t _e date of concrete (epsilon _sh (t _e, t _{0) 20} (× 10 ⁻⁶ )) and substituting the drying shrinkage strain (ε _sh (t _L , t ₀ ) (long-term material age t _L ) from equation (1) by determining the final value (ε _sh∞ ) of the drying shrinkage strain. × 10 ⁻⁶ )) is estimated.
In addition, according to the length change test prescribed | regulated to JIS A 1129-2 appendix A which measures the drying shrinkage | contraction strain of concrete, the regulation value of a drying shrinkage strain | stamp is normally 6 months old.

The above formula (1) is the Architectural Institute of Japan “Shrinkage Crack Control Design and Construction Guidelines (Draft) of Reinforced Concrete Buildings” (Non-Patent Document 1), and the above Formula (2) is the Japan Society of Civil Engineers “Concrete Standard Specification” (Non-patent) Reference 2) is adopted, and both of the above formulas are based on a large amount of data on drying shrinkage strain, and α = 0.16 (V / S) ^1.8 (V is the volume of the concrete specimen (mm ^3). ), S is defined as the surface area (mm ² ) of the specimen, and in the length change test for measuring the drying shrinkage strain defined in JIS standard (for example, JIS A 1129-2 Annex A), V / Since S = 22.2 mm, α = 42.5), β = 1.4 (V / S) ^−0.18 (β = 0.8), γ = 0.108, δ = 0.56 It stipulates.

The Architectural Institute of Japan “Construction Cracking Control Design and Construction Guidelines (Draft) of Reinforced Concrete Buildings” (Non-patent Document 1) and “Concrete Standard Specification” (Non-patent Document 2) of Japan Society of Civil Engineers By defining the experimental constant of equation (2), the operation of the estimation equation for drying shrinkage strain is enhanced, but on the other hand, a relatively short drying period (for example, from the drying start material age t ₀ to the concrete age 28) There is a problem that the estimated value of the drying shrinkage strain at the age of 6 months obtained from the measured data in the period until the day) is inaccurate, and the difference from the measured value of the drying shrinkage strain after the age of 6 months is 100 to 200. It may be (× 10 ⁻⁶ ).
Since the regulation value of the drying shrinkage strain according to the Architectural Institute of Japan “Building Construction Standard Specification (JASS5)” is 8 (× 10 ⁻⁴ ), it is 100 to 200 (× 10 ⁻⁶ ) as the difference from the measured value. The error is a numerical value that cannot be ignored.

  In addition, Imamoto et al. “A Study on Prediction of Drying Shrinkage Strain of Concrete Based on Short-term Data” (The Architectural Institute of Japan, No. 602, pp. 15-20, 2006. 4) In the same way as the above guideline, a method is proposed in which the drying shrinkage strain of concrete can be approximated by a specific prediction formula, and the final drying shrinkage strain is estimated by sequentially using all the short-term data.

  In Japanese Patent Application Laid-Open No. 2008-8753, as an early estimation method of concrete drying shrinkage, a drying factor that is 1/2 of the ultimate drying shrinkage is obtained from a time-dependent characteristic coefficient obtained by multiplying a factor that affects the drying shrinkage of concrete as a coefficient. A drying period calculation reference period that reaches the shrinkage rate is set, and an extrapolated primary complementary coefficient is obtained based on the drying period calculation reference period and one short-term drying period measurement data. An early estimation method of concrete drying shrinkage rate has been proposed, which is characterized by estimating the drying shrinkage rate of concrete when an arbitrary drying period has elapsed after the drying period calculation reference period from the first-order complementary coefficient.

However, these evaluation methods can give a very appropriate final drying shrinkage strain within a certain range of materials and blends, but they are not universal evaluation methods.
An example in which application of the rapid evaluation method shown in the prior art is not necessarily appropriate is shown in FIG. Fig. 1 shows the dry shrinkage strain of concrete with the composition shown in Table 1 below, measured using ordinary Portland cement, according to JIS A 1129-2 Annex A. The value is estimated.

Specifically, FIG. 1 shows the above-mentioned Architectural Institute of Japan “Restriction Cracking Control Design / Construction Guidelines (Draft) of Reinforced Concrete Buildings” (former rapid evaluation method 1) and Imamoto ’s “Concrete cracks based on short-term data”. This shows a case where the final value is estimated from the drying shrinkage strain data up to about 28 days using the “Research on Drying Shrinkage Prediction” (Previous Rapid Evaluation Method 2).
In addition, the prediction formula of the drying strain is predicted using the above formula (1) and the above formula (1) ′ (volume surface area ratio V / S = 22.2 mm).
From FIG. 1, it is clear from this FIG. 1 that the estimated value of the final value of the drying shrinkage strain obtained becomes larger when the period from the drying start material age t ₀ to the material age t days (hereinafter, the drying period) is short. Therefore, it is not a sufficient method for early estimation of concrete drying shrinkage.

JP 2008-8753 A

Rapid evaluation method of the Architectural Institute of Japan “Control Design for Shrinkage Cracks, Construction Guidelines (Draft), Commentary on Reinforced Concrete Buildings”, pp. 53-60, and the appendix pp. 186-190 Japan Society of Civil Engineers "Concrete Standard Specification [Design]", pp. 45-46 Keiichi Imamoto, Toshie Ishii, Tetsushi Kaneda, Haruki Momose, Keisuke Fujimori: Research on prediction of drying shrinkage strain of concrete based on short-term data, Structural Architectural Proceedings No. 602, pp. 15-20, 2006.4

The object of the present invention is to solve the above-mentioned problems, and is an early evaluation method for concrete drying shrinkage strain. From an actual measurement value of concrete short-term age shrinkage strain, concrete drying shrinkage strain at an arbitrary long-term age Is to provide an early evaluation method of concrete drying shrinkage strain, which can be determined with high accuracy and early.
Specifically, the drying corresponding to a material age of about 28 days when the ready mixed concrete to be used is determined until the start of construction, that is, the compressive strength of the concrete tested in the room is found to satisfy the nominal strength. In this period, we propose a rapid evaluation method for accurately estimating the drying shrinkage strain at a material age of 6 months.

The early evaluation method of the drying shrinkage strain of the concrete of the present invention is:
(1) For concrete to be evaluated, the temperature is 20 ± 2 ° C. and the humidity is 60 ± 5% (hereinafter abbreviated as “temperature 20 ° C.”) and the temperature is 80 ± 3 ° C. (humidity) after 7 days of age. Is not adjusted, but is dried for up to 28 days under conditions of approximately 0%, hereinafter referred to as “temperature 80 ° C.”), and drying shrinkage strain (ε _sh in a plurality of arbitrary drying periods up to 28 days) (T, t ₀ ) _{20 or 80} )
(2) Using the measured value (ε _sh (t, t ₀ ) ₈₀ ) (× 10 ⁻⁶ ) of the drying shrinkage strains measured in the above (1), the temperature is calculated according to the following equation (1). The final dry shrinkage strain value at 80 ° C. (ε _sh∞80 ) (× 10 ⁻⁶ ), α ₈₀ and β ₈₀ were calculated,
(In the following formula, ε _sh (t, t ₀ ) is the drying shrinkage strain (× 10 ⁻⁶ ) from the drying start material age t ₀ to the material age t day, and ε _sh∞ is the final value of the drying shrinkage strain. (× 10 ⁻⁶ ), α and β are coefficients representing the degree of progress of drying)

(3) The difference (Δε _sh80 ) between the final drying shrinkage strain value (ε _sh∞80 ) at a temperature of 80 ° C. and the actually measured value ε _sh (35, 7) ₈₀ on the drying period 28 days is calculated.
(4) The difference (Δε _sh80 ) between the final drying shrinkage strain value (ε _sh∞80 ) at a temperature of 80 ° C. and the drying shrinkage strain value ε _sh (35, 7) ₈₀ at a drying period of 28 days, which is determined in advance. Using the relational expression between the above-mentioned final drying shrinkage strain value (ε _sh∞20 ) at a temperature of 20 ° C. and the difference (Δε _sh20 ) between the drying shrinkage strain value ε _sh (35,7) ₂₀ of the drying period 28 days, Using the difference (Δε _sh80 ) value obtained in (3) above, the difference value (Δε _sh20 ) of the drying shrinkage strain of the target concrete at 20 ° C. is obtained, and from the difference value (Δε _sh20 ), the above ( The final shrinkage strain estimated value (ε _sh∞20 ) at a temperature of 20 ° C. is calculated from the measured value of the drying shrinkage strain at a temperature of 20 ° C. measured in 1) at a drying period of 28 days.
(5) In the above formula (1), the final shrinkage strain estimated value (ε _sh∞20 ) obtained in the above (4) and the drying shrinkage in the drying period t up to 28 days measured in the above (1) Applying the measured strain value (ε _sh (t, 7) ₂₀ ), α ₂₀ and β ₂₀ are calculated by the least square method,
(6) The final contraction strain estimate (ε _sh∞20 ) obtained in (4) above, α ₂₀ and β ₂₀ obtained in (5) above are applied to the above equation (1), and an arbitrary long-term This is an early evaluation method for dry shrinkage strain of concrete, characterized by estimating a dry shrinkage strain value (ε _sh20 (t _L , 7)) of _material age t _L.

Preferably, in the method for early evaluation of the drying shrinkage strain of the concrete of the present invention, the difference in drying shrinkage strain at the temperature of 80 ° C. (Δε _sh80 ) and the difference in drying shrinkage strain value at the temperature of 20 ° C. (Δε _sh20 ) Is an early evaluation method for drying shrinkage strain of concrete, characterized in that the coarse aggregate contained in the concrete differs between limestone and cases other than limestone.
More preferably, in the method for early evaluation of drying shrinkage strain of concrete according to the present invention, the method for early evaluation of dry yield strain of concrete is characterized in that any long-term drying period is a drying period of 6 months. .

Preferably, in the method for early evaluation of the drying shrinkage strain of the concrete according to the present invention, the difference between the drying shrinkage strain at the temperature of 80 ° C. (Δε _sh80 ) and the difference between the drying shrinkage strain values at the temperature of 20 ° C. (Δε _sh20 ). The relational expression is
(1) A plurality of concretes are dried under a condition of a temperature of 20 ° C. and a temperature of 80 ° C. after a age of 7 days, with a drying period of 6 months or 28 days, respectively, until a drying period of 6 months or 28 days. Measuring the drying shrinkage strain (ε _sh (t, 7) _{20 or 80} ) in a plurality of arbitrary drying periods of
(2) Using the measured value (ε _sh (t, 7) _{20 or 80} ) (× 10 ⁻⁶ ) of the drying shrinkage strains measured in the above (1), the following equation (1): Final dry shrinkage strain value (ε _sh∞20 ) (× 10 ⁻⁶ ) at a temperature of 20 ° C., α ₂₀ and β ₂₀ , and final dry shrinkage strain value (ε _sh∞80 ) at a temperature of 80 ° C. (× 10 ⁻⁶ ) , Α ₈₀ and β ₈₀ ,
(In the following formula, ε _sh (t, t ₀ ) is the drying shrinkage strain (× 10 ⁻⁶ ) from the drying start material age t0 to the material age t days, and ε _sh∞ is the final value of the drying shrinkage strain (× 10 ⁻⁶ ), α and β are coefficients indicating the degree of progress of drying)

(3) The respective final drying shrinkage strain values (ε _sh∞80 , ε _sh∞20 ) at a temperature of 20 ° C. and a temperature of 80 ° C. of the plurality of concrete, and an actual measurement value (ε _sh ( 35,7) ₂₀ , ε _sh (35,7) ₈₀ ) and the respective differences (Δε _sh80 , Δε _sh20 ) are calculated for each concrete, and the relationship between Δε _sh80 and Δε _sh20 is linear or quadratic. This is an early evaluation method for drying shrinkage strain of concrete, characterized in that a relational expression is determined by approximation with an equation.

  More preferably, in the early evaluation method of the drying shrinkage strain of the concrete according to the present invention, the relational expression is constructed separately when the coarse aggregate of concrete is limestone and when it is other than limestone. This is an early evaluation method for drying shrinkage strain of concrete.

  The method for early evaluation of concrete drying shrinkage strain according to the present invention measures an actual measurement value of dry shrinkage strain of concrete in a short-term age, thereby accurately measuring an arbitrary long-term age, for example, drying shrinkage strain in a drying period of 6 months. And it becomes possible to determine early.

It is a correlation figure of an example which shows the correlation with the estimated value of the drying shrinkage distortion by the early evaluation (comparative example) of the conventional drying shrinkage distortion, and a drying period. It is a correlation diagram of an example showing the correlation between the drying period and the measured value of drying shrinkage strain when various concrete specimens are dried at a temperature of 20 ° C. from 7 days of age. It is a correlation diagram of an example showing the correlation between the drying period and the measured value of the drying shrinkage strain when other various concrete specimens are dried at a temperature of 20 ° C. from 7 days of age. It is a correlation diagram of an example showing the correlation between the drying period and the measured value of the drying shrinkage strain when various concrete specimens are dried at a temperature of 80 ° C. from 7 days of age. It is a correlation diagram of an example showing the correlation between the drying period and the measured value of the drying shrinkage strain when other various concrete specimens are dried at a temperature of 80 ° C. from 7 days of age. When the coarse aggregate in the concrete specimen is limestone, the final dry shrinkage strain estimated from the respective dry shrinkage strains when various concrete specimens were dried for 28 days at a temperature of 80 ° C. from 7 days of age. And the final drying shrinkage estimated from each drying shrinkage strain when various concrete specimens were dried at a temperature of 20 ° C. for 6 months under the condition of a drying period of 28 days. It is a correlation diagram which shows correlation with the difference of a distortion | strain and the drying shrinkage | contraction distortion | strain of 28 days. In the case where the coarse aggregate in the concrete specimen is other than limestone, the final dry shrinkage estimated from the respective dry shrinkage strains when various concrete specimens were dried for 28 days at a temperature of 80 ° C. from the age of 7 days. The difference between the strain and the drying shrinkage strain of 28 days, and the final estimated from each drying shrinkage strain when various concrete specimens were dried for 6 months under the condition of a temperature of 20 ° C. from 7 days of age. It is a correlation diagram which shows the correlation with the difference of a drying shrinkage | contraction strain and the drying shrinkage | contraction strain | stamp of the drying period 28 days. The drying shrinkage strain when the concrete specimen was dried for 6 months at a temperature of 20 ° C. from 7 days of age and the estimated value of the drying shrinkage strain for the drying period of 6 months estimated by the method of the present invention. It is a figure which shows a relationship. It is a correlation diagram of an example which shows the correlation between the measured value and the estimated value by the method of the present application, regarding the drying period and drying shrinkage strain of various concrete specimens at a temperature of 20 ° C. It is a correlation diagram of an example which shows the correlation of the actual value and the estimated value by the method of this application about the drying period and drying shrinkage | contraction strain of other various concrete test bodies in temperature of 20 degreeC. It is a flowchart figure which shows schematically the procedure of the database construction for the early evaluation method of the drying shrinkage | contraction strain of this invention. It is a flowchart figure which shows schematically the procedure of the early evaluation method of the drying shrinkage | contraction strain of this invention.

The early evaluation method of the concrete drying shrinkage strain of the present invention will be described in detail below.
FIG. 11 shows dry shrinkage strain (ε _sh (t _L , t ₀ ) (× 10 ⁻⁶ ) at the long-term age t _L (day) of the concrete to be measured in the method for early evaluation of concrete dry shrinkage strain of the present invention. It is a flowchart figure which shows roughly construction | assembly of the relational expression of the database for calculating (). In addition, according to JIS A 1129-2 annex A, the drying start material age will be 7 days.
FIG. 12 shows the dry shrinkage strain (ε _{sh at} the long-term age t _L (day) of the concrete to be evaluated by using the relational expression of the database constructed above by the method for early evaluation of the concrete dry shrinkage strain of the present invention. The flowchart for calculating (t _L , t ₀ ) (× 10 ⁻⁶ )) is shown.

The early evaluation method of drying shrinkage strain in the present invention will be described in detail with reference to the flowcharts of FIGS.
A. Construction of relational expressions used in the evaluation method of the present invention (1) In order to eliminate as much as possible the estimation error of excessive final drying shrinkage strain that may occur when using the existing rapid evaluation method, a plurality of concrete specimens are made from the same concrete. Make a body.
As a suitable example, a total of 12 types of concretes having different materials and their blending amounts were prepared.
The following materials were used for concrete.
・ Cement: Ordinary Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.)
Fine aggregate: river sand or mountain sand. Table 3 shows the density and water absorption rate.
Coarse aggregate: river gravel, limestone, hard sandstone, tuff or sandstone. Table 3 shows the density and water absorption rate.
Admixture: Limestone fine powder (Blaine specific surface area 4580 cm ² / g, density 2.71 g / cm ³ )
・ Water: Tap water

  Table 2 shows the blending amount of concrete. In Table 2, the slump is measured according to JIS A 1101, the slump flow is measured according to JIS A 1150, and the air amount is a value measured according to JIS A 1128. Table 3 shows the physical properties (density and water absorption) of the coarse and fine aggregates used for each concrete.

  According to the JIS standard (JIS A 1129-2 Annex A) using each of the concrete Nos. 2 to 13 in Table 2 prepared above, each concrete has six concrete prism test specimens (100 × 100 × 400 mm prisms). Test specimen). Specifically, a concrete prismatic specimen was prepared in a constant temperature and humidity chamber with a room temperature of 20 ± 2 ° C and a humidity of 80% or more. After placing in the constant temperature and humidity chamber, the mold was removed one day, and the material age was 7 days. Underwater curing was performed at 20 ± 2 ° C. for the 6 days until.

Next, three specimens out of six concrete prismatic specimens Nos. 2 to 13 were subjected to conditions of temperature 20 ± 2 ° C. and humidity 60 ± 5% (JIS A 1129-2 Appendix A) after 7 days of age. 1 day, 3 days, 7 days, 14 days, 28 days (6 points required for actual measurement) and any drying period (t−t) shown in FIG. 2 and FIG. ₀ ) was measured for each concrete specimen in accordance with JIS A 1129-2 Annex A. The drying shrinkage strain (ε _sh (t, t ₀ ) ₂₀ ) in ₀ ) was measured. The measurement of the drying shrinkage strain up to the drying period of 6 months may be more than the above.
The results are shown in FIG. 2 and FIG. However, the actual measurement value of the drying shrinkage strain in each drying period was the average value of the above three specimens of each concrete specimen in the drying period.

(2) Using the measured value (ε _sh (t, t ₀ ) ₂₀ ) (× 10 ⁻⁶ ) of the drying shrinkage strain of each arbitrary age t shown in FIG. 2 and FIG. The final dry shrinkage strain value (ε _sh∞20 ) (× 10 ⁻⁶ ) at 20 ° C. and α ₂₀ and β ₂₀ were determined by the least square method. Table 4 below shows the final drying shrinkage strain (ε _sh∞20 ) obtained for each concrete specimen.

(3) Moreover, the final dry shrinkage strain obtained from the measured value (ε _sh (35,7) ₂₀ ) of the three drying period 28 days of each concrete specimen and the above equation (1). The difference in strain value from (ε _sh∞20 ) is also shown in Table 4 below.

(4) Moreover, among the concrete specimens of Nos. 2 to 13 in Table 2 prepared above, the remaining three concrete prismatic specimens (100 × 100 × 400 mm) are used (up to 7 days of age) For 6 days at 20 ± 2 ° C), dried under the condition of the material age 7 days to the temperature 80 ± 3 ° C (humidity is not adjusted, but almost 0%), and then until 28 days, 1 day, 3 days JIS A 1129-2 appendix shows the drying shrinkage strain (ε _sh (t, 7) ₈₀ ) in each drying period shown in FIG. 4 and FIG. Measured according to A for each concrete specimen. The measurement of the drying shrinkage strain up to the drying period of 28 days may be more than the above.
The results are shown in FIG. 4 and FIG. However, the actual measurement value of the drying shrinkage strain in each drying period was the average value of the above three specimens of each concrete specimen in the drying period.

Using the measured value (ε _sh (t, 7) ₈₀ ) (× 10 ⁻⁶ ) of the drying shrinkage strain from the drying start material age 7 days to each material age t days shown in FIG. 4 and FIG. 1), the final drying shrinkage strain value (ε _sh∞80 ) (× 10 ⁻⁶ ) and α ₈₀ , β ₈₀ at a temperature of 80 ° C. were determined by the method of least squares. The final drying shrinkage strain (ε _sh∞80 ) obtained for each concrete specimen is shown in Table 5 below.

Moreover, the final dry shrinkage strain (ε _sh ) obtained from the measured value (ε _sh (35,7) ₈₀ ) of the three drying periods 28 days of each concrete specimen and the above formula (1). The difference (Δε) in strain value from _∞80 ) is also shown in Table 5 below.

(5) Next, in Table 3 above, the difference (Δε ₂₀ ) between the actually measured drying shrinkage strain value (ε _sh (35,7) ₂₀ ) and the final shrinkage strain (ε _sh∞20 ) value on the 28th drying period is expressed as Y. The difference (Δε ₈₀ ) between the measured value (ε _sh (35, 7) ₈₀ ) and the final shrinkage strain (ε _sh∞80 ) of the drying period 28 days in Table 4 above is defined as the X axis. The coarse aggregate is divided into limestone coarse aggregate (mixing examples 3, 5, 7, 11, 12) and other aggregates (mixing examples 2, 4, 6, 8, 9, 10, 13). The correlation is shown in FIG. 6 (coarse aggregate is limestone) and FIG. 7 (coarse aggregate is other than limestone), and a correlation formula between X and Y is derived by the least square method.
In FIG. 6, the relationship between the two is a quadratic expression of X, and in FIG. 7, the relationship between the two is a linear expression (FIGS. 6 and 7).

In addition, using the correlation equation obtained in the above (5), the measured value (ε _sh (35,7) ₈₀ ) of the drying shrinkage strain value for 28 days at the temperature of 80 ° C. and the final drying shrinkage strain (ε _From the difference (increment) value of the strain value from _sh∞80 ), the measured value (ε _sh (35,7) ₂₀ ) and the final drying shrinkage strain (ε) of the drying period 28 days at a temperature of 20 ° C. The difference (increment) of the strain value from _sh∞20 ) is _obtained . The actual value (ε _sh (35,7) ₂₀ ) of the actual drying period 28 days and the difference obtained by using the correlation equation (the actual value of the drying shrinkage value 28 days of the drying period). By adding the difference (increment) of the strain value between (ε _sh (35,7) ₂₀ ) and the final dry shrinkage strain (ε _sh∞20 ), the final dry shrinkage strain estimate A at a temperature of 20 ° C. is estimated. can do.
On the other hand, the final drying shrinkage of the above formula (1) is calculated using the measured values (ε _sh (t, t ₀ ) ₂₀ ) of the drying shrinkage strains in a plurality of drying periods at a temperature of 20 ° C. of the concrete specimens of each blending example. After substituting the strain value A, α ₂₀ and β ₂₀ are obtained by the least square method.

Furthermore, the drying shrinkage strain for a drying period of 6 months is calculated from the final drying shrinkage strains α ₂₀ and β ₂₀ determined as described above. FIG. 8 shows the relationship between the above estimated value of the drying shrinkage strain during the drying period of 6 months and the actual measurement value.
From FIG. 8, the estimated value of the drying shrinkage strain in the drying period of 6 months and the measured value are relatively in agreement, and the method for estimating the drying shrinkage strain of the concrete using the above correlation equation (5) above. Is a practical estimation method.

B. Evaluation of Drying Shrinkage Strain of Concrete For example, a method for evaluating the drying shrinkage strain of concrete having a drying period of 6 months using the above relational expression will be described.
(6) The target concrete is dried under the conditions of a temperature of 20 ± 2 ° C. and a humidity of 60 ± 5% (JIS A 1129-3 Appendix A) in the same manner as (1) above after 7 days of age. Then, the drying shrinkage strain (ε _sh (t, t ₀ ) ₂₀ ) in a plurality of drying periods up to 28 days was measured for each concrete specimen according to JIS A 1129-2 Annex A (drying period 28 days ( ε _sh (35,7) ₂₀ ) is essential).
(7) Next, in the same manner as in the above (4), the actual measurement value (ε _sh (t, t ₀ ) ₈₀ ) of the drying shrinkage strain in each arbitrary drying period (t−t ₀ ) up to 28 days. × ^{10 -6)} with, the above equation (1), final drying shrinkage strain values at temperatures _{80 ℃ (ε sh∞80) (×} 10 -6) and alpha _80, were calculated by the least squares method beta ₈₀ . The difference (Δε ₈₀ ) between the measured value (ε _sh (28) ₈₀ ) of the drying shrinkage strain value on the 28th drying period and the final dry shrinkage strain (ε _sh∞80 ) obtained from the above equation (1). ) Was also calculated.

(8) Using the correlation equation obtained in (5) above, the actual measurement value (ε _sh (28) ₈₀ ) and the final drying shrinkage strain (ε _sh∞80 ) of the drying period 28 days From the difference (increment) value of the strain value of, the difference in strain value between the measured value (ε _sh (28) ₂₀ ) of the drying shrinkage strain value on the 28th drying period and the final drying shrinkage strain (ε _sh∞20 ) ( Increment).
However, if the target coarse aggregate of limestone is limestone, use the relational expression constructed using limestone to construct the above relational expression, and when the coarse aggregate evaluates concrete other than limestone. A relational expression constructed using coarse aggregates other than limestone is used.
Next, the actual value (ε _sh (35,7) ₂₀ ) of the actual drying period 28 days, the difference obtained by using the correlation equation (the drying shrinkage value 28 days). Of the measured value (ε _sh (35,7) ₂₀ ) and the difference (increment) of the strain value between the final drying shrinkage strain (ε _sh∞20 )) and the estimated final drying shrinkage strain value at a temperature of 20 ° C. A can be estimated.

(9) Next, the final dry shrinkage strain estimated value A obtained in the above (8) of the concrete test body, and a plurality of dry shrinkage strain actual measured values (measured values in the above (6)) up to the drying period of 28 days are used. Thus, α ₂₀ and β ₂₀ are obtained by the least square method according to the equation (1).
Next, the obtained α ₂₀ and β ₂₀ values and the final dry shrinkage strain estimation value A are put into the above formula (1), and the dry shrinkage in an arbitrary drying period of the concrete specimen to be evaluated, for example, the drying period of 6 months. Estimate and estimate the strain value.

(10) Even if the coarse aggregate contained in the concrete test specimen is a rock type different from the examples of the present application, it is basically the same as the above procedures (6) to (9), and the drying period at 80 ° C. An increase from 28 days to the final drying shrinkage strain ε _sh∞80 is determined, and the drying period 28 at a temperature of 20 ° C. is obtained from the approximate curve of FIG. 6 or 7 depending on whether the rock type is limestone or other. Increment to day and final drying shrinkage strain is obtained, and the final drying shrinkage strain is estimated by adding the obtained increment to the drying shrinkage strain of the drying period of 28 days under the condition of 20 ° C., which is performed separately. Next, α ₂₀ and β ₂₀ are determined by the least square method by the above equation (1) using the actual measurement values of the plurality of dry shrinkage strain measurement values up to the drying period of 28 days.
The obtained α ₂₀ and β ₂₀ values and the final dry shrinkage strain estimation value A are put into the above formula (1), and the dry shrinkage strain value in an arbitrary drying period of the concrete specimen of each blending example can be obtained. .

  The present invention can be applied to estimate dry shrinkage strain related to concrete cracks early and accurately depending on the type of coarse aggregate.

Claims (5)

(1) For concrete to be evaluated, the temperature is 20 ± 2 ° C. and the humidity is 60 ± 5% (hereinafter abbreviated as “temperature 20 ° C.”) and the temperature is 80 ± 3 ° C. (humidity) after 7 days of age. Is not adjusted, but is dried for up to 28 days under conditions of approximately 0% and hereinafter referred to as “temperature 80 ° C.”, and drying shrinkage strain (ε ₂₈₎ in a plurality of arbitrary drying periods up to a drying period of 28 days. (T, 7) _{20 or 80} )
(2) Using the measured value (ε _sh (t, 7) ₈₀ ) (× 10 ⁻⁶ ) of the drying shrinkage strain in the plurality of drying periods (t−t ₀ ) measured in (1) above, 1)

(In the above formula, ε _sh (t, t ₀ ) is the shrinkage strain (× 10 ⁻⁶ ) from the drying start material age t ₀ day to the material age t day, and ε _{sh ∞} is the final value of the drying shrinkage strain (× 10 ⁻⁶ ), α and β are coefficients representing the degree of drying)
To calculate the final drying shrinkage strain value (ε _sh∞80 ) (× 10 ⁻⁶ ), α ₈₀ and β ₈₀ at a temperature of 80 ° C.,
(3) Calculate the difference (Δε _sh80 ) between the above final drying shrinkage strain value (ε _sh∞80 ) at a temperature of 80 ° C. and the actual measurement value ε _sh (28) ₈₀ on the drying period 28 days,
(4) The difference (Δε _sh80 ) between the final drying shrinkage strain value (ε _sh∞80 ) at a temperature of 80 ° C. and the drying shrinkage strain value ε _sh (35, 7) ₈₀ at a drying period of 28 days determined in advance. Using the relational expression between the above-mentioned final drying shrinkage strain value (ε _sh∞20 ) at a temperature of 20 ° C. and the difference (Δε _sh20 ) between the drying shrinkage strain value ε _sh (35,7) ₂₀ of the drying period 28 days, Using the difference (Δε _sh80 ) value obtained in (3) above, the difference value (Δε _sh20 ) of the drying shrinkage strain of the target concrete at 20 ° C. is obtained, and from the difference value (Δε _sh20 ), the above ( The final shrinkage strain estimated value (ε _sh∞20 ) at a temperature of 20 ° C. is calculated from the measured value of the drying shrinkage strain at a temperature of 20 ° C. measured in 1) at a drying period of 28 days.
(5) In the above formula (1), the final shrinkage strain estimated value (ε _sh∞20 ) obtained in (4) above and the dry shrinkage strain measured value (ε) up to the drying period of 28 days measured in (1) above. _sh (t, 7) ₂₀ ) to calculate α ₂₀ and β ₂₀ by the least squares method,
(6) The final contraction strain estimate (ε _sh∞20 ) obtained in (4) above, α ₂₀ and β ₂₀ obtained in (5) above are applied to the above equation (1), and an arbitrary long-term An early evaluation method for drying shrinkage strain of concrete, wherein a dry shrinkage strain value (ε _sh20 (t _L , 7)) of age is estimated. In the early evaluation method of the drying shrinkage strain of concrete according to claim 1, the relational expression between the difference (Δε _sh80 ) of the drying shrinkage strain at the temperature of 80 ° C and the difference (Δε _sh20 ) of the drying shrinkage strain value at the temperature of 20 ° C. Is an early evaluation method for drying shrinkage strain of concrete, characterized in that the coarse aggregate contained in concrete differs between limestone and other than limestone.   3. An early evaluation method for drying shrinkage strain of concrete according to claim 1 or 2, wherein an arbitrary long-term drying period is a drying period of 6 months. In the early evaluation method of the drying shrinkage strain of the concrete according to any one of claims 1 to 3, the difference (Δε _sh80 ) of the drying shrinkage strain at a temperature of 80 ° C and the difference (Δε) of a drying shrinkage strain value at a temperature of 20 ° C. The relational expression with _sh20 ) is
(1) About several concrete, it is made to dry to 6 months or 28 days on the conditions of the temperature of 20 degreeC and the conditions of the temperature of 80 degreeC from 7 days after the age, respectively. Measuring the drying shrinkage strain (ε _sh (t, 7) _{20 or 80} ) during any drying period of
(2) Using the measured value (ε _sh (t, 7) _{20 or 80} ) (× 10 ⁻⁶ ) of the drying shrinkage strains measured in the above (1) for a plurality of drying periods,

(In the above formula, ε _sh (t, t ₀ ) is the drying shrinkage strain (× 10 ⁻⁶ ) from the drying start material age t ₀ to the material age t day, and ε _sh∞ is the final value of the drying shrinkage strain (× 10 ⁻⁶ ), α and β are coefficients indicating the degree of progress of drying)
The final drying shrinkage strain values at temperatures _{20 ℃ (ε sh∞20) (×} 10 -6), α 20 and beta _20, and final drying shrinkage strain values at temperatures _{80 ℃ (ε sh∞80) (×} 10 - ⁶ ) Calculate α ₈₀ and β ₈₀ ,
(3) The respective final drying shrinkage strain values (ε _sh∞80 , ε _sh∞20 ) at a temperature of 20 ° C. and a temperature of 80 ° C. of the plurality of concrete, and an actual measurement value (ε _sh ( 35,7) ₈₀ and ε _sh (35,7) ₂₀ ) and the respective differences (Δε _sh80 , Δε _sh20 ) are calculated for each concrete, and the relationship between Δε _sh80 and Δε _sh20 is _expressed by a linear expression or a secondary expression. An early evaluation method for drying shrinkage strain of concrete, characterized in that a relational expression is determined by approximation with a formula. 5. The early evaluation method for drying shrinkage strain of concrete according to claim 4, wherein the relational expression is constructed separately when the coarse aggregate of concrete is limestone and when it is other than limestone. ,
An early evaluation method for drying shrinkage strain of concrete.

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