JP2003294728A - Penetration speed estimation method of chloride ion into concrete - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an estimation method which can estimate the penetration speed of chloride ions into a cement with high precision regardless of the kind of the cement. <P>SOLUTION: Relationships between the penetration speed of chloride ions into a cement against the content of a reactive alumina in the cement paste and the strength of concrete are obtained beforehand. A penetration speed of a chloride ion into a cement to be measured is estimated from the content of a reactive alumina in the cement paste to be measured and the strength of concrete thereof. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting a chloride ion penetration rate into concrete. 2. Description of the Related Art In recent years, for example, prediction of chloride ion permeation of concrete has been conducted by the Concrete Committee of the Japan Society of Civil Engineers.
As described in the “11th edition of Concrete Standard Specifications”, a method of expressing the diffusion coefficient of chloride ions using the water-cement ratio as an index is often used. In this method, the correlation between the apparent diffusion coefficient of chloride ion of concrete experimentally obtained and the water-cement ratio of the concrete is obtained in advance, and then the diffusion coefficient of chloride ion is actually predicted. Then, the diffusion coefficient is obtained by applying the water-cement ratio of the concrete to the correlation, and the permeation rate is predicted from the obtained diffusion coefficient. In general, the relationship between the apparent diffusion coefficient of concrete and the water-cement ratio is expressed by different regression equations using the water-cement ratio as a parameter, and is used for predicting chloride ion penetration. [0004] However, the conventional prediction method based on the regression equation using the water-cement ratio as a parameter has a problem in that the influence of the type of cement used is relatively large. In other words, the regression equation is different for each type of cement used, and there has been a problem in that prediction cannot be performed in general. [0005] It is an object of the present invention to realize a method for generally predicting chloride ion penetration into various cements by using other indices. [0006] As an index that is deeply involved in chloride ion permeability in concrete, the amount of voids in concrete and the ability of cement to fix chlorides are cited. Concrete compressive strength expresses void volume, and reactive alumina content contained in cement paste in concrete expresses chloride fixing ability. The present inventors, by using the compressive strength δ of concrete, the reactive alumina content Al in the paste as a parameter, accurately predict the chloride ion penetration rate of concrete, and regardless of the type of cement used And completed the present invention. That is, the present invention relates to a method for predicting the chloride ion penetration rate into concrete, in which the correlation between the chloride ion penetration rate and the content of reactive alumina in cement paste and concrete strength is determined in advance. In advance, for the concrete for which the chloride ion penetration rate is to be predicted, the chloride ion penetration rate of the concrete is predicted by applying the reactive alumina content in the cement paste used and the strength of the concrete to the correlation. How to [0008] In the present invention, it is necessary to determine in advance the correlation between the permeation rate of chloride ions and the content of reactive alumina in cement paste and the strength of concrete using the cement. . Here, the content of reactive alumina is a content of alumina having a large surface area and rich in chemical reactivity, and specifically, γ-group alumina called so-called reactive alumina corresponds to this. To determine the correlation between the reactive alumina content and concrete strength, the chloride ion permeation rate of multiple types of concrete is experimentally determined, the strength of each concrete is determined, and the concrete The content of reactive alumina in the cement is determined. At this time, data on chloride ion penetration rate, strength and reactive alumina content in cement will be obtained for a wide range of concrete types such as concrete using different cements and concretes with different mixes. This is preferable because the accuracy is improved. Next, the correlation between the chloride ion penetration rate, strength, and the reactive alumina content in the cement paste is determined. The correlation is preferably represented by, for example, a regression equation. Although the type of the regression equation is not particularly limited, for example, the following equation can be given as the regression equation. ζ = k ₁ × √ {exp (k ₂ × δ)} / (Al + k ₃ ) (1) where ζ is a chloride ion permeation rate coefficient, δ is compressive strength of concrete, and Al is cement used for concrete. Reactive alumina content in paste, k ₁ , k ₂ , k ₃
Is a constant. Ζ can be obtained by experimentally determining the depth of chloride ion penetration into concrete and dividing the depth by the square root of the penetration time. Alternatively, in the case where the depth of chloride ions permeating concrete is determined by performing a dry / wet repetition test, the depth may be divided by the square root of the number of cycles of dry / wet cycles instead of the square root of the permeation time. On the other hand, δ does not depend on the measuring method, but can be determined by, for example, JIS A 1108 “Method for testing compressive strength of concrete”. Furthermore, Al
Although it does not depend on the measurement method, it can be determined, for example, by dividing the Al ₂ O ₃ content in cement determined by JIS R5201 by the sum of the volume of the cement and the volume of water used in the concrete. Optimum values obtained by obtaining combinations of ζ, δ, and Al for a plurality of types of concrete and fitting the regression equation to the combinations are defined as k ₁ , k ₂ , and k ₃ . Next, the chloride ion penetration rate of the target concrete can be determined by utilizing the correlation between the chloride ion penetration rate, strength, and the reactive alumina content in the cement paste. For example, δ for ζ as above
And when it is obtained as a regression equation with Al as a parameter, the Al of the cement paste in the concrete and the strength of the concrete are obtained and substituted into the regression equation to accurately predict ζ of the target concrete. Can be. Although the prediction method according to the present invention is not particularly affected by the environment in which concrete is placed, it can be applied particularly accurately to chloride ion permeation under dry and wet repeated conditions. The method for predicting the chloride ion permeation rate according to the present invention can be applied regardless of the type of cement used and the mix of concrete. That is, the present invention can be suitably applied to a case where ordinary Portland cement, early-strength Portland cement or blast furnace cement is used as cement. Further, even when the water-cement ratio of the concrete is changed or the unit amount of the concrete material is different, the method of the present invention can accurately predict. The value of Al used in the above-mentioned prediction formula can be applied to a case where a mixture is added to cement and used. For example, even when blast furnace slag, fly ash, metakaolin and the like are used as an admixture, Applicable. In this case, a correlation is obtained by using a value obtained by dividing the reactive alumina content in the so-called binder obtained by combining the cement and the mixture with the sum of the volume of the binder and the volume of water, and a correlation is obtained, and prediction is performed. EXAMPLES Concrete specimens using various types of cements, such as general-purpose cements in Japan and overseas, were prepared in various combinations.
Curing was performed in water at 20 ° C. until the age of 28 days. Table 1 shows the chemical composition of the cement used, and Table 2 shows the concrete composition, fresh properties and strength. These cements can be broadly divided into ordinary cement-based NPC, early-strength cement-based HPC, blast furnace slag cement-based BB, and other cements. [Table 1] [Table 2] Thereafter, drying was performed in a 3% aqueous sodium chloride solution at 20 ° C. for 3 days and in a constant temperature room at 20 ° C. and a relative humidity of 60% for 4 days. The test was performed. In this test, chloride ion penetration depth x (mm) in each cycle, reactive alumina content Al (g / L) contained in cement paste in concrete, compressive strength of concrete specimen at 28 days of age δ (N
/ Mm ² ). Al was determined by the following equation. Al = (Al ₂ O _{3 in} Table 1) × Cement unit amount / (Total volume of cement and water) On the other hand, δ was determined by JIS A 1108. The chloride ion permeation rate coefficient ζ is calculated by using the cycle number of repetition of dry and wet cycles instead of the permeation time t.
I asked. That is, ζ = x / (cycle) ^0.5 (2) Water / cement ratio of each concrete W / C, ζ, δ, A
l are summarized in Table 3. [Table 3] Next, k ₁ , k ₂ and k ₃ were obtained by fitting the data of Table 3 to the equation (1). That is, 回 帰 = 40.8 × に お け る {exp (−0.0492 × δ)} / (Al−18.8) (3) was obtained as the regression equation in this example. Next, for each concrete in Table 2, the correlation between ζ and the water-cement ratio (W / C) was determined by regression based on the conventional method. As a result, the following regression equation ζ = 0.0427 × (W / C) +0.1939 (4) was obtained. Next, based on the composition shown in Table 4, various kinds of cement were used, and concrete was newly kneaded to prepare test specimens. A chloride immersion test was performed on each concrete specimen in the same manner as described above, and the chloride penetration depth was measured. Meanwhile, for each concrete
The value of Al was substituted into equations (3) and (4) to predict ζ. Ζ based on chloride immersion test and ζ based on equations (3) and (4) were compared. Table 5 summarizes the results. From Table 5, it was confirmed that ζ according to equation (3) was in good agreement with ζ based on chloride immersion test regardless of the type of cement, whereas に 対 し according to equation (4) was inferior in accuracy. [Table 4] [Table 5] According to the method of the present invention, the cement used,
The chloride penetration rate of concrete can be accurately predicted without depending on the type of admixture and the strength of concrete.

Claims (1)

Claims: 1. A method for predicting a chloride ion permeation rate into concrete, comprising: a reactive alumina content in a cement paste with respect to a chloride ion permeation rate; and a concrete using the cement. The correlation with the strength is determined in advance, and for the concrete for which the chloride ion penetration rate is to be predicted, the reactive alumina content in the cement paste used and the strength of the concrete are applied to the correlation to apply the correlation to the concrete. A method for predicting chloride ion penetration rates.