Method for predicting relative humidity inside concrete
The method addresses humidity measurement inaccuracies in concrete by using a time function and compressive strength to predict relative humidity, improving prediction accuracy by considering concrete age.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TAIHEIYO CEMENT CORP
- Filing Date
- 2024-11-27
- Publication Date
- 2026-06-08
AI Technical Summary
Conventional methods for measuring humidity inside concrete, especially in thick concrete, face issues with accuracy due to sensor contact with water and specimen size increase, and fail to account for changes in the diffusion coefficient over time due to hydration progression.
A method for predicting relative humidity using a relational expression that considers the influence of concrete age by incorporating a time function and compressive strength, allowing for improved moisture transfer analysis.
The method provides a practical and realistic analysis of moisture movement with enhanced prediction accuracy by accounting for the age of the concrete.
Smart Images
Figure 2026092875000001_ABST
Abstract
Description
[Technical Field]
[0001] This invention relates to a method for predicting the relative humidity inside concrete. [Background technology]
[0002] Understanding the characteristics of moisture and humidity movement within concrete is crucial for enhancing its long-term durability and extending its lifespan. In recent years, various characteristics used in moisture movement analysis have been studied by measuring changes in moisture and humidity within concrete, and analyses that take into account the effects of moisture movement are being conducted (Non-Patent Documents 1-4). Furthermore, in order to understand the moisture transport characteristics, it is necessary to accurately measure the humidity inside the concrete, and the diffusion coefficient calculated using this humidity can be used in simulations of moisture transport, etc.
[0003] Conventionally, the method for measuring humidity inside concrete was: (i) Method of measuring by embedding a humidity sensor inside the concrete. (ii) A method of measuring humidity by covering the humidity sensor with a waterproof and breathable material and embedding it inside the concrete. (iii) A method of measuring humidity by drilling a hole in the concrete after it has hardened and inserting a humidity sensor. (iv) A method of measuring humidity by inserting a humidity sensor into a pipe that has been covered with a waterproof and breathable material, after concrete has been poured and the formwork has been removed. These are some examples.
[0004] However, a problem with the conventional measurement method described above is that the test specimen becomes large when the object being measured is thick concrete, such as mass concrete. Also, since humidity sensors generally use a capacitive method (a method that converts humidity from the amount of water vapor and the electrical resistance value), there are cases where the humidity sensor cannot measure correctly, such as when it comes into contact with water and shows a relative humidity of 100%. Therefore, if the humidity sensor is covered or inserted into a pipe to prevent contact with water, or if the concrete is drilled to insert the humidity sensor after it has hardened, problems arise such as a decrease in measurement accuracy due to drying and vibration.
[0005] Therefore, in order to address the above problems, the present inventors have proposed a method for easily and accurately measuring the relative humidity inside concrete (Patent Document 1), a method for easily measuring the relative humidity, drying shrinkage strain, and relative water content inside concrete using a single device, a method for obtaining the water content of concrete at multiple relative humidity levels simultaneously in a short period of time (Patent Documents 2 and 3, respectively), and a humidity measuring device that can accurately measure the humidity inside concrete without increasing the size of the test specimen (Patent Document 4).
[0006] However, the diffusion coefficient included in the relationship between humidity and diffusion coefficient used in conventional moisture analysis methods is the same whether it is immediately after drying or after a year of drying, and does not take into account fluctuations in the diffusion coefficient due to changes in pore structure as hydration progresses. However, in reality, the rate of humidity movement slows down as hydration progresses, so the relationship between humidity and the diffusion coefficient is expected to change over time. Therefore, in order to improve prediction accuracy, a relational equation that takes into account the effect of the concrete's age (effective age) is necessary. [Prior art documents] [Non-patent literature]
[0007] [Non-Patent Document 1] Toshinori Mizobuchi, Minoru Kure, Hideaki Nakamura, Naoyuki Osada, "Examination of Each Property Used in the Analysis of Moisture Transfer in Concrete", Transactions of the Japan Concrete Institute, Vol.42, No.1, pp.655-660, 2020
Non-Patent Document 2
Non-Patent Document 3
Non-Patent Document 4
Patent Document
[0008]
Patent Document 1
Patent Document 2
Patent Document 3
Patent Document 4
Summary of the Invention
Problems to be Solved by the Invention
[0009] Therefore, in view of the above problems, an object of the present invention is to provide a method for predicting relative humidity using a relational expression considering the influence of the age of concrete.
Means for Solving the Problems
[0010] As a result of studying a method for predicting relative humidity including a time function, the present inventor has found that as the hydration period becomes longer, the diffusion coefficient decreases and the compressive strength increases. Therefore, by introducing an equation that employs the compressive strength at an arbitrary age of concrete as a time function, a more practical and realistic moisture transfer analysis can be performed, and the prediction accuracy can be improved. The present invention having the following configuration has been completed.
[0011] [1] A method for predicting relative humidity inside concrete, including at least the following steps (A) to (C). (A) A step of measuring the relative humidity U inside concrete and obtaining a moisture diffusion coefficient D without considering the influence of the age of concrete. (B) A step including the following processes (B1) to (B3) of measuring the compressive strength Fc (te) of concrete and obtaining a moisture diffusion coefficient D (te) considering the influence of the age of concrete. (B1) A process of calculating coefficients c and d by regression analysis based on the following equation (1) and deriving a compressive strength equation F e including the effective age t c(te) . F c(te) = (c × t e ) / (d + t e ) ···(1) However, in equation (1), F c(te) represents the compressive strength (N / mm e ) of concrete at the effective age t 2 (days), and c and d represent coefficients. The above effective age (t e ) is the age obtained by converting the influence of the curing temperature on the hydration reaction so as to be equivalent to the degree of hydration when the curing temperature is 20°C. (B2) A process of deriving a time function CS c(te) of the following equation (2) including the above compressive strength equation F (te) . CS (te) = 1 / (F c(te) / F c(s) ) ···(2) However, in equation (2), CS (te) represents a time function, and F c(te)The effective age t e Compressive strength (N / mm²) 2 ) represents F c(s) This is the compressive strength (N / mm²) at the standard effective age. 2 This represents the effective age t. e If it is 7 days or less, CS (te) = 1. (B3) Moisture diffusion coefficient D and time function CS, without considering the effect of concrete age. (te) Using this, the moisture diffusion coefficient D of equation (3) below, which takes into account the effect of concrete age, is obtained. (te) The process of finding a solution. D (te) = D × CS (te) ...(3) However, in equation (3), D (te) D represents the moisture diffusion coefficient considering the effect of concrete age, D represents the moisture diffusion coefficient without considering the effect of age, and CS (te) This represents a time function. (C) Moisture diffusion coefficient D considering the effect of age (te) A process for predicting the relative humidity inside concrete by analyzing moisture transfer using [a specific method / tool]. [2] The method for predicting the relative humidity inside concrete as described in [1] above, wherein step (A) above is a step of determining the moisture diffusion coefficient D without considering the effect of age using equations (4) and (5) below. TIFF2026092875000002.tif19117 However, in equation (4), D is the moisture diffusion coefficient (cm) that does not take into account the effect of age. 2 U0 represents the relative humidity (%) at the start of drying, and λ is the Boltzmann variable (cm / day). 1 / 2 ) represents. TIFF2026092875000003.tif23115 However, in equation (5), λ is the Boltzmann variable (cm / day 1 / 2 ) represents the relative humidity (%), U0 represents the relative humidity (%) at the start of drying, and a and b represent coefficients. [Effects of the Invention]
[0012] The present invention's method for predicting relative humidity inside concrete uses a relational expression that includes a time function that takes into account the effect of the concrete's age, enabling a practical and realistic analysis of moisture movement and improving the accuracy of relative humidity prediction. [Brief explanation of the drawing]
[0013] [Figure 1] This is a schematic diagram showing an example of a humidity measuring device that simulates the space inside a concrete, used to measure the relative humidity inside the concrete in the above process (A). [Figure 2] This graph shows the relationship between the relative humidity of concrete N, measured using the humidity measuring device described above, and the drying period. [Figure 3] This graph shows the relationship between the relative humidity of concrete SRA measured using the humidity measuring device described above and the drying period. [Figure 4] This graph shows the relationship between the moisture diffusion coefficient, which does not take into account the age of the concrete and is calculated using equations (4) and (5) above, and the relative humidity. [Figure 5] This graph shows the relationship between compressive strength and effective age, using equation (1) above. [Figure 6] This graph shows the relationship between the ratio of the compressive strength at any effective age (Fc(te) / Fc(7d)) to the compressive strength at a standard effective age of 7 days, as shown in equation (2) above. [Figure 7] This is a schematic diagram showing the analytical model used in the present invention. [Figure 8] This is a schematic diagram of a concrete test specimen used to verify the prediction accuracy of the present invention. [Figure 9] This graph (Comparative Example 1) shows the relationship between relative humidity and drying period using concrete N and a moisture diffusion coefficient that does not include a time function. [Figure 10] This graph (Example 1) shows the relationship between relative humidity and drying period using concrete N and a moisture diffusion coefficient that includes a time function. [Figure 11] This graph (Comparative Example 2) shows the relationship between relative humidity and drying period using concrete SRA and a moisture diffusion coefficient that does not include a time function. [Figure 12] This graph (Example 2) shows the relationship between relative humidity and drying period using concrete SRA and a moisture diffusion coefficient that includes a time function. [Modes for carrying out the invention]
[0014] As described above, the present invention is a method for predicting the relative humidity inside concrete, comprising at least steps (A) to (C). The present invention will now be described in detail, divided into each of steps (A) to (C).
[0015] (A) process Step (A) is a process of measuring the relative humidity U inside the concrete and determining the moisture diffusion coefficient without considering the effect of the concrete's age. The method for measuring the relative humidity U inside the concrete is not particularly limited, but one example is a method for measuring the relative humidity in a space that simulates the inside of concrete. Specifically, as shown in the lower part of Figure 1, this method involves dividing a cylindrical acrylic housing into two halves along its length, and placing multiple concrete discs with their circumferences sealed inside one half (a trough-shaped half). Then, the two halves are joined together to form a cylindrical housing. A dummy specimen, with its end face covered as shown below, is inserted into one end of the cylindrical housing and sealed. A humidity measuring device (temperature and humidity sensor) is then inserted between the dummy specimen and the multiple concrete discs, and the measurement is performed using a humidity measuring device that simulates the inside of concrete.
[0016] Furthermore, as shown in the upper part of Figure 1, after cutting out multiple concrete discs and one dummy specimen (moisture-releasing material) from the concrete, the circumference of each concrete disc is sealed with a rubber ring (sealant), and one of the two end faces of the dummy specimen and the area around that end face are covered with a covering material such as aluminum foil adhesive tape.
[0017] (B) process Step (B) is the process of measuring the compressive strength of the concrete and determining the moisture diffusion coefficient that takes into account the age of the concrete, and consists of the following steps (B1) to (B3).
[0018] The process in (B1) is the process of deriving the compressive strength equation (1) by calculating the coefficients c and d in equation (1) above using regression analysis. The process in (B2) is the process of deriving equation (2), which is a time function that includes the above compressive strength formula. Here, the standard effective age in the above compressive strength formula can be set arbitrarily; for example, the standard effective age can be set to 7 days. The process in (B3) involves using the moisture diffusion coefficient of equation (3) above, which takes into account the effect of concrete age, with the moisture diffusion coefficient without considering the effect of concrete age, and a time function.
[0019] (C) process Process (C) is a step in which the relative humidity inside the concrete is predicted by moisture transport analysis using a moisture diffusion coefficient that takes into account the effect of age.
[0020] In this invention, the moisture diffusion coefficient, which does not include a time function, can be calculated using the above relative humidity and equations (4) and (5). Incidentally, the coefficients a and b in equation (5) are 0.048 and 0.30, respectively, for ordinary Portland cement-containing concrete, and 0.036 and 0.26, respectively, for ordinary Portland cement-containing concrete containing a shrinkage-reducing agent. [Examples]
[0021] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. 1.Materials used The materials used are shown in Table 1.
[0022] [Table 1]
[0023] 2. Preparation of concrete discs and concrete test specimens According to the concrete mix shown in Table 2, all of the above materials were added together to a 50-liter pan-type mixer and mixed for 2 minutes. The mixture was then poured into a formwork with an inner diameter of 10 cm and a height of 20 cm to form two types of concrete (N and SRA). In Table 2, "adjustment" means that the admixture addition rate was adjusted so that the slump of the concrete was 15 ± 1.5% and the air content in the concrete was 4.5 ± 1.5%.
[0024] [Table 2]
[0025] Next, the two types of concrete described above were sealed and cured at 20°C for 7 days before being demolded. After demolding, as shown in the upper part of Figure 1, five concrete discs with a diameter of 100 mm and a thickness of 10 mm, and one dummy specimen (moisture-releasing material) with a diameter of 100 mm and a thickness of 100 mm were cut out from the concrete. However, the concrete placement surface was discarded because its structure was weak due to bleeding. Furthermore, the circumference of each concrete disc was sealed with a rubber ring (sealant), and one of the two end faces of the dummy specimens and the area around that end face were covered with aluminum tape (adhesive tape made of aluminum foil).
[0026] 3. Calculation of the moisture diffusion coefficient without a time function (1) Measurement of relative humidity in a simulated concrete space As shown in the lower part of Figure 1, a cylindrical acrylic housing was divided longitudinally into two halves. Five sealed concrete discs were placed in the groove on the inside of one half of the housing (a trough-shaped half). Then, this half and the remaining half of the housing were joined together to form a cylindrical housing. Next, as shown in the lower part of Figure 1, the covered dummy specimen was inserted into one end of the cylindrical housing and sealed. Five humidity measuring devices (temperature and humidity sensors SHT35, manufactured by Sensirion) were inserted between the dummy specimen and the five concrete discs to create a humidity measuring device with five simulated spaces that mimic the inside of concrete.
[0027] Next, the humidity measuring device described above was stored in an environment with a relative humidity of 43%, and the relative humidity (U) in these simulated spaces was measured over an arbitrary drying period. The results are shown in Figure 2 (concrete used is N) and Figure 3 (concrete used is SRA). As shown in Figures 2 and 3, the humidity measuring device described above allows for the simultaneous and easy measurement of the change in relative humidity over time at distances of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm from the dry surface (opening of the enclosure) (excluding the open space).
[0028] (2) Calculation of the moisture diffusion coefficient (D) that does not include a time function Using the above relative humidity (U), the moisture diffusion coefficient (D), which does not include a time function, was calculated using equations (4) and (5) above. In equations (4) and (5), the Boltzmann variable λ is the value obtained by dividing the distance from the dry surface by half the drying period. A Boltzmann transform was performed on the measured relative humidity, and coefficients a and b were obtained by regression analysis using equation (5) above. Figure 4 shows the moisture diffusion coefficients, excluding the time function, for each relative humidity level.
[0029] 4. Calculation of the moisture diffusion coefficient including a time function (1) Measurement of the compressive strength of concrete Table 2 shows the effective age of concrete N and concrete SRA at 7 days (t 7d ), and any effective age (t eCompressive strength in ) (each, F c(7d) and Fc (te) The compressive strength of concrete was measured in accordance with JIS A 1108 "Test Method for Compressive Strength of Concrete".
[0030] (2) Regression analysis using the above compressive strength and effective age The above F c(te) and effective age (t e The coefficients c and d of equation (1) above were determined by regression analysis using ). As a result, for both ordinary Portland cement-containing concrete (N) and ordinary Portland cement-containing concrete containing a shrinkage-reducing agent (SRA), c=52.43 and d=5.88.
[0031] (3) Derivation of the time function The ratio of the compressive strength at any given age to the compressive strength at 7 days of age (Fc (te) / Fc (7d) Using ), the time function (CS) is obtained by equation (2) above. (te) ) was calculated. The ratio of the effective age (te) to the above compressive strength (Fc (te) / Fc (7d) Figure 6 shows a graph illustrating the relationship between the two.
[0032] (4) Calculation of the moisture diffusion coefficient including a time function The moisture diffusion coefficient (D) that does not include the above time function, and the above time function (CS (te) Using equation (3) above, we obtain the moisture diffusion coefficient (D) that includes a time function. (te) ) was calculated.
[0033] 5. Moisture transport analysis The moisture diffusion coefficient (D) without the above time function and the moisture diffusion coefficient (D) including the above time function (te) Using the analysis model shown in Figure 7, moisture transport analysis was performed using moisture diffusion coefficient analysis software (product name: ASTEA MACS (manufactured by the Computational Mechanics Research Center Co., Ltd.)).
[0034] Furthermore, in order to verify the analytical accuracy (predictive accuracy) of the present invention, concrete test specimens shown in Figure 8 were prepared and their internal relative humidity was measured. The above test specimen measured 300 mm in length, 300 mm in width, and 300 mm in height. With two sides excluding the casting surface designated as dry surfaces, the specimen was sealed and cured at 20°C for 7 days after casting. The relative humidity inside the concrete was measured using a capacitive temperature and humidity sensor by placing plastic pipes (10 mm in diameter, 100 mm in length) at distances of 10 mm, 25 mm, 50 mm, 75 mm, and 150 mm from the dry surface. Furthermore, a waterproof and breathable film was attached to the tip of the pipe embedded in the concrete to prevent concrete and water from entering the inside of the pipe. The pipe was embedded to a depth of 50 mm perpendicular to the sealing surface. These results are shown in Figure 9 (Comparative Example 1), which uses concrete N and a moisture diffusion coefficient without a time function; Figure 10 (Example 1), which uses concrete N and a moisture diffusion coefficient including a time function; Figure 11 (Comparative Example 2), which uses concrete SRA and a moisture diffusion coefficient without a time function; and Figure 12 (Example 2), which uses concrete SRA and a moisture diffusion coefficient including a time function. However, the curves in the figures show the results of the moisture transport analysis, and the plots show experimental values.
[0035] As can be seen by comparing Figures 9 and 10, and Figures 11 and 12, the relative humidity prediction method of the present invention, which takes time into account, has significantly higher prediction accuracy than the conventional relative humidity prediction method that does not take time into account.
Claims
1. A method for predicting the relative humidity inside concrete, comprising at least the following steps (A) to (C). (A) A step of measuring the relative humidity U inside the concrete and determining the moisture diffusion coefficient D without considering the effect of the concrete's age. (B) Compressive strength of concrete Fc （ｔｅ） The moisture diffusion coefficient D, which takes into account the age of the concrete, was measured. （ｔｅ） The following (B) is required to find the answer １ ) ~ (B ３ A process that includes the steps of ). (B １ Based on the following equation (1), coefficients c and d are calculated by regression analysis, and the effective age t is determined. ｅ Compression strength formula F c(te) The process of deriving it. F c(te) = ( c × t e ) / ( d + t e ) ・・・(1) However, in equation (1), F c(te) The effective age t ｅ Compressive strength of concrete in (Japan) (N / mm²) 2 ) represents the coefficients, where c and d represent the coefficients. (B ２ ) The above compressive strength formula F c(te) The time function CS in the following equation (2) （ｔｅ） The process of deriving it. CS (te) = 1 / ( F c(te) / F c(ｓ) ) ・・・(2) However, in equation (2), CS (te) represents a time function, F c(te) The effective age t ｅ Compressive strength (N / mm²) 2 ) represents F c(ｓ) This is the compressive strength (N / mm²) at the standard effective age. 2 This represents the effective age t. e If it is 7 days or less, CS (te) = 1. (B ３ ) Moisture diffusion coefficient D without considering the effect of concrete age, and time function CS （ｔｅ） Using this, the moisture diffusion coefficient D of the following equation (3), which takes into account the effect of concrete age, is obtained. （ｔｅ） The process of finding a solution. D (te) = D × CS (te) ・・・(3) However, in equation (3), D (te) D represents the moisture diffusion coefficient considering the effect of concrete age, D represents the moisture diffusion coefficient without considering the effect of age, and CS (te) This represents a time function. (C) Moisture diffusion coefficient D considering the effect of age （ｔｅ） A process for predicting the relative humidity inside concrete by analyzing moisture transfer using [a specific method / tool].
2. The method for predicting the relative humidity inside concrete according to claim 1, wherein step (A) above is a step of determining the moisture diffusion coefficient D without considering the effect of age using equations (4) and (5) below. However, in equation (4), D is the moisture diffusion coefficient (cm²) that does not take into account the effect of age. 2 U represents ( / day), U represents relative humidity (%), U 0 λ represents the relative humidity (%) at the start of drying, and λ is the Boltzmann variable (cm / day) 1 / 2 ) represents. However, in equation (5), λ is the Boltzmann variable (cm / day). 1 / 2 ) represents, and U represents relative humidity (%), U 0 represents the relative humidity (%) at the start of drying, and a and b represent coefficients.