JP2007024570A - Concrete deterioration progress estimation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concrete deterioration progress estimation method for estimating the progressing degree of actual concrete deterioration with a small error. <P>SOLUTION: Concrete is categorized into three phases, that is, a gaseous phase, a liquid phase, and a solid phase, and represented by using a model in consideration of mass transfer among them. Further, reactions related to concrete deterioration are enumerated and represented by using a model. Based on the models, a mass transfer equation and a rate equation are made up. Calculations are performed as to time and a depth direction by using these equations to estimate the progressing degree of concrete deterioration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a concrete deterioration progress prediction method for predicting the degree of progress of deterioration in a depth direction of a concrete structure including a hardened cement body and a reinforcing bar.

  Deterioration of concrete structures progresses in the depth direction over time, but it is extremely difficult to judge the extent of deterioration from the appearance. However, when the concrete deteriorates, cracks are generated in the concrete structure, and water, oxygen, carbon dioxide, etc. invade from the cracks, and the deterioration is promoted to reduce the strength of the concrete structure or to peel off. Therefore, it is necessary to predict the progress of deterioration of the concrete structure. Such deterioration of concrete mainly includes deterioration due to salt damage and deterioration due to neutralization.

  Deterioration due to salt damage refers to deterioration in which reinforcing bars embedded in concrete are corroded by salt contained in sand, which is a raw material of concrete, or salt that has come from the surrounding environment and permeated into the interior.

  Deterioration due to neutralization means that calcium hydroxide, which is a cement hydration product in concrete structures, reacts with carbon dioxide in the atmosphere to neutralize and become calcium carbonate, losing the protective function of reinforcing bars in an alkaline atmosphere. It means to end up.

For such deterioration of concrete, research for predicting the degree of deterioration has been conventionally performed (for example, Patent Document 1). Patent Document 1 discloses a deterioration prediction method for a concrete structure in which the deterioration of the concrete structure due to salt damage and neutralization is predicted by analyzing various deterioration factors by the finite element method. Specifically, a diffusion equation <1> represented by a chemical reaction formula including a cement hydration product in concrete and carbon dioxide in the atmosphere on one side and calcium carbonate on the other side; Two equations of diffusion equation <2> represented by a reversible chemical reaction formula containing calcium carbonate, aluminate and chloride on one side and Friedel's salt and carbon dioxide on the other side Represents the progress of complex deterioration, and the two equations are analyzed and predicted by the finite element method.
JP 2003-222622 A

  However, since the technique disclosed in Patent Document 1 represents deterioration only by two diffusion equations <1> and <2>, it can cope with deterioration due to salt damage and deterioration due to neutralization. Deterioration other than neutralization, for example, acid degradation, is not included in the equation, so there is a gap between prediction and reality.

  In addition, since the concept of the reaction equation is ambiguous in the two diffusion equations <1> and <2>, correct prediction cannot be performed. For example, the formula is such that gaseous carbon dioxide directly reacts with a solid component, but such a reaction does not actually occur.

  Furthermore, in the two diffusion equations <1> and <2>, since the reaction rate is not taken into consideration, the rate of progress of deterioration is different from the actual rate of progress. That is, in the two diffusion equations <1> and <2>, it is assumed that the reaction occurs instantaneously, and the change over time is calculated simply by calculating the diffusion of carbon dioxide and the diffusion of chloride using the diffusion equation. is there.

  As described above, in the method for predicting concrete deterioration disclosed in Patent Document 1, since the prediction is performed based on a reaction different from the reaction actually occurring, the prediction result is greatly deviated from the actual result. .

  This invention is made | formed in view of this point, The place made into the objective is to provide the concrete deterioration progress prediction method which can predict the progress degree of actual concrete deterioration with a small error.

  In order to solve the above problems, the inventors of the present application pay attention to the fact that a concrete structure including a hardened cement body and a reinforcing bar is composed of a solid phase, a liquid phase, and a gas phase. We arrived at the idea of predicting deterioration by considering the change of the substance in each phase and the phase change of the substance between the gas phase-liquid phase and between the liquid phase and the solid phase. Furthermore, the chemical reactions related to concrete deterioration in the concrete structure are listed, and the idea of using reaction rate equations in the solid phase, liquid phase, and gas phase for the prediction of deterioration has been reached, leading to the present invention.

  Specifically, the concrete deterioration progress prediction method of the present invention is a concrete deterioration progress prediction method for predicting the degree of progress of deterioration in the depth direction of a concrete structure including a hardened cement body and a reinforcing bar. The concrete which comprises the hardened body and the reinforcing bar and constitutes the concrete structure is divided into a gas phase, a liquid phase and a solid phase, a mass transfer model between each phase and in the depth direction, and in each phase A model creation step for creating a reaction model; a mass creation equation for creating a mass transfer equation according to the mass transfer model; and a reaction rate equation according to the reaction model; the mass transfer equation and the reaction rate equation And calculating with respect to time and the depth direction. Here, the concrete which comprises a hardened cement body and a reinforcing bar and constitutes a concrete structure means that “the cement, water, fine aggregate, coarse aggregate and admixture added as necessary are used as constituent materials. It is defined in JIS A 0203 as “mixed or mixed by other methods or cured”. Create a reaction model by enumerating the chemical reactions actually occurring in the solid phase, liquid phase, and gas phase existing in the concrete, and create a model of mass transfer between each phase and in the depth direction. Therefore, the deterioration phenomenon actually occurring is expressed almost faithfully in a macro manner. Since the reaction rate equation in the chemical reaction is created and calculated, the actual deterioration progress is predicted almost accurately.

The degree of progress of deterioration is preferably predicted based on a decrease in OH ⁻ concentration in the liquid phase.

The degree of progress of deterioration is preferably predicted by a decrease in the amount of Ca (OH) _{2 in} the solid phase.

The degree of deterioration progression is preferably predicted by an increase in the ratio of Cl ⁻ concentration to OH ⁻ concentration in the liquid phase.

Wherein the deterioration degree, Cl in the liquid phase ^- it is preferable to predict the increase in concentration.

  In the present invention, a reaction model is created by a chemical reaction actually occurring in each of a solid phase, a liquid phase, and a gas phase existing in a concrete structure, and mass transfer between each phase and in the depth direction is performed. Since the model is created, the actual degradation phenomenon can be expressed almost faithfully in a macro manner. And since the reaction rate formula in each chemical reaction is created and calculated using the reaction model, the actual deterioration progress can be predicted almost accurately.

  Before describing the embodiments of the present invention, the background of the present invention will be described.

  Concrete structures consist of cement, water, fine aggregate (sand), coarse aggregate (gravel), and admixtures added as needed, and these are mixed and cured by other methods. It consists of a certain concrete and a reinforcing bar. In concrete, there are voids formed by the hydration reaction between cement and water, together with air bubbles mixed in during mixing, and there is also water that was not used for hydration. And the liquid phase and the gas phase coexist. As described in the background art, the deterioration of concrete is mainly due to deterioration due to salt damage and deterioration due to neutralization. Degradation due to salt damage proceeds due to chloride ions, and deterioration due to neutralization proceeds as calcium hydroxide reacts with carbon dioxide in the atmosphere to become calcium carbonate. When actual reaction is observed, for example, The phenomenon that actually occurs is that carbon dioxide in the gas phase does not react suddenly with calcium hydroxide in the liquid phase or solid phase, but both dissolve and react in the liquid phase.

  Therefore, in order to accurately predict the progress of concrete deterioration, it is necessary to consider the actual structure inside the concrete and the phase in which the reaction related to the deterioration occurring inside the concrete occurs. It turns out that it is important to do. The inventors of the present application have considered these two points, and have devised a model that takes into account mass transfer and reaction rate based on these two points.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

A model of mass transfer and reaction in concrete containing hardened cement and reinforcing bars is shown in FIG. FIG. 1 shows in what form each substance in the solid phase, liquid phase, and gas phase exists, and the movement between phases and the reaction in each phase regarding substances related to concrete deterioration. ing. In this way, concrete is first divided into three phases, and a mass transfer model between each phase and in the depth direction and a reaction model within each phase are created. Here, ettringite is one of cement hydrates and is a compound represented by 3CaO.Al ₂ O ₃ .3CaSO ₄ .32H ₂ O. C ₃ A is a compound represented by 3CaO · Al ₂ O ₃ . Friedel said salt is a compound represented by _{3CaO · Al 2 O 3 · CaCl} 2 · 10H 2 O. C—S—H is calcium silicate hydrate. In the case of C ₃ S ₂ H ₃ , C—S—H is represented by 3CaO.2SiO ₂ .3H ₂ O.

  The mass transfer and reaction shown in FIG. 1 are specifically expressed in a mass transfer equation and a reaction rate equation as shown in the following formula 1. These formulas enumerate the mass transfer and reactions that are thought to actually occur in the solid phase, liquid phase, and gas phase of concrete.

  Equation 1 includes a chemical reaction equation, a mass transfer equation, and a reaction rate equation. As can be seen from FIG. 1, since the chemical reaction occurs in the liquid phase, the vaporization of water and the water vapor are stored together with mass conservation of the substances present in the gas phase and the liquid phase (equations (3), (4), (5)). The state of the liquid phase is accurately grasped by the balance of water (formula (38)) accompanying liquefaction (formula (37)), reaction and vaporization, and the like. Further, in Formula 1, carbonation of the cement hydration product accompanying the diffusion of carbon dioxide (formula (20), (22), (24), (28)), and chlorination accompanying the carbonation of the cement hydration product. The release and diffusion of chloride ions and the fixation of chloride ions in the uncarbonated part (Equations (24) and (25)) and the corrosion reaction of reinforcing bars (Equations (39) to (41) and (43)) The degradation phenomenon of concrete classified roughly is included, and these reactions are respectively (21), (23), (26)-(27), (30)-(36), (42), (44). Modeled by the equation (45).

  For example, concrete deterioration due to neutralization is directly expressed by the equations (22) and (23), but the carbon dioxide is dissolved in the liquid phase ((11) and (12)) and Production of carbonate ions (formulas (13) to (18)) is also greatly related. In other words, in the present embodiment, the reaction formula is not a reaction equation ignoring the actual phenomenon that carbon dioxide in the gas phase reacts with calcium hydroxide in the solid phase, but the relationship in the gas phase, liquid phase, and solid phase. The model is constructed by combining the reaction formulas related to concrete deterioration in consideration of all the reactions.

Moreover, in Formula 1, the actual reaction rate is considered by the formula including the reaction rate constant (represented by k _** . ** is various subscripts). Therefore, it is possible to accurately reflect the speed of the deterioration phenomenon actually occurring in the model.

  Based on Equation 1 described above, the concrete deterioration is predicted by performing calculations in the steps shown in FIGS. The calculation was performed using a computer.

  As shown in FIG. 2, first, initial conditions and boundary conditions are input. The initial conditions and boundary conditions naturally vary depending on the mix of concrete used and the environment in which the concrete structure is placed. An example of the initial conditions is shown in Equation 2.

  Examples of boundary conditions are: outside temperature: constant 25 ° C., outside humidity: 60% R.D. H. Constant, evaporation from the interface liquid phase part is allowed, and there is no diffusion of ions from the interface liquid phase part to the outside. Then, a 0.5 mm square cube inside the concrete is considered as a minute element, and calculation is performed considering chemical reaction and mass transfer in the minute element.

  The numerical value used for the calculation is shown in Equation 3.

  The initial conditions shown in Expression 2 and the numerical values shown in Expression 3 are numerical values known from literatures or are obtained by experiments.

  In the steps shown in FIGS. 2 to 5, calculation is performed using time as one parameter. The time is assumed to be 0.00001 days (0.864 seconds) as one unit, and the step proceeds every unit. That is, the calculation starts from the first step of time under the initial conditions and boundary conditions of FIG. In this calculation, the depth from the concrete surface is also given as an initial condition, and thereafter, the reaction and the mass transfer at a predetermined depth are calculated.

Subsequently, it is determined whether or not steel is present. If steel is present, calculate the rust of the steel. When Fe (OH) ₂ is present, it is rusted. If it is not rusted, it is determined whether [Cl ⁻ ] / [OH ⁻ ]> 3, and if the ratio is 3 or more, it is determined that the iron is rusted and the corrosion of the steel material is calculated. I do. As described above, when [Cl ⁻ ] increases, iron rusts.

Next, as shown in FIG. 3, how much oxygen in the gas phase is dissolved in the liquid phase is calculated. Then, calculate the decomposition and generation of Friedel's salt. At this time, Cl ^- is generated along with the decomposition. As described above, [Cl ⁻ ] is related to iron rust. Then calculate ettringite decomposition and generation.

Subsequently, decomposition of C—S—H and Ca (OH) ₂ by carbonic acid is calculated. As Ca (OH) ₂ decreases, deterioration due to neutralization proceeds. That is, the amount of Ca (OH) ₂ is one of indicators of deterioration due to the neutralization of concrete. Also in this case, OH in the liquid phase ^- molar concentration is an index of the degradation due to neutralization of the concrete, which means that the degradation has progressed this concentration decreases.

Then, as shown in FIG. 4, calculation is performed regarding dissolution / dissociation of carbonic acid. Since carbon dioxide is consumed in the deterioration reaction of concrete, CO _{2 in} the atmosphere dissolves in the liquid phase and is supplied into the concrete. Also, Ksp = [Ca ²⁺ ] [CO ₃ ²⁻ ]? Because is that whether satisfies the solubility product of CaCO _3, dissociation or precipitate CaCO ₃ so as to satisfy this solubility product. This determines the molar concentration of CaCO _{3 in} the solid phase.

Next, as shown in FIG. 5, [H ⁺ ] and [OH ⁻ ] are increased or decreased while maintaining the ionic product of water so as to satisfy the charge balance. Then, the vaporization of water and the liquefaction of water vapor are calculated, and the calculation of one loop is completed so as to satisfy the volume conservation law. The calculated various values, for example, in the liquid phase OH ^- concentration, the amount of Ca in the solid phase (OH) _2, in the liquid phase Cl ^- concentration of OH ^- ratio to the concentration, Cl in the liquid phase ^- Concentration , The total Cl amount and the like are output. Then, after one step has elapsed, the process returns to A1 in FIG. 2 again to calculate the next loop.

In this way, calculation and output are performed by repeating the loop from FIGS. 2 to 5 many times until the initially set period t _max (for example, 50 years) is reached.

  FIG. 6 to FIG. 13 are graphs showing the results of the above calculation for a period of 50 years. The horizontal axis is the depth position (mm) from the concrete surface. As a condition for calculation, since aggregate is mixed, the ratio of the hardened cement body to the whole concrete is set to 24%.

FIG. 6 represents the change in OH ⁻ concentration in the liquid phase. At the beginning of the production of the concrete structure, the OH ⁻ concentration in the liquid phase was 10 ⁻¹ (mol / L) or more on the surface, but gradually 10 ⁻¹⁰ (mol / L) from the surface over time. ) It decreases rapidly to the following, and after 50 years, the concentration is very low from the surface to about 55 mm. That is, when the OH ⁻ concentration (calculated value) in the liquid phase is observed from the deep part of the concrete toward the surface, it can be said that the depth position where the value rapidly decreases is the depth at which the concrete deterioration is progressing.

FIG. 7 represents the change in the amount of Ca (OH) _{2 in} the solid phase. As described above, this amount is an indicator of concrete deterioration due to neutralization. This change shows the same tendency as the change in the OH ⁻ concentration in the liquid phase of FIG. 6, and the depth at which the concentration changes abruptly is almost the same as in FIG. 6 in each elapsed period. That is, when the amount of Ca (OH) _{2 in} the solid phase (calculated value) is observed from the deep part of the concrete toward the surface, the depth position where the value rapidly decreases is the depth at which the concrete deterioration is progressing. it can.

FIG. 8 represents the change in the amount of CaCO _{3 in} the solid phase. This change is completely opposite to the amount of Ca (OH) _{2 in} the solid phase shown in FIG. 7, and when the amount of Ca (OH) _{2 in} the solid phase decreases, The amount of CaCO ₃ increases. Therefore, the amount of CaCO _{3 in} the solid phase can also be an indicator of concrete deterioration due to neutralization. Further, the depth at which the concentration rapidly changes in FIG. 8 is almost the same as that in FIG. 6 in each elapsed period. That is, when the amount of CaCO ₃ in the solid phase (calculated value) is observed from the deep part of the concrete toward the surface, it can be said that the depth position where the value rapidly increases is the depth at which the concrete deterioration is progressing.

FIG. 9 shows the change in the concentration of HCO ₃ ^{− in} the liquid phase. Increased, but the concentration is substantially zero, increasing the concentration at the surface As the time passes, even concentration in the concrete so as to correspond to it ^- initially manufacture of the concrete structure, HCO ₃ in the liquid phase is doing. In this case, when compared with FIGS. 6 to 8, the depth at which the concentration of HCO ₃ ⁻ in the liquid phase becomes almost 0 when viewed from the concrete surface can be said to be the depth at which the concrete deterioration is progressing.

FIG. 10 shows the change in the ratio of the Cl ⁻ concentration to the OH ⁻ concentration in the liquid phase. The larger the ratio, the more likely the steel bars to rust. This ratio is an index for determining the start of deterioration due to salt damage. As can be seen from the figure, the initial position is about 10 ⁻⁴ at any position in the depth direction, but increases rapidly with time, so the calculated OH ⁻ concentration of Cl ⁻ concentration in the liquid phase. When the value of the ratio to the surface is observed from the depth of the concrete toward the surface, if a reinforcing bar exists in a range where the value exceeds 3, it can be determined that the reinforcing bar starts to rust.

FIG. 11 shows the change in Cl ⁻ concentration in the liquid phase. It is known that the Cl ⁻ concentration in the liquid phase does not simply increase or decrease with time, but a concentrated region appears inside when it is neutralized at the same time. Also in the calculation of this embodiment, a peak appears at a position about 40 mm deep from the surface after 30 years, and the same result as an actual phenomenon appears. From this result, it can be seen that the model and calculation formula of this embodiment are appropriate. As the Cl ⁻ concentration in the liquid phase increases, the degree of rusting of the reinforcing bars increases, and this concentration is an indicator of deterioration due to salt damage. In this embodiment, a portion having a depth of 80 mm from the surface is set as the analysis target range. However, when 40 years or 50 years have elapsed, the change in the Cl ⁻ concentration in the liquid phase exceeds the analysis target range. Therefore, the graph does not show data for 40 or 50 years.

  FIG. 12 represents a change in the total Cl amount. As time elapses, the peak position of the total Cl amount moves deeper from the concrete surface. Even if the total amount of salinity present in the concrete is not high, this indicates that there is a high concentration of Cl in such a concentrated area, and if this area coincides with the location of the reinforcing bar, there is a possibility that the reinforcing bar will rust. It is necessary to consider. For this reason, the total amount of Cl is also an indicator of deterioration due to salt damage.

  FIG. 13 is a graph showing how the depth of deterioration due to neutralization changes depending on the elapsed years based on the above calculation. The liquid phase in concrete is usually alkaline with a pH of about 12.6 to 13.2, but when red becomes colorless by a phenolphthalein solution (discoloration range: pH 8.3 to 10), the portion is neutral. It is generally determined that Therefore, in this embodiment as well, it was determined that neutralization occurred when the pH became 10 or less. Degradation in the depth direction progresses relatively quickly for about 10 years from the beginning of the manufacture of the concrete structure, and then progresses somewhat moderately, but in any case, the deterioration depth due to neutralization is the number of years elapsed. The calculated value sufficiently reproduces the general tendency that is proportional to the square root.

  The degree of progress of deterioration predicted in this way can be used in various ways. For example, the prediction of deterioration due to salt damage can be used as a design decision material to determine how dense the concrete should be and where in the depth direction the rebar should be placed. Accurate service life can be calculated. Alternatively, in an existing concrete structure, it is possible to know an appropriate rebuilding time and repair time from the calculated predicted value, and it is possible to obtain safety and cost advantages. In other words, even if it is time for deterioration to progress, it is impossible to determine deterioration from the surface state unless the prediction of this embodiment is used, and the concrete structure collapses and becomes a dangerous state. If the deterioration prediction of this embodiment is used, avoid the situation where the progress of deterioration is not so advanced and there is no need for repair, but the concrete structure is repaired and there is an extra cost. Can do.

  The above-described embodiment is an example of the present invention, and the present invention is not limited to this example. As a calculation method, a finite element method or a difference method may be used. The initial conditions and boundary conditions are also examples, and the numerical values may be changed depending on the location where the concrete structure exists, the type of cement, the blending of concrete, and the like. Also, the numerical value to be substituted may be changed by performing a verification experiment. Another reaction may be added to the reaction model. As an index for predicting deterioration of concrete, an index other than the concentration and amount shown in FIGS. 6 to 13 may be used. Although the calculation is performed with the temperature being constant, it may be calculated using an actual temperature change by using a program or a computer that can calculate at a high speed. If a new reaction mechanism is found for the reaction formula, the reaction formula may be changed to the reaction formula. Furthermore, you may add acidic deterioration prediction. For acid degradation, when hydrochloric acid, sulfuric acid or the like is considered as an acid, the chemical reaction formulas shown in the formulas (20), (22), (24), and (28) are also applied to these acidic substances. By applying mutatis mutandis, deterioration prediction can be performed.

  As described above, the concrete deterioration progress prediction method according to the present invention can predict the actual deterioration progress almost accurately, and is useful as a concrete structure design, a service life prediction, a repair time estimation, and the like. .

It is the model figure which showed the mass transfer and reaction in concrete. It is a figure which shows a part of analysis flow of concrete deterioration prediction. It is a figure which shows a part of analysis flow of concrete deterioration prediction. It is a figure which shows a part of analysis flow of concrete deterioration prediction. It is a figure which shows a part of analysis flow of concrete deterioration prediction. It is a graph in which the horizontal axis represents the depth of concrete and the OH ⁻ concentration in the liquid phase represents the vertical axis. It is a graph in which the horizontal axis represents the depth of concrete and the amount of Ca (OH) _{2 in} the solid phase represents the vertical axis. It is a graph in which the horizontal axis represents the depth of concrete and the amount of CaCO _{3 in} the solid phase represents the vertical axis. It is a graph in which the horizontal axis represents the depth of concrete and the vertical axis represents the concentration of HCO ₃ ⁻ in the liquid phase. It is a graph in which the horizontal axis represents the depth of concrete and the ratio of the Cl ⁻ concentration in the liquid phase to the OH ⁻ concentration represents the vertical axis. It is a graph in which the horizontal axis represents the depth of concrete and the Cl ⁻ concentration in the liquid phase represents the vertical axis. It is the graph which took the depth of concrete on the horizontal axis, and took the total Cl amount on the vertical axis. It is the graph which took elapsed time on the horizontal axis and took the depth in which neutralization occurred on the vertical axis.

Claims (5)

A concrete deterioration progress prediction method for predicting the degree of progress of deterioration in a depth direction of a concrete structure including a hardened cement body and a reinforcing bar,
The concrete constituting the concrete structure including the hardened cement body and the reinforcing bar is divided into a gas phase, a liquid phase, and a solid phase, a mass transfer model between each phase and in the depth direction, and each phase A model creation step to create a reaction model at
Formula creation step for creating a mass transfer equation according to the mass transfer model and a reaction rate equation according to the reaction model;
A calculation step of calculating the mass transfer equation and the reaction rate equation with respect to time and the depth direction. The method for predicting the progress of deterioration of concrete according to claim 1, wherein the degree of progress of deterioration is predicted by a decrease in OH ^- concentration in the liquid phase. The concrete deterioration progress prediction method according to claim 1, wherein the deterioration progress degree is predicted by a decrease in the amount of Ca (OH) _{2 in} the solid phase. Wherein the deterioration degree, Cl in the liquid phase ^- OH concentrations ^- predicting the increase of the ratio to the concentration, concrete degradation progression prediction method according to claim 1. Wherein the deterioration degree, Cl in the liquid phase ^- to predict the increase in density, the concrete deterioration progresses prediction method according to claim 1.

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