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Durability Prediction System


>Introduction >Overview >Thermodynamic phase equilibrium model
 Mass transfer model
>Features >Example of durability prediction >Future prospects

Compared to conventional durability simulations, our simulation supports a variety of environmental conditions and degradation phenomena. The simulation possesses a high level of versatility which is not restricted by the mixtures of concrete structures or the type of materials.

By using the thermodynamic phase equilibrium model, this simulation enables calculation of the phase composition required for initial conditions. Calculations are based on the chemical composition of cement, reaction ratio of cement minerals, and concrete mixture.
In other words, unlike conventional simulations, our simulation is not restricted to certain types of materials or mix proportions. This enables durability prediction for diverse cases with a varied mix proportion, such as different types of portland cement and blended cement containing slag and fly ash.

Conventional durability prediction for chloride attack environment has focused only on chloride as the environmental factor. However, in our simulation, it is possible to input the exact seawater composition as the environmental conditions. This enables the durability prediction to consider the effect of sodium ions, magnesium ions, sulfate ions, and other ions other than chloride ions contained in seawater.
Furthermore, calculations in our simulation also consider the gas phase. Therefore, the simulation can respond to a wide range of environmental conditions which include carbon dioxide and humidity in the atmosphere.

By combining phase equilibrium and the mass transfer model, our simulation supports a wide range of diverse degradation phenomena.
This simulation is able to calculate composition changes in gas, liquid, and solid phases inside of hardened cement by coupling the phase equilibrium model with a mass transfer model which is used for the transfer of many types of species. As a result, the degradation phenomena for which durability prediction can be conducted is not limited to chloride attack; it also includes carbonation, sulfate attack, and a variety of other degradation. In addition, the simulation also supports coupled degradation in which chlorde attack and carbonation occur simultaneously.

What is coupled degradation?
Coupled degradation is a phenomenon in which multiple forms of degradation occur simultaneously in concrete. Normally, coupled degradation is more severe than when individual forms of degradation occur independently. Accordingly, it is extremely important to focus on coupled degradation when predicting durability.
Coupled degradation consisting of carbonation and chloride attack
When carbonation and chloride attack occur simultaneously in concrete, the pH of pore solution in the concrete decreases and enrichment of chloride occurs. This generates a higher concentration of chloride inside the concrete than if chloride attack was to occur independently, and also causes in a decrease in pH. As a result, there is a higher risk of corrosion for rebar installed in the concrete.
Mechanism of chloride enrichment caused by coupled degradation consisting of carbonation and chloride attack
Chloride enrichment caused by coupled degradation consisting of carbonation and chloride attack occurs when the decrease in pH due to carbonation causes decomposition of hydrates known as Friedel's salt, which are generated when cement components react with chloride. The decomposition of Friedel's salt causes chloride released into pore solution to move to deeper areas of the concrete, thus causing chloride enrichment.


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