Numerical approach for concrete carbonation considering moisture diffusion
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ORIGINAL ARTICLE
Numerical approach for concrete carbonation considering moisture diffusion Ju-young Hwang . Hyo-Gyoung Kwak
. Minsuk Shim
Received: 27 April 2020 / Accepted: 19 August 2020 Ó RILEM 2020
Abstract Carbonation is a common type of concrete deterioration, which can cause various physicochemical changes that adversely affect the performance of reinforced concrete structures. The reinforced concrete structures can be considerably damaged by the reinforcement corrosion caused by the neutralization of concrete under carbonation. This study introduces a numerical analysis approach to examine concrete carbonation with calcium hydroxide (Ca(OH)2), which decreases the alkalinity of concrete. Carbonation analysis is performed by considering the diffusion of carbon dioxide (CO2) and moisture, which play influential roles in the carbonation reaction. A detailed formulation process is established to apply the theoretical equations to the numerical analysis by considering the mentioned influential factors. Further, appropriate modification factors are applied to the numerical analysis under various environmental conditions. The proposed numerical analysis is verified by comparing the carbonation front depths with those obtained from the experimental results via thermogravimetric analysis. Furthermore, a carbonation experiment is conducted using a phenolphthalein solution, and the results are compared with those of the numerical analysis. The experimental carbonation
J. Hwang H.-G. Kwak (&) M. Shim Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea e-mail: [email protected]
front depth obtained using a phenolphthalein solution is half of that obtained using numerical analysis, which is consistent with the result obtained by other researchers in previous studies. These observations indicate that the proposed numerical analysis considering CO2 and moisture diffusion sufficiently simulates concrete carbonation. Keywords Concrete carbonation analysis Moisture diffusion Carbonation front depth Phenolphthalein indicator
1 Introduction Among the chemical compounds of concrete, calcium hydroxide (Ca(OH)2) and calcium–silicate–hydrate (C–S–H) react with carbon dioxide (CO2 ) to become a stable compound such as calcium carbonate (CaCO3 ). These chemical reactions are collectively referred to as concrete carbonation. Although carbonation results in certain structural advantages, including an increase in the compressive strength of the concrete material [1], the performance of the reinforced concrete (RC) structure is observed to decrease because of reinforcement corrosion. Carbonation with C–S–H in gel form can reduce the strength of the structure because of the disintegration of C–S–H. Alternatively, carbonation with CaðOHÞ2 reduces the hydroxide (OH ) within
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the concrete, decreasing the pH level [2]. This type of carbonation decreases the alkalinity of concrete f
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