PSI - Issue 63

Petr Konečný et al. / Procedia Structural Integrity 63 (2024) 21 – 26

22

chloride transport mechanisms in concrete, which is critical for the durability assessment and maintenance planning of concrete structures exposed to chloride environments. 2. Modelling approach This research focuses on the development and comparison of models for predicting chloride ion transport through concrete covers to the reinforcement level considering delay of chloride ion exposure, all of which are based on Fick's Second Law of diffusion. Moreover, these analytical models are advancement of original model (Collepardi et al., 1972) with constant diffusion coefficient and constant surface chloride concentration over the exposure period and improved model with consideration of time dependent diffusion coefficient over reflecting aging of concrete (Tang & Nilsson, 1996). The models aim to describe the diffusion process of chloride ions, a critical factor in assessing the durability and longevity of reinforced concrete structures exposed to chloride environments. Key parameters such as the chloride diffusion coefficient, concrete cover thickness, and environmental conditions are incorporated into the models to enhance their predictive accuracy. The primary outcome of this study is the evaluation and comparison of the time to corrosion initiation, a vital metric for the maintenance and service life prediction of concrete infrastructure. 2.1. Analytical formulas The proposed approach for describing chloride ingress with consideration of delayed exposure utilizes the analytical formula Eq. (1) developed by (Maage et al., 1997):

(1)

where C (t) is a chloride concentration, C s is the surface chloride concentration, x is a investigated depth, D 0 is a reference diffusion coefficient, n is aging factor, t ’ 0 is a reference concrete age, t is exposure period and t ’ ex is a concrete age when an exposure starts. It is worth mentioning that above mentioned approach was criticized in study (Tang & Gulikers, 2007) and approach suggested by the study was also adopted as another analytical approach Eq. (2) and (3): (2)

where is D a :

(3)

In order to evaluate the quality of above-mentioned model with zero delay in chloride ion exposure, following equation (4) based on (Mangat & Molloy, 1994) is used as a reference one.

(4)