Incorporating Cracks in Chloride Ingress Modeling and Service Life Predictions

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Title: Incorporating Cracks in Chloride Ingress Modeling and Service Life Predictions

Author(s): Jose Pacheco

Publication: Materials Journal

Volume: 116

Issue: 5

Appears on pages(s): 113-118

Keywords: chloride exposure; concrete cracking; service life

Date: 9/1/2019

Abstract:
The presence of uncontrolled or unexpected nonstructural cracking in reinforced concrete structures generally leads to conflict and disputes. The current industry practice aims to prevent or mitigate the presence of cracking at early ages (that is, plastic shrinkage, thermally induced cracking) or due to volumetric changes (restrained or drying shrinkage). However, cracking of concrete can still occur and lead to questioning the durability of concrete with prolonged service life expectations such as bridge decks, piers, or waterfront structures, to name a few. The effect of cracks on chloride penetration has been thoroughly studied, and evidence of the effect of cracks on accelerated ingress of chlorides is well established. Structural codes and guides, on the other hand, consider that the integrity of the concrete element is not significantly affected as long as the crack width does not exceed a recommended limit based on exposure conditions. Similarly, service life predictions based on chloride ingress modeling disregard the effect of cracks. Because crack-free concrete cannot be guaranteed, service life predictions that neglect the effect of cracks can be significantly inaccurate. A simplified approach is presented in this paper, where a correction to the chloride diffusion coefficient of concrete is performed to account for the effect of cracks. This correction is similar, in principle, to the so-called aging or decay coefficient in concrete. Results of Monte Carlo simulations on chloride ingress and estimations of the time-to-corrosion initiation are presented and discussed. Results indicate that a decrease of the reliability index (β), or an increase in the probability of failure (pf), can be calculated when accounting for the effect of cracks.