Keywords: chloride diffusivity, damage model, concrete durability, finite element simulation.

The design of concrete structures to withstand the mechanical loads imposed on them during their useful life span may seem inadequate in regions where aggressive environmental factors may lead to premature failure of the structure as a result of some durability requirements. These include environmental agents such as chloride ingress that promote reinforced concrete deterioration. Insufficiencies for durability requirements in these regions' design codes for concrete structures hinder the durability-based concrete design. Interestingly, researchers from many such areas continuously strive to define some guides or tools to aid in the basic understandings of their local structural durability requirements or problems through either experiment and, or numerical simulation.

This paper presents a study carried on the effect of damage imparted by the service loading on chloride diffusion in concrete. A review of existing damage models, such as the pioneering work of Kachanov [1], was made followed by the proposal of and the simulation of a linear damage model with an in-house FORTRAN computer code. This was written to solve the governing differential equation for concrete diffusivity and to capture the chloride ingress profiles in undamaged structures. To appreciate the practical engineering application of the phenomenon, a beam of specified span under the influence of both dead and live loads was, first, designed. The effect of the damage was evaluated using a simplified linear damage model which maps the stress distribution in the beam's cross-section to a dimensionless damage parameter. As a result of the low concrete tensile strength compared with its compressive strength, only the tensile zone was considered to be affected in the damage prediction. A 34x34x7 inch specimen was used in this study by discretizing it into a total of 100 elements (with nine nodes per element). A comparison was made between the damaged and non-damaged model to study the influence of the modification on the chloride ion ingress into the concrete sample tested. The results show that damage at grain-paste interfaces in tensile zones leads to an increase of rate of penetration of the aggressive chloride ions, which leads to a reduction in the useful life span of a structure.

In addition, in order to validate the model, two of the beams tested experimentally and simulated by [2] were simulated using the proposed approach in this study. A comparison was made between the results obtained here and those in [2] and a close agreement was found between the two.

1

L.M. Kachanov, "Time of the fractured process under creep conditions", Izv. Akad. Nauk. SSSR OTN Tekh. Nauk, 8(1), 26-31, 1958.

2

W.A. Al-Kutti, "Simulation of Chloride Transport in Concrete with Stress Induced Damage", PhD dissertation, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia, 2011.

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