Numerical assessment of non-uniform corrosion scenarios of rebar in concrete exposed to natural chloride environment

Abstract

Corrosion of embedded rebars is a classical deterioration mechanism that remains as one of the most significant problems limiting the service life of concrete structures exposed to chloride-laden environments. The primary objective of this study is to propose and verify a numerical framework that can efficiently quantify non-uniform corrosion penetration depth along the perimeter of the rebar in concrete exposed to chloride environment. This framework investigates the corrosion process during both the corrosion initiation and propagation phases by exploring the effects of not only the rebar existence but also its sizes and locations. The corrosion initiation phase is examined through a comprehensive chloride ingress model that identifies the most important parameters that influence the intrusion of chlorides into RC. The corrosion propagation phase is studied based on a decisive parameter, namely, the corrosion rate. In addition, the framework evaluates the non-uniform corrosion states that correspond to two scenarios of corrosion penetration depth: corrosion of segment of the rebar and uneven corrosion along the rebar perimeter. Numerical solution shows that, in general, chloride build-up along the perimeter of the corner bar is not only faster but also higher than that of the middle bar. Moreover, for the given values of cover thickness and water-to-binder ratio, time-to-corrosion initiation for the corner bar is faster than that for the middle bar. Furthermore, the larger the rebar, in general, the bigger the obstruction, and therefore, the higher the chloride build-up. Qualitative comparisons of the evaluated non-uniform corrosion scenarios with the variety of available laboratory and field data show good agreement.

List of symbols

B _c :

Chloride transfer coefficient at the exposed boundary

B _h :

Relative humidity transfer coefficient at the exposed boundary

B _T :

Temperature transfer coefficient at the exposed boundary

c _p :

Specific heat capacity of concrete/rebar

C _c :

Concrete cover thickness

C _{e n v} :

Chloride in the environment

C _f :

Free chloride content

${C_{f}^{b}}$ :

Free chloride at the exposed boundary

C _t :

Total chloride content

d :

Rebar diameter size

D _c :

Effective chloride diffusion coefficient

${D_{c}^{a}}$ :

Apparent chloride diffusion coefficient

D _{c,r e f} :

Reference chloride diffusion coefficient

D _h :

Relative humidity diffusion coefficient

D _{h,r e f} :

Reference relative humidity diffusion coefficient

D _T :

Thermal conductivity of concrete/rebar

h :

Relative humidity

h ^b :

Relative humidity at the exposed boundary

h _{e n v} :

Relative humidity in the environment

i _corr :

Corrosion rate

p _d :

Corrosion penetration depth

t :

Time

t :

Concrete age

t _e :

Exposure time

T :

Temperature

T ^b :

Temperature at the exposed boundary

T _{e n v} :

Temperature in the environment

T _{r e f} :

Reference temperature

w/b :

Water-to-binder ratio

w _e :

Evaporable water content

${\hspace *{-10pt}X_{c}^{b}}$ :

Chloride flux at the exposed boundary

${\hspace *{-10pt}X_{h}^{b}}$ :

Relative humidity flux at the exposed boundary

${\hspace *{-10pt}X_{T}^{b}}$ :

Temperature flux at the exposed boundary

ρ :

Density of concrete (or) rebar