Chloride diffusion and time to corrosion initiation of reinforced concrete structures

Abstract

The diffusion mechanism for chloride ions in concrete with varying water/cement ratio (w/c) is studied by chloride ion spray testing. A new model of chloride diffusion coefficient, which varies with the ingress depth of chloride ion and w/c, is developed. A spatial time-dependent reliability model of time to corrosion initiation (TCI) for reinforced concrete (RC) structures is developed, considering spatial variability of geometric, material and environmental parameters. The test results show that the chloride diffusion coefficient increases as w/c increases, and chloride diffusion velocity decreases as penetration depth increases. It is found that the probability of corrosion initiation considering spatial variability is 13.1–18.5% greater than that without consideration of spatial variability. This indicates that neglecting spatial variations in evaluating probability of corrosion initiation time overestimates the structural reliability. It is also found that the probability of corrosion initiation for future climate change is 9–11% higher than that obtained from constant temperature. The mean value of TCI based on a time-dependent chloride diffusion coefficient is 16.7% less than that obtained for a constant chloride diffusion coefficient. This suggests that it is more appropriate if penetration depth and w/c is considered when determining the time-dependent chloride diffusion coefficient.

Full text

Chloride diffusion and time to corrosion
initiation of reinforced concrete structures
Jianxin Peng
Professor, School of Civil Engineering, Changsha University of Science and
Technology, Changsha, Hunan, China
Huang Tang
Lecturer, School of Civil Engineering, Hunan City University, Yingyang,
Hunan, China; Industry Key Laboratory of Transportation Infrastructure
Security Risk Management of Changsha University of Science and
Technology, Changsha, Hunan, China (corresponding author:
tanghuang_123@163.com)
Linfa Xiao
PhD candidate, School of Civil Engineering, Changsha University of Science
and Technology, Changsha, Hunan, China
Xiaokang Cheng
Master, School of Civil Engineering, Changsha University of Science and
Technology, Changsha, Hunan, China
Jianren Zhang
Professor, School of Civil Engineering, Changsha University of Science
and Technology, Changsha, Hunan, China
The diffusion mechanism for chloride ions in concrete with varying water/cement ratio (w/c) is studied by chloride ion
spray testing. A new model of chloride diffusion coefficient, which varies with the ingress depth of chloride ion and
w/c, is developed. A spatial time-dependent reliability model of time to corrosion initiation (T
CI
) for reinforced concrete
(RC) structures is developed, considering spatial variability of geometric, material and environmental parameters. The
test results show that the chloride diffusion coefficient increases as w/cincreases, and chloride diffusion velocity
decreases as penetration depth increases. It is found that the probability of corrosion initiation considering spatial
variability is 13.1–18.5% greater than that without consideration of spatial variability. This indicates that neglecting
spatial variations in evaluating probability of corrosion initiation time overestimates the structural reliability. It is also
found that the probability of corrosion initiation for future climate change is 9–11% higher than that obtained from
constant temperature. The mean value of T
CI
based on a time-dependent chloride diffusion coefficient is 16.7% less
than that obtained for a constant chloride diffusion coefficient. This suggests that it is more appropriate if penetration
depth and w/cis considered when determining the time-dependent chloride diffusion coefficient.
Notation
Cchloride concentration
C
cr
critical chloride concentration
C
cr(i)
threshold of chloride concentration of element i
C
i
chloride concentration of element i
C
s
surface chloride concentration
C
s(i)
surface chloride content of element i
C(x,t) chloride content at time tof exposure, and at depth x
from the surface of the concrete
C
0
initial chloride concentration inside the
concrete structure
C
0(i)
initial concentration of chloride ions in concrete of
element i
Dchloride diffusion coefficient
D
exp
experimental chloride diffusion coefficient
D
real
chloride diffusion coefficient for real structure
D
real(i)
real diffusion coefficient of element i
d
x
model parameter (correlation lengths) for a
two-dimensional (2D) random field in xdirection
d
y
model parameter (correlation lengths) for a 2D random
field in ydirection
E
c
cover thickness
erf error function
F
c
specified concrete compressive strength
f
age
time correction factor
fTbtemperature correction coefficient
GCL;ipowerful function
mexperimental parameter
p
ci
probability of initiation of chloride-induced corrosion
for each element
p
r
probable symbol
Rgas constant
R
2
correlation coefficient
Sspatial segment at random field
Treal temperature where the assessed structure is located
T
b
average absolute temperature related to calculation
T
CI
time to corrosion initiation
T
0
temperature in the year 2000
T
28
absolute temperature corresponding to a curing of
28 days
tcalculated time
t
build
construction completion time of structure
t
exp
tested time
Uactivated energy during the diffusion process of
chloride ion in concrete
w/bwater/binder ratio
w/cwater/cement ratio
X(s) random field
xdepth from the surface of the concrete
γ(S) variance function
757
Cite this article
Peng J, Tang H, Xiao L, Cheng X and Zhang J (2021)
Chloride diffusion and time to corrosion initiation of reinforced concrete structures.
Magazine of Concrete Research 73(15): 757–770,
https://doi.org/10.1680/jmacr.19.00276
Magazine of Concrete Research
Research Article
Paper 1900276
Received 04/06/2019; Revised 19/05/2020;
Accepted 27/05/2020;
Published online 03/07/2020
ICE Publishing: All rights reserved
Keywords: compressive strength/
durability-related properties/modelling