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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4

C. G. NOGUEIRA | E. D. LEONEL | H. B. CODA

changing the w/c ratio. Moreover, keeping constant the w/c ratio,

0.50 for instance, and changing the cover depth from 30 to 40mm,

the maintenance time are 8 and 14 years, respectively, for C.A.II.

Therefore, by changing in 10mm the cover thickness, it results an

improvement of 75% on the maintenance time.

The abacuses involving the reliability index in function of w/c ratio

and cover depth values for category of aggressiveness III are pre-

sented in figures 15 and 16. Considering these two last figures, the

same remarks discussed for C.A.II can be done. However, in this

case, the intervals of time for maintenance are considerable redu-

ced due the aggressiveness of the environment analyzed, which is

higher than the observed for C.A.II.

It is important to emphasize that when the w/c ratio grows, small

values of cover depth tend to be prohibitive regarding the corro-

sion time initiation failure. Moreover, in this case, the time interval

for maintenance procedures will be drastically reduced. Therefo-

re, regarding concretes with high values of w/c ratio, maintenance

procedures in short periods of time and high values of cover depth

have to be used in order to prevent reinforcement’s corrosion.

Based on the results presented in this application, optimum con-

crete mixtures and cover depth values can be obtained in order to

guarantee the durability of reinforced concrete structures. Moreo-

ver, these parameters can be allied to construction, maintenan-

ce and reparation costs aiming to determine the global structural

cost taking into account the corrosion failure scenario. This type of

analysis will be considered by the authors in future works.

6. Conclusions

This paper presented a study for probabilistic corrosion initiation in

reinforced concrete structures using the coupling among second

Fick’s diffusion law and reliability algorithms. In this case, the cor-

rosion starts when the chemical protection surrounding the steel

bars is loss due chloride ingress. The analyses of probability of

corrosion initiation along time were carried out considering two

different categories of environment aggressiveness and several

combinations of cover depth and concrete properties (w/c ratio).

As verified in the results presented, the corrosion initiation depen-

ds on several parameters. However, the chloride concentrations at

the structural surface and the cover depth values have demonstra-

ted to have major importance on the probabilistic analysis. Equally,

the coefficient of diffusion is also important in order to measure the

material resistance against the chloride ingress and it can be de-

terminant for choose optimal values of the concrete cover.

According the results achieved in this paper, the durability of rein-

forced concrete structures has to be associated with more fair

values of cover depth, which are, in general, based only on inter-

national concrete standard design. This parameter is more rea-

listically evaluated using probabilistic approaches in order to take

into account the inherently randomness present on degradation

phenomenon, which affect structural durability.

Regarding the choice of optimum values of cover depth, it was

observed that this parameter strongly depends on the concrete

quality against porosity, which is reflected by w/c ratio, as well

as on the period of time attributed for structural interventions for

maintenance procedures. Evidently, the determination of optimum

combination among concrete material mixture, cover depth value

and construction/maintenance/reparation costs is next question to

be answered in order to become the structural design more eco-

nomic, safe and rational. However, the determination of these pa-

rameters based only on safety criterion has been shown in this

paper. Abacuses were developed in order to allow these analyses,

which were constructed using the probabilistic model proposed in

this paper.

7. Acknowledgements

The authors would like to thank FAPESP – São Paulo Research

Foundation for the finantial support and scholarships.

8. References

[01] ANGST, U.; ELSENER, B; LARSEN, C. K.;

Vennesland, Ø. Critical chloride content in

reinforced concrete — a review,

Cement and Concrete

Research

, 39:1122-1138, 2009.

[02] GUZMÁN, S; GÁLVEZ, J.C; SANCHO, J.M. Cover

cracking of reinforced concrete due to rebar corrosion

induced by chloride penetration,

Cement and

Concrete Research,

41:893-902, 2011.

[03] XIANG, T; ZHAO, R. Reliability evaluation of chloride

diffusion in fatigue damaged concrete,

Engineering

Structures

. 29:1539–1547, 2007.

[04] SARVESWARAN, V.; ROBERTS, M.B. Reliability

Figure 15 – Required reliability index

abacus for C.A.III and w/c = 0.40

-1.40

-1.00

-0.60

-0.20

0.20

0.60

1.00

1.40

1.80

5

7

9 11 13 15 17 19 21 23 25

Time (years)

Reliability index

p=10

p=20

p=30

p=40

p=50

p=60

target

Figure 16 – Required reliability index

abacus for C.A.III and w/c = 0.50

-1.80