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Overview of a two decades durability follow-up for two major bridges: Vasco

de Gama (Portugal) and Rion-Antirion (Greece)

Dr. Abdelkrim Ammouche / Dr Christophe

Carde / Dr Nouredine Rafaï

LERM - 23, rue de la Madeleine

13631 Arles cedex – FRANCE

E-mail:

Lionel Linger / François Cussigh

VINCI Construction - 5, cours Ferdinand

de Lesseps - 92851 Rueil-Malmaison cedex

- FRANCE

E-mail:

ABSTRACT

In Rion-Antirion Bridge and Vasco de Gama projects, a service lifetime of 120 years is required.

To achieve this goal, Vinci and Lerm have carried out an extensive research and test program

for relevant durability properties of the various types of concrete. For both cases, the strategy

adopted is the corrosion control of embedded steel by reducing the rate of chloride penetration

which is the main issue for the durability of concrete structures in marine environment. This

objective was based on the proper definition of exposure zones, the definition of the adequate

concrete covers and a proper characterization and evaluation of concrete at trial mixes stage and

during execution. In accordance with the Inspection and Maintenance Manuals, several detailed

inspections, in-situ and laboratory testing (mapping of concrete cover, concrete properties,…)

and recalibration of input data used for chloride penetration model have been performed

according to a specific time schedule. This article summarizes the main outcomes of the

durability follow-up corresponding to a period of about 15 years for Vasco de Gama and 10

years for Rion-Antirion. These in-field follow-up data-bases are key parameters for developing a

practical methodology for concrete structures service lifetime control.

Key words: Durability, marine environment, high performance concrete, QA/QC program,

service fife assessment.

1. INTRODUCTION

1.1 Vasco de Gama Project

The Bridge over the Tage in Lisbon, has been built between 1995 and 1998 in the estuary of the

river, and is then located in a maritime area [3]. With a total length of 18 500 meters, including

the interchanges, and with a width of 30 meters, the crossing is composed by five main

structures: North Viaduct, Expo Viaduct, Main Bridge, Central Viaduct and South Viaduct.

Fig. 1 - Vasco de Gama Project (VdG) overview

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1.2 Rion-Antirion Project

The Rion-Antirion Bridge [2], built between 1999 and 2004, consists of the longest multi-span

cable stayed bridge in the world with a continuous deck of 2 252 meters and more than 600

meters of approach viaducts and further access roads. It is located in the Gulf of Corinth of

Greece and, as part of European road network, links the Peloponnesus to Continental Greece.

The main bridge is a 5-span cable stayed bridge with 3 spans of 560m and 2 side ones of 286

meters. The highest pier/pylon has a height of 228,5m being 63,5m underwater.

Fig. 2 - Rion-Antirion (R-A) Project typical elevation

2. SPECIFICATIONS

For both projects, when the contracts were awarded, no durability specifications were included

in the job instructions, except the requirement for a 120 year service life. The long-term

performance of concrete structures in a marine environment is controlled by limiting the

penetration of chlorides and ensuring a sufficient cover of embedded steel. The durability

program began, then, by choosing relevant durability indicators to validate concrete mixes in

regard to marine environment and service life required. For each indicator, acceptance criteria

have been chosen based on available literature and experience. So, specific tests related to

concrete durability have been performed firstly on laboratory samples, secondly on samples

from site, and finally on cores from structure at different ages. A simultaneous validation of the

long-term performance of the critical areas concrete mixes has been undertaken with the LERM

predictive model [1], considering and verifying the reinforcement cover values. This long term

performance is continuously checked with updated in field collected data following maintenance

programs.

2.1 Vasco de Gama

During the design stage, performance-level tests and associated durability indicators thresholds

have been defined as detailed in the following table.

Table 1 – VdG cement (type IV or type I) dosage, W/C ratio and durability indicators thresholds Exposure classes O2 permeability RCPT

3 months

[Cl-] DRCM

3 months

Accelerated carbonation depth

(60 days)

Fully immersed - - - -

Splash zone 10-17

m2 < 1500 C 10

-12 m

2.s

-1 10 mm

Aerial 10-17

m2 - - 10 mm

Minimum cover for reinforcement bars have been defined as follows:

- 70 mm in marine environment (< 10 NGP) (Portugal general mean sea-level)

- 50 mm in open-air environment and for structures located > 10 NGP

-

2.3 Rion-Antirion

The table given below shows the acceptance criteria of concrete used in splash and tidal zone.

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Table 2 - acceptance criteria of concrete mixes used in splash and tidal zones

Exposure Cement content Weffective/C ratio Water depth

penetration RCPT at 90 days

Splash and tidal zone > 400 kg/m3 ≤ 0.4 ≤ 20 mm < 1000 C

The different covers of the structure have been defined in accordance to the durability criteria

selected. The table 3 summarizes the covers selected for the Rion-Antirion Bridge and applied

throughout construction for the different exposure zones.

Table 3 – R-A covers in relation to exposure zone (values are in mm)

Exposure Situation Nominal Cover

Immersed zone (below MSL –5) 60 mm

Tidal & Splash (MSL –5 to MSL +10m) 85 mm

Substructure externally exposed above MSL +10 50 mm

3. CONCRETE MIXES

For Vasco de Gama, concrete mixes have been designed using CEM I 42.5 seawater resistant

Portland cement for aerial structures (> 10 NGP) with or without fly-ash and CEM IV 32.5 (22

% fly-ash content) for marine structures (< 10 NGP). For Rion-Antirion, most of concrete mixes

have used cement type CEM III 42.5 PM ES with 60% to 64% of slag. For some applications in

aerial zones, a mix of CEM III 42.5 and CEM I 52.5 has also been used. Typical concrete mixes

used for both projects are given in the following table 4.

Table 4 – VdG & R-A typical concrete mixes Exposure classes Strength class Cement type Cement min. content Weff/C ratio

VdG Fully immersed C35/45 CEM IV 430 0,35

Splash zone C40/50 CEM IV 430 0,33

Aerial C45/55 CEM I 400 0,42

R-A Immersed zone and Splash zone C45/55 CEM III 420 0,39

Aerial C60/75 CEM I 450 0.33

4. DURABILITY INDICATORS VALUES

Measurements made on typical concrete mixes during construction on samples cored on site are

synthesized in the following tables. These tests also showed that concrete characteristics were

improved with time linked to the slow hydration of cements containing either fly ashes or slag.

Table 5 – VdG durability indicators representative routine control values Exposure class Age O2 Permeability Porosity RCPT [Cl

-] DRCM

Splash zone 28 d

90 d

0,5 10-17

m2

-

11-13 %

-

2800 C

900 C

1,3 10-12

m2/s

0,8 10-12

m2/s

Aerial zone 28 d 0,9 10-17

m2 12,5 % 6400 C 3,2 10

-12 m

2/s

Table 6 – R-A durability indicators representative routine control values Exposure Class RCPT at 90d DRCM at 28d DRCM at 120 d O2 Permeability

Splash zone [220-600] C 1.10-12

m2/s 0.5.10

-12 m

2/s < 1.10

-17 m

2

Aerial zone [1300-2100] C / / /

5. SERVICE LIFETIME ASSESSMENT

Service lifetime assessment for both projects is done through LERM model [1] allowing

chlorides penetration prediction with time. The main specificities of this model are: 1/

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consideration of interactions between chlorides and cement paste, 2/ variation of chlorides

diffusion coefficient and physic-chemical properties with space and time, and 3/ evolution of

boundary conditions toward time. The main input data of model used are:

- Initial diffusion coefficient (DRCM) measured at short term (28/90 days).

- Evolution law of chlorides diffusion coefficient with time. The law (t-

or e-t

forms),

which is experimentally calibrated, reflects decrease of chlorides diffusion coefficient

with time linked to hydration of cement paste.

- Initial chlorides content in the concrete.

- Chlorides binding capacity.

- Free chlorides content at the surface of concrete (limit condition).

- Time and depth.

These input data are continuously cross-checked and if necessary re-calibrated in the course of

measurements carried out according to the structures maintenance follow-up programs.

Experience gathered on Vasco de Gama and Rion-Antirion has allowed improving accuracy of

input data and therefore servicing lifetime assessment.

For Vasco de Gama project, a long term follow-up extensive (more than 70 zones) durability

program started after project completion on several parts of bridge in splash/tidal zones and

aerial zones to collect concrete in-field data (concrete cover mapping, corrosion monitoring

(potential and speed), total and free chlorides concentration profiles, carbonation depth,

chlorides diffusion coefficient). Chloride in-field profiles have been compared to predicted

figures given by numerical simulations. The choice of follow-up zones has been made including

parameters as position regarding sea level, exposure to predominant winds, and occurrence of

identified local defaults (reduced concrete cover, cracks). The corresponding results led to

decide, when necessary, to undertake locally some preventive additional protections to achieve

service life required.

For Rion-Antirion project, during initial concrete qualification stage, durability tests have been

performed on samples and cores coming from concrete mock-up elements. In order to verify the

relevancy of these initial results and to validate the consistency of the in-situ concrete in the

different structural elements, additional laboratory tests have also been performed on cores

extracted from several parts of the structure, selected and identified using non-destructive testing

of exposed concrete surfaces (sclerometry and ultrasonic methods). Achieved results were

consistent with input data collected during qualification stage. Finally, for the maintenance

program concrete durability follow up, one sacrificial reinforced concrete wall was cast on P2

pile cap during construction period and under the same circumstances (concrete mix design,

manpower, placing and curing conditions). This mock-up full-scale wall allowed measuring

chloride diffusion coefficient and in-field chlorides concentration profile at different ages to

check predicted figures provided by numerical simulations. Some additional cores also have

been extracted in concrete cover of structural elements located in the splash zone (M2 & M3

pylons) to compare chlorides ingress in concretes from mock-up wall and real structure.

5.1 Chloride surface concentration evolution toward time

Due to the wet/drying cycles linked to tides, chlorides content at the surface of concrete

increases with time until a maximum value which has to be considered for long term numerical

simulations as boundary condition. Results of durability program performed on both bridges

show that free chloride concentrations at the surface of in situ concrete (limit condition used in

model) increase during few years and stabilize after. Furthermore, significant variations are

observed at different location in splash and tidal zones. For Vasco de Gama (more than 10 years

exposure) and Rion-Antirion bridges (about 5 years exposure), in splash and tidal zones, the free

chloride contents at the surface of in situ concrete ranges respectively from 3.0 to 6.0 % and 3.5

to 5.5 % of cement mass. For a given project, these variations are certainly due to local concrete

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characteristic differences, effects of predominant winds, sample location (height compared mean

sea level), and sampling procedure.

5.2 Chloride binding capacity

The knowledge of bound chlorides is a major issue to have a relevant prediction of free

chlorides content with time, which acts in steel depassivation process potentially leading to

corrosion. Chloride binding capacity mainly depends on cement type and chlorides

concentration in concrete pore solution. It can be initially estimated in laboratory by determining

interaction isotherms on concrete crushed samples. The chloride binding capacity measured by

LERM for Rion-Antirion project is given in the following figure.

Fig. 3 - Interaction isotherms of chloride (bound chlorides versus total chlorides)

In a second stage, it can be checked by direct measurement on in field concrete exposed to

chloride during few years. For highest total chloride surface concentration measured in field (7-

8 %), results show that bound chloride at the surface of exposed concrete is around 25 % of total

chloride content for Vasco de Gama bridge after more than 10 years, and is around 20 % of total

chloride content for Rion-Antirion bridge after about 5 years.

5.2 Chloride diffusion coefficient evolution toward time

Chloride diffusion coefficient is one of the most important parameter for numerical simulations:

and the knowledge of its evolution with time is, then, essential. Evolution laws of chloride

diffusion coefficient with time have been defined for both projects. For Vasco de Gama,

chloride diffusion coefficient evolution with time is better described by an exponential law (e-t

)

during the first 5 years after casting. After 5 years and up to 13 years, in field measurements

show that the DRCM value is stabilized. For Rion-Antirion, chloride diffusion coefficient

evolution with time is better described by an exponent law (t-) and seems to stabilize between 5

to 10 years after casting. Main difference between the both laws (figure 4) is the kinetic of

decrease, which is mainly linked to the cement type used for each concrete. For Vasco de Gama

bridge concrete is designed using fly ashes whereas ground granulated blast furnace slag is

incorporated in concrete mix design used in Rion-Antirion. It’s highlighted that, for both cases,

chloride diffusion coefficients have not to be considered as continuously decreasing with time.

A final constant value need, then, to be included in the numerical model.

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0,00E+00

1,00E-12

2,00E-12

3,00E-12

0 20 40 60 80 100 120 140 160 180 200

Ch

lori

de

dif

fus

ion

co

eff

icie

nt

(m2/s

)

Time (month)

D = 2.10-12.e-0.0527t

(0 to 60 months)

D = 1.10-13 (> 60 months)

D = 1.10-12.t-0.215

(0 to 120 months)

D = 3.5 10-13

(> 120 months)

Results from Vasco de GamaResults from Rion Antirion

Fig. 4 - evolution of chloride diffusion coefficient of concretes from both bridges

5.4 Numerical simulations results

Based on results obtained during durability program performed on both bridges, the main input

data used for numerical simulations in splash and tidal zones have been defined as summarized

in the following table.

Table 7: input data used in model for splash and tidal zones Bridge Corrosion risk Free [Cl

-] at the concrete

surface (weight % of cement)

DRCM evolution law with time

Vasco de

Gama

Low

Critical

3.0

6.0

DRCM=2.10-12

e-0.0527t

, and

DRCM=0.1 10-12

m2/s for t > 60 months

Rion-Antirion Low

Critical

3.5

5.5

DRCM=1.10-12

t-0.215

, and

DRCM=0.35 10-12

m2/s for t > 120 months

Figure 5 below illustrates the last numerical simulations made on concrete elements

corresponding to splash and tidal zones for both bridges, compared to real chloride in field

profiles.

Vasco de Gama

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Rion-Antirion

Fig. 5 - examples of numerical simulations made on concrete from VdG and R-A (splash zone)

based on results obtained during durability program

Up to date numerical simulations based on justified and calibrated input data show that service

life required is complied with for both bridges. Furthermore, no re-calibration of model has been

necessary for both projects thanks to the satisfactory correlation between in-field and predicted

chloride profiles.

By using other input parameters, theoretically determined but non-justified by field

experimental data, predictions would have been significantly different. This is illustrated in the

following table as far as chloride diffusion coefficient would have been considered constant or

continuously decreasing toward time and with lower or higher chloride critical contents.

Table 8 – cover values for a 120 year design life depending on predictive model input

parameters Threshold

free Cl (%)

Vasco de Gama Rion-Antirion

DRCM (m²/s)

2.10-12

2.10-12

e-0.0527t

, and

0.1 10-12

m2/s for t

> 60 months

2.10-12

e-0.0527t

1.10-12

1.10-12

t-0.215

, and

0.35 10-12

m2/s

for t > 120

months

1.10-12

t-0.215

0.2 219 mm 68 mm 56 mm 146 mm 88 mm 78 mm

0.4 179 mm 54 mm 44 mm 119 mm 72 mm 63 mm

0.6 157 mm 47 mm 38 mm 104 mm 63 mm 55 mm

6. CONCLUSION

The durability studies carried out for these two major projects have allowed gathering numerous

results regarding concrete behavior in marine environment. These databases have been used to

improve chloride profiles prediction for long term service life assessment and identify key input

data. Many parameters (materials quality consistency, concrete production, placing,

reinforcements cover control, curing) are involved in concrete overall durability and it is then

compulsory to keep under control during project construction these parameters through a

relevant QA/QC system. The proposed approach, initiated 15 years ago, is based on a physical

model and updates only deal with limited major input data without adjusting additional

empirical parameters for better fitting. It is not relying on a full probabilistic approach finalized

during the design stages of these two projects. However, even with the fruitful feed-back

mentioned above, it appears that the definition of predictive model’s input parameters and their

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associated variability, which have been justified as relevant for a dedicated project, remains an

issue, and that a better understanding of the influence of key input parameters are still missing

prior to use a full-probabilistic approach for design life assessment. In particular, two major

influencing parameters, which cannot be easily determined during project’s design stage, are the

chloride diffusion evolution law and the critical chloride threshold value corresponding to steel

depassivation potentially allowing corrosion process. Further research is still needed for a better

justification of these parameters.

REFERENCES

[1] O. Houdusse, H. Hornain, G. Martinet, 2000,

“Prediction of Long-term durability of Vasco Da Gama bridge in Lisbon”, 5th

CANMET/ACI International Conference on Durability of Concrete, Barcelona.

[2] F. Cussigh, C. Carde, P. Papanikolas, A. Stathopoulos-Vlamis, 2010,

“Rion-Antirion bridge project – concrete durability towards corrosion risk”, 3rd fib

International Congress, Washington.

[3] G. Martinet, L. Linger, 2005,

“Pont Vasco de Gama à Lisbonne- Bilan de 10 ans de démarche durabilité”, GC’2005,

Paris