Comparative study of different test methods for reinforced

ORIGINAL ARTICLE

Comparative study of different test methods for reinforcedconcrete durability assessment in marine environment

Miguel Angel Bermudez Odriozola ÆPilar Alaejos Gutierrez

Received: 4 October 2006 / Accepted: 11 May 2007 / Published online: 14 June 2007

� RILEM 2007

Abstract There are many different test methods to

assess reinforced concrete durability. As in marine

environment reinforcement corrosion due to chloride

attack is the most important degradation process,

chloride penetration rate has been compared with

different durability tests results (concrete strength,

porosity, water absorption, water penetration depth

under pressure, capillarity, water and oxygen perme-

ability) carried out on concrete cores obtained from

the caissons of seven Spanish wharves. Data have

been studied separately, depending on concrete

location (chloride penetration rate is faster in

submerged concretes than in tidal zone concretes)

and cement type (mineral admixtures reduce perme-

ation rate due to pore size refinement). Results show

that it is advisable to control concrete water tightness

through water penetration under pressure test; addi-

tionally, in order to make sure a slow corrosion rate,

it should be advisable to control oxygen permeability

in tidal zone concretes.

Keywords Marine environment � Reinforced

concrete corrosion � Chloride ingress � Durability

tests � Cement type

1 Introduction

Nowadays, concrete structures are designed under

international technical standards, the Structural Con-

crete Instruction (EHE [1]) in Spain. The aim of these

standards is to guarantee that structures comply with

certain stability and resistance requirements, and

keep them during design working life.

For concrete durability control, Eurocode 2 [2]

requires a minimum compressive strength related to

the exposure environment, while ACI 318R [3] also

establishes a minimum w/c ratio, but also only

compressive strength tests are required. In Spain,

the Structural Concrete Instruction (EHE [1]) uses

water penetration depth under pressure test (UNE

83309:90 EX) as hardened concrete durability con-

trol. Depending on environmental conditions, there

are also some requirements related to concrete

composition (maximum w/c ratio and minimum

cement content).

Although not included in Spanish or international

standards, there can be found many test methods to

M. A. Bermudez Odriozola

Concrete Durability Division, Structures and Materials

Laboratory, CEDEX, Ministry of Public Works, Madrid,

Spain

P. Alaejos Gutierrez

Materials Science Program, Structures and Materials

Laboratory, CEDEX, Ministry of Public Works, Madrid,

Spain

M. A. Bermudez Odriozola (&)

Laboratorio Central de Estructuras y Materiales, CEDEX,

C/ Alfonso XII, 3 y 5, Madrid 28014, Spain

e-mail: [email protected]

Materials and Structures (2008) 41:527–541

DOI 10.1617/s11527-007-9263-8

assess concrete durability, which are representative of

different transport mechanisms in concrete: water

permeability, gas permeability, absorption, capillar-

ity, etc., but there is no agreement about which one is

the most suitable test to control durability of concrete.

The main objective of this study is to select a

durability test which guarantees the designed service

life of reinforced concrete structures located in tidal

zone, i.e., a durability test whose results were linked

to chloride penetration rate.

In order to select the appropriate test method for

reinforced concrete in marine environment, it must be

considered that there are different chloride penetra-

tion mechanisms overlapping depending on marine

exposure conditions: diffusion, capillarity, etc. [4, 5];

nevertheless, Fick’s second law is used to model

chloride penetration due to the different interacting

mechanisms (absorption, diffusion, chloride binding)

in marine environment, but then D is not a ‘‘true’’

diffusion coefficient and should be considered as an

‘‘apparent’’ diffusion coefficient [6, 7].

In this article, it has been compared the experi-

mental results from several durability tests with

chloride penetration rates measured in seven marine

structures (named Wharf A to Wharf G) of different

concrete quality and exposure times, to select the

most appropriate test methods to assess reinforced

concrete behaviour in full-scale structures. These test

results may be used to assess the effectiveness of

actual quality control standards requirements, i.e.

EHE Instruction, or the need to adopt new quality

control methods.

Then these are the objectives of this research

programme: to compare the effectiveness of labora-

tory test methods to assess the durability of concrete

marine structures; and to select the test method that

better assesses the real behaviour of concrete in

marine exposure.

2 Methodology

Methodology consisted of the following steps:

2.1 Data collection

Information was obtained from the wharves construc-

tion’s projects about the characteristics of the caissons

(dimensions, typology, reinforcement geometry, etc)

and the concrete used for construction (design cylinder

strength, w/c, etc).

Also the documents from the quality control

carried out during construction of the caissons have

been reviewed. Data on compressive strength of

concrete corresponding to the layers where cores

were drilled in this study have been collected and

compared with actual measured strengths; these data

have been used to select the caissons where cores had

to be extracted: one high strength caisson, one low

strength caisson and one or two average strength

caissons in each wharf were selected. When no data

on concrete quality were available, the caissons have

been selected from ultrasonic wave transmission test

results, carried out on all caissons of the wharf.

Finally, only in Wharf A the initial content of

chloride in concrete was known. Summary of all

these data can be seen in Table 1.

2.2 Drilling of concrete cores

Two different procedures of drilling the cores have

been followed, depending on concrete location:

permanently submerged (wharves A and B) or in

tidal zone (wharves C, D, E, F and G).

2.2.1 Submerged concrete

Concrete is permanently submerged in these caissons,

so just the concrete slab on them is over the sea level,

but it wasn’t the objective of this investigation. As it

is hard to drill concrete cores under the sea, it was

planned to drill two vertical borings from the

concrete slab per caisson.

Following this procedure, double concrete corings

were drilled in two wharves (A and B). Three

caissons were investigated per wharf, so finally 12

cores were extracted to study permanently submerged

concretes.

Moreover, concrete specimens (150 mm cubes and

150 · 150 · 300 mm prisms) were cast in laboratory

with different mix designs (see Table 2) and

submerged in seawater for 1 year, measuring chloride

penetration at different times (7, 28 and 119 days).

One group of specimens was cured in standard

conditions (for 7 or 28 days) before ponding in

seawater, while the second group was directly

submerged in seawater after removing from the

moulds (at 1 day). Chloride penetration depths were

528 Materials and Structures (2008) 41:527–541

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Materials and Structures (2008) 41:527–541 529

measured by means of splitting 5 cm thick slices from

the specimens and spraying the freshly fractured

concrete face with an AgNO3 solution at each

exposure age. Then the split surface of concrete

was waterproofed with a bituminous mixture and the

specimen returned to the seawater tank.

Results from cores and laboratory specimens were

analysed together as all of them were exposed to the

same environmental conditions and then their behav-

iour was quite similar.

2.2.2 Tidal zone concrete

The day of drilling was chosen to coincide with

minimum low tide level. Concrete cores were drilled

horizontally from the front face of the caissons.

Following this procedure, concrete cores were

extracted in five wharves (C, D, E, F and G) Several

caissons (3–5) were selected per wharf, so finally 20

cores were extracted to study concrete exposed to

tidal zone.

2.3 Selection of tests

The tests carried out to characterise physical

and mechanical properties of concrete cores have

been:

– Compressive strength (Spanish standard UNE

83.304/84, similar to European EN 12390-3).

– Ultrasonic pulse velocity (Spanish standard UNE

83-308-93, similar to European EN 12504-4).

– Water penetration under pressure depth (Spanish

standard UNE 83.309-90, similar to ISO (DIS)

7031).

– Water porosity (RILEM CPC 11.3).

– Water absorption (BS1881: Part 122).

– Capillarity (RILEM CPC 11.2).

– Oxygen permeability (CEMBUREAU method).

– Permeability coefficient was estimated by substi-

tuting the maximum water penetration depth and

concrete porosity data obtained in the equation

developed by Valenta [8]: k = Px2/2 ht, where

‘‘k’’ is the permeability coefficient, ‘‘P’’ is

porosity, ‘‘x’’ is water penetration depth, ‘‘h’’ is

hydraulic pressure and ‘‘t’’ is the time the

pressure is applied.

– Acid-soluble chloride penetration profile was

obtained through chemical analysis (as described

in standard ASTM C1152) of chloride content of

concrete samples 10 mm thick at different depths.

These tests aim to control the different chloride

transport mechanisms into concrete in marine envi-

ronment, as well as oxygen availability for corrosion

propagation: water and oxygen permeability, capil-

larity, absorption and diffusion.

2.4 Specimen distribution

Figure 1a and b shows typical specimen distribution

for wharves A and B cores (vertical borings in

submerged caissons), while Fig. 2 shows correspond-

ing distribution for wharves C, D, E, F and G cores

(horizontal drilling in tidal zone concretes).

As can be seen in Fig. 1a, a 100 mm height

specimen was cut from wharves A and B cores to

conduct the chloride tests. These specimens (Fig. 1b)

were sliced to obtain four samples 20 mm thick and

100 mm long, which were used for the chemical

analyses.

Figure 2 show typical specimen distribution for

wharves C, D, E, F and G cores. The first 95 mm of

the specimen were used to obtain the chloride

penetration profile, by means of several 10 mm thick

slices.

Table 2 Mix proportions, size and curing time of concrete specimens

Concrete 1 Concrete 2 Concrete 3 Concrete 4

Specimen size (mm) 150 · 150 · 150 150 · 150 · 300 150 · 150 · 300 150 · 150 · 300

Standard curing time (days) 7 28 28 28

Water/binder ratio 0.45 0.45 0.40 0.36

Cement content (kg/m3) 395 400 400 396

Silica fume (kg/m3) – – – 44

Type of cement CEM I 42.5N/SR CEM I 42.5R/SR CEM I 42.5R/SR CEM I 42.5R/SR


2.5 Chloride diffusion coefficient calculation

Chloride penetration rate is often described by an

error function model, which fulfils the condition of

Fick’s second law of diffusion [9]:

Cx � Cb ¼ Cs � Cbð Þ � 1� erfx

2ffiffiffiffiffiffiffiffiffiffi

D � tp

� �

;

where:

Cx = chloride content (% by concrete weight) at

depth x (cm).

Cs = chloride concentration at the concrete surface

(% by concrete weight).

Cb = initial chloride content (% by concrete

weight).

D = effective diffusion coefficient (cm2/s).

t = exposure time (seconds).

erf = error function.

Fig. 1 (a) Sketch of typical

specimen distribution for

testing. Wharves A and B.

Elevation view. (b)

Specimen for chloride

analysis. Wharves A and B.

Plan view

Fig. 2 Sketch of typical

specimen distribution for

testing. Wharves C, D, E, F

and G. Elevation view

WHARF A (4.5 years) - Submerged

y = -0.027x + 0.5315R2 = 0.9396

y = -0.0178x + 0.4064R2 = 0.9183

y = -0.0138x + 0.2666R2 = 0.9934

0.0

0.2

0.4

0.6

0.

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

) 8

0 5 10 15 20 25DEPTH (cm)

Caisson A1-A2 Caisson A3-A4 Caisson A5-A6

Fig. 3 Chloride penetration profile of Wharf A cores (sample

depth versus square root of chloride concentration)

WHARF B (6.5 years) - Submerged

y = -0.0232x + 0.4796

R2 = 0.692

y = -0.0371x + 0.7591

R2 = 0.8577

y = -0.0245x + 0.5892

R2 = 0.9452

0.0

0.2

0.4

0.6

0.8

0 5 10 15 20 25DEPTH (cm)

Caisson B1-B2 Caisson B3 Caisson B4-B5

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

)

Fig. 4 Chloride penetration profile of Wharf B cores (sample



This formula may be simplified by using a parabola

function [10]:

Cx � Cb ¼ Cs � Cbð Þ � 1� x

2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

3 � D � tp

� �2

The diffusion coefficient after an exposure time

‘‘t’’ has been obtained from core’s chloride penetra-

tion profiles. Experimental results are plotted in

Figs. 3–9 (expressed as square root of chloride

content). Finally, a linear regression is adjusted for all

the wharves, as can be seen in the same figures.

The chloride concentration has been corrected

subtracting the chloride content measured at the end

of the core, which corresponds to initial chloride

concentration of concrete. So the ‘‘Cx�Cb’’ values

(expressed as square root of chloride content) have

been plotted.

From the linear regressions adjusted (y = mx + b),

chloride concentration at concrete surface is obtained

from the formula b ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

Cs � Cb

pand diffusion coef-

ficient D at time ‘‘t’’ (wharf age) is calculated from:

m ¼ffiffiffiffiffiffiffiffiffiffi

Cs�Cb

pffiffiffiffiffiffiffiffiffiffiffi

12�D�tp .

Also must be taken into account that chloride

diffusion coefficient changes with time, according to

[11]: D(t) = D1*t�0.5; where ‘‘D(t)’’ is the diffusion

coefficient after an exposure time ‘‘t’’ and ‘‘D1’’ is

the diffusion coefficient after 1 year, if ‘‘t’’ is in

years. D1 values have been obtained from this

formula to compare the diffusion coefficients of the

seven wharves.

WHARF G (31years) - Tidal zone

y = -0.0617x + 0.7466

R2 = 0.7633

y = -0.0999x + 0.9494

R2 = 0.9633

y = -0.0784x + 0.8935

R2 = 0.9949-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15 20 25DEPTH (cm)

Caisson G1 Caisson G3 Caisson G4 Caisson G5

y = -0.0813x + 0.7788

R2 = 0.9999

SQ

.RO

OT

(%

CH

LO

R. B

Y

C

ON

CR

ET

E W

T)

Fig. 9 Chloride penetration profile of Wharf G cores (sample


WHARF D (5 years) -Tidal zoney = -0.0224x + 0.5697

R2 = 0.9313

y = -0.0165x + 0.441

R2 = 0.7181

y = -0.0226x + 0.5894

R2 = 0.9244

0.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15 20 25

DEPTH (cm)

Caisson D1 Caisson D2 Caisson D3 Caisson D4

y = -0.0225x + 0.5145

R2 = 0.9872

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

)

Fig. 6 Chloride penetration profile of Wharf D cores (sample


WHARF C (7.5 years) - Tidal zone

y = -0.0319x + 0.6484

R2 = 0.9428

y = -0.0613x + 0.7327

R2 = 0.999

y = -0.0288x + 0.6141

R2 = 0.80310.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15 20 25

DEPTH (cm)

Caisson C1 Caisson C2 Caisson C3

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

)

Fig. 5 Chloride penetration profile of Wharf C cores (sample


WHARF E (2years) - Tidal zone

y = -0.0854x + 0.6817

R2 = 0.9314

y = -0.2461x + 0.9332

R2 = 0.9859

y = -0.2552x + 0.8677

R2 = 0.9978

0.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15 20 25DEPTH (cm)

Caisson E1 Caisson E2 Caisson E3 Caisson E4

y = -0.1835x + 0.7295

R2 = 0.9748

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

)

Fig. 7 Chloride penetration profile of Wharf E cores (sample


WHARF F (2 years) -Tidalzone

y = -0.1302x + 0.8321

R2 = 0.9804

y = -0.1384x + 0.7182

R2 = 0.799

y = -0.1516x + 0.7941

R2 = 0.9907

0.00.20.40.60.81.0

0 5 10 15 20 25DEPTH (cm)

Caisson F1 Caisson F2 Caisson F3 Caisson F4

y = -0.1201x + 0.6345

R2 = 0.9838

SQ

.RO

OT

(%

CH

LO

R-

BY

CO

NC

RE

TE

WT

)

Fig. 8 Chloride penetration profile of Wharf F cores (sample



3 Results

Figures 3–9 show the chloride penetration profiles

(3–5 caissons) of the seven wharves. In these figures,

square root of acid-soluble chloride content (% by

concrete weight) as a function of depth is presented

graphically, as well as the linear regressions fitted for

all the profiles.

Analysing each wharf separately, it can be seen that

all the caissons show a very similar chloride penetra-

tion profile, except for some particular cores. In these

cases, the differences may be due to a better or worse

quality concrete used in particular caissons, what is

also reflected in the other concrete properties tested.

Comparing the chloride profiles obtained in the

different wharves, it can be seen that, despite using

similar mixes (see Table 1), wharves have been built

with different durability concretes, resulting in chlo-

ride penetration profiles very different too. So, except

for Wharves E and F (exposed to seawater just for

2 years), high chloride contents at rebar level have

been measured, despite concretes had a w/c ratio of

0.5 and cement contents of 300 kg/m3. When drilling

the cores some steel rebars were cut, which some-

times showed corrosion symptoms. The corroded bars

belong to tidal zone concretes (Wharves C and G, the

first one exposed to seawater just for 5 years, see

Fig. 10), while permanently submerged concretes

showed rebars without corrosion symptoms (Wharves

A and B, see Fig. 11). These observations point out that

although standards (EHE, BS 8110) establish a chloride

threshold for corrosion of 0.4% by cement weight, this

value depends on many parameters, as type of steel, type

of cement and, overall, exposure conditions.

Table 3 shows diffusion coefficients calculated

(actual D values and those corresponding to one year

exposure D1) for all the cores analysed, obtained

from linear regressions plotted in Figs. 3–9, as

explained in Sect. 2.5.

On the other hand, experimental results of com-

pressive strength, water penetration, porosity, water

permeability (estimated according to Valenta method

[8]), absorption, capillarity and oxygen permeability

tests are shown in Figs. 12–19, and will be discussed

in next section.

4 Discussion

Chloride diffusion coefficient has been taken as

reference parameter because it is representative of

‘‘global’’ penetration rate in marine environment as it

was explained in Sect. 1. Introduction. This param-

eter has been compared with the different durability

tests results, to evaluate their effectiveness.

Figures 12–19 show correlations between chloride

diffusion coefficient (1 year exposure value, mea-

sured in m2/s · 10�12) and all the tests results

measured in concrete cores of the seven wharves and

in laboratory specimens submerged in seawater.

Correlation coefficients obtained are considered good

enough in most cases, taking into account that they

come from the analysis of real structures built with

cast in place concretes, so chloride penetration rates

are representative of natural exposure conditions along

service life. Linear regressions were fitted as they

showed the highest correlation coefficient values.

Themainparametersaffectingconcretebehaviourare

the exposure conditions and the use of mineral admix-

tures (blended cements), as it is described as follows.

Fig. 10 Corroded bar, tidal zone concrete exposed for 5 years.

Chloride concentration at rebar level: 1.43% of cement weight.

Wharf C

Fig. 11 Not corroded bar, submerged concrete exposed for

4.5 years. Chloride concentration at rebar level: 1.49% of

cement weight. Wharf A


Table 3 Diffusion

coefficients calculated for all

the cores of the seven

wharves

Wharf Core Time (years) Diffusion D (*10�8 cm2/s) Diffusion D1 (*10�8 cm2/s)

A A1–A2 4.5 22.8 48.4

A3–A4 4.5 30.6 64.9

A5–A6 4.5 21.9 45.8

B B1–B2 6.5 17.4 44.4

B3 6.5 17.0 43.3

B4–B5 6.5 23.5 59.9

C C1 7.5 14.0 38.3

C2 7.5 6.7 18.4

C3 7.5 14.4 39.4

D D1 5 34.2 76.5

D2 5 37.8 84.5

D3 5 35.9 80.3

D4 5 27.6 61.7

E E1 2 8.4 11.9

E2 2 1.9 2.7

E3 2 1.5 2.2

E4 2 2.1 3.0

F F1 2 5.4 7.6

F2 2 3.6 5.0

F3 2 3.6 5.1

F4 2 3.7 5.2

G G1 31 1.3 7.0

G3 31 0.9 5.2

G4 31 1.1 6.1

G5 31 1.1 6.2

STRENGTH-DIFFUSION

y = -0,4421x + 69,021

R2 = 0,5006

y = -0,1045x + 40,221

R2 = 0,1206

0

20

40

60

80

100

C-S

TR

EN

GT

H (

N/m

m2 )

0 50

DIFFUSION COEF.(x10-12 m2/s)

100

opc-submerged admixt.-submerged

opc-tidal zone admixt.-tidal zone

Fig. 12 Chloride diffusion coefficient versus compressive

strength

POROSITY-DIFFUSION

PO

RO

SIT

Y (

%)

y = 0,1108x + 11,005

R2 = 0,6747

y = -0,007x + 17,052

R2 = 0,011

0

4

8

12

16

20

24

0 50DIFFUSION COEF. (x10-12m2/s)

100



Fig. 13 Chloride diffusion coefficient versus porosity


4.1 Influence of marine exposure conditions

Data have been separated in two different regres-

sions, depending on concrete location: submerged or

tidal zone (Figs. 12–18): chloride penetration rate for

similar quality concretes must be different in both

environments as the transport mechanisms are dif-

ferent too (see Sect. 1. Introduction). Besides, it has

been plotted separately data from ordinary portland

cement concretes (full shapes) and from blended

cement mixes (empty shapes).

Chloride penetration rate is faster in submerged

concretes than in tidal zone concretes, which is

clearly pointed out on figures with good correlation

coefficients (Figs. 12, 15–18). This behaviour has

also been confirmed by other marine structures data

collected from bibliography and can be explained

because chloride penetration rate in submerged

environments is mainly controlled by a very slow

but permanent pure diffusion transport mechanism

due to total water saturation of concrete. On the

other hand, capillarity is the main transport

W. PERMEABILITY-DIFFUSIONW

. PE

RM

. (×1

0-12

m/s

)

y = 0,2988x + 1,4138

R2 = 0,7438

y = 0,0956x- 0,156

R2 = 0,5747

0

10

20

30

40

0 50DIFFUSION COEF. (x10-12m2/s)

100



Fig. 17 Chloride diffusion coefficient versus water perme-

ability

ABSORPTION-DIFFUSIONA

BS

OR

PT

ION

(%

)

y = 0,0318x + 1,9147

R2 = 0,7925

y = -0,0022x + 3,5246

R2 = 0,0284

0

1

2

3

4

5

0 50DIFFUSION COEF. (x10-12 m2/s)

100

opc-ssubmerged admixt.-submerged


Fig. 14 Chloride diffusion coefficient versus water absorption

MAX. DEPTH-DIFFUSION

MA

XIM

UM

DE

PT

H (

mm

)

y = 0,4111x + 16,521

R2 = 0,4861

y = 0,873x + 22,39

R2 = 0,7349

0

20

40

60

80

100

120

0 50DIFFUSION COEF. (x10-12 m2/s)

100



Fig. 15 Chloride diffusion coefficient versus maximum

penetration depth

AVER. DEPTH-DIFFUSION

AV

ER

AG

E D

EP

TH

(m

m)

y = 0, 346x + 5 , 8446

R 2 = 0 , 53 77

y = 0 , 9826x + 1 0 , 898

R 2 = 0, 8392

0

20

40

60

80

100

120

0 5 0 DIFFUSION COEF. (x10-12 m2/s)

100



Fig. 16 Chloride diffusion coefficient versus average penetra-

tion depth


mechanism in tidal zone (a very fast mechanism, but

interrupted by wetting-drying cycles), overlapped

with a pure diffusion much slower than in submerged

zone. Additionally, in tidal zone chloride ions

may also diffuse outward to the concrete surface,

due to the external washing out of chlorides in

concrete subjected to cyclic wetting and drying. Final

balance of these complex mechanisms shows

an apparent diffusion rate in tidal zone slower than

in submerged zone.

Another interesting point is that apparent diffusion

rates are as much different in both environments as

poorer is concrete quality. Chloride diffusion rate for

submerged concretes of high permeability is extre-

mely high (Fig. 17). However, apparent diffusion rate

for good quality concretes come closer for both

exposure conditions.

4.2 Influence of cement type

Related to the effect of using mineral admixtures, it is

very important on concrete behaviour, changing its

micro-structure with different results on concrete

properties. To analyse this effect, it must be consid-

ered that mineral admixtures (GGBS, fly ashes and

silica fume) cause concrete pore refinement, reducing

small size pores volume [12]. This effect may not

have an important influence on total porosity (and

consequently on absorption and compressive

strength, see Figs. 12–14), but drastically decrease

permeation rate into concrete: capillarity, permeabil-

ity and water penetration are reduced due to pore size

refinement (see Figs. 15–18). Moreover, as can be

seen in all the figures (12–18), blended cement

concretes results (hollow symbols) are grouped in the

low diffusion coefficients area, highlighting this

effect.

Now results obtained on different concrete prop-

erties tests are going to be analysed separately.

4.3 Diffusion coefficient—compressive strength

Figure 12 shows correlations between chloride diffu-

sion coefficient and compressive strengths (in N/

mm2).

Tendencies obtained in linear regressions are as

expected: higher strength concretes show lower

diffusion coefficients. Related to the effect of mineral

admixtures on both properties, it can be seen that it

almost doesn’t affect the concrete strength but it

really does on chloride penetration rate. In submerged

environment, diffusion rate is faster, and increasing

as the concrete strength decreases.

However, concrete strength is not suitable to

control durability, as the graph shows similar strength

concretes with very different diffusion coefficients, in

the same exposure conditions. Furthermore, the effect

of adding mineral admixtures on concrete strength is

much smaller than on chloride penetration rate, so

strength test does not control properly their beneficial

effect on concrete durability.

OXYGEN PERM.-DIFFUSION

OX

YG

EN

PE

RM

. (x1

0-16

m2 ) y = -0,0348x + 4,6754

R2 = 0,0543

0

4

8

12

16

20

0 20 40 60 80 100

DIFFUSION COEF. (x10-12 m2/s)


Fig. 19 Chloride diffusion coefficient versus oxygen perme-

ability

CAPILLARITY-DIFFUSIONC

AP

ILL

AR

ITY

(m

m/m

in0.

5 )

y = 0,0002x + 0,1525

R2 = 0,0205

y = 0,0019x + 0,1287

R2 = 0,7189

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0 20 40 60 80 100

DIFFUSION COEF. (x10-12 m2/s)

opc-submerged opc-tidal zone admixt.-tidal zone

Fig. 18 Chloride diffusion coefficient versus water capillarity


4.4 Diffusion coefficient—porosity


sion coefficient and porosity (in %).

Linear regressions adjusted show a very poor

correlation coefficient for tidal zone concretes, while

quite a high one for submerged concretes. The

beneficial effect of fly ashes and GGBS on the

reduction of chloride penetration rate is not followed

by porosity test results. So, it can be seen that blended

cements results (hollow symbols) distort the regres-

sion adjusted for tidal zone concretes. Nevertheless,

these high porosity concretes have very low diffusion

coefficients, due to the typical pore distribution of

blended cement concretes, as explained: although the

effect of mineral admixtures on concrete total poros-

ity is not remarkable, they originate a pore size

refinement, reducing the chloride penetration rate. In

submerged silica fume concretes, initial porosity was

really low (w/c = 0.36), so pore size refinement was

smaller and linear regression fitted show high corre-

lation coefficient (triangular symbols).

Finally, analysing only full shaped data (OPC

concretes), no clear distinction between both different

environments results appears, as total porosity test

gives partial information about concrete durability,

because it doesn’t assess pore distribution.

In terms of durability control test, due to these

disagreements (not properly taking into account

mineral admixtures effect and no distinction of

different exposure conditions), total porosity is not

considered an appropriate concrete property to con-

trol the chloride permeation resistance.

4.5 Diffusion coefficient—absorption


sion coefficient and absorption (in %).

Absorption results are influenced by total pore

volume, so it is the same case as explained for

porosity test, where blended cement (fly ashes and

GGBS) concretes results distorted the linear regres-

sion fitted for tidal zone concretes. So, it can be seen

in Fig. 14 that both parameters correlate bad for tidal

zone concretes due to the beneficial effect of mineral

admixtures on concrete porosity, not reflected by

absorption test. In submerged concretes, linear

regression fitted well because blended cement con-

cretes correspond with very low w/c ratio mixes.

Similarly, considering only data from OPC concretes

(full symbols) submerged or tidal zone exposure

cannot be distinguished.

For these reasons, water absorption is not consid-

ered an appropriate test to control the chloride

permeation resistance of concrete in marine environ-

ment (tidal and submerged zones). Nevertheless, in

submerged zone absorption test results show the best

correlation coefficient, meaning that this transport

mechanism is significant in this exposure conditions.

4.6 Diffusion coefficient—water penetration

depth

Figures 15 and 16 show correlations between chloride

diffusion coefficient and water penetration depth

under pressure (maximum and average depths, in

mm).

Related to global results analysis, tendency

obtained is as expected: lower water penetration

depth concretes have lower diffusion coefficients too,

and submerged concretes show higher chloride

penetration rates. Also, in both exposure conditions

good correlation are obtained for both maximum and

average penetration depths.

In this case, it is clearly shown the extremely

beneficial effect of adding mineral admixtures on

reducing different transport mechanisms rate into

concrete: both chloride diffusion and water penetra-

tion are reduced; moreover, this test distinguish

between diffusion rates corresponding to different

exposure conditions, so water penetration depth

under pressure is considered an appropriate concrete

test to control the chloride permeation resistance, and

so on the durability of reinforced concrete in marine

environment.

4.7 Diffusion coefficient—water permeability


sion coefficient and water permeability (estimated

from water penetration depth and porosity test results,

in m/s · 10�12).

Water penetration depth test results are even

slightly improved by water permeability results:

higher correlation coefficients are achieved, showing

a good sensitivity to control the chloride diffusion.

Besides, it takes into account properly the beneficial

effect of adding mineral admixtures (results are


grouped in the area next to zero point) and distin-

guishes between different exposure conditions (both

linear regressions are clearly different). Tendency

obtained is as expected too: higher water permeabil-

ity concretes have higher diffusion coefficients, and

submerged concretes show higher chloride penetra-

tion rates. Similarly, when adding mineral admixtures

to cement, both transport mechanisms (water perme-

ability and chloride diffusion) are reduced.

Main disadvantage is due to the fact that water

permeability results are estimated from two tests

(water penetration depth and porosity), and it

improves just slightly the linear regressions obtained

with water penetration depth test. On the other hand,

the possibility of carrying out a water permeability

test instead of its calculation is not considered good,

as high quality concretes are studied, where it is very

difficult to carry out this test.

4.8 Diffusion coefficient—capillarity


sion coefficient and water capillarity (in mm/min0.5)

measured in concrete cores of the seven wharves and

in some laboratory specimens submerged in seawater.

In tidal zone concretes, tendency obtained in linear

regression is as expected (the higher the capillarity,

the higher the diffusion coefficient, showing high

correlation coefficient) and takes into account prop-

erly the effect of adding mineral admixtures. As

capillarity is the dominant transport mechanism in

this type of exposure conditions, the linear regression

shows a high correlation coefficient, so capillarity

reflects well the changes in chloride penetration rate.

However, in permanently submerged concretes the

dominant transport mechanism is diffusion and the

influence of other mechanism as capillarity is small

on apparent diffusion, so the linear regression

obtained shows worse correlation coefficient; the

effect of high initial permeation by capillarity seems

to vanish at later ages because of diffusion.

Due to its poor sensitivity in permanently sub-

merged environment, water capillarity is not consid-

ered an appropriate concrete property to control the

chloride permeation resistance in marine environment

(tidal and submerged zones). Nevertheless, in tidal

zone capillarity test results show almost the best

correlation coefficient, meaning that this transport

mechanism is significant in this exposure conditions.

4.9 Diffusion coefficient—oxygen permeability

Figure 19 shows the correlation between chloride

diffusion coefficient and oxygen permeability (in

m2 · 10�16) measured in concrete cores of five

wharves. There are not results corresponding to

submerged concretes because the cores were obtained

by drilling vertically the concrete caisson and using

this procedure the diameter of the cores were so small

to carry out the oxygen permeability test.

Linear regression fitted shows a very poor corre-

lation coefficient and oxygen permeability test results

don’t take into account properly the effect of adding

mineral admixtures, so this test is not considered an

appropriate concrete property to control the chloride

permeation resistance, during the corrosion initiation

period.

However, from a theoretical point of view, this test

could be useful to assess the corrosion propagation

period, which starts once the rebars are depassivated

due to chloride penetration, and depends only on the

presence of water and oxygen around the rebar.

Therefore, in permanently submerged and tidal zone

environments, where relative humidity is high, rebar

corrosion rate will depend mainly on concrete oxygen

permeability.

Figure 20 shows concrete oxygen permeability test

results versus chloride concentration (in % of cement

weight) at rebar level. Corroded and not corroded

bars results are plotted in different shapes. As can be

seen, low values of oxygen permeability (below

4 · 10�16 m2) reduce the risk of corrosion, at least till

CHLORIDES-OXYGEN PERMEABILITY

0

4

8

12

16

20

0 1 2 3 4 5CHLORIDES AT REBAR LEVEL

(% cement weigth)

YXO

P NEG

.MRE

01x(

1-

6m

2)

Corroded bars Not corroded bars

Fig. 20 Risk of corrosion depending on concrete oxygen

permeability


chloride concentration at rebar level is very high

(more than 2% by cement weight, approximately).

From a conservative point of view, the couple of

values oxygen permeability-chloride concentration

that can origin a significant corrosion rate (line

plotted in Fig. 20) can be estimated.

4.10 Overall analysis of results

Correlation coefficients obtained can be classified

into two groups:

• R-squared values lower than 0.20: very poor

coefficients, meaning that they are not-significant

values (porosity and absorption in tidal zone;

capillarity in submerged zone).

• Rest of correlation coefficients. These coefficients

may not be considered so poor (R2 over 0.50),

taking into account that they are not laboratory

concretes but they come from the analysis of real

structures made of cast in place concretes (in situ

curing and consolidation, etc), built in different

areas, with different materials and separately in

time (concrete technology has changed so much);

so they may be considered significant values.

These significant correlation coefficients can be

analysed in terms of ‘‘relevance’’ of results: in tidal

zone, capillarity is the main transport mechanism [4]

(and consequently shows a high correlation coeffi-

cient: R2 = 0.72), while water penetration under

pressure and water permeability are not the main

transport mechanisms, but show high correlation

coefficients (R2 > 0.70). Compressive strength,

porosity and absorption are not significant

(R2 < 0.2). Capillarity should be the selected dura-

bility test in tidal zone.

In submerged zone, absorption is the main trans-

port mechanism (R2 = 0.79), while compressive

strength, porosity, water penetration under pressure

and water permeability are not the main transport

mechanisms, but show high correlation coefficients

(R2 > 0.50). Capillarity is not significant (R2 < 0.2).

Absorption should be the selected durability test in

submerged zone.

Water penetration under pressure is not the main

transport mechanism in any of both marine zones, but

correlation coefficients obtained are good enough in

both exposure conditions (R2 = 0.84 and 0.54,

respectively). So, from a practical point of view, it

may be selected as the only durability test to control

concrete durability in marine environment.

5 Conclusions

Based on the result obtained from this study, the

following conclusions may be drawn:

(1) In marine environment, reinforced concrete

durability depends mainly on the risk of rebar

corrosion due to chloride penetration.

(2) The experimental study carried out has com-

pared the sensitivity of different durability test

methods to predict chloride penetration into

concrete, using chloride diffusion rates ob-

tained from seven concrete structures. To

evaluate these test methods, it has been taken

into account if they properly reflect the effect

of adding mineral admixtures (and its effect on

pore size distribution) and if they distinguish

between permanently submerged and tidal

zone exposure results.

(3) Chloride penetration rate is higher in perma-

nently submerged concretes than in tidal zone

concretes, considering similar quality con-

cretes. Moreover, apparent diffusion rates are

as much different in both environments as

poorer is concrete quality.

(4) Adding mineral admixtures has a beneficial

effect on concrete quality, as they decrease

permeation rate: capillarity, diffusion, perme-

ability and water penetration are reduced due

to pore size refinement.

(5) Concrete durability control must be carried out

by means of specific tests, and compressive

strength test results must be considered just as

indicative values, as this test doesn’t reflect

properly the beneficial effect of adding min-

eral admixtures on concrete durability.

(6) Porosity and absorption test are not considered

appropriate to assess chloride permeation

resistance of concrete, as they don’t show

properly the effect of adding mineral admix-

tures and neither distinguish properly chloride

permeation rates in concretes exposed to

different marine environments.

(7) Capillarity test can distinguish between differ-

ent marine environments permeation rates


(permanently submerged and tidal zone), as well

as properly assess the effect of adding mineral

admixtures. However, it shows a very poor

sensitivity in permanently submerged concretes,

as in this environment capillarity is much less

important than diffusion and then it can’t eval-

uate properly global chloride penetration rate.

(8) Oxygen permeability test is not appropriate to

assess corrosion initiation period as it doesn’t

show properly chloride penetration rate, nei-

ther the effect of adding mineral admixtures,

but it is valid to evaluate corrosion propaga-

tion period, especially in permanently sub-

merged and tidal zone environments, where

relative humidity is high and corrosion rate is

controlled by oxygen availability.

(9) Water penetration depth and water permeabil-

ity tests are considered to assess properly

chloride permeation resistance of concrete, as

they show high correlation coefficients, which

proves their sensitivity to assess apparent

diffusion rates in tidal zone and permanently

submerged concretes. Moreover, these tests

take into account properly the effect of adding

mineral admixtures and distinguish between

chloride penetration rates in concretes exposed

to different marine environments. Water per-

meability coefficient is harder to obtain, as it

requires carrying out two tests: water penetra-

tion depth and porosity, so water penetration

depth test is considered the most suitable test.

(10) Finally, results show that it is advisable to

control concrete water tightness through

water penetration under pressure test, in

compliance with UNE 83.309-90 standard

(similar to ISO (DIS) 7031). Additionally, in

order to make sure an slow corrosion rate, it

should be advisable to control oxygen per-

meability in tidal zone concretes, by means

of Cembureau method [13], consisting of

measuring oxygen flux through a 5 cm thick

concrete disk, preconditioned at 20 ± 28C and

65 ± 5% RH for 28 days.

6 Future research

This article shows results obtained in the study of

concrete behaviour in marine environment (perma-

nently submerged and tidal zones). However, this

investigation is continuing with the following

objectives:

– Calculation of mineral admixtures efficiency

coefficient, in terms of chloride penetration

permeability.

– Modelling chloride diffusion for concretes (made

of OPC or blended cements) located in perma-

nently submerged or tidal zones, from chloride

profiles measures in full-scale structures.

– Assessing the influence of curing concrete with

seawater on its properties, especially on chloride

penetration rate.

Acknowledgements The authors wish to thank the financial

support given by Ports of Spain. Thanks to General Directionsof CEDEX for initiatives to promote postgraduate training and

development of doctoral thesis. Thanks to College of CivilEngineer for all the support at all stages during the preparation

of this experimental study.

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