Basic equations related to the selection of protective paints according to elot en 1504 2 against...

Selection of Protective Coatings according to ELOT EN 1504-2 Against

Concrete Carbonation

Chris A. Rodopoulos, Dipl-Ing, MSc, Dr-Ing, CEng, Eur-Ing, Prof. of Structural Integrity, Monash University,

Clayton, Australia.

a) Introduction

Paint systems or coatings are considered as the ultimate protection system against concrete carbonation and

against the subsequent probability of reinforcement corrosion. In this article the author is trying to explain the

use of protective paint systems and the equations describing the resulted degree of protection, making reference

to fundamental parameters controlling the carbonation process and speed. The article is written in such way as

to assist engineers involved with the protection of concrete structures either during the design or rehabilitation

phase. Examples referring to the particular environment of Greece are also included to enhance assistance to

the reader.

Typical structural failure due to indoor carbonation

b) Carbonation as a Process

The atmosphere contains substantial amounts of carbon dioxide. Yet, gaseous CO2 cannot, react directly with

the hydrates of the cement paste. Thus the CO2 gas must first dissolve in water and form carbonate ions that in

turn will react with the Ca ions of the pore water solution of the cement paste. The type of carbonate ions

depends on the pore solution pH. When CO2 comes into contact with water at neutrality it forms bicarbonate

(HCO3-). Inside concrete, the pH is high and as a result the bicarbonate dissociates and forms carbonate ions

(CO32-

). Thus in the carbonated layer bicarbonate forms but closer to the uncarbonated cement paste this

carbonate ions form (due to higher pH) and precipitate into calcium carbonate crystals (CC). Calcium carbonate

crystals exist in three crystallographic forms, aragonite (Αραγωνίτης), vaterite (Βατερίτης) and calcite

(ασβεστίτης), Figure 1. Calcite and vaterite are commonly found in carbonated concrete, Figure 2.

a) Calcite

Figure 1. Photos

Figure 2. Calcite crystal in cement paste

The carbonation process can be described by the following chemical equations,

1. CO

2.

The carbonate ion will react with Ca ions in the pore solution to form,

This will lead to lower concentration of Ca

hydroxide (CH). Since the solubility of CC is much lower than that of CH

4. Ca(OH)

5. Ca

b) Aragonite c) Vaterite

Photos of calcium carbonate crystals taken from SEM.

Calcite crystal in cement paste along with Wollastonite needles

The carbonation process can be described by the following chemical equations,

1. CO2 (g) + H2O = HCO3- (bicarbonate ion) +H

+

2. HCO3- = CO3

2- (carbonate ion) + H

+

The carbonate ion will react with Ca ions in the pore solution to form,

3. Ca2+

+ CO32-

= CaCO3

This will lead to lower concentration of Ca2+

which in turn will result into the dissolution of primarily

he solubility of CC is much lower than that of CH,

4. Ca(OH)2 = Ca2+ + 2 OH-

(solubility 9.95 x 10-4)

5. Ca2+

+ CO32-

= CaCO3 (solubility 0.99 x 10-8

)

c) Vaterite

of calcium carbonate crystals taken from SEM.

Wollastonite needles.

dissolution of primarily calcium

Ca(OH)2 (CH) will dissolve and CaCO

consumed.

The rate of carbonation depends on the solubility and speed of diffusion. Diffusion is controlled by

concentration differences. Thus we must consider the diffusion processes and the effect on the

carbonated layer. In simple terms is a process with inward diffusion of carbon dioxide gas and carbonate ions.

Gas diffusion is much faster than ion diffusion. Thus the speed of carbonation depends on the moisture content

of concrete. In other words the level that concrete pore system or network is filled with water

In dry concrete the carbon dioxide can penetrate deeply but there is not enough water for the carbonation

reaction. In fully water saturated concrete, only carbonate ions can move and hence carbonation is slow. Thus

there is an optimum where the speed of carbonations is at maximal, Figure 4.

found to increase at elevating ambient temperature

lead to faster carbonation, given that all the other

concrete structures in low temperature regions will exhibit lower carbonation rates.

0

Degree of Carbonation Speed

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Figure 4. Effect of environmental humidity on carbonation rate

(CH) will dissolve and CaCO3 (CC) will precipitate and the process will continue until all of the CH is


concentration differences. Thus we must consider the diffusion processes and the effect on the



ther words the level that concrete pore system or network is filled with water

Figure 3. Typical concrete porosity.


y water saturated concrete, only carbonate ions can move and hence carbonation is slow. Thus

there is an optimum where the speed of carbonations is at maximal, Figure 4. Carbonation rate has also been

elevating ambient temperatures. Indoor climate or exposure in warmer regions will

lead to faster carbonation, given that all the other affecting parameters remain invariable


Relative Humidity of Air in Equilibrium to Concrete

10 20 30 40 50 60 70 80 90 100

C20/25

ffect of environmental humidity on carbonation rate on a C20/25 class concrete

process will continue until all of the CH is


concentration differences. Thus we must consider the diffusion processes and the effect on the structure of the



ther words the level that concrete pore system or network is filled with water, Figure 3.


y water saturated concrete, only carbonate ions can move and hence carbonation is slow. Thus

Carbonation rate has also been

Indoor climate or exposure in warmer regions will usually

invariable. In contrast, outdoor


on a C20/25 class concrete.

Perhaps the most intriguing parameters affecting carbonation rate is the

near surface refers to depths between 0.1

Figure 5. Concrete near surface porosity. The images shows increased porosity at the first 450

Near surface porosity is affected by a variety of parameters including curing temperature, W/C ratio, formwork

compaction, wind speed, mix design etc.

Carbonation gives rise to volume changes. Transformation of CH to calcite gives a volume change of 11 %

to the metastable vaterite 14 %. The volume changes will affect the porosity in the carbonated layer and thus the

speed of diffusion. We know that the volume changes do not affect the mechanical stability of the carbonated

layer which remains stable and hard. This indicates that, normally, the surplus volume of calcite precipitation

mainly fills empty space in the capillary system and thus

c) The speed of Carbonation

Concrete will carbonate whenever carbon dioxide and some water are available.

environmental conditions, carbonation should be considered as an inevitable phenomenon. As explained in

section b), the speed of carbonation depends on

into the concrete and react with the cement paste.

water saturated conditions, carbonation will take

manner. When the capillary pore system

difficulty to diffuse. Thus, for concrete submerged in water

the concentration of carbonate ions in water and not the concentration of CO

applications, like retaining walls, deep foundations, piles, etc,

CO2 concentration, but on the other hand

be slow.

Therefore, the question is not whether carbonation will occur

According to Model Specification for Protective Coatings for

Kong- Civil Engineering Department in 1994

Χcrit≤ Cmin-5mm where Cmin is the minimum concrete cover thickness

or

Perhaps the most intriguing parameters affecting carbonation rate is the porosity of the near surface. The term

ace refers to depths between 0.1-2 mm from the surface, Figure 5.

Concrete near surface porosity. The images shows increased porosity at the first 450


compaction, wind speed, mix design etc.

Carbonation gives rise to volume changes. Transformation of CH to calcite gives a volume change of 11 %

The volume changes will affect the porosity in the carbonated layer and thus the


nd hard. This indicates that, normally, the surplus volume of calcite precipitation

mainly fills empty space in the capillary system and thus reduces the porosity of the

Concrete will carbonate whenever carbon dioxide and some water are available.


carbonation depends on how fast the carbon dioxide and/or the carbonate ions can move

the concrete and react with the cement paste. Even in the case of concrete submerged in water or under

water saturated conditions, carbonation will take place but at much slower rate and

system of the cement paste is blocked with water, carbon dioxide gas has

for concrete submerged in water (i.e. damns, water tanks, etc)

n of carbonate ions in water and not the concentration of CO2 in gaseous form.

walls, deep foundations, piles, etc, the decay of organic matter may result into a high

concentration, but on the other hand the speed of the diffusion of CO2 gas or carbonate ions in the soil may

Therefore, the question is not whether carbonation will occur? but rather, when carbonation become

Model Specification for Protective Coatings for Concrete, issued by the Government of Hong

Civil Engineering Department in 1994, such limit, xcrit, is considered when

is the minimum concrete cover thickness over the stir-

porosity of the near surface. The term

Concrete near surface porosity. The images shows increased porosity at the first 450µm.


Carbonation gives rise to volume changes. Transformation of CH to calcite gives a volume change of 11 % and

The volume changes will affect the porosity in the carbonated layer and thus the


nd hard. This indicates that, normally, the surplus volume of calcite precipitation

reduces the porosity of the cement paste.

Concrete will carbonate whenever carbon dioxide and some water are available. Independently of the local


how fast the carbon dioxide and/or the carbonate ions can move

Even in the case of concrete submerged in water or under

but at much slower rate and in potentially another

is blocked with water, carbon dioxide gas has

(i.e. damns, water tanks, etc) we have to consider

gaseous form. Similarly in soil

the decay of organic matter may result into a high

gas or carbonate ions in the soil may

when carbonation becomes critical?

, issued by the Government of Hong

, is considered when

-up

Χcrit≤ Caver - 7mm where Caver is the average concrete cover thickness over the stir-up

To better understand the two critical limits previously suggested, it is worth examining the following example.

Cover thickness and carbonation measurements were performed on several external columns of a 6-storey

building in Athens, Greece in 2013, Figure 6.

Figure 6. Typical carbonation measurement using the colour indicator procedure.

The results are shown in Table 1.

Table.1. Measurement matrix

Carbonation

Depth (mm)

Cover

Thickness (mm)

6 17

8 20

7 22

8 19

6 18

5 19

6 22

8 24

5 20

6 21

6 22

5 23

6 24

As per the Cmin approach, the critical depth of carbonation is Xcrit=17mm-5mm=12mm. Similarly according to

Caver approach, Xcrit=20.84 mm-7mm=13.84 mm.

The speed of carbonation can be determined either in terms of Equation 1,

� = �√� (Eq.1)

where X is the carbonation depth in mm, K is the carbonation rate coefficient in mm year-1/2

and T is the

exposure time in years.

Similarly the speed of carbonation can be determined in terms of Equation 2,

� = √2� (Eq.2)

where X is the carbonation depth in mm, D is the carbonation diffusion coefficient in mm2 / year and T is the

exposure time in years.

Equations 1 and 2 are obviously related resulting into,

�√ = √2 → � = √2 � = �� (Eq.3)

It is worth noting that Eqs.(1,2) are quite simplistic in describing the phenomenon, but at the same time they

represent a sound tool in the hands of a practicing engineer.

d) Determination of Safe Life

Whether corrosion of the reinforcement will initiate as a result of low pore solution pH - values of cement pore

solution pH ≤9.2-8.6 are considered critical for loss of reinforcement passivity - is not something that engineers

around the world should bother with in terms of protecting or performing a durability analysis. In every report,

standard, building code once carbonation depth becomes equal or larger than the stir-up cover thickness;

carbonation corrosion is considered as being initiated. Hence, in the literature such condition is referred as

"corrosion threshold due to carbonation".

Based on the above we can now transform the statement

Therefore, the question is not whether carbonation will occur? but rather, when carbonation becomes critical?

to

What shall we do in order to prevent reaching the corrosion threshold due to carbonation?

Estimation of the critical corrosion threshold can be made using Eqs (1 or 2) if we know the time of exposure T

being Τcurrent-Tinitial. Τcurrent is taken as the date of performing the measurements, in the case of the example 2013

and Tinitial is the date that concrete was first poured. Lets us considered that the construction of the 6-storey

building started in 2002. In this case equation 1 becomes,

� = �√� → 8�� = �√2013 − 2002 → �� = �� ! = 2.41��/�%&'�

Herein, we have considered the worst case scenario of X being the maximum value of the sample (8mm). Using

Eq.(3), the carbonation diffusion coefficient D is,

�� = ��2 = 2.90mm�/year

In the case of engaging the average value of the sample, the carbonation rate coefficient results into,

� = �√� → 6.30�� = �√2013 − 2002 → ��/� = 0.12�� ! = 1.90��/�%&'�

and the

�/� = ��/� �2 = 1.80mm�/year

Perhaps the reader will raise the question,

what is the difference between having a “fair face” concrete and having a concrete over coated with plaster of

a particular thickness and paint?

The answer is none. Table 1 contains values obtained from examining only the concrete depth. Whether the

measurements are the result of (paint+plaster+concrete) or just concrete, they do not affect the parameters K or

D. In other words, equations 1 and 2 examine the “end effect”.

Another potential questions emerging from the so far analysis could “why shall I calculate Ks' and Ds' for both

maximum and average values?”

Table 1, in terms of carbonation depth exhibits a probability distribution profile (normal distribution) having a

rather small standard deviation (1.10mm). As such the value of 8mm is quite close to the average of 6.30mm

with probability of only 6.11% being outside the distribution. Reality however is somehow different. Concrete

cracking, surface blow outs, temperature, humidity and so many other factors are parameters playing a major

role on standard deviation; Figure 7 shows the effect of a crack.

Figure 7. Effect of cracking on carbonation depth.

To better understand the relationship between K and Xcrit, visualization of the results is needed, Figure 8.

Years of Exposure

0 5 10 15 20 25 30 35 40 45 50 55

Carbonation Depth (mm)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Kmax=2.41 mm year -1/2

(8 mm, 11 years)DATE =2013

Protection Limit

(12 mm, 24.8 years)DATE=2027 Xcrit for Cmin

Cmin

Figure 8. Visualization of the problem in terms of Kmax.

From Figure 8 we can deduct the following conclusions,

a) In 2027 being 14 years since our measurements, carbonation depth would be equal to Xcrit and therefore

corrosion due to carbonation will materialize (safe life limit).

b) The protection limit in terms of remaining protection depth is 4mm.

e) Examining ELOT EN 206-1

For over 50 years, engineers have learned that avoidance of corrosion due to carbonation or due to chloride

ingress was achieved via concrete cover thickness. Several National Building codes refer specifically, to certain

cover limits. The concept of concrete cover thickness is also postulated in EN 206-1, while and not for the first

time, see KTS'97 (Κανονισµός Τεχνολογίας Σκυροδέµατος), is related to minimum cement content and

Water/Cement or Water/Binder ratio.

Let us take for example the draft version of ELOT EN 206-1:2000, as shown in Figure 9.

Figure 9. Minimum requirements of cover and concrete class against environmental load.

Herein we can transform the requirements in terms of

action are depicted in Table 2. In Table 2, of course we do not have taken into account the effect of cement

content or W/C ratio. Such action is not

time and cover thickness in the equations provide by Ceb/FiP

Concrete) in Eurocode.

Table.2. Ks and Ds according to ELOT EN 206

Category

Min. Cover

W/C

Cement (Kgr)

K (mm year

D (mm2 / year)

T (years)

To better evaluate the minimum requirements as expressed in the draft version of ELOT EN 206

making a certain comparison with realistic data taken from Greece, Figure

Minimum requirements of cover and concrete class against environmental load.

Herein we can transform the requirements in terms of K or D using equation 1 and 2. The results

In Table 2, of course we do not have taken into account the effect of cement

content or W/C ratio. Such action is not necessarily unsound, since K and D are controlled only by the exposure

time and cover thickness in the equations provide by Ceb/FiP (The International Federation for Structural

Ks and Ds according to ELOT EN 206-1 for the case of carbonation

Category XC1 XC2 XC3 XC4

Cover (mm) 25 25 35 35

W/C 0.65 0.6 0.55 0.5

(Kgr) 280 300 300 320

mm year-1/2) 3.54 3.54 4.95 4.95

/ year) 6.25 6.25 12.25 12.25

(years) 50 50 50 50

To better evaluate the minimum requirements as expressed in the draft version of ELOT EN 206

making a certain comparison with realistic data taken from Greece, Figure 10.

Minimum requirements of cover and concrete class against environmental load.

using equation 1 and 2. The results from such

In Table 2, of course we do not have taken into account the effect of cement

necessarily unsound, since K and D are controlled only by the exposure

The International Federation for Structural

e case of carbonation

XC4

35

0.5

320

4.95

12.25

50

To better evaluate the minimum requirements as expressed in the draft version of ELOT EN 206-1, it is worth

Carbonation Rate of Major Cities in Greece

Age in Years

0 10 20 30 40 50


0

10

20

30

40

50

60

Age vs Crete-Hrakleio

Age vs Athens Centre

Age vs Kalamata

Age vs Thessaloniki-Centre

Age vs Volos

Age vs Mykonos

Age vs Kifisia-Athens

Age vs Ioannina

Age vs Larissa

Figure10. Carbonation rate measured from structures at major cities in Greece. Concrete strength in all cases

had a minimum strength category of C16/20.

To better appreciate the results in Figure 9, we project on top of them the carbonation depth as results from

Table 2, Figure 11.

Carbonation Rate of Major Cities in Greece

Age in Years

0 10 20 30 40 50 60


0

10

20

30

40

50

60

Age vs Crete-Hrakleio

Age vs Athens Centre

Age vs Kalamata

Age vs Thessaloniki-Centre

Age vs Volos

Age vs Mykonos

Age vs Kifisia-Athens

Age vs Ioannina

Age vs Larissa

K=3.54 mm year-1/2

(XC1, XC2)

K=4.95 mm year-1/2

(XC3, XC4)

Figure 11. Comparison between the data from Figure 10 and the projected carbonation curves as defined in

ELOT EN 206-1.

Close examination reveals that application of ELOT EN 206-1 provides insufficient protection over the defined

period of 50 years with first indication of failure taking place at 17 years. At T≥25 years, being half the

designed life of the structure, it is obvious that over 50% of the sample will experience corrosion by

carbonation. Similar conclusions have been drawn in several other works.

At this point it is clear that the above analysis is under the assumption of full engagement of the cover

thickness. Obviously if the recommendation of Xcrit is introduced deficiencies in protection will further increase.

Whether Equation 1 reliably estimates the speed of carbonation and whether other models can provided more

accurate predictions is not the case examined in this work. In this work we examine requirements and equations

belonging in the EU Building Code.

Whether sample data depicted in Figure 10 are indicative for comparison to a newly used minimum class of

C20/25, is again something of academic dispute. In brief, someone can claim that the Table shown in Figure 9 is

under laboratory conditions having no influence of parameters like quality of construction, compaction errors,

curing parameters, formwork, concrete cover variations, etc.

f) Examining ELOT EN 1504-2 - Paint Systems - Case A - Without Paint Degradation

In paragraph d) we concluded that in 2027 carbonation depth would be equal to Xcrit while the remaining

protection depth is 4mm. In order to select a particular paint system (surface protecting coatings according to

EN1504-2) as protection medium, it is necessary to first calculate the equivalent concrete thickness, Sc,

34 = 56�7�89:;<:6=<5;��95;<5>= (4)

where

Sc= Equivalent concrete thickness (mm)

Xo= carbonation depth prior to the application of the coating (mm)

D= carbonation diffusion coefficient (mm2 /year)

Tm= Protection period (years)

To= Time of exposure prior to the application of the coating (years)

Xm= Maximum permitted carbonation depth (Xcrit) after the application of the coating at the end of the

protection period (mm).

In the case of the example, Eq 4. results into,

34 = 56�7�89:;<:6=<5;��95;<5>= = ��7�∙�.@2A;;�

BCDEF∙9G2<��=<��HH�

�9��<��= = 18.27��

The equivalent concrete thickness is transformed into Equivalent Air Layer Thickness, Sd,CO2 being the

thickness of a static layer of air that has the same carbonation resistance as the building material of thickness

t expressed in meters. Transformation of Sc into Sd,CO2 is made according to,

3J,LM� = N3O (5)

considering that the carbon dioxide equivalent resistance of concrete µ=400, the Equivalent Air Layer

Thickness for Sc=18.27mm is,

3J,LM� = 400 ∙ 18.27�� = 7308�� or 7.3 m

The minimum requirement of Sd,CO2 according to EN 1504-2 is 50 m. Of course most coating manufacturers

produce Sd,CO2 in the region 200-400 m.

In US, UK and Australia, the parameter Sd,CO2 is designated by the letter R. A snapshot from the Model

Specification for Protective Coatings for Concrete is shown in Figure 12.

Figure.12. Recommended values of Equivalent Air Layer Thickness according to Model Specification for

Protective Coatings for Concrete.

g) Examining ELOT EN 1504-2 - Paint Systems against ELOT EN 206-1

Equation 4 can also be used in order to calculate the Equivalent Air Layer Thickness of concrete cover as this is

defined according to ELOT EN 206-1. For example in the case of XC1 and considering Xcrit=Cmin-5mm,

34 = 56�7�89:;<:6=<5;��95;<5>= = ��7�∙0.�GA;;�

BCDEF∙9G2<�=<�2HH�

�9��<�2��= = 5.61�� or 3J,LM� = 2.2�

The results for all carbonation categories are shown in Table 3.

Table.3. Results of ELOT EN 206-1 in terms of Equivalent Air Layer Thickness for Xcrit=Cmin-5mm


Min. Cover (mm) 25 25 35 35

W/C 0.65 0.6 0.55 0.5

Cement (Kgr) 280 300 300 320

K (mm year-1/2) 3.54 3.54 4.95 4.95

D (mm2 / year) 6.25 6.25 12.25 12.25

Sd,CO2 (m) 2.20 2.20 8.43 8.43

T (years) 50 50 50 50

It is easily seen that under the limitation of Xcrit and the values of D as suggested by ELOT EN 206-1, the

durability requirements of the standard are below the limit of >50m set by EN 1504-2. ELOT EN 206-1

becomes partially valid only in the case of Xcrit=Cmin, Table 4.

Table.4. Results of ELOT EN 206-1 in terms of Equivalent Air Layer Thickness for Xcrit=Cmin


Min. Cover (mm) 25 25 35 35

W/C 0.65 0.6 0.55 0.5

Cement (Kgr) 280 300 300 320

K (mm year-1/2) 3.54 3.54 4.95 4.95

D (mm2 / year) 6.25 6.25 12.25 12.25

Sd,CO2 (m) -0.23 -0.23 4.80 4.80

T (years) 50 50 50 50

Hence, for ELOT EN 206-1 can be claimed that only for the categories XC1, XC2 provides marginal protection.

Categories XC3 and XC4 do fail below the requirements of ELOT EN 1504-2. Of course under the principles of

ENV 1990-part 0 limitation that carbonation is under the minimum reliability index of β=3.8 such marginal

protection is not accepted.

i) Examining ELOT EN 1504-2 - Paint Systems - Case B - With Performance life Limitation

In almost every case, the coating manufacturer provides time limitations regarding the performance life of its

product. Performance life is defined by several parameters that in one or the other way degrade the paint below

the 50m limit of the Equivalent Air Layer Thickness. Typical values of Performance Life usually found in

Product Data Sheets (PDS) range from 10 to15 years. To better appreciate the 50m limit of the Equivalent Air

Layer Thickness set by ELOT EN 1504-2, we considered that we apply a paint being just at the limit of 50m. In

other words Sc=125mm.

The depth of carbonation 10 years after the first application of a paint following ELOT EN 1504-2 with

Sc=125mm is given by,

�QR!S,Q�TUS = VW3O� + �QY − 3O (6)

where

�Q = 23O�R + �R� + 2�� (7)

Te= is the time between the first application of the paint and today (Performance life), i.e. 10 years.

In the case of the example, Eq.(7) results into,

�Q = 23O�R + �R� + 2�� = 2 ∙ 125�� ∙ 8�� + 98��=� + 2 ∙ 0.�G�� ∙ 10%&'�Z = 2189��

The depth of carbonation 10 years after the application of the paint is,

�QR!S,Q�TUS = VW3O� + �QY − 3O = �9125��/%&'�=� + 2189�� − ��G�� = 8.46��

In other words just by using the absolute minimum requirement of ELOT EN 1504-2, the actual increment of

carbonation depth after another 10 years of exposure is a mere 0.46mm.

In order to calculate the Sc for the second application (another 10 years), we once again make use of Eq.(4),

34 = �R� + 29�� − �R= − ��29�� − �2= = 8.46�� + 26.25Wmm2/yearY950 − 21=years − 12mm2

2912 − 8.46=�� = 40.97��

or 3J,LM� = 16.38� which is below the 50m limit.

Repetition of the above calculations per 10 year increment, can be performed to the end of the 50 years of

design life.

k) Examining ELOT EN 1504-2 - Paint Systems - Case B - With Performance life Limitation and Water

Vapor Permeability Limitation

The number of coating applications according to ELOT EN 1504-2 is only limited by the water vapor

permeability limitation of Sd,H2O<5m. The value is related to the Dry Film Thickness. It is imperative that the

manufacturer defines the maximum coating dry thickness to prevent reduction of breathability. Such limitation

is quite critical when evaluating the performance characteristics of the paint. Since re-application of the paint

increases the total dry film thickness, it is possible during application No. 3 being for example after 30 years to

increase Sd,H2O over the limit of 5m. In this case removal of previous paint coatings is required.

Hence, the two simultaneous limits being Sd,H2O<5m and Sd,C2O>50m represent perhaps the most vital ratio to

perform a quality evaluation of the pool of paints under investigation. To better appreciate such ratio is worth

bringing into the equation the cost of scaffolding required for a single application of paint.

Concussions

Perhaps the only thing that shall remain in the mind of the reader is that

a) ELOT EN 206-1 on its minimum limits is not applicable for the environmental load of Greek cities and the

committee responsible for producing the National Annex shall pay particular attention,

b) ELOT EN 206-1 on its minimum limits contradicts against the required reliability index of the Eurocode

c) ELOT EN 206-1 contradicts against the minimum requirements being set by ELOT EN 1504-2

d) Even the minimum requirements of ELOT EN 1504-2 are designed in order to provide a reliable and

performance based protection against carbonation.

Acknowledgement

The author would like to thank the participating students of the 2014 class attending the Continuous

Professional Development Programme on Principles of Protection, Rehabilitation and Structural Upgrade

according to ELOT EN 1504, TUV Academy, for being the driving force behind this article.

References

1. Soroca I, Concrete in Hot Environments, E& FN Spon publishers, 1993.

2. Ali, A., Dunster), A., Durability of reinforced concrete -effects of concrete composition and

curing on carbonation under different exposue conditions. BRE-report, Garston UK 1998.

3. Currie, R. J., Carbonation depth in structural-quality concrete, BRE report, Garston, UK 1986

4. Parrot, L.J., A reveiw of carbonation in reinforced concrete, A review carried out by C&CA

under a BRE contract. July 1987,

5. Tuutti, K., Corrosion of steel in concrete. CBI research 4:82 CBI, Stockholm, Sweden 1982.

6. C. Rodopoulos, Evaluation of Commercial Protecting Coatings against concrete carbonation, Report 1547-

2013, 2013.

7. Stepkowska E. T, Pérez-Rodríguez L. J, Sayagués M. J, Martínez-Blanes J. M, Calcite, vaterite and

aragonite forming on cement hydration from liquid and gaseous phase, Journal of Thermal Analysis and

Calorimetry, 73(1), 247-269, 2003.

8. Model Specification for Protective Coatings for Concrete, issued by the Government of Hong Kong, Civil

Engineering Department,1994.

9. CEB-FIP: Durable of Concrete Structures, Design Guide, T. Thelford, London, 1992.

10. CEB-FIP: Eurocode, 2000.

11. Marques P, Chastre C and Nunes A, Carbonation service life modelling of RC structures for concrete with

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