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.

1. Page 1
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
(CO3
2-
). 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.

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+
+ CO3
2-
= 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+
+ CO3
2-
= CaCO3 (solubility 0.99 x 10-8
)
Page 2
c) Vaterite
of calcium carbonate crystals taken from SEM.
Wollastonite needles.
dissolution of primarily calcium

3. 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
DegreeofCarbonationSpeed
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
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
ther words the level that concrete pore system or network is filled with water
Figure 3. Typical concrete porosity.
In dry concrete the carbon dioxide can penetrate deeply but there is not enough water for the carbonation
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
concrete structures in low temperature regions will exhibit lower carbonation rates.
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
Page 3
process will continue until all of the CH is
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 structure of 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
ther words the level that concrete pore system or network is filled with water, Figure 3.
In dry concrete the carbon dioxide can penetrate deeply but there is not enough water for the carbonation
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
concrete structures in low temperature regions will exhibit lower carbonation rates.
on a C20/25 class concrete.

4. 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
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 %
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
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.
environmental conditions, carbonation should be considered as an inevitable phenomenon. As explained in
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-
Page 4
porosity of the near surface. The term
Concrete near surface porosity. The images shows increased porosity at the first 450µm.
Near surface porosity is affected by a variety of parameters including curing temperature, W/C ratio, formwork
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
speed of diffusion. We know that the volume changes do not affect the mechanical stability of the carbonated
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
environmental conditions, carbonation should be considered as an inevitable phenomenon. As explained in
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

5. Page 5
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,
ߕ = ߈ √ܶ (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,

6. Page 6
ܺ = √2‫ܶܦ‬ (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,
߈√ߒ = √2ߒ‫ܦ‬ → ‫ܭ‬ = √2‫ܦ ݎ݋ ܦ‬ =
௄మ
ଶ
(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,
ߕ = ߈ √ܶ → 8݉݉ = ‫3102√ܭ‬ − 2002 → ‫ܭ‬௠௔௫ =
଼௠௠
ඥଵଵ ௬௘௔௥௦
= 2.41 ݉݉/ඥ‫ ݎܽ݁ݕ‬
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,
‫ܦ‬௠௔௫ =
‫ܭ‬௠௔௫
ଶ
2
= 2.90 mm ଶ
/year
In the case of engaging the average value of the sample, the carbonation rate coefficient results into,
ߕ = ߈ √ܶ → 6.30 ݉݉ = ‫3102√ܭ‬ − 2002 → ‫ܭ‬௔௩௘௥ =
଺.ଷ଴௠௠
ඥଵଵ ௬௘௔௥௦
= 1.90 ݉݉/ඥ‫ ݎܽ݁ݕ‬

7. Page 7
and the
‫ܦ‬௔௩௘௥ =
‫ܭ‬௔௩௘௥
ଶ
2
= 1.80 mm ଶ
/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.

8. Page 8
Years of Exposure
0 5 10 15 20 25 30 35 40 45 50 55
CarbonationDepth(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.

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.
Page 9
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

10. Page 10
Carbonation Rate of Major Cities in Greece
Age in Years
0 10 20 30 40 50
CarbonationDepth(mm)
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
CarbonationDepth(mm)
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)

11. Page 11
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,
ܵܿ =
௑೚
మାଶ஽ሺ்೘ି்೚ሻି௑೘
మ
ଶሺ௑೘ି௑బሻ
(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,

12. Page 12
ܵܿ =
௑೚
మାଶ஽ሺ்೘ି்೚ሻି௑೘
మ
ଶሺ௑೘ି௑బሻ
=
଼௠௠మାଶ∙ଶ.ଽ଴ ൬
೘೘మ
೤೐ೌೝ
൰∙ሺହ଴ିଵଵሻିଵଶ୫୫మ
ଶሺଵଶ௠௠ି଼௠௠ሻ
= 18.27݉݉
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,
ܵௗ,஼ைଶ = ߤ ܵ௖ (5)
considering that the carbon dioxide equivalent resistance of concrete µ=400, the Equivalent Air Layer
Thickness for Sc=18.27mm is,
ܵௗ,஼ைଶ = 400 ∙ 18.27݉݉ = 7308݉݉ 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,
ܵܿ =
௑೚
మାଶ஽ሺ்೘ି்೚ሻି௑೘
మ
ଶሺ௑೘ି௑బሻ
=
ଵ௠௠మାଶ∙଺.ଶହ ൬
೘೘మ
೤೐ೌೝ
൰∙ሺହ଴ିଵሻିଶ଴୫୫మ
ଶሺଵ௠௠ିଶ଴௠௠ሻ
= 5.61݉݉ or ܵௗ,஼ைଶ = 2.2݉
The results for all carbonation categories are shown in Table 3.

13. Page 13
Table.3. Results of ELOT EN 206-1 in terms of Equivalent Air Layer Thickness for Xcrit=Cmin-5mm
Category XC1 XC2 XC3 XC4
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
Category XC1 XC2 XC3 XC4
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.

14. Page 14
The depth of carbonation 10 years after the first application of a paint following ELOT EN 1504-2 with
Sc=125mm is given by,
ߕ௣௢௦௧,௣௔௜௡௧ = ට൫ܵ௖
ଶ + ‫ܭ‬௣൯ − ܵ௖ (6)
where
‫ܭ‬௣ = 2ܵ௖ܺ௢ + ܺ௢
ଶ
+ 2‫ܶܦ‬௘ (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,
‫ܭ‬௣ = 2ܵ௖ܺ௢ + ܺ௢
ଶ
+ 2‫ܶܦ‬௘ = 2 ∙ 125݉݉ ∙ 8݉݉ + ሺ8݉݉ሻଶ
+ 2 ∙
଺.ଶହ௠௠మ
௬௘௔௥
∙ 10 ‫ݏݎܽ݁ݕ‬ = 2189 ݉݉ଶ
The depth of carbonation 10 years after the application of the paint is,
ߕ௣௢௦௧,௣௔௜௡௧ = ට൫ܵ௖
ଶ + ‫ܭ‬௣൯ − ܵ௖ = ඥሺ125݉݉ଶ/‫ݎܽ݁ݕ‬ሻଶ + 2189݉݉ −
ଵଶହ௠௠మ
௬௘௔௥
= 8.46݉݉
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),
ܵܿ =
ܺ௢
ଶ
+ 2‫ܦ‬ሺܶ௠ − ܶ௢ሻ − ܺ௠
ଶ
2ሺܺ௠ − ܺ଴ሻ
=
8.46݉݉ଶ
+ 2 6.25൫mm2 /year൯ሺ50 − 21ሻyears − 12mm2
2ሺ12 − 8.46ሻ݉݉
= 40.97 ݉݉
or ܵௗ,஼ைଶ = 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 of5m. 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.

15. Page 15
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.

16. Page 16
11. Marques P, Chastre C and Nunes A, Carbonation service life modelling of RC structures for concrete with
Portland and blended cements, Cement & Concrete Composites 37, 171–184, 2013.