In Brazil, the air-entrained concrete has been extensively used as structural walls of popular housing units. Some of these units built recently in urban areas were inspected. Upon inspection, a significant variation of the potential corrosion measurement was obtained and reddish stains on the surface of the reinforcement, were also observed indicating active state of corrosion. Not always the concrete was fully carbonated and there wasn´t chloride contaminations. In order to understand the occurrence of premature corrosion of the inspected reinforcement, a complementary study was conducted at the laboratory to characterize air-entrained concretes and evaluate the behavior of steel bars immersed in solutions that simulate the water in the pores of these concrete and compare them to the pore solution of an ordinary Portland concrete. The steel bars were evaluated under three conditions: blasted, corroded and galvanized. The behavior of the bars was monitored by visual examination and by electrochemical measurements. Finally, the corrosion rate was calculated. Tests on concrete specimens were also conducted to validate the results. The characterization tests showed an inferior quality of the air-entrained concretes, having both high concentrations of pores, many of them fully interconnected. This justified the high deep carbonation observed in a short period of time and a variable electrical resistivity detected in the field. The pore solution immersion tests showed the higher corrosion susceptibility of metallic reinforcement in air-entrained concretes. In the studied air-entrained concretes, the corrosion occurred preferentially under the sealant applied on the bar extremities. In one of them, corrosion was also observed on the free surface of the blasted bars. The corrosion was also observed in the air-entrained concrete specimens, confirming the tests solution results. No Brasil, o concreto com ar incorporado tem sido intensamente utilizado como parede estrutural de unidades habitacionais. Algumas dessas unidades construídas recentemente (inferior a três anos) em regiões urbanas, do norte, sul e sudeste do país, foram inspecionadas. Na inspeção, foram detectadas manchas avermelhadas na superfície das armaduras, indicando um estado ativo de corrosão do aço-carbono. Diante desse fato, foi conduzido um estudo experimental objetivando avaliar o comportamento de barras imersas em soluções que simulam a água presente nos poros do concreto com ar incorporado e do concreto convencional. As barras foram avaliadas em três condições: aço jateado, aço já em processo de corrosão e aço zincado. Em algumas barras foram fixados anéis de material não metálico para estudo da corrosão em frestas. O comportamento das barras foi acompanhado por exame visual e por medidas eletroquímicas. Ao final, a taxa de corrosão foi calculada. As soluções foram obtidas pela mistura de água destilada e do material resultante da moagem de co

2. • introduction: overview of the results obtained in
field inspections that motivated
the present study;
o objectives of the study;
o methodology;
o results;
o conclusions.

3. Recently, the air-entrained concrete has been
extensively used as structural walls in Brazilian
popular housing units.
One of the biggest unit constructions, 18 thousand houses.

4. Some houses and their construction system
House formwork Reinforcement and concrete placement

5. ACI concrete terminology: causes the
development of a system of microscopic air
bubbles in concrete, usually to increase the
concrete workability and frost resistance.
The concrete is delivered
to the site (in a truck agitator).
The air-entraining admixture
is incorporated at that
point.
Carbon steel weld wire
mesh is used as
reinforcement
(Ø 3.6 mm - 150 mm x 150 mm)
In the housing units:
This admixture is used to increase the
concrete workability (self-compacting
concrete) and thermal and acustıc
comfort of the houses.
Corroded bars
(outdoor storage)

6. • urban atmosphere (mostly in tropical regions);
• built by different constructers (less than 3 years ago).
Visual inspection (concrete and bars surface) Potential and electric resistivity
Concrete coverChloride ions profile Carbonation front
Some houses (6 units) were inspected, all were:
The usual tests were performed during the inspection:

7. Insıgnıfıcant chloride
ions content
Variations in
concrete cover
and porosoty
In all the units inspected were detected:
High carbonation front
(it reaches the steel in some walls)
Intense
reddish stains
and corrosion
products on
the surface of
the bars
They were present
in carbonated
and integrity
concrete!

8. high presence of air bubbles was visualized (by naked
eyes and SEM images) in:
Concerning the porosity:
Soylev, T.A.; Francois, R. (2003): the porosity and the density variation of the concrete enhance the corrosion of steel
embedded due the lack of chemical and physical protection supplied. Jingak, N. et al (2005): the corrosion initiated
preferentially at an air void along the steel-concrete interface. Glass, G.K. et al (2000): the absence of calcium
hydroxide at the location of the entrapped air voids in steel-concrete interface is a dominant effect in initiate a
corrosion process by chlorides. Page, C. L. (1975): local heterogeneities in the zone adjacent to steel are liable to
influence its corrosion behavior in the presence of aggressive agents. Lambert et al (1991): the interface macro-defect
disrupts the integrity of the cement hydration-product layer.
Concrete-steel interface
Concrete bulk
and at the surface
The entrapped air voids
disrupt the integrity of the
buffering layer of cement
hydration products. This
may result in a missing
passivation for parts of the
steel and the premature
corrosion in the defect
areas (crevices).
The literature reports the interface defects and its impact on the corrosion:

9. Dispersed areas
Wire ties
Dispersed areas
Concerning the corrosion in the integrity concrete:
The stains and the corrosion products were visualized (naked eyes) in
dispersed areas of the bars’ surface and in wire ties and weld areas.

10.  Ecorr: mostly more positive than -250 mVCSE, most
potential gradients were less than 200 mVCSE;
GONZÁLEZ et al. (2004) low levels of wetness can confuse active and passive based only in Ecorr measurement. The
most value Ecorr will be that one obtained when the concrete resistivity is less than 20 kΩ.cm. The electric resistivity
between 100-50 kΩ.cm indicate low risk of corrosion, between 50-20 kΩ· cm there is a high risk and less than 20 kΩ·
cm very high risk. ASTM C876 (2009) not considers normally applied for carbonated concrete the criteria (i.e.: 90 %
probability of corrosion for Ecorr values ≥ -350 mV, CSE). LIVECON D3.1 (2003) considers significant potential gradient
≥ 200 mV (in 1 m). The gradient has more weight then the absolute potential value. BROOMFIEL (1991) considers that
the Ecorr measured by a reference electrode is not the true value, but a mixed potential of an unknown area of the
rebars. GONZÁLZ et al. (1979) considering the Nernst formula, the concrete pH reduction (~7-8) by carbonated
reactions mean a 250 mV to -300 mV increase. ELSENER et al. (1990) when surface potentials are taken, they are
essentially remote from the reinforcement due the concrete cover. The potential thereby measured are, in fact,
mixed potentials. It can not be interpreted in a straightforward manner.
The measurement results were not in agreement with the
results obtained from the visual examination. The small
diameter bars embedded in high depth must have
affected the measurements, as well as the surface wetness
variation and its impregnation with paint product.
…the literature mentions restrictions in the measurements:
In all the units inspected:
 Resistivity: usually above 50 KΩ· cm.

11. The present study complements the presented
results by:
 characterization of air-entrained concrete;
 Evaluation of the behavior of steel bars
immersed in solutions that simulate the water
in the pores of the air-entrained concrete.

13. Concrete bulk analysis: calculation of quantity and
diameter of the air bubbles in petrographic samples
prepared according to ASTM C856 (2011) and observed in SEM
(associated with Scandium program);
Physical and mechanical tests: performed according
to Brazilian standards.
2 air-entrained concretes - AC1 and AC2
(specimens were casted in the field, in 2 different units)
1 ordinary concrete (reference) – OC
(specimens were casted in the laboratory)

14. The pore solutions were obtained from the mixtures
prepared with distilled water and the powder obtained by
grinding the concrete specimens (AC1, AC2 and OC).
3 different conditions of the bar were
defined(deformed, Ø 3.6 mm):
• blasted (BS),
• corroded - open air exposition (CS);
• chromate treated galvanized (GS).
Cupper wire - electric contact
Sealant over epoxy paint in the
bars extremity
o-ring wrapped around
the bar (middle of the
exposed length)
1 bar to simulate crevice corrosion
3 replicate bar +
Experimental set-up (bar immersed
in the supernatant of the solution)

15. Cylindrical concrete specimens were used (Ø 5 cm x 10 cm).
They were cured in laboratory atmosphere.
1 blasted bar + 2 corrode bars
To validate the results in pore solution, tests on air-
entrained concrete specimens (AC1 and AC2)
were also conducted
Bar embedded in a
concrete specimen

16. Potentiostat (Solartron), using
three-electrode cell
(saturated calomel electrode, SCE).
The Stern-Geary equation
was applied.
IR drop compensation for
concrete specimens measures.
After 1 day and 10 days of the bars immersed in the solutions
(AC1, AC2 and OC) and after 28 days of the concrete specimens
cure (AC1 and AC2), the bars were assessed by means of
corrosion potential (Ecorr) and linear polarization resistance
measurements of instantaneous corrosion current density
(icorr) and visual (naked eyes) examination. Ecorr was monitoring
during in the immersion tests.
… the usual electrochemical procedure for concrete studies was followed:

18. Materials
AC1 AC2
Ratio Features Ratio Features
Datasupliers
Water 185 l W/C 0.66 185 l W/C 0.71
Admixture 0.5 l
Air-entraining
based on pitch
soap, 0.18 % by
weight of blinder
0.5 l
Air-entraining
based on pitch
soap, 0.19 % by
weight of blinder
Fine aggregates 943 kg - 839 kg -
Coarse aggregates 725 kg - 796 kg -
Portland cement 280 kg
CP IV 32
(pozzolanic-
modified cement)
260 kg
CP II E 40
(slag-modified
cement)
Fiber 0.3 kg
Polypropylene
microfiber
0.2 kg
Polypropylene
Microfiber
Testsresults
Compressive
strengh
6.5 MPa 6.2 MPa
Voids content 37.5 % 36.8 %
Density 1730 kg/m³ 1650 kg/m³
Water absorption 22.7 % 22.4 %
The tests showed the inferior quality of the air-entrained concretes. Both
do not fulfill the Brazilian standard (design of structural concrete).
The poor quality must affect the performance
OC
Ratio Features
166 l W/C 0.55
2.11 kg
Polycarboxylate,
0.7% by weight of
blinder
257 kg -
284 kg -
301 kg CP II E 32
- -
38.8 MPa
11.2 %
2280 kg/m³
4.8 %
Soylev e Francois (2003): the corrosion rate is a function of concrete quality and
it increases as the class of concrete strength decreases

19.  high presence of air bubbles with
variation of size and distribution;
 proximity of the air bubbles,
some of them communicating;
 trend of concentration of the air
bubbles surrounding the
aggregates in AC2.
OCAC2AC1
The AC1 and AC2 poor quality was
confirmed by microstructure
analysis, being detected:
20 % 35 %
Ø 40 to 60 µm
10 %
Bubble content 18 % Bubble content 4.5 %Bubble content 17 %
OCAR1 AR 2
Ø 120 to 140 µm
Amount
Diameter

21. Solution Calcium (Ca2+)
Inorganic compounds (mg/l) pH Temperature (oC)
Chloride (Cl-) Sulfate (SO4
2-) Initial Final Initial Final
PSAC1 0.21 ± 0.01 4.5 ± 0.2 12.0 ± 1.0 12.4 11.7 23 23
PSAC2 0.11 ± 0.01 6.7 ± 0.4 5.9 ± 0.2 12.2 11.7 22 19
PSOC 0.25 ± 0.01 2.4 ± 0,2 25.7 ± 0.6 12.2 11.7 21 21
Blasted surface - BS
(some corrosion areas) Corroded surface - CS
Galvanized layer- GS
(bubbles and irregularities in
the layer and cracks at the
surface)
In the 3 solutions, the chloride content is not significant.
During the tests, the pH is found to be similar.
Pretest (SEM image plus EDS) showed the presence of
cracks in the surface of GS bars and bubbles and
irregularities in its layer.

22. BS - solution results:
BS4 - PSAC2
Ecorr 5 day was less
than -300 mV
PSAC1, PSAC2 and PSOC
Most values of Ecorr remained more
positive than -300 mV, except to
ASTMC876(2009)
PSAC1
icorr ≤ 0.15 µA/cm2
PSAC2
icorr ≤ 0.10 µA/cm2
PSOC
icorr ≤ 0.11 µA/cm2
PSAC1
icorr ≤ 0.11 µA/cm2
PSAC2
icorr ≤ 0.24 µA/cm2
PSOC
icorr ≤ 0.25 µA/cm2
BS2
BS4
10
The corrosion levels were
low* in all the solution
(icorr ≤ 0.5 µA/cm2) after
1 and 10 days of immersion.
1
BS2 29 µA/cm2
* RILEM TC 154 (2004)
BS3 1.6 µA/cm2
BS2 – PSAC2
Ecorr 5-10 days was
less than -300 mV
The exceptions were...

23. All bars presented
corrosion - spots
under the sealant
and the o-ring.
PSAC1
BS – visual analysis: PSAC2
BS2 and BS4 presented
severe corrosion:
initiated under the sealant
and propagated toward
the free surface.
BS1 and BS3 presented
corrosion under the
sealant.
BS2 BS4
BS2
Ecorr max.: -498 mVSCE
BS4
Ecorr max.: -329 mVSCE
BS4BS2
BS2
Ecorr max.: -282 mVSCE
BS4
Ecorr max.: -211 mVSCE
PSOC
Only BS4 presented
corrosion - under
the sealant and the
o-ring.
BS4
Ecorr max.: -202 mVSCE
BS4

24. CS - solution results: PSAC1, PSAC2 and PSOC
Most values of Ecorr remained more
positives than -150 mV, except to
101
Although the values of Ecorr indicates the passive state of the bars in all
the solutions, high corrosion levels were obtained (higher than 3 µA/cm2)
CS2 – PSAC2
Ecorr = -168.89 mV
The no change in the surface of the bars confirmed the passive state.
CS1 – PSAC2
Ecorr = -174.22 mV
RILEM TC 154 (2004): the Rp values cannot be correctly determinate if the
steel is passive.

25. GS - solution results:
The values of Ecorr
were more
negative than
-600 mV in the
beginning and
went up later
(passivation
process).
The values of Ecorr remained
more positive than -600 mV
PSAC1
icorr ≤ 1.4 µA/cm2
PSAC2
icorr ≤ 0.8 µA/cm2
PSAC1
Icorr ≤ 3.7 µA/cm2
PSAC2
icorr ≤ 2.1 µA/cm2
PSOC
icorr ≤ 0.3 µA/cm2
10
In the solution PSAC1 and PSAC2, the
corrosion levels were moderate to high
after 1 and 10 days of immersion .
In the PSOC, the corrosion levels were low
after 1 and 10 days
1
PSAC1 and PSAC2
The values of Ecorr had a tendency to
drop (depassivation process)
PSOC

26. -1200
-1100
-1000
-900
-800
-700
-600
-500
-400
-300
-200
0 2 4 6 8 10 12 14 16 18 20
Tempo (dias)
PSAC1 PSAC2 PSOC3
The solution tests for GS bars was repeated …
And the tendency of the bars be
depassivated in PSAC1 and PSAC2
It also showed the tendency of the
GS bars be passivated in PSOC
16
days
2 h
PSAC2PSAC1
PSAC2PSAC1
PSOC
PSOC
Localized
corrosion takes
place (dark spots
and H2 bubbles at the
surface)
pH ~ 12.2
pH ~ 11.5
White corrosion
products at the
surface
2 h
The SEM images showed the
formation of crystals on the
surface of coating at the PSOC.
Similar crystals are found in
other studies. They are
formatted during the zinc
passivation.

27. BS1 - AC1
Ecorr = -520 mVSCE icorr = 0.8 µA/cm2
CS1 - AC1
Ecorr = +58 mVSCE icorr = 5.6 µA/cm2
CS2 – AC1
Ecorr = +54 mVSCE icorr = 8.9 µA/cm2
CS1 – AC2
Ecorr = -123 mVSCE icorr = 9.7 µA/cm2
BS1 – AC2
Ecorr = -160 mVSCE icorr = 3.2 µA/cm2
CS2 - AC2
Ecorr = +83 mVSCE icorr = 4.5 µA/cm2
The results obtained in the concrete specimens were in
agreement with the pore solution tests: In the BS bars there
was crevice corrosion under the sealant. For the CS bars
the potential indicated a passive state, being obtained a
high corrosion level.

28. The characterization tests showed the low quality of
the air-entrained concretes and the pore solution tests
indicated the greatest susceptibility of steel corrosion in
these concretes. The obtained results are in agreement
with the inferior performance of the air-entrained
concretes in the field in relation to the usually observed
in a variety of ordinary concretes.
The air-entrained concrete AC2 showed greater
susceptibility to corrosion. This was clearly observed in
the pore solution tests with blasted bar (BS) and
confirmed by concrete specimen tests.

29. The crevice corrosion was detected in the solutions. Thıs
corrosion takes place under the sealant and the o-ring
in the blasted bars (BS) in the 3 solutions. In the AC2
solution the corrosion propagated towards the free
surface of the blasted bars.
A tendency to depassivation of the galvanized bars
(GS) was detected in the air-entrained concrete
solutions. Localized corrosion was observed in the 3
solutions, being probably related to the surface
defects.
It´s important to conduct detailed studies in the air-
entrained concrete. These have to consider the bare
and galvanized steel and a new system for protection of
the bars extremities.

30. Thank you
for your attention!
aaraujo@ipt.br