FIELD SURVEY FOR CARBONATION DEPTH OF
REINFORCED CONCRETE BUILDINGS IN THE PHILIPPINES
Nobuaki Otsuki, Graduate School of Tokyo Institute of Technology
Ronaldo S. Gallardo, De La Salle University
Toshiki Annaka, Graduate School of Tokyo Institute of Technology
Satoshi Takaki, Graduate School of Tokyo Institute of Technology
Takahiro Nishida, Graduate School of Tokyo Institute of Technology
37th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 29 - 31 August 2012,
Singapore
Article Online Id: 100037033
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37 Conference on Our World in Concrete & Structures
29-31 August 2012, Singapore
FIELD SURVEY FOR CARBONATION DEPTH OF
REINFORCED CONCRETE BUILDINGS IN THE PHILIPPINES
Nobuaki Otsuki*, Ronaldo S. Gallardo†, Toshiki Annaka‡,
Satoshi Takaki‡ andTakahiro Nishida‡
*
Graduate School of Tokyo Institute of Technology
2-12-1 S6-12 Ookayama, Meguroku, Tokyo 152-8552, Japan
e-mail: <otsuki @ide.titech.ac.jp>
webpage: http://www.ide.titech.ac.jp/~otsukilab/English/o-ce-labo.html
Keywords: Carbonation, field survey, reinforced concrete, paint coating
Abstract. The service life of reinforced concrete buildings is said to be
100 years with the appropriate construction and maintenance. However,
some of the buildings are deteriorated in a few decades due to various
causes, such as carbonation. In the carbonated concrete, pH around the
steel bars in concrete is decreased and these steel bars start to corrode.
Although many of survey results were reported in many countries, there
is little information about carbonation phenomena on existing structures
in South-east Asian countries.
From above backgrounds, the measurements of carbonation depth of
existing buildings located in the Philippines were conducted in the
present study. Especially the influence of paint coating or wet/dry
condition of concrete surface was focused. Additionally the rates of
carbonation were calculated using carbonation models of concrete
proposed in literature surveys.
As the results of this study, it was confirmed that the influence of paint
was relatively high compared with that of wet or dry condition. Also the
rates of carbonation in the Philippines were smaller than those in Japan. .
It was considered that the high resistance of concrete against
carbonation in the Philippines derived from relatively small water cement
ratio (0.28-0.44), and paint coating. Especially, Re-painting makes life
time of building longer than no re-painting. Also Masuda’s equation was
found to be useful to evaluate the effect of painting and re-painting.
1
INT RODUCT ION
According to Architecture Institute of Japan, the ser vice life of reinf orced concrete
buildings is said to be 100 years with the appropriate constr uction and m aintenance.
However, s om e of the buildings are deterior ated in a few decades due to various
causes, such as carbonation. Steel bars have passivit y with alk aline environm ent in
hardened concrete. However, in the car bonated concrete, pH around the steel bars in
concrete is decreased and passivit y around the steel bars dis appears and these steel
bars start to c orrode. Equation ( 1) shows the r eaction of carbonation.
†
‡
Department of Civil Engineering, De La Salle University
Graduate School of Tokyo Institute of Technology
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
Ca(OH2)+CO2→CaCO3+H2O
(1)
1
Deter ior ation process of carbonation is defined b y four stages as shown in T able
1. In the pres ent study, initiation stage is focused, and rate of carbonation was
evaluated.
In the previous research, painting affects carbonation r ate. T o estim ate rate of
carbonation of paint coating str uctures, Masuda’s equation is used.
Rate of carbonation is also influenced by m ix proportion of concrete and its
environm ent such as c oncentration of CO 2 and tem perature.
T here is little inform ation about carbonation phenom ena on existing str uctures,
although clim ate of South-east As ia is seem ed to be strict environm ent against
carbonation. T o understand the rate of carbonation of real structures in South-east
Asian countr y, m easur em ents of carbonation depth wer e c onducted in the Philippines.
T o achieve these objectives, following two m atters ar e conducted. First, the
m easurem ents of carbonation depth of existing buildings located in the Philippines
were conducted. Second, the rate of carbonation of real structures in the Philippines
was calc ulated us ing c arbonation m odels proposed in literature s urveys.
Fig 1 shows flow of the pres ent stud y. In chapter 2, outline of field sur ve y is
explained. In chapter 3, investigations of effect of paint coating, W /C and rain are
conducted. In chapter 4, rate of carbonation bas ed on the m easured data and
Masuda’s equation wer e evaluated.
T able 1: Eac h deter ior ation process of carbonation
Stage
Definition
Initiation
stage
Propagation
stage
Acceleration
stage
Until the depth of carbonation r eaches the
lim it state for the occurrence of corrosion
From the initiation of corrosion of steel
until crack ing due to corrosion
Stage in which steel corrodes at a high
rate due to crack ing due to corrosion
Stage in which load bearing capacity is
reduced considerabl y due to increased
steel corrosion
Deter ior ation
stage
Factor determ ining
the stage
Rate of
carbonation
Rate of steel
corrosion
Rate of corrosion
of steel with crack s
Chapter 1: Introduction
Chapter 2: Outline of Field survey
Chapter 3: Effect of Paint, W/C and rain
Chapter 4: Prediction of rate of carbonation
Chapter 5: Conclusion
Fig 1: F low of pres ent stud y
2
OUT LINE OF FIELD SURVEYS
T he carbonation depth and the thick ness of concrete cover were m easured in this
surve y, Also the m ix pr oportion of concrete structures was estim ated in this surve y.
Carbonation depth was m easured based on drilling m ethod, NDIS 3419 pr oposed
by the Japanese Society for Non- Destructive Inspection. F igure 2 s hows the m ethod
of NDIS 3419. Concrete was dr illed and filter paper with phenolphthalein put under
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
drill. T he depth of carbonation was judged when the filter paper changed to redpurple. After the test, the hole was filled in b y back filling m aterial.
T hick ness of concrete cover was m easured using steel bar detector as shown in
Figur e 3.
Mix proportion of conc rete was estim ated using f-18 m ethod proposed by Japan
Cem ent Assoc iation. Proper partic le size of concrete powder was dissolved to
hydr ochlor ic acid and it was filtr ated. From filtrate and residual m aterial, cem ent
content and aggregate content were estim ated. T o estim ate bound water , concret e
powder was ignited.
Fields of this sur ve y are Manila cit y Philippines. T he data of Japan was used
2
m easured in T suk uba . T able 2 shows the clim ate of Manila city and T suk uba cit y.
Average tem perature and prec ipitation of Manila cit y is high and m ore than that of
Japan. Relative hum idity and CO 2 c oncentration are sim ilar in both cities.
T able 3 shows the m easured structures and its condition. T he m easurem ents of
carbonation depth conducted on 8 buildings, 119 points in the Philippines. Except P5,
all structures ar e paint coated, and P2, P4, P6 are r epainted once ever y five years.
P5, P6, P7, J 1 were measured car bonation depth of the area with and without paint
coating.
Carbonation depth
Phenolphthalein was soaked into filter paper
Concrete cover
Figur e 2: Dr illing m ethod, NDIS 3419
Figur e 3: Steel bar detector
T able 2: Clim ate and CO 2 concentration of each site
Site
T em p.
/°C
Precipitation
/mm
R/H
/%
CO2 conc entr ation
/ppm
Manila
(Philippine)
27.7
2201
73.8
404
T suk uba
(Japan)
13.8
1283
71.2
450
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
Table 3: Structures and itsh condition
Site
Structure nam e
P1
P2
P3
P4
P5
P6
P7
J1
Philippine
Japan
3
Age of structur es
/ year
60
15
25
35
14
16
30
11
Paint coating
W ith
W ith
W ith
W ith
W ith
W ith
W ith
W ith
and without
and without
and without
and without
SEVER AL F ACT ORS AFFECT ING T O RAT E O F C ARBON AT ION B AS ED ON
FIELD SURVEY
3.1 Effect of p aint coatin g
3, 4, 5
In the liter atur e, paint coating is said to restrict carbonation rate
. In this
chapter, the effect of paint coating was evaluated.
T able 4 shows the car bonation depth of paint coated structur es in the Philippines .
Carbonation depth was alm ost 0.5 to 1.4 mm except P1. Conc rete of P1 was
influenced by m aterials segregation and it seem ed to m ak e carbonation depth deeper.
Figur e 4 shows com parison of the car bonation depth with or without paint coating
area in the sam e structures. J1 and P5 wer e paint coated without re-painting. T he
carbonation depths of these str uctures wer e found to be r estricted about half b y paint
coating. P6 wer e re- painting once ever y 5 years. Re-painting was found to m ak e
carbonation depth about quarter.
T able 4: Carbonation depth and total life span of paint coated structures
Structure
P2
P3
P4
P5
P6
P1
Age of
structures
/year
15
25
16
14
35
60
Carbonation
depth
/mm
0.75
0.46
0.72
0.64
1.4
23
Carbonaiton depth /mm
3.5
Paint coated
3
No paint coated
2.5
re-painting once
every five years
2
1.5
1
no re-painting
0.5
0
J1
11 years
P5
14 years
P6
16 years
Figur e 4: com parison of the carbonation depth with or without paint c oating ar ea in
sam e structures
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
3.2 Effect of W/C
In the literature, it is s aid sm all W /C m ak es rate of carbonation slow. T he effect of
W /C was evaluated in this chapter.
T able 5 shows the c arbonation depth of no paint coated structur es. W /C of these
structures was under 0.5, and it was lower than that of J1, 0.55.
T able 5: Carbonation depth of no paint coated structures
Age of
structures
/year
60
16
30
11
Structure
P5
P6
P7
J1
Carbonation
depth
/mm
4.7
1.4
1.3
3.1
W /C
0.44
0.28
0.42
0.55
According to T able 5, carbonation rate was es tim ated by equation ( 2).
X=A t
(2)
W here,
X : Carbonation depth
A : Carbonation rate coefficient
t : T im e
T able 6 shows the car bonation r ate coefficient of no paint coating s tructures in the
Philippines and Japan. According to table 6, rate of carbonation coefficient in the
Philippines was under 0.5 and that in J apan wer e 4.0. Low W /C seem ed to m ak e
carbonation rate low.
T able 6: Average car bonation rate coefficient in each countr y
Site
Philippine
Japan
Carbonation rate c oefficient
/ mm /year
0.2
4.0
3.3 Effect of shelt ered from rain
In the previous research, shelter ing from rain is said to be the m ain factor to
decide the carbonation rate.
Figur e 6 shows the effect of sheltered from rain in P3. Figur e 7 and T able 6 show
the com parison of carbonation depth between sheltered or not from rain in the
Philippines. T o evaluate the deference between sheltered or not from rain, F-test and
t-test were conducted. W elch’s m ethod was applied in t-test, since F value was larger
than F Boundar y value. From the results of t-test, shelter ing from rain is found to be
hardly influence to car bonation depth.
Carbonation depth(mm)
2
1.5
1
0.5
0
Sheltered
from rain
No Sheltered
from rain
Figur e 6: Effect of Sheltered from rain in P3
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
Sheltered from rain
No sheltered from rain
-1
-0.5
0
0.5
1
1.5
2
Carbonation depth /mm
Figur e 7: Influence of rain on carbonation
T able 7: Results of F-test and t- test
F value
3.960
4
F-test
F Boundar y value
2.637
t-test(W elch’s m ethod)
t value
t boundar y value
0.528
2.080
PREDICT ION OF C AR BON AT ION DEPT H CO NSIDERING P AINT COAT ING
Paint coating and W /C affect were seem ed to affect rate of carbonation from
chapter 3. In this chapter, carbonation depth was estim ated considering paint coating.
Masuda’s equation is able to cons ider the influence of paint coating. Cons ideration
of appl ying the Masuda’s equation to the survey of the Philippines is conducted.
(
X = A t + R2 − R
)
(3)
R = ke −0.171t
W here,
X : Carbonation depth
A : Rate of carbonation coefficient
R : Res istant of carbonation of paint c oating
t : T im e
Equation (3) repr esents Masuda’s equation. Carbonation r esistant of Japan and
Philippines were estim ated at R = 19 e −0.171t and R = 16 e −0.171t respectively.
Figur e 7 shows calculated carbonation depth of structures with paint coating from
the m easured depth of without paint coating by equation (2) and (3). In case of J1
and P5, ages of structures wer e substituted for t. In c ase of P6, 5 years was
substituted for t of R because structures of DLSU were re-painted once ever y 5 years.
Carbonation depths of the str uctures in Japan and school in the Philippines wer e
found to be r estricted about half b y paint c oating. Carbonation depth of De La Salle
Univers it y in the Philippines was found to be r estricted about quarter by re-paint
coating. From this r esult Masuda’s equation was able to evaluate the paint coating
effect on carbonation in concrete.
Nobuaki Otsuki, Ronaldo S. Gallardo, Toshiki Annaka, Satoshi Takaki and Takahiro Nishida
with paint, measured
without paint, measured
without paint, calculated
Carbonaiton depth /mm
3.5
3
re-painting once
every five years
2.5
2
1.5
1
0.5
no re-painting
0
J1
11 years
P5
14 years
P6
16 years
Figur e 7: Calculated carbonation depth from Masuda’s equation
5
CONCLUSIONS
Carbonation depth was large influenced by paint coating. T o estim ate the
carbonation depth, Masuda’s equation is able to consider the paint c oating.
High resistance of concrete against carbonation in the Philippines derived from
relativel y sm all water cem ent ratio (0.28- 0.44) , and paint c oating.
Acknow ledgement
Grateful ack nowledgem ent is m ade o HEIW A NAKAJIMA OUNDAT ION for helpful
suppor t of research budget to conduct this research.
Also great thank s to students of De La Salle Univers it y, Manila for helping the field
surve y.
References
[1] Concrete Committee of JSCE, Standard Specifications for Concrete Structures2007, Maintenance,
JSCE, Tokyo.
[2] Takuya Hasegawa, Osamu Senbu, Akio Baba, Tsugumichi Watanabe, A study on the
carbonation protection effects of sur face finis hing materials using a model building at
the age of eleven year s, No584, 15-21, Oct. 2004
[3] Masanor i Kono, Yos hihiro Masuda, T ak anori Ok ihashi, Yusuk e Nak am ura, Study
on the Prediction of Carbonation Progr ess of Concrete Considering the Aging of
Coating Materials for Textured F inishes on Diffusion Theory , Cem ent Science and
Concrete T echnolog y, No.62, 2008
[4] Masanor i Kono, Yos hihiro Masuda, T ak anori Ok ihashi, Yusuk e Nak am ura, Study
on the carbonation suppressive effects of concrete considering the aging of coating
materials for textur ed finishes, Architectural Institute of Japan, No584, 15- 21, Oct.
2004
[5] T om oyuk i Karasawa, Yoshihir o Masuda, Youngran Lee, Research on carbonation
suppressiv e effect of coating materials for textured finishes and air permeability
coefficient based on the result of a survey of an ex isting structure, Architectural
Institute of Japan, Vol.76, No669, 15-21, Nov. 2011