Deterioration model of acid-rain-affected concrete and
test results of ordinary and super quality concrete
H Ueda*, Railway Technical Research Institute, Japan
Y Kimachi, Meisei University, Japan
S Ushijima, Aoki Corporation, Japan
K Shyuttoh, Maeda Corporation, Japan
26th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 27 - 28 August 2001,
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Deterioration model of acid-rain-affected concrete and
test results of ordinary and super quality concrete
H Ueda*, Railway Technical Research Institute, Japan
Y Kimachi, Meisei University, Japan
5 Ushijima, Aoki Corporation, Japan
K Shyuttoh, Maeda Corporation, Japan
Abstract
To quantitatively estimate of the durability of concrete attacked by acid rain, deterioration of
concrete is modeled on the basis of the decomposition of calcium-silicate-hydrate.
In this model, the
deterioration of concrete attacked by acid rain is estimated by using several factors such as absorption
quantity of acid, mix proportion of concrete and contact time between concrete and acid.
several tests using ordinary concrete and Super Quality Concrete are carried out.
Furthermore,
As a result, we find
that the model is suitable for the estimation of the deterioration of acid-affected-concrete.
Keywords: acid rain, durability, deterioration model, estimation, concrete, super quality concrete,
high performance concrete
1.
Introduction
Since the average pH value of rain is about 4.5-5.5 in Japan [1], it is said that concrete is little
influenced by acid rain [2][3].
local areas [4].
However, it is reported that rains with a low pH value are observed in
Furthermore, it is assumed that the pH value of rain drops with the industrialization of
surrounding countries.
To improve the maintenance of concrete, therefore, we should clarify the
influence of acid rain on concrete.
quantitatively is proposed.
In this study, a model to verify the deterioration of concrete
The proposed method has been verified through several tests using
ordinary concrete and Super Quality Concrete (high strength and self-compacting concrete).
2.
Deterioration of concrete by acid rain
2.1 Phenomena assumed to occur on acid-attacked concrete
Fig. 1 shows the phenomena assumed to occur on acid-attacked concrete.
When concrete is
Ca(OH)2 in the concrete.
attacked by acid rain, neutralization reaction occurs between acid rain and Ca(OHh
Next, the pH value in the concrete drops and the calcium-silicate-hydrate (C-S-H) decomposes [5].
Since the cement paste corrodes from the surface, sand and aggregates are exposed to corrode
reinforcement bars.
These processes are accelerated by cracks.
665
On the other hand, other
phenomena occur such as discoloration on
Consumption of Ca(OHhll Unexpected Conditionsl
•
the concrete with metal ion dissolved by
acid,
formation
of
unexpected conditions.
select
the
process
products
I Drop of pH
IColor Changel
and
•
In this study, we
to
corrosion
of
reinforcement bars because this process
Deterioration
particularly
influences
Accelerated
durability.
The crack effect is
the
concrete
r-.
studied.
•
+
I
Formation
Aggregate
of Products
Exposure
+
I Reduction of Cover Concrete
by Cracks
also
C-S-H Decomposition
•
I Corrosion of Reinforcement Bars I
2.2 Construction of estimation system
An index for quantitative estimation,
Fig. 1 Phenomena assumed to occur on acidattacked concrete
limit state and deterioration velocity are
required to construct the estimation system.
The pH value is most suitable as the index because it is related to all phenomena.
However, Ca(OHh
consumption depth and corrosion depth are adopted as index because the measurement of pH value
at arbitrary place and time is difficult.
The limit state is not dealt with in this study.
The deterioration
velocity is estimated by using the following time-dependence deterioration model.
3.
Deterioration model of acid-rain-affected concrete
3.1 Introduction
When an acid affects concrete, it
flows on the concrete surface after
saturated.
on
Therefore, the acid effect
concrete
is
divided
into
the
following two parts (Fig. 2).
(Acid effect) = (Effect by the acid
Fine
Rainfall
Dry
~-
Concrete
Rainfall
Fine
After
saturated
•
Acid flown
on the concrete
absorption) + (Effect by the acid flown
Fig. 2 Effects of Acid on Concrete
on the concrete)
The first term shows the effect of
the wet to dry cycle, while the second the effect of the contact time between acid and concrete.
As
the pH value drops when Ca(OHh disappears, the area where pH has dropped is equal to the depth of
Ca(OHkdisappeared area.
Thus, the Ca(OH)2 consumption depth d1 and corrosion depth (C-S-H
decomposed depth) d2 are given by the following equation.
d1=d1A+d1B
(1)
d2=d 2A+d 2B
(2)
where dA is the depth of Ca(OH)2 consumed by acid absorption; and dB is the depth of Ca(OH)2
consumed by the acid flown on the concrete surface.
from inner concrete are excluded.
occur after pH dropped.
Other factors including the OH· ions that diffuse
d2 is smaller than d1 because corrosion of concrete is made to
The relationship between d1 and d2 is shown by the following equation.
d2= d1- box
(3)
d 2A= d1A -boxA
(4)
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(5)
3.2 Effect of absorbed acid
In this model, the d1A is estimated and the d 2A is derived from equation 4.
When a concrete block
of unit surface area of the depth do is affected by acid from one side, the Ca(OH)2 consumption depth
d1A is given by the following equatiun.
d 1A= d o*{Ca(OHh}/{(Ca(OHh)o}
(6)
{Ca(OHh} = {(Ca(OH)~'rai:l}*n
(7)
{(Ca(OH)2),rain} = {H,rain}*R
(8)
{H,rain} = (W,rain}*C
(9)
where {Ca(OHh}: amount of Ca(OHh consumption, {(Ca(OH)2)O}: initial amount of Ca(OHh,
{(Ca(OHh),rain}: amount of Ca(OHh consumption at a rainfall, {H,rain}: amount of hydrogen ion that
affected the concrete at a rainfall, {W,rain}: amount of absorbed water at a rainfall, n: number of rainfalls,
R: constant based on the kind of acid and c: concentration of acid.
In these equations, the time factor is characterized by the interval of rainfalls.
The effect of
cracks is estimated by using {W,rain}'
3.3 Effect by the acid flown on the concrete surface
The Ca(OHh consumption depth by the acid flown on the concrete surface is estimated by using
the diffusion of acid.
However, the diffusion coefficient is difficult to obtain.
estimated and the d 1B is derived from equation 5.
Therefore, the d 2B is
The corrosion depth is expressed by the following
function by using acid concentration c and contact time t [6].
d 2B = k*c'"*tn
(10)
where k, m and n are constant.
Though m and n should be estimated from experiments, we used
m=n=0.5 for the purpose of convenience [7].
proportion.
Concrete with W/C=0.6 is taken as a standard mix
Its corrosion depth is
d 2B st= kst*cm*tn
(11)
The corrosion depth of arbitrary mix proportion is estimated by the following equation.
d 2B = S*kst*cm*tn
where S=kl kst .
(12)
S shows the degree of suppression according to the concrete quality and is related
with the degree of concrete denSity.
When the index "Filling Factor
a" is defined as the binder to
hardened cement paste volume ratio; the following equation is given.
a= VbinJ(Vbind + Vw + V air)
(13)
where V bind : volume of the binder, Vpaste: volume of the hardened cement paste, V w: volume of water,
V air : volume of air.
Therefore, the following equation is given based on the equation (13).
a = mbinJ(mbind +0.01 *(Air[%])* P bind+mbin/ P bin/(W/B»
(14)
where m bind : mass of the binder, P bind: density of the binder, W/B: water-to-binder ratio.
of the standard mix proportion.
The
a of the arbitrary mix proportion is shown by the equation (11).
ala st = {3
(15)
We call {3 "the Filling Factor Index."
S is shown by the equation (16) by using {3.
S=(1/(a*{3P»
where a and p are constant.
a st is the a
(16)
We take a=p=1 at the first stage.
667
According to these equations, the
corrosion depth of the arbitrary mix proportion is shown by the following equation.
d2B = (1/(a* BP))*kstcm*tn
(17)
By this equation, d2B is estimated as a function of time.
Moreover, the effect of the kind of acid is
included in kst .
4.
Verification experiment
4.1 Proposition of experimental method
To verify the proposed model, several experiments are planned (Table 1) [8][9].
The experiments
are set up to estimate the factors of the model as the number of acid rainfalls, absorption amount by
one rainfall, concentration of acid, contact time between concrete and acid rain and mix proportion of
concrete (especially, W/B and the kind of binder).
The basic experiments consist of a wet to dry cycle
test to verify the number of acid rainfalls and the absorption amount by a rainfall.
This test consists of
two different cycles; one is one-day wet and six-day dry cycle, and the other one-day wet and 20-day
dry cycle.
On the other hand, an acid immersing test is also performed.
The concentration of acid
adopted is pH2, 3 and 4.
The composition of acid is
Sulfuric acid: Nitric acid
2:1
according
average
to
=
component
pH
every cycle.
of
is adjusted
Specimens
with 0.2mm and 0.5mm
cracks are subjected to an
acid shower test to verify
the effect of crack.
acid
immersing
is
pH
Wet to dry cycle test
One-day wet and six-day dry
One-day wet and 20-day dry
Acid immersing test
Acid shower test
Composition test between wet to dry cycle test
and fleeze-saw cycle test
Specimen placed in cold and warmer regions
pH2,3,4,7
pH2,3,4,7
pH3,7
pH3
pH3
-
An
and
freezing-thawing
test
Item
the
acid rain in Japan [10].
There,
Table 1 Contents of Verification Experiment
cycle
performed
Table 2 Mix Proportion of Concrete
as
concrete is affected by
Specimen
Kind of
sja(%)
binder
W/B(%)
(kg/m3)
Air(%)
specimen is placed in cold
Water Cement Binder
45.1 60.0
267
160
OP29 OPC
LC
52.9 38.6
472
165
LC72
OPC+BS 52.9 41.5
165
199
199
BS72
BL
52.3 32.6
165
BL96
506
75
BS120 BL+BSS 47.2 22.0
165
675
and warmer regions for
*OPC: ordinary Portland cement, LC: low heat Portland
verification
cement, BS: brast-furnace slag, BL: Belite cement, BSS: brast-
both
acid
rain
and
freezing-thawing cycle in
cold
regions.
Furthermore,
environment.
mix
the
in the
real
Several
proportions
are
furnace slag (fine)
*Specimen number indicates target strength.
adopted to investigate the
effect of W/B and the kind
of binder (Table 2).
668
4.4
4.3
3.7
4.5
3.1
4.2 Results and discussion of the experiment
From each test, the following results are obtained.
on the pH value and acid concentration [8].
The corrosion depth of concrete is dependent
Specimens with cracks absorb a larger amount of acid.
As an example of the results, specimens immersed in a pH 3 acid solution (one-day wet and six-day
dry cycle) are explained below.
The color of the concrete surface changes to light brown because Fe
ions concentrate on the concrete surface [11 ][12].
This phenomenon shows the reduction of pH.
3 shows the corrosion depth of each mix proportion.
As the corrosion depth depends on
Ft,
considered that it satisfies the equation (10) and becomes small as the strength increases.
shows the absorption amount of each mix proportion.
depth of each mix
when
OP29 is used to the
standard
mix
proportion.
The
{(Ca(OHh)o} in d1A is
decided by using the
previous report [13].
I::!. xA is 0 in this report
because d2 is little
.- 1.8
E 1.6
E 1.4
1.2
a>
1
'"0
c 0.8
0
"00 0.6
....0 0.4
() 0.2
0
-a
d1A
value
after
-O-OP29
--.- LC72
---B872
-BL96
--l:r- B8120
e
o
affected by I::!. xA as
20
7
40
60
80
100 120
Wetto dry cycle
cycles is only 0.00.2mm.
Fig.3 Corrosion Depth of Concrete
Accordingly,
dB
is
dominant compared
with dA under this
condition.
The
calculated d2 and the
measured corrosion
depth
are
agreement.
in
--
.-
....
ctS
~
'"0
result, we find that
.0
is suitable for the
verification
of
the
deterioration of acidrain-affected
80
-o-OP29
+-'
As a
the proposed model
100
0')
a>
a>
----B872
....
en
20
0
.0
«
~LC72
60
40
-BL96
--fr-
B8120
0
0
50
100
Test Period (week)
concrete.
Fig.4 Time Dependence of Absorbed Water of Concrete
669
it is
Fig. 4
Table 3 shows /3, calculated values of d2 and
measured corrosion
proportion
Fig.
5.
Table 3 Corrosion Depth of Concrete
Conclusions
1. A deterioration model of
acid-rain-affected
proposed.
concrete
is
In this model, the
deterioration of the concrete is
dependent on the acid absorption
amount into the concrete,
Specimen
mix
Filling Factor
Index [3
OP29
LC72
8S72
8L96
8S120
1.00
1.30
1.25
1.42
1.71
d2
Corrosion Depth
(calcuration) (measurement)
1.14
0.88
0.87
0.91
0.79
0.66
0.94
0.71
0.68
proportion and contact time or
interval of rainfalls.
2. Several experiments such as a wet to dry cycle test are carried out to estimate the factors of the
model.
3. The model is suitable for the estimation of the deterioration depth.
Acknowledgements
This work was carried out by the Association for the Development & Propagation of Super Quality
Concrete Structures.
The authors wish to thank Dr. Okamura, H., Dr. Maekawa, K. and Dr. Ozawa, K.
for their helpful advice.
References:
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[2] The Ministry of Construction: A Study of Concrete Affected by Acid Rain, Doboku-kenkyu-shiryo,
march 1992
[3] Japan Cement Association: Effect of Acid Rain on Concrete, Cement Concrete, Vol. 569, pp. 25-35,
1994
[4] Makaino, S. : Outdoor Structures Damaged by Acid Rain, Hyomen Gijutsu, Vol. 46, No.6, 1995
[5] E. Revertegat, C. Richet and P. Gegout : Effect of pH on the Durability of Cement Pastes, Cement
and Concrete Research, Vol. 22, pp. 259-272, 1992
[6] V. Pavrik : Corrosion of Hardened Cement Paste by Acetic and Nitric Acids Part III: Influence of
Water/Cement Ratio, Cement and Concrete Research, Vol. 26, No.3, pp. 475-490, 1996
[7] V. Pavrik : Corrosion of Hardened Cement Paste by Acetic and Nitric Acids Part I: Calculation of
Corrosion Depth, Cement and Concrete Research, Vol. 24, No.3, pp. 551-562, 1994
[8] Makishima, 0., Tanaka, K., Kimachi, Y. and Tsuzaki, J. : Experimental Study on Resistance to Acid
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Having Initial Crack, Proceedings of JCI, Vol. 21, No.2, pp. 397-402, 1999
[10] Murano, K. : Acid Rain and Acid Fog, Shoukabou, 1993
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