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Effect of carbonation on microstructural properties of cement stone
CEMENTand CONCRETERESEARCH. Vol. 4, pp. 149-154, 1974. Pergamon Press, Inc Printed in the United States.
EFFECT
OF CARBONATION PROPERTIES
OF
ON MICROSTRUCTURAL CEMENT
STONE
S . E . P i h l a j a v a a r a and E s k o P i h l m a n T e c h n i c a l R e s e a r c h C e n t r e of F i n l a n d , C o n c r e t e Laboratory, Materials Section 02150 O t a n i e r n i , F i n l a n d
(Communicated by F. H. Wittmann) (Received November 6, 1973) ABSTRACT T h e c a r b o n a t i o n of c o n c r e t e is an e v e r - p r e s e n t p h e n o m e n o n a f f e c t i n g the p r o p e r t i e s of c o n c r e t e in v a r i o u s w a y s . In t h i s p a p e r d i f f e r e n t a s p e c t s of the e f f e c t of c a r b o n a t i o n on the p r o p e r t i e s of c e m e n t s t o n e h a v e b e e n b r i e f l y d i s c u s s e d on the b a s i s of e x p e r i m e n t a l r e s u l t s , the c e n t r a l p a r t of w h i c h is the t h e r r n o g r a v i r n e t r i c a n a l y s i s of CO an d H_O Z c o n t e n t in c e m e n t s t o n e s a m p l e s k e p t at diffe2rent h u m i d l t i e s. Karbonatisierung yon Beton ist eine irnmer anwesende E r s c h e i n u n g , di e d i e B e t o n e i g e n s c h a f t e n in r n a c h e r W e i s e b e e i n D u s s t . In d i e s e r n A r t i k e l w e r d e n v e r s c h i e d e n e S t a n d p u n k t e d e s E i n f i u s s e s d e r K a r b o n a t i s i e r u n g a u f di e E i g e n s c h a f t e n des Z e r n e n t s t e i n e s auf Grund d e r V e s u c h s e r g e b n i s s e in K f i r z e b e r i c h t e t . D a s H a u p t g e w i c h t w i r d au£ die t h e r m o g r a v i r n e t r i s c h e A n a l y s e d e s G e h a l t e s y o n CO_ und H 2 0 d e r bei verschiedenen Feuchtigkeiten gehaltenen ~roben aus Z ernentstein gelegt.
149
150 Vol. 4, No.2 CARBONATION, CEMENTPASTE, WATERCEMENTRATIO, MICROSTRUCTURE I.ntroduction In a l o n g - t e r m experimental investigation conducted at the Technical Research Centre of Finland, Concrete Laboratory, different aspects of carbonation have been studied. The results h a v e b e e n p u b l i s h e d in F i n n i s h (1). A r e v i e w o f t h e f o l ! o w i n g r e s u l t s o b t a i n e d a r e o f f e r e d h e r e .
SO
tJ
o
%
0 0 0 ,,IJ
ID ,,i.J ,rID'I
t~
o~ :1:
4O
÷
o~ (9
w / c = 0,45 =
.o
E U L
40%
O O o
,30
.o
®
O
%
m 0 E D
E >
/
3: s¢
,
20
d~ 1
rf
i
Le0 ,i.I
/I
r
L
H20
T
0
E t3
(9
¢-
>
IO
"IJ
o
,/,..-i t / ,,,:f-'" It/
(0 n .J °~
0
100
300
500
700
°C
I000
Temperoture FIG.
1
T h e r m o g r a v i m e t r i c (I05°C ... 1000°C) results of C O and H ~ O contents in crushed c e m e n t paste w / c = 0.4~ carbol~ated in climate r o o m R H 40 %, z0°C.
Vol. 4, No. 2 151 CARBONATION, CEMENTPASTE, WATERCEMENTRATIO, MICROSTRUCTURE Main features
o f t h e investigati...on
Main features of the investigation along with the thermogravimetric results o f t h e C O a n d H O c o n t e n t in h a r d e n e d c e m e n t p a s t e s a m p l e s of w/c= 0 , 4 5 a r e i ~ l u s t r a t e 2 d in F i g s . ] a n d 2. T h e t e s t a p p a r a t u s is s h o w n in F i g . 3. N o t e t h a t t h e s a m p l e s h a v e b e e n c a r b o n a t e d a t Z 0 ° C in t w o s e p a r a t e
o,,,
50
T ÷
P
%
0 0 0
o o
u
c
.12 I;n ,~
>
w / c ---0,45
0
IIJ
=70%
--' r-
30
U ft._
/
/
/
co~ f ,/
.--..
o~
/ 0 rU
.o
T
/
20
(9
,/1
P O
0
if)
/
t-
T
H~O
O
E o
>
O 10
"0 L
"S"
_J
0
|00
A 300
500
700
°C
1000°C)
results
1000
Temperature FIG. Thermogravimetric
(105°C
2 ...
and HzO contents in crushed cement paste w/c carbonated in climate room RH 70 %, 20°C.
of CO_
= 0.4~
152
Vol. 4, No. 2 CARBONATION, CEMENT PASTE, WATERCEMENT RATIO, MICROSTRUCTURE
c l i m a t e r o o m s , a t 40 % a n d 70 % R . H . , r e s p e c t i v e l y . The c e m e n t p a s t e has been precured approximately for 9 months under sealed conditions prior to c r u s h i n g : f r a c t i o n s 0. 25 to l m m s e r v e as s a m p l e s . A f t e r the d e t e r m i n a t i o n of the d e s o r p t i o n a n d a b s o r p t i o n i s o t h e r m s u n d e r n o n c a r b o n a t i o n c o n d i t i o n s , the s a m p l e s c a r b o n a t e d in a f o r e m e n t i o n e d c l i m a t e r o o m s f o r a p p r o x i m a t e l y 2 , 5 y e a r s . (The s o r p t i o n i s o t h e r m s for n o n c a r b o n a t e d and c a r b o n a t e d c e m e n t p a s t e s a r e p r e s e n t e d p r e v i o u s l y in ( 2 ) ) . CO c o n t e n t of t h e s a m p l e s is m e a s u r e d w i t h the aid of g a s c h r o m a t o g r a p h v ~ F i g . 3). T h e m a i n p a r t of b o u n d w a t e r is h b e r a t e d b e t w e e n 105 C a n d 500 C, b u t the s t r o n g e s t l i b e r a t i o n of C O g b e g i n s a f t e r 5 0 0 ° C , F i g . 2 s h o w s t h a t the a m o u n t of b o u n d CO_ w a s o n e t h i r d of the o r i g i n a l c e m e n t b y w e i g h t , a l t h o u g h o t h e r i n v e s t i g a t i o n s h a v e i n d i c a t e d t h a t CO c o n t e n t f o l l o w i n g c o m p l e t e c a r b o n a t i o n c a n be m u c h h i g h e r . - F i g s . 12, 2 a n d 3 c o r r e s p o n d to F i g s . 10, 11 a n d ] in the F i n n i s h p a p e r (1). •
O
T h e e f f e c t of c a r b o n a t i o n
on t h e p o r o s i t y
"
of c e m e n t
O
"
paste
T h i s e f f e c t h a s b e e n s t u d i e d w i t h the a i d of s o r p t i o n i s o t h e r m s , d e t e r m i n e d gravimetrically a t d i f f e r e n t r e l a t i v e h u m i d i t i e s a n d d e r i v e d a l s o w i t h the a i d of m e r c u r y p o r o s i m e t r y . T h e r e s u l t s h a v e b e e n p r e s e n t e d in (2/. T h e e f f e c t of c a r b o n a t i o n on the s o r p t i o n i s o t h e r m s a n d , t h u s , on the p o r o s i t y or microstructure of h a r d e n e d c e m e n t p a s t e is q u i t e s i g n i f i c a n t . T h e e f f e c t of w a t e r - c e m e n t
r a t i o on the m a x i m u m
amount
o f the c a r b o n d i o x i d e i n t a k e T h e r e s u l t s s h o w t h a t in w / c = 0 . 4 5 p a s t e t h e m a x i m u m a m o u n t of the c a r b o n d i o x i d e i n t a k e had b e e n a b o u t 50 % h i g h e r t h a n in w / e = 0 . 30 p a s t e . T h e a m o u n t of rr~axirnum b o u n d w a t e r w a s a b o u t 40 % h i g h e r in w / c = 0 . 4 5 p a s t e t h a n in w / c = 0 . 30 p a s t e s ( w h e n k e p t in s e a l e d s t o r a g e f o r " c o m p l e t e " h y d r a t i o n ) • T h e a m o u n t of the c a r b o n d i o x i d e i n t a k e is thus d e p e n d e n l on the bound w a t e r c o n t e n t as a n t i c i p a t e d .
The maximum
amount
of the c a r b o n
dioxide
intake
The maximum CO_ i n t a k e w a s a b o u t 4 0 . . . 50 % g r e a t e r a t 70 % R . H . t h a n a t 40 % R . H . , ~ d e p e n d i n g t h u s on the r e l a t i v e h u m i d i t y of the storage air.
w/c
CO 2 % b y w e i g h t a t
R. ri. 40 %
IO00°C
R.H.
0.30
14
19
0.45
21
3Z
70 %
Vol. 4, No. 2 153 CARBONATION, CEMENT PASTE, WATERCEMENT RATIO, MICROSTRUCTURE The
greatest
maximum
amount
o f the
carbon
dioxide intake
T h e g r e a t e s t m a x i m u m CO_z i n t a k e o f the c e m e n t p a s t e s t e s t e d w a s a b o u t 35 % b y w e i g h t a t 1 0 0 0 ° C . A s d i s c u s s e d in (3) t h i s m a x i m u m c a n be a s h i g h a s 45 %.
The
effect of carbonation on bound or fixed water content
T h e effect varies in the tests so m u c h that the reliability of the determinations s e e m s questionable. T h e average weight ratio of differences is about l o s s of b o u n d w a t e r gain of c a r b o n dioxide Earlier 0.4 for
r e s u l t s of the the r a t i o .
author
(3) g a v e a m o r e
~N2
=0.2 reasonable
value
of about
l,.
I
II thermobalance furnace with t h e r m o e l e m e n t and s a m p l e x x -recorder for temperature and weight change 1 2 6 - w a y valve cold trap for liberated H 2 0 and C O 2 (liquid N2) d e w a r container with liquid nitrogen d e w a r container with oil gas c h r o m a t o g r a p h recorder for c h r o m a t o g r a m s FIG.
3
Thermogravimetric m e t h o d w i t h t h e a i d of g a s c h r o m a t o g r a p h y f o r d e t e r m i n a t i o n of CO arid H _ O c o n t e n t s o f c r u s h e d c e m e n t 2 Z p a s t e s a m p l e s , N Z- g a s c a r r i e d the l i b e r a t e d CO and H O
f r o m oven (drying
l hour at fixed t e m p e r a t u r e )
~o cold ~Ap,
f r o m w h i c h t h e t r a p p e d CO_ a n d H O w e r e l i b e r a t e d b y s u d d e n h e a t i n g in oil b a t h 2 0 0 ° C an~ c o n d u2c t e d to g a s c h r o m a t o g r a p h y f o r CO 2 d e t e r m i n a t i o n .
154
Vol. 4, No. 2 CARBONATION, CEMENT PASTE, WATER CEMENT RATIO, MICROSTRUCTURE T h e effect of c e m e n t on carbonation
Five ordinary portland c e m e n t s m a d e in three different Finnish factories have been studied. The basic chemical composition of the c e m e n t s is generally speaking relatively similar, although there are s o m e m a r k e d differences in s o m e features of the different cements. The differences of the m a x i m u m C O 2 intake are of the order of several %-units, but the population used in this investigation is too small and the results too scattered for reaching a decision of statistical significance. H o w e v e r , the results indicate that different ordinary portland c e m e n t s can take different an~ounts of C O Z.
References I.
S.E. Pihlajavaara and E. Pihlman, Concrete Laboratory Report 22, Technical R e s e a r c h Centre of Finland, Otaniemi (197Z).
2.
S.E. Pihlajavaara,
Materials and Structures l, p. 521,
(1968). 3.
S.E. Pihlajavaara, Publication 100, Technical R e s e a r c h Centre of Finland, Helsinki (1965).
EFFECT
OF CARBONATION PROPERTIES
OF
ON MICROSTRUCTURAL CEMENT
STONE
S . E . P i h l a j a v a a r a and E s k o P i h l m a n T e c h n i c a l R e s e a r c h C e n t r e of F i n l a n d , C o n c r e t e Laboratory, Materials Section 02150 O t a n i e r n i , F i n l a n d
(Communicated by F. H. Wittmann) (Received November 6, 1973) ABSTRACT T h e c a r b o n a t i o n of c o n c r e t e is an e v e r - p r e s e n t p h e n o m e n o n a f f e c t i n g the p r o p e r t i e s of c o n c r e t e in v a r i o u s w a y s . In t h i s p a p e r d i f f e r e n t a s p e c t s of the e f f e c t of c a r b o n a t i o n on the p r o p e r t i e s of c e m e n t s t o n e h a v e b e e n b r i e f l y d i s c u s s e d on the b a s i s of e x p e r i m e n t a l r e s u l t s , the c e n t r a l p a r t of w h i c h is the t h e r r n o g r a v i r n e t r i c a n a l y s i s of CO an d H_O Z c o n t e n t in c e m e n t s t o n e s a m p l e s k e p t at diffe2rent h u m i d l t i e s. Karbonatisierung yon Beton ist eine irnmer anwesende E r s c h e i n u n g , di e d i e B e t o n e i g e n s c h a f t e n in r n a c h e r W e i s e b e e i n D u s s t . In d i e s e r n A r t i k e l w e r d e n v e r s c h i e d e n e S t a n d p u n k t e d e s E i n f i u s s e s d e r K a r b o n a t i s i e r u n g a u f di e E i g e n s c h a f t e n des Z e r n e n t s t e i n e s auf Grund d e r V e s u c h s e r g e b n i s s e in K f i r z e b e r i c h t e t . D a s H a u p t g e w i c h t w i r d au£ die t h e r m o g r a v i r n e t r i s c h e A n a l y s e d e s G e h a l t e s y o n CO_ und H 2 0 d e r bei verschiedenen Feuchtigkeiten gehaltenen ~roben aus Z ernentstein gelegt.
149
150 Vol. 4, No.2 CARBONATION, CEMENTPASTE, WATERCEMENTRATIO, MICROSTRUCTURE I.ntroduction In a l o n g - t e r m experimental investigation conducted at the Technical Research Centre of Finland, Concrete Laboratory, different aspects of carbonation have been studied. The results h a v e b e e n p u b l i s h e d in F i n n i s h (1). A r e v i e w o f t h e f o l ! o w i n g r e s u l t s o b t a i n e d a r e o f f e r e d h e r e .
SO
tJ
o
%
0 0 0 ,,IJ
ID ,,i.J ,rID'I
t~
o~ :1:
4O
÷
o~ (9
w / c = 0,45 =
.o
E U L
40%
O O o
,30
.o
®
O
%
m 0 E D
E >
/
3: s¢
,
20
d~ 1
rf
i
Le0 ,i.I
/I
r
L
H20
T
0
E t3
(9
¢-
>
IO
"IJ
o
,/,..-i t / ,,,:f-'" It/
(0 n .J °~
0
100
300
500
700
°C
I000
Temperoture FIG.
1
T h e r m o g r a v i m e t r i c (I05°C ... 1000°C) results of C O and H ~ O contents in crushed c e m e n t paste w / c = 0.4~ carbol~ated in climate r o o m R H 40 %, z0°C.
Vol. 4, No. 2 151 CARBONATION, CEMENTPASTE, WATERCEMENTRATIO, MICROSTRUCTURE Main features
o f t h e investigati...on
Main features of the investigation along with the thermogravimetric results o f t h e C O a n d H O c o n t e n t in h a r d e n e d c e m e n t p a s t e s a m p l e s of w/c= 0 , 4 5 a r e i ~ l u s t r a t e 2 d in F i g s . ] a n d 2. T h e t e s t a p p a r a t u s is s h o w n in F i g . 3. N o t e t h a t t h e s a m p l e s h a v e b e e n c a r b o n a t e d a t Z 0 ° C in t w o s e p a r a t e
o,,,
50
T ÷
P
%
0 0 0
o o
u
c
.12 I;n ,~
>
w / c ---0,45
0
IIJ
=70%
--' r-
30
U ft._
/
/
/
co~ f ,/
.--..
o~
/ 0 rU
.o
T
/
20
(9
,/1
P O
0
if)
/
t-
T
H~O
O
E o
>
O 10
"0 L
"S"
_J
0
|00
A 300
500
700
°C
1000°C)
results
1000
Temperature FIG. Thermogravimetric
(105°C
2 ...
and HzO contents in crushed cement paste w/c carbonated in climate room RH 70 %, 20°C.
of CO_
= 0.4~
152
Vol. 4, No. 2 CARBONATION, CEMENT PASTE, WATERCEMENT RATIO, MICROSTRUCTURE
c l i m a t e r o o m s , a t 40 % a n d 70 % R . H . , r e s p e c t i v e l y . The c e m e n t p a s t e has been precured approximately for 9 months under sealed conditions prior to c r u s h i n g : f r a c t i o n s 0. 25 to l m m s e r v e as s a m p l e s . A f t e r the d e t e r m i n a t i o n of the d e s o r p t i o n a n d a b s o r p t i o n i s o t h e r m s u n d e r n o n c a r b o n a t i o n c o n d i t i o n s , the s a m p l e s c a r b o n a t e d in a f o r e m e n t i o n e d c l i m a t e r o o m s f o r a p p r o x i m a t e l y 2 , 5 y e a r s . (The s o r p t i o n i s o t h e r m s for n o n c a r b o n a t e d and c a r b o n a t e d c e m e n t p a s t e s a r e p r e s e n t e d p r e v i o u s l y in ( 2 ) ) . CO c o n t e n t of t h e s a m p l e s is m e a s u r e d w i t h the aid of g a s c h r o m a t o g r a p h v ~ F i g . 3). T h e m a i n p a r t of b o u n d w a t e r is h b e r a t e d b e t w e e n 105 C a n d 500 C, b u t the s t r o n g e s t l i b e r a t i o n of C O g b e g i n s a f t e r 5 0 0 ° C , F i g . 2 s h o w s t h a t the a m o u n t of b o u n d CO_ w a s o n e t h i r d of the o r i g i n a l c e m e n t b y w e i g h t , a l t h o u g h o t h e r i n v e s t i g a t i o n s h a v e i n d i c a t e d t h a t CO c o n t e n t f o l l o w i n g c o m p l e t e c a r b o n a t i o n c a n be m u c h h i g h e r . - F i g s . 12, 2 a n d 3 c o r r e s p o n d to F i g s . 10, 11 a n d ] in the F i n n i s h p a p e r (1). •
O
T h e e f f e c t of c a r b o n a t i o n
on t h e p o r o s i t y
"
of c e m e n t
O
"
paste
T h i s e f f e c t h a s b e e n s t u d i e d w i t h the a i d of s o r p t i o n i s o t h e r m s , d e t e r m i n e d gravimetrically a t d i f f e r e n t r e l a t i v e h u m i d i t i e s a n d d e r i v e d a l s o w i t h the a i d of m e r c u r y p o r o s i m e t r y . T h e r e s u l t s h a v e b e e n p r e s e n t e d in (2/. T h e e f f e c t of c a r b o n a t i o n on the s o r p t i o n i s o t h e r m s a n d , t h u s , on the p o r o s i t y or microstructure of h a r d e n e d c e m e n t p a s t e is q u i t e s i g n i f i c a n t . T h e e f f e c t of w a t e r - c e m e n t
r a t i o on the m a x i m u m
amount
o f the c a r b o n d i o x i d e i n t a k e T h e r e s u l t s s h o w t h a t in w / c = 0 . 4 5 p a s t e t h e m a x i m u m a m o u n t of the c a r b o n d i o x i d e i n t a k e had b e e n a b o u t 50 % h i g h e r t h a n in w / e = 0 . 30 p a s t e . T h e a m o u n t of rr~axirnum b o u n d w a t e r w a s a b o u t 40 % h i g h e r in w / c = 0 . 4 5 p a s t e t h a n in w / c = 0 . 30 p a s t e s ( w h e n k e p t in s e a l e d s t o r a g e f o r " c o m p l e t e " h y d r a t i o n ) • T h e a m o u n t of the c a r b o n d i o x i d e i n t a k e is thus d e p e n d e n l on the bound w a t e r c o n t e n t as a n t i c i p a t e d .
The maximum
amount
of the c a r b o n
dioxide
intake
The maximum CO_ i n t a k e w a s a b o u t 4 0 . . . 50 % g r e a t e r a t 70 % R . H . t h a n a t 40 % R . H . , ~ d e p e n d i n g t h u s on the r e l a t i v e h u m i d i t y of the storage air.
w/c
CO 2 % b y w e i g h t a t
R. ri. 40 %
IO00°C
R.H.
0.30
14
19
0.45
21
3Z
70 %
Vol. 4, No. 2 153 CARBONATION, CEMENT PASTE, WATERCEMENT RATIO, MICROSTRUCTURE The
greatest
maximum
amount
o f the
carbon
dioxide intake
T h e g r e a t e s t m a x i m u m CO_z i n t a k e o f the c e m e n t p a s t e s t e s t e d w a s a b o u t 35 % b y w e i g h t a t 1 0 0 0 ° C . A s d i s c u s s e d in (3) t h i s m a x i m u m c a n be a s h i g h a s 45 %.
The
effect of carbonation on bound or fixed water content
T h e effect varies in the tests so m u c h that the reliability of the determinations s e e m s questionable. T h e average weight ratio of differences is about l o s s of b o u n d w a t e r gain of c a r b o n dioxide Earlier 0.4 for
r e s u l t s of the the r a t i o .
author
(3) g a v e a m o r e
~N2
=0.2 reasonable
value
of about
l,.
I
II thermobalance furnace with t h e r m o e l e m e n t and s a m p l e x x -recorder for temperature and weight change 1 2 6 - w a y valve cold trap for liberated H 2 0 and C O 2 (liquid N2) d e w a r container with liquid nitrogen d e w a r container with oil gas c h r o m a t o g r a p h recorder for c h r o m a t o g r a m s FIG.
3
Thermogravimetric m e t h o d w i t h t h e a i d of g a s c h r o m a t o g r a p h y f o r d e t e r m i n a t i o n of CO arid H _ O c o n t e n t s o f c r u s h e d c e m e n t 2 Z p a s t e s a m p l e s , N Z- g a s c a r r i e d the l i b e r a t e d CO and H O
f r o m oven (drying
l hour at fixed t e m p e r a t u r e )
~o cold ~Ap,
f r o m w h i c h t h e t r a p p e d CO_ a n d H O w e r e l i b e r a t e d b y s u d d e n h e a t i n g in oil b a t h 2 0 0 ° C an~ c o n d u2c t e d to g a s c h r o m a t o g r a p h y f o r CO 2 d e t e r m i n a t i o n .
154
Vol. 4, No. 2 CARBONATION, CEMENT PASTE, WATER CEMENT RATIO, MICROSTRUCTURE T h e effect of c e m e n t on carbonation
Five ordinary portland c e m e n t s m a d e in three different Finnish factories have been studied. The basic chemical composition of the c e m e n t s is generally speaking relatively similar, although there are s o m e m a r k e d differences in s o m e features of the different cements. The differences of the m a x i m u m C O 2 intake are of the order of several %-units, but the population used in this investigation is too small and the results too scattered for reaching a decision of statistical significance. H o w e v e r , the results indicate that different ordinary portland c e m e n t s can take different an~ounts of C O Z.
References I.
S.E. Pihlajavaara and E. Pihlman, Concrete Laboratory Report 22, Technical R e s e a r c h Centre of Finland, Otaniemi (197Z).
2.
S.E. Pihlajavaara,
Materials and Structures l, p. 521,
(1968). 3.
S.E. Pihlajavaara, Publication 100, Technical R e s e a r c h Centre of Finland, Helsinki (1965).