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The Porosity and Permeability of Macrodefect free Cements
F. Rodriguez-Reinoso et al. (Editors), Characterization of Porous Solids ZZ 0 1991 Elsevier Science Publishers B.V., Amsterdam
669
THE POROSITY AND PERMEABILITY OF MACRODEFECT FREE CEMENTS
K.S.W.
S i n g and M.
Yat.es
Department o f Chemistry, Brunel U n i v e r s i t y , Uxbridge, Middlesex, England
ABSTRACT Very h i g h s t r e n g t h c e m e n t s o f l o w p o r o s i t y h a v e b e e n p r o d u c e d from b o t h O r d i n a r y P o r t l a n d Cement (OPC) a n d High Alumina C e m e n t (HAC) b y t.he i n c o r p o r a t i o n of a w a t e r s o l u b l e p o l y m e r a t t h e e a r l y m i x i n g st-age. T h e s e m a t e r i a l s h a v e b e e n t e r m e d m a c r o d e f e c t free (MDF) c e m e n t s d u e t o t h e e x c l u s i o n I n t.he o f the w i d e r pores b r o u g h t a b o u t by t h i s m a n u f a c t u r i n g process. p r e s e n t s t u d y t h e e f f e c t o f h e a t t r e a t m e n t and r e h y d r a t i o n on t h e s e t w o s y s t e m s h a s been i . n v e s t 3 q a t e d by t h e u s e o f mercury p o r o s i m e t r y and methane gas permeability. T h e s e s t u d i e s were complemented by t h e r m o g r a v i m e t r y a n d g a s a d s o r p t i o n m e a s u r e m e n t s . The r e s u l t s o b t a i n e d show t h a t . d e c o m p o s i t i o n o f t h e p o l y m e r was t h e c o n t r o l l i n g f a c t o r i n t h e f o r m a t i o n o f t h e p o r e volume. However, t h e p o r e s i z e d i s t r i b u t i o n s of t h e t w o s y s t e m s were v e r y d i f f e r e n t b0t.h b e f o r e a n d a f t e r r e h y d r a t i o n a n d t h i s h a s a d i r e c t b e a r i n g on t-he measured p e r m e a b i l i t y . INTRODUCTION
U n t i l r e c e n t l y it was w i d e l y a c c e p t e d t - h a t t h e s t r e n g t h of OPC was g o v e r n e d by t h e i n i t i a l w a t e r / c e m e n t r a t i o w h i c h d i r e c t l y l e d t o a p a r t i c u l a r 1 volume f r a c t i o n o f pores i n t h e h a r d e n e d c e m e n t p a s t e However, t h e work Of
.
Birchall e t
d e m o n s t r a t e d t h e e f f e c t . o f t.he wider p o r e s on t h e s t r e n g t h
and r e v e a l e d t h a t c o n s i d e r a b l e i m p r o v e m e n t c o u l d b e made e s p e c i a l l y i n t h e f l e x u r a l s t r e n g t h by t h e i r removal. To p r o d u c e t h e t w o c e m e n t s s t - u d i e d a w a t e r s o l u b l e p o l y m e r
(polyvinyl
a l c o h o l ) i s added t o t h e c e m e n t / w a t e r s y s t e m t o a c t a s a r h e o l o g i c a l a i d d u r i n g t h e h i g h s h e a r m i x i n g , t h u s l e a d i n g t.o closer p a c k i n g of t.he i n d i v i d u a l cement g r a i n s p r i o r t o h y d r a t i o n and f i n a l s e t .
This s p e c i a l processing
t e c h n i q u e is f u n d a m e n t a l t o t h e l o w p o r o s i t y / h i g h s t r e n g t h n a t u r e o f t h e MDF m a t e r i a l s . The main o b j e c t i v e o f t h e work d e s c r i b e d h e r e was t o s t - u d y t h e e f f e c t .
of removing t h e p o l y m e r on t h e p o r o s i t y a n d p e r m e a b i l i t y o f t h e MDF c e m e n t s . T h i s was a s s e s s e d u s i n g t h e t e c h n i q u e s o f m e r c u r y p o r o s i m e t - r y a n d m e t h a n e g a s permeability.
I n a d d i t i o n t o t.hese t e c h n i q u e s thermogravimet.ric a n a l y s i s w a s
u s e d t o f o l l o w + h e d e c o m p o s i t i o n o f t h e p o l y m e r a n d l o s s o f w a t e r from t h e materials during heat-treatment.
Gas a d s o r p t i o n m e a s u r e m e n t s were a l s o u s e d
t o st.udy t h e c h a n g e s i n t h e m i c r o s t - r u c t u r e c a u s e d b y t h e d e c o m p o s i t i o n o f t h e polymer.
EXPERIMENTAL The samples o f MDF cement s h e e t s were p r e p a r e d a t t h e Runcorn Heath I C I laboratories.
The GPC u s e d w a s a s t a n d a r d g r a d e Type I cement powder
produced by Blue C i r c l e and t.he HAC was S e c a r 71 produced by L a f a r g e . The t h r e e components
(cement, polymer and water) were premixed i n a n
o r b i t a l mixer t o g i v e a d r y g r a n u l a r "crumble".
T h i s g r a n u l a r dough was
c h i l l e d ( t o r e t a r d h y d r a t i o n ) and f e d i n t o a t w i n r o l l - m i l l , where it was converted i n t o a t h i n s h eet.
Any remaining o c c l u d e d a i r was removed by
p r e s s i n g t h e s h e e t ( a t 4MPa) f o r 16h a t ambient t e m p e r a t u r e .
The s h e e t w a s
t h e n l e f t t o c u r e f o r 5 d a y s a t a m b i e n t t e m p e r a t u r e and f i n a l l y d r i e d a t 8OoC overnight. The samples were examined b e f o r e and a f t e r h e a t - t r e a t m e n t rehydration.
and a f t e r
H e a t - t r e a t m e n t c o n s i s t e d of h e a t i n g t h e samples a t 5OC min-'
to
t h e s t a t e d t e m p e r a t u r e and h o l d i n g f o r 4 h o u r s b e f o r e c o o l i n g i n a d e s i c c a t o r . R e h y d r a t i o n was accomplished by immersing t h e s a m p l e s i n w a t e r f o r 1 week t h e n d r y i n g a t 8OoC o v e r n i g h t . Kercury p o r o s i m e t r y measurements were made u s i n g a C a r l o Erba 2000 porosimeter.
The c o n t a c t a n g l e of t h e mercury was t a k e n a s 141'
s u r f a c e t e n s i o n a s 480mN in-'. C a r l o Erba S o r p t o m a t i c 1800.
and t h e
Gas a d s o r p t i o n s t u d i e s were c a r r i e d o u t on a G a s p e r m e a b i l i t y measurements were made on a
home b u i l t a p p a r a t u s f o l l o w i n g a d e s i g n used by t h e B r i t i s h Cement Association4.
Thermogravimetric s t u d i e s were c a r r i e d o u t on a S t a n t o n
R e d c r o f t STA 780. a t 50cm3 min-' respectively,
A l l measurements were made i n a n atmosphere o f a i r f l o w i n g
w i t h a h e a t i n g r a t e o f S°C min-'
t o 150°,
300°
and 4.5OoC
i n o r d e r t o d u p l i c a t e t h e h e a t t r e a t m e n t regimes.
RESULTS The p r o p e r t i e s of t h e v a r i o u s t r e a t e d and u n t r e a t e d s a m p l e s o f MDF cements a r e summarised i n T a b l e 1 and r e p r e s e n t a t i v e i n t r u s i o n - e x t r u s i o n mercury p o r o s i m e t r y c u r v e s a r e shown i n F i g u r e s 1-4.
I t w i l l be noted t h a t
t h e o r i g i n a l GPC-MDF had a s m a l l b u t m e a s u r a b l e p o r o s i t y whereas t h e HAC-MDF
was a l m o s t non-porous.
I n t h e i r o r i g i n a l s t a t e b o t h cements e x h i b i t e d no
d e t e c t a b l e g a s p e r m e a b i l i t y , which i n d i c a t e s t h a t t h e pores i n t h e GPC-MDF d i d n o t e x t e n d a s a c o n t i n u o u s network t h r o u g h t h e sample.
I n b o t h cases h e a t
t r e a t m e n t b r o u g h t a b o u t a p r o g r e s s i v e i n c r e a s e i n p o r e volume, p e r m e a b i l i t y and s u r f a c e a r e a .
671 TABLE 1 Properties of MDP cements. Cement
Treatment
OPC-MDF
NONE
15OoC* 15OoC R+ 3OO0C* 3OO0C R+ 4 50oc* 45OoC R+
HAC- MDF
NONE
15OoC* 15OoC R+ 3OO0C* 3OO0C R+ 45OoC* 45OoC R+
,I ,I
*
P o r e Volume cm3g-1 0.020 0.046 0.030 0.055 0.032 0.082 0.034 0.002 0.011 0.021 0.066 0.044 0.086 0.015
P e r m e a b i 1i t y Barrer x
0
1.2-1.6 0.2-0.3 5.6-7.1 0.3-0.4 9.7-17.3 0.4-0.5
Flex strength MPa 82.2 15.7 23.4 14.0 47.3 11.2 33.4
0 0.1-0.2 07.6-346.8 40.7-182.9 0.6- 1 5 . 4 125.4-303.8 0.8-7.4
S u r f a c e Area m'9-l 3.9 16.4
-
21.5
-
24.5
-
0.1 24.1
-
32.6
-
30.1
-
Heated t o s p e c i f i e d t-emperature f o r 4 h o u r s.
+ Immersed i n w a t e r f o r 1 week.
Comparison o f F i g u r e s 1 a n d 3 r e v e a l s t h a t t h e pore s i z e d i s t r i b u t i o n of t h e h e a t e d s a m p l e s o f HAC-MDF was much b r o a d e r t h a n t h a t of t h e
c o r r e s p o n d i n g h e a t e d GPC-MDF.
Although t h e r e s u l t a n t p o r e volumes ( a s
d e t e r m i n e d by m e r c u r y p o r o s i m e t r y ) were n o t d i s i m i l a r , l a r g e r i n t e r n a l s u r f a c e a r e a s were g e n e r a t e d by h e a t t r e a t m e n t o f t h e HAC-MDF.
These heated samples
w e r e also f o u n d t o b e h i g h l y p e r m e a b l e , a l t h o u g h t h e r a t - e o f f l o w o f m e t h a n e was n o t e a s y t o r e p r o d u c e .
A p r o n o u n c e d d e c r e a s e i n p e r m e a b i l i t y was f o u n d
when 300° and 45OoC samples o f HAC-MDF were immersed i n w a t e r . A p a r t f r o m t h e u n e x p e c t e d b e h a v i o u r o f t h e 15OoC s a m p l e o f HAC-TDF. immersion i n water g e n e r a l l y p r o d u c e d a s u b s t a n t i a l r e d u c t i o n i n p o r o s i t y and permeability.
T h e s e e f f e c t s were e s p e c i a l l y s t r i k i n g i n t h e c a s e o f t h e 45OoC
s a m p l e Of HAC-MDF. H e a t t - r e a t m e n t of t h e OPC-MDF - e v e n a t 15OoC loss of f l e x u r a l s t r e n g t h .
-
resulted i n a drastic
T h i s was t o some e x t e n t r e s t o r e d by r e h y d r a t i o n ,
b u t t h e maximum v a l u e a t t a i n e d was s t i l l c o n s i d e r a b l y lower t h a n t h e o r i g i n a l strength.
612
F i g u r e 1. a t 15O0C
(-
Mercury p o r o s i m e t r y c u r v e s f o r OPC-MDF: O r i g i n a l (-) - ) , 3OO0C ( - . - ) a n d 45OoC ( - . - - ) .
and heated
Mercury p o r o s i m e t r y c u r v e s f o r OPC-MDF: O r i g i n a l (-) and F i g u r e 2. r e h y d r a t e d a f t e r h e a t t r e a t m e n t a t 15OoC ( - - ) , 3OO0C ( - . - ) a n d 45OoC ( - . ' - )
673
F i g u r e 3. Mercury p o r o s i m e t r y c u r v e s f o r HAC-MDF: a t 150°C (- - ) , 3OO0C ( - - - ) a n d 45OoC ( . . . . )
.
O r i g i n a l (-)
and h e a t e d
Mercury p o r o s i m e t r y c u r v e s f o r HAC-MDF: O r i g i n a l (--) and F i g u r e 4. a n d 45OoC ( . - . . ) . r e h y d r a t e d a f t e r h e a t t r e a t m e n t a t 15OoC ( - - ) , 3OO0C ( - . - I
674 DISCUSSION It is e v i d e n t t h a t t h e p e r m e a b i l i t y o f t h e h e a t e d and r e h y d r a t e d
c e m e n t s was n o t s i m p l y c o n t . r o l 1 e d by t h e p o r e volume a s d e t e r m i n e d by m e r c u r y porosimetry.
However, t h e s h a p e o f some o f t h e m e r c u r y i n t . r u s i o n c u r v e s i n
F i g u r e s 1-4 i n d i c a t e s t h a t a t t h e maximum a t t a i n a b l e p r e s s u r e m e r c u r y d i d n o t p e n e t - r a t e i n t o t h e n a r r o w e s t p o r e s of t h e h e a t e d or r e h y d r a t e d s a m p l e s . Furthermore,
t h e e x t e n s i v e i n t r u s i o n - e x t r u s i o n h y s t e r e s i s and t h e l a r g e
e n t r a p m e n t o f m e r c u r y a r e f e a t u r e s g e n e r a l l y a s s o c i a t e d w i t h complex p o r e n e t w o r k s made u p o f i n t e r c o n n e c t i n g c h a n n e l s a n d c a v i t i e s o f d i f f e r e n t dimensions
.
Alt-hough i t is n o t p o s s i b l e t o a r r i v e a t . a n u n a m b i g i o u s i n t e r p r e t a t i o n of t h e m e r c u r y p o r o s i m e t r y d a t . a , t h e r e i s l i t t l e d o u b t t h a t . on h e a t t r e a t m e n t t.he p o r e s i z e d i s t r i b u t i o n o f t h e HAC-MDF became much b r o a d e r t h a n t h a t o f t h e CPC-MDF.
I t seems t h a t t h e d e v e l o p m e n t o f t h e w i d e r pores i n the HAC s a m p l e s
was r e s w n s i b l e f o r t h e a p p e a r a n c e o f t h e i r v e r y h i g h p e r m e a b i l i t i e s .
On t.he
o t h e r h a n d , t h e c o m p l e t e removal of t h e p o l y m e r by h e a t t r e a t m e n t of t h e AAC-MDF a t 45OoC e v i d e n t l y l e d t o t h e f o r m a t i o n of a h i g h l y r e a c t i v e m a t e r i a l and an u n s t a b l e p o r e s t r u c t u r e .
The c u r i o u s r e s u l t o b t a i n e d on r e h y d r a t i o n o f
t h e 15OoC s a m p l e o f HAC-MDF was p r o b a b l y d u e t o t h e l e a c h i n g o u t o f r e s i d u a l polymer which i n t u r n l e d t o p o r e wid e n in g and i n c r e a s e d p e r m e a b i l i t y . I n T a b l e 2 t h e v a l u e s of p o r e volume a s d e t e r m i n e d by m e r c u r y p r o s i m e t r y a r e compared w i t h t-hose c a l c u l a t e d f r o m t h e l o s s o f p o l y m e r d u r i n g lieat treatment.
The 1att.er a r e c a l c u l a t e d from t h e t - h e r m o g r a v i m e t r i c c u r v e s .
The a g r e e m e n t b e t w e e n t h e two s e t s o f v a l u e s i s o n t h e w h o l e f a i r l y good a n d a p p e a r s t o confirm t h a t t h e p o r o s i t y g e n e r a t e d o v e r t h e t e m p e r a t u r e range of 150-450°C
i s m a i n l y d u e t o t h e t h e r m a l removal o f p o l y m e r .
TABLE 2
C o m p a r i s o n of P o r e V o l u m e s D e t e r m i n e d by M e r c u r y P o r o s i m e t r y a n d l o s s of P o l y m e r . Cement CPC-MDF
EiAC- MDF
*
Treatment NONE
15OoC* 3OO0C* 4 5OoC* NONE
15OoC* 3OO0C* 45OoC*
P e r c e n t a g e Polymer Decomposition
Calculated Pore Volume cm3g-l
0.0% 47.3% 81.3% 100.0%
0 0.031
0.0% 0.0% 31.9%
0 0.024 0.077 0.102
100.0%
Beated t o s p e c i f i e d temperature f o r 4 hours.
0.052
0.058
Measured P o r e Volume cm3g-l 0.020 0.046 0.055 0.082 0.002
0.011 0.066 0.086
675 W e s h o u l d l i k e t o a c k n o w l e d g e t h e s u p p o r t of B r i t i s h Gas a n d I C I i n
f u n d i n g t h e r e s e a r c h a n d i n p a r t i c u l a r t h e h e l p o f Norman P a r k y n s , Anthony Howard a n d P e t e r Cardew.
W e a l s o t h a n k David Lawrence of t h e B r i t i s h Cement
A s s o c i a t i o n f o r h i s h e l p and a d v i c e c o n c e r n i n g t h e p e r m e a b i l i t y measurements.
REFERENCES 1 2 3 4
H . J . G i l k e y ; J. Amer. Concr. I n s t . 5 8 , 1851-1878 ( 1 9 6 1 ) . J . D . B i r c h a l l ; I n d . Chem. B u l l . 167-170 ( 1 9 8 3 ) . K. K e n d a l l , A . J . Howard a n d J . D . B i r c h a l l ; P h i l . T r a n s . R.
139-153 ( 1 9 8 3 ) . C.D.Lawrence; 8 t h C o n g r e s s of Cement, B r a z i l
(1986).
SOC. Lond. A310,
669
THE POROSITY AND PERMEABILITY OF MACRODEFECT FREE CEMENTS
K.S.W.
S i n g and M.
Yat.es
Department o f Chemistry, Brunel U n i v e r s i t y , Uxbridge, Middlesex, England
ABSTRACT Very h i g h s t r e n g t h c e m e n t s o f l o w p o r o s i t y h a v e b e e n p r o d u c e d from b o t h O r d i n a r y P o r t l a n d Cement (OPC) a n d High Alumina C e m e n t (HAC) b y t.he i n c o r p o r a t i o n of a w a t e r s o l u b l e p o l y m e r a t t h e e a r l y m i x i n g st-age. T h e s e m a t e r i a l s h a v e b e e n t e r m e d m a c r o d e f e c t free (MDF) c e m e n t s d u e t o t h e e x c l u s i o n I n t.he o f the w i d e r pores b r o u g h t a b o u t by t h i s m a n u f a c t u r i n g process. p r e s e n t s t u d y t h e e f f e c t o f h e a t t r e a t m e n t and r e h y d r a t i o n on t h e s e t w o s y s t e m s h a s been i . n v e s t 3 q a t e d by t h e u s e o f mercury p o r o s i m e t r y and methane gas permeability. T h e s e s t u d i e s were complemented by t h e r m o g r a v i m e t r y a n d g a s a d s o r p t i o n m e a s u r e m e n t s . The r e s u l t s o b t a i n e d show t h a t . d e c o m p o s i t i o n o f t h e p o l y m e r was t h e c o n t r o l l i n g f a c t o r i n t h e f o r m a t i o n o f t h e p o r e volume. However, t h e p o r e s i z e d i s t r i b u t i o n s of t h e t w o s y s t e m s were v e r y d i f f e r e n t b0t.h b e f o r e a n d a f t e r r e h y d r a t i o n a n d t h i s h a s a d i r e c t b e a r i n g on t-he measured p e r m e a b i l i t y . INTRODUCTION
U n t i l r e c e n t l y it was w i d e l y a c c e p t e d t - h a t t h e s t r e n g t h of OPC was g o v e r n e d by t h e i n i t i a l w a t e r / c e m e n t r a t i o w h i c h d i r e c t l y l e d t o a p a r t i c u l a r 1 volume f r a c t i o n o f pores i n t h e h a r d e n e d c e m e n t p a s t e However, t h e work Of
.
Birchall e t
d e m o n s t r a t e d t h e e f f e c t . o f t.he wider p o r e s on t h e s t r e n g t h
and r e v e a l e d t h a t c o n s i d e r a b l e i m p r o v e m e n t c o u l d b e made e s p e c i a l l y i n t h e f l e x u r a l s t r e n g t h by t h e i r removal. To p r o d u c e t h e t w o c e m e n t s s t - u d i e d a w a t e r s o l u b l e p o l y m e r
(polyvinyl
a l c o h o l ) i s added t o t h e c e m e n t / w a t e r s y s t e m t o a c t a s a r h e o l o g i c a l a i d d u r i n g t h e h i g h s h e a r m i x i n g , t h u s l e a d i n g t.o closer p a c k i n g of t.he i n d i v i d u a l cement g r a i n s p r i o r t o h y d r a t i o n and f i n a l s e t .
This s p e c i a l processing
t e c h n i q u e is f u n d a m e n t a l t o t h e l o w p o r o s i t y / h i g h s t r e n g t h n a t u r e o f t h e MDF m a t e r i a l s . The main o b j e c t i v e o f t h e work d e s c r i b e d h e r e was t o s t - u d y t h e e f f e c t .
of removing t h e p o l y m e r on t h e p o r o s i t y a n d p e r m e a b i l i t y o f t h e MDF c e m e n t s . T h i s was a s s e s s e d u s i n g t h e t e c h n i q u e s o f m e r c u r y p o r o s i m e t - r y a n d m e t h a n e g a s permeability.
I n a d d i t i o n t o t.hese t e c h n i q u e s thermogravimet.ric a n a l y s i s w a s
u s e d t o f o l l o w + h e d e c o m p o s i t i o n o f t h e p o l y m e r a n d l o s s o f w a t e r from t h e materials during heat-treatment.
Gas a d s o r p t i o n m e a s u r e m e n t s were a l s o u s e d
t o st.udy t h e c h a n g e s i n t h e m i c r o s t - r u c t u r e c a u s e d b y t h e d e c o m p o s i t i o n o f t h e polymer.
EXPERIMENTAL The samples o f MDF cement s h e e t s were p r e p a r e d a t t h e Runcorn Heath I C I laboratories.
The GPC u s e d w a s a s t a n d a r d g r a d e Type I cement powder
produced by Blue C i r c l e and t.he HAC was S e c a r 71 produced by L a f a r g e . The t h r e e components
(cement, polymer and water) were premixed i n a n
o r b i t a l mixer t o g i v e a d r y g r a n u l a r "crumble".
T h i s g r a n u l a r dough was
c h i l l e d ( t o r e t a r d h y d r a t i o n ) and f e d i n t o a t w i n r o l l - m i l l , where it was converted i n t o a t h i n s h eet.
Any remaining o c c l u d e d a i r was removed by
p r e s s i n g t h e s h e e t ( a t 4MPa) f o r 16h a t ambient t e m p e r a t u r e .
The s h e e t w a s
t h e n l e f t t o c u r e f o r 5 d a y s a t a m b i e n t t e m p e r a t u r e and f i n a l l y d r i e d a t 8OoC overnight. The samples were examined b e f o r e and a f t e r h e a t - t r e a t m e n t rehydration.
and a f t e r
H e a t - t r e a t m e n t c o n s i s t e d of h e a t i n g t h e samples a t 5OC min-'
to
t h e s t a t e d t e m p e r a t u r e and h o l d i n g f o r 4 h o u r s b e f o r e c o o l i n g i n a d e s i c c a t o r . R e h y d r a t i o n was accomplished by immersing t h e s a m p l e s i n w a t e r f o r 1 week t h e n d r y i n g a t 8OoC o v e r n i g h t . Kercury p o r o s i m e t r y measurements were made u s i n g a C a r l o Erba 2000 porosimeter.
The c o n t a c t a n g l e of t h e mercury was t a k e n a s 141'
s u r f a c e t e n s i o n a s 480mN in-'. C a r l o Erba S o r p t o m a t i c 1800.
and t h e
Gas a d s o r p t i o n s t u d i e s were c a r r i e d o u t on a G a s p e r m e a b i l i t y measurements were made on a
home b u i l t a p p a r a t u s f o l l o w i n g a d e s i g n used by t h e B r i t i s h Cement Association4.
Thermogravimetric s t u d i e s were c a r r i e d o u t on a S t a n t o n
R e d c r o f t STA 780. a t 50cm3 min-' respectively,
A l l measurements were made i n a n atmosphere o f a i r f l o w i n g
w i t h a h e a t i n g r a t e o f S°C min-'
t o 150°,
300°
and 4.5OoC
i n o r d e r t o d u p l i c a t e t h e h e a t t r e a t m e n t regimes.
RESULTS The p r o p e r t i e s of t h e v a r i o u s t r e a t e d and u n t r e a t e d s a m p l e s o f MDF cements a r e summarised i n T a b l e 1 and r e p r e s e n t a t i v e i n t r u s i o n - e x t r u s i o n mercury p o r o s i m e t r y c u r v e s a r e shown i n F i g u r e s 1-4.
I t w i l l be noted t h a t
t h e o r i g i n a l GPC-MDF had a s m a l l b u t m e a s u r a b l e p o r o s i t y whereas t h e HAC-MDF
was a l m o s t non-porous.
I n t h e i r o r i g i n a l s t a t e b o t h cements e x h i b i t e d no
d e t e c t a b l e g a s p e r m e a b i l i t y , which i n d i c a t e s t h a t t h e pores i n t h e GPC-MDF d i d n o t e x t e n d a s a c o n t i n u o u s network t h r o u g h t h e sample.
I n b o t h cases h e a t
t r e a t m e n t b r o u g h t a b o u t a p r o g r e s s i v e i n c r e a s e i n p o r e volume, p e r m e a b i l i t y and s u r f a c e a r e a .
671 TABLE 1 Properties of MDP cements. Cement
Treatment
OPC-MDF
NONE
15OoC* 15OoC R+ 3OO0C* 3OO0C R+ 4 50oc* 45OoC R+
HAC- MDF
NONE
15OoC* 15OoC R+ 3OO0C* 3OO0C R+ 45OoC* 45OoC R+
,I ,I
*
P o r e Volume cm3g-1 0.020 0.046 0.030 0.055 0.032 0.082 0.034 0.002 0.011 0.021 0.066 0.044 0.086 0.015
P e r m e a b i 1i t y Barrer x
0
1.2-1.6 0.2-0.3 5.6-7.1 0.3-0.4 9.7-17.3 0.4-0.5
Flex strength MPa 82.2 15.7 23.4 14.0 47.3 11.2 33.4
0 0.1-0.2 07.6-346.8 40.7-182.9 0.6- 1 5 . 4 125.4-303.8 0.8-7.4
S u r f a c e Area m'9-l 3.9 16.4
-
21.5
-
24.5
-
0.1 24.1
-
32.6
-
30.1
-
Heated t o s p e c i f i e d t-emperature f o r 4 h o u r s.
+ Immersed i n w a t e r f o r 1 week.
Comparison o f F i g u r e s 1 a n d 3 r e v e a l s t h a t t h e pore s i z e d i s t r i b u t i o n of t h e h e a t e d s a m p l e s o f HAC-MDF was much b r o a d e r t h a n t h a t of t h e
c o r r e s p o n d i n g h e a t e d GPC-MDF.
Although t h e r e s u l t a n t p o r e volumes ( a s
d e t e r m i n e d by m e r c u r y p o r o s i m e t r y ) were n o t d i s i m i l a r , l a r g e r i n t e r n a l s u r f a c e a r e a s were g e n e r a t e d by h e a t t r e a t m e n t o f t h e HAC-MDF.
These heated samples
w e r e also f o u n d t o b e h i g h l y p e r m e a b l e , a l t h o u g h t h e r a t - e o f f l o w o f m e t h a n e was n o t e a s y t o r e p r o d u c e .
A p r o n o u n c e d d e c r e a s e i n p e r m e a b i l i t y was f o u n d
when 300° and 45OoC samples o f HAC-MDF were immersed i n w a t e r . A p a r t f r o m t h e u n e x p e c t e d b e h a v i o u r o f t h e 15OoC s a m p l e o f HAC-TDF. immersion i n water g e n e r a l l y p r o d u c e d a s u b s t a n t i a l r e d u c t i o n i n p o r o s i t y and permeability.
T h e s e e f f e c t s were e s p e c i a l l y s t r i k i n g i n t h e c a s e o f t h e 45OoC
s a m p l e Of HAC-MDF. H e a t t - r e a t m e n t of t h e OPC-MDF - e v e n a t 15OoC loss of f l e x u r a l s t r e n g t h .
-
resulted i n a drastic
T h i s was t o some e x t e n t r e s t o r e d by r e h y d r a t i o n ,
b u t t h e maximum v a l u e a t t a i n e d was s t i l l c o n s i d e r a b l y lower t h a n t h e o r i g i n a l strength.
612
F i g u r e 1. a t 15O0C
(-
Mercury p o r o s i m e t r y c u r v e s f o r OPC-MDF: O r i g i n a l (-) - ) , 3OO0C ( - . - ) a n d 45OoC ( - . - - ) .
and heated
Mercury p o r o s i m e t r y c u r v e s f o r OPC-MDF: O r i g i n a l (-) and F i g u r e 2. r e h y d r a t e d a f t e r h e a t t r e a t m e n t a t 15OoC ( - - ) , 3OO0C ( - . - ) a n d 45OoC ( - . ' - )
673
F i g u r e 3. Mercury p o r o s i m e t r y c u r v e s f o r HAC-MDF: a t 150°C (- - ) , 3OO0C ( - - - ) a n d 45OoC ( . . . . )
.
O r i g i n a l (-)
and h e a t e d
Mercury p o r o s i m e t r y c u r v e s f o r HAC-MDF: O r i g i n a l (--) and F i g u r e 4. a n d 45OoC ( . - . . ) . r e h y d r a t e d a f t e r h e a t t r e a t m e n t a t 15OoC ( - - ) , 3OO0C ( - . - I
674 DISCUSSION It is e v i d e n t t h a t t h e p e r m e a b i l i t y o f t h e h e a t e d and r e h y d r a t e d
c e m e n t s was n o t s i m p l y c o n t . r o l 1 e d by t h e p o r e volume a s d e t e r m i n e d by m e r c u r y porosimetry.
However, t h e s h a p e o f some o f t h e m e r c u r y i n t . r u s i o n c u r v e s i n
F i g u r e s 1-4 i n d i c a t e s t h a t a t t h e maximum a t t a i n a b l e p r e s s u r e m e r c u r y d i d n o t p e n e t - r a t e i n t o t h e n a r r o w e s t p o r e s of t h e h e a t e d or r e h y d r a t e d s a m p l e s . Furthermore,
t h e e x t e n s i v e i n t r u s i o n - e x t r u s i o n h y s t e r e s i s and t h e l a r g e
e n t r a p m e n t o f m e r c u r y a r e f e a t u r e s g e n e r a l l y a s s o c i a t e d w i t h complex p o r e n e t w o r k s made u p o f i n t e r c o n n e c t i n g c h a n n e l s a n d c a v i t i e s o f d i f f e r e n t dimensions
.
Alt-hough i t is n o t p o s s i b l e t o a r r i v e a t . a n u n a m b i g i o u s i n t e r p r e t a t i o n of t h e m e r c u r y p o r o s i m e t r y d a t . a , t h e r e i s l i t t l e d o u b t t h a t . on h e a t t r e a t m e n t t.he p o r e s i z e d i s t r i b u t i o n o f t h e HAC-MDF became much b r o a d e r t h a n t h a t o f t h e CPC-MDF.
I t seems t h a t t h e d e v e l o p m e n t o f t h e w i d e r pores i n the HAC s a m p l e s
was r e s w n s i b l e f o r t h e a p p e a r a n c e o f t h e i r v e r y h i g h p e r m e a b i l i t i e s .
On t.he
o t h e r h a n d , t h e c o m p l e t e removal of t h e p o l y m e r by h e a t t r e a t m e n t of t h e AAC-MDF a t 45OoC e v i d e n t l y l e d t o t h e f o r m a t i o n of a h i g h l y r e a c t i v e m a t e r i a l and an u n s t a b l e p o r e s t r u c t u r e .
The c u r i o u s r e s u l t o b t a i n e d on r e h y d r a t i o n o f
t h e 15OoC s a m p l e o f HAC-MDF was p r o b a b l y d u e t o t h e l e a c h i n g o u t o f r e s i d u a l polymer which i n t u r n l e d t o p o r e wid e n in g and i n c r e a s e d p e r m e a b i l i t y . I n T a b l e 2 t h e v a l u e s of p o r e volume a s d e t e r m i n e d by m e r c u r y p r o s i m e t r y a r e compared w i t h t-hose c a l c u l a t e d f r o m t h e l o s s o f p o l y m e r d u r i n g lieat treatment.
The 1att.er a r e c a l c u l a t e d from t h e t - h e r m o g r a v i m e t r i c c u r v e s .
The a g r e e m e n t b e t w e e n t h e two s e t s o f v a l u e s i s o n t h e w h o l e f a i r l y good a n d a p p e a r s t o confirm t h a t t h e p o r o s i t y g e n e r a t e d o v e r t h e t e m p e r a t u r e range of 150-450°C
i s m a i n l y d u e t o t h e t h e r m a l removal o f p o l y m e r .
TABLE 2
C o m p a r i s o n of P o r e V o l u m e s D e t e r m i n e d by M e r c u r y P o r o s i m e t r y a n d l o s s of P o l y m e r . Cement CPC-MDF
EiAC- MDF
*
Treatment NONE
15OoC* 3OO0C* 4 5OoC* NONE
15OoC* 3OO0C* 45OoC*
P e r c e n t a g e Polymer Decomposition
Calculated Pore Volume cm3g-l
0.0% 47.3% 81.3% 100.0%
0 0.031
0.0% 0.0% 31.9%
0 0.024 0.077 0.102
100.0%
Beated t o s p e c i f i e d temperature f o r 4 hours.
0.052
0.058
Measured P o r e Volume cm3g-l 0.020 0.046 0.055 0.082 0.002
0.011 0.066 0.086
675 W e s h o u l d l i k e t o a c k n o w l e d g e t h e s u p p o r t of B r i t i s h Gas a n d I C I i n
f u n d i n g t h e r e s e a r c h a n d i n p a r t i c u l a r t h e h e l p o f Norman P a r k y n s , Anthony Howard a n d P e t e r Cardew.
W e a l s o t h a n k David Lawrence of t h e B r i t i s h Cement
A s s o c i a t i o n f o r h i s h e l p and a d v i c e c o n c e r n i n g t h e p e r m e a b i l i t y measurements.
REFERENCES 1 2 3 4
H . J . G i l k e y ; J. Amer. Concr. I n s t . 5 8 , 1851-1878 ( 1 9 6 1 ) . J . D . B i r c h a l l ; I n d . Chem. B u l l . 167-170 ( 1 9 8 3 ) . K. K e n d a l l , A . J . Howard a n d J . D . B i r c h a l l ; P h i l . T r a n s . R.
139-153 ( 1 9 8 3 ) . C.D.Lawrence; 8 t h C o n g r e s s of Cement, B r a z i l
(1986).
SOC. Lond. A310,