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Diffusion measurements in cement paste by water replacement using
propan-2-ol
-
Ser
National Research
Conseil national
ITH1
Council Canada
de recherches Canada
N2ld
no.
1481
Institute for
lnstitut de
c. 2
Research in
recherche en
BLDG
Construction
construction
Diffusion Measurements in
Cement Paste by Water
Replacement Using Propan-2-01
by R.F. Feldman
Reprinted from
Cement and Concrete Research
Vol. 17, No. 4, 1987
p. 602
-
61 2
(IRC Paper No. 1481)
Price $3.00
On a mesurt! l e s c h a n g e m e n t s d e l o n g u e u r e t d e p o i d s d e p d t e s d e c i m e n t P o r t l a n d p r s p a r s e s d a n s d e s r a p p o r t s eau-ciment d e 0,3
3
0 , l e t immergges d a n s du propanol-2 e t du methanol. On a d6terminG l a d i f f u s i v i t s e t l e t a u x d e d i f f u s i o n , q u i o n t s t 6 compargs aux p a r a m P t r e s d e s t r u c t u r e d e s p o r e s mesurBs p a r i n t r u s i o n d e m e r c u r e . L e s m e s u r e s d e l o n g u e u r i n d i q u e n t q u e l e m g t h a n o l r 6 a g i t a v e c l e c i m e n t hydrati5 e t n e c o n v i e n t d o n c p a s p o u r m e s u r e r l a d i F E u s i v i t & . P a r c o n t r e , l e propanol-2 e s t r e l a t i v e m e n t i n e r t e e t p r o d u i t d e s v a l e u r s d e d i f f u s i v i t g s i m i l a i r e s 3 c e l l e s o b t e n u e s p o u r l e s i o n s c h l o r u r e d a n s d e s m a t e r i a u x s i m i l a i r e s .
CEMENT and CONCRETE RESEARCH. Vol. 17, pp. 602-612, 1987. P r i n t e d i n t h e USA. 0008-8846/87 $3.00+00. C o p y r i g h t ( c ) 1987 Pergamon J o u r n a l s , L t d .
DIFFUSION MEASUREMENTS I N CEMENT PASTE BY WATER REPLACEMENT USING PROPAN-2-OL
R.F. Feldman
I n s t i t u t e f o r Research i n C o n s t r u c t i o n N a t i o n a l Research Council Canada Ottawa, Ontario, Canada KIA OR6
(Communicated by F.H. W i ttmann) (Received March 20, 1987) ABSTRACT
Length and weight changes were measured when s a t u r a t e d p o r t l a n d cement pastes prepared a t water-cement r a t i o s o f 0.3 t o 1.0 were immersed i n b o t h propan-2-01 and methanol. D i f f u s i v i t i e s and d i f f u s i o n r a t e s were determined, and were c o r r e l a t e d w i t h p o r e s t r u c t u r e parameters, measured by mercury i n t r u s i o n . Length measurements i n d i c a t e t h a t methanol i n t e r a c t s w i t h t h e h y d r a t e d
i
cement and i s t h e r e b y u n s u i t a b l e f o r measuring d i f f u s i v i t i e s .I Propan-2-01 on t h e o t h e r hand i s r e l a t i v e l y i n e r t and produces
I
d i f f u s i v i t y values s i m i l a r t o t h o s e o b t a i n e d f o r c h l o r i d e i o n s i n s i m i l a r m a t e r i a l s .I
Most p h y s i c a l and e n g i n e e r i n g p r o p e r t i e s i n c l u d i n g durabi 1 i t y o f hardened cement pastes and concretes a r e r e l a t e d t o t h e i r m i c r o s t r u c t u r e
( 1 5 ) .
The p h y s i c a l p r o p e r t y most d i r e c t l y r e l a t e d t o d u r a b i l i t y and m i c r o s t r u c t u r e i s p e r m e a b i l i t y . Permeation may occur i n t h e l i q u i d s t a t e , which may i n v o l v e v a r i o u s ions, o r i n t h e gaseous s t a t e . I n many i n s t a n c e s t h e t r a n s p o r t mechanism i n v o l v e s d i f f u s i o n , eg. p e n e t r a t i o n of c h l o r i d e i o n s , and i s r e l a t e d t o pore s t r u c t u r e parameters, as i s p e r m e a b i l i t y (6).S p e c i f i c a t i o n s f o r c o n c r e t e have m o s t l y been based on 28-day
s t r e n g t h s b u t i t i s c l e a r where d u r a b l e h i g h - q u a l i t y c o n c r e t e i s t h e m a j o r concern, permeabi 1 i t y o r d i f f u s i v i t y becomes v e r y i m p o r t a n t .
Several techniques f o r measuring permeabi 1 i t y o r d i f f u s i v i t y have been used (6). However, some o f these techniques may i n v o l v e a p a r t i c u l a r form o f d r y i n g t h a t may unduly damage o r a l t e r t h e s t r u c t u r e of t h e pores, *even t o t h e p o i n t of causing c r a c k i n g (4). I n a d d i t i o n , t h e s p e c i f i c
t e c h n i q u e may n o t be r e l e v a n t t o t h e p a r t i c u l a r form o f m a t e r i a l a t t a c k t h a t t h e c o n c r e t e may be s u b j e c t e d t o .
P a r r o t t (7) showed t h a t several o r g a n i c s o l v e n t s c o u l d r e p l a c e a l a r g e p o r t i o n o f t h e water i n cement p a s t e and suggested t h a t t h e process o f exchange o f water from t h e s a t u r a t e d specimen was a simple p h y s i c a l process o f c o u n t e r d i f f u s i o n . He used methanol t o determine a v a l u e eTi
V o l . 17, No. 4 603 DIFFUSION, LENGTH, WEIGHT CHANGE, SOLVENT REPLACEMENT
t h e t i m e t a k e n t o exchange methanol w i t h h a l f t h e water p r e s e n t i n t h e paste, and used t h i s parameter as a measure o f t h e d i f f u s i v i t y of t h e specimen.
Other workers ( 8 ) measured t h e replacement o f water by methanol from c o n c r e t e and m o r t a r . These a u t h o r s considered t h e i r r e s u l t s
encouraging w i t h r e g a r d t o t h e development o f a t e s t which can i n d i c a t e t h e p o t e n t i a l d u r a b i l i t y o f a specimen. However, several workers (9-11) have suggested t h a t methanol r e a c t s w i t h b o t h Ca(OH)2 and CSH i n h y d r a t e d p a s t e t o form c a l c i u m methoxide o r a m e t h y l a t e d complex. Thus measurements u s i n g methanol may n o t y i e l d r e a l i s t i c values. Propan-2-01 does n o t r e a c t w i t h h y d r a t e d p a s t e and t h u s t h e use o f propan-2-01 as a s o l v e n t f o r d r y i n g s h o u l d be more a p p r o p r i a t e . This paper i n v e s t i g a t e s t h e use of propan-2-01 as a s o l v e n t t o measure t h e i n t r i n s i c d i f f u s i o n c o e f f i c i e n t s o f cement
i
pastes by c o u n t e r - d i f f u s i o n . ExperimentalM a t e r i a l s
Normal Type I p o r t l a n d cement was used. Pastes were prepared a t water/cement r a t i o s o f 0.3, 0.40, 0.5, 0.60, 0.80 and 1.0. A l l samples were cured i n s a t u r a t e d Ca(OH)2 s o l u t i o n f o r more t h a n 1 0 y e a r s except t h e sample prepared a t a water-cement r a t i o o f 0.5, which was cured f o r o n l y 1.4 years.
Reagent grade anhydrous methanol and propan-2-01 were used i n t h i s work.
P r o p e r t i e s
Pore s i z e d i s t r i b u t i o n (Hg p o r o s i m e t r y t o a p r e s s u r e o f 414 MPa) was determined on a1 1 p a s t e p r e p a r a t i o n s . Specimens were d r i e d by soaking pieces o f p a s t e 1.14 mn t h i c k i n anhydrous propan-2-01 f o r 10 days.
Samples were t h e n m a i n t a i n e d i n vacuum f o r a p p r o x i m a t e l y 17 h and t h e n h e a t e d f o r 24 h a t 38OC w h i l e b e i n g m a i n t a i n e d i n vacuum.
Evaporable and non-evaporable w a t e r c o n t e n t s were measured by d e t e r m i n i n g t h e l o s s i n weight between t h e s a t u r a t e d c o n d i t i o n and 100°C, and between 100°C and 1000°C u s i n g a Thermogravimetric Module o f t h e DuPont 1090 system.
Length change was measurzd u s i n g a m o d i f i e d Tuckerman o p t i c a l
s t r a i n gauge. Specimens o f each p a s t e were s l i c e d from t h e i r d i s c s (which had been c u t from c y l i n d e r s by a diamond saw) and were r e c t a n g u l a r ,
a p p r o x i m a t e l y 30 x 10 mm and u s u a l l y 1.14 mm t h i c k . The e f f e c t of t h i c k n e s s on l e n g t h change was a l s o i n v e s t i g a t e d by u s i n g a d d i t i o n a l specimens 2.33 and 3.45 mm t h i c k .
D i f f u s i o n Measurements
S l i c e s o f p a s t e c u t from s a t u r a t e d c y l i n d e r s 30 mm i n d i ameter were used t o measure t h e r a t e o f d i f f u s i o n o f propan-2-01 ( o r methanol) i n t o t h e pores. The s l i c e s were i n t h e form o f d i s c s g e n e r a l l y 1.14 mm t h i c k . The r d i s c s were wiped f r e e o f excess water j u s t b e f o r e weighing and were t h e n
immersed i n anhydrous a l c o h o l . The volume o f t h e a l c o h o l i n t h e
containment vessel (a d e s s i c c a t o r ) was l a r g e (1.5 l i t r e s ) compared t o t h e s i z e o f t h e specimen (25 g ) . Specimen weight was recorded a f t e r s u r f a c e d r y i n g and weighing every few minutes and t h e a l c o h o l was renewed a f t e r 1, 2, 4, 8 and 24 h, and t h e n every 24 h and l e s s f r e q u e n t l y a f t e r 7 days. Some measurements were t a k e n a f t e r 65 days o f immersion. S i m i l a r changes i n t h e i n t a k e o f a l c o h o l were made d u r i n g measurement o f l e n g t h change.
V o l . 17, No. 4
R. F. Feldman
R e s u l t s ( i ) Length Change
The r a t e s of change of l e n g t h o f w a t e r - s a t u r a t e d p a s t e specimens
(when immersed i n propan-2-01) a r e presented i n F i g u r e 1. These specimens
were prepared a t W/C r a t i o o f 0.8, and were 1.14, 2.33 and 3.45 mm t h i c k . The l e n g t h response i s a shrinkage and i t may be observed t h a t t h e r a t e of shrinkage i s g r e a t e s t f o r t h e t h i n n e s t sample a t t h e e a r l i e s t p e r i o d s p r o b a b l y because i t i s s u b j e c t e d t o l e s s e r r e s t r a i n i n g i n f l u e n c e t h a n t h e t h i c k e r specimens. The t h i c k e r specimens a f t e r 500 h o f immersion show l e s s l e n g t h change t h a n t h e sample o f 1.14 mm t h i c k n e s s a f t e r o n l y 6 0 h immersion. T H I C K N E S S 0 1. 1 4 rnv 2 . 3 3 rnm 0 3 . 4 5 rnrn I N M E T H A N O L ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ ' ~ i ~ ' 0 4 0 80 120 160 2 0 0 2 4 0 2 8 0 3 7 0 3 6 0 4 0 0 4 4 0 4 8 0 5 2 0 T I M E , h o u r s
FIG.
1Length change versus t i m e on immersion o f water s a t u r a t e d p a s t e specimens i n propan-2-01.
The 1.14 mm t h i c k specimen was removed from t h e propan-1-01 a f t e r
140 h immersion and p l a c e d i n methanol. The l e n g t h change response was a
r e 1 a t i v e l y r a p i d expansion, a p p r o x i m a t e l y 0.11 per cent i n 10 h, compared t o a shrinkage o f 0.057 p e r c e n t i n t h e same time, when t h e water s a t u r a t e d
sample was immersed i n propan-2-01. A f t e r 360 h o f immersion t h e sample
had n o t r e - a t t a i n e d t h e l e n g t h when i n t h e w a t e r - s a t u r a t e d s t a t e , and had expanded t o a t o t a l o f a p p r o x i m a t e l y 0.14 p e r cent.
Samples prepared a t water-cement r a t i o s of 0.3, 0.4, 0.5, 0.6, 0.8
and 1.0 and immersed i n propan-1-01
,
showed shrinkages of 0.21, 0.137,0.173, 0.12, 0.14 and 0.16 p e r c e n t r e s p e c t i v e l y when steady s t a t e was a t t a i n e d a f t e r p e r i o d s o f immersion i n propan-2-01 v a r y i n g from 6 t o 10
days
.
Length change as a f u n c t i o n o f time' o f t h e w a t e r - s a t u r a t e d p a s t e 1 prepared a t water-cement r a t i o o f 0.8 (1.14 mm t h i c k ) on immersion i n
methanol i s presented i n F i g u r e 2. Length change i s p l o t t e d as a f u n c t i o n of t h e square r o o t o f immersion time, and t h e r e s u l t s o f propan-2-01
immersion a r e a l s o i n c l u d e d f o r comparison. The response t o methanol immersion i s an expansion which exceeds 0.10% a f t e r 32.5 h and appears t o be c o n t i n u i n g w h i l e t h e response t o propan-2-01 immersion i s a shrinkage which appears t o t e r m i n a t e a f t e r 100 h.
Vol. 17, No. 4 605 DIFFUSION, LENGTH, WEIGHT CHANGE, SOLVENT REPLACEMENT
( i i ) Weight change on immersion i n methanol o r propan-2-01.
The w a t e r - s a t u r a t e d specimen o f p a s t e l o s e s weight when immersed i n w a t e r - f r e e methanol o r propan-2-01. T h i s i s due t o t h e displacement o f t h e denser water by t h e a l c o h o l
.
A knowledge o f t h e d e n s i t i e s of t h e f l u i d s a l l o w s a c a l c u l a t i o n o f t h e q u a n t i t y o f a l c o h o l (Wt) d i f f u s i n g t h r o u g h t h e pores i n t o t h e specimen. The r e s u l t f o r t h e 1.14 mm t h i c k paste, prepared a t a water-cement r a t i o o f 0.8 i s presented i n F i g u r e 3. These a r e p l o t t e d as Wt/W, versus square r o o t o f time, where W, i s t h e value a t t a i n e d a t a p p r o x i m a t e l y equi 1 i b r i u m c o n d i t i o n s , a f t e r 240 h. The curves a r ea p p r o x i m a t e l y l i n e a r up t o 2.25 h f o r methanol and 6.25 h f o r propan-2-01, and i n d i c a t e d t h a t t h e i n i t i a l processes o f water replacement by t h e a1 coho1 s a r e d i f f u s i o n c o n t r o l l e d . 0 . 1 2 l , , , , , l p l l 1 1 I -
-*--*!*--I-.--i*-=*
0.08--
---
- - - /** se 0 . 04- 0 *'-
W / W I C = O . 8-
U-
0,
Z.'
< o< METHANOL-
I-
"o, 0 PROPAN-2-OL - U-
0-
Z -0.08'
- O - " 3-
- -0.12-
\
-
0-0-0 - o . l b A ' ~ l ~ l ~ ' ~ l l l l l l i l l 0 2 4 6 8 10 12 1 4 16 18 FIG. 2Length change versus ( t i m e ) & on immersion o f water s a t u r a t e d p a s t e specimens i n methanol and propan-2-01 r e s p e c t i v e l y
.
- -
-
METHANOL - O P R O P A N - 2 - O L --
--
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 n " 7 - 4 6 8 1 0 1 2 1 4 16 1 8 TIME. m s Fig. 3 R e l a t i v e r a t e o f d i f f u s i o n (Wt/W,) o f propan-2-01 and methanol i n t o water- s a t u r a t e d paste.Vol. 17, No. 4 R.F. Feldman
A comparison o f F i g u r e s 2 and 3 shows t h a t when 90 p e r cent of t h e methanol has e n t e r e d t h e specimen, o n l y 0.03 per cent expansion o r l e s s t h a n 30 p e r c e n t o f t h e u l t i m a t e expansion has t a k e n place. On t h e o t h e r hand a t t h e same 1 eve1 o f e n t r y o f propan-2-01 a shrinkage o f 0.095 per c e n t o r 68 p e r c e n t o f t h e u l t i m a t e shrinkage has t a k e n place.
( i i i ) Rate o f d i f f u s i o n o f propan-2-01 on immersion as a f u n c t i o n o f water-cement r a t i o .
Water s a t u r a t e d p a s t e specimens, 1.14 mm t h i c k were used a t
water-cement r a t i o s o f 0.30, 0.4, 0.5, 0.6, 0.8 and 1.0 t o measure r a t e s o f d i f f u s i o n o f propan-2-01 i n t o t h e specimens. R e s u l t s i n u n i t s o f weight of propan-2-01 e n t e r i n g t h e pores per u n i t volume o f sample as a f u n c t i o n of square r o o t t i m e a r e presented i n F i g u r e 4. R e s u l t s a r e g i v e n f o r t h e FIG. 4 D i f f u s i o n o f propan-2-01 (q/m3)- i n t o water- s a t u r a t e d pastes. versus ( t i m e 1 f as a f u n c t i o n o f water-cement r a t i o . ' I l ' l l l I 1 ' 1 ' 1 ' 1 ' 1 ' 1 ' C 0 . 1 0 . 2 0 . 3 0 . 4 0.5 0.6 0 . 7 0 . 8 0 9 1 . 0 W A T E R I C E M E N T R A T I O FIG.
5
Rate of d i f f u s i o n o f propan-2-01 i n t o water- s a t u r a t e d pastes as a f u n c t i o n o f water- cement r a t i o .
Vol. 17, No. 4 607 DIFFUSION, LENGTH, WEIGHT CHANGE, SOLVENT REPLACEMENT
d i f f e r e n t water-cement r a t i o s a t a c o n s t a n t t h i c k n e s s , and a r e l i n e a r up t o between 65 and 85 per cent o f t h e t o t a l d i f f u s i o n . The slopes o f t h e l i n e a r p o r t i o n s were e s t a b l i s h e d w i t h i n l e s s t h a n one hour. The r e s u l t s f o r t h e sample prepared a t water-cement r a t i o o f 0.5 a r e n o t i n c l u d e d i n t h i s f i g u r e s i n c e t h e y p a r t i a l l y c r o s s over t h e o t h e r curves as can be i n f e r r e d from F i g u r e 5. I n F i g u r e 5, t h e r a t e o f d i f f u s i o n
1)
inu n i t s o f grams o f a l c o h o l per cubic metre o f sample per hour
,
versus water-cement r a t i o . This v a l u e decreases w i t h water-cement r a t i o except-
f o r t h e v a l u e o f t h e specimen prepared a t water-cement r a t i o o f 0.4 whichi s g r e a t e r t h a n t h e v a l u e f o r t h e specimen prepared a t water-cement r a t i o of 0.5 and which i n t u r n i s about equal t o t h e v a l u e o f 0.3. However a t each water-cement r a t i o , t h e r e i s some spread i n t h e r e s u l t s . These
f e a t u r e s i n t h e r e s u l t s a r e probably due t o d i f f i c u l t y i n compaction d u r i n g sample p r e p a r a t i o n a t water-cement r a t i o s o f 0.4 and 0.3. S i m i l a r r e s u l t s were observed i n p l o t s o f d i f f u s i v i t y (m2/s) and rr (h) versus
water-cement r a t i o . rr i s t h e parameter used by s b o t h e r workers and
r e p r e s e n t s t h e t i m e t a k t n f o r h a l f o f t h e t o t a l methanol t o d i f f u s e i n t o t h e specimen. Values o f d i f f u s i v i t y were c a l c u l a t e d from a form o f F i c k ' s Law: ( 6 )
W t / Y , = 1.127
where D i s t h e d i f f u s i v i t y , ni2/s, ' t ' t h e time, s and L (m) i s h a l f t h e t h i c k n e s s o f t h e specimen. Values o f t h e v a r i o u s d i f f u s i o n parameters, c o r r e l a t i o n c o e f f i c i e n t s f o r t h e Wt/W, vs
fi
p l o t s , and values f o r t h e evaporable, non-evaporable water c o n t e n t and p o r o s i t y a t each water-cement r a t i o , a r e presented i n Table I.i v ) R e l a t i o n s h i p between l e n g t h and w i g h t changes due t o immersion i n a1 coho1
.
The p l o t o f t h e l e n g t h change versus weight change due t o immersion of t h e p a s t e prepared a t waterlcement r a t i o o f 0.8 i n t h e a l c o h o l s i s presented i n F i g u r e 6. The f a c t t h a t methanol causes an expansion and propan-2-01, a shrinkage i s immediately c l e a r . However, i n a d d i t i o n t h e i n i t i a l l e n g t h per u n i t weight change response t o methanol immersion i s much l o w e r t h a n f o r propan-2-01; up t o 6 p e r c e n t weight change, t h e l e n g t h
W E I G H T C H A N G E , 70
FIG. 6
Length versus weight changes due t o immersion of w a t e r - s a t u r a t e d p a s t e (waterlcement = 0.8) i n a l c o h o l s .
Vol. 17, No. 4 R.F. Feldman
change f o r propan-2-01 i s t w i c e as g r e a t and a t 8 percent i t i s f o u r times. However, i n t h e f i n a l 0.15 p e r c e n t weight change i n methanol immersion t h e r e i s an expansion o f 0.04 per cent, a l a r g e i n c r e a s e i n slope and r e s u l t i n g i n a t o t a l expansion o f 0.10 p e r cent. T h i s compares t o a t o t a l s h r i n k a g e o f 0.14 per c e n t f o r propan-2-01 immersion. The f i n a l l e n g t h change t o weight change r a t i o (AE/E)/(AW/W) i s unexpectedly h i g h f o r
methanol, 0.27, e l i m i n a t i n g p o s s i b i l i t i e s t h a t a d s o r p t i v e f o r c e s can
,
e x p l a i n t h e expansion due t o methanol immersion (12).
The e f f e c t o f water-cement r a t i o on t h e l e n g t h - w e i g h t change 1
r e l a t i o n s h i p due t o propan-2-01 immersion i s presented i n F i g u r e 7. For
specimens prepared a t water-cement r a t i o s o f 1.0 and 0.8, when 80 p e r cent I
o f t h e weight change has occurred o n l y 25 per cent o f t h e l e n g t h change was recorded. At water-cement r a t i o o f 0.3, however 88 p e r cent o f t h e l e n g t h change has occurred a t t h e above l e v e l o f weight change. I n t e r m e d i a t e t r e n d s were observed f o r water-cement r a t i o s between 0.8 and 0.3.
S H R I N K A G E . % FIG. 7
Length versus weight changes due t o immersion i n propan-2-01 o f water- s a t u r a t e d pastes prepared a t d i f f e r e n t water-cement r a t i 0s.
The model o f a coarse p o r e s t r u c t u r e a t h i g h e r water-cement r a t i o s h a v i ng access t o a f i ner pore s t r u c t u r e adequately expl a i ns these r e s u l t s . The coarse p o r e s t r u c t u r e i s e l i m i n a t e d a t l o w water-cement r a t i o s and most of t h e l e n g t h change occurs when t h e propan-2-01 d i r e c t l y e n t e r s t h e f i n e r pores. Most o f t h e s u r f a c e area o f t h e h y d r a t e d p a s t e i s a s s o c i a t e d w i t h t h e f i n e r pores. High s u r f a c e area m a t e r i a l s a r e a s s o c i a t e d w i t h a
s i g n i f i c a n t amount o f s u r f a c e energy. When a f o r e i g n m a t e r i a l i s adsorbed on t h e surface, an i n t e r a c t i o n occurs, t h e e x t e n t depending on t h e n a t u r e o f t h e adsorbent, ( t h e h y d r a t e d cement) and adsorbate ( t h e a l c o h o l and t h e water). Normally t h e i n t e r a c t i o n r e s u l t s i n a decrease i n s u r f a c e energy and an expansion; however i n t h i s case water i s being removed from t h e s u r f a c e and r e p l a c e d by propan-2-01 which i n t e r a c t s t o a l e s s e r degree t h a n water. The n e t r e s u l t of' t h e rep1 acement o f several mol e c u l a r l a y e r s o f water c l o s e t o t h e s u r f a c e o f t h e h y d r a t e d cement by m o l e c u l a r l a y e r s o f . propan-2-01 should t h u s be a shrinkage.
Vol. 17, No. 4 609 DIFFUSION, LENGTH, WEIGHT CHANGE, SOLVENT REPLACEMENT
P O R E D I A M E T E R . urn
FIG. 8
Pore s i z e d i s t r i b u t i o n o f pastes prepared a t d i f f e r e n t water-cement r a t i o s and d r i e d by propan-2-01 treatment.
( v ) Pore s i z e d i s t r i b u t i o n .
I The pore s i z e d i s t r i b u t i o n s f o r t h e s i x specimens prepared a t t h e
I
d i f f e r e n t water-cement r a t i o s a r e presented i n F i g u r e 8. At h i g h e rpressures, ca. 414 MPa t h e t o t a l volume o f mercury i n t r u d e d decreases w i t h
!
water-cement r a t i o . However t h e volume o f mercury i n t r u d e d i n pores>
;
0.088 pm diameter (880 A), i s r e l a t i v e l y low f o r a l l water-cement r a t i o s except 0.8 and 1.0. Both d u r a b i l i t y and p e r m e a b i l i t y have been shown t o beI
more s t r o n g l y r e l a t e d t o pores o f t h i s s i z e range t h a n t h e t o t a l p o r o s i t yI ( 1 3, 6). The values a r e t a b u l a t e d i n Table I. The p l o t i n F i g u r e 9 f o r
I
d i f f u s i v i t y versus p o r o s i t y>
880 A i l l u s t r a t e s t h e s i m i l a r i t y betweenspecimens prepared a t water-cement r a t i o s o f 0.3, 0.4, 0.5 and 0.6. The
1
spread between p o i n t s w i t h i n a specimen t y p e prepared a t one water-cement r a t i o i s g r e a t e r t h a n t h e d i f f e r e n c e between values f o r specimens preparedP O R O S I T Y . % V O L U M E 2 8 8 0 R D I A M E T E R
F I G . 9
D i f f u s i v i t y o f propan-2-01 i n pastes as a f u n c t i o n o f p o r o s i t y 2 880 A diameter.
Vol. 17, No. 4
R.F. Feldman
a t several water-cement r a t i o s . There may be several reasons f o r t h i s , one b e i n g t h a t t h e r e i s a l a r g e v a r i a t i o n i n p o r e s t r u c t u r e w i t h i n one
water-cement r a t i o formed d u r i n g p r e p a r a t i o n , and t h a t t h e pore s t r u c t u r e measured does n o t necessari 1 y r e p r e s e n t t h e average v a l ue f o r t h e s p e c i f i c sample f o r which t h e d i f f u s i v i t y was measured. Another reason i s t h a t t h e d e t e r m i n a t i o n o f $, which t a k e s l o n g e r p e r i o d s o f t i m e t o measure, might cause e r r o r i n t h e c a l c u l a t i o n o f t h e d i f f u s i v i t y due t o t h e i n c l u s i o n o r e x c l u s i o n o f dead-end o r almost i so ated pores.
1
A p l o t o f d i f f u s i o n r a t e( W t per u n i t volume o f sample per h determined a t constant sample t h i c k n e s s ) versus p o r o s i t y i s presented i n F i g u r e 10. T h i s d i f f u s i o n
parameter, d i f f u s i o n r a t e , i s now f r e e o f t h e i n f l u e n c e o f W,. As can be seen i n F i g u r e 5 t h i s parameter decreases c o n t i n u o u s l y w i t h water-cement r a t i o if t h e v a l u e a t 0.5 i s not considered. Although t h e r e i s an
i n c r e a s e d d i f f e r e n c e between r e s u l t s f o r samples prepared a t water-cement r a t i o s o f 0.6 t o 0.3 on t h e one hand and 0.8 t o 1.0 on t h e o t h e r i n t h e p l o t i n F i g u r e 10, t h e r e i s no c l e a r d i f f e r e n t i a t i o n between t h e lower water-cement r a t i o p r e p a r a t i o n s w i t h r e g a r d t o p o r o s i t y . P O R O S I T Y , % V O L U M E * 8 8 0
W
D I A M E T E R FIG. 10 D i f f u s i o n r a t e o f propan-2-01 i n pastes as a f u n c t i o n o f p o r o s i t y > 800 A diameter. D i s c u s s i o nP r e v i o u s workers (9-11) have discussed t h e p o s s i b i l i t y t h a t
methanol r e a c t s w i t h components o f h y d r a t e d p o r t 1 and cement. Length change measurements c a r r i e d o u t i n t h i s work c o n f i r m these f i n d i n g s . Displacement of water adsorbed on porous s i l i c a g l a s s by methanol produces l i t t l e o r no l e n g t h change, showing t h a t t h e i n t e r a c t i o n o f b o t h water and methanol w i t h porous s i l i c a g l a s s i s s i m i l a r . The t o t a l l e n g t h change measured when t h e g l a s s d r i e d t o zero per cent r e l a t i v e h u m i d i t y i s s a t u r a t e d w i t h water i s 0.30 per cent (13). Thus i n comparison t h e expansion o f a p p r o x i m a t e l y 0.10 p e r c e n t observed when w a t e r - s a t u r a t e d h y d r a t e d p o r t l a n d cement p a s t e i s immersed i n methanol i s r e l a t i v e l y l a r g e . Other evidence i n c l u d i n g a d e t e c t i o n of a c o n s i d e r a b l e d e c l i n e o f Young's modul us f o l 1 owing immersi on i n methanol, a l a r g e shrinkage on d e s o r p t i o n o f methanol immersed specimens ( 1 4 ) and i n c r e a s e s i n s u r f a c e area due t o v a r i o u s t r e a t m e n t s w i t h methanol (15) suggest t h a t methanol p e n e t r a t e s t h e l a y e r e d s t r u c t u r e of t h e c a l c i u m s i l i c a t e s and i n c r e a s e s t h e s e p a r a t i o n o f t h e sheets.
Vol. 17, No. 4 61
1
DIFFUSION, LENGTH, WEIGHT CHANGE, SOLVENT REPLACEMENT
The values f o r t h e d i f f u s i o n c o e f f i c i e n t t a b u l a t e d i n Table I v a r y between a p p r o x i m a t e l y 5 x 1 0 - l 2 t o 2 x 1 0 - l 1 m2/s. T h i s i s i n t h e same rapge as values o b t a i n e d by o t h e r workers f o r i o n s such. as ~a', C1-, I-, Cs d i f f u s i n g t h r o u g h w a t e r - s a t u r a t e d o r d i n a r y p o r t l a n d cement (6). The c o e f f i c i e n t s were determined by b o t h t r a n s i e n t and steady s t a t e methods. Page e t a1 (16) r e p o r t e d a v a l u e o f 4.5 x 1 0 - l 2 m2/s f o r t h e e f f e c t i v e d i f f u s i v i t y o f c h l o r i d e i o n s t h r o u g h o r d i n a r y p o r t l a n d cement paste prepared a t water-cement r a t i o o f 0.5. T h i s i s remarkably s i m i l a r t o t h e v a l u e o b t a i n e d h e r e f o r t h e d i f f u s i o n o f propan-2-01 i n p a s t e prepared a t t h e same water-cement r a t i o .
T h i s t e c h n i q u e shows promise as a r a p i d method o f t e s t i n g f o r t h e q u a l i t y o f concrete. It appears p o s s i b l e t o e v a l u a t e t h i n c o n c r e t e s e c t i o n s i n such areas as cover over r e i n f o r c i n g s t e e l . This method, r e q u i r i n g o n l y simple equipment, i s b e i n g developed f o r i n v e s t i g a t i o n s o f m o r t a r s and concrete.
Conclusions
1. Methanol i n t e r a c t s w i t h h y d r a t e d p o r t l a n d cement by p e n e t r a t i o n o f t h e l a y e r e d s i l i c a t e s t r u c t u r e . It i s t h u s u n s u i t a b l e f o r use when
d i f f u s i o n c o e f f i c i e n t s a r e t o be measured.
2. Counter-di f f u s i on o f propan-2-01 i n t o w a t e r - s a t u r a t e d h y d r a t e d p o r t 1 and cement y i e l d s d i f f u s i o n c o e f f i c i e n t s s i m i l a r t o those o b t a i n e d f o r c h l o r i d e i o n d i f f u s i o n i n t o s i m i l a r m a t e r i a l s .
3. Propan-2-01 i s an a c c e p t a b l e f l u i d f o r d i f f u s i o n c o e f f i c i e n t
measurements o f h y d r a t e d p o r t l a n d cement s i n c e no i n t e r a c t i o n s seem t o occur.
4. Propan-2-01 can be used t o assess t h e q u a l i t y and d u r a b i l i t y o f concrete.
TABLE I. D i f f u s i v i t y and R e l a t e d Parameters f o r Pastes o f D i f f e r e n t Water-Cement R a t i o s
11 - - D i f f u s i o n - -- -
W/C D x 10
,
Corr. e ~ ~ Rate, , Evap. Non-Evap. P o r o s i t y , 2 34
Water, Water, % Vol % 2Vol. 17, No. 4 R.F. Feldman
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T h i s p a p e r i s b e i n g d i s t r i b u t e d i n r e p r i n t f o r m by t h e I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n . A l i s t of b u i l d i n g p r a c t i c e a n d r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n , N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a , O t t a w a , O n t a r i o ,
