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The measurement of paste content in hardened concrete using automatic image analyzing technique
CEMENT and CONCRETERESEARCH. Vol. 9, pp. 607-612, 1979. Printed in the U.S,A. 0008-8846/79/050607-06502.00/0 Copyright (c) 1979 Pergamon Press, Ltd.
THE M E A S U R E M E N T OF P A S T E C O N T E N T IN H A R D E N E D C O N C R E T E U S I N G A U T O M A T I C IMAGE A N A L Y Z I N G T E C H N I Q U E
H a l l d o r G u d m u n d s s o n , S. C h a t t e r j i , A. D a m g a a r d Jensen, Niels Thaulow, Preben Christensen. Teknologisk Institut DK-2630 Taastrup Denmark
(Communicated by G.M. Idorn) (Received June 12, 1979) ABSTRACT T h i s p a p e r d e s c r i b e s a t e c h n i q u e for the m e a s u r e m e n t of p a s t e c o n t e n t s of m o r t a r s and concretes. The t e c h n i q u e i n v o l v e s e t c h i n g the p o l i s h e d s u r f a c e s of samples w i t h a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h y l alc o h o l : w a t e r m i x t u r e w h i c h does not a f f e c t l i m e s t o n e agg r e g a t e s . T h e c o n t r a s t d i f f e r e n c e b e t w e e n the e x p o s e d a g g r e g a t e s and the e t c h e d areas is then e n h a n c e d by p a i n t i n g the a g g r e g a t e s b l a c k and f i l l i n g the e t c h e d areas w i t h a w h i t e powder. An a u t o m a t i c image a n a l y z e r can then m e a s u r e e i t h e r the b l a c k e n e d a g g r e g a t e s or the w h i t e n e d e t c h e d areas. A r t i k l e n b e s k r i v e r en m e t o d e for m A l i n g af pasta i n d h o l d i m ~ r t e l eller beton. D e n f o r u d s a t t e r en a t s n i n g af en s l e b e t o v e r f l a d e i en m a t t e t s a l i c y l s y r e o p l ~ s n i n g i 80:20 b l a n d i n g af m e t h y l a l k o h o l / v a n d . D e n n e o p l ~ s n i n g a n g r i b e r ikke k a l k p a r t i k l e r . K o n t r a s t f o r s k e l l e n m e l l e m de f r i l a g t e p a r t i k l e r og d e n a t s e d e o v e r f l a d e er siden u n d e r s t r e g e t v e d at farve p a r t i k l e r n e sorte og f y l d e de e t s e d e o m r & d e r m e d h v i d t pulver. De s ~ l e d e s f r e m b r a g t e sorte eller hvide o m r & d e r kan siden m & l e s v e d h j a l p af a u t o m a t i s k b i l l e d ana ~ lyse.
Introduction C e m e n t paste, i.e. w a t e r + cement, is the m o s t i m p o r t a n t c o n s t i tuent of c o n c r e t e . In c o n c r e t e w i t h sound a g g r e g a t e s it d e t e r m i n e s strength, s h r i n k a g e , etc. In any d i s p u t e a b o u t the q u a l i t y of a g i v e n c o n c r e t e , one of the f i r s t q u e s t i o n s to be r a i s e d is r e g a r d i n g the a m o u n t and d i s t r i b u t i o n of the c e m e n t p a s t e in the concrete; this is p a r t i c u l a r l y t r u e of old c o n c r e t e . F u r t h e r more, the v o l u m e d i s t r i b u t i o n of p a s t e can also be u s e d in the q u a l i t y c o n t r o l of m i x i n g and p l a c i n g of concrete. At present, however, t h e r e is no e a s y m e t h o d a v a i l a b l e of d e t e r m i n i n g the 607
608
Vol. 9, No. 5 H. Gudmundsson, et al.
paste c o n t e n t of c o n c r e t e . T h i s paper d e s c r i b e s an a d a p t i o n of the a u t o m a t i c image a n a l y z i n g t e c h n i q u e to this problem, relying on the fact that w h e n a g r o u n d and p o l i s h e d surface of a c o n c r e t e sample is d i p p e d into acid, the acid tends to d i s s o l v e (etch) the paste p r e f e r e n t i a l l y to the a g g r e g a t e s . T h e e t c h i n g of the p o l i s h e d s u r f a c e of a c o n c r e t e to c r e a t e the f o l l o w i n g d i f f i c u l t i e s :
specimen
tends
(i)
u n l e s s the c o n c e n t r a t i o n of the e t c h a n t and time of e t c h i n g is c o n t r o l l e d , the small and s h a l l o w a g g r e g a t e p a r t i c l e s m a y get d e t a c h e d from the surface.
(ii)
if i n o r g a n i c acid is u s e d as an etchant, p r e s e n t in the c o n c r e t e d i s s o l v e s away.
any
limestone
In a m a n u a l m e a s u r e m e n t , the o p e r a t o r can be r e l i e d u p o n to d e t e c t and c o r r e c t the a b o v e - m e n t i o n e d d e f i c i e n c i e s . W h e n a u t o m a t i c m e a s u r e m e n t t e c h n i q u e s are used, this has to be avoided, and, furthermore, the c o n t r a s t d i f f e r e n c e b e t w e e n e t c h e d paste and aggregate p a r t i c l e s has to be i m p r o v e d for their easy d e t e c t i o n . The m a i n i n n o v a t i o n s of this paper are (a) an o b s e r v a t i o n that a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h a n o l : w a t e r m i x ture d i s s o l v e s c e m e n t p a s t e at a m o d e r a t e rate, but c a l c i u m carb o n a t e at a v e r y slow rate, w h i c h a l l o w e d for c o n t r o l l e d etching of p a s t e w i t h o u t d i s s o l v i n g l i m e s t o n e and (b) a r e a l i z a t i o n that the c o n t r a s t e n h a n c i n g t e c h n i q u e a l r e a d y d e v e l o p e d for air b u b b l e m e a s u r e m e n t c o u l d be u s e d for the p r e s e n t o b j e c t i v e as well. As b o t h p a s t e and air c o n t e n t is m e a s u r e d w i t h this method, it is n e c e s s a r y to c o r r e c t the m e a s u r e m e n t r e s u l t s w i t h the air content, i.e. a paste m e a s u r e m e n t m u s t be p r e c e d e d by air c o n t e n t measurement. Sample
Preparation
Eight types of sand, w i t h d i f f e r e n t a m o u n t s of l i m e s t o n e and a b a t c h of o r d i n a r y P o r t l a n d c e m e n t w e r e u s e d to m a k e samples. For each m i x 2.5 kg cement, 1.25 kg water, and 7.5 kg sand w e r e m i x e d in a l a b o r a t o r y mixer. A n u m b e r of 4 0 x 4 0 x 1 6 0 m m p r i s m s w e r e cast from each of these mixes. A f t e r 28 d a y s w a t e r curing, one p r i s m from e a c h of eight m i x e s w a s c h o s e n at r a n d o m for p a s t e m e a s u r e ment. E a c h of these p r i s m s was t h e n cut l o n g i t u d i n a l l y to y i e l d 4 0 x 1 5 x 1 6 0 m m halves, w h i c h in turn was cut into halves, y i e l d i n g a 80x40 m m area for the a c t u a l m e a s u r e m e n t . Surface
preparation
and
etchin~
The f i r s t step is to p r e p a r e a s u r f a c e for the m e a s u r e m e n t of the air c o n t e n t of the sample. T h i s is d o n e f o l l o w i n g the t e c h n i q u e d e s c r i b e d in (i). A f t e r the air c o n t e n t m e a s u r e m e n t , the sample is c l e a n e d w i t h w a t e r and then d r i e d at 50°C for 30 m i n u t e s . After c o o l i n g to r o o m t e m p e r a t u r e , the s u r f a c e is d i p p e d in a c e t o n e for a b o u t 5 m i n u t e s so as to s a t u r a t e the s u r f a c e region. This step stops the d e e p p e n e t r a t i o n of the e t c h a n t and allows for c o n t r o l l e d etching.
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609 PASTE CONTENT, CONCRETE, IMAGE ANALYSIS, MICROSCOPY
The sample is then laid, face down, in the e t c h a n t (a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h a n o l : w a t e r mixture) to a d e p t h of about 1 cm for 1-4 minutes. The time n e c e s s a r y for the p r o p e r d e p t h of etching d e p e n d s upon the n a t u r e of the sample. At intervals, the d e p t h of etching should be i n s p e c t e d by m e a n s of a s t e r e o m i c r o s c o p e at a b o u t 40 x m a g n i f i c a t i o n . When the proper d e p t h of etching (% 4U) has b e e n achieved, the sample is removed and the acid w a s h e d off w i t h r u n n i n g acetone. F i n a l l y the a c e t o n e is allowed to dry at 50°C. The exposed a g g r e g a t e surfaces are then b l a c k e n e d , and the etched areas are filled first w i t h a Z n O - p a s t e and then g y p s u m f o l l o w ing the t e c h n i q u e d e s c r i b e d in (i). D u r i n g the b l a c k e n i n g of the e x p o s e d a g g r e g a t e surface, care should be taken to avoid pressing the b l a c k e n i n g fluid in b e t w e e n aggregates, e s p e c i a l l y the n a r r o w c h a n n e l s b e t w e e n the fine a g g r e g a t e particles. The sample is now r e a d y for the m e a s u r e m e n t of the paste content. Figs. 1 and 2 show a m o r t a r and a c o n c r e t e s u r f a c e at this stage. If it is d e s i r e d to m e a s u r e the paste c o n t e n t at d i f f e r e n t d e p t h s the etched surface should be r e m o v e d by g r i n d i n g or sawing, and all the surface p r e p a r a t i o n o p e r a t i o n s repeated. Instrumentations A Leitz ~ e x t u r e ~ n a l y z e r S y s t e m (TAS) has been used b o t h for air and paste c o n t e n t m e a s u r e m e n t s . For the paste c o n t e n t m e a s u r e m e n t a m a c r o a n a l y z e r stage, w h i c h a l l o w e d for an e l e c t r o n i c resol u t i o n of 5~, has b e e n found convenient. The image of the sample s u r f a c e was projected, by m e a n s of a 1:4/50 objective, on to the p h o t o s e n s i t i v e layer of the TV c a m e r a of the TAS. Measurement
Procedures
The first step is to m e a s u r e the air c o n t e n t of the s p e c i m e n surface (i). A f t e r this step the s p e c i m e n surface is etched, b l a c k -
~,~.~
~.
,
I.:~,~;~.~. ~',~&: ~/&"4.] ~ , ~ ,"
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Fig.
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t . . . . . . . ~.:~ ~- :" "~',,.;::2-.;~, 4 , - ~ j g ~ ' , w ..: , . , A . . a-~ ! . ' ~ m -
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Shows a f i n i s h e d m o r t a r measurement.
'~
Ca~--.
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sample,
I
r e a d y for
510
Vol. 9, No. 5 H. Gudmundsson, et al.
Fig.
2.
Shows ment.
a concrete
sample,
TABLE Air
and
paste
ready
for m e a s u r e -
I.
contents
of
the
samples.
Samples
Measured % Air cont.
Measured % P a s t e + Air
i
6.8
43 .7
39.6
(3) x)
2
10.7
48.9
42.8
(6)
3
9.5
47.2
41.7
(4)
4
8.3
45.6
40.7
(2)
5
5.1
45.9
43.0
(2)
6
9.8
47.8
42.1
(1)
7
13.5
50.5
42.8
(i)
8
8.4
47.0
42.1
(i)
9.1
47.2
41.9
SD
x)
2.51
1.25
% paste content calc u l a t e d on the b a s i s of a i r f r e e m o r t a r .
1.17
T h e f i g u r e s in p a r e n t h e s i s s h o w in how m a n y d i f f e r e n t p l a n e s the s a m p l e has b e e n m e a s u r e d . T h e v a l u e s , t h e r e f o r e , are m e a n v a l u e s of t h e s e m e a s u r e m e n t s .
Vol. 9, No. 5
611 PASTE CONTENT, CONCRETE, IMAGE ANALYSIS, MICROSCOPY
ened, filled w i t h Z n O - p a s t e and gypsum. The s p e c i m e n is then attached to the m i c r o a n a l y z e r taking care that the s p e c i m e n s u r f a c e is p a r a l l e l to the focal p l a n e of the o b j e c t i v e lens. The specim e n s u r f a c e is d i v i d e d into several fields and all the fields are s u c c e s s i v e l y examined. T h e a c t u a l steps of m e a s u r e m e n t are s i m i l a r to those of air c o n t e n t m e a s u r e m e n t (i). For each field p a r a m e t e r s m e a s u r e d are (a) total s u r f a c e area of the s p e c i m e n and (b) area o c c u p i e d by p a s t e and air. F r o m the above m e a s u r e m e n t s the m e a n f r a c t i o n a l area o c c u p i e d by air and p a s t e is calculated. F r o m these r e s u l t s , the v o l u m e c o n t e n t of the paste, on the b a s i s of a i r f r e e m o r t a r , is c a l c u l a t e d u s i n g the i d e n t i t y that the m e a n f r a c t i o n a l a r e a of a c o m p o n e n t is equal to its f r a c t i o n a l volume.
Results
and D i s c u s s i o n s
F r o m the m i x p r o p o r t i o n s it c a n be c a l c u l a t e d that the p a s t e (cement + water) c o n t e n t of each of the m i x e s was 42% by volume. T a b l e I shows the m e a s u r e d air and paste c o n t e n t s . It can be seen from the table that the m e a s u r e d air c o n t e n t v a r i e d f r o m 36.9 to 40.8%; however, w h e n the c o r r e c t i o n was done for corr e s p o n d i n g air contents, t h e n p a s t e c o n t e n t v a r i e d b e t w e e n 39.6 to 43.0% w i t h a m e a n v a l u e of 41.9 and an o v e r a l l s t a n d a r d dev i a t i o n of 1.17. An i n t e r e s t i n g case is s a m p l e No. 2. T h e p a s t e c o n t e n t of the s a m p l e was m e a s u r e d at 6 d i f f e r e n t d e p t h s w i t h a m e a n v a l u e of 38.2 and s t a n d a r d d e v i a t i o n of 6.37; the c o r r e s p o n d i n g air content was m e a s u r e d at 4 d e p t h s w i t h a m e a n v a l u e of 10.7 and a s t a n d a r d d e v i a t i o n of 1.39. T h e s e r e s u l t s i n d i c a t e that even in a l a b o r a t o r y m a d e m o r t a r s p e c i m e n , m i x i n g and p l a c i n g m a y leave s o m e t h i n g to d e s i r e w i t h r e s p e c t to h o m o g e n e i t y . In e v a l u a t i n g the r e s u l t should be b o r n in mind:
of a m e a s u r e m e n t ,
of air c o n t e n t
the f o l l o w i n g
points
I.
the q u a l i t y
2.
the d e p t h of the e t c h i n g of the sand.
3.
the q u a l i t y of the b l a c k e n e d surface, pores on the s u r f a c e w i l l be m e a s u r e d as paste.
4.
in j u d g i n g the e t c h i n g of the b o r d e r l i n e s of the aggregate, it is i m p o r t a n t that t h e y are s h a r p and c l e a r l y d r a w n and that n a r r o w straits b e t w e e n a g g r e g a t e s are f r e e f r o m paste.
5.
g r a i n size of sand. In the c a s e of f i n e - g r a i n e d be n e c e s s a r y to use a m a g n i f i e d image.
sand
6.
if a p a r t of the a g g r e g a t e be t a k e n into account.
also has
7.
the d e g r e e
of c a r b o n a t i o n
measurement.
in r e l a t i o n
is porous,
of paste.
to the g r a i n
this
and
fact
size
scratches
itmay
to
612
Vol. 9, No. 5 H. Gudmundsson, et al.
The total time i n v o l v e d in this m e a s u r e m e n t c o n s i s t s of one hour for the g r i n d i n g o p e r a t i o n s t a r t i n g w i t h a sawn off sample. It takes a p p r o x i m a t e l y 15 m i n u t e s to p r e p a r e the sample for air content m e a s u r e m e n t . Air c o n t e n t m e a s u r e m e n t takes a p p r o x i m a t e l y 5 minutes. The etching process, w a s h i n g and d r y i n g included, takes a p p r o x i m a t e l y 60 m i n u t e s and the m e a s u r e m e n t itself a n o t h e r 5 m i n u t e s . An a d d i t i o n a l 30 m i n u t e s s h o u l d be given, if the air pore d i s t r i b u t i o n and the s p e c i f i c s u r f a c e of the air pore s y s t e m are needed. A b o v e does not i n c l u d e the time n e e d e d to dry the sample at d i f f e r e n t stages of surface p r e p a r a t i o n . T h o u g h the t e c h n i q u e has been i l l u s t r a t e d w i t h r e s u l t s from m o r t a r samples, it can and has been scaled up to c o n c r e t e samples.
P o s s i b l e use of p a s t e c o n t e n t d a t a in e s t i m a t i n g o r i g i n a l w a t e r / c e m e n t ratio. O n c e the paste c o n t e n t of a sample has been m e a s u r e d , it m a y be p o s s i b l e to e s t i m a t e the o r i g i n a l w a t e r / c e m e n t ratio of the sample. For this the f o l l o w i n g i n f o r m a t i o n is necessary: a)
an e s t i m a t e of the p o r o s i t y of the aggregate.
b)
the w a t e r a b s o r p t i o n c a p a c i t y by v o l u m e of the sample.
c)
an e s t i m a t e of the d e g r e e of h y d r a t i o n of cement.
The r e q u i r e d i n f o r m a t i o n can be e a s i l y o b t a i n e d from the sample itself. This p o s s i b i l i t y is being a c t i v e l y persued.
Reference
(1)
Chatterji
& Gudmundsson
- C e m e n t and C o n c r e t e Research, ~, 423, 1977.
THE M E A S U R E M E N T OF P A S T E C O N T E N T IN H A R D E N E D C O N C R E T E U S I N G A U T O M A T I C IMAGE A N A L Y Z I N G T E C H N I Q U E
H a l l d o r G u d m u n d s s o n , S. C h a t t e r j i , A. D a m g a a r d Jensen, Niels Thaulow, Preben Christensen. Teknologisk Institut DK-2630 Taastrup Denmark
(Communicated by G.M. Idorn) (Received June 12, 1979) ABSTRACT T h i s p a p e r d e s c r i b e s a t e c h n i q u e for the m e a s u r e m e n t of p a s t e c o n t e n t s of m o r t a r s and concretes. The t e c h n i q u e i n v o l v e s e t c h i n g the p o l i s h e d s u r f a c e s of samples w i t h a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h y l alc o h o l : w a t e r m i x t u r e w h i c h does not a f f e c t l i m e s t o n e agg r e g a t e s . T h e c o n t r a s t d i f f e r e n c e b e t w e e n the e x p o s e d a g g r e g a t e s and the e t c h e d areas is then e n h a n c e d by p a i n t i n g the a g g r e g a t e s b l a c k and f i l l i n g the e t c h e d areas w i t h a w h i t e powder. An a u t o m a t i c image a n a l y z e r can then m e a s u r e e i t h e r the b l a c k e n e d a g g r e g a t e s or the w h i t e n e d e t c h e d areas. A r t i k l e n b e s k r i v e r en m e t o d e for m A l i n g af pasta i n d h o l d i m ~ r t e l eller beton. D e n f o r u d s a t t e r en a t s n i n g af en s l e b e t o v e r f l a d e i en m a t t e t s a l i c y l s y r e o p l ~ s n i n g i 80:20 b l a n d i n g af m e t h y l a l k o h o l / v a n d . D e n n e o p l ~ s n i n g a n g r i b e r ikke k a l k p a r t i k l e r . K o n t r a s t f o r s k e l l e n m e l l e m de f r i l a g t e p a r t i k l e r og d e n a t s e d e o v e r f l a d e er siden u n d e r s t r e g e t v e d at farve p a r t i k l e r n e sorte og f y l d e de e t s e d e o m r & d e r m e d h v i d t pulver. De s ~ l e d e s f r e m b r a g t e sorte eller hvide o m r & d e r kan siden m & l e s v e d h j a l p af a u t o m a t i s k b i l l e d ana ~ lyse.
Introduction C e m e n t paste, i.e. w a t e r + cement, is the m o s t i m p o r t a n t c o n s t i tuent of c o n c r e t e . In c o n c r e t e w i t h sound a g g r e g a t e s it d e t e r m i n e s strength, s h r i n k a g e , etc. In any d i s p u t e a b o u t the q u a l i t y of a g i v e n c o n c r e t e , one of the f i r s t q u e s t i o n s to be r a i s e d is r e g a r d i n g the a m o u n t and d i s t r i b u t i o n of the c e m e n t p a s t e in the concrete; this is p a r t i c u l a r l y t r u e of old c o n c r e t e . F u r t h e r more, the v o l u m e d i s t r i b u t i o n of p a s t e can also be u s e d in the q u a l i t y c o n t r o l of m i x i n g and p l a c i n g of concrete. At present, however, t h e r e is no e a s y m e t h o d a v a i l a b l e of d e t e r m i n i n g the 607
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Vol. 9, No. 5 H. Gudmundsson, et al.
paste c o n t e n t of c o n c r e t e . T h i s paper d e s c r i b e s an a d a p t i o n of the a u t o m a t i c image a n a l y z i n g t e c h n i q u e to this problem, relying on the fact that w h e n a g r o u n d and p o l i s h e d surface of a c o n c r e t e sample is d i p p e d into acid, the acid tends to d i s s o l v e (etch) the paste p r e f e r e n t i a l l y to the a g g r e g a t e s . T h e e t c h i n g of the p o l i s h e d s u r f a c e of a c o n c r e t e to c r e a t e the f o l l o w i n g d i f f i c u l t i e s :
specimen
tends
(i)
u n l e s s the c o n c e n t r a t i o n of the e t c h a n t and time of e t c h i n g is c o n t r o l l e d , the small and s h a l l o w a g g r e g a t e p a r t i c l e s m a y get d e t a c h e d from the surface.
(ii)
if i n o r g a n i c acid is u s e d as an etchant, p r e s e n t in the c o n c r e t e d i s s o l v e s away.
any
limestone
In a m a n u a l m e a s u r e m e n t , the o p e r a t o r can be r e l i e d u p o n to d e t e c t and c o r r e c t the a b o v e - m e n t i o n e d d e f i c i e n c i e s . W h e n a u t o m a t i c m e a s u r e m e n t t e c h n i q u e s are used, this has to be avoided, and, furthermore, the c o n t r a s t d i f f e r e n c e b e t w e e n e t c h e d paste and aggregate p a r t i c l e s has to be i m p r o v e d for their easy d e t e c t i o n . The m a i n i n n o v a t i o n s of this paper are (a) an o b s e r v a t i o n that a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h a n o l : w a t e r m i x ture d i s s o l v e s c e m e n t p a s t e at a m o d e r a t e rate, but c a l c i u m carb o n a t e at a v e r y slow rate, w h i c h a l l o w e d for c o n t r o l l e d etching of p a s t e w i t h o u t d i s s o l v i n g l i m e s t o n e and (b) a r e a l i z a t i o n that the c o n t r a s t e n h a n c i n g t e c h n i q u e a l r e a d y d e v e l o p e d for air b u b b l e m e a s u r e m e n t c o u l d be u s e d for the p r e s e n t o b j e c t i v e as well. As b o t h p a s t e and air c o n t e n t is m e a s u r e d w i t h this method, it is n e c e s s a r y to c o r r e c t the m e a s u r e m e n t r e s u l t s w i t h the air content, i.e. a paste m e a s u r e m e n t m u s t be p r e c e d e d by air c o n t e n t measurement. Sample
Preparation
Eight types of sand, w i t h d i f f e r e n t a m o u n t s of l i m e s t o n e and a b a t c h of o r d i n a r y P o r t l a n d c e m e n t w e r e u s e d to m a k e samples. For each m i x 2.5 kg cement, 1.25 kg water, and 7.5 kg sand w e r e m i x e d in a l a b o r a t o r y mixer. A n u m b e r of 4 0 x 4 0 x 1 6 0 m m p r i s m s w e r e cast from each of these mixes. A f t e r 28 d a y s w a t e r curing, one p r i s m from e a c h of eight m i x e s w a s c h o s e n at r a n d o m for p a s t e m e a s u r e ment. E a c h of these p r i s m s was t h e n cut l o n g i t u d i n a l l y to y i e l d 4 0 x 1 5 x 1 6 0 m m halves, w h i c h in turn was cut into halves, y i e l d i n g a 80x40 m m area for the a c t u a l m e a s u r e m e n t . Surface
preparation
and
etchin~
The f i r s t step is to p r e p a r e a s u r f a c e for the m e a s u r e m e n t of the air c o n t e n t of the sample. T h i s is d o n e f o l l o w i n g the t e c h n i q u e d e s c r i b e d in (i). A f t e r the air c o n t e n t m e a s u r e m e n t , the sample is c l e a n e d w i t h w a t e r and then d r i e d at 50°C for 30 m i n u t e s . After c o o l i n g to r o o m t e m p e r a t u r e , the s u r f a c e is d i p p e d in a c e t o n e for a b o u t 5 m i n u t e s so as to s a t u r a t e the s u r f a c e region. This step stops the d e e p p e n e t r a t i o n of the e t c h a n t and allows for c o n t r o l l e d etching.
Vol. 9, No. 5
609 PASTE CONTENT, CONCRETE, IMAGE ANALYSIS, MICROSCOPY
The sample is then laid, face down, in the e t c h a n t (a s a t u r a t e d s o l u t i o n of s a l i c y l i c acid in 80:20 m e t h a n o l : w a t e r mixture) to a d e p t h of about 1 cm for 1-4 minutes. The time n e c e s s a r y for the p r o p e r d e p t h of etching d e p e n d s upon the n a t u r e of the sample. At intervals, the d e p t h of etching should be i n s p e c t e d by m e a n s of a s t e r e o m i c r o s c o p e at a b o u t 40 x m a g n i f i c a t i o n . When the proper d e p t h of etching (% 4U) has b e e n achieved, the sample is removed and the acid w a s h e d off w i t h r u n n i n g acetone. F i n a l l y the a c e t o n e is allowed to dry at 50°C. The exposed a g g r e g a t e surfaces are then b l a c k e n e d , and the etched areas are filled first w i t h a Z n O - p a s t e and then g y p s u m f o l l o w ing the t e c h n i q u e d e s c r i b e d in (i). D u r i n g the b l a c k e n i n g of the e x p o s e d a g g r e g a t e surface, care should be taken to avoid pressing the b l a c k e n i n g fluid in b e t w e e n aggregates, e s p e c i a l l y the n a r r o w c h a n n e l s b e t w e e n the fine a g g r e g a t e particles. The sample is now r e a d y for the m e a s u r e m e n t of the paste content. Figs. 1 and 2 show a m o r t a r and a c o n c r e t e s u r f a c e at this stage. If it is d e s i r e d to m e a s u r e the paste c o n t e n t at d i f f e r e n t d e p t h s the etched surface should be r e m o v e d by g r i n d i n g or sawing, and all the surface p r e p a r a t i o n o p e r a t i o n s repeated. Instrumentations A Leitz ~ e x t u r e ~ n a l y z e r S y s t e m (TAS) has been used b o t h for air and paste c o n t e n t m e a s u r e m e n t s . For the paste c o n t e n t m e a s u r e m e n t a m a c r o a n a l y z e r stage, w h i c h a l l o w e d for an e l e c t r o n i c resol u t i o n of 5~, has b e e n found convenient. The image of the sample s u r f a c e was projected, by m e a n s of a 1:4/50 objective, on to the p h o t o s e n s i t i v e layer of the TV c a m e r a of the TAS. Measurement
Procedures
The first step is to m e a s u r e the air c o n t e n t of the s p e c i m e n surface (i). A f t e r this step the s p e c i m e n surface is etched, b l a c k -
~,~.~
~.
,
I.:~,~;~.~. ~',~&: ~/&"4.] ~ , ~ ,"
-"
Fig.
!.
.:"
"
,r
~."'~N~
.~'~
""~'.
~,~qe,~" . _ ~ • .
t . . . . . . . ~.:~ ~- :" "~',,.;::2-.;~, 4 , - ~ j g ~ ' , w ..: , . , A . . a-~ ! . ' ~ m -
.a,
~
~-,~,
Shows a f i n i s h e d m o r t a r measurement.
'~
Ca~--.
.~'"
sample,
I
r e a d y for
510
Vol. 9, No. 5 H. Gudmundsson, et al.
Fig.
2.
Shows ment.
a concrete
sample,
TABLE Air
and
paste
ready
for m e a s u r e -
I.
contents
of
the
samples.
Samples
Measured % Air cont.
Measured % P a s t e + Air
i
6.8
43 .7
39.6
(3) x)
2
10.7
48.9
42.8
(6)
3
9.5
47.2
41.7
(4)
4
8.3
45.6
40.7
(2)
5
5.1
45.9
43.0
(2)
6
9.8
47.8
42.1
(1)
7
13.5
50.5
42.8
(i)
8
8.4
47.0
42.1
(i)
9.1
47.2
41.9
SD
x)
2.51
1.25
% paste content calc u l a t e d on the b a s i s of a i r f r e e m o r t a r .
1.17
T h e f i g u r e s in p a r e n t h e s i s s h o w in how m a n y d i f f e r e n t p l a n e s the s a m p l e has b e e n m e a s u r e d . T h e v a l u e s , t h e r e f o r e , are m e a n v a l u e s of t h e s e m e a s u r e m e n t s .
Vol. 9, No. 5
611 PASTE CONTENT, CONCRETE, IMAGE ANALYSIS, MICROSCOPY
ened, filled w i t h Z n O - p a s t e and gypsum. The s p e c i m e n is then attached to the m i c r o a n a l y z e r taking care that the s p e c i m e n s u r f a c e is p a r a l l e l to the focal p l a n e of the o b j e c t i v e lens. The specim e n s u r f a c e is d i v i d e d into several fields and all the fields are s u c c e s s i v e l y examined. T h e a c t u a l steps of m e a s u r e m e n t are s i m i l a r to those of air c o n t e n t m e a s u r e m e n t (i). For each field p a r a m e t e r s m e a s u r e d are (a) total s u r f a c e area of the s p e c i m e n and (b) area o c c u p i e d by p a s t e and air. F r o m the above m e a s u r e m e n t s the m e a n f r a c t i o n a l area o c c u p i e d by air and p a s t e is calculated. F r o m these r e s u l t s , the v o l u m e c o n t e n t of the paste, on the b a s i s of a i r f r e e m o r t a r , is c a l c u l a t e d u s i n g the i d e n t i t y that the m e a n f r a c t i o n a l a r e a of a c o m p o n e n t is equal to its f r a c t i o n a l volume.
Results
and D i s c u s s i o n s
F r o m the m i x p r o p o r t i o n s it c a n be c a l c u l a t e d that the p a s t e (cement + water) c o n t e n t of each of the m i x e s was 42% by volume. T a b l e I shows the m e a s u r e d air and paste c o n t e n t s . It can be seen from the table that the m e a s u r e d air c o n t e n t v a r i e d f r o m 36.9 to 40.8%; however, w h e n the c o r r e c t i o n was done for corr e s p o n d i n g air contents, t h e n p a s t e c o n t e n t v a r i e d b e t w e e n 39.6 to 43.0% w i t h a m e a n v a l u e of 41.9 and an o v e r a l l s t a n d a r d dev i a t i o n of 1.17. An i n t e r e s t i n g case is s a m p l e No. 2. T h e p a s t e c o n t e n t of the s a m p l e was m e a s u r e d at 6 d i f f e r e n t d e p t h s w i t h a m e a n v a l u e of 38.2 and s t a n d a r d d e v i a t i o n of 6.37; the c o r r e s p o n d i n g air content was m e a s u r e d at 4 d e p t h s w i t h a m e a n v a l u e of 10.7 and a s t a n d a r d d e v i a t i o n of 1.39. T h e s e r e s u l t s i n d i c a t e that even in a l a b o r a t o r y m a d e m o r t a r s p e c i m e n , m i x i n g and p l a c i n g m a y leave s o m e t h i n g to d e s i r e w i t h r e s p e c t to h o m o g e n e i t y . In e v a l u a t i n g the r e s u l t should be b o r n in mind:
of a m e a s u r e m e n t ,
of air c o n t e n t
the f o l l o w i n g
points
I.
the q u a l i t y
2.
the d e p t h of the e t c h i n g of the sand.
3.
the q u a l i t y of the b l a c k e n e d surface, pores on the s u r f a c e w i l l be m e a s u r e d as paste.
4.
in j u d g i n g the e t c h i n g of the b o r d e r l i n e s of the aggregate, it is i m p o r t a n t that t h e y are s h a r p and c l e a r l y d r a w n and that n a r r o w straits b e t w e e n a g g r e g a t e s are f r e e f r o m paste.
5.
g r a i n size of sand. In the c a s e of f i n e - g r a i n e d be n e c e s s a r y to use a m a g n i f i e d image.
sand
6.
if a p a r t of the a g g r e g a t e be t a k e n into account.
also has
7.
the d e g r e e
of c a r b o n a t i o n
measurement.
in r e l a t i o n
is porous,
of paste.
to the g r a i n
this
and
fact
size
scratches
itmay
to
612
Vol. 9, No. 5 H. Gudmundsson, et al.
The total time i n v o l v e d in this m e a s u r e m e n t c o n s i s t s of one hour for the g r i n d i n g o p e r a t i o n s t a r t i n g w i t h a sawn off sample. It takes a p p r o x i m a t e l y 15 m i n u t e s to p r e p a r e the sample for air content m e a s u r e m e n t . Air c o n t e n t m e a s u r e m e n t takes a p p r o x i m a t e l y 5 minutes. The etching process, w a s h i n g and d r y i n g included, takes a p p r o x i m a t e l y 60 m i n u t e s and the m e a s u r e m e n t itself a n o t h e r 5 m i n u t e s . An a d d i t i o n a l 30 m i n u t e s s h o u l d be given, if the air pore d i s t r i b u t i o n and the s p e c i f i c s u r f a c e of the air pore s y s t e m are needed. A b o v e does not i n c l u d e the time n e e d e d to dry the sample at d i f f e r e n t stages of surface p r e p a r a t i o n . T h o u g h the t e c h n i q u e has been i l l u s t r a t e d w i t h r e s u l t s from m o r t a r samples, it can and has been scaled up to c o n c r e t e samples.
P o s s i b l e use of p a s t e c o n t e n t d a t a in e s t i m a t i n g o r i g i n a l w a t e r / c e m e n t ratio. O n c e the paste c o n t e n t of a sample has been m e a s u r e d , it m a y be p o s s i b l e to e s t i m a t e the o r i g i n a l w a t e r / c e m e n t ratio of the sample. For this the f o l l o w i n g i n f o r m a t i o n is necessary: a)
an e s t i m a t e of the p o r o s i t y of the aggregate.
b)
the w a t e r a b s o r p t i o n c a p a c i t y by v o l u m e of the sample.
c)
an e s t i m a t e of the d e g r e e of h y d r a t i o n of cement.
The r e q u i r e d i n f o r m a t i o n can be e a s i l y o b t a i n e d from the sample itself. This p o s s i b i l i t y is being a c t i v e l y persued.
Reference
(1)
Chatterji
& Gudmundsson
- C e m e n t and C o n c r e t e Research, ~, 423, 1977.