Strength development of slag and ternary blend concrete

CEMENT and CONCRETE RESEARCH. Vol. 20, pp. 120-130, 1990. Printed 0008-8846/90. $3.00+00. Copyright (c) 1990 Pergamon Press plc.

STRENGTH

DEVELOPMENT

OF SLAG AND

TERNARY

BLEND

in the U S A

CONCRETE

M.N. Haque and T. Chulilung Dept. of Civil Engineering, ADFA, ACT 2600, Australia

(Communicated by F.H. Wittmann) (Received March 22, 1989) ABSTRACT

Ground granulated blast furnace (GGBF) slag is increasingly used in concrete construction due to its technical and economic benefits. This paper describes the strength development of 3 grades of plain cement concretes, portland blast furnace slag (slagment) concretes and concretes in which 15 and 35% of slagment was replaced by flyash (ternary blends). These concretes were cured in standard and nonstandard curing conditions using standard and nonstandard cylindrical specimens. The straight replacement of portland cement by slagment (65% cement and 35% slag) gave higher strength for low to medium strength concretes (20 and 35 MPa). The results also suggest that the strength of the concretes made with slagment was less affected under inadequate curing conditions as compared to the strength of the plain cement concretes. It was also found that the indicated strength of the smaller cylinders (75x150 mm) was adversely affected in the drying curing regimes whereas it was only marginally different from the strength of 150x300 mm cylinders under continuous fog curing. For all the concretes tested, initial curing for 7 days seems to be the most appropriate as it is both practicable and gives adequate strength. Introduction Use of supplementary cementitious materials like flyash and ground granulated blast furnace (GGBF) slag in concrete construction is wide spread because of economic, technical and environmental benefits of these materials. However concrete made with flyash and GGBF slag are reported to be sensitive to lack of curing (i-8). In fact some codes take into account the sensitivity to curing and recommend longer curing period for concretes containing GGBF slag (9). However, it is also reported that even badly cured slag blended cement concrete will provide a very effective barrier to the ingress of chlorides and an excellent sulphate resistance when slag percentage is high (i0). The indicated strength of concrete is known to be dependent on the size of the specimen (11-13). Concrete cast in thin sections is clearly more at risk than that cast in thicker sections and there is evidence to suggest that in relatively thick sections there will be little difference between

120

Vol. 20, No.

l

121 SLAG, TERNARY

BLENDS,

STRENGTH

the performance of concrete with and without slag (8). performance of flyash concretes is known to be better laboratory cast specimens (14). Accordingly,

Likewise insitu than the small

the objectives of this paper were:

to investigate the possibility of using slagment (65% cement and 35% instead of plain cement to manufacture structural grade concretes; to characteristise slagment by flyash;

the ternary blends concrete by replacing a

to provide more data on the performance of concrete containing and flyash under inadequate and nonstandard curing conditions;

slag)

portion

of

slag and slag

and finally to explore the effect of specimen size on the indicated strength of concretes both under standard and nonstandard curing regimes. Experimental

details

The materials used were 20 and i0 mm maximum size crushed gravel, river sand, type A portland cement, slagment (35% slag and 65% cement) and a bituminous flyash (ASTM class F). Chemical composition of cement, slagment and the flyash used are given in Table i. TABLE 1 Characteristics

and Properties of Cement, Cement

Slagment and Flyash

Slagment

Flyash

3.01

2.10 370 9.5

Physical property Bulk Density (t/m3)2 3.15 Specific Surface (m /kg) Residue on 45 um sieve (%) Chemical Composition

(%)

CaO SiO 2 A1203 Fe203 SO 3 MgO Na20 K20 Ign Loss

64.7 20.6 4.6 5.0 2.4 i.i 0.08 0.45 2.0

57.0 24.0 7.8 2.5 2.6 3.0

1.4 61.4 25.5 4.2 0.2 i.i 3.3 2.0

M i x Design

Three reference plain portland cement concretes of 20, 35 and 50 MPa strength were cast. These mixes were recast replacing cement by slagment. Finally, 15% and 35% of slagment was replaced by flyash, on equal weight basis. The materials required to produce a cubic metre of concrete,

122

Vol. M.N.

Haque

and

T.

in e a c h m i x , a r e i n c l u d e d in T a b l e 2. In a l l a d j u s t e d to m a i n t a i n a s l u m p of 2 0 - 5 0 mm. Each mix

where

is d e s i g n a t e d -

contents

= d e s i g n e d s t r e n g t h of c o n t r o l c o n c r e t e = p e r c e n t a g e of s l a g m e n t by w e i g h t = 0 no slagment (normal portland cement concrete) = p e r c e n t a g e of s l a g m e n t r e p l a c e d by f l y a s h . 2

Details

Fly ash

Water

( k g / m 3)

( k g / m 3)

Coarse

agg.

Fine

( k g / m 3)

agg.

( k g / m 3)

Slump (mm)

0 - I00 85 65

-

0 0 15 35

(249) 259 220 166

0 0 40 88

196 166 166 187

1257 1302 1313 1278

628 641 615 581

20 20 35 50

35 0 35 - i00 35 85 35 65

-

0 0 15 35

(356) 367 304 232

0 0 55 126

200 167 187 195

1236 1271 1249 1241

552 576 531 492

40 30 30 35

50 50 50 50

-

0 0 15 35

(482) 461 412 313

0 0 74 170

197 159 186 201

1183 1165 1193 1178

500 481 468 416

35 45 50 50

Casting

and

0 - i00 85 65

Specimens

For 100x200

They

mm and

were

All then

each

were

form:

N1 N2

(Cement) Slagment ( k g / m 3)

No.

N3

Mix

20 20 20 20

following

water

-

TABLE

Mix

concretes,

N1

N3

N2

in t h e

20,

Chulilung

Curing mix

150x300

3 different

size

cylinders

cast

were:

75x150

specimens were demoulded within 18-24 s t o r e d in t h e f o l l o w i n g f o u r d i f f e r e n t

hours curing

after casting. regimes.

(i) (ii)

F - f o g r o o m k e p t at 2 3 ~ 2 °C a n d 95+__3% R . H ; C - c o n t r o l r o o m k e p t at 2 3 ~ 2 °C a n d 4 5 ~ 5% R.H;

(iii)

7C - f i r s t 7 d a y s in fog r o o m and then transferred to the control room until testing; SF - a f t e r d e m o u l d i n g s p e c i m e n s w e r e sealed in plastic b a g s a n d t h e n p l a c e d in t h e fog r o o m u n t i l t e s t i n g .

(iv)

mm,

mm.

l

Vol.

20,

No.

l

123 SLAG,

TERNARY

BLENDS,

STRENGTH

Testing C o m p r e s s i o n t e s t s w e r e p e r f o r m e d at 28 a n d 91 d a y s . E a c h v a l u e is a n a v e r a g e of t w o or t h r e e s p e c i m e n s . A t t e s t i n g , s p e c i m e n various curing regimes w e r e s u r f a c e dry. Accordingly, surface condition did not affect the strength results. The results of t e s t i n g a r e i n c l u d e d in T a b l e 3 a n d 4. TABLE 28 D a y s

3

Compressive

Strength .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

100x200 .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

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.

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.

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.

.

.

.

.

.

.

.

.

mm .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Curing Mix

SF

F

C

Strength

(MPa) .

.

.

75x150 .

strength from the moisture strength

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

mm .

.

.

.

.

.

.

.

.

150x300 .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

mm

.

Regime

7C

F

C

7C

F

20 20 20 20

-

0 i00 85 65

-

0 0 15 35

16.1 27.1 21.1 13.3

19.5 29.8 21.4 12.6

12.3 17.3 i0.i 7.5

20.0 29.3 21.4 13.1

18.6 28.8 21.2 12.6

17.3 23.4 18.8 9.3

21.5 32.0 24.9 14.9

20.4 31.2 23.4 15.7

35 35 35 35

-

0 i00 85 65

-

0 0 15 35

33.0 33.8 35.3 25.4

39.3 45.1 41.9 28.6

23.5 26.4 23.2 12.0

37.6 43.3 37.6 26.2

37.6 41.6 36.3 25.1

31.7 37.3 29.8 19.9

38.9 44.9 41.0 29.4

39.8 46.4 43.2 30.7

50 50 50 50

-

0 i00 85 65

-

0 0 15 35

40.3 47.8 44.4 40.4

47.9 51.0 46.5 46.7

36.2 39.8 28.3 21.7

51.8 56.6 43.3 40.9

47.5 51.6 40.9 42.7

41.0 47.7 36.8 30.4

47.2 56.9 46.2 40.6

48.1 54.2 48.8 45.0

1 5 0 x 3 0 0 m m c y l i n d e r s f r o m C a n d 7C c u r i n g r e g i m e s w e r e a l s o t e s t e d at 91 d a y to m o n i t o r t h e 2 - h o u r w a t e r p e n e t r a t i o n d e p t h . T h e s e r e s u l t s are i n c l u d e d in T a b l e 5. Results Effect

of Using

Slagment

and

and

Discussion

Flyash

on the

Strength

of C o n c r e t e

It is apparent from the Table 2 that the total replacement of cement by s l a g m e n t r e s u l t e d in l o w e r i n g t h e w a t e r d e m a n d . Certainly this ability of t h e s l a g m e n t to l o w e r t h e t o t a l w a t e r d e m a n d (as compared to p l a i n c e m e n t c o n c r e t e s ) is r e f l e c t e d in s t r e n g t h of t h e s l a g m e n t concretes. Also 35% r e p l a c e m e n t of s l a g m e n t by t h e f l y a s h s e e m s to h a v e negated the b e n e f i c i a l e f f e c t of s l a g m e n t in l o w e r i n g t h e w a t e r d e m a n d a n d a g a i n t h i s is r e f l e c t e d in t h e s t r e n g t h of t h e s e c o n c r e t e s . A s s h o w n in T a b l e 3, f o r a l l t h e t h r e e g r a d e s of c o n c r e t e a n d both the adequate (fog) a n d i n a d e q u a t e c u r i n g c o n d i t i o n s , t h e strength the c o n c r e t e m a d e w i t h t h e s l a g m e n t is on t h e a v e r a g e , 3 0 % h i g h e r t h a n concrete made with cement o n l y . A g a i n , at 91 d a y s (see Table 4),

for of the the

124

Vol. M.N.

Haque

and

T.

TABLE 91

Days

4

Compressive

Strength

Strength .

.

.

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.

100x200 .

.

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mm

.

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.

( MPa .

.

.

.

.

.

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.

.

.

.

.

.

.

.

Curing Mix

SF

F

.

.

.

.

.

.

) .

.

.

.

.

.

.

.

.

.

.

.

mm

.

.

.

.

.

.

.

.

.

150x300

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

ram

.

C

7C

F

C

7C

F

20

-

0

-

0

19.5

20.8

12.7

19.2

21.1

19.8

26.5

27.5

20

-

i00

-

0

29.6

36.4

16.9

29.6

33.6

23.0

32.3

35.3

20

-

85

-

15

25.9

25.5

13.5

24.6

25.8

18.3

26.6

26.7

20

-

65

-

35

18.6

18.6

7.4

14.2

16.5

9.7

15.4

21.0

35

-

0

-

0

36.1

41.1

22.5

35.5

36.6

31.8

44.1

40.3

35

-

i00

-

0

46.6

50.4

29.8

45.8

52.0

37.6

44.2

44.9

35

-

85

-

15

42.0

49.8

22.6

36.1

49.4

30.8

42.5

48.3

35

-

65

-

35

34.0

37.5

13.2

26.7

31.1

20.0

31.3

38.9

50

-

0

-

0

54.4

61.4

37.6

55.3

60.7

43.6

51.5

54.4

50

-

i00

-

0

51.4

54.1

38.1

54.8

58.9

48.1

54.0

49.9

50

-

85

-

15

55.7

63.0

32.7

45.4

63.1

40.0

51.2

48.7

50

-

65

-

35

47.0

56.5

23.5

40.5

52.9

31.2

43.0

48.6

Water .

.

Regime

TABLE

.

.

75x150 .

20,

Chulilung

.

.

.

.

.

.

.

.

.

.

.

.

.

.

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.

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.

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.

.

Penetration .

.

.

.

.

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.

.

.

.

.

.

.

Depth

5

from .

.

.

.

of

.

.

.

Outside .

.

.

Water

.

.

.

.

.

.

Surface .

.

.

.

.

.

.

.

.

.

.

.

(nun) .

Mix

.

Penetration .

.

.

.

=

~

C

7C

20

-

0

-

0

40

20

20

-

I00

-

0

32

16

20

-

85

-

15

28

12

20

-

65

-

35

60

25

35

-

0

-

0

22

12

35

-

i00

-

0

25

13

35

-

85

-

15

27

13

35

-

65

-

35

43

13

50

-

0

-

0

15

i0

50

-

i00

-

0

17

7

50

-

85

-

15

13

8

50

-

65

-

35

33

14

=

=

=

=

=

=

=

=

No.

l

Vol.

20,

No.

|

125

SLAG, TERNARY BLENDS, STRENGTH

strength of the slagment concrete in the 20 and 35 MPa strength concretes is,on the average, 33% higher than the strength of the plain cement concretes. It is only in the 50 MPa strength concretes that the direct replacement of cement by slagment resulted in some lowering of the strength in certain exposure conditions. Since the slagment was cheaper than the cement, the economic benefits of using slagment are apparent, especially for the low to medium strength concretes. The effect of using slagment (and flyash) on the strength development on the three grades of concretes is also shown in Figs. i, 2 and 3. The strength ratio, which is the strength of a given grade of concrete to the corresponding strength of the plain cement concrete, is indicative of the effect of slagment on the compressive strength of concretes. More importantly, the superior strength development characteristics of slagment concretes under inadequate curing conditions are noteworthy. 15% replacement of slagment by flyash, in most cases, decreased the beneficial effect of using 100% slagment. At 35% replacement level, the longer term strength development characteristics of the ternary blends concrete are very poor as shown in Table 3 and Figs. i, 2 and 3. The relatively poorer performance of these high flyash ternary blends concrete under inadequate curing conditions is also apparent in these figures. Effect of Curing Regime Since the concretes with GGBF slag and flyash are known to be more sensitive to lack of curing, the effect of curing regime is compared in terms of curing strength ratio. It is defined as the ratio of strength from a particular curing regime to the strength of corresponding standard fogcured, same size and same grade of concrete. The 91 day results of curing strength ratios for the 20, 35 and 50 MPa concretes are included in Figs. 46 respectively. It is evident (from Tables 3 and 4) that both at 28 and 91 days, control room curing decreased strength of all concretes. The extent of loss in strength corraborates the findings of Haque et al (i), Haque and Gopalan (2), Gopalan and Haque (3) and Bloem (15, 16). However, it is interesting to 180

LI -¢:

100

.201000 [] []

iiEll3Elllrrl-l-

--

1

20-85-15 20-65-35

" 100x200 rnm *" 75x150 mm "**

150x300 mm

~ 8o 60 40 2O 0 SF*

F"

C'"

7C*" F'* C***7C'**F*** curing reglrnes

for

various

FIG. 91 d a y s

strength

ratio

1 specimen

-

2 0 MPa c o n c r e t e s .

126

Vol. 20, No. l M.N.

1

o

Haque and T. Chulilung

0

0

"

~

lOOx200 mr~ 75x150 m m

"*

80

***

1 5 0 x 3 0 0 mm

~ 6o 4O 2O 0 SF*

91 d a y s s t r e n g t h

F"

ratio

C**

for

7C** g °* C°'*7C***F curing regimes

***

FIG. 2 various specimen

- 35 NPa c o n c r e t e s .

120 1 O0

•

50-1000

[] []

50-85-15 50-65-35

*" "**

.c

1 0 0 x 2 0 0 mm

"

80 o

75x150 mm 1 5 0 x 3 0 0 mm

60

40

20

SF*

F"

C'"

7C** F'" curlngr~lmes

C**'7C**'F**"

FIG. 3 91 days strength ratio for various specimen - 50 MPa concretes

•

2o-o-o 20 100 0 2 0 85 15 2O-65-35

[]

iilIg:llii./

[] [] *

*" ***

O

100x200

mm

75x150 mm 150x300 mm

~ SF*

C**

7C °* C*** cudmg regimes

7C °*"

FIG. 4 91 days curing strength ratio - 20 MPa concrete~ •

Vol.

20, No. ]

]27

SLAG, TERNARYBLENDS, STRENGTH

l

• [] [] []

i

350-0 35 100-0 35-85 15 35-65-35 •

"" *'*

SF"

C'*

7C'" C*'* curlngmglmes

100x200 mm 75x150 mm 150x300 mm

7C''"

FIG. 5 91 days curing strength ratio - 35 MPa concretes.

lOOl

•

50-0-0

[] 5o-~oo-o A

m []

8O

o .,c

50 85-15 50 65 35

* 100x200 mm 60

*" **"

75x150 mm 150x300 mm

40

2O

0 SF"

C*"

7C'" C''" curing regimes

7C''"

FIG. 6 91 days curing strength ratio - 50 MPa concretes. note, that on the average, in drying ambient conditions of C curing regime, the curing strength ratio of slagment concretes is 82% as compared to 77% for the plain portland cement concretes (for 150x300 mm cylinders). This is indicative of the better strength developing characteristics of slagment concretes under inadequate curing conditions. Certainly, as the proportions of flyash in concretes increased, lack of curing adversely affected the ternary blends concrete (see Figs. 4-6). Again, the superiority and adequacy of 7C curing regime is shown in Figs. 4-6. On the average, 7C curing regime gave strength similar to that of fog curing for plain, slagment and ternary blends concrete with 15% flyash (for 150x300 mm cylinders). The average curing strength ratio for these concrete are I00, 99 and 98% respectively. On the average, curing strength ratio, for plain, slagment and ternary blends concretes under sealed conditions (SF curing) is identical (90-91%). Comparing with the C curing regime, the strength development of

128

Vol. M.N.

20,

No.

Haque and T. Chulilung

concretes in sealed conditions is much superior. Since the concrete with SF curing regime simulates the core concrete, it is indicative of the insitu strength of real concretes. Effect of Size of the Specimen Effect of size of specimen in the F, 7C and C curing regimes is shown in Figs. 7, 8 and 9 respectively. Generally, the smaller the specimen, the lower was the strength. However, it seems that the size strength ratio is d e p e n d e n t on the strength grade and type of curing. In higher strength concretes and under proper curing conditions, the size effect is less pronounced and even the theory of weak link in the chain governing the strength of concrete seems to hold (see Figs. 7 and 8) - that is the smaller the specimen the higher the indicated strength (13). Certainly, under inadequate curing conditions the strength of the smaller specimen is a d v e r s e l y affected as compared to a bigger size specimen. For all the concrete cured in the fog r o o m , the average value of the ratio of strength between the 75 mm and 150 mm diameter cylinders was 98%. However, this value for the C exposure regime was 75% and that for 7C 91%. In summary, it can be concluded that under n o n s t a n d a r d drying curing conditions, the smaller size specimens u n d e r e s t i m a t e the potential strength of the concrete. Accordingly, smaller size specimens exposed to drying ambient conditions should only be used to assess the strength of exposed thin structural elements whose surface to volume ratio is large. Water Penetration

As shown in Table 5, on the average, there more depth of water p e n e t r a t i o n in the i n a d e q u a t e l y those of the i n i t i a l l y 7 day cured ones. This can premiss of a d d i t i o n a l hydration and pore filling due

is a p p r o x i m a t e l y 100% cured specimens than be explained on the to the e x t e n d e d curing.

Among all the three grades of concrete, m a x i m u m water penetration was obtained in 20 MPa concrete and m i n i m u m in the 50 MPa one - almost 50% of that of the 20 MPa concrete. Again it was expected and can be explained on the basis of p e r m e a b i l i t y and strength r e l a t i o n s h i p of concrete. In the same class of concrete m a x i m u m water p e n e t r a t i o n resulted in concrete with 65% slagment and 35% flyash. This is related with the strength of concrete as the flyash proportion increased, the strength decreased, and so the p e r m e a b i l i t y would have increased (8). On the overall, the w a t e r p e n e t r a t i o n of slagment concretes, cured in 7C, was less than that in the plain cement concretes (see Table 5). This result is suggestive of the improved c h a r a c t e r i s t i c s of the slag concrete when a d e q u a t e l y cured. Conclusions 1. The low and m e d i u m strength concretes (20 and 35 MPa) cast with slagment gave higher strength than those cast with plain cement alone. However, replacement of slagment by flyash g e n e r a l l y decreased the strength of ternary blend concretes. 2. All concretes are sensitive to lack suggest that the slagment concretes are than the plain cement concretes. Again 7C strength as standard fog curing e v e n at

of curing. However, the results less sensitive to lack of curing curing regime resulted in similar 91 days. Hence for p r a c t i c a l and

I

Vol.

20,

No.

1

129

SLAG, TERNARY BLENDS, STRENGTH

70

/

A

~. 60

/if

/ E E

40

~

30

I f

/

ii/

, I"1. ~ 10 10

20 30 40 50 60 Strength - 150x300 turn cylinders (MPa)

70

10

S

i

El~

D

i?I

10

20

30

40

50

60

Strength - 1 5 0 ~ 0 0 m m cylinders (MPa)

FIG. 8 Effect of specimen size on the strength of concrete specimens - 7C curing.

FIG. 7 Effect of specimen size on the strength of concrete specimens F curing.

50

/

A

//

4o

.,"i J ~

~ 3o

FIG, 9 E f f e c t o f s p e c i m e n s i z e on t h e strength of concrete specimens - C curing.

20

• 1

,

/

"/// 0 0

10

20

30

40

50

Strength - 150x300 mm cyllndere ~ P a )

economical reasons, 7C like curing regime is more than adequate to the full strength potential of insitu concretes.

develop

3. The results of SF curing regime are suggestive of the similar strength development characteristics of the plain, slagment and ternary blends (with 15% flyash) insitu concretes. 4. Curing conditions affected the strength of different size specimen differently. Dry curing conditions gave lowest strength ratio between 75 and 150 mm diameter cylinders for all concretes. However, high strength concrete seems to be less affected by the specimen size and type of curing condition. It seems expedient to use smaller size specimens to monitor the strength development of concretes exposed to higher humidities. 5. On the average, the depth of water penetration in the inadequately cured concretes was 100% more than those of the initially 7 days cured ones. Also increasing flyash content in inadequately cured concretes decreased their

130

Vol. M.N.

strength and penetration.

increased

20,

No.

Haque and T. C h u l i l u n g

permeability

and

thereby

caused

more

water

References i. Haque, M.N; Gopalan, M.K; Joshi, R.C. and Ward, M.A. " Strength d e v e l o p m e n t of i n a d e q u a t e l y cured high flyash c o n t e n t and s t r u c t u r a l c o n c r e t e s " C e m e n t and c o n c r e t e R e s e a r c h 16, 363(1986). 2. Haque, M.N. and Gopalan, M.K. " T e m p e r a t u r e and h u m i d i t y e f f e c t on the strength of p l a i n and flyash c o n c r e t e ", Proc. Instn. Civ. Engrs. 8_~3, Part 2, 649(1987). 3. Gopalan, M.K. and Haque, M.N. " E f f e c t of curing regimes on the p r o p e r t i e s of f l y a s h c o n c r e t e ", ACI M a t e r i a l s J, 8_~4, 14(1987). 4. Gopolan, M.K. and Haque, M.N. " S t r e n g t h d e v e l o p m e n t of c y c l i c a l l y cured p l a i n and flyash c o n c r e t e s ", Proc. 13th A R R B Conf. i_~3, Part 5, 27(1985). 5. Swamy, R.N. ' F l y a s h u t i l i z a t i o n in c o n c r e t e c o n s t r u c t i o n ", S e c o n d Int. Conf. o n A s h Tech. and Marketing, London, 359(1984). 6. Walsh, P.F. and Lewis, R.K. "Durability, the d r a f t code and flyash", C o n c r e t e I n s t i t u t e of A u s t r a l i a News, 9, No. 3, 7(1983). 7. C o m m i t t e e R e p o r t " G r o u n d g r a n u l a t e d blast f u r n a c e slag as a c e m e n t i t i o u s c o n s t i t u e n t in c o n c r e t e ", ACl M a t e r i a l s J, 84, 327(1987). 8. W a i n w r i g h t , P.J. and Reaves, C.H. " P r o p e r t i e s of slag concrete - UK e x p e r i e n c e ", C o n c r e t e 88 W o r k s h o p (Sydney), Editor, Ryan, W.G; 168(1988). 9. B r i t i s h S t a n d a r d BS 8110 : Parts 1 and 2 " S t r u c t u r a l use of c o n c r e t e , (1985). i0. Cook, D.J; H i n c z a k , I . and Cao, H.T. " Hydration and morphological characteristics of cement c o n t a i n i n g b l a s t f u r n a c e slag ", Concrete 88 W o r k s h o p (Sydney), Editor, Ryan, W.G; 443(1988). ii. Neville, A.M. " A g e n e r a l r e l a t i o n for s t r e n g t h s of c o n c r e t e specimens of d i f f e r e n t shapes and sizes ", ACI Journal, Proc. 16, 1095(1966). 12. M a l h o t r a , V.M. " Are 4x8 inch c o n c r e t e c y l i n d e r s as g o o d as 6x12 inch cylinders for q u a l i t y control of c o n c r e t e ", ACI Journal, Proc. 73, 33(1976). 13. Neville, A.M. " P r o p e r t i e s of C o n c r e t e ", P i t m a n P u b l i s h i n g , 687(1977). 14. Dunstan, M.R.H. " D i s c u s s i o n on d e v e l o p m e n t of high flyash content c o n c r e t e ", Proc. Instn. Civ Engrs. 78, Part I, 413(1985). 15. Bloem, D.L. " C o n c r e t e s t r e n g t h m e a s u r e m e n t - cores v e r s u s c y l i n d e r s , Proc. ASTM, 65, 668(1965). 16. Bloem, D.L. " C o n c r e t e s t r e n g t h in s t r u c t u r e s , ACl Journal, 65, 176(1968).

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