Characterization of granulated and pelletized blast furnace slag

CEMENT and CONCRETE RESEARCH. Vol. 16, pp. 662-670, 1986. 0008-8846/86 $3.00+00. Pergamon Journals, Ltd.

Printed in the USA.

CHARACTERIZATION OF GRANULATED AND PELLETIZED BLAST FURNACE SLAG

E. Douglas and R. Zerbino* Construction Materials Section CANMET, Energy, Mines and Resources Canada Ottawa, Canada KIA 0GI *Construction Department Engineering Faculty, UN~P 1900 La Plata, Argentina

(Communicated by M. Regourd) (Recevied June i0, 1986)

ABSTRACT The objective of this study is the characterization of slags from different sources by their chemical composition, glass content, rate and total heat of hydration and compressive strength development with a vlew to establish a relationship between some of their properties and compressive strength. Binders incorporating 50 per cent slag present the same classification derived from total heat evolved as from slag activity indexes. Introduction The increasing use of blast furnace slag in blended cements in North America makes it relevant to find ways to characterize the behaviour of the slag in cement mixes. This is especially important when new sources of blast furnace slags become available. According to some investigators, conduction calorimetry is a sensitive and fast method to compare blended cements and to establish a classification within less than fifteen hours of hydration (i). This classification would be the same as the one found in compressive strength development with time, due to the correlation between the increasing degree of hydration and the compressive strength at the same age, although there is not a simple quantitative relationship between degree of hydration and mechanical resistance (2). Many factors affect at the same time the microstructure and the macroscopic characteristics of the material, making it difficult to establish a relationship between both structural levels. The hydration of portland ~ement and of portland cement-slag binders produce similar final hydration products. The difference resides in the rate and the intensity of the hydration reactions (3). The hydration reactions are affected not only by the substitution of part of the portland cement by the slag but also by the mechanism of the hydration reactions which evolves in different ways. 662

Vol. 16, No. 5

663 SLAG, GLASS CONTENT, COMPOSITION, HYDRATION RATE

The objective of this study is the characterization and evaluation of slags from different sources by their chemical composition, glass content, rate and total heat of hydration and compressive strength development with a view to establish a relationship between some of their properties and compressive strength. Materials A Canadian (Hamilton, Ontario) pelletized blast furnace slag, an American (Sparrow's Point) granulated blast furnace slag and a Canadian (Sault Ste. Marie, Ontario) granulated blast furnace slag were identified as blast furnace slags A, B and C, respectively. Ordinary portland cement Type i0 CSA was used for the proportioning of the binders. Experimental Methods Chemical analysis The slag samples were analysed by inductively coupled argon plasma spectrometr~ SO 3 was determined by a wet technique. Loss on ignition was determined as well. Glass content Glass content was determined by a Quantitative X-ray diffraction method (QXRD) whereby the combined amounts of the crystalline phases enables, indirectly, the calculation of the glassy content by difference. The mass present for each crystalline phase is computed from the characteristic peak intensity of the crystalline phase as a ratio to the peak intensity of an added internal standard. The mass fraction of each phase is then determined by comparison of the intensity ratio in the sample to the intensity ratio for pure synthetically produced phases (4,5). Heat evolution rate A conduction calorimeter as developed by Forrester (6) was us@d to determine the rate of heat evolution and the total heat evolved during the first three days of hydration, since approximately 50 per cent of the total heat evolution occurs during that time (7). Samples with 35 per cent portland cement replaced by blast furnace slag were prepared with slags A, B and C. Slag C was tested at specific surfaces of 4000 and 6000 cm2/g (C 1 and C 4) determined by the Blaine method. Mixes with 50 per cent portland cement replaced by blast furnace slag were tested as well For comparison purposes, heat evolution rates of mixes of portland cement incorporating 35 and 50 per cent sand, respectively, were also determined. Slag activity index Mortars incorporating 50 per cent blast furnace slags A, B and C were prepared for testing according to ASTM C 989. Slag C, ground to 4000, 5000, 5500 and 6000 cm2/g (CI, C2, C 3 and C4) , was tested. Compressive strength was also determined on a control sample with I00 per cent portland cement. For another series of tests, compressive strength of mortars incorporating i00 per cent slags were also determined.

664

Vol. 16, No. 5 E. Douglas and R. Zerbino

Results Table i shows the chemical composition of the slags and the cement. The high MgO content of approximately 19 per cent has to be noted in sample C. X-ray diffraction analysis failed to detect any periclase. Consequently, it was assumed that MgO was in the form of a calcium-magnesium alumino glass.

TABLE i.

Chemical Composition, weight percent

Material

A B C4

slag slag slag cement

Chemical Composition of Materials

SiO o

AI203

Fe203

38.8 35.1 38.0 21.6

6.55 9.34 8.74 3.43

1.30 0.98 0.55 2.93

CaO

MgO

Na20

K20

TiO 2

P205

SO 3

LOI

35.1 40.1 32.0 63.5

12.1 9.62 18.6 3.09

0.37 0.18 0.22 0.47

0.47 0.22 0.76 0.50

0.30 0.34 0.36 0.17

0.02 0.02 0.01 2.07

3.30 2.90 2.45 2.81

0.84 1.84 1.98 1.28

Table 2 shows the glass content of slags A, B and C, determined by QXRD as described above. Values were slightly higher for sample C. Table 3 present values of specific surface by the Blaine method and the percent retained on sieve No. 325 (45 ~m), by the wet method. Heat evolution rate curves of portland cement incorporating 35 or 50 per cent slags are shown in Fig. i and 2, respectively. In mixes incorporating 35 per cent slag a similar height of the second peak of reaction can be found.

TABLE 2.

Slag A

Glass Content of Slags Determined by QXRD

Glass content (%) 88.3

B

88.1

C

90.3*

*mean value of measurements on sample C ground to C1, C2 and C4 s i z e s ,

Mixes of portland cement incorporating 35 or 50 per cent sand were also tested to study the effect of portland cement dilution in the portland cement-slag binders. It can be seen that for the portland cement-sand samples the curves of heat evolution rate are the lowest ones, reaching the portland cement-slag curves only after 36 hours hydration in both cases, showing the contribution of the portland cement to the heat evolution rate. The total heat evolved during the first 72 hours of hydration for portland cement and for mixes incorporating 35 or 50 per cent slags is shown in Table 4. The total heat evolved in the portland cement-sand mixes is also shown for comparison purposes. It can be seen that the total heat evolved in the

Vol. 16, No. 5

665 SLAG, GLASS CONTENT, COMPOSITION, HYDRATION RATE

portland cement-sand mixes is approximately 65 and 50 per cent, resp of that of the control with i00 per cent portland cement.

TABLE 3.

Material

ively,

Fineness Analysis of Blast Furnace Slags

Pass sieve 45 ~ m %

Specific surface area (cm2/g) Blaine method

A slag B slag C 1 slag C 2 slag C 4 slag G cement

83 99 93 97 98 90

4176 5400 3700 4620 6080 3780

An analysis of the total heat evolved in mixes of portland cement incorporating 50 per cent slags (Table 4 and Fig. 2) shows that the second highest value is given by the portland cement incorporating granulated slag B. A shoulder in the curve of the same binder after the second peak, indicates the contribution of slag B to the hydration reactions after 12 hours hydration.

TABLE 4.

Total Heat of Hydration in Mixes Incorporating Blast Furnace Slag

Addition

(%)

Total heat evolved (j.g-l)

none slag slag slag slag sand slag slag slag slag sand

A B CI C4

A B C1 C4

2nd hydration peak Time (hours)

Value (J.g.-l.s-l)

0 35 35 35 35 35

334 247 250 265 265 212

10.6 9.7 9.7 9.9 10.2 9.7

34.6 20.0 25.0 22.7 24.1 19.1

50 50 50 50 50

210 269 214 224 161

10.2 i0.i 8.8 9.2 9.2

19.1 20.9 16.4 20.0 14.0

An indication of the degree of hydration is given by the time of occurrence and height of the second peak of the heat evolution rate curve (8). It has to be noted (Table 4) that the time of occurrence of the second peak is slightly shorter for all slags, indicating an acceleration of the hydration reactions. As expected, the height of the peak of the samples of portland cement incorporating inert sand are the lowest.

666

Vol. E. D o u g l a s

100

1

16, No. 5

and R. Zerbino

I

I

I

I

I

!

o

80 ¢n

100%

-.j

u;

CEMENT

35% SAND

60

.....

n-

35% SLAG A 35% SLAG B

Z 0

40

35% SLAG CI 35% SLAG C4

0 LU

20

ILl

12

24

36

48

60

72

T I M E , hours

Fig.

1 - Heat evolution rate in mixes of OPC i n c o r p o r a t i n g f u r n a c e slag.

100

i

l

!

I

35% blast

I

I

,,¢ I

o x

80

O)

100% CEMENT t-.<

50% SAND

60

50% SLAG A 50% SLAG B 40

~

50% SLAG CI

2o

=J

I

I

I

I

I

t

12

24

36

48

60

72

TIME, hours

Fig. 2 - Heat e v o l u t i o n rate in mixes of OPC i n c o r p o r a t i n g f u r n a c e slag.

50% blast

Vol. 16, No. 5

667 SLAG, GLASS CONTENT, COMPOSITION, HYDRATION RATE

1

35%

I

I

I

I

I

REPLACEMENT .CEMENT 100%

300

.~

SLAG SLAG

S~LSLAG j"

< uJ -r

200

jJ

..J .< IO I-

~/// ,"

jf

f

J

t"

SLAG

C~ C1 . A

.... 8 A N D

J

j jr f

/

100

/

l 12

I 24

I 36

,

I 48

; 60

I 72

TIME, hours

Fig. 3 - Cummulative heat evolution in portland cement-slag binders incorporating 35% slags.

Cumulative rates of heat evolution are shown in Fig. 3 and 4. All slags have values distributed between the curves for portland cement and portland cementsand samples. Increasing differences can be observed in the samples with 50 per cent replacement level (Fig. 4); higher cumulative heat evolution is presented for slag B; slag C I has less activity than slag C 4 and slag A has in general a lower heat evolution. Compressive strength values of mortars prepared according to ASTM C 989 are shown in Table 5. Slag activity index at 7 and 28 days are also shown. In another series of tests compressive strength as a function of time was measured in portland cement mortars incorporating 50 per cent blast furnace slag C2, according to ASTM C989. The slag had been ground to 5000 cm2/g (Blaine method). Tests on mortars with i00 per cent portland cement and with I00 per cent blast furnace slag were also conducted (Table 6). The results

668

Vol. 16, No. 5 E. Douglas and R. Zerbino

I

|

50%

I

I

I

I

REPLACEMENT

CEMENT 100% 300 SLAG B O~

,¢

ILl -I-

.~SLAG C4 / SLAG C1 f-~ SLAG A

/

200

..J

< I-O I-

/SANO

/ /f". 100

I/,,;, d,'"

i

I

t

i"

J

i"

...I

/,';'i" / / ,,~,/ / / I 12

I 24

I 36

1 48

I 60

I 72

TIME, hours

Fig. 4 - Cummulative heat evolution in portland cement-slag binders incorporating 50% slags.

of compressive strength tests on mortars with i00 per cent blast furnace slag C 2 show that this slag has hydraulic properties, with values corresponding to 15 per cent of those found for the control sample.

Discussion Glass content is considered an important factor in relation with slag activity. In this case it is shown that, regardless of the very similar glass content, the slags behave differently. Comparison of the rate of heat evolution curves shows that the height of the second peak is higher for the portland cement-slag mixes than for the portland cement-sand mixes, indicating that the slags contribute to the heat of hydration from the beginning of the reaction. The heat evolved in the

Vol. 16, No. 5

669 SLAG, GLASS CONTENT, COMPOSITION, HYDRATION RATE

TABLE 5.

Slag Activity Index of Blast Furnace Slags (ASTM C 989)

Compressive strength (MPa)

Sample

Control A B C1 C2 C3 C4 Note:

Note:

TABLE 6.

Slag activity index

7d

28d

7d

26.8 16.5 27.8 18.1 18.7 20.3 21.7

31.4 27.7 39.5 28.6 31.4 35.9 36.2

i00 61.6 104.1 67.5 69.8 78 81

Sample A: B: CI: C9: C3: C4:

Canadian American Canadian Canadian Canadian Canadian

28d i00 88.2 125.8 91.1 i00.0 103 115.3

pelletized granulated granulated, ground to 4000 cm2/g granulated, ground to 5000 cm2/g granulated, ground to 5500 cm2/g granulated, ground to 6000 cm2/g

(Blaine) (Blaine) (Blaine) (Blaine)

Average of three values

Compressive Strength and Slag Activity Index of a Binder of OPC and a Canadian Granulated Slag (C 2) Ground to 5000 cm2/g (Blaine)

Sample

Control 50% replacement 100% replacement

Compressive strength 7d

28d

28.0 18.8 3.9

37.2 32.5 7.1

Slag activity index 7d i00 67.1 . .

28d I00 108.3 .

.

first 72 hours gives a trend of a classification according to reactivity that could be used for comparative purposes. Evolution of total heat with time at 50% replacement level ha~ an order similar to the one presented by compressive strength tests (Table 4 and 5). Particularly for the sample incorporating 50 per cent slag, the classification obtained according to the cummulative heat of hydration follows the same pattern as the one obtained from slag activity indexes. Concludin$ remarks i. Binders with 50 per cent portland cement replaced by slag present the same classification derived from total heat evolved as from slag activity indexes. 2. Measurements of cummulative heat evolved during the first 24 hours of the hydration process indicate that this parameter is related to the degree of reactivity of the slag. 3. The results of this study show that glass content is not directly related to slag reactivity.

670

Vol. 16, No. 5 E. Douglas and R. Zerbino

References i. M. Regourd, Panel discussion, 7th International Congress on the Chemistry of Cement, Vol. 4, 74, Paris (1980). 2. P. Fierens, Panel discussion, 7th International Congress on the Chemistry of Cement, Vol. 4, 75, Paris (1980). 3. J.G.M. de Jong, Silicates industriels, (1977-1). 4. H.P. Klug and L.E. Alexander, X-ray diffraction procedures for polycrystalline and amorphous materials. Jo~in Wiley & Sons (1954). 5. R.D. Hooton, Pelletized slag cement: hydraulic potential and autoclave reactivity, Ph.D. Thesis, McMaster University, Hamilton, Ontario, Canada, (1981). 6. J.A. Forrester, Cement Technology, 95-99, May-June (1970). 7. M.A. Smith and J.D. Mathews, Cem. Concr. Res. 4, 45-55 (1974). 8. D.M. Roy and G.M. Idorn, ACI Journal ~(6), 444-457 (1982). 9. B.J. Dagleish, A. Ghose, H.M. Jennings and P.L. Pratt, International Conference on Concrete at Early Ages, Vol. I, 137-143, Ecole National des Ponts et Chauss6es, Paris (1982).