11. Slag cement is manufactured to a considerable extent in Europe and is beginning to assume some importance in the United States. It is a pozzolana cement in which the silica ingredient is supplied by blast furnace slag. Pozzolana cements have been defined as "products obtained by intimately and mechanically mixing, without subsequent calcination, powdered hydrates of lime with natural or artificial materials which generally do not harden under water when alone, but do so:

Table 2. (Continued) Analyses Of Portland Cement

No.

Si02.

A1203.

Fe203.

CaO.

MgO.

Na2O, K20.

so3.

H20 & Loss.

1

20

26

8

.62

2

71

63

22

2

34

1.34

0

76

2

22

62

8

76

2

66

61

46

2

92

1

52

3

24

90

8

00

3

22

59

38

0

38

0.50

0

98

2.16

4

21

30

7

65

2

85

60

95

2

95

1.15

1

81

1.41

5

22

90

6

80

3

60

63

90

0

70

1.10

0

40

0.60

6

21

30

6

95

2

00

62

30

1

20

0

98

4.62

7

23

72

6

85

3

41

61

54

1

44

1

72

0.90

8

23

44

6

35

3

99

63

21

1

15

1

22

9

21

24

7

85

4

14

63

22

0

28

0.68

1

11

1.32

10

19

35

7

00

4

50

63

75

5.40

11

20

14

7

51

3

33

62

71

2

34

1

64

12

22

04

6

45

3

41

60

92

3

53

2

25

13

21

14

6

30

2

50

66

04

1

11

2.91

14

23

36

8

07

4

83

58

93

1

00

0.50

0

50

2.46

15

21

60

9

27

3

80

61

78

1

27

1

53

16

21

50

10.

50

63

50

1

80

0.40

1

50

0.80

17

19

75

7

48

5

01

60

71

1

28

0.75

0

97

3.38

18

22

26

9.

49

62

46

2

65

1

56

19

23

20

7

03

2

41

64

19

0

97

2.20

20

22

06

4

80

1

66

65

44

3

82

0

90

21

19

06

7

47

2

29

61

23

2

83

1.41

1

34

4.52

22

21

18

7

03

2

41

63

06

2

05

23

21

20

7

90

2

82

63

14

2

40

1

37

24

22

24

7

26

2

54

64

96

2

26

0

41

0.33

25

20

30

7

60

3

40

62

60

1

70

1.70

1

30

1.10

26

20

54

8

55

3

84

63

85

0

66

1.34

27

21

25

8

25

4

21

61

25

1

50

2.00

1

38

28

23

62

8

21

2

71

61

92

1

78

1

32

0.52

29

21

08

7

86

2

48

63

68

2

62

1

25

30

21

22

7

51

3

83

63

75

0

82

1

58

1.02

31

23

20

8

00

2

40

62

10

2

00

0

90

0.80

32

22

00

7

74

4

61

59

50

0

90

1.20

0

80

When mixed with hydrates of lime (such materials being pozzolana, Santorin earth, trass obtained from volcanic tufa, furnace slag, burnt clay, etc.), the mixed product being ground to extreme fineness." 1

Slag cement somewhat resembles Portland in its properties, but is more like some of the natural cements in its constituents, while in the manner of occurrence of these constituents and in the method of manufacture it is quite different from either of these classes.

1 "Report of Board of Engineers on Steel Portland Cement," Washington, 1900.

12. As this cement is a mixture of lime and pozzolanic materials, its value depends largely upon its extreme fineness and the intimate mixture of the ingredients. Its specific gravity is low, about 2.7 to 2.8, and it sets very slowly, although the setting may be hastened by the addition of certain substances such as caustic soda. On account of the sulphide present, most slag cements are not suited to use in air, as they crack and soften in this medium; neither are they suitable for use in sea water, nor in freezing weather, but when mixed with two or three parts of sand and kept constantly wet with fresh water, they give quite satisfactory results.

Slag cement has an approximate composition of silica, 20 to 30 per cent., alumina, 10 to 20 per cent., and lime, 40 to 50 per cent. It usually contains calcium sulphide, the amount sometimes reaching three or four per cent. The characteristic greenish tint which slag cements exhibit when they harden in water is due to this ingredient, as is the odor of hydrogen sulphide sometimes given off by a briquet when broken, especially if it has hardened in sea water. Some slag cements have also quite a percentage of magnesia.1