Table 56. Varying The Granulometric Composition Of River Sand. Effect On Value Of, For Use In Cement Mortar

Composition of Sand as to Fineness.

Tensile Strength, Pounds per Square Inch.

Parts Used that Passed No. 20 Sieve and Retained on

No. 30.

Parts Used, 30-40

Parts Used that Passed No. 40

Sieve.

Portland Cement with Two Parts Sand to One Cement by Weight, at age of

Natural Cement with Three Parts Sand to One Cement by Weight, at age of

M

F

V

28 da.

6 mo.

lyr.

2yr.

28 da.

6 mo.

1 yr.

2 yr.

10

0

0

342

471

560

591

77

267

348

341

4

1

5

300

448

515

507

77

237

304

319

2

4

4

290

425

494

503

79

278

291

325

1

3

6

246

384

455

442

46

222

234

251

1

2

7

271

366

456

438

67

226

247

251

Note. River sand, mostly quartz, obtained at Point aux Pins. Each result mean of five briquets, all made by one molder.

262. Effect Of Moisture

The effect of a small amount of moisture on the bulk of a given weight of sand is not usually appreciated, but it may easily be shown that it is very marked. The results in Table 57 were obtained by adding small amounts of water to a given bulk of dry sand. Each time, after the water was added, the sand was stirred up and the weight of a given volume of the moist sand was obtained. It appears that the finer sands are affected more than coarse ones.

In the case of the limestone screenings 40-80, if we add but 3.7 per cent, water to a given quantity of dry sand, the bulk of the sand is so increased that if we take 1,000 c.c. of the, moist sand it will contain but 720 c.c. of dry sand. The voids are, of course, correspondingly increased from 54.5 per cent, to 67.2 per cent.

The cause of this increase in bulk is that each grain of sand is surrounded by a film of water which prevents the grains from lying close together after they have been disturbed. A large amount of air is also imprisoned in the mass. It may be noticed that the difference in bulk between moist and dry sand is greater when the measurements are made " loose".

Table 57. Volume Of Sand And Voids As Affected By The Addition Of Water

Ref.

Sand.

water

Expressed as Per Cent of Dry Sand by Weight

Weight of Dry Sand in One Liter of Moist Sand.

volume of Dry Sand in One Liter of

Moist Sand.

Percent. Voids in Sand by

volume.

kind.

fineness.

loose, grams.

shaken, grams.

loose, cu. cent.

shaken, cu. cent.

loose.

shaken.

a

b

c

d

e

f

g

h

i

Crushed

1

Limestone.

10-20

0.0

1288

1489

1000

1000

2

"

"

4.8

1094

1367

849

919

. .

3

"

"

7.7

1023

1295

794

869

4

"

"

11.9

996

1276

773

857

. .

.

5

"

40-80

0.0

1214

1481

1000

1000

54.5

44.5

6

"

"

0.85

1124

1489

926

1005

57.9

44.2

7

"

"

1.5

1059

1470

872

993

60.3

44.9

8

"

"

2.2

950

1383

782

934

64.4

48.2

9

"

"

3.7

875

1298

720

877

67.2

51.4

10

"

"

6.3

824

1274

679

860

69.1

52.8

11

"

"

7.8

799

1266

658

855

70.0

52.6

12

"

"

12.3

817

1280

672

864

69.4

52.0

13

"

"

16.8

829

1306

683

881

69.0

51.1

14

"

"

20.2

836

1274

689

860

68.6

52.3

15

"

"

25.3

891

1357

783

916

66.6

49.1

16

"

"

30.3

1049

1270*

864

858*

. .

. .

17

"

Pass 80

0.0

1185

1500

1000

1000

. .

. .

18

"

"

2.4

1038

1394

873

929

. .

. .

19

"

"

5.1

835

1281

704

854

. .

. .

20

"

"

12.2

806

1310

680

873

. .

. .

21

"

Point aux

"

17.7

806

1260

680

840

. .

. .

22

Pins.

0.0

1725

. .

1000

. .

. .

. .

23

"

2.0

1405

. .

815

. .

. .

. .

24

"

4.0

1400

. .

810

. .

. .

. .

25

"

6.0

1400

. .

810

. .

. .

. .

26

"

10.0

1415

. .

820

. .

. .

. .

27

"

11.6

1425

. .

825

. .

. .

. .

28

"

18.4

1485

. .

860

. .

. .

. .

* Not jarred down in measure as much as usual. water rose to surface, Sand crumbled like damp earth.

Sieves No.

Fineness of Point Approx. size aux Pins Sand holes =

Percent, passing

20

30

40

50

80

.033

.022

.017

.012

.007

96.0

82.3

46.6

6.7

1.2

Note. 10-20 = passing No. 10 sieve (holes about .08 in. sq.) and retained on No. 20 sieve.

263. This subject is of great importance in proportioning mortars, because, in construction, the amounts of cement and sand are usually measured. Suppose it is desired to use a mixture of one hundred pounds of cement to four hundred pounds of sand, and for convenience we will suppose the packed cement and dry sand each weigh one hundred pounds per cubic foot. If now we use damp sand, containing about 3.5 per cent, water, instead of dry sand, and measure the materials, we would have four cubic feet of damp sand to one cubic foot of cement; but damp sand would contain only about 4 X 75 = 300 pounds of dry sand, and we would really have a one-to-three mixture instead of a one-to-four.