456. Deposition In Running Water

A few tests were made to show the effect of depositing concrete in rapidly running water. The molds were placed in the stream and weighted down in twelve inches of water. The concrete for two bars was deposited as soon as mixed, that for two other bars was allowed to stand in the air three hours before deposition, until it should have acquired an initial set, and two bars were made after the mortar had been allowed to stand five hours and twenty minutes before deposition; by this time the mortar had set quite hard. No attempt was made to ram the concrete, which was deposited by lowering it carefully into the water with shovels, the molds being filled as rapidly as possible. A very large amount of the cement was washed out by the current in all cases. After a few months the bars were removed from the stream and covered with earth as usual. The tests at eleven months did not appear to show any advantage in allowing the mortar to stand some time before deposition, but the tests at two years showed a distinct advantage in this treatment.

457. Use Of Concrete In Freezing Weather

Table 157 gives the results obtained with Portland cement concrete made in the open air during cold weather. The conditions as to temperatures and the character of the materials are fully given in the table. The experiments are too limited to permit of drawing definite conclusions, but the following points are indicated by the results obtained. The use of warm water, 100° to 156° Fahr., in freezing weather appears to give somewhat better results than cold water. Salt should not be used unless the temperature is below the freezing point, but in very cold weather the use of enough salt in the water to lower its freezing point below the temperature of the air seems to hasten the hardening as well as to increase the ultimate strength. (For tests of mortars in freezing weather, see Art. 50).

Table 157. Transverse Tests Of Concrete Bars. Use Of Concrete In Low Temperatures

Date Made.

Proportions in Concrete.

Temperatures. Dec Fahr.

Per Cent.

No.

Tests.

Age.

Modulus Rupture.

Remarks.

Cement, Lbs.

Sand, Lbs.

Stone Loose, Cu. Ft.

water, Cu. Ft.

Air When Moulded.

water Used.

Salt in water.

4 ft. Span.

20 in. Span.

Mo. Da. Yr.

Mos.

2 12 94

135

270

7.32

0.90

9

40

...

1

1

16

30

202

188

a a

" " "

"

"

"

44

8

100

...

1

2

16

30

245

224

b b

" " "

"

"

"

0.84

12

156

...

1

2

16

30

227

242

c c

2 18 94

"

"

"

0.84

8

40

...

1

1

16

30

223

318

d d

" " "

"

"

"

...

12

44

12.5

1

2

16

30

273

419

e e

" " "

"

"

"

...

9

40

18.75

1

2

16 30

351

333

e e

11 12 94

120

240

7.00

0.80

27

...

...

2

4

10

20

332

351

...

" " "

"

"

"

44

27

...

10

2

1

10

20

326

417

...

12 0 94

"

"

"

0.74

27

34

...

2

3

9 20

433

559

...

" " "

"

"

"

0.68

85

35

10

2

4

9 22

386

517

...

12 18 94

"

"

"

4 4

88

37

...

2

3

9

22

447

570

...

" " "

"

"

"

4 4

34

40

10

2

3

9 22

385

429

...

1 5 95

"

'

"

0.74

14

32

...

2

1

8

21

(82)

487

...

" " "

"

"

"

0.68

18

40

14

2

4

8

21

311

460

...

3 9 95

60

120

3.5

0.33

12

...

...

1

2

19

26

206

238

...

" " "

"

"

"

"

15

...

5

1

2

19

28

301

380

...

" " "

"

"

"

"

20

...

12

1

2

19

26

376

451

...

" " "

"

"

"

"

27

165

12

1

2

19 26

288

458

...

Remarks: — a, Concrete frozen after 10 to 20 min.; b, frozen in 45 min.; c, began to freeze in 15 min.; d, frozen hard following morning after molding; e, concrete still soft 9 a.m. morning after molding; f, bar defective.

Notes:—Cement, Portland, Br. R. Sand, " Point aux Pins." Stone, Potsdam sandstone.