e to h, stored in open air, January, Northern Michigan. water used: a and e, 10.4 per cent, fresh water.

b and f, 11.9 per cent, fresh water. c and g, 13.3 per cent, fresh water. d and h, 11.9 per cent, water containing 15 per cent. salt.

396. Fineness Of Sand And Effect Of Frost

The briquets reported in Table 110 were made from mortar containing one and two parts limestone screenings to one cement, the screenings varying from coarse to fine. In general, the results follow the rule applicable to mortars used in ordinary temperatures, namely, that the coarse sands give the best results; but it appears that the briquets made with fresh water and exposed in open air reverse this rule, either the finest sand, 40/80, or the 20/40 giving the best result.

Table 110. Effect Of Degree Of Fineness Of Sand On Ability Of Portland Cement Mortars To Withstand Low Temperatures

Ref.

Parts

Limestone screenings to one cement by weight.

Sample portland cement, brand R.

Temp.

air where briquets made,

DeG. Fahr.

Per cent.

salt in water used in

Gaging.

Date Made.

Briquets Stored.

Tensile Strength, Pounds per Square Inch.

Briquets Broken Dry. or Immersed Some Hours Just Before Breaking.

Fineness of Limestone Screenings Retained between Sieves

4 and 10.

20 and 40.

40 and 80.

Pass 10.

Mo. Da.

1

1

JJ

15-18

0

2 15

Open air

494

826

855

695

Broken dry.

2

1

"

"

"

"

"

367

572

604

524

Immersed 19 hrs.

3

1

"

12-13

14

2 19

"

738

781

666

687

Broken dry.

4

1

"

"

"

"

"

675

591

523

534

Immersed 48 hrs.

6

2

GG

16-18

0

2 15

"

440

762

642

515

Broken dry.

6

2

"

"

"

"

"

378

572

536

453

Immersed 19 hrs.

7

2

"

12-14

14

2 19

"

721

697

550

532

Broken dry.

8

2

"

"

"

"

"

533

483

343

413

Immersed 48 hrs.

0

1

"

13-20

0

2 14

Canal

686

634

583

687

Broken wet.

10

1

JJ

"

18

2 16

"

668

726

634

689

"

11

2

GG

13-21

0

2 14

"

544

452

393

351

"

12

2

"

10-12

18

2 16

"

685

659

516

624

"

Notes. Cement, Portland, Brand R. Sand, limestone screenings, sifted as indicated. Materials used, 40° Fahr.

Briquets made with fresh water raised in molds.

Briquets left three days where made in warehouse before storage.

Age of briquets when broken, six months.

397. Conclusions

The following conclusions concerning the use of cement mortars in freezing weather appear to be indicated by the foregoing tests:

1st

Mortars should not be mixed wet for use in low temperatures.

2d

Portland cement mortars made in cold weather usually develop a good tensile strength, especially when exposed to the open air.

3d

Portland cement mortars for open air exposure may be benefited by the use of from three to seven per cent, salt in the water used in gaging, and from ten to twenty per cent, salt in the gaging water may prove beneficial for mortars hardening in cold water.

4th

Warming the materials for Portland cement mortar appears to have but little effect on its frost resisting qualities.

5th

Coarse sand usually gives the best results in Portland mortars made in cold weather, but fresh water briquets exposed in open air appear to give better results with fine sand.

6th

Some natural cements give fairly good results in freezing weather, while others are practically destroyed by severe exposure. The effect of variations in treatment on different brands of natural cement is so varied that no general conclusions can be drawn from the above tests, but the indications are that salt water for gaging is beneficial if the mortar hardens in cold water, but detrimental for mortars exposed to the open air.