1 In computing adhesion, or shear, or pounds pull per square inch of area in contact, perimeter considered circumference of a circle of diameter equal to the distance between opposite edges of rod after twisting. A core of mortar of this diameter, was torn from bar in pulling.

To perceive effect twisting, compare pounds pull per inch depth imbedded.

Table 125. Resistance To Pulling Of Iron Rods Imbedded In Mortar. Variations In Depth Imbedded And In Richness Of Mortar

Parts Sand to

One Cement.

Adhesion, Pounds per Square Inch of Surface in Contact for Different Depths Imbedded.

Depths Imbed-ded.ln

1.9-2.2

3.2

4

4.5-4.8

5.8-6

7.8-8

8.8

9.6-10

No. Results.

Mean.

0 2 4

....

....

....

340 272 74

...

294

...

346 270 119

...

262

...

313 255 117

...

247 100

228

...

...

340 275 142

5 15 10

313 264 111

Notes : Cement, Portland, Brand R.

Sand, "Point aux Pins," river sand. Mortar one month old when rods pulled. Rods, round, 1 inch diameter.

417. Tables 126 and 127 are from similar tests made by Messrs. Peabody and Emerson.1 The rods in Table 126 were of various shapes and included some having rivets through them. The 1/4 inch by 1 inch bars gave lower adhesion per square inch than the square and round rods. When two rods are twisted together and imbedded in a small specimen, the tendency is to split the specimen. The bars containing rivets broke before the adhesion was overcome, although the depth imbedded was but six inches.

In Table 127 neat cement paste and concretes of several compositions are tried. These results are of interest as showing that concretes show as great adhesion to steel rods as do mortars. The very low result obtained with neat cement in this table is not explained and is in opposition to the results in Table 125.

1 Engineering News, March 10, 1904.

Table 126. Adhesion Of Mortar To Steel Rods Of Various Shapes, Imbedded About Six Inches

No.

Perimeter

Pounds Pull.

of

Tests.

Description of Rod.

of Rod, Inches.

Per Inch Depth Imbedded.

Per Square Inch Area in Contact.

4

3 4 4 4

Plain, 1/4" square. Plain, 1/2" square. Plain, 1/2" round. Twisted, 1/2" square. 1/4" by 1 ".

1.0 2.0 1.57

...

2.5

369 864 804 1259 744

369 432 512

...

293

4

Two 1/4" rods twisted together.

Three specimens split.

One rod broke at 8,000 lbs., or when adhesion was 1,250 lbs. per inch depth.

4

1/4" by 1" with 3/8" rivets through.

One specimen split.

Three rods broke at first rivet with 9,800 to 10,500 pounds, or when adhesion was 1,500 to 1,660 lbs. per inch depth.

Notes: Tests by Messrs. George A. Peabody and Samuel W. Emerson.

Mortar composed of one part cement (Portland) to three parts sand. Specimens approximately 6 inch cubes. One rod imbedded in each, 6 to 6 1/2 inches. Rods pulled forty and eighty days after mortar was made.

Table 127. Adhesion Of Mortars And Concretes Of Various Compositions To One Inch Square Steel Rods Imbedded About Ten Inches

No.

of TEST8.

Composition of Mortar or Concrete.

Pounds Pull.

Per Inch Depth Imbedded.

Per Square Inch Area in Contact.

Cement.

Sand.

Stone.

Gravel.

4

1

0

0

0

1112

278

4

1

3

0

0

1644

411

4

1

3

6

0

1912

478

4

1

3

0

6

2062

516

4

1

2

4

0

2348

587

4

1

2

0

4

2187

547

Note: Tests by Messrs. George A. Peabody and Samuel W. Emerson.