Materials

a Hammered bar iron.

b Potsdam sandstone, cleavage surface.

c Drummond Id. limestone, cleavage surface.

d Ground plate glass.

e Kelleys Id. limestone, sawn surface.

f Soft terra cotta, filed surface.

g Soft red building brick, sawn surface.

403. The Adhesion Of Neat And Sand Mortars

Table 115 shows the cohesive and adhesive strengths of different mortars, the adhesion blocks being all of the same material, Kelleys Island limestone. The Portland mortar giving the highest adhesive strength at six months is that containing one-half part sand to one part cement, though the greatest cohesive strength is given by the one-to-one mortar. With natural cement the one-to-one mortar gives the highest strength, both in adhesion and cohesion. The ratio of the adhesive strength to the cohesive strength is greater for natural than for Portland. It also appears that between twenty-eight days and six months the adhesive strength increases more than the cohesive strength.

404. Effect Of Consistency On Adhesion

Table 116 gives the results of tests to show the relative effects of the consis-. tency of the mortar on the adhesive and cohesive strength. It is seen that the effect of consistency on the adhesive strength is less than on the cohesive strength, but that the best results in adhesion are given by a mortar that is considerably more moist than that which gives the highest strength in cohesion. The practical bearing of this point on the use of mortars is evident.

Table 115. Adhesion Of Mortars Containing Different Amounts Of Sand

Ref.

Cement.

Age of Specimens.

Cohesion or

Adhesion.

Cohesive or Adhesive Strength, Lbs.

per Square Inch, of Mortars with Sand, Parts by Weight.

None.

One-Half Part Sand.

One Part.

Two Parts.

Kind.

Brand.

1

Port.

R

28 days

Cohesion

686

710

747

467

2

"

"

"

Adhesion

270

233

221

169

3

"

"

6 mos.

Cohesion

631

787

816

551

4

"

"

"

Adhesion

335

346

287

209

5

Nat.

An

28 days

Cohesion

183

198

218

186

6

"

"

"

Adhesion

94

104

116

66

7

"

"

6 mos.

Cohesion

263

334

383

376

8

"

"

"

Adhesion

228

222

233

171

Notes : Sand, crushed quartz, 20 to 30.

Adhesion blocks, 1 in. X 1 in. X 1/4 in., Kelleys Id. limestone, sawn surface, saturated before used.

Table 116. Adhesion Of Mortars. Varying Consistency

Ref.

Cement.

Age of Specimens.

Cohesion or

Adhesion.

Cohesive or Adhesive Strength, Lbs.

per Square Inch, Mortar of Consistency:

Trifle

Dry.

Trifle

Moist.

Quite

Moist.

Very

Moist.

Kind.

Brand.

1

Port.

R

28 days

Cohesion

541

502

443

372

2

"

"

"

Adhesion

148

160

145

136

3

"

"

6 mos.

Cohesion

697

660

616

539

4

"

"

"

Adhesion

191

209

228

192

5

Nat.

An

28 days

Cohesion

239

212

151

112

6

"

"

"

Adhesion

96

96

87

70

7

"

"

6 mos.

Cohesion

397

385

314

285

8

"

"

"

Adhesion

146

165

164

126

Notes: Sand," Point aux Pins," pass No. 10 sieve, one part to one cement by weight.

Adhesion blocks, 1 in. X 1 in. X 1/4 in., Kelleys Id. limestone, surfaces filed smooth, saturated with water before used.

405. Effect Of Regaging On Adhesive Strength

The tests given in Table 117 were designed to show the effect of regaging on the adhesion of cement mortar to stone. A comparison is made between mortars used fresh and those that were allowed to stand three hours and gaged once an hour. There are but few tests from which to draw conclusions and the treatment is very severe, but it appears that while the regaging to which these mortars were subjected usually resulted in a slight increase in cohesive strength, the adhesive strength was considerably impaired. The decrease in adhesive strength was greater for natural cement than for Portland, and greater for rich than for poor mortars. The effect of regaging on the cohesive strength is treated in Art. 47.

Table 117. Effect Of Regaging On Adhesive Strength

Cement.

Adhesion or Cohesion.

Adhesion or Cohesion, Lbs. per Sq. In.

One Part Sand to One Cement.

Three Parts Sand to One Cement.

Fresh.

Regaged.

Fresh.

Regaged.

Portland, Brand X

Adhesion

178

141

62

41

"

"

202

170

59

61

"

Cohesion

718

764

327

343

Natural, Brand An

Adhesion

142

90

17

...

"

"

180

120

31

28

"

Cohesion

352

361

235

227

Notes: Sand, crushed quartz, 20/30. Each result, mean of two to five specimens, broken at age of six months.

In adhesive tests, pieces Kelleys Id. limestone, 1 in. X 1 in. X 1/4 in., placed in center mold and two ends mold filled with mortar.

Results in columns headed "Fresh" from mortar treated as usual.

Results in columns headed "Regaged" mortar allowed to stand three hours before use, mortar being regaged each hour.

406. Character Of Surface Of Stone

In the tests recorded in Table 118 all of the adhesion blocks were of Kelleys Island limestone, but part of them were finished with smooth filed surfaces, while the others were grooved with a coarse rasp. In the twenty-eight-day tests there is but little difference in the adhesion to the different surfaces, but at six months the adhesion to the smooth surfaces appears to be slightly greater, ex-cept in the case of one-to-two natural cement mortar.

Table 118. Adhesion Of Mortars. Effect Of Character Of Surface Of Stone

Cohesion or Adhesion and

Character of Surface.

Age of Specimens.

Adhesion or Cohesion, Lbs. per Sq. In.

Portland Brand R.

Adhesion or Cohesion, Lbs. per Sq. In.

Natural Brand D.

Parts Sand to One Cement.

1

2

1

2

Cohesion........

28 days

539

377

343

289

Adhesion, smooth surface . .

"

151

. 85

138

113

" grooved surface

"

152

115

129

98

Cohesion........

6 mos.

714

503

387

304

Adhesion, smooth surface . .

"

238

176

141

68

" grooved surface

"

223

154

115

96

407. The Effect Of Plaster Of Paris On The Adhesion Of Mortar To Stone

The results in Table 119 show the effect on the adhesive strength of adding small percentages of plaster of Paris to cement mortars of Portland and natural cement. The Portland cement used was a quick setting sample, neat cement pats of which began to set in eighteen minutes. The effect of plaster of Paris on the cohesive strength of mortars from these samples hardened in dry air, is shown in Table 92, § 378. It is seen that the addition of from one to three per cent, plaster has no deleterious effect on the adhesive strength of these samples at one year. Six per cent, plaster, however, ruins the Portland and the neat natural cement.

Table 119. Effect Of Plaster Of Paris On The Adhesive Strength Of Cement Mortars

Ref.

Cement.

Parts P.P. Sand to One Cement.

Age of Specimens.

Adhesive Strength, Lbs. per Sq. In., of Mortars in which Per Cent, of Cement Replaced by Plaster of Paris.

Kind.

Brand.

Sample.

0

l

2

3

6

1

Port.

R

26 R

0

1 year

263

311

376

291

89

2

"

R

"

2

"

130

107

144

157

34

3

Nat.

An

L

0

"

88

97

87

133

a

4

"

An

"

2

"

64

74

89

82

93

Notes : Adhesion pieces between two halves of briquet were of Kelleys Id. limestone, sawn surfaces, saturated with water before used. Cement and plaster Paris passed through No. 50 sieve. All briquets stored in tank in laboratory. Each result, mean of four to ten briquets.

Found badly cracked and separated from limestone prisms after three days.

408. The Adhesion Of Cement Mortar To Brick

Tests of the adhesion of cement mortar to brick were made by cementing pairs of brick in a cruciform shape, with a one-fourth inch joint of mortar. The brick were placed together flatwise, with the bed down, so that in the case of stock brick, one stock mark, or depression in one side, was filled with mortar. The mortar was made more moist than was ordinarily used for briquets, but not so moist as would be used in brickwork. The top brick of each pair was slightly tapped to place with the handle of a pointing trowel, and the excess mortar cut away. About forty-eight hours after cemented, the pairs of brick were packed in damp sand in a large box prepared for the purpose, and the sand was kept in a moist condition by a thorough daily sprinkling. For pulling the bricks apart, a special clip was devised to equalize the pull on the two ends of each brick, and a simple lever machine was used to measure the force required.