METHOD OF MAKING, PROTECTING, CURING

& TESTING CONCRETE CYLINDERS


 

SCOPE

 

This method covers procedures for making, protecting, and curing, according to AASHTO T23. This method also covers testing concrete cylinder specimens for compressive strength, according to AASHTO T22. This test procedure is a supplement and not a replacement for the beam test to determine when a structure may be put in service.

 

I.       MAKING, PROTECTING & CURING SPECIMENS

 

A.     Apparatus for Making Specimens

 

1.     6 in. x 12 in. or 4 in. x 8 in. steel, brass, or single-use plastic vertical molds meeting the requirements of AASHTO M205.

 

2.     Molds shall be the vertical type.

 

3.     Tamping rods shall comply with AASHTO T23 and the following:

 

Mold Size

Tamping Rod Diameter

4 in. x 8 in.

 

3/8 in.

6 in. x 12 in.

 

5/8 in.

 

4.     Internal or external vibrators may be used. They shall comply with AASHTO T23 with the exception that the diameter of the vibrating element of the internal vibrator shall vary for each specimen size, as stated below. External vibrators shall be either a table type or a plank type.

 

5.     Rubber hammer

 

6.     Wood float or equivalent

 

B.     Making Test Specimens

 

1.     The concrete shall be sampled in accordance with IM 327, Sampling Freshly Mixed Concrete.

 

2.     Before casting specimens, the inside surfaces of the steel or brass molds should be clean and treated with a thin coating of light grease or form oil.

 

3.     Consolidation may be rodding with a tamping rod, or by vibration, either internal or external. Concrete with slump greater than 3 inches shall be consolidated by rodding. Concrete with slump of 1 inch to 3 inches shall be consolidated by rodding or vibration. Concrete with slump of less than 1 inch shall be consolidated by vibration.

 

a.     Rodding. Specimens shall receive the proper number of roddings evenly distributed per layer as indicated in the table. The bottom layer shall be rodded throughout its depth. For each upper layer, the rod shall penetrate 1 inch into the underlying layer. After rodding each layer, the sides and ends of the mold shall be tapped with a rubber hammer until the surface of the concrete is relatively smooth. Use an open hand to tap the single-use molds. After consolidation, strike off the horizontal surface and finish with a float or trowel.

 

Mold Size

No. of Equal Depth Layers

No. of Roddings per Layer

4 in. x 8 in

 

2

25

6 in. x 12 in.

 

3

25

 

b.     Internal Vibration. Specimens shall receive the required number of insertions of a vibrator layer as indicated in the table. If more than one insertion is required, distribute the insertion uniformly in each layer. Each layer shall be vibrated only long enough to make the surface relatively smooth. The time required will vary with the consistency of the concrete. Over vibration may cause segregation. In compacting the concrete, the vibrator shall not rest on or touch the sides of the mold. When vibrating the top layer, the element shall penetrate about 1/2 inch into the bottom layer. After vibrating, tap the sides of the mold with a rubber hammer to ensure removal of entrapped air bubbles at the surface of the mold. Use an open hand to tap the single-use molds. When consolidation is complete, strike off and finish with a wood float or trowel.

 

Mold Size

Vibrator Diameter

No. of Equal Depth Layers

No. of Insertions per Layer

4 in. x 8 in

 

to I inch

 

2

1

6 in. x 12 in.

 

to I 1/2 inch

 

2

2

 

c.      External Vibration. Each layer shall be vibrated only until the surface is relatively smooth. Take care to ensure that the mold is rigidly attached or securely held against the vibrating table or vibrating surface. After consolidation, strike off and finish with a trowel or float.

 

C.    Protecting & Curing

 

1.     Initial Curing. During the first 24 hours after molding, specimens shall be stored under conditions that maintain the temperature immediately adjacent to the specimens in the range of 50F to 80F and prevent loss of moisture from the specimens. This may be done by covering specimens with wet burlap and placing a plastic sheet over the burlap, or use other suitable methods to ensure that the foregoing requirements are met.

 

2.     Curing to Determine Form Removal Time or When a Structure May be Put in Service. Cure test specimens as nearly as practicable in the same manner as the concrete in the structure. After 48 4 hours, remove specimens from the molds. They shall be stored as near as possible to the point in the structure they represent and shall be afforded the same temperature protection and moisture environment as the structure until the time of testing. Specimens shall be tested while in the moisture condition resulting from the curing they receive.

 

3.     Curing To Check the Adequacy of Laboratory Mix Proportions for Strength or As a Basis For Acceptance or For Quality Control. For this purpose, specimens are to be removed from the molds at the end of 16 to 24 hours and stored in a moist condition at 68F to 81.5F until the time of test. This condition can be met by immersion in saturated limewater. NOTE: Lime-saturated water is prepared by mixing 0.4 ounces of hydrated lime, with 1 gallon of water. Hydrated lime should be a minimum of 90 percent calcium hydroxide (CaOH).

 

4.     Steam Curing. When artificial heat is used to accelerate curing, concrete specimens shall be placed with the unit being cured and shall receive the same curing as the concrete they represent. Prior to testing the specimens, the temperature of the concrete shall be lowered to the temperature of the surrounding air at a rate not to exceed 40F per hour.

 

5.     Special care must be given to ensure that specimens are not damaged during handling. For 16 to 24 hours after molding, specimens shall not be moved.

 

II.     TESTING CONCRETE SPECIMENS FOR COMPRESSION

 

A.     Apparatus

 

1.     The testing machine shall conform to AASHTO T22. Manually operated testing machines will be accepted.

 

B.     Time of Testing

 

1.     Make compression tests of moist cured specimens as soon as practicable after removal from curing. Keep specimens moist by use of wet burlap or other suitable covering, which will ensure similar protection until actual time of testing.

 

2.     The time to test specimens otherwise cured will be as directed by the engineer.

 

C.    Test Specimens

 

1.     Neither end of compressive test specimens when tested shall depart from the perpendicularity to the axis by more than 0.5 degrees (approximately 1/8 in. in 12 in.)

 

2.     The ends of the specimens that are not plane within 0.002 in. shall be capped. The planeness of the ends of every tenth specimen should be checked by means of a straightedge and feeler gauge, making a minimum of three measurements on different diameters, to insure that the end surfaces do not depart from a plane by more than 0.002 in.

 

3.     The top surface of vertically cast specimens shall be capped.

 

D.    Capping

 

1.     Capping equipment and procedures shall comply with that described in AASHTO T231.

 

2.     Unbound caps and equipment shall comply with ASTM C1231.

 

E.     Test Procedure

 

1.     Placing Specimen

 

a.     Place the plain (lower) bearing block with its hardened face up, on the table or platen of the testing machine directly under the spherically seated (upper) bearing block.

 

b.     Wipe clean the bearing faces of the upper and lower bearing blocks and of the test specimen.

 

c.      Carefully align the axis of the specimen with the center thrust of the spherically seated block.

 

d.     As the spherically seated block is brought to bear on the specimen, rotate its moveable portion gently by hand so that uniform seating is obtained.

 

2.     Rate of Loading

 

a.     Apply the load continuously and without shock. Apply the load at a constant rate within the range of 20 to 50 psi per second. During the application of the first half of the estimated maximum load, a higher rate of loading may be permitted.

 

b.     Do not make any adjustment in the controls of the testing machine while the specimen is yielding, especially in the period just before failure.

c.      Increase the load until the specimen yields or fails, and record the maximum load carried by the specimen during test.

 

d.     Note the type of failure (Figure 1) and the appearance of the concrete if the break appears to be abnormal.

 

F.     Calculations

 

1. Calculate the compressive strength of the specimen by dividing the maximum load carried by the specimen during the test by the cross sectional area, and express the result to the nearest 10 psi. The attached tables may be used to facilitate these computations.

 

Figure 1. Compressive Fracture Types

 

Figure 2. Compression Testing Machine


 

 

(Load in Thousands) Table for Computing lb./in. on 6 in. x 12 in. Cylinders

Area = 28.2744 in.

Load

Psi

Load

Psi

Load

Psi

Load

Psi

Load

Psi

40

1410

90

3180

140

4950

190

6720

240

8490

41

1450

91

3220

141

4990

191

6760

241

8520

42

1490

92

3250

142

5020

192

6790

242

8560

43

1520

93

3290

143

5060

193

6830

243

8590

44

1560

94

3320

144

5090

194

6860

244

8630

45

1590

95

3360

145

5130

195

6900

245

8670

46

1630

96

3400

146

5160

196

6930

246

8700

47

1660

97

3430

147

5200

197

6970

247

8740

48

1700

98

3470

148

5230

198

7000

248

8770

49

1730

99

3500

149

5270

199

7040

249

8810

 

 

 

 

 

 

 

 

 

 

50

1770

100

3540

150

5310

200

7070

250

8840

51

1800

101

3570

151

5340

201

7110

251

8880

52

1840

102

3610

152

5380

202

7140

252

8910

53

1870

103

3640

153

5410

203

7180

253

8950

54

1910

104

3680

154

5450

204

7220

254

8980

55

1950

105

3710

155

5480

205

7250

255

9020

56

1980

106

3750

156

5520

206

7290

256

9050

57

2020

107

3780

157

5550

207

7320

257

9090

58

2050

108

3820

158

5590

208

7360

258

9120

59

2090

109

3860

159

5620

209

7390

259

9160

 

 

 

 

 

 

 

 

 

 

60

2120

110

3890

160

5660

210

7430

260

9200

61

2160

111

3930

161

5690

211

7460

261

9230

62

2190

112

3960

162

5730

212

7500

262

9270

63

2230

113

4000

163

5760

213

7530

263

9300

64

2260

114

4030

164

5800

214

7570

264

9340

65

2300

115

4070

165

5840

215

7600

265

9370

66

2330

116

4100

166

5870

216

7640

266

9410

67

2370

117

4140

167

5910

217

7670

267

9440

68

2410

118

4170

168

5940

218

7710

268

9480

69

2440

119

4210

169

5980

219

7750

269

9510

 

 

 

 

 

 

 

 

 

 

70

2480

120

4240

170

6010

220

7780

 

 

71

2510

121

4280

171

6050

221

7820

 

 

72

2550

122

4310

172

6080

222

7850

 

 

73

2580

123

4350

173

6120

223

7890

 

 

74

2620

124

4390

174

6150

224

7920

 

 

75

2650

125

4420

175

6190

225

7960

 

 

76

2690

126

4460

176

6220

226

7990

 

 

77

2720

127

4490

177

6260

227

8030

 

 

78

2760

128

4530

178

6300

228

8060

 

 

79

2790

129

4560

179

6330

229

8100

 

 

 

 

 

 

 

 

 

 

 

 

80

2830

130

4600

180

6370

230

8130

 

 

81

2860

131

4630

181

6400

231

8170

 

 

82

2900

132

4670

182

6440

232

8210

 

 

83

2940

133

4700

183

6470

233

8240

 

 

84

2970

134

4740

184

6510

234

8280

 

 

85

3010

135

4770

185

6540

235

8310

 

 

86

3040

136

4810

186

6580

236

8350

 

 

87

3080

137

4850

187

6610

237

8380

 

 

88

3110

138

4880

188

6650

238

8420

 

 

89

3150

139

4920

189

6680

239

8450

 

 

 

 


(Load in Thousands) Table for Computing lb./in. on 4 in. x 8 in. Cylinders

Area = 12.5666 in.

Load

Psi

Load

Psi

Load

Psi

Load

Psi

10

800

50

3980

90

7160

130

10350

11

880

51

4060

91

7240

131

10420

12

950

52

4140

92

7320

132

10500

13

1030

53

4220

93

7400

133

10580

14

1110

54

4300

94

7480

134

10660

15

1190

55

4380

95

7560

135

10740

16

1270

56

4460

96

7640

136

10820

17

1350

57

4540

97

7720

137

10900

18

1430

58

4620

98

7800

138

10980

19

1510

59

4700

99

7880

139

11060

 

 

 

 

 

 

 

 

20

1590

60

4770

100

7960

140

11140

21

1670

61

4850

101

8040

141

11220

22

1750

62

4930

102

8120

142

11300

23

1830

63

5010

103

8200

143

11380

24

1910

64

5090

104

8280

144

11460

25

1990

65

5170

105

8360

145

11540

26

2070

66

5250

106

8440

146

11620

27

2150

67

5330

107

8520

147

11700

28

2230

68

5410

108

8590

148

11780

29

2310

69

5490

109

8670

149

11860

 

 

 

 

 

 

 

 

30

2390

70

5570

110

8750

150

11940

31

2470

71

5650

111

8830

151

12020

32

2550

72

5730

112

8910

152

12100

33

2630

73

5810

113

8990

153

12180

34

2710

74

5890

114

9070

154

12260

35

2790

75

5970

115

9150

155

12330

36

2860

76

6050

116

9230

156

12410

37

2940

77

6130

117

9310

157

12490

38

3020

78

6210

118

9390

158

12570

39

3100

79

6290

119

9470

159

12650

 

 

 

 

 

 

 

 

40

3180

80

6370

120

9550

160

12730

41

3260

81

6450

121

9630

161

12810

42

3340

82

6530

122

9710

162

12890

43

3420

83

6610

123

9790

163

12970

44

3500

84

6680

124

9870

164

13050

45

3580

85

6760

125

9950

165

13130

46

3660

86

6840

126

10030

166

13210

47

3740

87

6920

127

10110

167

13290

48

3820

88

7000

128

10190

168

13370

49

3900

89

7080

129

10270

169

13450