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. 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. (152.4 mm x 304.8 mm) or 4 in. x 8 in. (101.6 mm x 203.2 mm) 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

(101.6 mm x 203.2 mm)

3/8 in. (9.5mm)

6 in. x 12 in.

(152.4 mm x 304.8 mm)

5/8 in. (16mm)

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 (75 mm) shall be consolidated by rodding. Concrete with slump of 1 inch to 3 inches (25 mm to 75 mm) shall be consolidated by rodding or vibration. Concrete with slump of less than1 inch (25 mm) 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 (25 mm) 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

(101.6 mm x 203.2 mm)

6 in. x 12 in.

(152.4 mm x 304.8 mm)

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 (13 mm) 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

(101.6 mm x 203.2 mm)

¾ to I inch

19 to 25 mm

6 in. x 12 in.

(152.4 mm x 304.8 mm)

¾ to I 1/2 inch

19 to 38 mm

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 50°F to 80°F (10°C to 27°C) 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 68°F to 81.5°F (20°C to 27.5°C) until the time of test. This condition can be met by immersion in saturated limewater. NOTE: Lime-saturated water is prepared by mixing 1 teaspoon (12 g) of hydrated lime, with 1 gallon (3.8 liters) 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 40°F (22°C) 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. (3 mm in 300 mm)]

2. The ends of the specimens that are not plane within 0.002 in. (0.05 mm) 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. (0.05 mm).

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 (138 kPa to 345 kPa) 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 (0.1 MPa). The attached tables may be used to facilitate these computations.

Figure 1. Compressive Fracture Types

Figure 2. Compression Testing Machine

Table for Computing MPa/1000 kPa on 6 in. to 12 in. (154.mm x 304.8 mm) Cylinders

Area = 0.01824m²

Load (kN) MPa Load (kN) MPa Load (kN) MPa Load (kN) MPa Load (kN) MPa

175 9.59 425 23.30 675 37.01 925 50.71 1175 64.42

180 9.87 430 23.57 680 37.28 930 50.99 1180 64.69

185 10.14 435 23.85 685 37.55 935 51.26 1185 64.97

190 10.42 440 24.12 690 37.83 940 51.54 1190 65.24

195 10.69 445 24.40 695 38.10 945 51.81 1195 65.52

200 10.96 450 24.67 700 38.38 950 52.08 1200 65.79

205 11.24 455 24.95 705 38.65 955 52.36

210 11.51 460 25.22 710 38.93 960 52.63

215 11.79 465 25.49 715 39.20 965 52.91

220 12.06 470 25.77 720 39.47 970 53.18

225 12.34 475 26.04 725 39.75 975 53.45

230 12.61 480 26.32 730 40.02 980 53.73

235 12.88 485 26.59 735 40.30 985 54.00

240 13.16 490 26.86 740 40.57 990 54.28

245 13.43 495 27.14 745 40.84 995 54.55

250 13.71 500 27.41 750 41.12 1000 54.82

255 13.98 505 27.69 755 41.39 1005 55.10

260 14.25 510 27.96 760 41.67 1010 55.37

265 14.53 515 28.23 765 41.94 1015 55.65

270 14.80 520 28.51 770 42.21 1020 55.92

275 15.06 525 28.78 775 42.49 1025 56.20

280 15.35 530 29.06 780 42.76 1030 56.47

285 15.63 535 29.33 785 43.04 1035 56.74

290 15.90 540 29.61 790 43.31 1040 57.02

295 16.17 545 29.88 795 43.59 1045 57.29

300 16.45 550 30.15 800 43.86 1050 57.57

305 16.72 555 30.43 805 44.13 1055 57.84

310 17.00 560 30.70 810 44.41 1060 58.11

315 17.27 565 30.98 815 44.68 1065 58.39

320 17.54 570 31.25 820 44.96 1070 58.66

325 17.82 575 31.52 825 45.23 1075 58.94

330 18.09 580 31.80 830 45.50 1080 59.21

335 18.37 585 32.07 835 45.78 1085 59.48

340 18.64 590 32.35 840 46.05 1090 59.76

345 18.91 595 32.62 845 46.33 1095 60.03

350 19.19 600 32.89 850 46.60 1100 60.31

355 19.46 605 33.17 855 46.88 1105 60.58

360 19.74 610 33.44 860 47.15 1110 60.86

365 20.01 615 33.72 865 47.42 1115 61.13

370 20.29 620 33.99 870 47.70 1120 61.40

375 20.56 625 34.27 875 47.97 1125 61.68

380 20.83 630 34.54 880 48.25 1130 61.95

385 21.11 635 34.81 885 48.52 1135 62.23

390 21.38 640 35.09 890 48.79 1140 62.50

395 21.66 645 35.36 895 49.07 1145 62.77

400 21.93 650 35.64 900 49.34 1150 63.05

405 22.20 655 35.91 905 49.62 1155 63.32

410 22.48 660 36.18 910 49.89 1160 63.60

415 22.75 665 36.46 915 50.16 1165 63.87

420 23.03 670 36.73 920 50.44 1170 64.14

(Load in Thousands) Table for Computing lb./in.² on 6 in. x 12 in. Cylinders

Area = 28.2744 in.²

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.² on 4 in. x 8 in. Cylinders

Area = 12.5666 in.²

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

Table for Computing MPa on 4 in. x 8 in. (101.6 mm x 203.3 mm) Cylinders

Area = 0.008107 m²

Load (kN) MPa Load (kN) MPa Load (kN) MPa Load (kN) MPa

45 5.55 245 30.22 445 54.89 645 79.56

50 6.17 250 30.84 450 55.51 650 80.18

55 6.78 255 31.45 455 56.12 655 80.79

60 7.40 260 32.07 460 56.74 660 81.41

65 8.02 265 32.69 465 57.36 665 82.03

70 8.63 270 33.30 470 57.97 670 82.64

75 9.25 275 33.92 475 58.59 675 83.26

80 9.87 280 34.54 480 59.21 680 83.88

85 10.48 285 35.15 485 59.82 685 84.49

90 11.10 290 35.77 490 60.44 690 85.11

95 11.72 295 36.39 495 61.06 695 85.73

100 12.34 300 37.01 500 61.68 700 86.35

105 12.95 305 37.62 505 62.29 705 86.96

110 13.57 310 38.24 510 62.91 710 87.58

115 14.19 315 38.86 515 63.53 715 88.20

120 14.80 320 39.47 520 64.14 720 88.81

125 15.42 325 40.09 525 64.76 725 89.43

130 16.04 330 40.71 530 65.38 730 90.05

135 16.65 335 41.32 535 65.99 735 90.66

140 17.27 340 41.94 540 66.61 740 91.28

145 17.89 345 42.56 545 67.23 745 91.90

150 18.50 350 43.17 550 67.84 750 92.51

155 19.12 355 43.79 555 68.46 755 93.13

160 19.74 360 44.41 560 69.08 760 93.75

165 20.35 365 45.02 565 69.69

170 20.97 370 45.64 570 70.31

175 21.59 375 46.26 575 70.93

180 22.20 380 46.87 580 71.54

185 22.82 385 47.49 585 72.16

190 23.44 390 48.11 590 72.78

195 24.05 395 48.72 595 73.39

200 24.67 400 49.34 600 74.01

205 25.29 405 49.96 605 74.63

210 25.90 410 50.57 610 75.24

215 26.52 415 51.19 615 75.86

220 27.14 420 51.81 620 76.48

225 27.75 425 52.42 625 77.09

230 28.37 430 53.04 630 77.71

235 28.99 435 53.66 635 78.33

240 29.60 440 54.27 640 78.94