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)

2

25

6 in. x 12 in.

(152.4 mm x 304.8 mm)

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 (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)

to I inch

19 to 25 mm

2

1

6 in. x 12 in.

(152.4 mm x 304.8 mm)

to I 1/2 inch

19 to 38 mm

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 (10C to 27C) 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 (20C to 27.5C) 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 40F (22C) 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 = 0.01824m

 

Load (kN)                 MPa       Load (kN)   MPa         Load (kNMPa       Load (kNMPa 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. 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

 

 

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

Area = 0.008107 m

 

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