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Sampling and Testing Concrete Mixes

Sampling and Testing Concrete Mixes

MATERIAL TESTING LABORATORY

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Purpose

Testing on freshly and hardened concrete is necessary to ensure that specific properties are achieved

It is indispensable part of the construction process imparting quality control and acceptance criteria

Purpose

Testing on freshly and hardened concrete is necessary to ensure that specific properties are achieved

It is indispensable part of the construction process imparting quality control and acceptance criteria

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Sapling Freshly Mixed ConcreteSapling Freshly Mixed Concrete

ASTM C 172 and ACI 318 (Latest Edition)

Perform by qualified field testing technicians Frequency - once a day, or once every 150 cu yd of concrete, or once for each 5,000 sq ft of surface for slabs or walls Not required for less than 50 cu yd with evidence of satisfactory strength

ASTM C 172 and ACI 318 (Latest Edition)

Perform by qualified field testing technicians Frequency - once a day, or once every 150 cu yd of concrete, or once for each 5,000 sq ft of surface for slabs or walls Not required for less than 50 cu yd with evidence of satisfactory strength

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Sample from middle part of the batch discharge

Sample from the mixer delivery point unless other locations are required by specifications

Sample from middle part of the batch discharge

Sample from the mixer delivery point unless other locations are required by specifications

Sapling Freshly Mixed Concrete (Cont.)Sapling Freshly Mixed Concrete (Cont.)

SamplingSampling

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Sapling Freshly Mixed Concrete (Cont.)Sapling Freshly Mixed Concrete (Cont.)

Elapsed time - no more than 15 minutes between first and last portions.

Size of Sample - minimum of 1 cu ft.

Transport samples to area where tests or molding will be performed

Combine and remix to ensure uniformity

Elapsed time - no more than 15 minutes between first and last portions.

Size of Sample - minimum of 1 cu ft.

Transport samples to area where tests or molding will be performed

Combine and remix to ensure uniformity

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Testing Freshly Mixed ConcreteTesting Freshly Mixed Concrete

Consistency - ASTM C 143 (Slump Test) Standard cone 100 mm (4 in.) (top),

200 mm (8 in.) (bottom) diameters, and 12 in. tall

Fill mold in 3 equal volume layers– 70 mm (2 ⅝ in.)– 160 mm (6 ⅛ in.)– Top

Consistency - ASTM C 143 (Slump Test) Standard cone 100 mm (4 in.) (top),

200 mm (8 in.) (bottom) diameters, and 12 in. tall

Fill mold in 3 equal volume layers– 70 mm (2 ⅝ in.)– 160 mm (6 ⅛ in.)– Top

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Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

Tamp each layer 25 times with round steel rod 16 mm (5/8 in.) diameter and 600 mm (24 in.) long

Level top of the cone

Tamp each layer 25 times with round steel rod 16 mm (5/8 in.) diameter and 600 mm (24 in.) long

Level top of the cone

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Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

Lift up cone 300 mm (12 in.) in a single movement in 5 ± 2 sec.

Measure vertical difference between top of mold and specimen original center

Within 2.5 minutes

Lift up cone 300 mm (12 in.) in a single movement in 5 ± 2 sec.

Measure vertical difference between top of mold and specimen original center

Within 2.5 minutes

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Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

Temperature - ASTM C 1064

Temperature limits are usually set for concrete mixes

Thermometer accurate to ± 0.5 °F Wait for 2 minutes or until reading stabilizes 76 mm (3 in.) minimum should surround the sensing portion Complete reading within 5 minutes after obtaining sample

Temperature - ASTM C 1064

Temperature limits are usually set for concrete mixes

Thermometer accurate to ± 0.5 °F Wait for 2 minutes or until reading stabilizes 76 mm (3 in.) minimum should surround the sensing portion Complete reading within 5 minutes after obtaining sample

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Unit Weight and Yield - ASTM C 138

To Determine:

• Unit weight - Weight / Volume

• Yield – Ratio of measured unit weight of concrete by sum of weight of individual components

• Air content - percentage of voids

• Cement content

Unit Weight and Yield - ASTM C 138

To Determine:

• Unit weight - Weight / Volume

• Yield – Ratio of measured unit weight of concrete by sum of weight of individual components

• Air content - percentage of voids

• Cement content

Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

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Procedures

Deposit concrete in 3 equal layers

Compact each layer with a standard rod with the following frequency:

25 strokes for volumes less than 0.5 ft3

50 strokes for 1 ft3

One per 3 in.2 of surface for larger volumes

Tap the exterior with a mallet 10 to 15 times

Strike-off top surface and finish it

Measure weigh of sample and container

Procedures

Deposit concrete in 3 equal layers

Compact each layer with a standard rod with the following frequency:

25 strokes for volumes less than 0.5 ft3

50 strokes for 1 ft3

One per 3 in.2 of surface for larger volumes

Tap the exterior with a mallet 10 to 15 times

Strike-off top surface and finish it

Measure weigh of sample and container

Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

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Computations

• Unit weight:

D = (Wt – Wm) / Vm

• Yield:

Y (ft3) = Mix weight / (D x 27)

• Cement Content:

C = Wcement / Y

• Air Content:

A = [(Dtheo – D) / Dtheo] x 100

Computations

• Unit weight:

D = (Wt – Wm) / Vm

• Yield:

Y (ft3) = Mix weight / (D x 27)

• Cement Content:

C = Wcement / Y

• Air Content:

A = [(Dtheo – D) / Dtheo] x 100

Testing Freshly Mixed Concrete (Cont.)Testing Freshly Mixed Concrete (Cont.)

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Testing Hardened ConcreteTesting Hardened Concrete

Preparing and Curing Specimens from the field - ASTM C 31

Specimens of cylindrical shape are prepared to determine compressive (ASTM C 39) and split-tensile strengths (ASTM C 496)

Molds (length-to-diameter ratio 2):

• 150 mm by 300 mm (6 in. by 12 in.) for aggregates less than 50 mm (2 in.)

• 100 mm by 200 mm (4 in. by 8 in) for aggregates less than 25 mm (1 in.)

Preparing and Curing Specimens from the field - ASTM C 31

Specimens of cylindrical shape are prepared to determine compressive (ASTM C 39) and split-tensile strengths (ASTM C 496)

Molds (length-to-diameter ratio 2):

• 150 mm by 300 mm (6 in. by 12 in.) for aggregates less than 50 mm (2 in.)

• 100 mm by 200 mm (4 in. by 8 in) for aggregates less than 25 mm (1 in.)

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Testing Hardened Concrete (Cont.)Testing Hardened Concrete (Cont.)

Procedures

Place molds in level, rigid, horizontal surface

Deposit concrete in 3 equal layers

Compact each layer applying 25 strokes with a standard rod, and tapping the exterior of the mold with a mallet 10 to 15 times

Procedures

Place molds in level, rigid, horizontal surface

Deposit concrete in 3 equal layers

Compact each layer applying 25 strokes with a standard rod, and tapping the exterior of the mold with a mallet 10 to 15 times

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Testing Hardened Concrete (Cont.)Testing Hardened Concrete (Cont.)

Finish top surface

Cover with nonabsorbent, nonreactive plate or sheet of impervious plastic

Initial curing (up to 48 hours) - away from direct sun rays and radiant heating devices at temperatures between 60 to 80°F

Standard curing - remove from mold and store in humid condition at a temperature of 73.4 ± 3 °F until time of testing

Finish top surface

Cover with nonabsorbent, nonreactive plate or sheet of impervious plastic

Initial curing (up to 48 hours) - away from direct sun rays and radiant heating devices at temperatures between 60 to 80°F

Standard curing - remove from mold and store in humid condition at a temperature of 73.4 ± 3 °F until time of testing

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Compressive Strength of Concrete (Cont.)Compressive Strength of Concrete (Cont.)

ACI 318

Strength - average of two cylinders from the same sample tested at 28 days Acceptance criteria

Average of three consecutive tests is equal or exceed design strength No individual strength test falls below design strength by 500 psi

ACI 318

Strength - average of two cylinders from the same sample tested at 28 days Acceptance criteria

Average of three consecutive tests is equal or exceed design strength No individual strength test falls below design strength by 500 psi

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Compressive Strength of ConcreteCompressive Strength of Concrete

ASTM C 39

Testing Machine - Enough capacity and appropriate loading speed

Displacement - 0.05 in/minPressure - 20 to 50 psi/sec. (565 to 1,414 lb/sec. for 6” cyl.)

Strength - Maximum load / Average cross- sectional area Length correction factors - length-to- diameter ratios (L/D) smaller than 1.8

L/D: 1.75 1.50 1.25 1.00

Factor: 0.98 0.96 0.93 0.87

ASTM C 39

Testing Machine - Enough capacity and appropriate loading speed

Displacement - 0.05 in/minPressure - 20 to 50 psi/sec. (565 to 1,414 lb/sec. for 6” cyl.)

Strength - Maximum load / Average cross- sectional area Length correction factors - length-to- diameter ratios (L/D) smaller than 1.8

L/D: 1.75 1.50 1.25 1.00

Factor: 0.98 0.96 0.93 0.87

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Concrete BehaviorConcrete Behavior

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EVALUATION OF HARDENED CONCRETEEVALUATION OF HARDENED CONCRETE

Conventional Methods

Compression TestSplit-Tension TestFlexural Strength Test

Non-Conventional Methods

Rebound Hammer Test (ASTM C805)Penetration Resistance Test (ASTM C803)Ultrasonic Pulse Velocity Test (ASTM C597)Maturity Test

Conventional Methods

Compression TestSplit-Tension TestFlexural Strength Test

Non-Conventional Methods

Rebound Hammer Test (ASTM C805)Penetration Resistance Test (ASTM C803)Ultrasonic Pulse Velocity Test (ASTM C597)Maturity Test

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Rebound Hammer Test (ASTM C 805)Rebound Hammer Test (ASTM C 805)(Schmidt or Swiss Hammer Test)(Schmidt or Swiss Hammer Test)

Rebound Hammer Test (ASTM C 805)Rebound Hammer Test (ASTM C 805)(Schmidt or Swiss Hammer Test)(Schmidt or Swiss Hammer Test)

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Some Details

Concrete 4 in. thick and fixed to the structure Avoid areas with honeycomb, scaling, or high porosity Prepare at least 6 in. area Smooth surface with abrasive stone Use readings from the same hammer for

comparisonsMinimum of 10 readings, 1 in. or more apart (discard reading lower than 7 units from the average. Only 2 are allowed)

Some Details

Concrete 4 in. thick and fixed to the structure Avoid areas with honeycomb, scaling, or high porosity Prepare at least 6 in. area Smooth surface with abrasive stone Use readings from the same hammer for

comparisonsMinimum of 10 readings, 1 in. or more apart (discard reading lower than 7 units from the average. Only 2 are allowed)

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Limitations

Sensitive to local conditions Hard aggregates produce high rebound number Air voids produce low rebound number Do not compare grounded with ungrounded surfaces Interior condition of concrete is not evaluated

Limitations

Sensitive to local conditions Hard aggregates produce high rebound number Air voids produce low rebound number Do not compare grounded with ungrounded surfaces Interior condition of concrete is not evaluated

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Penetration Resistance Test (ASTM C 803)(Winsor Probe)

Penetration Resistance Test (ASTM C 803)(Winsor Probe)

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Some Details

Concrete should have certain resistance

to penetration Probes should be firmly embedded Probes have to be at least 7 in. apart Minimum of 3 probes to be considered as a test. Discard probes that exceed the average established by ASTM and make another reading Test is insensitive to surface conditions

Some Details

Concrete should have certain resistance

to penetration Probes should be firmly embedded Probes have to be at least 7 in. apart Minimum of 3 probes to be considered as a test. Discard probes that exceed the average established by ASTM and make another reading Test is insensitive to surface conditions

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Limitations

Aggregate type affect penetration for the same concrete strength

Limitations

Aggregate type affect penetration for the same concrete strength