1. Sampling and Testing Concrete Mixes MATERIAL TESTING LABORATORY

2. 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
SAMPLING AND TESTING CONCRETE MIXES

3. Sapling Freshly Mixed Concrete
ASTM C 172 and ACI 318 (Latest Edition)
Perform by qualified field testing technicians
Frequency - once a day, or once every cu yd of concrete, or once for each ,000 sq ft of surface for slabs or walls Not required for less than 50 cu yd with evidence of satisfactory strength
SAMPLING AND TESTING CONCRETE MIXES

4. Sapling Freshly Mixed Concrete (Cont.)
Sample from middle part of the batch discharge
Sample from the mixer delivery point unless other locations are required by specifications
Sampling
SAMPLING AND TESTING CONCRETE MIXES

5. 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
SAMPLING AND TESTING CONCRETE MIXES

6. Testing 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
SAMPLING AND TESTING CONCRETE MIXES

7. 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
SAMPLING AND TESTING CONCRETE MIXES

8. 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
SAMPLING AND TESTING CONCRETE MIXES

9. 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
SAMPLING AND TESTING CONCRETE MIXES

10. Testing Freshly Mixed Concrete (Cont.)
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
SAMPLING AND TESTING CONCRETE MIXES

11. Testing Freshly Mixed Concrete (Cont.)
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
SAMPLING AND TESTING CONCRETE MIXES

12. Y (ft3) = Mix weight / (D x 27) A = [(Dtheo – D) / Dtheo] x 100
Testing Freshly Mixed Concrete (Cont.)
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
SAMPLING AND TESTING CONCRETE MIXES

13. Testing 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.)
SAMPLING AND TESTING CONCRETE MIXES

14. 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
SAMPLING AND TESTING CONCRETE MIXES

15. 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 ± 3 °F until time of testing
SAMPLING AND TESTING CONCRETE MIXES

16. 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
SAMPLING AND TESTING CONCRETE MIXES

17. Compressive Strength of Concrete
ASTM C 39
Testing Machine - Enough capacity and appropriate loading speed
Displacement in/min
Pressure - 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:
Factor:
SAMPLING AND TESTING CONCRETE MIXES

18. Concrete Behavior
SAMPLING AND TESTING CONCRETE MIXES

19. EVALUATION OF HARDENED CONCRETE
Conventional Methods
Compression Test
Split-Tension Test
Flexural Strength Test
Non-Conventional Methods
Rebound Hammer Test (ASTM C805)
Penetration Resistance Test (ASTM C803)
Ultrasonic Pulse Velocity Test (ASTM C597)
Maturity Test
SAMPLING AND TESTING CONCRETE MIXES

20. Rebound Hammer Test (ASTM C 805) (Schmidt or Swiss Hammer Test)
SAMPLING AND TESTING CONCRETE MIXES

21. Concrete 4 in. thick and fixed to the structure
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 comparisons
Minimum of 10 readings, 1 in. or more apart (discard reading lower than 7 units from the average. Only 2 are allowed)
SAMPLING AND TESTING CONCRETE MIXES

22. Sensitive to local conditions
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
SAMPLING AND TESTING CONCRETE MIXES

23. Penetration Resistance Test (ASTM C 803)
(Winsor Probe)
SAMPLING AND TESTING CONCRETE MIXES

24. Concrete should have certain resistance to penetration
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
SAMPLING AND TESTING CONCRETE MIXES

25. Aggregate type affect penetration for the same concrete strength
Limitations
Aggregate type affect penetration for the same concrete strength
SAMPLING AND TESTING CONCRETE MIXES