Sampling and Testing Concrete Mixes MATERIAL TESTING LABORATORY

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

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 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 SAMPLING AND TESTING CONCRETE MIXES

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

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

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

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

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

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

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

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

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

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

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

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 SAMPLING AND TESTING CONCRETE MIXES

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

Compressive Strength of Concrete ASTM C 39 Testing Machine - Enough capacity and appropriate loading speed Displacement - 0.05 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: 1.75 1.50 1.25 1.00 Factor: 0.98 0.96 0.93 0.87 SAMPLING AND TESTING CONCRETE MIXES

Concrete Behavior SAMPLING AND TESTING CONCRETE MIXES

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

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

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

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

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

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

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