Sab 2112 - L10 Test Of Hardened Concrete

TEST OF HARDENED CONCRETE

Types of Test Destructive test – compressive strength, flexural strength, cylinder splitting strength

Non-destructive test – Ultrasonic Pulse Velocity, Rebound Hammer, Covermeter

Compressive strength test To determine the compressive strength of concrete Samples – 100 or 150 mm cube or cylinder 150 mm cube – 3 layers – 35 strokes 100 mm cube – 2 layers – 25 strokes Hand compaction or external vibrator (poker)

Cont. Hand compaction – steel bat 25 mm square face, 380 mm long, 1.8 kg After compaction, the surface of sample is trowel as smooth as possible Curing – cover the samples using wet gunny for 24 hours Demould after 24 hours and placed in water tank for further curing

Compaction

Curing

Compressive Strength Test

Mode of Failure

Cont. Test the samples at the required age – 3, 7, 28 days Three samples per test age Load the sample until failure Compressive strength = (Ult. Load) Area

Flexural test Determine the modulus of rupture of concrete Sample – 150x150x750 mm or 100x100x500 mm 150x150x750 mm – 3 layers – 170 strokes 100x100x500 mm – 2 layers – 100 strokes Compaction – by hand or vibrator Curing will be the same as concrete cube/cylinder

Cont. Test under four-point load Record the ultimate load Modulus of Rupture = Pl bd2

Cylinder splitting test Determine the tensile strength of concrete Sample – 100x200 mm or 150x300 mm Compaction – vibrator or by hand Curing – the same as cube/prism Test until failure Tensile Splitting Strength = 2P πLd

Not Properly Compacted

NON-DESTRUCTIVE TEST

Ultrasonic Pulse Velocity Measure the velocity of pulse through solid material Transmitter generate pulse, receiver receive the pulse Time (microsecond) taken by the pulse to travel from point a to B is recorded Velocity = Distance Time

Methods of propagating and receiving ultrasonic pulse Direct transmission Semi-direct transmission Indirect or surface transmission

Concrete Quality

Rebound Hammer Also known as Schmidt hammer test Based on the principle that the rebound of an elastic mass depends on the hardness of the surface against which the mass impinges The test is sensitive to the presence of aggregate and voids immediately underneath the plunger

Cont. Take 10 to 12 readings over the area to be tested No unique relation between hardness and strength of concrete BUT experimental relationships can be determined for a given concrete Higher value indicate better quality of concrete

Covermeter test Can be used to determine the depth of concrete cover and locating the direction and size of reinforcement Consist of searcher unit connected to the main unit containing the cells, circuits and indicator scale Has the working range of up to 100 mm depth Accuracy of ± 15%

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