Non-destructive test are


Core test

To assess the compressive strength of concrete.

Ultra sonic pulse velocity test

The ultra sonic pulse velocity test is also done on the extracted/grinded core sample in order to check the integrity of the concrete.

Acceptance criteria

Acceptance criteria was decided based on clause 17.4.3 of Is 456:2000 which is as follows.

a)    For core test

1.   Average equivalent cube strength of the cores for a particular sample of concrete shall be equal to at least 85 percent of the cube strength of specified grade of concrete.

2. No individual core for a particular sample of concrete shall have an equivalent cube strength less than 75 percent of the cube strength of specified grade of concrete.


Methodology adopted

  • The reinforcement is detected at planned location with the help of Rebar Locator called Profometer to avoid cutting of reinforcement.
  • The core cutting equipment is fixed at the planned locating and core is extracted.
  • Both the ends are prepared by grinding up to the tolerance limit as specified by clause 4.8 of BS 1881; Part 120: 1983 for flatness and parallelism.
  • A thin layer of Micro silica or sulphar capping is applied to ends to ensure proper contact.
  • Now the cores are ready for compression testing.



Testing

The cores were tested for compression in laboratory. As per guidelines given in IS 516 – 1959.


Diameter of core

Minimum diameter of core shall be 3 times the normal size of aggregate.


 Fig.



Estimation of cube strength

As per IS: 516 – 1959, the equivalent cube strength is calculated by formula. 

Equivalent cube strength = 1.25 x fc x k

Where k = 0.87 + 0.13 ( (L/d) – 1 )


Ultrasonic pulse velocity test

The test is performed as per guidelines by IS: 13311 (Part – I): 1992 and BS 1881: Part 203: 1986.

The details of the apparatus used for the test are as follows:
Name
Ultrasonic Pulse Velocity Concrete Tester – Ultrasonic 4600
Manufacturer
M/s. Roop Telesonic Ultrasonic Ltd. Mum.
Transit Time Range
0.1 μ Sec to 9999.9 μ Sec
Resolution
0.1 μ Sec
Penetration Range
10 mm to 5 m in concrete
Transducer Frequency
100 KHz
Power
7.2 V.D.C. or 230 V.A.C. mains
Operating Temp.
00 C to 500 C.


Following methodology is adopted for carrying out the test

  • For testing smooth, clean, dry surface without any defect like honey combing, cracks and hollow sound is selected.
  • The area of approx. 300 mm x 300 mm is rubbed with carborandum stone to remove loosely adhering scales, or remains of plaster mortar, if any.
  • Two points are marked on opposite faces of the concrete members for direct transmission of ultrasonic pulses i.e. is in case of columns and on the same surface for indirect transmission of ultrasonic pulses i.e. in case of slab.
  • Grease is applied as a coupling medium to ensure proper contact of the transducers with concrete surface so that ultrasonic pulse is transmitted through the medium without much disturbance.
  • Now both the transducers are held at correct test locations by applying constant pressure and ultrasonic pulses are transmitted through the concrete.
  • The machine displays the time taken to travel the known path in microseconds.
  • The velocity is calculated from the reading obtained against each known path.




Following velocity criterion for concrete quality grading is given by IS 13311 (Part – I) : 1992


Sr. no.
Ultrasonic Pulse Velocity by Cross probing (Km/Sec.)
Concrete quality grading
1
Above 4.5
Excellent
2
3.5 to 4.5
Good
3
3.0 to 3.5
Medium
4
Below 3.0
Doubtful

Based upon above criterion grading of concrete quality is determined.