Rebound hammer test.
BY BY: AKSHAY R MANOHARMTech-Construction Technology CIVIL ENGINEERING DEPT.
NMAMIT-NITTE.
REBOUND HAMMER(ASTM C 805-79)
CONTENTS
• INTRODUCTION • PRINCIPLE• PROCEDURE• ADVANTAGES• DIS-ADVANTAGES• CONCLUSION
INTRODUCTION
• The rebound hammer test is one of the non-destructive tests used to check the compressive strength of concrete .
• An empirical relationship has been determined between the a absorbed by the concrete when given a high impact and its compressive strength .
• the rebound hammer is designed to carryout instant non-destructive test on concrete structure without damage and gives an immediate indication of the compressive strength of the concrete using the calibration curve applied each instrument .
• the hammer is simply pressed firmly against the concrete whereupon a powerful internal spring is first compressed and thin tripped to deliver a hammer blow through the hardened concrete trip to the surface being tested.
Rebound hammer test
• Rebound hammer test is done to find out the compressive strength of concrete by using rebound hammer as per IS: 13311 (Part 2) – 1992.
• Principle of the rebound hammer test is: The rebound of an elastic mass depends on the hardness of the surface against which its mass strikes.
• When the plunger of the rebound hammer is pressed against the surface of the concrete, the Spring-controlled mass rebounds and the extent of such a rebound depends upon the surface hardness of the concrete.
• The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete.
• The rebound value is read from a graduated scale and is designated as the rebound number or rebound index.
• The compressive strength can be read directly from the graph provided on the body of the hammer.
Procedure
• Should be tested against the test anvil.• Apply light pressure on the plunger and allow
it to extend to the ready position for the test.• Apply a gradual increase in pressure until the
hammer impacts.• Take the average of about 15 readings.
•Assessing the likely compressive strength of concrete .
•Assessing the quality of concrete in relation to standard requirements.• NDT
Rebound Hammer test:
Interpretation of Results:
The rebound reading on the indicator scale has been calibrated by the manufacturer of the rebound hammer for horizontal impact.
Average Rebound Number Quality of Concrete
>40 Very good hard layer
30 to 40 Good layer
20 to 30 Fair
< 20 Poor concrete
0 Delaminated
Table:- Average Rebound number and quality of concrete
RELATIONSHIP B/W REBOUND HAMMER AND COMPRESSIVE STRENGTH
cube compressive strength is N/sq.mm plotted against rebound number
A)Strength Assessment:
• To assess the relative strength of concrete based on the hardness.
• Casting cubes were tested under controlled conditions.
• This is due to hardening of concrete surface due to carbonation.
• It restricted to relatively new structures only.
B)Survey of weak and delaminating concrete:
• It helps to identify relative surface weakness in cover concrete and to determine the relative compressive strength of concrete.
• This survey is carried by dividing the member into well-defined grid points.
• The grid matrix should have a spacing of approximately 300mm x 300mm.
ADVANTAGE
• Simple to use. No special experience is needed to conduct the test.
• Establishes uniformity of properties.• Equipment is inexpensive and is
readily available.• A wide variety of concrete test hammers is
available with an operational range of M10 to M70.
• For rehabilitation of old Monuments..
DISADVANTAGE
• Evaluates only the local point and layer of masonry to which it is applied.
• No direct relationship to strength or deformation properties.
• Unreliable for the detection of flaws.• Cleaning maintenance of probe and spring
mechanism
Conclusion
• The rebound value can be measured discretionary, whereas the number of crushed specimens is limited.
• The combination of both methods is the best and most reliable procedure to determine the compressive strength of concrete structures.
• The method does not damage the structure like the classical method, where cores must be taken for the evaluation of the compressive strength.
• It is a fast, inexpensive and easy to perform method using a light and portable test equipment.
REFERENCE
• Estimating the Strength of Concrete Using Surface Rebound Value and Design Parameters of Concrete Material. Jen-Chei Liu, Mou-Lin Sue and Chang-Huan Kou*Department of Civil Engineering and Engineering Informatics‚ Chung-Hua University,Hsin Chu, Taiwan 300‚ R.O.C
• CONCRETE TECHNOLOGY – A text book- ML Gambhir.
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