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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