Rebound Hammer

INTRODUCTION

A rebound hammer, commonly referred to as a Schmidt Hammer, is a mechanical device used to measure the compressive strength of in-place concrete. The device consists of a plunger and a spring-loaded hammer. When When triggered, the hammer strikes the free end of the plunger that is in contact with the concrete, which in turn causes the plunger to rebound. The etent of the rebound is measured on a linear scale attached to the device. This test is covered in American Society for Testing Testing and !aterials "AST!# $%&'-(), *Standard Test !ethod for +ebound umber of Hardened $oncrete.

THEORY

+ebound hammer test is done to find out the compressive strength of concrete by using rebound hammer as per S/ 01100 "2art 3# 4 0((3. The underlying 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 pring-controlled mass rebounds and the etent 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 inde. The compressive strength can be read directly from the graph provided on the body of the hammer.

OBJECTIVE

To apply on-5estructive method to evaluate the structure of concrete building an to estimate strength of concrete in structures.

EQUIPMENT AND MATERIALS Equipment

+ebound hammer type 

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ANALYSIS

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7 30.& 8 31.' 8 39.& 8 33.' 8 3'.& 8 3).& 8 3:.' 8 33.' 8 3'.& 8 1&.& 8 1&.& 8 3).' " $'%#+

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DISCUSSION

=sing the rebound hammer is considered as a nondestructive test as no destroyed specimens takes place in itwhen we tested the compressive strength of concrete. The main  principle of this test is that it measures the rebound of an elastic mass when it collides with the concrete surface under the test, this rebound depends on the hardness of concrete and on the energy it absorbs from the collision. The tested concrete had been smooth and firmly supported. The hammer is pressed against the concrete, and then the mass inside the hammer is rebounded from the plunger and gives a reading on the scale. We had test the rebound hammer to a 0'&mm  0'&mm cube, column, stairs, floor and wall that is all of the materials are concrete. The plunger always be normal to the concrete in test. The hammer position relative to the vertical affects the rebound number because of the effect of gravity on the mass inside the device. The calibration graph relating the rebound number and the compressive strength contains a curve for each angle that is measured from the hori>ontal to the hammer ais. After take 0 3 of the rebound

hammer reading scale for each of the places, we estimated the scale by using compressive strength graph and the data was collected.