Plunger Test

CHAPTER 8

MISCELLANEOUS TOPICS
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8.1 INTRODUCTION

8.1.1 Destructive
Destructive testing, tests are carried out to the specimen's failure, in order to understand a specimen's structural performance or material performance under dissimilar loads. These tests are usually much easier to carry out, yield more information, and are easier to interpret than nondestructive testing. Destructive testing is most suitable, and economic, for objects which will be mass-produced, as the cost of destroying a small number of specimens is negligible. It is

The test is based on the principle that the rebound of an elastic mass depends on the hardness of the surface against which the mass impinges. Fig. 8.2 shows the rebound hammer. The spring controlled hammer mass slides on a plunger within a tubular casing. The plunger retracts against a spring when pressed against the concrete surface, and this spring is automatically released when fully tensioned, causing the hammer mass to impact against the concrete through the plunger. When the spring controlled mass rebounds, it takes with it a rider which slides along a graduated scale and is visible through a small window in the side of casing on which the observation gives the rebound number. Then the calibration chart is used to relate the rebound number to compressive strength of concrete. The typical calibration chart is shown in Fig. 8.3. This test can be performed horizontally or vertically. The results obtained from rebound hammer test are affected by smoothness of surface, age of specimen, moisture condition of concrete, carbonation of concrete surface

Procedure :
In this test method, the ultrasonic pulse is produced by the transducer which is held in contact with one surface of the concrete member under test. After traversing a known path length Q in the concrete, the pulse of vibrations is converted into an electrical signal by the second transducer held in contact with other surface of the concrete member and an electronic 2 timing circuit enables the transit time (T) of the pulse to be measured. The pulse velocity (V) is given by :
V = L/T

8.3.2 Ultrasonic Pulse Velocity Method
This method involves the measurement of velocity of electrostatic pulses passing through concrete from a transmitting transducer to a receiving transducer. The pulse also can be generated by hammer blow. The pulse generator circuit consists of electronic circuit for generating pulses and a transducer for transmitting these electronic pulses into mechanical energy having frequency 15 to 50 kHz. The time of travel between initial onset and the reception of the pulse is measured electronically. A typical test circuit is shown in Fig.