TITLE:
NON-DESTRUCTIVE TESTING OF CONCRETE BY REBOUNDHAMMER
OBJECTIVES:
APPARATUS REQUIRED:
The Rebound Hammer consisting of a spring controlled mass that slides on a plunger within a tubular housing.
THEORY:
Schmidt hammer test consists of a spring controlled hammer that slides on a plunger within a tubular housing.
When the plunger of rebound hammer is pressed against the surface o....Show More
TITLE:
NON-DESTRUCTIVE TESTING OF CONCRETE BY REBOUNDHAMMER
OBJECTIVES:
APPARATUS REQUIRED:
The Rebound Hammer consisting of a spring controlled mass that slides on a plunger within a tubular housing.
THEORY:
Schmidt hammer test consists of a spring controlled hammer that slides on a plunger within a tubular housing.
When the plunger of rebound hammer is pressed against the surface of the concrete, the mass rebounds from the plunger. It retracts against the force of the spring. The hammer impacts against concrete and the spring control mass rebounds.The rebound is read off along a graduated scale and is designated as the rebound number or rebound index.
Some advantages of this test are:
PROCEDURE:
For testing, smooth, clean and dry surface was selected since the rough surfaces resulting from incomplete compaction, loss of grout, spalled or tooled surfaces do not give reliable results and should be avoided.
The test hammer was operated mostly vertically. The point of impact was kept at least 20 mm away from any edge or shape discontinuity.
The test hammer was plunged at exactly right angles to the surface of the concrete being tested. The plunger was pressed slowly and uniformly until released.
Taking only one reading at a given point, a minimum of 11 readings were taken.
Very high reading may be caused by the rock or steel near the surface of the point of impact and very low readings may be caused by the trapped air pockets near the surface at the point of impact.
The compressive strength was then determined from the rebound number by using the Central Lab calibration chart for that particular test hammer.
OBSERVATION:
RESULTS
From the above observations, it is found that the rebound number increases as the strength increases.
Thus the average compressive strength is found to be 433.2 KN.
DISCUSSION:
The rebound number are indicative of compressive strength of concrete to a limited depth from the surface. If the concrete in a particular member has internal microcracking, flaws or heterogeneity across the cross-section, rebound hammer indices will not indicate the same. As such, the estimation of strength of concrete by rebound hammer method cannot be held to be very accurate and probable accuracy of prediction of concrete strength in a structure is of ±25 percent.
The average Rebound reading with the condition of concrete as given by BS 1881-202 is,
Average Rebound Reading | Quality of concrete |
>40 | Very good,hard layer |
30 - 40 | Good layer |
20 - 30 | Fair |
< 20 | Poor concrete |
0 | Delaminated |
Guest
