Rebound Hammer

1.0) • • •

Objectives

To check the uniformity of concrete To determine the properties of the surface of the concrete To estimate strength of concrete in structures

2.0)

Equipment and materials

Equipment 

Rebound hammer type N

Figure 1.0 Rebound hammer type N

Material 

lose te!tured concrete "#eam$ slab and column%

3.0)

Procedure

a. Method of testin i.

& rebound hammer is selected appropriately to the type of concrete tested. 't is checked before used to make sure it is (orking correctly and its reading on the steel

ii.

reference an)il. & suitable test locations "hori*ontal$ up(ards and do(n(ards direction% is chose.

iii. i).

+nly smooth surfaces should be tested. The readings of a test to an area not e!ceeding ,00 mm ! ,00 mm is confined. & regular grid of lines is dra(n ,0 mm apart to take the intersections of the lines as

).

test points. T(el)e readings are obtained at a location.

b. Procedure of usin rebound hammer

i.

The hammer is pressed against concrete. -lunger retracts against spring and the

ii.

hammer is ready to be used. The hammer is pressed to the test location until the mass hammer impact against the

iii. i).

surface through the plunger. ammer should be operated perpendicular to the surface hori*ontally. The button is pressed at the side of hammer and the amount of rebound of the mass$ R 

).

is read from the indicator. The compressi)e strength is referred to the calibration cur)e on the standard steel

)i.

an)il. The compressi)e strength is estimated.

!.0)

"iscussion

Rebound hammer test is done to find out the compressi)e strength of concrete by using a rebound hammer. The underlying principle of the rebound hammer test is the rebound of an elastic mass depends on the hardness of the surface against (hich its mass strikes. /hen 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 are taken to be related to the compressi)e strength of the concrete. The rebound )alue is read from a graduated scale and is designated as the rebound number or rebound inde!. The compressi)e strength can be read directly from the graph pro)ided on the body of the hammer. uring the e!periment$ the systematic error occurred because of the rebound hammer. This is due to the rebound hammer (as not functioning (ell (hile (e (ere using it against the (all. Reading of the results (as taken directly from the rebound hammer and graphs (ere obtained from it as (ell. From the table$ the result sho(s 12 times of hits by the rebound hammer  to(ards the concrete and the )alues are )ary e)ery knock at each location. The all 12 )alue (ill be calculated to get the mean and as (ell as to get the estimation compressi)e strength of  concrete in structure. This test sho(s that e)ery location has different compressi)e strength. 'n comparison to the theoretical )alues$ the e!perimental are slightly different. For the first location (ith mean of ,3 and angle of 40$ our compressi)e strength is 52.0 M-a (hereas theoretically the )alue is ,6M-a. Ne!t location (ith mean of ,2 and angle 0$ the compressi)e strength is 27.8M-a (hereas in theory the )alue is 27.4 M-a. Mo)ing on to our third location (hich is flat surfaced concrete (ith mean of ,2 and angle of 40$ compressi)e strength is 14.3M-a (hereas in theory the )alue is 27.4M-a. Forth location (ith mean of ,3 and angle of 58$ the compressi)e strength is 50 M-a (hereas theory is ,6M-a. 9ast but not least$ (ith mean of ,1 and angle of 58$ the compressi)e strength is 21M-a (hereas in theory the )alue is 28.2 M-a. These )alues are different due to the angle that (e took in this e!periment. ¬her factor (ould be error on the rebound hammer as it needs to be calibrated frequently.

#.0)

"ata anal$sis

%est &ef.

1

%est location

,7.0 ,4.8 ,8.0 ,4.8

oncrete

&ecorded value ,1.8 50.8 ,7.0 52.8

Mean$ R  36.0 + 31.5 + 34.5 + 39.5 + 40.5 + 39.5 + 35.0 + 36.0 + 43.5 + 39.5 + 42.5 + 34.5

:

12

: ,3

ompressi)e strength is obtained from the graph on the rebound hammer.

,5.8 ,4.8 5,.8 ,5.8

3.0%

onclusion

/e (ere able to carry out surface hardness testing by rebound hammer. Rebound hammer is used to measure the elastic properties or strength of concrete or rock $ mainly surface hardness and penetration resistance. #ased on the table abo)e$ e)ery concrete has different surfaces so$ from this test$ (e can conclude that uniformity of concrete is none. &ccording to the compressi)e graph$ compressi)e strength for each location is obtained by on the mean$ R and angle.