Rebound hammer test PowerPoint presentation pdf PDF

Preview

Summary

Rebound hammer test is a non destructive test for assessing compressive strength of concrete. To gives idea about homogenity and uniformity of concrete....

Description

REBOUND HAMMER TEST Presented by Akshaya K

•R e b o u n d h a m m e r t e s t i s a N o n - d e s t r u c t i v e t e s t ( N D T ) o f C o ncre te a n d s imp le co n c re te te st w h ic h is u s e d to tes t the

Compressive

strength

of

concrete

without

any

damage. •M o r e o v e r ,

the

best

part

of

Rebound

hammer

test

is

concrete can be tested in real time at the site instead of going to the lab with out any damage. 2

•C o n c r e t e R e b o u n d h a m m e r t e s t w a s f i r s t c o v e r e d b y I S 1 3 3 11 ( P a r t 2 ) – 1 9 9 2 . •S w i s s e n g i n e e r E r n s t S c h m i d t i s t h e n a m e of

the

scientist

who

first

introduced

Rebound hammer test, and it is also called as Schmidt hammer test or Swiss Hammer Te s t . 3

5

1. 2. 3. 4. 5. 6. 7.

Concrete surface Impact spring Rider on guide rod Wi n d o w a n d s c a l e Hammer guide Release catch; Locking button

8. Compressive spring 9. Housing 10.H ammer mass 11.Plunger

6

•

The rebound hammer correlates the rebound height of a spring driven mass after it impacts the surface of the concrete.

•

The spring driven mass slides on a guide rod in the tubular housing.

•

While the impact plunger is pressed tightly against the concrete surface, a trigger releases the spring-loaded mass causing it to impact the plunger and transfers the energy to the concrete surface. 7

•

The mas s after that rebounds and the rebound height is correlated to th e surface hardness of the concrete.

• A common calibration chart relates the rebound number to the cube compressive strength for the underwater r e b o u n d h a m m e r.

8

9

Objec tive of Re bound Hammer Te st •

As p e r t h e I n d ia n c o d e I S : 1 3 3 11 ( 2 ) - 1 9 9 2 , t h e r e b o u n d hammer test have the following objectives:

•

To d e t e r m i n e t h e c o m p r e s s i v e s t r e n g t h o f t h e c o n c r e t e b y relating the rebound index and the compressive strength

•

To a s s e s s t h e u n i f o r m i t y o f t h e c o n c r e t e .

•

To

assess

the

quality

of

the

concrete

based

on

the

standard specifications. •

To r e l a t e o n e c o n c r e t e e l e m e n t w i t h o t h e r i n t e r m s o f quality 10

Principle of Test When the plunger of rebound hammer is pressed agains t the s urface of the concrete, the s pring controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. • The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete. • The rebound is read off alo ng a graduated scale and is designated as the rebound number or rebound index. •

11

PROCEDURE •

T h e c o n c r e t e s u r f a c e s h o u l d b e s m o o t h , c l e a n a n d d r y.

•

Ant loos e particles s hould be rubbed off from the concrete surface with a grind ing wheel or stone, before hammer testing.

•

Rebound hammer test should not be conducted on rough surfaces as a result of incomplete compaction, loss of grout, spalled or tooled concrete surface. 12

•

The point of

impact of

rebound hammer

on

concrete

surface should be at least 20mm away from edge or shape d i s c o n t i n u i t y. Six readings of rebound number is taken at each point of testing and an average of value of the readings is taken as

rebound

index

for

the

corresponding

point

of

observation on concrete surface. 13

I n te r p r e ta t io n o f Re b o u n d H a m m e r Te s t

Resul ts •

After

obtaining

the

correlation

between

compressive

s t r e n g t h a n d r e b o u n d n u m b e r, t h e s t r e n g th o f s t r u c t u r e can be assessed. •

In general, the rebound number increases as the strength increases and is also affected by a number of parameters i.e. type of ce ment, type of aggregate, surface condition and moisture content o f the concrete, curing and age of concrete, carbonation of concrete surface etc. 14

15

•

Moreover

the

rebound

index

is

indicative

of

compressive strength of concrete up to a limited depth from the surface. •

The internal cracks, flaws etc. or heterogeneity across the cros s s ection will not be indicated by rebound numbers. 16

Quality of Concrete for different values of rebo und number Average rebound hammer

Quality of concrete

> 40

Very good hard layer

30 to 40

Good layer

20 to 30

Fair

< 20

Poor concrete

0

Delaminated

17

The advantages of Rebound hammer tests •

Apparatus is easy to use

•

D e te rmin e s u nifo rmity p ro pe rtie s o f th e s u rfa c e

•

The equipment used is inexpensive

•

Used for the rehabilitation of old monuments

18

T h e d i s a d v a n t a g e s o f R e b o u n d H a m m e r Te s t •

The results obtained is based on a local point.

•

The test results are not directly related to the strength and the deformation property of the surface.

•

The probe and spring arrangement will require regular cleaning and maintenance.

•

F l a w s c a n n o t b e d e t e c t e d w i t h a c c u r a c y. 19

Factors

Influencing

Rebound

Hammer

Te s t

1 . Ty p e o f A g g r e g a t e 2 . Ty p e o f C e m e n t 3. Surface and moisture condition of the concrete 4. Curing and Age of concrete 5. Carbonation of concrete surface 20

1 . I n f l u e n c e o f Ty p e o f C e m e n t •

Concretes made with high alumina cement can give strengths 100 percent higher than that with ordinary Portland cement. Concretes made with super sulphated cement can give 50 percent lower strength than that with ordinary Portland cement. 21

2 . I n f l u e n c e o f Ty p e o f A g g r e g a t e •

Different types of aggregate used in concrete give different

correlations

between

compressive

strength

and rebound numbers. •

Normal aggregates such as gravels and crushed rock aggregates give similar correlations, but concrete made with lightweight aggregates require special calibration. 22

3.Influence of Surface Condition and Mo isture Content of Concrete •

The rebound hammer method is suitable only for close texture concrete.

•

Open

texture

honeycombed

concrete

typical

concrete

or

of

masonry

no-fines

blocks,

concrete

are

unsuitable for this test. •

All

correlations

strength

of

assume

partially

full

compacted

compaction, concrete

unique relationship to the rebound numbers.

as bears

the no 23

•

Trowelled and floated surfaces are harder than moulded surfaces, and tend to overestimate the strength of concrete.

•

A

wet

strength

surface of

will

concrete

give

rise

calibrated

to

underestimation

under

dry

of

conditions.

the In

structural concrete, this can be about 20 percent lower than in an equivalent dry concrete.

24

5.Influence of Curing and Age of Concrete •

The relationship between hardness and strength varies as a function of time.

•

Va r i a t i o n s

in

initial

rate

of

hardening,

subsequent

cu rin g and conditions of exposure also influence the relationship. •

Separate calibration curves are required for different curing regimes but the effect of age can generally be ignored for concrete between 3 days and 3 months old. 25

6.Influence of Carbonation of Concrete •

The influ ence of carbonation of concrete surface on the rebound number is very significant.

•

Carbonated concrete gives an overestimate of strength which in e xtre me cases can be up to 50 percent.

•

It

is

possible

to

e s ta blis h

c o rre c tio n

factors

by

removing the carbonated layer and testing the concrete with

the

rebound

hammer

on

the

un-carbonated

concrete. 26

27...