The Scmidt hammer test is based on the elastic rebound of hammer which presses on
concrete surface and it measures the surface hardness of concrete. Since the test is very sensitive to the presence of aggregates and voids at the concrete surface, it is necessary to take more than 10 readings over the area of test. However, it should be noted that Schmidt hammer test measures surface hardness only but not the strength of concrete. Therefore, it may not be considered a good substitute for concrete compression test.
The Scmidt hammer test is based on the elastic rebound of hammer which presses on
concrete surface and it measures the surface hardness of concrete. Since the test is very sensitive to the presence of aggregates and voids at the concrete surface, it is necessary to take more than 10 readings over the area of test. However, it should be noted that Schmidt hammer test measures surface hardness only but not the strength of concrete. Therefore, it may not be considered a good substitute for concrete compression test.
The Schmidt Hammer test is only really usefull to gather an initial indication of concrete strength, usually the average of 12 blows is taken. Carbonation of the concrete causes the surface to harden and would therefore provide misleading readings. The better strength test method is to take at least 2 concrete core samples in each area (at least 50mm diameter), and have them compression tested at a reputable laboratory. To ensure steel reinforcement is not struck during coring (compressive tests cannot be done on a sample that contains steel), it is customery to scan the surface with a cover meter that will identify the arrangement of and depth of embedded reinforcement; cores can then be extracted between the bars. I have carried out this activity many times in my current role.
Taking a core is not a easy task. Concrete may disturbed significantly during core cutting as well as processing of core samples at lab. For 20 mm downgraded aggregate, it is better to take 60 mm core.
Schmidt hammer can give you an indication of compressive strength. Calibration is needed to judge compressive strength with a reasonable accuracy.
You can also do UPV test. Same as Schmidt hammer, you need calibration.
thanks to
Tarek Uddin Mohammed
John Kirwan
Asad Hanif
P.L. Ng
Amjad Albayati
for clarifying
I agree with Mr. John Kirwan, that the Core test is more accurate test in case of the fail of the cube compression test. Also, Schmidt hammer test is depend on the human utility specially at inclined surfaces.
This is an interesting question, and you need to ask yourself why are you trying to find other ways to pass concrete that has essntially failed so give some thought to the following.
Do you not have faith in the compression tests that you have done and if not why?
compression tests.can fail for a number of reasons
a) concrete is not up to standard due to poor mix design or mix design fine but incorrect portioning.
b) mixing issues where mix was not mixed through properly.
c) sampling issues where mix is actually fine but was sampled incorectly or cast incorectly.
d) callibration problems with testing machine.
Some questions you need to consider.
1. how many compression tests did you do?
2. assuming you did more than 1 test what wasvthe results and was there a variation between them and if so how much?
3. how did the compression tests fail and did you examine the specimens?
4. did you weigh or measure density of the samples before you tested them ?
Now you need to be honest and decide if there is a problem with the concrete or the test?
we never gives the preference to rebound hammer over the compression test,
either rebound hammer or UPV gives only a rough idea about the compression strength, only core test can gives ore accurate result or its result is very much close to true result only if the core is truly represent the concrete.
rebound hammer test gives only rough ideas about concrete strength due to certain limitation. Result from rebound hammer test sometimes also influence by person who carried out the test. UPV test not gives directly the concrete strength but depending upon data, homogeneity and density of concrete etc. can be co-related for concrete strength. Best way to predict about concrete strength is to take core from members of concrete and test by using standard procedure.
what about loading test Bhavin Buddhdev. I think this test give you a good vies for the behavior of overall structure ???
If you want to know the strength of concrete, you have to take cores and figure out its strength via compression test. On the other hand, if you want to check the overall structural element then you have to perform loading test as Dr.Abbas suggested.
No i dont prefer it. It only gives surface roughness. I advice to you windsor probe
Dear Ertug Aydin
Can you give more clarifying for your comment
The rebound number can be used to assess the uniformity of concrete in situ, to delineate zones or areas of poor quality or deteriorated concrete in structures. The test method is not intended as an alternative for the compressive strength determination of concrete, but with suitable correlation, it can provide an estimate of in situ strength.
In selecting an area to be tested the following factors should be considered: the strength of the concrete; type of surface; type of concrete; moisture condition of the surface; movement of the concrete under test; direction of test; types and sizes of rebound hammers. A test area shall be approximately 300 mm x 300 mm
Also the rebound hammer tests can be used to find a relationship between surface hardness and compressive strength to be able to estimate the strength of concrete with an acceptable error. To find a reliable method for strength estimation one should study all the influencing factors that can have any effect on the hardness measurement, and also that can have any effect on the variability of the strength of the concrete structure examined. The estimation should be based on an extensive study with the number of test results high enough to provide
Can you Dr Mohannad send a copy from ACI 228.1 R with pleasure???
Dear Dr Abbas
Did you mean this standards
http://bpesol.com/bachphuong/media/images/book/2281r_95.pdf
Can someone give more details about Acoustic Emission technique AE??
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