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Practical Lab Assessment Test 5 - Schmidt Hammer Test
Infrastructure management (Royal Melbourne Institute of Technology)
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Schmidt Test
Surface hardness defines a material’s ability to resist deformation. The Schmidt Hammer test
is suitable for casting comparisons between samples. Rebound energy recorded through
testing is inversely proportional to the energy absorbed by the concrete. This recorded value
is a non-dimensional value representing surface hardness providing an indication of surface
properties. Converting this value using the Schmidt Hammer chart affixed to the apparatus
produces corresponding compressive strength relating to the quality of concrete sample.
Appropriate use of the Schmidt Hammer test is critical ensuring accuracy of outputs. The
Schmidt Hammer is positioned at 90 degrees to the sample surface under assessment.
Samples assessed were samples Block 1, Block 2 & Block 3.
Methodology:
The method outlined was diligently followed to successfully produce accuracy within results.
1. Three concrete samples are setup with a calibrated Schmidt Hammer. Each sample
surface is marked with 12 locations identifying testing points.
2. Each sample surface is inspected for any imperfections prior to testing to gauge if
results will contain discrepancies
3. The Schmidt Hammer plunger is held to the sample surface at 90 degrees. It is then
pressed into the surface to release the internal spring in preparation for testing.
4. Pressure is then applied to the hammer as it is pressed into the surface. A loud click is
the result of the hammer mass being released.
5. The lock button is pressed before releasing to ensure that the value is locked on the
scale of the Schmidt Hammer. The value is recorded across the 12 testing points on
each sample block.
6. Values are converted using the conversion chart affixed to the Schmidt Hammer. The
value is transposed to a kg/m2 measurement – compressive strength. Multiplying
compressive strength by 0.098 converts this result to MPa.
Once results are tabulated, the mean and standard deviation is calculated followed by a
comparative analysis.
Figure 1 Schmidt Hammer operation [1]
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Results:
Schmidt Hammer test results were tabulated as shown below in Table 1-3. The average and
standard deviation was calculated using equations below:
Average:
μ=
Standard Deviation:
σ=
∑ xi
n
√
∑ ( x i−μ )2
n
Specimen A
Table 1: Specimen A hammer test results
Specimen A
Test Location
Hammer Rebound
1
2
3
4
5
6
7
8
9
10
11
12
47
50
44
46
45
44
46
48
44
45
44
44
Average
Standard Deviation
Figure 2: Specimen A: testing points
45.58
1.80
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Specimen B
Table 2: Specimen B: hammer test results
Specimen B
Test Location
1
2
3
4
5
6
7
8
9
10
11
12
Hammer Rebound
40
36
30
38
40
36
38
30
38
42
33
38
Figure 3: Specimen B: testing points
36.58
3.52
Average
Standard Deviation
Specimen C
Table 3: Specimen C: hammer test results
Specimen C
Test Location
Hammer Rebound
1
50
2
38
3
47
4
50
5
47
6
52
7
41
8
30
9
48
10
47
11
52
12
45
Average
Standard Deviation
Figure 4: Specimen C: testing points
45.58
6.01
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Discussion:
Impairment of results is probable granted the variable factors influencing outputs. A. Aydin
and A. Basu [2] highlight issues influencing the consistency and reliability of Schmidt
Hammer test results such as specimen dimensions, surface smoothness and imperfections,
weathering, and analysis methodology. There were evident signs of the aforementioned issues
on the specimen samples tested, which may have led to greater result variances and
inconsistencies.
Observed in a study of the Schmidt Hammer test by M. Kazemi, R. Madandoust, J. de Brito
[3] was the relationship concerning surface hardness, concrete compressive strength and
surface properties - larger surface hardness outputs correspond with increased concrete
compressive strength and lower readings of surface hardness indicate weaker surface
properties. Furthermore,
Amongst the three specimen samples pertaining to this experiment, specimen A & C
measured the same average hammer test reading of 45.58. However, their standard deviations
were considerably different with a measurement of 1.80 for specimen A and 6.01 for
specimen C. This difference is indicative of the uniformity of the sample’s surface properties
suggesting that specimen A was the strongest sample.
References
[1]
The Constructor. 2020. Rebound Hammer Test On Concrete - Principle, Procedure,
Advantages & Disadvantages. [online] Available at:
https://theconstructor.org/concrete/rebound-hammer-test-concrete-ndt/2837/
[Accessed 19 March 2020].
[2]
A. Aydin, A. Basu, “The Schmidt hammer in rock material characterization”,
Engineering Geology, Volume 81, Issue 1 2005, Pages 1-14
[3]
M. Kazemi, R. Madandoust, J. de Brito, “Compressive strength assessment of
recycled aggregate concrete using Schmidt rebound hammer and core testing”,
Construction and Building Materials, Volume 224 2019, Pages 630-638
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