What are the formulae used in the compressive strength correlation curves in the OS8000 and OS8200 rebound hammers?
The formulae applied to determine compressive strength correlation curves for the OS8000 and OS8200 rebound hammers are provided in the Schmidt Hammer Conversion Curve Database referenced below:
- Original Schmidt OS8000 Type N
|
Curve |
Min R |
Max R |
Unit |
Form factor |
Equation |
|---|---|---|---|---|---|
|
Proceq B (14 - 56 day mean) |
15 |
55 |
N/mm2 |
150 mm cube |
Fck = 1.05 x ( 0.01078R2 + 0.904R - 12.91) |
|
Proceq A (7 days mean) |
15 |
55 |
N/mm2 |
150 mm cube |
Fck = 1.05 x ( 0.012516R2 + 0.706R - 7.49) |
|
Portland Cement J |
15 |
55 |
kg/cm2 |
150 mm cube |
Fck = 1.05 x ( 0.133R2 +8.82R - 122) |
|
Early strength J |
15 |
55 |
kg/cm2 |
150 mm cube |
Fck = 1.05 x ( -0.0803R2 + 20R - 253) |
|
Blast Furnace J |
15 |
55 |
kg/cm2 |
150 mm cube |
Fck =1.05 x ( 0.2R2 + 1.83R + 22.4) |
|
Averag Curve J |
15 |
55 |
kg/cm2 |
150 mm cube |
Fck = 1.05 x ( 0.0485R2 + 12.3R - 146) |
|
Characteristic strength R |
20 |
75 |
N/mm2 |
150 mm cube |
Step function (see below) |
The characteristic strength curve is based on the reference table for the screening test provided in the Annex to EN13791. This curve provides a safe estimate with <5% probability of over-estimating the strength.
R value - Strength (N/mm2)
20 to 29 - <10
30 to 32 - 10
33 to 34 - 15
35 to 37 - 20
38 to 39 - 25
40 to 42 - 30
43 to 46 - 37
47 to 48 - 45
49 to 50 - 50
51 to 52 - 55
53 to 56 - 60
57 to 59 - 67
60 to 64 - 75
65 to 68 - 85
69 to 75 - 95
Impact angle conversion is applied to the measured R value before calculation of the compressive strength according to these curves. The impact angle correction is based on this formula:
Rcorr=R +(-a0+R*a1)*sin(angle)
|
a1+ |
0.08 |
|
a0+ |
7.1 |
|
a1- |
0.043 |
|
a0- |
4.3 |
Take a0+ and a1+ for angles >= 0°, a0- and a1- for angles < 0°
2. Silver Schmidt OS8200 Type N
|
Curve |
Min Q |
Max Q |
Unit |
Form factor |
Equation |
|
< 10% (old) |
22 |
75 |
N/mm2 |
150 mm cube |
fck = 2.77e^0.048Q |
|
Ref EU (old) |
21 |
62 |
N/mm2 |
150 mm cube |
fck = 1.8943e^0.064Q |
|
Ref CN |
20 |
75 |
N/mm2 |
150 mm cube |
fck = 0.0244Q^2-0.6129Q+10 |
|
Ref RUS |
20 |
77 |
N/mm2 |
150 mm cube |
fck = 0.03Q^2-0.86Q+9.5 |
|
Mean strength |
10 |
75 |
N/mm2 |
150 mm cube |
fck = 3.6473e^0.0475Q |
|
Characteristic strength Q |
10 |
95 |
N/mm2 |
150 mm cube |
Step function (see below) |
No angle correction is required for measurements with the Silver Schmidt.
Note! The Ref EU curve was determined with very high quality concrete and gives very high strengths.
The characteristic strength curve is based on the reference table for the screening test provided in the Annex to EN13791. This curve provides a safe estimate with <5% probability of over-estimating the strength.
Q value - Strength (N/mm2)
10 to 33 - <10
34 to 39 - 10
40 to 44 - 15
45 to 48 - 20
49 to 51 - 25
52 to 55 - 30
56 to 59 - 37
60 to 61 - 45
62 to 63 - 50
64 to 65 - 55
66 to 67 - 60
68 to 70 - 67
71 to 72 - 75
73 to 74 - 85
75 to 80 - 95