Creating New Conversion Curve - Proceq DIGI-SCHMIDT 2000 ND Operating Instructions Manual

Standard Conversion Curve for Concrete Test
Hammer Model LD
Mean value has already been corrected in relation to
the impact direction
Fig. 8.2 Model LD: Conversion curve based on the average
compressive strength of a cylinder and the rebound
value R
Limits of Distribution
fck : The max. and min. values are set so that 80 %
cyl.
of all test results are included.
20 Appendix
8.3

Creating New Conversion Curve

Experience has shown that deviations from the normal con-
version curves occur under the following circumstances:
- Artificial stone products with an unusual concrete com-
position and small dimensions. It is recommended to
perform a separate series of tests for each product in
order to determine the relationship between the rebound
value R and the resistance to pressure.
- Aggregates made from low strength, lightweight or clea-
vable stone (e.g. pumice, brick rubble, gneiss) result in
a strength value lower than shown on the conversion
curve.
- Gravel with a preponderance of smooth, polished surfa-
ces and spherical shape results in values for compres-
sive strength which are lower than those ascertained by
the rebound measurements.
- A strong, dry mixed concrete (i.e. with low sand content)
which has not been worked adequately may contain
gravel agglomerations which are not visible from the
surface. These affect the strength of the concrete
without however influencing the rebound values R.
- The concrete test hammer gives inadequate rebound
values R on recently applied, green concrete or con-
crete which has hardened under water. The concrete
must be dried before the test.
- Very high values for compressive strength (> 70 N/mm2)
can be achieved by adding pulverized fuel ash or silica.
However, these strengths cannot reliably be ascertained
using the concrete test hammer.
© 2001 PROCEQ SA