Proceq N Mode D'emploi page 34

Example:
A cube with a side length of 200 mm is used for the
determination of the compressive strength with the pres-
sure testing machine.
In this case the strength values shown in the conversion
curves in Fig. 2.9 and Fig. 2.10 on page 9 (for cylinders Ø
6"x12") must be multiplied by the shape coefficient of 1.19.
2 .5 .3 Time Coefficient
The age of the concrete and its carbonate penetration
depth can significantly increase the measured rebound
values R. It is possible to obtain accurate values for the
effective strength by removing the hard, carbonate-
impregnated surface layer using a manual grinding
machine over a surface area of about Ø 120 mm and per-
forming the measurement on the non-carbonate-
impregnated concrete. The time coefficient, i.e. the
amount of the increased rebound values R, can be
obtained by taking additional measurements on the
carbonate-impregnated surface.
R
m carb.
Time coeff. Z =
f
R
m n.c.
R : Average rebound value R, measured on
m carb.
carbonate-impregnated concrete surface
R : Average rebound value R, measured on non-
m n.c.
carbonate-impregnated concrete surface
12 Measurement
R
m carb.
⇒ R =
m n.c.
Z
f
Another possibility to consider the carbonation depth is
given by the chinese standard JGJ/T 23-2001.
In Table A of the standard JGJ/T 23-2001, compressive
strengths for rebound values from 20 to 60 (in steps of
0.2 R) and for carbonation depths from 0 to 6 mm (in
steps of 0.5 mm) are shown. For carbonation depths
higher than 6 mm, the values for 6 mm apply (no further
changes). The values in the table are based on compre-
hensive tests performed on concrete of different places
of origin and of different ages.
Based on Table A, Proceq has developed reduction
curves as a function of rebound value and carbonation
depth. These factors can now be applied to the Proceq-
curves and the curves of chapter 2.4.3.
Rebound values may be reduced by up to 40%.
The curves shown in Fig. 2.11, are exclusively valid for
the ORIGINAL SCHMIDT and DIGI-SCHMIDT concrete
test hammers from Proceq SA.
© 2017 Proceq SA