Endress+Hauser Solitrend MMP20, Руководство по эксплуатации

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SWZ probe Solitrend MMP20 (Option D)
30 Hauser
8.4 Potential problems in the laboratory and at the
concrete plant
8.4.1 Situation 1: Mixing the concrete with dry aggregates
Depending on the rock, it can take some time for dry aggregates to become saturated after
the mixing process. This can range from 3 to 5 min for relatively absorbent aggregates, to
up to one hour for less absorbent aggregates. Given that the SWZ probe only "sees" one
third of the core water, we recommend that you wait a "certain amount of time" after
mixing dry aggregates before checking the water content with the SWZ probe.
Example: A dry, highly absorbent rock can absorb up to 30 l of water per cubic meter in a
relatively short period of time. Due to the equilibrium moisture content, however, the rock
that is used and stored is not entirely dry. Rather, it has a water content typically of 7 l/m³.
For a concrete formulation with 175 l/m³ effective water content, 175 l + 23 l = 197 l
were then used. Directly after the concrete has been mixed, the SWZ probe would measure
approx. 185 l here and then display a reading of 175 l relatively quickly after approx.
3 to 5 min (depending on the rock). For the handheld device, two thirds of the maximum
core water would have been entered for the G-Set parameter. In this case, two thirds of the
30 l maximum core water would have been entered in the handheld for the G-Set, i.e. G-
Set = –20 l, if the effective water is to be measured.
When mixing with dry aggregates, it is important to wait a certain amount of time -
depending on the rock type - before taking a reading with the SWZ probe!
8.4.2 Situation 2: Subsequent addition of water to the concrete
Problems and non-conformities during a laboratory test, which was performed as follows:
1. The water content of approx. 8 l of fresh concrete was measured in a bucket with the
SWZ probe. A reading of 178 l/m³ was measured, for example.
2. After this, 50 g of water were added to the fresh concrete, which would correspond to
an increase in the water content from 178 l/m³ to 184.25 l/m³, for example. After
mixing the concrete for approx. one minute in a small mixer, the concrete was then
tested with regard to the raw density and flow class. The concrete used to determine
the density and flow class was then poured back into the measuring bucket for the
purpose of determining the water content afterwards with the SWZ probe.
3. Then, the concrete water content was measured again with the SWZ probe. This
time, however, the result was only 181 l/m³ and not 184.25 l/m³ as expected.
 When the concrete is mixed in the small mixer, some of the water already
escapes. This is because when relatively small quantities of concrete are mixed in
an open container, the water adheres to the wall of the container over a large
surface area and evaporates. If this concrete is then also used afterwards to test
the flow class and raw density, then no gravel and hardly any sand sticks to the
outer walls of the testing instruments but the water and fines "cling" to these
surfaces as a result of the adhesion of water. This effect can be easily checked.
After the first SWZ probe reading of 178 l/m³, mix the concrete again for approx.
one minute and then check the water content again with the SWZ probe. The
2 to 3 l/m³ reduction in the water content is then an indicator for the evaporative
effect as a result of mixing.
Subsequent mixing of the concrete causes considerable deviations in the water
content readings!
8.4.3 Situation 3: Sampling in the concrete plant
1. Before the concrete was transferred to a truck mixer, a concrete sample was taken
directly from a twin-shaft mixer and transferred to a bucket.