Pre-Wet Water - Hydronix Hydro-Control VI Operator's Manual

Understanding the Mix Cycle

2 Pre-wet Water

What is Pre-wet Water?
2.1
Pre-wet Water is a quantity of water that may be optionally added at the beginning of the mix
cycle before the Dry Mix phase.
Why use Pre-wet Water?
2.2
Pre-wet Water may be used for several reasons. These include:
1. To reduce cycle times. This is especially true for large batches requiring large quantities
of water. The Pre-wet Water (typically 2/3 of the total water) is dosed with the addition
of the aggregates. This enables the bulk of the required water to be mixed into the
material earlier in the mix cycle. The moisture sensor is then used to accurately dose
the remaining water.
2. To improve the efficiency of the mixing process when using certain admixtures, so that
when the chemicals/dyes are added they are not being added to dry material.
3. To wet the aggregates before adding the cement to the mixer. This may be necessary
for a number of reasons, for example to aid the mixing of cement into the material
(preventing 'balling up') or perhaps a particular colour admixture needs to be added to
a wet mix before the cement is added. Another benefit of adding Pre-Wet before the
cement is to loosen the material and reduce the mixing power, useful in mixers that are
not capable of mixing all dry materials together.
4. To wet the aggregates to bring them above their Water Absorption Value (WAV – also
known as the SSD – "Saturated Surface Dry" point), typical for lightweight or synthetic
aggregates.
Example case:
If the water needed to produce a repeatable concrete mix varies between 55 and 68 litres
(depending on the moisture of the raw materials), then the recipe could be setup to put 40
litres of pre-wet water. The remainder of the water can be added in the main water phase.
Additional I/O for Pre-wet Water
2.3
When adding Pre-wet Water to the aggregates the Hydro-Control VI has an output called "Pre-
wet Done" which is activated at the end of the pre-wet phase in the cycle. This can be used by
a batch control PLC to control the loading of the cement.
If using the "Pre-wet Done" signal it is best practice to pause the Hydro-Control until the cement
has finished loading. For this the Hydro-Control VI has an input called "Cement In". After the
"Pre-wet Done" output is given, the Hydro-Control waits for the "Cement In" before continuing
onto the Dry Mix phase.
Whilst the Hydro-Control is paused, there is a timer running that will trigger an alarm if the
"Cement In" input is not received within a set amount of time. If the "Cement In" input is not
used then the Cement Timeout parameter in the recipe must be set to zero to disable the alarm.
22 Hydro-Control VI Operators Guide HD0456 Rev 1.7.1
Chapter 4