How Volumetric Mixers Align With Intake Structures
Simple or complex, the purpose of an intake structure is to help control water flow and quality for a wide range of supply sources:
- Erosion control,
- Screening solids, and
- Turbulence reduction.
Since many of these structures are in remote locations, it can be difficult to receive optimal concrete every time. Volumetric mixers allow you to schedule the pour at a certain time with the full knowledge the concrete won’t begin mixing until the unit is on-site and you’re ready.
Types Of Intake Structures
Depending on the specific water and sewer project, one or both types may be used.
As the name suggests, this type is entirely underwater and is frequently used to supply water from lakes and larger rivers. An intake channel lies below the lake or river bed with the inlet end protruding from the bed, with a concrete or timber crib protects the inlet itself.
Several advantages of using submerged intakes include:
- Minor obstruction to the river flow;
- Generally unencumbered by floating debris and/or material; and
- Minimal issue if ice forms on the water surface.
Towers are the most common form of an exposed intake. They’re used in two situations: a wide fluctuation in water level or to remove water from a more desirable depth. These concrete structures have multiple openings — intake ports — at varying heights for water removal.
This type of tower fills with water to the supply source level, which filters through penstocks and then discharges into the tower. From there the water pumps to the treatment plant.
The tower houses intake pipes that carry source water directly to the treatment plant. This leaves the tower accessible for operation and inspection as needed.
Volumetrics Remove Hassle, Headaches Often Associated With Pouring Intake Structures
As many of these projects are located in remote areas, the use of a traditional barrel mixer presents several issues, namely timeliness. For example, if inclement weather delays the scheduled job, it’s likely an entire load of concrete is now wasted as it was premixed and delivered to the site. Traffic delays are also common reasons for rejected deliveries and subsequent project delays.
A volumetric allows the operator to change the mix design — such as PSI — as the project dictates without making additional trips to a batch plant for different concrete. For example, an underwater intake needs a high enough strength to withstand water pressure whereas an exposed structure may or may not be partially submerged.
A type of high-performance concrete, underwater concrete (UWC) needs to meet three criteria:
- Highly flowable,
- Self-consolidating, and
- Quickly buildup viscosity during mixing.
Admixtures, such as a hydrosizer, are common with UWC as it’s effective in fresh and saltwater situations, along with reducing excessive washout. The amount can be increased or decreased as needed throughout the pour. However, once the amount is set for a specific mix design in a volumetric mixer, it rarely needs to be adjusted.