Uniform mixing

Concrete Producer, The, August, 2004 by Rick Yelton

High-performance concrete is becoming a worldwide topic. Chemists and mix design engineers are working hard to develop new ingredients to cast concrete as a Space Age material.

Just as importantly, equipment manufacturers are developing new equipment to help producers batch mixes that may require special attention.

At Bauma 2004, attendees saw the future of high performance concrete--German style. Maschinenfabrik Gustav Eirich, a German mixing equipment manufacturer, displayed a sample concrete bridge. At first glance, observers thought the 8-foot-long span was a piece of artwork. But on closer examination, they learned the element had been cast with a performance concrete, enabling a thin, slick design.

The producer needed a mixer that was a step above the norm, said Peter Nold, Eirich's director of technical sales. The bridge deck material had to be mixed thoroughly and completely to take advantage of the full engineering properties of the ingredients.

In recent years, German block producers have been buying the units to increase mix uniformity. The dual action provides better pigment blending. And the variable setting feature allows the operator to accurately batch an absolutely homogeneous concrete slump or spread.

A century of mixing

Eirich engineers developed their version of the planetary mixer in 1906. In 1924, the manufacturer opted to discontinue manufacturing the fixed base unit to development its own style of intensive mixers.

Unlike all other mixing systems, the Eirich mixer allows the speed of the working tool to be adapted with optimum effect. The Eirich design allows the operator to mix with circumferential speeds of between 2 meters/second and 40 meters/second. The flexibility provides the operator greater control on the full energy input into the mix. This feature combines with the rotary mixing pan design, resulting in more uniformity in highly fluid mixes.

The Eirich mixer differs from other planetary mixers in two significant ways. The drive unit allows the producer to set the speed mixing tool. And the mix pan rotates in opposition to the blades.

Testing for uniformity

To quantify uniformity improvements from their mixing design, Eirich engineers engaged the Institute for Pre-fabricated Element Technology and Pre-fabricated Building in Weimar to conduct an independent research study on "planetary mixers versus Eirich mixers."

The study compared facing concrete mix from a planetary mixer and an Eirich mixer (R-Type). Compared to planetary mixers of identical capacity, the Eirich intensive mixer achieved a preset uniformity of mix quicker. Along with a reduced mixing interval, researchers found a high uniformity in the quality parameters of the fresh concrete prepared with the Eirich mixer.

Fresh concrete density fluctuated by 0.19% on five samples taken from the Eirich mixer and by 0.46% on five samples from the planetary mixer. Results were similar for water content, the solids content, and de-icing salt resistance.

Self-consolidating concrete is another great opportunity. A new study by the Munich Technical University suggests producers can mix SCC in an Eirich R-type mixer within 60 seconds (mixing time from beginning water plus superplasticizer, in addition to the dry component).

For more information, contact Eirich Machines, 847-336-2444, or visit www.eirich.com. Circle 1 on the reader service card.