Lighter and stronger slabs with less cement

When producing hollow-core slabs, efficient shear compaction is needed to remove the air out of the mix. Traditionally, vibration technology has been used for this purpose, but the a major downside of this has been a very high noise level. Vibration is not only tiring to the operators’ ears but causes significant wearing on the machine parts and structure. These are the reasons behind the development of shear compaction technology, an extruding innovation that changed the perception of precast quality.

At the end of the 1970s, Elematic started a project to decrease the noise levels of concrete compaction. In 1985, shear compaction technology was commercialized, and the first shear compaction machine was launched. In shear compaction, no vibration is used. The concrete mix passes screws pushing it forward. Compaction takes place when the mix is extruded under pressure, creating and shearing stress is created.

Long development path

“Currently, the fourth generation of our extruder technology is on the market. We have gathered customer feedback actively along the way,” says Elematic’s Technical Director, Lassi Järvinen.

In the mid-eighties, the first first-generation machine reduced the noise caused by concrete compaction. But the quality of the slabs remained the same as those manufactured with vibration technology. In 1989, the next generation of shear compaction introduced a remarkable improvement in wear part lifetime. The third generation in 1995 brought improvements in strand bond and placement, resulting in a lower number of rejected slabs. Higher shearing power allowed better dimensional accuracy of the end product.

“At the same time, we got rid of the excess weight in slabs,” Järvinen explains. ”A weight-optimized slab can save up to 1,000 cubic meters of concrete per 100,000 square meters of production.”

Low cement consumption

The current generation of shear compaction, – extruder the E9 extruder –, saw the light of day in 2010 when the new patented screw structure was introduced, bringing more shearing power, and a remarkably lower cement consumption level. In addition, the slab surface became more even, demanding substantially less topping for leveling at the construction site.

Cement forms even up to 70 percent of the total CO2 load of a precast element. Optimizing the cement content through efficient compaction plays a major part in reducing the CO2 emissions of precasting. It is a win-win situation, with less cement used and less waste produced.

“With our machinery, even up to 100 kilos less of cement can be used per one cubic metre of concrete,” says Järvinen. “ So it is easy to calculate that the extruder investment pays for itself in one year. During the past 30 years, we have been able to reduce approximately 10 – 15 kilos of the end product weight per square meter.” With the global slab production of 10 million square meters per year, the savings in material costs become are remarkable. Efficient shearing leads into a stronger and lighter end product. Since it was established five years ago, the worldwide E9 deliveries have exceeded already 150 extruders.

Lassi Järvinen

Extruder according to production capacity

“Elematic’s flagship E9 is the first extruder in the world with 100 percent shear compaction automation, incorporating remote monitoring,” says Elematic’s Product Director at Elematic, Jani Eilola, explains. Extruder The E9 extruder is a highly automated, robust machine for continuous production of slabs up to 500 millimetres millimeters in height. The E9 does not require an operator to oversee the production.

The extruder S5 extruder enables represents a lower-cost investment for new entering entrants to the market with a smaller production capacity. It was released in at the beginning of 2014. The little sister of E9 incorporates the same shear compaction technology with less automation. The lighter S5 is a lighter extruder that can produce slabs up to a height of 320 millimetres.

Easy serviceability

The serviceability features of the E9 and S5 bring savings to the customer. Developing the extruders’ maintainability has cut the number of hours of spent replacing the screws and bearings in half, for example. “Both extruders have a modular structure, allowing the use of several nozzles with the same power unit. Changing the nozzle for to producing produce different end product types is easy: locating most technology in the power unit makes the nozzle affordable, and quick to replace,” Eilola says.

“With the latest technology, a very low level of strand slippage can be achieved. A new strand guide was developed to hold the strands in a right place,” Eilola explains.

“To predict production performance, the ability to plan service is vital. With shear compaction technology, maintenance of the machinery can be carried out as planned,” Eilola says. A reliable fleet equals reliable precast production and delivery – on time, every time.

Jani Eilola