In the mix - developments in concrete construction
By Steve Skinner30 November 2009
This year's SAIE exhibition in Italy was note-worthy for the number of new concrete mixing and batching plants on show. From innovative new systems to enhanced versions of existing technology, SAIE demonstrated that equipment behind the production of concrete is evolving at a pace.
Armando Chillon unveiled its new range of single shaft concrete mixers. Ideally suited to precast and ready mix applications as well as large scale on-site production, the AC mixers are capable of mixing up to 5 m3 of concrete in just 30 seconds.
At the heart of the mixers is a belt-driven solid steel input shaft to which two helical shovels are attached. At 20 rpm, the shovels turn the material 40 times in 30 seconds to achieve a fast yet high quality mix in which water content is continually measured with a microwave probe.
With limited moving parts and the incorporation of a cast iron liner designed with a lifespan throughput of 1 million m3, the AC range discharges mixed concrete in under 10 seconds through a hydraulically operated gate.
In situations where drum cleaning might be required between batches, Chillon also has an optional 10 nozzle high pressure automatic cleaning system for the AC range.
Partner in the company, Lisa Chillon told iC, "This new mixing technology is available to both manufacturers of batching plants and to end users. The Chillon AC mixer is extremely strong mechanically and requires a much lower power motor than alternative mixing systems, so is kinder to the environment and is cost efficient to operate."
Officine Piccini used the show to launch its new four strong series of concrete batching and mixing plants featuring capacities of between 30 and 120 m3. Customer Care Representative Marianna Martucci told iC, "We used to manufacture bespoke plants, but we noticed that demand usually fell in the same areas so we decided to produce a standard series.
"The new series represents easy to use simple batching plants with all components manufactured by Piccini. We are confident that a standard offering suits the current market demands," she said.
O. Cuoghi launched its concrete high technology turbo (CHTT) mixer for the production of cement paste.
Technical and commercial manager, Salvatore Roccaforte said, "The CHTT mixer can be combined with an existing dry batching plant to convert it into a full wet concrete plant.
"This system saves on cement yet the concrete is extremely consistent and has better flowability over dry mix," he told iC.
Mixing takes place under pressure, while additional disturbers are mounted within the drum to add turbulence to improve the mix. The CHTT mixer is equipped with a 45 kW electric centrifugal pump and the drum sits on electronic weight sensors for accurate batching.
"We believe that through mixing cement paste with this system a producer can achieve a better class slump from the same quantities of materials," said Mr Roccaforte.
The mixer features four water jets that operate at 200 bar to clean the drum automatically after each batch, and the water is kept within the system to act as the batching water for the next cycle.
Mr Roccaforte told iC, "Another significant advantage of this system is that it uses up to -75% less energy than classic planetary or twin-shaft mixers while producing more homogeneous concrete with better mechanical properties."
The CHTT mixer features the capacity to produce 12 m3 batches in six minutes, including loading and cleaning, so has a maximum throughput of 120 m3 per hour.
Kimera, a division of the Socage Group, showed its truck mounted batching and mixing plant at SAIE. Featuring an output capacity of 60m3 per hour, the unit mixes a cement paste, which is in turn mixed with aggregate, a process that takes just 20 seconds for an 8 m3 batch.
Engineering manager at Kimera, Danilo Maffei told iC, "This unit is ideal for long distance and urban construction where a traditional drum mixer would be impractical. It also suits hot climates such as the Middle East and South America because the concrete is only mixed when it's needed."
Featuring four 800 l water tanks, the 40 tonne truck can be loaded with 12 m3 of aggregates and 5 tonnes of cement, yet with its continuous flow capability and low regulated height can also be fed with materials transported separately.
"This system is particularly ecologically friendly because there's no footprint and operators only mix the exact quantity that's needed. Furthermore, because the unit's fully mobile, operators don't need to worry about obtaining planning permission to set-up on site," said Mr Maffei.
Following the launch, Kimera is already designing a smaller unit to fit a twin axle truck in the 9 to 11 tonne range.
Beyond SAIE, Ammann's Amix twin-shaft paddle mixer features an optimised plate design and has been designed with wear resistant coatings on the feeder lining, mixing arms and blades to prolong service intervals and reduce operating costs.
Marketing assistant Marion Ciaffoni said, "Ecology and safety are key aspects in new product development here at Ammann. Furthermore, to address a growing demand for high capacity plants that can be easily relocated, we are now working on the expansion of our range to include a semi-mobile plant featuring a large volume Amix mixer."
BHS -Sonthofen has extended its range of mixers to suit advanced concrete recipes and enable its systems to be configured more precisely to mix designs.
Managing director, Christof Kemmann told iC, "Most recently we launched a twin-shaft batch mixer with two opposite mixing arms to introduce more shear forces into the mix. This has proved particularly useful with mixes such as ultra high performance concrete (UHPC) featuring high quantities of fine materials and a high proportion of chemical additives."
BHS -Sonthofen also introduced a concept for increasing the efficiency of dry batching plants, through the addition of a small continuous mixer to reduce dust and enhance the saturation of the cement.
"By adding the small continuous mixer, a producer can pre-mix the cement, water and additives before discharging into the truck mixer," he said. "This makes better use of the cement which is then mixed with the aggregate in the truck mixer."
Extreme placingIn western China, at an altitude of 3380 m above sea level, two Putzmeister SPM 500 PC concrete wet spray machines are being used to wet-shotcrete two 32.6 km long railway tunnels being driven through the Guanjiao Mountains.
With temperatures as low as -360 C and atmospheric pressure reduced by -33% as a result of the altitude, site workers have experienced shortness of breath, exhaustion, headaches and nausea. Despite the effects on the workforce, a Putzmeister spokesman said the compressor output of the shotcrete units had remained at 100%, and while the low static pressure had a minimal effect on pump suction, the units were still able to maintain a delivery rate of 30 m3 per hour.
The tunnel project valued at RBM 2.5 billion (US$ 366 million) is scheduled for completion in 2012 and will complete the link between Xining, capital of the Qinghai Province, and the city of Golmud.
Also in China, Zoomlion has launched its new generation 56 m, six section RZ boom truck mounted pump on a four axle chassis. Featuring a 56 m vertical and 51 m horizontal reach, the new unit is the result of the technology amalgamation following the Zoomlion and Cifa merger according to a Zoomlion statement.
A smaller Zoomlion ZLJ5261THB four section, 37 m, Z boom truck mounted pump has become the first Chinese concrete pump to start operations in Greece. Mounted on a Mercedes chassis with X style hydraulic outriggers at the Spanos factory in Thessalonika, the unit features automatic energy saving, boom vibration reduction, automatic anti-pipeline blocking and intelligent self-diagnostics.
As well as Rexroth hydraulic pumps, HBC proportional remote control and a Brevini gear motor, the ZLJ5261THB also features hard faced and carbide wear parts, easy to service multi-piece piston cups, a high pressure water pump, pneumatic lubrication and hard chromed concrete cylinders.
At the SAIE show in Italy, Mecbo launched its new 5 tonne Cingolo concrete pump featuring the company's hydraulic Pulsar ‘S' valve. Capable of pumping up to 40 m3 per hour, the track mounted Cingolo is self-propelled and with dimensions of 1.6 m by 4.3 m, and a height of 2.5 m, has been designed for easy movement around sites.
Also at SAIE, Mecbo debuted its MB24L Lineare truck mounted mixer pump with a three section, 24 m boom and carbon steel pipeline. The 400 l hopper can either be fed by the truck's own mixer drum or by additional truck mixers due to its low level mounting.
Maurizio Negroni of Mecbo's commercial office told iC, "Because of the offset of the boom, the outriggers only protrude on one side of the truck. This means the unit has a total operating width of just 3.7 m, yet still offers a horizontal reach of 19.5 m and a vertical reach of 23.8 m."
The up to 17.8 tonne MB24L Lineare unit can be equipped with mixing drums of either 7, 8 or 9 m3 capacity and is fitted with Mecbo's Pulsar 4 hydraulic ‘S' valve pump with a maximum output of 60 m3 per hour.
While the concrete sector is far from facing a revolution, mix designs and the equipment to produce and manage them are evolving. As BHS-Sonthofen's Mr Kemmann told iC, "Contractors are under tough competition and are looking for more benefits such as reduced energy consumption set against excellent mix quality."We also see a growing number of contractors looking for increased flexibility in their equipment so they can produce both standard and advanced concrete recipes with the same tools."