Chemistry's influence on equipment for concrete construction
By Steve Skinner06 May 2009
The development of additives, alternative aggregates and modified mixes is revolutionising concrete construction. Steve Skinner reports on the latest equipment designed to work across the full range of mixes.
Concrete is evolving at a pace and there's no greater example of this than work carried out by chemical engineer Dale Bentz of the National Institute of Standards and Technology in the US, who is researching viscosity-enhancing nanomaterials in a bid to double the service life of concrete.
Mr Bentz and his colleagues have successfully integrated a nano-sized additive into concrete that slows penetration of chloride and sulphate ions from road salt, sea water and soils.
"Rather than change the size and density of the pores in concrete, we have changed the viscosity of the solution in the concrete at the micro-scale to reduce the speed at which chlorides and sulphates enter the concrete," said Mr Bentz.
"There are still some technical and educational hurdles remaining but I believe nano-level engineering holds great promise because it can be applied in the solution and solid phases of cement-based materials," Mr Bentz told iC.
In Thailand, Eurosia Trading has reached sole-distributor rights with Germany's Dennert to become the latest country to launch Poraver aggregate later this year. Poraver is an innovative lightweight aggregate developed by Dennert and made from 100% recycled glass.
The glass is ground to a fine powder, mixed with water, binding and expanding agents and then heated to 9000 C. The processed aggregate features individual granules that entrap microscopic pockets of air.
"As an aggregate Poraver offers low density and high compressive strength, resistance to bacterial and chemical attack and superior levels of thermal and sound insulation," said Soonthorn Tangpaosak, managing director of Eurosia.
"Poraver is a new concept for Thailand, but we believe there is a promising market here," said Mr Tangpaosak.
Additives and specialist aggregates aside, mass concrete has properties that make it an excellent material for the construction of radiation shields.
"Lead is the obvious choice, but it is about 30 times more expensive than concrete for the equivalent shielding capacity," said George Burfitt, a consulting engineer and specialist in nuclear structures.
Due to its excellent shielding properties and value, Doncasters Group of the UK elected to use mass concrete for the construction of a new industrial X-ray testing facility for its aerospace and industrial gas turbine products.
"The X-ray facility uses a high powered linear accelerator (LINAC) to penetrate metal components in order to detect any microscopic imperfections," said Mr Burfitt.
The concrete ‘bunker', measuring 17 m by 14 m and 6.7 m in height features wall thicknesses of between 600 mm and 2.8 m and has a 1.5 m thick roof cap. The complete structure was cast in three pours and the walls alone required more than 400 m3 of concrete.
"The integrity of the formwork to contain the massive volume of slow-curing concrete was vital," said Scott Fanning, account manager at SGB. "We used SGB Logik 60 to withstand the pressures and did so using lots of small panels to gain maximum stiffness and strength."
High concrete pressures are an increasingly common issue following the advent of self compacting concretes (SCC). Tabla is one company that has reviewed its entire falsework and formwork range to see what adaptations were necessary to better handle current and future SCC mixes.
"In horizontal pours, SCC doesn't really generate great hydrostatic loads, but leakage, particularly with regard to modular systems, has the potential to cause problems," said CEO, Paul Gillespie.
As a result Tabla honed its system through the incorporation of an improved architectural bridge strip and the introduction of a new inexpensive spring clip. Mr Gillespie told iC, "These second generation modifications provide a flatter surface while the panel joints are now sealed against leakage of very wet concrete. Attention to detail has produced a highly effective solution."
In vertical pours, SCC has the potential to generate extremely high hydrostatic pressures due to its curing behaviour. "SCC remains liquid for a longer period and as a result taller pours generate full liquid head pressures which can easily exceed 144 kN/m2," Mr Gillespie told iC. "Consequently, we redesigned our TB1 wall form system to boost our performance in this area."
Tabla's TB1 wall form now features a matrix of horizontal and vertical members which provide four way support to the facings, while eliminating the fixed tie positions and incorporating built-in continuous walers allows for the introduction of additional ties and an increase in tie diameters.
"The in-built walers and continuous tie-off capabilities as well as the ability to lock clamps and tie plates thereto have greatly enhanced vertical forming procedures with SCC," said Mr Gillespie.
With regards concrete production, SBM Mineral Processing of Austria launched its 170 m3/hour capacity Euromix 4000 mobile concrete mixing plant last year. The Euromix 4000 represents the next step in the Euromix range that starts with the 60 m3 per hour capacity 1000.
"Customers need increasingly high capacities per hour to produce economically," said Engineer Gerhard Gschwandtner. "Our Euromix machines are produced with reference back to operators and we have taken into account all of the needs of our key customers in the design process to ensure our machines are user-friendly and easy to handle."
Also last year, Liebherr started work in November on installing its first mixing facility for pre-cast concrete production in the UK, providing Cemex with a dedicated and virtually continuous chute-fed output for its customer Centrum Pile.
The twin Betomix 2.25 mixing facility was fast-tracked throughout planning, design, installation and commissioning to come on line in just four months of the order being placed.
"Liebherr's specialist knowledge was invaluable in assisting us to develop this very special facility," said Anthony Groom, Cemex engineering manager.
"The modular yet versatile construction of the Betomix system allowed us to stick to the very tight manufacturing schedule, in spite of the numerous modifications required to accommodate the needs of Centrum Pile."
Meanwhile, Lintec entered the UAE market at the beginning of 2009 when it shipped a CC3000B unit from its headquarters in Germany to its first customer in the Emirates. Capable of producing 120 m3/hour of concrete, the new facility is lighter than its predecessor and, according to the company, passed ‘test erection' prior to shipping with flying colours.
Last autumn, Schwing unveiled a redesign for its S39SX truck-mounted concrete pump.
The popularity of the S39SX has partly been attributed to its overall length of less than 12 m and weight of below 26 tonnes. These characteristics mean that operators do not require special authorisation or permits from authorities for on-road driving. At the same time, the S39SX offers operators the opportunity to compete in the 40 m class.
"The new plastic water tank has +30% more capacity, up to 600 l, and has been installed near the feeding hopper," said a Schwing spokesman. "We have also increased the volume of the hydraulic reservoir by +10% to 600 l.
"In combination with arc-shaped outriggers to the fore and H-type outriggers at the rear, the machine offers short set-up times and a space-saving installation process requiring up to -80% less set-up space than a comparable machine. That said, the pump provides the operator with a stable 2000 working range and a placing performance of 100 m3/hour," confirmed the spokesman.
Zoomlion used last month's Intermat show to launch its new ZLJ5263THB truck-mounted concrete pump. Mounted on a Volvo FM400 chassis, the ZLJ5263THB features a 37 m Z-boom and boasts an output of 120 m3/hour at a maximum pumping pressure of 7 Mpa.
"All our truck mounted placing booms operate from a small footprint and this makes them ideal for duties in constrained environments," said Jimmy Pan, head of concrete products at Zoomlion.
Mr Pan told iC, "Long distance transportation is a real challenge, not only as regards equipment, but also regarding concrete technology. Not all concrete can be pumped and we envisage that the next step forward will come as a result of high performance pumping agents.
"These agents will alter the properties of concrete for the pumping period and then break-down leaving the concrete properties as originally specified. This will represent a step-change for concrete construction."
Alongside its truck mounted pumps, Zoomlion has developed a range of high powered trailer pumps especially for use with high performance concrete (HPC) and specifically for C80 and C100 HPC. The range starts at 220 kW and goes up to 572 kW.
"The maximum pressure that we've attained is 40 Mpa and theoretically this means we should be able to pump 90 m3/hour," said Mr Pan. "We recently pumped C100 concrete to 437 m for the Guangzhou west tower, China, which I believe is a world record and we've also pumped to 1000 m horizontally for the China high speed railway."
In the US, Putzmeister introduced a range of modifications at February's World of Concrete show in Las Vegas, including a new boom sensor, hydraulic connector and on-board hydraulic oil dehydrator and filter.
The on-board hydraulic oil dehydrator and filter has been designed to remove water from the hydraulic oil, preventing degradation of the oil to ensure longer component life. Using the chassis' existing pneumatic system (the air is forced through a column of oil that is trapped between two elements which allow air and water to pass through, but not oil) as opposed to replaceable cartridges, the system is now available as an option on all of the company's truck-mounted concrete boom pumps.
The boom sensor activates both an audible and visual warning in the cab should the boom not be in full rest position, while the ‘hydraulic quick disconnect' means that all of the hydraulic pipes can be connected at once using a snap-shut handle. "The hydraulic quick disconnect offers exceptional efficiency while retaining excellent hydraulic security," said Kelly Hayes, US marketing manager.
The right chemistry between concrete as a product and the equipment manufacturers is essential for the best use of the new generation mixes. "Concrete technology is a wide and complex science which you cannot define generally," Jürgen Kronenberg of Putzmeister told iC.
"Besides the new additives, aggregate size is most important and that is why we've developed more sophisticated and precisely regulated equipment. In this respect our ergonic pump system (EPS) adapts the hydraulic pressure of our concrete pumps to match individual concrete mixes."Putzmeister is certainly not alone in matching equipment to concrete mix, and there's little doubt the significance of this relationship will become increasingly important in the future development of concrete construction.