Feature: Concrete technology
By Chris Sleight10 November 2010
Mix designs can vary enormously, yet any variation has a profound effect on the equipment being used and on the final integrity and finish of the project. Marketing services manager at Stone Equipment, Kathryn Reissig told iC, "The primary focus for the future is in the mixes themselves, to make them lighter, yet stronger and more environmentally friendly.
"The biggest challenge for us is dealing with the abrasiveness of concrete. It requires making products with thicker steel or designing in easily replaceable components to reduce the issue of wear for contractors."
An example of developments in mixes comes from iCrete's new marine concrete mix, the design of which has been optimised for strength and improved uniformity and reduced bleeding and segregation while wet.
Chief scientist Per Andersen told iC, "The cementitious composition has been optimised to reduce the risk of corrosion through reducing the speed of any potential chloride penetration.
"We have also increased the mortar density and reduced porosity by maximising particle packing during the mortar phase."
President and chief operating officer Tom Schneider said, "The new marine mix is designed to withstand the assault of a hostile saltwater environment, yet still meet the lifespan and structural reliability standards required for mega-projects such as bridges and tunnels crossing international waterways."
Meva spokesman Jens Lutzow-Rodenwoldt concedes that today's many different concrete recipes and the growing use of complex and flowable concrete types makes judging the precise setting time of concrete very difficult.
"Knowing the exact setting time of fresh concrete and its load on vertical formwork is crucial for the building process and safety," he said.
"To date, the setting time had to be guessed using the so-called knead-bag test and thumb pressure, which is entirely person specific. This added up to +25% of waiting time to the construction process."
In response Meva has launched a battery-powered ultrasonic measuring device (USM), which calculates precise setting times by measuring the reflective behaviour of ultrasonic waves through concrete.
"Some of the fresh concrete delivered to site is poured into the USM device, which immediately starts measuring the setting process. The display shows exactly how much time the fresh concrete will take to set completely, thus saving on construction time," said Mr Lutzow-Rodenwoldt.
Load is an area that Doka has addressed with the introduction of its I tec 20 formwork beam. Spokesman Stefan Pruckmayr said, "The new I tec 20 beam redefines the standard for timber formwork beams. Compared to conventional beams, it has over +80% higher load capacity, yet weighs about the same."
The I tec 20 beam is fitted with the same end-reinforcement as found on Doka's exisiting Top beams, but it is also reinforced with plastic along its flange. "The I tec 20 beam reduces the quantity of equipment that a contractor needs and enhances the performance of our new wall and floor-slab formwork systems," said Mr Pruckmayr.
Esser's new Pro-5 single-layer pipe features a wall thickness of 4.5 mm, a pipe diameter of 125 mm and can withstand a maximum concrete pressure of 85 bar. General manager at Esser Pipe Technology, Eric Zimmermann said, "This pipe has a service life several times that of ST 52 steel pipes, yet it's easy to weld. Our induction-hardening process strengthens the overall pipe system and also ensures uniform hardness of up to 57 HRc throughout."
At Bauma, Cifa unveiled its new Carbotech K62H truck mounted concrete pump. The pump features a six-section 62 m boom, the last three sections of which are manufactured from carbon fibre to reduce weight while maintaining performance and rigidity.
The weight saving achieved through the use of carbon fibre means the K62H is mounted on a five-axle truck, which offers savings in comparison to Cifa's existing 58 m truck mounted pump manufactured from steel that uses a six-axle truck.
With a double-layer pipe diameter of 125 mm and an RZ folding system in conjunction with a HPG 1808-IF9 close loop concrete pump, the K62H is -25% lighter than Cifa's traditional 58 m unit . Available in high pressure specification with 130 bar pumping pressure, the unit features a maximum output of 110 m3 per hour, while in low pressure configuration output increases to 180 m3 per hour at a pumping pressure of 80 bar.
A Cifa spokesman told iC, "The Carbotech K62H and its sibling, the K45H are the jewels in Cifa's crown. Every component has been optimised and the carbon fibre sections are stronger and have greater rigidity than steel.
"Customers will be surprised at how close the cost of the carbotech pumps is to our existing steel units. We have fatigue tested the units to 10 years and site tested them in the harshest work site environments and the results show greater strength and rigidity than steel."
On the road
Power Curbers spokesman Stephen Bullock said, "The challenge for us in working throughout so many different countries, and especially developing nations, is to get consistent concrete from job-to-job and country-to-country.
"Achieving quality control and getting a contractor and ready mix supplier to understand what's required from a slipform machine is perhaps one of our biggest challenges."
Power Curbers sends technicians to concrete plants to help them get the mix right, but Mr Bullock says that even then with the right recipe issues can still be encountered because of the use of manufactured or natural sand or crushed aggregate over river stone.
He told iC, "There is not a lot of latitude as regards the mix. It needs to be pretty precise to get a good finish and consistency. We have so far been able to overcome mix issues in every environment, but it can be frustrating."
General manager at Power Pavers Fred Hite said, "The key elements in producing a quality finished product are consistency, consistency and consistency! Consistency in the concrete mix of each and every load, consistency in delivery and consistency in the paving speed of the machine.
"If all of these areas can be addressed, it reduces the need to constantly readjust the paving machine to compensate for variation in aggregate gradation and concrete slump. It avoids the need to stop the paving machine to wait for material and it enables the machine to keep moving at a smooth, continuous speed, thus allowing for an optimum extrusion process."
Fujian South Highway Machinery (NFLG) spokeswoman Irena YiYi belives that there is a tremendous demand for concrete from developing countries and this trend will remain for at least a decade.
New products from the Chinese manufacturer include a new mobile concrete mixing plant, a concrete reclamation unit and a truck-mounted concrete and asphalt mortar mixing plant, designed specifically for the construction of the high speed railway in China.
Differing concrete quality and the advancement of new mix designs and alternate aggregates call for equipment that's more versatile as well as being more advanced.
Cifa's introduction of carbon fibre to concrete pumping booms and the development of systems to measure the setting time of fresh concrete are both examples of advancing technology, yet Power Pavers' design philosophy of keeping equipment simple, rugged and functional can also be of value to contractors.
While there is a balance to be met between robust mechanics and advanced technology, all the time manufacturers pursue the balance from both directions the choice for contractors grows.