Concrete construction: Working under pressure

By Helen Wright07 December 2012

Contractor Sherwood Construction incurred a penalty of US$ 10,000 per day for running over schedule

Contractor Sherwood Construction incurred a penalty of US$ 10,000 per day for running over schedule on a runway paving project at the Tulsa International Airport in Oklahoma, US.

The ever-present drive to increase efficiency in the construction industry continues to fuel developments in the concrete sector, and manufacturers are working closer than ever with contractors to get projects completed on time.

If projects run over schedule, contractors are often liable to incur daily penalties. Tighter and tighter timetables mean they are always on the look-out for ways to accelerate concrete construction while keep the job site safe and ensuring high quality is maintained.

Manufacturers are also working hard to develop new machines and techniques that can outperform their predecessors. Chinese company Zoomlion and its Italian subsidiary Cifa, for instance, have unveiled the tallest concrete pump in the world – the prototype Pump 101, which has a 101 m long, seven-section boom.

The last four sections of the boom are made of carbon fibre to reduce their weight, and Zoomlion said the machine beat its previous record of an 80 m long boom.

Technical Area Manager Mauro Cortellini said, “The carbon used in the Zoomlion-Cifa Pump 101 has a high modulus of elasticity, and is a very different material from the one used in the (Cifa) Carbotech range to date.”

Paolo Maini, a member of the calculation team on the project, added, “The most important thing is that the pump structure is mounted on a vehicle chassis, not on a special vehicle, which means that it will comply with the maximum dimensions and footprints imposed for road transport.”

The company said the target market for the Pump 101 was China, but Cifa managing director Davide Cipolla was optimistic that the machine would sell in other markets as well.

“Pump 101 is currently at the prototype stage, and is due to undergo a detailed structural and functional analysis, with very strict tests. There may well also be demand from Europe in future,” Mr Cipolla said.

There have also been new launches in the concrete mixing sector, including a new plant from Rapid International that aims to offer higher production rates. The Rapidmix 400CW incorporates a 1200 mm belt conveyor between the aggregates hopper and the continuous mixing chamber, and offers full weighing options for all materials as well as automated record keeping.

The first customer for the Rapidmix 400CW in the US was Texas-based Rollcon. The new machine has been put to work on the latest phase of the Port of Houston development project, producing up to 400 tonnes of material per hour.

Meanwhile SBM, which until now has focussed on mobile plants, said it planned to add stationary horizontal mixing plants, tower mixing plants and special, bespoke models to its portfolio in the coming months. The company will also offer modernisations, modifications and expansions of existing stationary plants.
Formwork

Flexibility like this is desirable to contractors, and no-where can this be better demonstrated than on the biggest infrastructure project currently underway in the world – the expansion of the Panama Canal in Central America.

Work on the US$ 5.25 billion scheme to construct a third set of locks for the canal started in 2007 and is scheduled for completion by the end of 2014. Peri is supporting the contractors with the planning and delivery of huge quantities of formwork and scaffolding systems – the largest order in its 40-year history.

In order that the tight schedule can be maintained, Peri said over 4,200 site personnel were processing 6,300 m³ of concrete on a daily basis in two shifts. Construction site facilities also include 70 cranes and 30 concrete pumping stations.

Peri’s new, modular Single-sided Climbing System (SCS) is being used on-site, together with its Vario girder wall formwork Trio panel formwork and Up modular falsework.

“The required system equipment was produced within a few months and then shipped to Central America in more than three hundred 40 ft (12 m) containers,” Peri said.

“The systems used have been optimally adapted to suit site requirements and include the integration of safe access means such as the Up scaffold staircase. With the help of Peri formwork and falsework, massive components can be quickly and cost-effectively realised,” the company explained.

Doka faced similar challenges on another high-rise project – the 555 m tall Lotte World Tower in Seoul, South Korea. Designed by architects Kohn Pedersen Fox, it is scheduled for completion in 2015.

Contractor Lotte Engineering & Construction used Doka’s SKE100 and SKE50 formwork plus automatic climbers and the Xclimb 60 protection screen to support construction. Bespoke solutions were also necessary here, and Doka developed telescoping protection screens and platforms to deal with the structure’s continuous taper.

For the construction of the 498 m tall reinforced concrete core, for example, Doka’s 132 SKE100 automatic climbers are being used in combination with large-area formwork Top 50, which is being climbed ahead of the floor-slabs in casting sections that are 4.5 m high for a typical storey.

“The constantly changing shape of the structure presented the formwork experts with a great challenge in the planning phase,” Doka said. “The team’s answer was to develop a new, telescoping protection screen especially for the Lotte World Tower. This screen takes little or no modification to adapt to tapering structure shapes. The screen elements can be adjusted to widths of between 3 m and 5 m.”

Falsework and formwork from Meva was also put to the test in Switzerland supporting construction Europe’s largest hydro power plant – the Linthal project in the Glarus Canton.

The scheme is an underground pumped storage hydro power plant that will pump water out of Lake Limmern back to Lake Mutt, which is located 600 m higher up, increasing the power output of the current Linth-Limmern power plants from around 480 MW to 1,480 MW.

Working conditions are difficult due to harsh snowy weather in the autumn and winter, and the remote location of the project. A new, 1000 m long concrete dam is being built on Lake Mutt, while the underground caverns for the power plant equipment are 156 m long, up to 30 m wide and up to 53 m high. Construction is scheduled to last seven years.

Concrete works are currently in progress on the inlet and outlet gallery on Lake Mutt. The 12 m high walls are being poured using single and double-sided Meva STB 450 support frame and Mammut 350 wall formwork. Meva said exceptionally high concrete pressure required back anchoring instead of standard props.

The equipment has to be hauled from the base camp at 800 m above sea level to the building sites at 1700 m and 2500 m. To do so, a special cable car and an access tunnel with a funicular railway equipped are being used.

Slipforming

Back on ground level, concrete paving equipment manufacturers are working on machines that can complete projects as efficiently as possible, with minimal waste or need for extra finishing.
Contractor Sherwood Construction faced a tough spec and a tight schedule, when it was brought in to build a new runway at the Tulsa International Airport in Oklahoma, US.

Last March, Sherwood began work on the removal and replacement of 1,500 ft (457 m) of the old runway, which consisted of 18 in (457 mm) of dowel-jointed concrete pavement. The company then bought a new S850QB concrete paver from Guntert & Zimmerman (G&Z) and set it up on the Tulsa project to pave eight lanes that altogether measured 150 ft (45.7 m) wide.

The tough part was the specification set forth by the Federal Aviation Administration (FAA), which requires surface smoothness deviations of no more than a quarter of an inch
(6 mm) on hardened concrete.

Production averaged between 180 to 250 yd3 (164 to 228 m3) per hour, and ranged up to 300 yd3 (274 m3) per hour. Despite good progress and high quality result from the paver, Sherwood didn’t get the job finished within the tight timetable stipulated – a fact which had financial repercussions for the company.

“We had 70 days to do all the construction – removal of the old runway, replacement with 18 in (457mm) of new concrete pavement, and getting it ready for aircraft,” said Scott Middleton, project manager.

“We didn’t make the schedule; we came in late. But we had anticipated taking about 15 days more than they gave us. We knew that going in, and that was figured into our bid. We worked 12- to 14-hour days, six days a week. The penalty for not meeting the deadline was US$ 10,000 per day,” he explained.

This penalty demonstrates the kind of pressure that contractors are under to complete jobs to the highest possible quality and within strict schedules.

On another job site, two self-erecting cranes from Potain helped turn a three-week weather delay into an early completion on a project at Cedarville University in Ohio, US. The HDT 80 cranes played a central role in the construction of the University’s new US$ 16.5 million Health Science Center.

The three-story building was constructed as a cast-in-place concrete structure, so the cranes lifted a variety of materials including rebar, forms and concrete. To get the job back on track, the cranes used their full-length 147 ft (45 m) jibs and lifted maximum loads of 6.6 tonnes.

Keith Jenkins, sales and marketing manager at Capital City, the rental company that supplied the cranes, said, “The self-erectors didn’t need foundations or much land preparation. They can be transported at 50 mph on one truck and erected and ready to work in no time. Benefits like this, on a project with a tight budget and an even tighter schedule, made them an ideal choice.”

As these two examples show, the stakes are high when it comes to completing contracts on time, with the highest praise reserved for jobs that are finished early, but potentially dire financial consequences for running late. It is crucial that manufacturers keep working closely with concrete contractors to ensure the right equipment is being used, and to tackle any problems as soon as they arise.

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