Concrete construction: Call the experts
12 December 2011
Concrete construction projects are often helped by the expert input of equipment manufacturers and suppliers. Chris Sleight reports.
Concrete construction is a broad discipline made up of many niches and specialised techniques. For many contractors, winning a new job means tackling a new type of project or construction technique and this is where inexperience can sometimes lead to delays, spiralling costs and unsuccessful schemes.
However, help is often at hand from equipment manufacturers and suppliers, which often have decades of experience to fall back on. They are not only able to advise on the best machines for the job, but can also often provide in-depth technical knowledge to help make things run smoothly on site.
For example, Harsco designed and constructed a bespoke support girder system to aid the construction of a new 1500 seat theatre at a cramped site in Bordeaux, France. Surrounded by existing buildings, the system was needed to support formwork for a series of 1.8 m x 2.1 m x 32 m cast in-situ concrete beams. These structural members span the stage area and support five floors of offices and apartments above.
Working for Portuguese contractor Buildin, Harsco devised a bespoke solution using its H33 braced truss-girder system which was sufficiently flexible and reliable to satisfy this demand.
However a lack of working space on the site meant that Harsco had to adapt the traditional methods used to construct the system.
"We actually did much of the construction work on the girders about 10 km away from the site itself," explained Harsco spokesman Ingo Schnelting. "This meant that we could prefabricate the girder sections under more controlled conditions, which made it far easier to ensure that they complied fully with the drawings. That way we were able to avoid any unexpected problems on site and be confident that the girders would fit neatly into place."
Harsco then partially dismantled the girders for transportation, which minimised disruption to other activities on the site itself. Lack of on-site storage space meant that Harsco had to adopt a just-in-time schedule for these deliveries and also co-ordinate this with special permission from the city authorities to operate extended length transport vehicles.
Currently under construction in the Qatari capital Doha is a new airport, which will have the capacity for 50 million passengers and 320000 aircraft movement per year by 2015.
The Tayseeir Contractors Company Joint Venture, which includes Consolidated Contractors International Company (CCIC), is currently at work on the site slipforming some 100000 m3 of 100 mm thick aprons using a paving train from Gomaco. This comprises a PS-2600 placer/spreader, a four-track GP-2600 slipform paver with an Auto-Float attachment, and a T/C-400 texture/cure machine.
It is a challenging project - not least because the original design did not foresee the use of slipforming to construct the aprons - but also because of factors like the 40° C average summer temperatures and the large number of contractors working on other aspects of the build.
"The project was just an obstacle course with us having to go over or around lamppost bases, fire hydrants, fuel pits, electrical pits and all the other different types of pits," said CCIC concrete paving manager Kevin Robinson. "We really had to be on top of our game and keep everything carefully coordinated and planned so we could put concrete on the ground every day.
"There was a grated water trench just inside the aprons that varied in size in different areas, so we had to alter the width of the paving equipment nine different times to suit the design. On any other project we'd be able to pave 2000 m3 per day, but this one was just so difficult. The most we ever accomplished was 856 m3. It's all due to the difficult areas of design, which would have up to 20 headers and footers per shift."
But despite the challenges of a project that was not ideally suited to slipforming, Mr Robinson was positive about how the project worked out and the performance of the paving train.
"The GP-2600 performed very well through all of it and the crew learned quickly how to work on and around the Gomaco equipment. We met all of the tolerances specified by the engineers and the paver laid the concrete as flat as you can get," he said.
In a different type of construction, Putzmeister is using its knowledge of concrete pumping to help streamline the process for the contractor as well as learn about its own machine's performance.
As part of its work on the Wetfleet offshore wind farm project, Strabag Offshore Wind is fabricating bases and the lower part of the pylon of each turbine mast on dry land, before assembling whole, competed windmills and transporting them out to sea using a purpose-built ship.
The concrete bases are poured using concrete pumps, and as well as testing the structures it manufactures, Strabag is also checking the pumps to make sure they can handle the special mix efficiently. A Putzmeister BSF 42-5.16HLS is currently in use to help place the C70/85 concrete and the pumpability of the mix is being checked using a Putzmeister Sliding Ring Rheometer.
"Using the rheometer the time and effort spent on pumping tests can be reduced and thus costs saved. At the same time, this new technology facilitates a quality check, as well as a simple prognosis option with regard to the pumping behaviour of concrete and other thick matter," said Putzmesiter concrete technologist Dr Knut Kasten.
Semi conductor company Meyer Berger broke ground on a new headquarters building in January 2010, and expects to move in at the start of 2012. The new structure consolidates more than 20 individual facilities that were spread around the Thun area of Switzerland, and includes a 18.8 m high, 13.8 m wide, 43 m long warehouse within the production hall.
The walls of this structure were poured using Meva's Mammut 350 heavy-duty wall formwork and KAB 190 scaffolding to provide a safe working platform. This allowed pours up to 4 m high to be undertaken by main contractor Frutiger, and saw the warehouse finished in six weeks instead of the planned seven.
"Saving time was only possible thanks to Meva's excellent support all the way from planning the job until finishing it," said Frutiger foreman Rolf Isler.
Construction of a new 300 km highway between the cities of Muscat and Suhar in north-east Oman involves crossing a series of river deltas, or wadis, which make for difficult construction conditions and a threat of flooding to the finished road.
In order to take the road over these danger areas, a system of box culverts are being built in the water channels. Running at right angles to the road, and in the direction of the river's flow, these provide a channel for the water, while taking the road across the small valleys, effectively on a series of small bridges.
Paschal has supplied a formwork carriage to Hyderabad, India-based contractor NCC for the construction of these culverts, which allows a 12 m length to be cast in a single cycle.
The carriage is based on forms from Paschal's Modular/GE universal range. By placing four carriages side-by side, the contractor is able to form several culverts at once with a minimum of formwork.
Doka meanwhile has supplied huge amounts of its Staxo 40 shoring towers to the Manipal University project in Dubai, UAE. The striking building features cantilevered floor slabs and a series of high entrance halls, and main contractor Sobha Contracting has used Doka's support system to shore some 14468 m2 of floors.
The contractor is using some 8000 m² of Dokaflex 1-2-4 floor-slab formwork and some 3600 Staxo 40 load-bearing tower frames to cast the curved floor slabs, and Doka says the intuitive design of its towers is helping the contractor move ahead much quicker than would be possible with conventional cuplock systems.
Sobha Contracting project manager V.K. Prasad said, "Before, with other systems, we had too many small parts and the chance of losing them or not assembling them properly was higher. But here it has all been made with a minimum number of components so safety-wise its much more reliable, and it is more economical."
In Ukraine meanwhile, Peri's formwork engineers are working on the redevelopment of the Olympic stadium and Ocean Plaza business centre, two schemes that are timed to be complete for next year's European Football Championship. When complete Ocean Plaza will have a total of 250000 m² of floor space and 3000 underground parking spaces along with a hotel, cinema and restaurants and shops.
The 700 mm thick columns of the structure are being constructed using SRS circular and Trio square column forms, while Multiflex girder slab forms are being used for the floors along with Pep 20 and Multiprop props. In some places the Multiprop props are connected to form modular shoring towers.
However, large areas of the complex are column free, and in these parts Peri has supplied various shoring towers, with footprints of 1.5 m to 2.0 m and heights of up to 13.8 m.
Close consultation with the site management team during the tendering phase meant that formwork and scaffolding requirements were analysed together and the system equipment individually tailored to meet project demands.
Ask the experts
These case studies illustrate how contractors can call on suppliers' knowledge and expertise to not only build structures on time and on budget, but often to exceed clients' expectations.