Concrete control: Infra works in Ulaanbaatar
Wirtgen slipform pavers deliver a runway near the remote Mongolian capital of Ulaanbaatar
Ulaanbaatar in Mongolia is a hub for a rising economy built on trade and industry. However, as the capital of the world’s second largest landlocked country, it depends on aircraft traffic to bring in and take out its passengers and cargo.
As its existing Chinggis Khaan International Airport was built in 1956 (and only upgraded in 1987 and 1997 for international traffic), today it is badly outmoded and in need of an upgrade.
In the meantime, a new airport, the New Ulaanbaatar International Airport (NUBIA), is set to increase passenger capacity by three times and cargo handling ten-fold, when delivered.
Enkhbat Navaantseden, project director, details: “The current airport faces safety, usability and operation difficulties such as unidirectional landing due to the 2.5% slope of the runway and high mountains to the south; flight delays caused by the limited range of visibility and domestic heating smoke pollution in winter time; and deficiencies in the passenger terminal building’s configuration and capacity.”
For this reason, the new airport is located in the Khushigiin Khundii valley of the province of Tuv, 52km away from Ulaanbaatar, on an easily accessible elevated plain with no mountains in the immediate take-off and landing air corridor.
As a project of national importance, the tender demanded a contractor that could deliver high-quality paving to a tight project deadline.
After the main construction contract was awarded to Samsung C&T, it chose to subcontract Sungdo Construction, a South Korean company specialised in slipform paving jobsites, to carry out the concrete paving work.
In order to lay the quality of runway required for the for extreme climate and larger aircraft, the subcontractor, as a long-term customer of Wirtgen, selected two Wirtgen pavers, an SP1600 and an SP500, and began the concrete paving operation in May 2014.
Dongin Park, Samsung C&T’s project manager for the NUBIA project, summarises the construction challenges as follows: “We had to face the extreme continental climate with short, hot summers and long, icy winters. This gave us a construction window of only three to four months during summer time. The wind from the Gobi desert and the intensive sunlight could quickly dry out the concrete. That’s why the main paving operation with the SP1600 had to happen during night shifts.”
As the flagship among the large Wirtgen slipform pavers, the SP1600 can pave slabs at widths of up to 16m. A booster kit is available for integration into the SP1600 to enable the machines to economically pave dual-course concrete slabs during a single operation.
For the new airport, the SP1600 is paving the 45m-wide and 3,600m-long runway in several segments with a paving width of 11.25m and a paving thickness of 38 cm on average.
The first layer paved by the SP1600 was a 27cm-thick cement concrete slab, followed (through the use of the booster kit) by a second layer consisting of an 11cm-thick cement concrete slab paved — wet-on-wet — immediately after the first layer to achieve a perfect bond between top layer and bottom course.
Wire bar fabric was placed between the two layers for additional reinforcement, according to the specifications of a Japanese company, Azusa Sekkei and Oriental Consultants Joint Venture, which developed the airport design.
Subsequently, the specified compaction of the material was achieved through the use of up to 48 electric vibrators set to a high vibrational frequency. The surface properties of the concrete were then achieved with the SP1600’s oscillating beam and super smoother.
With the SP1600, Sungdo laid a total of 135,000m3 of concrete worth $20m across the runway, taxiways and aprons. The single SP500 was then used to take care of the slightly curved aprons and some taxiway sections, where up to five parallel 5.625m-wide slabs would be laid by the more manoeuvrable machine. In total, around 50,000m2 of taxiway and 7,500m2 of apron was paved by the SP500.
Sungdo Construction prepared in advance for the project by bringing several containers of spare and wear parts with it to the remote jobsite. The significant operation was also supported by the regional service network of the Wirtgen Group from several angles.
If there was a need for additional spare parts, they were flown in via a direct daily flight from Incheon in South Korea. If Sambo Heavy Industries, the Wirtgen dealer in South Korea, was unable to supply spare parts, they could also be ordered direct from Wirtgen’s headquarters in Windhagen, Germany.
Such provisions were particularly relevant given that any breakdown in bulk asphalt or concrete paving operations can lead to the spoiling of large quantities of queued material.
In general, however, the twice-weekly connection from Berlin-Tegel Airport in Germany to Ulaanbaatar was sufficient to ensure the timely delivery of essential parts. Engineers from Wirtgen China or Germany could also be on the site within 24 hours.
Seunghwan Lee, one of Sungdo’s managers, adds: “With the SP1600, we saved a lot of time and money. Instead of using four SP500 pavers, we knew we could go just for one SP-1600, as we have had good experiences with this high-performance paving train in the past. Dual-layer paving sped up our operation.”
Staying on track: The high performance SP1600 from Wirtgen was typically in operation from 7p.m. to 6 a.m., installing dual-course concrete paving with an average thickness of 38 cm.
Shoulder to shoulder on the jobsite: The project team of Samsung C&T carried out the project with specialised slipform paving subcontractor Sungdo Construction from South Korea.
Limited window: The SP1600 could not pave during the daytime, as the direct exposure to intense sunlight and the strong winds from the Gobi desert would dry out the concrete too quickly.