Precision work after just two days of set-up
The owner of the slipform paver, the Lehman Construction Company, got to work on the site as soon as the two days required for set-up of the machine were over. The 25cm-thick concrete layer was paved on a prepared base course which was also 25cm thick. Apart from dowel bars spaced at transverse intervals of 45cm and longitudinal intervals of 3.8 m, the runway does not have any continuous reinforcement. Some 20,000 m³ of concrete in total was laid on the runway, which is 1.8 km long and 30 m wide.
“The specification for surface evenness allowed for a maximum permitted deviation of 7.0 in per mile (18 cm per 1.61 km)”, explains Tim Nash, Director Concrete Products Wirtgen at Wirtgen America. “Since the machine first went into operation, we have not had a deviation of more than 1.0 in / mile (2.54 cm per 1.61 km) on any paving job. Usually, in fact, it was 0.0 in.”
Lehman achieved this high standard of evenness with practically unchanged factory settings, i.e. with no major modifications on the job site. The productivity was also impressive: each day the SP 94i paved concrete over an area up to 750 m long and 7.50 m wide. Due to high daytime temperatures of over 30°C, paving largely took place during the night hours.
Edges at 90° angle
The authorities also had stringent requirements on how the edges of the runway were shaped – the angle was to be exactly 90°. “The representatives of the construction inspection authority confirmed to us that they had never yet seen such precise edges,” Tim Nash recalls. “A vertical concrete edge is crucial for laying the next slab,” confirms John Gibson, Test Engineer at Burns & McDonnell, the company responsible for inspecting the construction work. “And this machine delivered a very good edge”.
Construction expert impressed by the quality
The SP 94i performed impressively in every respect: „The weight of the machine and the well-thought-out design ensure an outstanding surface. The quality is more or less built in, you can see that even in the tiniest details. It’s very impressive.”
Investment in leading technology pays off
Lehman’s decision to buy the new Wirtgen SP 94i slipform paver has been thoroughly vindicated. Kenny Lehman, Owner and Director of the Lehman Construction Company, put it this way: “We wanted to try out something new, because I’d heard that this machine could achieve a smoother surface than machines of competitors. With the SP 94ik we’re actually achieving even better surface accuracy than we had expected.” The process of setting the concrete paver up at the job site – which includes positioning and zeroing the crawler tracks and the swivel arms – is quick and easy with the SP 94i. “The crawler units work very well and the set-up time for the sensor system is short. All the settings can be done very quickly,” says Lehman.
Boosting competitiveness with the SP 94i
“The specifications in our contracts are frequently very strict, so everything has to be just so,” the owner added. “This machine will boost our competitiveness. The requirements on motorways can be met much more easily with the SP 94i. We’re really happy with this slipform paver.” The first project was already a complete success – Lehman delivered a first-class runway. Now the pilots taking off and landing at Jefferson City Memorial Airport can put this to the test.