WIRTGEN’s Slipform Paving Manager, Patrick Zanen, was in Sydney recently to attend the opening of the company’s purpose-built facility. Construction Contractor caught up with Zanen at the event and found him to be passionate and knowledgeable about the art and science of concrete slipform paving.

What are the basic advantages of concrete slipform paving compared with asphalt?
Concrete has an added value in terms of the lifetime of the product. In Europe, its lifetime is considered to be 35 years – this is 35 years without major repair work. Concrete is also a perfect load carrier. In areas where you have a lot of loads to be taken care of – harbours, airfields, hyper-density ring roads and cities – concrete is really a more suitable option. A new development is the improvement of concrete road surface structure and the result is reduced noise. At the same time, there is also an increase the anti-skid resistance which is very important in wet conditions.

There’s also the ecological aspect. Today, we adopt a two layer application when paving concrete roads. The bottom layer is recycled concrete while the top is virgin material. There are other factors too: for example, we have been involved in studies showing that travel on a concrete road consumes less fuel compared with travel on an identical asphalt road.

Since concrete is obviously more expensive, in how many years will it pay for itself compared with asphalt?
You cannot go by one standard formula because concrete thickness and road design need to take into account traffic density and soil structure below. But if you consider this from a strictly maintenance point of view, concrete will easily beat asphalt three to four times over the time frame of 35 years.

How do you compare the time taken to lay asphalt versus concrete?
Well there is definitely a big difference. At one extreme, there are sophisticated concrete designs – put it down and a few hours later one can drive on it. These are used for repair work. But with normal concrete roads, you put it down and then wait the theoretical 28 days to allow the hardening process to get to full strength.

What about the machines themselves? Have they changed recently?
One recent feature, at least in our brand, is that we can operate our machine wirelessly. It’s not on the GPS – it’s on a total station. In the past, the topographic information would have been implemented into the string line. We have now implemented this in a total station in a digital map and this system has already been proven in Europe.

Have you used slipform paving in harsh conditions similar to what we have in Australia?
We have used it in Singapore Airport – in the new terminal building that was built for docking the Airbus A380. And Singapore does get pretty hot. In India, we have 55 machines in the country and you often see ambient temperatures go up to 45°C. There are definitely measures to be taken care of during the execution of the paving process in hot weather conditions. But if you do the job properly from a design point of view, experience has proven that concrete is a good solution. The critical aspect is not just the machine – it is the temperature of the concrete supplied in front of the machine. A theoretical value of 30°C is specified and if you go above this, you may be in a bit of trouble.

Compare operator training for asphalt versus concrete. Does the latter require more intensive training?
We don’t see that big a difference. Obviously there is a big difference between handling the asphalt and concrete materials. But if you see an asphalt operation and a concrete operation done properly, I would not say there is extra time either way. The key message is to prepare well before starting with the job – designing the concrete mix, devising proper logistics, determining how best to bring concrete from the batching plant to the slipform paver in a continuous process. It’s important to avoid start/stop actions during the paving processes. The key elements to ensure success are: machine, crew, concrete supply and concrete quality.

Is there any specific grade or mix of concrete that you would specify?
Basically, we are talking about compressive strength and flexible strength which are made to client specifications. These two major aspects are linked to the thickness of the concrete. But it would not be correct to mention or predict the formula of a mix design because the quality of aggregates varies between countries and even within a country. You always have to find the proper mix design and mix properties using the individual qualities in order to finally meet the standards. It would certainly not be out of place to mention that each contractor obviously tries to meet specifications by seeking out the most economic mix design for the job.

You mentioned that your machines are built to a contractor’s requirements for a job. After the job is complete, what does the purchaser do with that machine?
Basically you start with a basic set of machine standards – minimum and maximum widths, minimum and maximum paving thicknesses. Within the needs of a contractor’s initial job, we try to determine the kind of machine he needs. After the first job site he will not need to purchase a new machine. No, it’s not that. The machine is multi-functional. After building a road or an irrigation canal, the contractor may go on to an airport job just by modifying the machine. He may have to add on a few items but gains the added value of the multi-functionality. We have models which can be suitable for safety barriers, road construction, airfields, harbour areas as well as high speed train applications – just with the different attachments.

What’s the estimated life of a slipform paver?
Unfortunately, too long from a manufacturing point of view. For our brand, we see machines used for up to 15 years. You cannot compare a slipform paver with a milling machine – it’s a totally different operation. We have contractors who adopt a proper maintenance plan and run machines with 15,000 hours on the clock without a problem. The biggest challenge for the buyer is that he does not always know what kind of jobs he will be taking on over the next five or ten years. My message to them is: go for a multi-function machine so you are able to modify it to suit the requirements of any job. And if they select a Wirtgen, so much the better!