In Bad Fredeburg, Germany, two Hamm H 25i VC compactors with a special crusher drum were used to simultaneously crush slates and compact in order to build a 15-metre dam for a new bypass.
VC compactors are designed to streamline the construction process, removing the need for a separate stone crusher and reducing the amount of transport required.
Michael Tillmann, Straßen- und Tiefbau's construction manager, first became aware of the H 25i VC at Bauma 2019.
"We were immediately won over by the roller's design. But we never had the right project before," explains Tillmann.
Not long after, there was a project to build a dam for a new bypass using locally available slate. "As soon as I saw the stone, I had a feeling that the Hamm compactor would be perfect for crushing this material," said Tillmann.
The stone in question was Fredeburg slate, also known as schisty greywacke. The material would normally have to be broken up on-site to a maximum particle size of 200 mm by several crushers, before being loaded onto trucks by excavators and transported to the dam site. Bulldozers would then be used to spread out the rock, then compactors would compress it into layers.
The team from Sauerland presented a simpler and more efficient alternative to this process - without a crusher and using much fewer transports - employing two H 25i VC compactors.
A trial quickly showed that the VC compactors from Hamm provided an ideal fracture pattern for this application. In collaboration with the soil surveyor, a height of 40 cm per layer was then determined. The optimum void content was determined to be 6 percent, with a permissible maximum of 10 percent.
To ensure that the water content was also correct, each layer had to be sprayed with water. "After a few days, it was clear that we were working much faster than when using crushers. The main reason for this is working in layers," explains Tillmann.
Rock crusher and padfoot roller all in one machine
150 quick-change toolholders are welded onto the drum of the VC compactor. These holders can house different tools: chisels or padfoot inserts.
Equipped with chisels, the vibrating drum generates high point loads of up 50 t which breaks up the stone. The ground is compacted at the same time. This allows the VC compactors to both crush the stone and relieve tension in the rock. When compacting cohesive soil, the drum can be equipped with special padfoot inserts.
Hamm currently has two different chisels in its range for crushing rock and relieving tension: A classic chisel and a special mining chisel for hard rock applications. Their geometries, together with the integral solid carbide tips, are specially designed for materials with different compressive strengths.
The design of the quick-change toolholder prevents contamination of the tools, and ensures they are easy to change.
Incidentally, the chisels are not destroyed during the changing process. They can be repeatedly used until they are worn out.
When crushing the Bad Fredeburg slate, the chisel also exhibited a low level of wear: "We only had to change a few chisels the whole time we were working," says machine operator Marvin Gallus.
Reducing costs by nearly 50 percent
On most comparable construction sites, the construction process consists of the following steps: Removal and loading, transport, feeding the crushers, crushing, loading, transport, spreading and compacting. With the VC compactor, this process is shortened.
The steps remaining are removal and loading, transport to the construction site, spreading with bulldozers, breaking up and compacting. This allows projects to be completed at a considerably lower cost.
In Bad Fredeburg, there was about a 50 percent reduction in the costs for breaking up and compacting. This is because considerably fewer machines were needed. Straßen- und Tiefbau only required two VC compactors and a Caterpillar vehicle. The two crushers, two baggers and two dumpers originally planned for crushing the slate were not required. Personnel and operating costs were also reduced accordingly.
Marvin Gallus was behind the wheel of one of the H 25i VC compactors in Bad Fredeburg. The operators were given detailed instruction on how to use the crusher-rollers by a service technician.
"We found everything very clear and simple after this. The roller is easy to use," says Gallus. "By combining the process steps, we were able to handle approximately 4500m³ per day. This is almost twice as much as set out in the original planning schedule."
