Kemroc drum cutter attachment in Second World War bunker conversion

16 March 2023

German concrete cutting manufacturer Kemroc has played a key role in the final stages of a project to convert a former Second World War bunker to a residential building.

The partial demolition method of contractor Wilko Wagner included the use of a 35 t crawler excavator with a Kemroc KR 165 drum cutter attachment. (Photo: Kemroc)

The bunker, in Hamburg, is one of more than 400 constructions of its kind that have survived in the north German city – including many with the majority of the building above ground – and turning them into homes has become a trend in recent years.

Specifically, this involves demolishing the sections of the bunkers that have no value and converting the remainder. But with these bunkers often being located near existing housing, the project had to be completed in a low-noise, low-vibration environment, which is where Kemroc, and its KR 165 drum cutter, came in.

The contract to demolish part of this bunker in preparation for the actual conversion was awarded to the Hamburg-based company, Wilko Wagner. The bunker is closely surrounded by inhabitants of other residential buildings.

Regulations for the conversion of high-rise bunkers say the street façade, the free-standing gable wall and the side walls directly facing neighbouring buildings must remain in place. The back wall facing the courtyard was to be demolished.

Kemroc KR 165 drum cutter 2 Using the normal top to bottom demolition method, the excavator operator started with the removal of the 220 cm thick and 400 t heavy building reinforced concrete roof. (Photo: Kemroc)

The inside of the bunker, originally consisting of six floors each with a ceiling height of around 2 m (6 ft 6 in), was to be completely gutted out, in the usual way from top to bottom.

To do this, a shaft was first created by making a hole by hand through each of the 25 cm (10 in) thick floors and using a wire saw to cut an opening through a wall on the ground floor, through which around 7,000 cubic metres (247,200 cu ft) of demolished concrete material could later be transported away by small loader. At a later stage, the interior of the building will be completely rebuilt.

To create additional living space, the plan includes penthouse apartments to be built high up on the roof of the new residential building. In preparation for this, the existing massive reinforced concrete roof, around 220 cm (7 ft 2 in) thick and weighing 400 t, had to be removed.

In May 2022, preparation work started which included installation of noise protection panels and ceiling supports. Demolition work started two months later with a 35 t excavator placed on the concrete roof.

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After removing the top bitumen layer, the excavator operator then cut a foxhole through the concrete roof above the shaft using a Kemroc KR 165 drum cutter attachment. Material created during demolition was discharged through this hole.

“First, we marked out the area and drilled four holes in the bunker walls corresponding to the corners of the floor-to-ceiling window openings,” said Wilko Wagner’s technical director Norbert Klatz.

“Then, using our excavator and the Kemroc drum cutter attachment, the bunker wall between these corners was ground out leaving a thin section of wall.

“The third step involved removal of the remaining thin section of wall using an excavator with shearer.”

The Kemroc KR range of rotary drum cutter attachments use planetary gears which the company says makes them very rugged and reliable and suitable for short boom carriers working in confined spaces and for low-vibration and low-noise demolition of reinforced concrete.

German demolition companies awarding projects to Kemroc in the past 12 months include CK Abbruch und Erdbau, BERB, and Leinweber.

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