New manufacturing method for prestressed hollow-core slabs

Hollow-core slabs weigh up to 40% less than solid floor slabs, thus requiring less concrete in manufacturing. Therefore, they are widely used all over the world; however, the width of the slab is strongly limited due to the manufacturing process. Service ducts and concrete block-outs or lifting anchors are not possible. Reinforcement wire mesh and connecting reinforcement can be incorporated only to a limited extent, which is the reason why hollow-core slabs in many cases are only restrictedly suitable for earthquake zones. This is now going to change by the Motus construction system of Vollert.

Modern precast concrete architecture is changing the method of construction throughout the world. New residential and office complexes, universities, hospital buildings, logistics centers and parking garages are built in the growing megacities in Asia, South America and in all other parts of the world using industrially prefabricated walls, floors, and special building components. However, new technologies are required in order to make use of this construction system in high-risk earthquake zones efficiently, too.

Nominated as Bauma Innovation Award finalist

Already in 2015, Vollert developed together with the BauMax construction company a special construction system, based on solid concrete elements, for the earthquake prone Chile. On the occasion of Bauma 2019, they now presented an earthquake-resistant construction system with prestressed hollow-core slabs for the first time. In this system, the hollow-core elements are no longer manufactured in an extrusion process or by a slipformer, but using the principle of a pallet circulation system. Each hollow-core slab is manufactured precisely to the geometry and dimensions of the requested building component without cutting waste, hence, after the casting process, it is no longer necessary to cut a continuous slab to size according to the site requirements. The costs for cutting are eliminated as well as the scrap costs owing to scrap sections produced in the cutting process.

The reinforcement wire mesh and connecting reinforcement make an earthquake-proof force-locking connection of the floor elements at the construction site; the absorption of tensile forces on all sides increases the load-bearing capacity considerably. In longitudinal direction, a tension wire overhang is easy to realize, additional reinforcement can be provided laterally to ensure a force-locking connection of all floor elements. In this way, truly earthquake-resistant prestressed hollow-core slabs can be manufactured now, according to the manufacturer.

Motus construction system offers a lot of options

In addition, much larger slab widths of up to 3 m and a thickness of the hollow-core slab from 12 cm to approx. 26.5 cm are achieved, reducing the number of site crane lifts as well as the installation time at the construction side in comparison to hollow-core slabs manufactured by extrusion. Additional lifting elements can be realized as well, enabling easy lifting of the hollow-core slabs. So far, lifting was only possible with the aid of special lifting equipment (clamps), which constitutes a considerable accident risk owing to the risk of falling.

Hollow-core creators are only used temporarily during the concrete placing process. The number and the geometry of the hollow cores can be adapted in an extremely flexible manner; this is not possible in a continuous casting process. Electric and water ducts as well as ventilation shafts can also be incorporated as well as special embedded parts. This provides structural engineers and building services planners with completely new options as against conventional prestressed hollow-core slabs. For this reason, the Motus construction system, filed for patent, was nominated as Bauma Innovation Award finalist. On the basis of the innovative construction system, an intelligent combination of special concrete sandwich components, solid concrete components for interior walls and the new hollow-core slabs, the Uzbek company DSK Binokor will annually manufacture up to 500,000 m² of wall and floor area in the near future. In close cooperation with construction engineers of Vollert, residential buildings up to 12 stories high are currently in an additional planning phase.