Steinbeis experts develop fair-faced concrete street furniture with added functionality
FiberCrete, the Chemnitz-based Steinbeis Innovation Center, develops, tests, and finalizes new fiber- and textile-reinforced building materials, composites, and technologies for production. As part of a joint project, the experts from Steinbeis worked with construction material specialist LIMEX-VENUSBERG to develop FurCrete, an organically molded range of street furniture made from carbon concrete. This furniture, which also offers heating, lighting, and charging functions, has for the first time been used in the design of an outdoor display at the Carlowitz Congress Center in Chemnitz. The project received funding under the Central Innovation Program for SMEs (ZIM).
Fair-faced or exposed concrete is being used more and more in recent years. This is particularly in response to architecture trends, which are moving toward natural designs, functionality, and aesthetics. As a functional material, concrete also offers excellent mechanical properties, it’s highly durable, and it’s inexpensive to produce. On the down side, it consumes a large number of resources – i.e. raw materials and energy – and it produces high levels of carbon emissions due to the methods of producing solid materials, although these are a necessity given the material characteristics of precast steel-reinforced concrete elements. This motivated the Steinbeis experts from Chemnitz to look for new, sustainable solutions for modern, durable street furniture.
Reinforced concrete is predestined for producing thin-walled shelled elements. Reinforcing concrete with non-corroding elements, such as fibers and grid-mesh textiles made from alkali-resistant glass (AR glass) – or carbon – makes it possible to reduce the outer concrete shell from several centimeters to just a few millimeters, thus saving a considerable amount of concrete. The result is delicate lightweight materials that offer tremendous potential and are well suited to producing carbon concrete street furniture.
The goal: sustainable and functional street furniture
The aim of the project realized by the Steinbeis experts from Chemnitz was to develop and produce free-formed, functionally integrated street furniture in lightweight architectural concrete. It should be very different from products currently on the market, especially in terms of sustainability, design, and function. The furniture should be based on the development of a flowable, fiber-reinforced fine concrete, which is processed as wet-cast concrete in fully surrounding open molds to produce pore-free and shrinkage-free elements.
The experts placed particular emphasis on multifunctionality factors. This entailed the use of indirect LED lighting elements, the integration of inductive charging spots, and heating zones on the seating areas, which were created by fitting carbon-fiber heating fabric. The grid-mesh carbon elements simultaneously provided reinforcement and fulfilled a heating function.
Material development: five materials, one goal
Development of the materials involved a complex, dovetailed process, from assembling the high-quality fair-faced concrete to integrating reinforcement fabrics and functional textiles in specific areas of the furniture, and processing – which in turn involved an intensive mixing process, molding, and demolding. For the material development, the team led by Steinbeis entrepreneur Professor Dr.-Ing. Sandra Gelbrich created two basic mixtures: one a gray, concrete-color formulation, the other a white mixture that allows other colors to be added as desired. Both were based on a modern mixture comprising five constituent materials: cement, aggregate, water, additives, and admixtures specifically selected for the project.
“Our focus lay in optimizing resources to be sustainable by replacing cement with alternative additives. It was also particularly important to match the rheological properties of the top layer of the concrete with the delicate nature of the material, which needed to be extremely robust. The materials should also deliver in terms of straightforward processing, the desired visual qualities, extended durability, and mechanical properties,” explains Sandra Gelbrich. Material testing showed that the developed FurCrete base mixes deliver robust 28-day compressive and bending tensile strength, they offer the required processing properties (for example, they are self-compacting), and they have a strong visual appeal.
The formwork concept – a fiber-plastic composite in combination with wood
To produce a premium feel on the surface of the fair-faced concrete – with no pores, blowholes, or blemishes – a holistic, closed formwork concept was needed bringing together basic and functional elements. Since the casting process involves using highly flowable mixtures of fine concrete, it was important that the closed molds were totally watertight. Accordingly, the project team designed a multiple-part formwork system comprising glass fiber-reinforced plastic (GRP) in combination with MDF wood, consisting of an outer mold and a mold core with reinforcements.
Since the surface of the concrete is entirely visible, the formwork concept avoids using a classic sprue side. The outer mold, which reproduces the visible surfaces of the concrete furniture, was created in a monolithic slab shape. Doing without a multi-part outer mold means there are no borders or ridges on the cast concrete furniture in the area of mold release – a feature with the potential to significantly enhance visual and tactile properties. To produce the range of furniture, molds were created for a stool, a bench, a table, a planter, a lamp, and a trash can.
Execution of the technology – carefully planned from start to finish
Development focused on mapping a process chain from start to finish, from mixing the components of the fair-faced concrete through to logistical implementation. Drawing on the results of laboratory-scale development, the project team at LIMEX produced a series of prototypes. For this purpose, they first applied a wax-based mold-release compound to the formwork and mixed the ingredients in a pugmill mixer. The molds were then filled via a concrete silo using an adaptable hose system. After leaving the mixture to cure for twelve hours, the formwork was removed from the inner mold before finally lifting the concrete furniture out of the outer mold. As a final step, the furniture was finished and a hydrophobic coating was applied.
Adding new functions with heating, a charging station, and lighting
To add new functions to the new FurCrete carbon concrete street furniture, the stool and bench are heated by a flat carbon heater, an inductive charging station has been integrated into the table unit, there is a light on the table, and there is a separate lighting element.
To heat the stool, a heating fabric was developed using carbon fibers. This has been integrated into the stool and bench, which delivers highly efficient heating using electrical resistance. To do this, carbon-fiber rovings were placed on an alkali-resistant glass grid and sealed into position. The system has a surface heating capacity of 600 watts per square meter. The carbon-fiber heating fabric warms up quickly and evenly due to the highly efficient structure of the roving. Positioning the heating elements just under the surfaces of the stool and the bench ensures that the components heat up quickly and (importantly) without producing cracks, thus delivering a high degree of functionality and durability.
A charging station has been fitted just below the surface of the concrete to ensure the unit is not visible from the outside and is thus fully integrated into the table. The unit has a maximum wireless charging capacity of 20 watts and is compatible with all Qi-enabled devices. A connection cable for the charging station has been fitted along one side of the table.
To fit the furniture with indirect lighting, the Steinbeis experts developed a concrete lamp. The table also includes an illumination option. This was created by adding a placeholder to both the lamp and the table, with an added connection attachment on the outer core. Once the concrete has been poured, lighting modules are inserted into the lamp unit and the table. The lamp modules, which comply with the IP54 safety rating, are easy to replace during renovations.
The new free-form, function-integrated, lightweight architectural concrete street furniture is unique in terms of sustainability, design, and functionality. To launch the FurCrete range, the furniture was unveiled to a public audience as a trade show prototype. It received an extremely warm reception. Further prototypes are on display in the show garden at LIMEX. Also, for the first time ever the new carbon concrete street furniture will be used on the terrace at the Carlowitz Congress Center in Chemnitz.