In the context of sustainability, natural and in particular renewable raw materials are advantageous. However, the general rule is that the fewer resources taken from nature and the more products that are reprocessed into raw materials at the end of their lifecycle, the more sustainable is the overall value-added process. Xella has set itself the objective of closing the raw material loop as often as possible in terms of its production processes and the products themselves.
The most important components of all Xella products are natural raw materials. Sand, lime, cement and water form the basis of Ytong autoclaved aerated concrete, Silka calcium silicate blocks, Multipor mineral insulation boards and Hebel compound units. Fermacell uses paper fibers, gypsum, cement and other mineral aggregates. These basic materials are found everywhere in nature and are extracted naturally. Wherever possible we use secondary raw materials and endeavor to apply the Cradle to Cradle principle.
Further reducing bulk density
Xella has been involved for many years in researching how to reduce the bulk density of Ytong autoclaved aerated concrete. This would offer two decisive advantages: Improved insulation and lower weight. Air is the best medium for insulating exterior walls. The greater the number of air entrainments in aerated concrete, the better its thermal insulating properties.
At a bulk density of 250 (kg/m³) for the Ytong block this equates to 0.07 W/(m2 K) – one of the best insulation values for solid construction materials. A low bulk density also ensures lower weight. This means that the building material is easier to work with, saves energy during transportation and consumes fewer raw materials.
Fly Ash as a Secondary Raw Material?
Fly ash, which is produced in power stations as an anorganic concentrate of non-flammable impurities in coal, is a very common secondary raw material. However, for quality assurance reasons, Xella uses no fly ash at its autoclaved aerated concrete plants.
Negative impact on the quality of autoclaved aerated concrete:
- A high proportion of SiO2 affects the strength and shrinkage properties
- Quality fluctuations make achieving uniform product quality difficult
- High quality fly ash is expensive and rare
- Dark coloration
- Possible contamination with pollutants
But the blocks may not exhibit any shortcomings in terms of their structural loading – the stability and load-bearing strength of the walls must still be guaranteed. This reflects the importance of product development. The exact opposite is true in the case of Silka calcium silicate blocks for interior walls. These must offer the highest possible bulk density while not becoming overly voluminous. This is the only way to achieve a high level of sound insulation in the smallest space.
Gypsum waste as a new raw material source
Gypsum fiberboard from Fermacell is manufactured from gypsum, recycled paper fibers and water – without the addition of binders – in a resource-conserving process. No waste is generated within the manufacturing process; the raw materials remain within a practically endless cycle of use (Cradle to Cradle) while production-related waste products and wastewater are fully reintegrated into the manufacturing process.
Although the gypsum needed to manufacture the boards does occur naturally, we primarily use FDG gypsum which is a by-product of the flue gas desulfurization process at power stations. Tests have confirmed that FDG gypsum possesses the same mineralogical structures as naturally occurring raw materials and is even of above average purity. During the coal burning process, flue gases are generated that are subsequently desulfurized using lime. The material cycle is perfectly complemented with the use of recycled paper to manufacture Fermacell gypsum fiberboards. Fermacell Aestuver fire protection boards utilize recovered glass in the form of foam glass, reducing product weight and therefore transportation costs.
Aerated concrete granulate for feline hygiene
All production waste from Xella’s aerated concrete and calcium silicate block factories can be reused. Residual waste material, for instance from the modeling process, is returned to the mixing process. Already hardened production waste is ground into granulate or returned to the mixer in crushed form, along with any dust produced in the process. At the Alzenau factory for example, some 100,000 tons of demolished aerated concrete is processed into 25,000 tons of granulate each year. Depending upon its quality, Ytong granulate from Germany is marketed as a levelling fill for floors, an oil binding agent or as cat litter, and has received an Environmental Product Declaration (EPD) for environmentally friendly products.
For the love of animals
The Xella company SILIKALZIT sells 60,000 tons of aerated concrete granulate each year. In addition to litter for animal hygiene, its product range includes various binding agents for oil and chemicals released during fires and oil spills, chemical accidents and industrial leaks, together with agents for changing the consistency of fluids or viscous substances. Furthermore, calcium silicate hydrate, from which aerated concrete is made, is also suitable for preventing long-term consequences for nature and the environment, e.g. through soil or water contamination. Of the 90,000 tons of aerated concrete waste that Xella processes into granulate each year, SILIKALZIT markets 41,000 tons for animal hygiene products alone.
In addition to the marketing of aerated concrete granulate, SILIKALZIT has a further recycling market in its sights: Phosphate. Large amounts of this essential salt are found in sewage sludge, but it has to-date been impossible to extract them. SILIKALZIT is currently investigating whether phosphate can be recycled using a process it has developed together with the University of Darmstadt. These investigations are now at the testing stage.
Conserving process water
The water needed to manufacture autoclaved aerated concrete mostly comes from wells located directly onsite. This water is used both for mixing raw materials and generating process steam. A large proportion of this steam, which is used for pressure hardening, condenses and is channeled back into the mixer. Our production plant therefore allows almost one hundred percent of this condensate to be recovered and recycled.
The condensate is also used for other applications, for instance in our sanitary facilities. At some of our factories the condensate is treated and fed into the local drainage system. Rainwater – as well as ground and fissure water from quarries – is also used in production and for washing processes. The cooling water required for saws is repeatedly used in a closed loop.
Resource-efficient processing of limestone
The lime is quarried, transported and then classified according to its intended application. This allows all processes to be operated in the most energy and resourceefficient manner possible. The required fresh water is extracted from either natural streams or on-site wells.
Lime products from Fels are fired in industrial kilns which, thanks to optimized combustion processes and waste heat recovery, achieve thermal efficiencies of up to 85 percent. Systematic noise reduction programs are implemented at all Fels factories with the objective of decreasing noise emissions. Using digital models it has been possible to identify – and significantly reduce – the main sources of noise affecting our neighbors.