Product design using secondary raw materials in the construction materials and ceramics industry


Secondary raw materials in the form of building rubble represent one of the largest waste streams in Bavaria. The depletion of natural resources and the increasing scarcity of landfill space cannot be addressed by the current technological developments in the sector of construction waste recycling. About 61% of building rubble, which is mainly made up of brick, concrete and mortar, is currently recycled, but only just under 17% of it undergoes high-grade recycling, such as in building construction. At present, recycled construction materials are mainly used in road construction or earthworks. The project aims to develop processing methods for construction and ceramic rubble in order to obtain high-quality secondary raw materials with defined properties.

Construction waste in Bavaria in 2012 (total: 45,579,000 t):


The aim of the project is to develop an innovative technology for the production of porous recycling granules with defined properties from heterogeneous, fine-grained mineral and ceramic secondary raw materials. These would be intended for use in building construction, as an aggregate for lightweight concrete, for thermal insulation, sound insulation, or as a carrier material for plant nutrients. The project also aims to produce new ceramic products from pressed granulate waste, broken pipe fragments, faulty unfired ceramic products, broken ceramics and secondary material from spray granulation by mixing these with high proportions of secondary building materials. This is expected to result in high-quality reuse of construction material and ceramic waste as well as an increase in the ceramic raw material flow, which in turn will enable cost-effective and competitive ceramic products to be created.

The sulphate issue:

Gypsum is found in around 10 % of German buildings, for example as plaster, screed or in the form of panels.  To date, construction material waste containing gypsum has mainly been landfilled due to the sulphate it contains. During recycling, this can dissolve – resulting in the legally regulated, permissible amount of sulphate in wastewater being exceeded.

The project is therefore investigating possibilities for reducing sulphate content using model construction materials. Comminution and fractionation can be used to enrich the sulphate in certain fractions, for example. For this purpose, two test benches meeting the necessary standards for the production of eluates have been installed at Nuremberg Tech. Analysing the pollutants in the eluates can provide important information for the construction materials and recycling industry about the amount of sulphate contained in the construction materials.

Selective comminution has created a tool that makes it possible to enrich the sulphate content in certain fractions and to selectively remove it from recycling. In addition, the sulphate content in the construction materials has been reduced by leaching, which has created a further possibility for reducing pollutants.


The recycling process chain:

To achieve a closed material cycle within building construction, thereby avoiding downcycling or disposal, a recycling process was created:

The process consists of various comminution stages for the starting material, simultaneous particle characterization, and subsequent shaping by agglomerating the material flows. The resulting green granulates are then thermally stabilized. Two different hardening processes are suitable, depending on the mechanical and thermal properties required of the granulates. One option is through biscuit firing or sintering in a kiln; alternatively, good results can be achieved through hydrothermal hardening, as is usual when producing sand-lime brick.

In addition to the applications in building construction, a pourable slurry can also be produced from broken bricks and ceramics, which after shaping and firing can be used as an inexpensive and therefore competitive tableware ceramic.

The project was carried out within the framework of the ForCYCLE research association.

We would also like to thank our project partners, Porzellanfabrik Walküre and Fraunhofer ICT.

Further information is available at:



Kevin Hefele

Main areas of work:

-    Comminution of construction materials
-    Characterization of the properties of the recycled material
-    Agglomeration and green granulate production
-    Characterization of product properties

-    Thermal hardening of green granulates

-    Selective comminution

-    Standardized elution and determination of pollutants in construction materials