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NanoKiesel – Nanoscale silica slurry – Technology developments on nanoscale silica slurry use in mineral building materials with the aim of improving material properties

Siliceous filter residues (FR) occur as wet filter cakes during treatment of sewage from the chemical industry. These residues are currently disposed of for a fee in landfills or are used for open pit backfilling. Due to their high content of amorphous silica and large specific surfaces, the filter residues have properties resembling those of micro-silica, a by-product of silica production which today is indispensable in the manufacturing of building materials.

This research project focused on investigating the use of two types of filter residues from different production processes in the building materials industry with the objective of improving certain properties. The filter residues were characterised extensively and their high amorphous silica contents were confirmed. The detected sulphate and chloride contents may limit the use of the residues.

Based on the results of characterisation, some feasible uses were preselected and verified experimentally:

• Pore-forming agents for brick production→ bulk density reduction through one of the investigated types of filter residues
• Concrete additive → increase in strength for both types of filter residues
• Constituent of composite concrete → increase in strength for both types of filter residues
• Special-render additive→ no effects confirmed
• Stabiliser for bentonite suspension→ impairment of properties

The technological conditions for using filter residues in the production of brick or concrete goods have been discussed. Comparative considerations on energy consumption and energy consumption costs identify the use of filter residues in bricks as being the least costly option.

Project Lead

Dr.-Ing. Barbara Leydolph, Weimar Institute of Applied Construction Research (IAB)

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