Rock dust/fillers and crushed sands are quartz-poor tempers and drying agents that are added to brick masses. Improved sintering behaviour above 950 °C can strongly increase the body strength. Ideally, rock dust is wetted before transportation and processing in the brick plant.
The maximal grain size of rock fillers is d < 0,6 mm. Therefore the raw material does not have to be further processed to be used in the brick industry. At the same time the Winkler triangle shows, that the grain size of problematic masses can be influenced to increase the amount of support grains.
Rock fillers are dust-dry mineral products that are produced in large quantities during the dry processing of solid rock. Many quarries invest in equipment for controlled wetting of rock dust. Crushed sands contain bigger grains up to 2 mm. Depending on the brick raw material rock dusts and crushed sands can be used with a share of up to 20 %.
The mineralogical characteristic of rock fillers is determined by the type of solid source rock. Magmatic rocks and fillers with high contents of feldspar and phyllosilicates are very common. Rock fillers can be used to optimize the drying and firing process. Resulting firing colours vary between light cream, grey and red to dark brown.