Influence of Type of Secondary Raw Material on Consistency of Fresh Mixture for AAC Production

Abstract

Autoclaved aerated concrete (AAC) is, mainly in Europe, widely used construction material. It has an optimal combination of bulk density, strength and thermal conductivity coefficient for load-bearing and non-load-bearing structures of civil facilities. The production technology is based on a mixture of ground silica sand, lime, cement, gypsum, aluminium powder and additives. The grinding of sand is most often carried out in a wet way, and the sand sludge is consequently used in production technology. The aim of the experiment was verification of the effect of partial replacement of sand with the alternative raw materials in sand sludge on the rheology of the mixture. This parameter determinates how the modified mixtures affect the sludge pumpability. As a reference the consistency of the sand sludge of the normal production density of 1.65 g/cm3 was compared to the sand sludges of different density (1.60, 1.70 and 1.75 g/cm3) and with a fresh aerated concrete (FAC) mixture of 1.60 g/cm3. Then the sludges were modified by 30 % of alternative raw materials (recycled glass, coal slag, FBC ash, FBC bottom ash) as the partial weight replacement for sand. This partial replacement resulted in water/solids ratio adjustment which recommended value is 0.47 for recycled glass and coal slag, 0.59 for fluidized bed combustion (FBC) bottom ash and for FBC fly ash it is 0.70.