Properties of cement concretes modified by mechanically activated siliceous fly ash

The results of compressive strength, water absorption and shrinkage of concrete prepared with addition of mechanically activated siliceous fly ash are presented. The activation of fly ash was characterized by the breaking part of grains, mainly bigger grains and grains containing voids. As a consequence of mechanical activation an increase of specific surface of fly ash was observed, the activity of fly ash increased and the microstructure of hardened paste was improved. The compressive strength tests were carried out after 7, 28, 56, 84 and 168 days of concrete curing and water absorption tests were performed after 28, 56 and 84 days of curing. The shrinkage of concrete was monitored over the period of 6 months. The concrete mixes were prepared with different fly ash/cement ratio (Pl/C = 0.2; 0.4; 0.6) and different water/binder ratio (W/S = 0.350; 0.425; 0.500). Fly ash was used as a part of binder. As the result of replacing non-activated (base) fly ash with activated fly ash the compressive strength of concrete increased and water absorption of concrete decreased, both after 28 days of concrete curing. Several fly ash/cement ratios (Pl/C) and water/binder ratios (W/S) were investigated. Replacing the base fly ash with activated fly ash had no effect on concrete shrinkage.