invEstigation oF usagE oF thE Fly ashEs From PowEr Plants kakanj and tuzla in Portland CEmEnt ProduCtion

The fly ash, a massive solid waste from coal fired power plants is produced with a crude estimation of 700 billion t per year in the world, and only 6% of this quantity are utilised in cement production. The aim of the present work is to investigate the possibility of using the fly ashes from power plants Kakanj and Tuzla for cement production. The fly ash utilisation has economical as well as ecological benefits. According to national standard BAS EN 197-1, the fly ash is used as a supplement in cement production. On the basis of chemical composition fly ash can be classified in two main categories: alumino silicate and calcium silicate fly ashes. Both investigated ashes belong to the group of calcium silicate ashes with high CaO content. However, fly ash from power plant Tuzla has higher content of Cao and lower content of Sio2 comparing to fly ash from power plant Kakanj. Regardless on fly ash content in the cement, the initial setting time is longer than 60 min, and this condition is defined by standard. The initial setting time increases with increasing the fly ash content in the cement. The soundness was investigated on samples with different fly ash content. It was observed that all the samples tested shown expansion much smaller than standard limited expansion. This is consequence of very low free Cao content and it is very important characteristic concerning the durability of cement-based products. Generally, cements with fly ash content gain strength more slowly at early ages (28 days). It was determined that samples manufactured of cement with fly ash from power plant Kakanj have greater strength than samples with flay ash from powerplant Tuzla. The results obtained show that the fly ash from power plant Kakanj is more favourable supplement for cement production. Apart from chemical composition, this fly ash has other advantages over the fly ash from power plant Tuzla such as high content of glassy phase (>50%), low content of unburned coal and free CaO and very high content of fine particles (<20 μm).