Recycle of coal oil ashes for the manufacture of building materials

In this paper coal fuel ashes have been characterized in terms of leaching behaviour and reactivity against lime and gypsum in hydratory systems for the manufacture of building materials. Their behaviour was also compared to that of coal ashes. Metal release was measured in a dynamic leaching test with duration up to 16 days. The results have shown that coal-fuel oil ashes behave very similarly to coal ashes. The reactivity of coal-fuel oil ashes against lime and gypsum was measured in mixtures containing only lime and in mixtures containing both lime and gypsum. These systems were hydrated at 25 and 40°C under 100% R.H. The results have shown that the main hydration products are the same as those that are usually formed in similar coal ashes-based systems. That is, calcium silicate hydrate in coal-fuel oil/lime systems and calcium silicate hydrate plus calcium trisulfoaluminate hydrate in coal-fuel oil/lime/gypsum systems. From the quantitative point of view, hydration runs showed that both chemically combined water and reacted lime are significantly higher in the case under investigation. Finally the measurement of unconfined compressive strength proved that the systems have potentiality for the manufacture of pre-formed building blocks.