Impact of separated bottom ashes on the parameters of concrete mix and hardened concrete

Polish energy industry is based primarily on the combustion of coal in conventional boilers and increasingly in fluidised bed boilers. As a result of combustion, by-products are formed, such as fly and bottom ashes. In the case of fly ashes, a number of methods of utilising them have already been developed, e.g. for the production of cement, concrete and in other industries. With regard to bottom ashes, whose properties differ significantly from those of fly ashes, methods are still being researched for the possibility of their industrial application. Similarly to fly ashes, it seems reasonable to move in the direction of bottom ashes being used in the wider construction industry, including for the production of concrete. This paper analyses the impact of the addition of bottom ashes obtained from hard coal combustion in conventional and fluidised bed boilers on the properties of fresh and hardened concrete. A concrete mix composition was developed by an experimental method, which was then modified with the use of bottom ashes. The impact of the substitution of cement and aggregates with bottom ash on the concrete properties was examined. For all the obtained series of concretes, tests were performed for the consistency of the fresh concrete using the concrete slump test, the compressive strength and tensile strength of the concrete after 3, 7 and 28 days of maturing and their absorption. The experiments have shown significant declines in the strength parameters of the concretes being analysed in the case of the substitution of cement with separated bottom ash. However, substituting relevant aggregate fractions with separated bottom ash resulted in an increase in both the compressive strength and the tensile strength in the analysed concretes