Use of circulating fluidized bed combustion fly ash and slag in autoclaved brick

Circulating fluidized bed combustion (CFBC) fly ash and slag are wastes from CFBC power plant, and have such a high sulfur content (usually more than 5% SO3 by weight) that would result in a great risk of destructive expansion when used in building materials, which are produced in normal temperature. This work investigated the preparation conditions of autoclaved brick with CFBC fly ash and slag, and compared the long-term volume stability and the hydration products between the autoclaved brick and adobe one. It is shown that the autoclaved brick could be made up of 77% CFBC fly ash, 20% CFBC slag and 3% cement by weight, and exhibited good long-term volume stability, and achieved the compressive strength of up to 14.3 MPa, and that there was no dihydrate gypsum and ettringite formation in the autoclaved brick so that the destructive expansion could be avoided. This work has carried out practical production and application of the autoclaved brick. It is concluded that CFBC fly ash and slag can be used to make high-quality brick as long as it is autoclaved.

► We investigated to make use of CFBC fly ash and slag containing about 10% SO3.
► Up to 97% of CFBC fly ash and slag can be used to make an autoclaved brick.
► The compressive strength of the autoclaved brick reached 14.3 MPa.
► The autoclaved brick had no destructive expansion even cured in water for 270 days.
► There was no AFt and dihydrate gypsum in the autoclaved brick.