Examination of the system fly ash–lime–calcined gypsum–water

The feasibility of the utilization of the system fly ash–lime–calcined gypsum (β-hemihydrate)–water (the mass ratio 2:1:2:2.5) for the production of building ceramics was investigated. The system was cured under different conditions, i.e., tap water and ambient air. It was confirmed by X-ray diffraction analysis that three hydration products (gypsum, portlandite and ettringite) were formed in the water-cured system and two (gypsum and portlandite) in the air-cured system. Due to the formation of these products, a compressive strength of 4.01 MPa in the water-cured and 7.83 MPa in air-cured system developed. When the air-cured system was exposed to three alternate heating–cooling or three alternate cooling–heating cycles, the compressive strength increased (from 7.83 to 9.47 and 10.55 MPa, respectively). The fly ash–lime–calcined gypsum–water systems prepared in this work can be applied for the manufacture of products for internal walls (bricks and blocks).