Production of high performance building materials from flue-gas gypsum

Abstract

Flue-gas gypsum, from the desulfurization of SO2 emitting from the power plant, was used as a starting materials for the synthesis of α-hemihydrate which is used for the interior building plaster components. α-hemihydrate was prepared by calcining the flue-gas gypsum in an autoclave at temperatures of 120-163℃ and pressures of 2-7 bars. The effect of calcining time upon the phase of plaster obtained and also the effects of various additives on the properties of the products were studied. It was found from the experimental results that the specimens having equivalent quality to those from natural gypsum could be obtained. The maximum flexural strength of the hydrated specimens was 14.36 MPa. However, the disadvantage of gypsum products is its ability to absorb water from ambient condition leading to the reduction in mechanical strength. This disadvantage of gypsum products could be improved by the combination of gypsum with amorphous silica (SiO2), alumina (Al2O3) and hydrated lime (Ca(OH)2) to produce the insoluble phases of calcium silicate hydrate (3CaO.2SiO2.3H2O) and calcium sulfoaluminate hydrate (ettringite, 3CaO.Al2O3.3CaSO4.31H2O) from pozzolanic reaction. The composite containing the mentioned phases could be used as a building component for both interior and exterior applications. The effects of raw material proportioning and accelerating methods upon the physical and mechanical properties of the composite, and also the effect of wetting/drying cyclic storage on the dimensional stability were studied. It was found from the experimental results that the maximum compressive strength and linear change after cyclic storage (100 cycles) of the 90-day composite was 154.5 MPa and 0.0007%, respectively.