Activity of low-calcium fly ash in phosphate hardening binders

Light, strong and heat-resistant structures obtained by the interaction of low-calcium fly ash with phosphoric acid may be of interest for the technology of heat-insulating high-temperature materials. However, the activity of fly ash in the interaction with solutions of orthophosphoric acid and the ability to form artificial stone as a result of this interaction depend on the chemical composition and nature of the glass phase of the ash. From the examples presented in this work, it follows that, along with fly ash, which easily enters this reaction at ordinary temperatures, there exist also ashes that show noticeable activity  in mixtures with H3PO4 only at higher temperatures or remain inert even under these conditions. The result of the chemical interaction of ash with acid is phosphate rock whose strength reaches 10 MPa or more (at a density of 1.4—1.5 g/cm3), and after firing at 900° C — about 15 MPa (at a density of 1.2 g/cm3).

Author: A.S. Brykov, M.Ye. Voronkov

Section: Waste utilization

Keywords: low-calcium fly-ash, phosphoric acid, phosphate binder