HARDENING OF CEMENT MORTARS WITH THE ASH AND SLAGS OF BOILERS WITH CIRCULATING FLUIDIZED BED

Abstract

Properties of ash and slag waste in boilers with circulating fluidized bed are under consideration. Several new generations of boilers are operated in the Donetsk region, thus permitting to burn poor coal. Ashes and slag, obtained in this case, have somewhat other properties different from those obtained at a traditional waste fired CHP plant.Models of cement hydration with blast furnace slag were studied. Hydration of two components (slag and Portland cement) was studied individually, although they can be uniformly mixed in cement and interact with each other. However, cement obtained by mixing Portland cement clinker and steel slag known as Portland slag cement. The chemical composition of blast-furnace slag for mixing with Portland cement clinker is adjusted to be identical to the chemical composition of the clinker.Chemical composition of ashes and slags in power plants is not regulated as that of steel slag because they are after coal combustion waste. Their chemical composition depends on coal deposits. But because fossil fuels are accompanied by clay rocks, chemical composition of ashes and slags in power plants is similar to the chemical composition of argillaceous rocks with minor variations in the number of major oxides. The most dangerous oxides in the chemical composition of waste are considered to be sulfates, gypsum or anhydrite.Some harmful oxides in ash and slag are known to be able to react with minerals of the Portland cement clinker or with hydration products. Portland cement is gaining strength mainly due to the hydration of calcium silicate C3S and C2S. As a result of hydration, calcium hydrosilicates of C-S-H type and calcium hydroxide CH are formed. Calcium hydroxide is able to react with the silicon oxide contained in the ash and slag in thermal power plants, and to form calcium silicate. However, calcium aluminate may interact with calcium sulfate contained in ash and slag of TPP and form secondary etrinhit that can cause destruction of the cement stone.The aim of this study is to determine the effect ash and slag boilers with circulating fluidized bed on the process of Portland cement hydration and on the kinetics of ash and slag cement mixtures thickening.