Investigation of hydration products of fly ash–slag pastes

Abstract

The paper presents the results of the research identifying the hydration products present in hardened fly ash–slag pastes considered as alternative non-clinker binder. Thermal analysis (TG/DTG), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used as complementary methods. The pastes contained the binder made of two components: fly ash from circular fluidized bed combustion of brown coal and ground granulated blast furnace slag. The components were mixed accordingly to five formulas differing in proportions, but with constant water/binder ratio (w/b = 0.5). No chemical activators were used to initiate the binding reaction of blast furnace slag. The results of thermal analysis, IR spectroscopy and scanning electron microscopy as well as the increase of compressive and flexural strength in time revealed the progression of hydration process in time and formation of products similar to ones present in hardened cement pastes. SEM observations of pastes after 90 days of curing showed fibrous (type I) and similar to honeycomb form of C–S–H phase, ettringite and calcium aluminates.