Performance and microstructural examination on composition of hardened paste with no-cement SFC binder

• A new no-cement SFC binder with slag, Type F fly ash and CFBC fly ash is proposed.
• The hardened paste of SFC binder has a compressive strength of 68.4 MPa at 28 days.
• The main hydration products are ettringite and calcium aluminum silicate hydrate.

This research aims to present the engineering performance and microstructural examination on compositions of hardened paste with a no-cement SFC binder, which is fabricated with mixture of ground granulated blast furnace slag (GGBFS) (S), Type F fly ash (FA) (F) and circulating fluidized bed combustion (CFBC) fly ash (C). Specimens with four FA/GGBFS weight ratios (0, 1/9, 3/7 and 1) are prepared to estimate the effects of FA on the engineering performance. CFBC fly ash, around 10–25 wt.% of the mixture, is used as the main activator. The results show that the optimum mixtures are obtained by 15–20 wt.% CFBC fly ash and 10–30 wt.% FA. They have higher compressive strengths than those without FA. The early hydration of CFBC fly ash and GGBFS provides sufficient alkalis and releases heat, both play a crucial role in the pozzolanic reaction of FA particles. The main hydration products of the hardened paste are ettringite (AFt) and calcium aluminum silicate hydrate (C–A–S–H) gel, as examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).