Structure and properties of naoh activated cement free binder (CFB) concretes

Increasing emphasis on sustainability of the built environment has resulted in attempts to drastically reduce the cement consumption in concrete and replace it with waste/recycled materials. This study reports the development of concretes with cement free binders (CFB) and the evaluation of their properties. A Class F fly ash and a ground granulated blast furnace slag (GGBFS) are used as the binding materials. The activating agent used in this study is sodium hydroxide (NaOH), at concentrations ranging from 6 M to 10 M. The optimal temperature and curing duration required to achieve desirable compressive strengths of CFB concretes are reported. The influence of the binding material and the concentration of the activator on the compressive strength and porosity of the CFB concretes are studied. The compressive strength of CFB concretes with fly ash as the binding material increases with increase of activating solution concentration but for CFB concretes with GGFBS as the binder, activation with 8 M NaOH is seen to result in the highest compressive strength. The strength-porosity relationship of CFB concretes shows an exponential trend, similar to that of conventional cement based materials. Microstructure and the phase composition of the reaction products are also discussed.