ECO-FRIENDLY BINDERS BASED ON FLY ASH

The paper presents data on the synthesis, interaction processes and properties of alkaline cements based on fly ash. This type of binders consists in a solid compound - a mixture of fly ash and lime and an activator solution - sodium silicate with/without sodium hydroxide or sulfates (Na2SO4 and CaSO4). The fly ash-sodium silicate-lime system has binding properties at room temperature. The presence in the system of sodium silicate determines the dissolution of the aluminosilicate structures form the fly ash, and facilitate the binding of Ca(OH)(2) in calcium silicate hydrates (C-S-H) phases, with positive influence on the developed compressive strength. The increase of the binding system's basicity when using NaOH addition, increases furthermore the hardening processes rate and consequently the compressive strength values. The use of small amounts of sodium or calcium sulfate has a positive effect on the mechanical strength development most probably due to the formation of ettringite (3CaO.Al2O3.3CaSO(4).31H(2)O).