Mechano-chemical activation of high-Ca fly ash by cement free blending and gypsum aided grinding

• The presence of Ca, Al, K and sulphate in biomass fly ashes found very influential.
• Optimisation of the blend constituents ensuring successful activation was achieved.
• Dispersing the blend particles by plasticiser found effective than NaOH activation.
• The role of gypsum as grinding aid and contributing SO4-2 dissolution was revealed.
• Hydration products and strength development in new blend were similar to cement.

This paper presents a laboratory study exploring the pozzolanic reactivity of a calcium rich fly ash by blending and grinding in a cement free system. A synergistic physico-chemical composition was achieved through individual grinding and ternary blending with another alkali sulphate rich fly ash and silica fume. The beneficial role of Flue gas desulfurisation gypsum as a grinding aid as well as a sulphate activator for fly ashes was also reported. The new blend’s parameters sensitivity revealed the physico-chemical features analogous to cement. The dispersion of the ground reactive blend particles by super plasticiser was found more effective than further alkali activation by NaOH. The potential of the developed blend as a new cementitious material is highlighted in this study. Progressive mortar compressive strength up to 90 days and 46 MPa after 28 days of curing was reported by the cement free system of activated fly ashes.