Effects of chemical composition of amorphous phase on the reactivity of phosphoric acid activation of volcanic ashes

Abstract

Two volcanic ashes with differences in mass percentages of oxides in chemical composition of amorphous phase were activated by phosphoric acid (P2O5 / H2O molar ratios between 0.04 and 0.15). Amorphous phase was mainly composed of SiO2, Al2O3, CaO, MgO and Fe2O3 oxides. Heat released and initial setting time correlated with the sum of mass percentages (SMP) of Al2O3, Fe2O3, CaO and MgO oxides of amorphous phase: the greater the SMP, the greater was heat released and the lower was initial setting time. Compressive strength increased with the increase of P2O5 / H2O molar ratio up to a limit. Mass percentages of Al2O3 and Fe2O3 in amorphous phase along with P2O5 / H2O molar ratios plaid key roles on the variation and the highest value of compressive strength. Qualitative and quantitative determinations of chemical composition of amorphous phase of volcanic ash are useful parameters allowing getting appreciable view of its reactivity.