Effect of fly ash to slag ratio and Na2O content on leaching behaviour of fly Ash/Slag based alkali activated materials
Lakshmikanth Srinivasamurthy, Venkata S. Chevali, Zuhua Zhang, Hao Wang
Abstract
Alkali–activated materials (AAMs) with variable levels of activator and precursor loading were evaluated for their long–term leaching behaviour. On a series of fly ash (FA)/slag–based binder mixes containing varying amounts of slag (0 – 30 wt%) and Na2O (5 – 9 wt%), 90–day leaching was conducted, and the resultant leaching products were characterized using X–ray diffraction, nuclear magnetic resonance 23Na and 27Al, and Fourier–transform infrared spectroscopy. The microstructural, mechanical, and physical properties of the samples were analysed as a function of the concentrations of activators and precursors. C–A–S–H and N–A–S–H gels were formed due to the inclusion of slag, which enhanced mechanical properties and decreased porosity. As the slag content in AAMs increased, the porosity decreased and the leaching ability of Na+ and Si4+ decreased. A long–term leaching process leached Ca2+ and Al[IV] from structural gels, including the N–A–S–H/C,N-A-S-H gel, and caused degradation with a corresponding decrease in compression strength and split tensile strength.