Microstructural and Mineralogical Analysis of Alkali Activated Fly Ash-Slag Pastes

Abstract

The performances of alkali activated materials (AAM) are strongly related to their microstructures. The microstructure development is mainly affected by chemistry of the primary raw materials. In the present study the influence of different proportions of fly ash and slag (100:0, 70:30, 50:50, 30:70, 0:100 wt.%, named S0, S30, S50, S70, S100, respectively) on the microstructure and mineralogy of the alkali activated fly ash and slag based pastes has been investigated through XRD, TGA/DTGA, ESEM/EDX techniques. XRD has been used for the qualitative and quantitative analysis of different reaction products.
The Rietveld refinement method and TGA/DTGA analysis have demonstrated that the increase of slag content increased the amount of amorphous phase associated with gel formation. From ESEM results, a more refined and denser matrix has been deduced in slag rich mixtures. These results are in agreement with higher strength values observed for S70 and S100 mixtures (~100 MPa at 28d and ~120 MPa after 90d curing). Depending on the fly ash to slag ratio, two types of gel have been distinguished by EDX analysis, a N-A-S-H gel in the fly ash rich mixtures and a C-A-S-H gel in the slag rich pastes.