Effects of ground granulated blast furnace slag on the mechanical and microstructure of fly ash-based geopolymer binders

Effects of ground granulated blast furnace slag on the mechanical and microstructure of fly ash-based geopolymer binders

The effects of addition of ground granulated blast furnace slag on mechanical properties and microstructure of fly ash-based geopolymers were investigated via compressive strength testing, X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The compressive strength of geopolymers increased with the slag ratio increasing. The alkaline activation of slag and fly ash forms a kind of homogeneous product with microstructure between typical alkali aluminosilicate gels (N-A-S-H) and calcium silicate hydrates (C-S-H). Distinct phase separation has not been found as the slag ratio varies or the modulus of the alkali activator decreases from 1.2 to 2.0. The FTIR bands assigning to T-O-Si (T=Al or Si) asymmetric stretching vibrations of the geopolymer binders shift towards lower regions as slag is incorporated, and this shift is explained due to the decrease of poly-degree of the aluminosilicate networks. The increased XRD diffraction hump and FTIR bands that assigned to aluminosilicate gels suggests improved quantity of alkaline activation products as the content of slag increases, and this is related to the increased compressive strength.

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