Spectroscopic and microscopic study of alkali activated mortars based on Tunisian phosphate washing waste

Abstract

The calcination of phosphate washing waste has a significant effect on the microstructure and mechanical properties of the phosphate washing waste-based alkali activated mortars. This study aims to investigate the reaction products of the phosphate washing waste activated with sodium hydroxide (SH) and sodium silicate (SS) with mass ratio of the two solutions SH/SS = 1.Different techniques were used to characterize the obtained mortars including: Compressive strength, X-ray diffraction XRD, Solid state magic angle spinning nuclear magnetic resonance (MAS-NMR) of 3 nuclei (27Al, 29Si and 31P), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and Electron microscope scanning and energy dispersive spectroscopy (SEM-EDS). The obtained results reveal that the alkali activation of phosphate washing waste generate 2 types of reactions and 2 types of products (N-A-S-H)/(C,N)-A-S-H as 3D network and C–S–H/C-(A)-S-H as 2D gel. The Al and reactive Ca have a strong effect on the final mechanical properties.