Synthetic precursor to make hybrid alkaline cements

Abstract

The present work explores the effect of thermal treatment on the reactivity of a synthetic precursor, prepared with a chemical composition similar to a type-C fly ash (~ 20% CaO wt., SiO2/CaO = 3, SiO2/Al2O3 =3). Three temperatures were selected; 1000 ºC, 1100 ºC and 1250ºC. The precursor obtained was used to make hybrid alkaline cements (30% PC +70% precursor) which were hydrated in the presence and absence of a solid alkaline activator (5%). Cements with 70% sand (instead of precursor) were also prepared and used as a reference system. Mechanical compressive strength was determined at 2 and 28 days. Kinetics of hydration was determined by isothermal conduction calorimetry. Both, the precursors and the hybrid alkaline cements (hardened paste) were characterized by different techniques: Xray diffraction (XRD), Fourier Transform Infrared Analysis (FTIR), Scanning Electron Microscopy (BSEM/EDX) and Nuclear Magnetic Resonance (NMR).