Influence of quicklime and Portland cement, as alkaline activators, on the reaction products of supersulfated cements based on pumice

Abstract

This is a study of the microstructure and chemical, mineralogical and structural composition of the reaction products of supersulfated cements based on pumice (SSC-PM), prepared with 20 % of quicklime or Portland cement, as alkaline activators, and 5–10 % of a sulfatic activator of anhydrite (An). Paste specimens were cured at 20 °C or 60 °C for 24 h. The characterization by FTIR, DRX, DTA/TGA, SEM, EDS and NMR indicated the type of alkaline activator influenced the type and amount of hydration products, as well as the resulting microstructure, which in turn affects the compressive strength. After 28 days, the quicklime favored the pumice dissolution, leading to degrees of reaction higher than with Portland cement, promoting the conversion AlIV→ AlVI in the reaction products to form high amounts of ettringite (AFt ≥27 %) and reducing aluminum uptake into the C–S–H on Q2 and Q3 sites with an AlIV/Si ≤ 0.06. On the other hand, the Portland cement increased the medium chain length (MCL) and favored the intertwining of long needle-shaped AFt with the C-A-S-H, densifying the microstructure, favoring the compressive strength. The best strength of 24 MPa was for a binder with 5%An-20%PC (ICT:60 °C) with MCL = 9 (Ca/Si = 0.94).