The hydration products were further studied by Fourier transform
infrared spectroscopy (FTIR). A platinum ATR QuickSnapTM sampling
module was used allowing direct measurement of powder instead of
pellets. Microstructural investigations were carried out employing a
scanning electron microscope (SEM, XL30, Philips) on bulk samples.
The specimens were prepared by drying for at least 2 days at 40 °C
in air.
Compressive strengthwas measured on mortar specimens after 3, 7,
28 and 90 days of hydration. For this purpose mortar samples were
prepared according to EN 196–1 using CEN standard sand. The sand
to binder mass ratio was 3:1. To maintain the flow of mortars in
accordance with EN 1015–3, the l/b ratio was adjusted to 0.75 for
mechanically activated samples. Alkali activated mortarswere prepared
using NaOH solution, whereas the l/b mass ratio was adjusted to 0.66
and the amount of Na2O equal to 8% by mass of the binder. All samples
were stored in an air-conditioned room at 20 °C and relative humidity
higher than 95% until testing. After the designated time, the mortars
were tested for compressive strength using a Schenck-RM100
compression testing machine. For each activation method and curing
time four samples were measured and the average values were
reported.