Synthetic γ-C2S was prepared from analytical grade CaCO3 and SiO2.
The compounds were mixed and homogenised as an ethanol suspension
for at least 12h (Turbula T2C). After drying, the mixture was sintered in a
platinum crucible using a bottom loading furnace (AGNI ELT 160–02).
The sintering consisted of 3 steps: heating at 5 °C/min, holding at
1450 °C for 20 h and slow cooling at 1 °C/min. The produced material
was milled and sieved below 125 μm. Mechanical activation (MA) was
performed by additional milling in a high energy bead mill (Dispermat
SL-12-C1, VMA). Approximately 100 g of powder was milled in 500 ml
of ethanol at 5000 rpm for 6 h using 1mm ZrO2 milling balls.
The particle size distribution was measured using the laser scattering
method (MasterSizer Micro Plus, Malvern) and the surface area was
determined by the nitrogen sorptionmethod BET (Micromeritics TriStar
3000 V6.04 A) after drying at 150 °C for 12 h. The mineralogy was
determined by X-ray diffraction analysis (Philips, PW 1830) using
CuKα radiation of 45 kV and 30 mA. The X-ray patterns were collected
with a step size of 0.02° and step time 2 s. Quantitative XRD results
were obtained adopting the Rietveld method [33,34]. ZnO was used as
an internal standard to determine the amorphous content.
Isothermal calorimetry, carried out at 20 °C, was used to study the
early hydration (TAM Air device, TA Instruments). For this purpose,
the γ-C2S powder was mixed with water keeping the liquid to binder
(l/b) mass ratio equal to 1. In the case of alkali activation, an alkali