Hydration of alite containing alumimium

The most important phase in cement is tricalcium silicate which leads during its hydration to the nucleation and growth of calcium silicate hydrate (referred to C-S-H (CaO)x-SiO2-(H2O)y). The development of this hydrate around the cement grains is responsible for the setting and hardening of cement pastes The general term for designating the tricalcium silicate in cements is alite. This name relates to all polymorphs containing various foreign ions inserted in their structure. These ions may influence the intrinsic reactivity and once released during the dissolution, they may interact also with C-S-H. The melt phase during clinkering is rich in aluminium and moreover the pore solution during hydration contains aluminate ions. For these reasons, the aluminium is one of the most important ion and one the most likely to influence the hydration of alite. In order to investigate these effects, an alite containing 0.1% of aluminium by weight has been synthesised. Following its hydration and comparing with pure tricalcium silicate hydration, it has been observed that aluminium presence increases the delay before reaction acceleration. The ions concentrations evolution at very early age show the formation of a C-S-H containing aluminium ions and it has been evidence that this hydrate does not act as nuclei to C-S-H growth.