Hydration of alite containing aluminium

Abstract

The most important phase in Portland cement is tricalcium silicate, which leads during its hydration to the nucleation and growth of calcium silicate hydrate [referred to as 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. One of the most likely species to be inserted in the alite structure is aluminium. In order to investigate if aluminium plays an important role in C3S reactivity, alite containing 0·1 wt-% aluminium has been synthesised. Alite hydration was followed and compared with pure tricalcium silicate one. The ion concentration evolution at a very early age shows the formation of a C–S–H containing aluminium ions, and it has been evidenced that this hydrate does not act as nuclei to C–S–H growth that induces a delay before acceleration of hydration commonly named ‘dormant period’.