Hydration behaviour, structure and morphology of hydration phases in advanced cement-based systems containing micro and nanoscale pozzolanic additives

This paper deals with the early hydration and structure development aspects of advanced cement-based systems that contain micro and nanoscale pozzolanic additives. We have used highly reactive colloidal silica produced by pyrogenic route (pyrogene oxides) as representative of nanoscale pozzolanic additives. Colloidal silica shortens the induction period to an extent that can be qualitatively correlated to the size of its primary silica particles and the specific surface area. Colloidal silica accelerates the early hydration reactions by providing large amounts of reactive siliceous surface, which serves as a site for the early C–S–H precipitation. Additionally the use of pozzolanic additives as cement replacement smoothes and reduces the heat of hydration evolved. The high performance specimens that contain microscale additives and especially those that contain both micro and nanoscale additives are characterised by very tight structure and are made up of finer structures in closer contact than the normal performance specimen without pozzolanic additive.