A proposed mechanism for the growth of C-S-H during the hydration of tricalcium silicate

This paper presents a novel theory that can explain some previously mysterious aspects of the structure of C-S-H gels in cement pastes. The structure is seen as a consequence of the growth mechanism, taking as a model the growth of C-S-H during the hydration of tricalcium silicate. It is postulated that C-S-H grows as wavy or buckled sheets or ribbons. Growth occurs mainly at the edges of the sheets, or ends of the ribbons, except when new sheets nucleate on top of an existing sheet, which can only occur in certain well-ordered flat regions. This can lead to exponentially increasing growth rates at early ages, before steric hindrance of the sheets is significant. The model can also explain other unusual aspects of the structure of the final hydrated product, in particular the possible occurrence of nanocrystalline regions of different composition (tobermorite-like, jennite-like and even portlandite-like), allowing for a wide range of calcium/silica ratios in the product, as a function of the solution composition during the growth process. (C) 1997 Elsevier Science Ltd.