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 my sterious 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 silicat e. It is postulated that C-S-H grows as wavy or buckled sheets or ribb ons. Growth occurs mainly at the edges of the sheets, or ends of the r ibbons, except when new sheets nucleate on top of an existing sheet, w hich can only occur in certain well-ordered flat regions. This can lea d to exponentially increasing growth rates at early ages, before steri c hindrance of the sheets is significant. The model can also explain o ther unusual aspects of the structure of the final hydrated product, i n particular the possible occurrence of nanocrystalline regions of dif ferent composition (tobermorite-like, jennite-like and even portlandit e-like), allowing for a wide range of calcium/silica ratios in the pro duct, as a function of the solution composition during the growth proc ess. (C) 1997 Elsevier Science Ltd.