Abstract
Cement pastes containing reactive forms of silica, particularly silica glass particles, have been examined using scanning electron microscopy and transmission electron microscopy. Rims of reaction product are observed at the surfaces of particles and also within cracks in the particles. Using transmission electron microscopy, it is shown that the product is a calcium silicate hydrate gel of compact structure and of Ca/Si ratio slightly greater than 1·0. Very low Ca/Si ratio gel is not widely observed even in specimens which have expanded by amounts approaching 1%. It is suggested that significant expansion and mechanical weakening may arise from the formation of a rim of calcium silicate hydrate gel. Addition of pulverised fuel ash to the mortar reduces the expansion of the mortar and the thickness of the calcium silicate hydrate gel reaction rims.
MST/995
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