In C-S-H there is no strict ratio of silicate to calcium
(usually around 0.4-0.5). It is dependent on the ratio of alite to belite in
the original cement mix, and also what proportion of the Portland cement, if
any, has been replaced by a cement replacing material.
During hydration, C-S-H expands into any capillary pores
present in the cement and forms much smaller gel pores within its structure;
these don’t have a structural capacity but reduces porosity.
C-S-H is directly
vulnerable to thaumasite sulphate attack in situations where sulphates,
carbonates and water are present in cool temperatures.