Physical surface adsorption is not considered as being part of the pozzolanic activity, because no irreversible molecular bonds are formed in the process.
The product CaH2SiO4·2 H2O is a calcium silicate hydrate, also abbreviated as C-S-H in cement chemist notation, the hyphenation denotes the variable stoichiometry.
Sufficient amount of free calcium ion and a high pH of 12 and above is needed to initiate and maintain the pozzolanic reaction.
Prolonged grinding[clarification needed] results in an increased pozzolanic activity by creating a larger specific surface area available for reaction.
Even materials which are commonly not regarded to behave as a pozzolan, such as quartz, can become reactive once ground below a certain critical particle diameter.
In this respect, the thermodynamic driving force behind the pozzolanic reaction serves as a rough indicator of the potential reactivity of a (alumino-)silicate material.
A material is considered pozzolanically active when it contributes to the compressive strength, taking into account the effect of dilution.
At lower water to binder ratios (pastes), thermal analysis or X-ray powder diffraction techniques are commonly used to determine remaining calcium hydroxide contents.
Other methods indirectly determine the extent of the pozzolanic activity by measuring an indicative physical property of the reacting system.