The influence of biogenic micro-silica-rich rocks on the properties of blended cements

Diatomaceous rock samples of a different origin and with amorphous, biogenic micro-silica (opal-A) as their major siliceous constituents were studied and their behaviour as a cement additive was determined. The raw materials were collected from Hungary, Romania and Greece. These diatomite rocks varied in geological age from Miocene to Pleistocene, and were deposited respectively in lacustrine, brackish and marine conditions. The depositional environment affected the size of the opal-A particles, those of lacustrine origin being the smaller (<10 μm). Most of the opal-A particles were represented by disk-shaped diatom frustules. Laboratory tests showed that these diatomite rocks exhibited good pozzolanic properties and could replace the most commonly used natural pozzolanas. The use of diatomaceous rocks as cement additives has drawbacks such as higher water demand, but the compressive strength of the laboratory produced cements exhibit higher values than OPC. The highest compressive strength values were obtained with the use of the Hungarian diatomite rock that had the greatest amount of reactive silica content reflecting its high opal-A content.