Silica is an oxide of silicon with the chemical formula SiO2, which most commonly is found in nature as quartz and in various living organisms. Silica has various forms which can be important when considering its potential commercial application. Highly crystalline silica, such as in quartz is not reactive, but non-crystalline or amorphous silica, as produced from leaching mica minerals in acid, is extremely reactive.
Amorphous silica also acts as a pozzolanic material. Pozzolanic materials do not react with water other than in the presence of lime, which occurs in concrete as a result of cement hydration. Lime is liberated from cement during its hydration at ambient temperatures. Amorphous silica materials form a class of Supplementary Cementitious Materials (SCM’s), which can be used to replace Ordinary Portland Cement in the manufacture of concrete and in so doing increase its compressive strength and resistance to chemical attack while reducing its carbon footprint.
SCM’s include fly ashes, slag cement (ground, granulated blast-furnace slag), silica fume and amorphous silica. These can be used individually with Portland Cement or blended cement or in different combinations.
Concrete is the most widely used material other than water worldwide. There is about 3.5 billion cubic metres of concrete produced annually worldwide primarily for use in construction related applications.