A pozzolan is any amorphous, high silica powder that reacts with the lime produced when you add water to Portland cement. The lime produced is the source of efflorescence, a chalky discoloration on concrete surfaces that streaks the natural color or obscures the vibrant color of the pigment used for decorative concrete. When glass pozzolan is added, the reaction converts the lime into calcium silicate hydrate (CSH), which is the strength-builder in concrete. When driven to completion the concrete will be stronger. This also allows for a brighter concrete.