Today’s concrete consists of various chemical and mineral admixtures to meet the rising demands for constructability, service life and performance. In addition to portland cement, supplementary cementitious materials such as fly ash, slag and silica fume have become commonplace in concrete, particularly in situations where the concrete is exposed to aggressive environments, requires high strengths and high durability. More recently, engineered pozzolans have been introduced that give early age reduction in permeability, and high ultimate strengths similar to silica fume, while contributing to long-term refinement of pore structure and reduction in porosity. These products have been termed “highly reactive pozzolans” and include ultrafine fly ash, metakaolin, rice husk ash, zirconium fume and others.