Pozzolan

Mixtures of calcined lime and finely ground, active aluminosilicate materials were pioneered and developed as inorganic binders in the Ancient world.

Architectural remains of the Minoan civilization on Crete have shown evidence of the combined use of slaked lime and additions of finely ground potsherds for waterproof renderings in baths, cisterns and aqueducts.

[citation needed] Over the course of the 20th century the use of pozzolans as additions (the technical term is "supplementary cementitious material", usually abbreviated "SCM") to Portland cement concrete mixtures became common practice.

Deposits of sedimentary origin are less common, with diatomaceous earths, formed by the accumulation of siliceous diatom microskeletons, a prominent source.

Blending of pozzolans with Portland cement is of limited interference in the conventional production process and offers the opportunity to convert waste (for example, fly ash) into durable construction materials.

The properties of hardened blended cements are strongly related to the development of the binder microstructure, i.e., to the distribution, type, shape and dimensions of both reaction products and pores.

The increased chemical resistance to the ingress and harmful action of aggressive solutions constitutes one of the main advantages of pozzolan blended cements.

The improved durability of the pozzolan-blended binders lengthen the service life of structures and reduces the costly and inconvenient need to replace damaged construction.

One of the principal reasons for increased durability is the lowered calcium hydroxide content available to take part in deleterious expansive reactions induced by, for example, sulfate attack.