pozzolanske

Pozzolanske (pozzolanic) materials are siliceous or aluminosiliceous substances that, when finely divided and in the presence of water and calcium hydroxide, react to form cementitious compounds. They do not harden on their own like Portland cement, but participate in the hydration process to enhance binding. The term derives from Pozzuoli, near Naples, where ancient Romans used volcanic ash (pozzolana) in construction.

The pozzolanic reaction occurs when reactive silica or alumina in the material reacts with calcium hydroxide released during cement hydration, forming additional calcium silicate hydrates (C-S-H) and calcium aluminate hydrates. This consumes calcium hydroxide, refines the pore structure, and can increase long-term strength and durability while reducing permeability.

Types include natural pozzolans such as volcanic ash (pozzolana), pumice, diatomaceous earth, opoka, and metakaolin (calcined clay). Artificial pozzolans include fly ash from coal combustion, silica fume (micro silica), and certain processed clays. The effectiveness depends on fineness, amorphous silica/alumina content, and the availability of calcium hydroxide.

Applications and benefits: Pozzolanic materials are widely used as supplementary cementitious materials (SCMs) in concrete and mortars, typically blended with Portland cement. They can improve workability, reduce heat of hydration, enhance long-term strength, decrease permeability, and improve resistance to sulfate attack and alkali-silica reactions. The performance depends on source material, processing, and the concrete mix design.

Standards and testing: Various national and international standards specify requirements for pozzolanic materials and their use in cementitious systems, including tests for pozzolanic activity, fineness, and compatibility with cement and aggregates.