Pozzolans

Durability Guaranteed - Pulhamite Rockwork - Its conservation and repair, published by Historic England in 2008, defines pozzolans as: ‘Materials consisting of silica and alumina which react with calcium hydroxide in the presence of moisture to produce a hydraulic set, with properties like hydraulic lime. Pozzolans are derived from natural sources such as volcanic earth or from manufactured ones such as low-fired clay products.’

Low Carbon Concrete Routemap, Setting the agenda for a path to net zero, draft for consultation published by the Institution of Civil Engineers in 2021, defines pozzolan as: ‘A siliceous and aluminous material that, in the presence of moisture, chemically reacts with calcium hydroxide to form compounds possessing cementitious properties; such as calcined (kaolinate) clays, fly ash, volcanic ash and silica fume.’

Hot-mixed Lime Mortar, published by Historic Environment Scotland in April 2015 states: ‘Pozzolans are natural or man-made materials including brick dust and pulverised fuel ash (PFA), or proprietary additives, which are added in small, measured, quantities to lime mortars, just before use, to impart hydraulic properties.’

Short Guide, Lime Mortars in Traditional Buildings, published on 1 March 2013 by Historic Scotland, defines pozzolan as: ‘A natural or man-made material that can be added to a mortar to enhance the set (i.e. speed up the curing of the mortar and give the mortar strength). Pozzolans are typically silicates and/or aluminates that bind with the lime to produce binding calcium-silicate-hydrates and/or calcium-silicate-aluminates, effectively creating a hydraulic lime. The term ‘pozzolana’ refers to a natural material of volcanic origin from which the more general term pozzolan is derived.’

[edit] Related articles on Designing Buildings

• Cement.
• Clay.
• Concrete.
• Gauged mortar.
• Historic England.
• Hydraulic lime.
• Lime mortar.
• Sand.
• Silica.