Feebly hydraulic limes

Silica and alumina, in the form of clay, silt and sand are commonly found as heterogeneous impurities in features such as faults and bedding planes, and also occur as homogenous impurities. When limestones containing 5 to 10 % of clayey matter are calcined, they produce feebly hydraulic limes those containing 15 to 30 % produce highly hydraulic limes [3.12] (see also section 26.9.2). 

Feebly-hydraulic limes (also called semi hydraulic) are limes which possess slight hydraulic properties. 

The limestone is generally calcined in shaft kilns [16.59], which must be controlled closely to ensure that as much of the silica and alumina as possible reacts, without sintering the free lime, lypical calcining temperatures are 950 to 1250 °C the required temperature rises as the cementation index (see section 26.9.2) increases (i.e. from feebly to eminently hydraulic limes). 

Natural hydraulic limes have traditionally been classified in three categories feebly hydraulic, moderately hydraulic, and eminently hydraulic. 

Another classification uses the terms semi-hydraulic and hydraulic , corresponding approximately to feebly and eminently hydraulic respectively. Eminently hydraulic lime is also called Roman lime. 

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