Production of Hydraulic Limes

Natural hydraulic limes, as defined in [16.60] (see section 26.9), are produced from siliceous or argillaceous limestones containing more or less silica, alumina and iron [16.61]. Typical levels in the limestone are [16.6]  

The calcium plus magnesium carbonate content can range from 78 to 92 %. 

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). 

The calcined lime is hydrated with sufficient water to convert the free CaO into Ca(OH)z- If the free CaO content is greater than 10 to 15 %, the hard sintered lumps disintegrate into a powder. Otherwise, the lime must be ground before hydration. It may also be necessary to grind the hydrated product to achieve the required degree of fineness and setting rate. 

These are also defined in [16.60] and are produced by intimately blending powdered hydrated limes with pulverised pozzolanic or hydraulic materials. 

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