Sandlime bricks

Sandlime bricks, also called calcium silicate bricks, are produced by moulding, under high pressure, a moist mixture of silica sand (or crushed siliceous stone, or flint) and hydrated lime. The green bricks are then autoclaved using steam pressures of at least 11 atmospheres. Under these conditions, the hydrated time reacts with the silica to form hydrated calcium silicate, which bonds the aggregate particles into a strong and durable brick [26.47]. Other shapes, such as blocks and building elements are also produced. 

Because hydrated calcium silicate is white, the autoclaved products are an attractive near-white colour. This enables pigments to be used to produce a wide range of coloured products. 

Although the calcium silicate brick process was patented in the UK in 1866, its commercial exploitation only occurred in Germany towards the end of the 19th Century. In that country, the sandlime brick industry now accounts for some 40 % of the brick production. The process is also used in many other countries, but its penetration has varied considerably, depending on traditional construction methods and on the relative costs of competitive products [26.48]. 

The lime may be purchased by the brick manufacturer either as hydrated lime, or as quicklime. Ail of the processes can use damp sand — there is no need to pre-dry it. 

Sandlime brick plants using hydrated lime (see Fig. 26.4) are relatively simple to operate and low in capital cost. The operating costs, however, tend to be higher than for quicklime, owing to the higher delivered cost of hydrated lime per unit weight of available lime. 

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There are many applications where magnesium is regarded as an undesirable impurity. These include the production of hydrated lime (at atmospheric pressure), aerated concrete, sandlime bricks, and precipitated calcium carbonate, for which MgCOa levels should preferably be less than 2 % and, ideally, less than 1 % in the limestone. 

Mainly aircrete, sandlime bricks, other calcium silicate products and refractories. Mainly mortar, render, plaster, and drying/improvement/stabilisation of soils. Mainly potable water, sewage, liquid effluent and gaseous effluent treatment. 

A more direct way of identifying expansive components is to make a small sandlime brick, using the coarse fraction extracted from the milk of lime produced in the reactivity test. Any expansion on autoclaving the brick at 10 Bar for 8 hours is indicative of expansive components in the quicklime. 

BS 187 Specification for calcium silicate (sandlime and flintlime) bricks , 1978. 

Sandlime (calcium silicate) bricks . Technical Service Note, No. TS/E/19, ICI Mond Division, 1980. 

Sandlime (or calcium silicate) bricks are produced by autoclaving a mixture of sand and lime. 

BS 187 Specification for calcium silicate (sandlime and flintlime) bricks , 1978. BS 594, Part 1 Hot rolled asphalt for roads and other paved areas — Specification for constituent materials and asphalt mixtures , 1992. 

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