Special Concretes

Sulphur concrete is a possible alternative in prefabricated blocks and elements. It is cast by mixing melted sulphur (120-150 °C) with sand and pouring it quickly into a mould for cooling. This is a very simple process and the use of energy is low. Sulphur blocks are even waterproof as long asthereare not many fibres inthe mix. Sulphur concrete is visually attractive and virtually maintenance-free, without the'ageing lines'that occur with Portland concrete. The development of a sufficiently sound sulphur concrete has not yet been achieved. For some reason the interest in this material disappeared after a very prolific period of use near the end of the nineteenth century, and the idea was first taken up again about 20 years ago by the Minimum Housing Group at McGill University in Canada, which has built a number of houses in sulphur concrete. Since then, experiments have been carried out in Germany and several other countries.

One of the weaknesses of sulphur concrete isthat it does not tolerate frequent freezing and thawing -small cracks appear inthe block and it will quickly start to decay.This can be remedied by adding materials such as talcum, clay, graphite and pyrites, in proportions up to 20% by volume. Another problem to consider is fire risk, but it has proved difficult to set fire to a sand-mixed sulphur concrete.

Lime sandstone is produced from a mixture of slaked and unslaked lime (5-8%), mixed with 92-95% quartz sand.The quartz sand isexcavated from beaches or sandstone with a high quartz content. The stone is crushed to a grain size between 0.1 and 0.8 mm and mixed with pulverized lime. Water is added and the mixture is cast into blocks that harden fori 0 hours in a kiln at 200 to 300 °C.Limesandstone is used structurally like brick, but isalso used asstone lining. It cannot be recycled as newaggregate, but can be used as a stable mass.

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