Civil Engineering Reference
In-Depth Information
Special concretes
Sulphur concrete
Sulphur concrete is most common in
prefabricated blocks and elements
which are cast by mixing smelted sul-
phur (120-150°C) with sand and pour-
ing 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 as there
are not many fibres in the mix. Sulphur
concrete is visually attractive and virtu-
ally maintenance-free, without the
'ageing lines' which 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 dis-
appeared 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 is that it does not tolerate frequent
changes of temperature, between freezing and thawing - small cracks appear in the
block and it will start to decay. This can be remedied by adding materials such as tal-
cum, clay, graphite and pyrites, in proportions up to 20 per cent by volume. Another
problem to consider is fire risk, but it has proved difficult to set fire to a sand-mixed
sulphur concrete, and if an accident should occur, the fire can be extinguished with
water.
Figure 13.1: Building with sulphur blocks in both walls and
vaults constructed in Rennes, France, in 1983, by the Institut
National des Sciences. Source: Ortega 1989
Lime sandstone
Lime sandstone is produced from a mixture of slaked and unslaked lime (5-8 per cent),
mixed with 92-95 per cent quartz sand. The quartz sand is excavated 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
which harden for 10 hours in a kiln at 200-300°C. Lime sandstone is used structurally as
brick, but is also used as stone lining. It cannot be recycled as new aggregate, but can be
used as a stable mass.
The durability of concrete products
There are many examples of pure lime mortar keeping its functional properties
for 2000 to 3000 years, but there are examples of Portland cement mortars that
have crumbled within 10 years (Grunau, 1980). Some concrete buildings with
Portland cement have stood undamaged for over 100 years.
