Civil Engineering Reference
In-Depth Information
Blocks or bricks are usually laid with mortar between them. The Southwest
Research Institute in Texas has developed a fibre-reinforced sulphur mortar
which can be sprayed onto both sides of a wall built completely dry.
Mortars have different elasticity coefficients and strengths. This is critical
for the different tasks they perform, but also important for any later disman-
tling of components. Pure cement mortar is, for example, twice as strong as
pure lime mortar; hydraulic lime mortar is somewhere between these. The use
of lime mortars, hydraulic lime mortars and lime cement mortars rich in lime
makes it possible to dismantle walls of bricks, concrete blocks and lightweight
concrete blocks, etc for re-use. Lime cement mortars must contain a minimum
of 35 per cent cement, partly because a smaller percentage does not strength-
en the mortar and partly because the cement slows down the curing of the
lime.
Mortar products are based mainly on materials with rich reserves. Their
consumption of primary energy lies somewhere between that of timber and
steel. Pollution during the production of binders is mainly in the form of dust
and the emission of a considerable amount of nitrogen oxides, sulphur diox-
ide and carbon dioxide. Binders containing pozzolana create the least pollu-
tion.
Mortars were once entirely mixed on site with local aggregates; it is more nor-
mal today to use ready-mixed mortars. Centralized production means an
increased use of transport energy, since even the aggregate has to be transported
greater distances. However, the aggregates used are light and give better thermal
insulation in the finished structures. Mortars cause no problem once in place, as
long as no volatile organic compounds have been added.
Sulphur mortars can be recycled. This is true for pure lime mortars, in theory,
because they can be reburned, but it is difficult to achieve in practice. Cement
mortars can be ground into aggregate for low quality concrete structures.
As waste, mortars are normally inert and can be used as fill. Ground lime mor-
tars can be used for soil improvement. Sulphur pollution can develop from gyp-
sum waste because of microbial decomposition. Sulphur waste should be
deposited at special dumps, preferably neutralized by adding lime.
Adhesives and fillers
Archaeological exploration indicates that animal glue adhesives were in use as
far back as 3000-4000 BC. In China and Egypt casein glue was used in finer
joinery. Somehow this knowledge disappeared, but was rediscovered in
Europe around the sixteenth century. The first glue factory was built in the
Netherlands in 1690. Around 1875 the manufacture of plywood started, and at
the turn of the century laminated timber construction began. Synthetic resins
