Civil Engineering Reference
In-Depth Information
the capacity of a bolt to transfer loads. These connectors have spikes which are
pressed into the timber so that the forces are transferred to the surface of friction
between the two parts. The bolt's task is thereby reduced to simply holding the
two structural parts together.
Generally speaking, metals have limited reserves. In certain cases scrap metal
is used. The use of primary energy and pollution during production is high.
There is an over-investment of quality in the use of galvanized steel products
in dry, indoor environments. Untreated steel products have a far better envi-
ronmental profile. Metal products do not cause environmental problems in
buildings. In a fire, however, they will quickly become red hot and burn
through adjacent timber.
The durability of metal products is generally good. If a metal component is
exposed to great variations in temperature, condensation can form on it. This has
a deteriorating effect on the adjacent timber through electrolytic activity. If tim-
ber is damp when a metal component is added, the same effect could occur.
Timber impregnated with salt can also corrode metal.
Nails and nailplates have no re-use value, and will probably not be saved for
material recycling. Exceptions can occur when demolition material is burnt and
metals are cleaned from the ashes. Screw and bolts can be retained and re-used
or recycled. Use of screw and bolt connections also means that materials they join
together can be easily dismantled and re-used.
Metal that cannot be recycled should be deposited at special tips.
Chemical binders
Mortars, adhesives and fillers are important binders in the building industry.
Mortar and adhesives are used to bind together different or similar components;
fillers are a sub-group used to fill cracks and stick to the surfaces that surround
them.
Mortars
A mortar is usually a mixture of lime or cement with sand and water, sometimes
with additives, used as a binder for different types of mineral building-stones,
slabs, tiles, bricks, blocks and in certain circumstances roof tiles. (See also
'Hydraulic binders' and 'Non-hydraulic binders', pp. 94-97.) Fine or coarse
sand is used, according to the smoothness of finish required. In lime mortar, fine
sand is usually chosen, preferably beach sand. Small amounts of fibre can be
added to increase its strength. Mineral fibres or organic alternatives such as
