Современная архитектура и строительство. Рябцева Е.В - 8 стр.

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5. In designing a building the choice of construction materials is of vital importance, isn’t it?
Concrete technology has undergone a constant process of development over the past 50 years. Today, it
provides planning engineers and architects with a broad range of possibilities in terms of both structural and
formal design. In office construction, for example, high-strength concrete offers scope for saving space by re-
ducing the dimensions of the load-bearing structure and thereby increasing the rentable floor area. This type of
concrete also allows the construction of building elements that have a great resistance to weathering, that are
durable and that, in certain circumstances, can protect the environment against harmful liquids.
High-strength concrete has a long tradition. With extremely low water/cement ratios (below 0.4) and with
the addition of pozzolanic, highly-reactive aggregates such as powdered silica or metakaolin, a compression
strength of up to 150 N/mm
2
can be achieved (compared with a strength of 20-50 N/mm
2
for normal concrete).
Assuming the same amount of reinforcement and the use of concrete C70/85, the cross-section could be re-
duced by 30 per cent. In many situations, a reduction in the amount of reinforcement may be required instead,
in order to facilitate the execution of the work. In most cases, however, a solution will be sought between these
two extremes.
Only by using this type of concrete was it possible to keep the thickness of the walls on the lower floors
within reasonable limits. With concrete of standard strength, a wall thickness of about 2 m with a very large
amount of reinforcement would have been necessary. It was possible to reduce the thickness to roughly 1.40 m
and to use only a moderate amount of reinforcement. Nevertheless, for walls of this thickness, it is necessary to
reduce the cement content to well below normal levels and to add pulverized fly ash to the mix. Preliminary
trials allowed the appropriate combination of cement and fly ash to be determined in order to avoid deleterious
cracking through the discharge of setting heat. In Germany, solutions of this kind require a special certification
of the relevant state planning authorities. Even with the use of an optimum mix of concrete, however, newly
constructed concrete elements still need appropriate curing subsequently to prevent heat escaping too quickly.
In view of the very low water/cement ratio and the addition of pozzolanic additives, high-strength concrete
is not only strong, but also dense. Both properties can be exploited in areas like bridge building, where highly
durable concrete is required to ensure long life as well as slender cross-sectional dimensions. Where harmful
liquids are used in buildings such as clinics, hospitals or chemical laboratories, additional measures will be nec-
essary to protect the ground and groundwater from contamination. Dense concrete mixes have proved particu-
larly suitable in such cases.
The advantages of high-density concrete slabs include their greatly reduced permeability in comparison
with normal concrete, and their higher tensile strength. In slabs of smaller area (up to a maximum dimension of
15 m), their greater strength means that they are not subject to cracking. Cracks in construction elements are
especially critical in buildings where water-polluting organic liquids are used. With the use of high-density
concrete, it is often possible to do without an additional protective coating.
As far as cementicious building materials are concerned, new developments have taken place in recent
years that will considerably extend the use of concrete in this area. This applies in particular to high-strength
concretes with compressive strengths of up to 800 N/mm
2
(in comparison with standard applications of about
300 N/mm
2
). Considerable reductions in the cross-sections of reinforced and prestressed concrete members can
be achieved with this type of concrete. Slender elements also mean a lower overall weight, as well as a more
sustainable form of construction through the conservation of resources.
New methods of construction are also emerging through the use of so-called "reactive-powder concrete", as can
be seen in the bridge constructed by Bouyges in Quebec, Canada, in 1997. In the meantime, this technology has
been applied to other structures, such as the footbridge in Seoul, South Korea.
Vocabulary List
– to undergo – испытывать
– in terms of – с точки зрения
– scope – возможности
– to protect – защищать, предохранять
– silica – кварц, кремнезем
– reinforcement – арматура, укрепление
– to facilitate – облегчать, способствовать
– deleterious – вредный, ядовитый
– a discharge – выделение, выпускание
– subsequently – впоследствии, потом
– a ratio – коэффициент

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