In the United Kingdom expanded clay aggregate was used for the con- struction of sea-going ships and barges during the war and some of these are still in use. This type of material. and also concrete made with sintered pulverised fuel ash ag gregate has since found application in multi-storey buildings in the form of cast insitu reinforced concrete floor and roof slabs as well as for frame structures both for inside work and on exposed surfaces. Foamed slag concrete, being some- what heavier than the other types of lightweight concrete. has been used less frequently for structural work in fully compacted mixes but in more porous forms it has found widespread application for cast insitu and precast loadbearing walls either with or without reinforce- ment. For houses having two more storeys wall plates made with well compacted foamed slag concrete containing adequate reinforcement have been cast monolithically with less well compacted cast insitu load- bearing walls.
or
Where expanded clay concrete is used with exposed outer surfaces the effect is pleasing, even after prolong- ed weathering, provided care taken to avoid excessive crazing on the exposed surfaces; crazing is
13
likely to occur if the aggregate con- tains a large proportion of dust. In general, however, the long term be- haviour of cast insitu lightweight concrete structures has been satis- factory both in Britain and abroad.
CORRECTION
We are informed by the Build- ing Research Station that in Table 1 of "Lightweight Aggregate Concretes" (Vol. 17. No. 5. page 116) the figures against Exfoliated Vermiculite in Column 5 "Thermal conductivity in Btu in ft 2 H°F" should read “0.65-1.5” and NOT *1.0-1.5."
roof
Precast concrete floor and slabs ranging in span from about 3 ft. to 12 ft. have been in general use, particularly in Europe, for the past 40 years, using mainly foamed slag and natural pumice aggregates. More recently prestressed precast floor slabs made with expanded clay aggregate and with pretensioned steel have been produced in the United Kingdom.
Precast wall panels using light- weight concrete, usually of sand- wiched construction, are normally of single storey height and varying widths and frequently incorporate window and door openings. Units
of the full width of a dwelling house have also been produced in
but such
some
large-panel
countries methods of construction are more commonly used in Europe than in the United Kingdom. To justify the large initial capital investment quired there must be a considerable demand for identical units.
re-
In a form of construction which has found widespread use mainly in the U.S.A. prestressed lightweight concrete beams are used with post- tensioned steel. Because of their lower self-weight such members can be made to span over much greater distances than gravel concrete beams. without intermediate supports, thus in Britain and abroad on the factory both in Britain and abroad.
The availability of lightweight ag. gregates and considerations of technical and financial advantage help to make structural lightweight concrete an important new method of construction in the United King. dom. Provided that its properties are taken into consideration the ma- terial can be used safely in most cases where gravel aggregate con- crete is normally used.
Prepared at the Building Research Station. Garston. Herts. August 1962 Crown Coypright.
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