Civil Engineering Reference
In-Depth Information
ceum
roofs. Concrete wall construction has long been discussed, but the practical
details of placing concrete to build arcuated rooi ng are not examined in relevant
publications. Spoken of here is the construction of an exposed vault or dome as a
structural form, not a vaulted or domical ceiling overlaid by mass concrete. Such
passages of construction are ot en illustrated (cf) obviously here the placing of the
concrete follows the normal procedure.
As might be expected the earliest concrete vaulted structures are seen to detach
themselves from mortared rubble vaulting. h e rubble aggregate is set radially,
and the only factor which distinguishes them as concrete is probably the cementi-
tious pozzulana mortar (cf niches at Palestrina ca 110 BC, Adam, p. 17, i g 424;
in general R. Mainstone, p. 115, L.C. Lancaster, p. 59).
From these beginnings the line of development is to assimilate the placing of the
concrete in vaults to the normal process of alternate horizontal layers of aggregate
and mortar as far as possible in view of the totally dif erent spatial context of the
structure—not a simple process. Within this development a part was played by
inset brick work, which in some way, may be compared with the through courses
of brick in
opus testaceum
walls. It is well to say in advance that the following
remarks are elementary observations only, since virtually no consideration of
detail appears in publications. Also it may be noted that much comment does not
distinguish clearly between construction and structure, i.e. between the process of
building and the properties of what is built.
Whatever the manner of their fabrication the centering and shuttering were raised
up into position from inside the building. However when they were completed
they sealed of all access to higher levels of construction from within the building.
h us placing concrete above the shuttering required a new access for workmen
and materials to be arranged from outside the building. h ere are theoretical
qualii cations to this statement. Communication from within the building with
higher levels was perhaps possible through the oculus of a dome if such existed.
Also there is a further contingency—although it is a remote one. It has been sug-
gested on occasion that concrete domes were built up in stages. In this way the
entire centering was not completed i rst and then the dome concrete placed over
it. Rather the centering for, say, the lower third of the dome was set in place and
then the concrete placed in position over this and let to solidify. h is operation
was then repeated for, say, two more successive stages so that the dome was built
up piecemeal. h e motive for this proposition was economising in the supply of
wooden centering. h e centering for the limited construction could be dismantled
when the concrete had solidii ed and then reused for the further stages of construc-
tion. In fact such a procedure is an unhandy one and has nothing to recommend
it (cf L.C. Lancaster,
Concrete Vaulted Construction
, p. 48). It would, however,
permit access for the concreting work from within the building.
Placing
Concrete
