Civil Engineering Reference
In-Depth Information
it imported into ancient building construction in general—changes which outlasted
the use of the material as such.
Although Roman Concrete construction has always been regarded as a highly
individual development, in fact the formation of the material (and indeed some
concrete constructions) are not radically distinct from building in other materials.
Opus incertum
walling is structurally (and aspectually) little dif erent from many
earlier random rubble walls (a core of irregular smaller stones drowned in thick beds
of mortar and faced with more regular i eld stones). Equally there is little dif erence
in construction between some
opus testaceum
walling (notably where the core is
made up largely of broken brick fragments) and some later brick masonry walls of
l at bricks set in thick beds of mortar. Also there were other highly cementitious
mortars besides that from Pozzolana, e.g. gypsum and bitumen mortars evoked
comment in Antiquity for their strength.
Notwithstanding that it is rarely spelt out, by far the most signii cant ef ect
exercised by Roman Concrete construction on the history of building was the
capacity to roof over very large areas of unencumbered l oor space (cf R. Main-
stone, p. 116).
Before the development of monumental buildings in Roman Concrete during
the 1st cent AD, the maximum “carry” of monumental rooi ng across unencum-
bered l oor space was something up to 7 m, as born on prodigiously massive stone
beams, dii cult to fabricate and to set in place. If, on the other hand, a background
was sought in dressed stone arcuated rooi ng of Hellenistic times, the carry was
not extended—indeed it fell short of this i gure. h e only advantage lay in the
convenience in fabricating and setting the relatively small units (voussoirs). h us
whereas previously ashlar vaulting of any nature erected with the aid of heavy
wooden centering was limited to spans of a few metres only, within a generation
or two Roman builders were able to roof l oor spaces of something up to ten times
that span (e.g. 40 m) with Roman concrete supported on similar wooden centering
(cf R. Mainstone, p. 116—“a revolution”).
Moreover if precedent is sought for Roman Concrete rooi ng not in Classical
Ashlar building, but in older traditional building modes which did not make use
of centering (e.g. the mud brick construction of the ancient Middle East, or the
dry stone corbelling of the Western Mediterranean) then the situation remains
unchanged. Such rooi ng was all restricted to spans of a few metres only.
h e at ermath of Roman Concrete rooi ng tells an equally emphatic story. h e
revolutionary development in scale ef ected in Roman Concrete rooi ng was main-
tained at er the discontinuance of Roman Concrete construction (post 330 AD)
and its replacement by brick construction employing essentially similar procedures
(e.g. the rooi ng of Ayia Sophia 537 AD). Moreover the spanning capacity attained
in Roman Concrete rooi ng although maintained in later ages (e.g. the Renaissance
dome of St Peter's) was never exceeded until the revolution in building materials
Prime
impor-
tance,
large
span
rooi ng
381
404-413
255-259
269
354, 355,
369-373
