STRENGTHENING OF STONE MASONRY ARCH BRIDGES THREE ...

History
a) b)
Fig. 1.2 – Common roman building stone. a) Shape; b) Lifting device
The Romans were not interested in record-breaking spans, only in utility and durability.
That some of their bridges remain after about 2000 years of continuous scouring, in
rivers which are subject to frequent heavy flooding, says it all. Military action has
removed many that would otherwise have survived.
The existent data seem to indicate that the Romans didn't divert the course of the rivers
to build the foundations of the pillars. The technique of placing concrete under water by
the tremie process was known; a cofferdam was built composed by two rings of wood
stakes filled out amongst themselves with compacted clay, and the material was dredged
out until a satisfactory bottom had been reached, when concrete was placed, the
pozolana addition (ash obtained starting from a volcanic rock) it turned this concrete
extremely hard and resistant to the water.
Fig. 1.3 – Cofferdam for foundation
Piles were used where ground conditions made spread footings inadequate. The piers
were usually pointed upstream but flat backed downstream; hydraulically this is not a
good shape and must have led to scour problems. Masonry inverts were built
Leonardo da Vinci Program 8