“Mechanical properties of Roman adobe walls”
Dott. Ing. Enrico Quagliarini*(a), Prof. Ing. Stefano Lenci (a), Ing. Quintilio Piattoni (a),
Prof. Sandro De Maria (b), Dott. Mirco Zaccaria (b)
*
Corresponding author: e.quagliarini@univpm.it
(a)
Department of Architecture, Buildings and Structures, Polytechnic University of Marche,
via Brecce Bianche, 60131, Ancona, Italy.
(b)
Department of Classical Archaeology, P.zza S. Giovanni in Monte 2, 40126, Bologna, Italy.
The recent discovery of adobe walls belonging to a Republican domus sited in Suasa (Ancona,
Italy) was the starting point of the present work. Adobe is a construction technique that uses raw
earth mixed and moulded to form sun-dried blocks to realize a bearing wall. Romans were also used
to add sand or coarse sand into the mixture to “degrease” clay and to allow to make it into a
mixture. Fibers such as straw were often added into the mixture to reduce hygrometric shrinkage.
Anyway, ancient home brick-makers have not had a chance to do scientific experimental
investigation on the balance of ingredients and the optimisation of this production. Thus, through an
experimental and analytical approach, starting from the Suasa’s on-situ soil (at about 2 m of depth
from the ground floor, as to reach as far as possible the ancient Roman ground floor at that time), as
Romans were used to do, this paper elaborates on how workability and mechanical properties of
Roman ancient adobe earthen walls change varying the percentage of straw and coarse sand into the
mixture to produce them.
Adobe bricks and quarters of adobe bricks of 10 different mixtures have been tested by compression
after 2 and 4 months of seasoning. The experimental results of compressive tests have permitted to
determine the mechanical performances of the earthen specimens and the influence of the size
factor. Predictive models of the elastic properties, which have been developed for modern
composite material, have been applied to the experimental results. The good agreement of the
theoretical values with the experimental ones has made it possible to extend the experimental data
for specimens of different composition.
This has allowed to use only a single mixture to manufacture four adobe walls to be tested by
compression and shear, after a seasoning period of 4 months. From these compression tests,
compression strength, first cracking compression stress, Young modulus and breaking manner have
been evaluated. As well, compression results show a possible two-storey structure for the Roman
earthen Republican domus at Suasa. This is an important result in order to support the
archaeological hypothesis about its reconstruction, and to increase knowledge on ancient adobe
bearing elements in general. From the shear tests, a proportional law seems to regulate the relation
between the maximum value of the mean tangential tensions and the vertical compression the
sample is subjected to. This could be the starting point for a future seismic analysis.