Flexural behaviour of ferrocement.

Ferrocement is often believed to be a form of reinforced concrete.
However, in spite of the similarities between the two materials there are
still major differences, indicating that ferrocement requires a separate
study to establish its structural performances. On the other hand, although
a large amount of research has been carried out on ferrocement, its flexural
behaviour is still not fully understood.
The aim of this investigation is to study the structural behaviour of
ferrocement plates under flexural loading and the influence of the different
variables on the strength and deformation characteristics. The variables
studied were the mesh number, strength, opening and distribution, presence of
steel bars, and the thickness of the section and the mortar cover.
The experimental programme included 49 plates, 1000x300 mm in dimensions,
reinforced with woven type steel wire mesh and tested under two lines load.
Deformation measurements were taken from first application of the load up till
failure and about10000 crack measurements (crack width and spacing) were
recorded.
The crack width data were dealt with statistically. The effect of the
variables on the crack width was studied, quantitatively, by comparing the
rate of growth of crack width of the plates. It was found that ferrocement
cracking behaviour is characterized by almost a full development of the cracks
at relatively early stages of the load (about 30-50% of the ultimate load)
and the crack width is smaller and more uniformly distributed than in reinforced
concrete. The mesh number and yield strength influenced significantly the
crack width and spacing. There was a limit for the mesh number after which
the enhancement in the cracking performance of the plates slowed down
noticeably. Crack width prediction equations were derived from these tests showed good correlation, whereas the published crack width formulae largely
overestimated or underestimated the measured crack width.
The strength and deformation were influenced mainly by the yield strength
and fraction volume of reinforcement in the loading direction. The deflection
is most likely to exceed the serviceability criteria before the crack width.
For a span-deflection ratio of 180, the mean crack width was mostly below 20
microns, and the load was about 15-30% of the ultimate load.
A procedure is proposed to analyse ferrocement sections under flexural
loading. While application of reinforced concrete theory to predict the
ultimate moment largely underestimated the experimental results, the proposed
procedure predicted closely the experimental moment and deflection at first
cracking, yielding and failure of the tested plates.