 |
 |
Materials Science Division |
HighlightsSEM Imaging of GeoconcreteSEM Imaging of Geoconcrete Scientific Achievement In
this proposal we study the effect of the exposure of building
materials such as mortars and concretes to aggressive environments. Both the microstructural
features and the
macrostructural properties of a geopolymers as sole binder are compared. In the first experiment
carried out at EMC we
assessed geopolymeric cement samples before the exposure to the
aggressive
environment, at different ages of curing, in order to identify their
microstructural features, and the preliminary distribution of reacted
and
unreacted particles. It
was possible to
identify a growing densification of the material with the time of
curing, which
is coherent with the increase of the compressive strength (determined
in bulk
concrete samples). This
could be
associated to the formation of silicate-calcium-hydrate (C-S-H) phases
whose
Si/Ca ratios, determined by energy
dispersive X-ray
(EDS),
differ from the ones reported in the literature about conventional
cements and
other geopolymers. We
expected those
results as a consequence of the differences of the raw materials used
to
produce our samples. Currently,
we are
analyzing the role of the chemical differences of this phase in the
degradation
process of geopolymers through the correlation of SEM results with
those
obtained by XRD and FTIR. Preliminary
experiments were conducted on one of the samples exposed to an
aggressive CO2 environment.
Using these results we identified how the reaction between
the
geopolymers and CO2 generates a substantial
change in the matrix
structure (whitish and spongy particles
with a shape
type layers and pores can be found). The chemical composition of the
observed
particles changed as well. The
main
characteristic was a significant reduction of calcium, silicon and
aluminum in
the initial C-S-H phase. To
explain this
phenomenon we need to conduct further experiments. At
the moment, we conclude that a strong relationship between the
geopolymers microstructure and the concrete properties exists. The exposure of
geopolymers to atmospheric
environments can induces substantial changes in the microstructure of
the
material, which leads to significant decreases of the mechanical
properties of
the concretes based on these novel cements.
Significance Geopolymers
are a promising alternative to Portland cement for the
production of concrete. The
development
of these materials has reached a level such that commercial
implementation of
the technology is imminent. However,
much about the chemistry of these cements is still unknown or poorly
understood. More
critically, the
long-term performance of geopolymers is still poorly explored. Thus, any effort to
understand the
degradation of this material is very important to validate their
potential
application on an industrial scale.
To
date the partial results of our research have been presented in Proceedings
of the 23rd Int'l. Conf. on Solid Waste Tech.
& Management,
945-956 (2008). Performers 
|
|
||||
|
||||
