Compressive strength of GMWMpaste is significantly lower
than compressive strength of GMWM mortars independent of
aggregate type. In conventional concrete, the aggregates form a
rigid skeleton of granular elements which are responsible for
compressive strength. In the case of mortars with low content of
aggregates i.e. aggregate/binder mass ratio below 2.0 aggregates
do not form a rigid skeleton but a set of inclusions trapped
in a continuous paste matrix. One suggests that strength
behaviour can only be explained by the chemically active role
played by the aggregates, which may be due to the dissolution
of quartz in the presence of alkalis enhancing bond between
paste and aggregates as reported by Shi et al. [23] even despite
the low solubility of aluminosilicate minerals in alkaline
medium. Furthermore the similar strength results obtained
when using aggregates with different size and water absorption
(schist and granite) prevents the explanation relying on the
localized water near them, as it happens in OPC systems.
For an aggregate/binder ratio of 0.5GMWMmortar mixtures
with limestone aggregates achieve a maximum strength at early
ages and that strength level keeps stable with curing age
(Fig. 2). For the same aggregate/binder ratio silicon based
aggregates (granite and schist) showed increased strength with
curing time. That behaviour is somehow different from OPC
systems where similar mechanical behaviour is presented by
different aggregates [20]. In fact there's evidence confirming
that aggregates have some influence in OPC binder systems as
stated by other authors [21,22] but not at the same level
presented in this work.
3.3. Tensile strength
Tensile strength of GMWM binders is shown in Fig. 3. Test
results indicate that GMWM mortars possess very high tensile
strength when compared to OPC systems (ft/fc ratio is around
10%). The bonding of GMWMbinders to the aggregates is very
high being confirmed by the fact that GMWM specimens
submitted to flexural test, always show aggregates that have
been cut and not pull-out as it happens in OPC binders. Tensile
strength of GMWM paste is significantly lower than tensile
strength of GMWM mortars being independent of aggregate
type as seen previously for compressive strength, but different
aggregates influence in a different manner tensile strength. For