| dc.description.abstract | Geopolymers are a sustainable alternative to Ordinary Portland Cement (OPC). These
binders with a lower CO2 footprint are produced by alkaline activation of a source of
amorphous aluminosilicates. The geopolymers can exhibit better performance
depending on the synthesis conditions than OPC. However, there are still barriers to
its large-scale adoption, as the need for a deeper understanding about its behavior in
the fresh state, including controlling setting times and alternatives to adjust the
workability. The organic admixtures widely used to improve the rheology and
workability of OPC-based systems show lower efficiency in geopolymers due to the
high alkalinity of the activator solution. In this scenario, the geopolymers behavior in
fresh state can only be controlled by its composition, expressed by the
synthesis/activation conditions. Here, fresh state behavior was evaluated to
understand the effects generated by different synthesis conditions in geopolymers
produced with metakaolin. The effect of the water/binder ratio (a/l: 0.70, 0.75 and 0.80),
alkali content (15% and 20% of M2O) and alkali type (sodium or potassium) were
assessed. The analysis was based on monitoring the time-dependent behavior of the
samples, using oscillatory tests to quantify the storage (G’) and loss (G”) moduli. In
addition, the results of oscillatory rheometry were correlated with reactions kinetics by
isothermal calorimetry. It was also determined the setting times of the samples. The
results showed that alkali type has the greatest impact on the geopolymer’s behavior
in fresh state, given that the systems activated with potassium had less pronounced
hardening, and more time to be handle when compared to those systems activated
with. The increase in alkali content (% M2O) was also effective to extend the workability
during a longer period. Increasing a/l ratio was not effective to modify the rheological
parameters evaluated, mainly in systems with higher alkali content. | |
