EFFECT OF TiO_2 AND ZnO NANOPOWDERS ON METAKAOLIN-SODIUM HYDROXIDE GEOPOLYMERS

摘要

Nanoparticles were used as potential nucleation seeds to gain insights into the reaction mechanism of alkali-activated metakaolin binders. Commercially available titanium dioxide and zinc oxide nano-powders were added in small dosages and their effect on the reaction mechanism was studied by monitoring heat evolution though isothermal calorimetry. A selective chemical dissolution (Hydrochloric acid attack) method was used to quantify the amount of unreacted metakaolin at different ages. Calorimetry results show that TiO_2 accelerates the reaction at early ages and the same was verified through selective dissolution data. ZnO were observed to retard the reaction and adding TiO_2 in this system was seen to reverse the retardation process. This indirectly gave proof of TiO_2 acting as a nucleation seed. Microstructural improvement was seen at 24h age through compressive strength testing, although no significant differences were observed at later ages. Effects of alumina and ZnO when compared with that from literature did not show expected trends, which indicated differences in reaction mechanism of geopolymers prepared from different precursors.