ThE EFFECT OF METAKOLIN, MICROSILICA AND NANOSILICA ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF CEMENT MORTAR

Different mineral admixtures of Indian metakaolin, Iranian silica fume and nanosilica were used to produce high performance mortars. Two different sands types with grain size of ۰.۰۱۵-۴mm were mixed with type II Portland cement, polycarboxylate superplasticizer,mineral admixture with ۶۵۰kg/m۳ cement content and water/cement ratio of ۰.۳۵. Different amount of cement was replaced by metakaolin or silica fume (۵-۱۵wt%) or nanosilica (۰.۸-۵wt%). After mixing, moulding and curing, compressive strength, electrical resistivity and abrasion resistance were studied. The maximum compressive strength of ۲۸ days samples were ۷۶MPa, ۷۹MPa and ۷۵MPa for ۱۵wt% substitution of cement with metakaolin, silica fume and ۵wt% with nanosilica. The compressive strength of these samples showed ۲۸%, ۳۳% and ۲۶% increment in comparison with reference sample, respectively. X-ray patterns showed that replacing silica fume leads to reduction of Portlandite (Ca(OH)۲) phase. This can be attributed to the pozzolanic reaction and formation of new hydrated calcium silicate phase (CSH) that caused improvement of strength of admixtures containing samples. The microstructure of silica fume containing sample also showed better bond between sand and matrix. The electrical resistivity of samples with ۱۵wt% metakaolin or silica fume and ۵wt% nanosilica reach to ۲۱kΩ.cm, ۱۵ kΩ.cm and ۱۰kΩ.cm, respectively. These samples showed high durability and corrosion resistance relative to reference samples (۳.۴ kΩ.cm). The abrasion resistance of different admixtures, specially silica fume containing samples were improved.

Keywords:

Metakaolin , microsilica , nanosilica , cement mortar