Mechanical and Durability Performance of Nano Metakaolin Blended Cement Mortars

Although works have been carried out to explore the influence of adding Kaolin (K), silica fume (SF) or fly ash (FA) in micro size and nano metakaolin (NMK) mixture on the main characteristics of blended cement mortar as partial replacement of cement by weight separately or combination of nano-micro mixture. The synergistic role of nano-micro mixture was rarely studied on the elevated heat temperatures and sulphate resistance performance of blended cement mortars specially for an economic nano material as NMK. This research is to investigate the efficiency of adding NMK, K, SF or FA mixture, as cement partial replacement added separately with different percentages, on durability properties of blended cement mortar. Moreover, studding the combination of NMK with other SCMs as SF and FA with different percentage of cement replacement by weight was studied on some durability characteristics related to elevated heat and sulphate protection. In addition, the influence of adding kaolin in micro size without dispersion and NMK with dispersion to mixture (size effect) was also studied on some durability characteristics. Mortar specimens were tested at normal temperature and tested after 2-hour exposure at higher elevated temperatures of (200, 400, 600 and 800oC) at 28 days age. Based on the maximum mortar compressive strength for (K, NMK, SF, FA) added separately %5 NMK was the optimum replacement ratio and with combination of micro and nano size 10%NMK+5% SF were the optimum cement replacement ratios, while for elevated heat resistance of blended cement mortars were remarkably enhanced by using 10% NMK+5%FA and 10%NMK+10%FA mixtures for the reduction in compressive strength values at 800oC, and for sulphate resistance using 10%NMK+15%FA mixture instead of using optimum K and NMK cement replacement ratio. Summing up, Adding the optimum dose of nano-particles helped to produce a denser microstructure and more durable matrix. Finally, the results showed that the compressive strength of the cement mortars with NMK at normal or elevated heat were higher than plain cement mortar with the same w/b ratio. At 5% NMK, the enhancement in compressive strength was 66.66% at 60 days age, while the enhancement in compressive was 22.74% at 200oC.