Synergic effect of nano-silica and natural pozzolans on transport and mechanical properties of blended cement mortars

Abstract

The mechanism of the synergic effect of nano-silica and natural pozzolans on the structure of mortar samples in single, binary, and ternary blends was investigated. Mortar mixtures were prepared by replacing 2, 3, and 4% of cement mass with nano-silica and 15% with zeolite, trass or pumice as natural pozzolans with w/cm ratio of 0.485 and flow ranged from 14 to 16 cm. Compressive strength, electrical resistivity, chloride permeability, capillary absorption, and SEM analysis were carried out on mortar samples. Considering the results, nano-silica improved mechanical and durability properties of all mortar samples, but in binary samples, the nano-silica's effect on the mechanical properties improvements in the early ages was more pronounced. Interestingly, in ternary blends nano-silica had remarkable effect even at older ages. Furthermore, the combination of nano-silica and natural pozzolan showed a superior effect on the properties of mortars. As a consequence, the combined positive effect of three-component blends on the compressive strength of control samples was superior to the summation of the progressive effects of nano-silica and natural pozzolans in binary blends. It can be concluded that natural pozzolans amplified the ameliorating effect of nano-silica at older ages (90 days). The synergic effect of components was more pronounced with the increase in the percentage of nano-silica replacement and the selection of more active natural pozzolan. Finally, the ternary blends containing nano-silica and natural pozzolans outperformed the binary ones containing Portland cement and nano-silica not only in terms of reducing costs and negative environmental effects, but also in improving the mechanical properties and durability. Ternary mixtures incorporating 4% nano-silica together with 15% zeolite demonstrated the best results in all tests at the age of 90 days. Compared to the control sample, it improved compressive strength by 51.9% with changing from 48.2 to 73.2 MPa and chloride ions migration coefficient by 570.7% with changing from 16.7 to 2.5 *10 −12 m2/s.