Effect of nano silica on strength and permeability of concrete

Abstract

Nanomaterials are extremely active in altering the characteristics of cementitious composites at the nano scale due to their nano size. The hydration process, which is proportional to the available surface area, changes the characteristics of cementitious composites more quickly as a result of the larger surface area of these materials. Even a very small percentage of cement replacement can improve concrete strength and permeability. In the present study, of the available nanomaterials (silica fume, nano-silica, nano-alumina, fly ash, etc.), the effect of nano-silica inclusion on the mechanical properties and permeability characteristics of cementitious composites has been examined. Cement replacement is ranging from 0.5 percent to 2.0 percent for a nominal mix of concrete (Grade M20). Experimental works are carried out in accordance with Indian Standards to have an insight into the mechanical and permeability properties of concrete, and to analyze the microstructure of the developed nanocomposites. A total of 105 specimens were cast to test the compressive, tensile, and flexural strength of nano-modified concrete at various ages. The findings of the tests showed that the permeability of concrete reduced with age while its compressive strength greatly improved in the early age. At 1.5 percent, a maximum decrease in permeability was observed, while concrete with 2 percent nano-silica showed a marginal increase in permeability. The aggregation of nanoparticles could be the cause. The influence of the nano-filler and the improved pozzolanic reaction resulted in a more homogeneous and less porous microstructure of the cementitious composites. It is concluded that nano-silica due to its pozzolanic activity additional calcium silicate hydrates are formed, thus imparting higher strength and improved microstructure leading to a low permeable concrete.