Effect of Nano- and Micro silica on compressive and bond strength in saline environments: An experimental and microstructural study

Simultaneous using of nanosilica (NS) and microsilica (MS) can improve the chemical and microstructural reactions of concrete. Hence, this improvement can increase the bearing capacity of reinforced concrete structures by increasing the compressive strength of concrete and the bond strength between rebar and concrete, especially in saline environments. Therefore, in this study, 14 mixes including different percentages of NS and MS based on two types of cement strength class have been designed to evaluate the compressive and bond strength in salt solution with two concentrations of 15% for cement 42.5 MPa (C42.5) and the concentration of 20% for cement 52.5 MPa (C52.5) cement. Scanning electron microscope (SEM) was also used to study the microstructural part of the rebar-to-concrete bonding surface. Experimental results showed that replacement of cement with 7% MS + 3% NS, increased compressive strength by 90% and the bond strength by 66% for C42.5. Also for C52.5, 5% MS + 5% NS improved 88% compressive strength and 59% bond strength. In addition to dependency of optimum mix design to cement type, it is seen that the increasing of CSC can control the degradation caused by increasing salt concentration.

Keywords:

Nanosilica , Microsilica , Compressive strength , Bond strength , Microstructure.