Physical and chemical effects of siliceous particles at nano, micro, and macro scales on properties of self-consolidating mortar overlays

Abstract

The aim of this experimental investigation is to study the effect of siliceous particle at nano (0, 1, and 2% of pyrogenic nanosilica), micro (silica fume with 0, 5, and 10% cement weight replacement), and macro scales (sand with SiO2 percentages of 0, 50 and 100%) on mechanical properties, durability, and surface characteristics of self-consolidating mortars as an overlay. For this purpose, 27 self-consolidating mortar overlays (SCMOs) with a water to cement ratio of 0.4 and different mixture proportions were prepared. Mini-slump flow and V-funnel time values were determined experimentally in fresh SCMOs. Moreover, the compressive and flexural strength of mechanical strength, water absorption, porosity, abrasion resistance (as a durability property), skid resistance (as a surface characteristic), and early age shrinkage were measured. The interfacial transition zone and the microstructures were studied using scanning electron microscope (SEM), thermogravimetric analysis (TGA), and atomic force microscope (AFM). Based on the results, the synergic effect of silica based particles in nanoscale and microscale improved mechanical, durability, and frictional properties. SEM images showed that samples containing limestone sand had denser interfacial transition zone (ITZ) than siliceous sand samples due to better interlocking. Using the AFM images, high-silica sand mortar samples exhibit lower skid resistance compared to limestone type sand. Besides, incorporating siliceous sand improves the abrasion resistance (as a durability factor of the slip resistance) about 45.8% compared to lime-based samples. In addition, improvement in wear resistance caused by mineral additions is reduced by increasing the SiO2 percentage in the sand. The relation among porosity, compressive strength, and abrasion resistance was stronger in limestone type mixtures.