Systematic investigation into mechanical strength, pore structure and microstructure of high performance concrete incorporating nano-hybrids

Abstract

In this study, high performance concrete (HPC) containing two types of nanoparticles: carbon nano tubes (CNTs) and nano silica (NS) and hybrid nanoparticles (CNTs + NS) were prepared. The compressive strength, phase composition, pore size distribution, surface area, surface morphology and microstructural characteristics were investigated at 7 and 28 days of hydration. In addition, the combined effect of CNTs and silica fume (SF) on the properties of concrete has been investigated in this study for comparison reasons. The results indicated that, all kinds of the utilized nanoparticles provided an enhancement in the compressive strength of the hardened concrete at early and later ages of hydration. Furthermore, Thermogravimetric analysis (TGA) patterns revealed no great difference in the hydration degree of cement with the addition of CNTs. However, Due to its large specific surface area and the pozzolanic activity, CNTs+NS nanohybrid showed the best acceleration efficiency. The concrete containing CNTs+NS nanohybrid exhibited the highest improvement in compressive strength. The pozzolanic reaction induced by NS and silica fume (SF) led to remarkable increase in the surface area and the nanoporosity/gel pores assigned to calcium silicate hydrate (CSH) phase. The SEM analysis showed that, CNTs resulting in bridging nano-size and micro-size pores or gaps within cement hydrates; however, SF and NS are more efficient in filling the pores and gaps between the hydration products and providing more compact microstructure.