Effect of Nano-clay on Mechanical Properties and Microstructure of Ordinary Portland Cement Mortar

— The effect of nano-clay on the mechanical properties and microstructure of Portland cement mortar was investigated. The main objective of this research is to constitute a blended cement mortar with high mechanical properties. The nano-clay used in this investigation was nano-kaolin. The nano-metakaolin (NMK) was prepared by thermal activation of kaolin clay for 2 hours at 750 o C. The blended cement used in this investigation consists of ordinary Portland cement (OPC) and nano-metakaolin. The OPC was partially substituted by NMK of 0, 2, 4, 6 and 8% by weight of cement. The blended cement mortar was prepared using cement-sand ratio of 1:2 by weight with water-binder ratio (w/b ratio) as 0.5. The fresh mortar pastes were first cured at 100% relative humidity for 24 hours and then cured in water for 28 days. The compressive strength, tensile strength, phase composition and microstructure of mortar were investigated. The results showed that the compressive strength and the tensile strength of the cement mortars with NMK were higher than plain cement mortar with the same w/b ratio. The enhancement in tensile strength was 49%, whereas the enhancement in compressive was 7% at 8% NMK I. INTRODUCTION Nano-SiO 2 has been used to increase strength, flexibility and aging resistance of polymers [1]. The effect of nano-SiO 2 on the mechanical properties of high-volume fly ash high-strength concrete (HFAC) has been studied [2-7]. The heat of hydration, strength and pore size distribution was also investigated. A comparison was made between fly ash incorporating nano-SiO 2 , fly ash, and nano-SiO 2 alone in terms of weight change after immersion in saturated lime solution. The addition of nano-SiO 2 to high-volume high-strength concrete leads to an increase in strength. The pozzolanic activity of nano-SiO 2 can activate fly ash, causing weight increment. The addition of fly ash causes higher porosity at short curing time, whereas nano-SiO2, which acts as an accelerating additive, produces better compacted structures, even at short curing times [2].