Abstract
The addition of metakaolin (MK) in cementitious composites leads to a considerable improvement in compressive strength; yet negligible increases in flexural strength and toughness are observed. This research investigates the effect of carbon nanotubes (CNTs) on the tensile load carrying capacity and strain energy absorption capability of metakaolin based cementitious composites at the elastic and post-crack stages, and the microstructure and chemical composition of the Interfacial Transition Zone (ITZ) between the nanomodified cementitious matrix and aggregates. The addition of 0.1 wt% CNTs in 20% MK mortars significantly increases the nanocomposites’ flexural strength and Young’s modulus by 88% and 107%, respectively. An exceptional improvement in the tensile strain energy absorption capacity of the CNT reinforced MK cementitious composites is indicated by the 1.8x higher post-crack flexural toughness and 45–110% increased toughness indices I5, I10 and I20. Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM/EDS) analysis of the ITZ of nanoreinforced MK cementitious mixes showed that CNTs at amounts as low as 0.1 wt% decreased the Ca/Si ratio of the Calcium Silicate Hydrate (CSH) products in the ITZ and increased the polymerization of the silicate chain within CSH. Therefore, addition of CNTs in MK cementitious mixes strengthens the ITZ, and greatly improves the tensile strength and modulus, and post crack ductility.
Published Version
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