International Concrete Abstracts Portal

Title: Nano-Modified Calcined Clay-Based Cement Concrete: A High Modulus Concrete with Low Carbon Footprint

Author(s): Panagiotis A. Danoglidis

Publication: CRC

Volume:

Issue:

Appears on pages(s): 22

Keywords:

DOI:

Date: 8/25/2023

Abstract:
Typically, MK-based cementitious materials can exhibit negligible tensile strain energy absorption capacity due to their brittle behavior. The experimental study shows that the addition of small amounts of well-dispersed CNTs (0.1 wt%, by mass of binder) in metakaolin-based cementitious composites with 20% replacement can lead to substantial improvements in MOE and post-crack ductility. The pozzolanic reaction of MK densifies the microstructure leading to an improvement in compressive strength by 21% and MOE by 34% compared to OPC mortar. Compared to the MK-Mortar, the CNT reinforced MK-Mortar nanocomposite exhibited 88% increase in flexural strength and 107% increase in MOE. Moreover, the tensile strain energy absorption capacity was improved by 1.8x at the elastic stage. The I5, I10 and I20 toughness indices showed improvements of 45%-110%, which demonstrates the ability of the MK-based cementitious nanocomposite to absorb energy at the post-crack stage. This performance can be related to the proper function of MWCNTs in bridging nano cracks, increasing the ultimate strain capacity and, by extension prolonging the elastic stage and failure of nano reinforced mortars. Using Quantitative Nanomechanical Mapping (QNM) technique, significant strengthening of the interfacial transition zone between the sand and cementitious matrix was observed for MK-cement mortar using low concentrations of monodispersed carbon nanotubes (CNT). Nanoscale imaging and property mapping at the ITZ revealed that the local structure/morphology of the interface has improved, resulting in an impressive increase in the modulus of elasticity (+27%). Addition of 0.1 wt% CNTs modified the polymerization of the silicate chain within the C-S-H of the interface between sand and cementitious matrix at the nanoscale level. This helps in explaining the observed increases in the macro-mechanical properties. The incorporation of CNTs in MK-OPC concrete provides concrete with a toughening mechanism by reinforcing the nanostructure of C-S-H and by modifying the interface between the aggregates and the cementitious matrix. This enhances the concrete’s load transfer efficiency at large deformations.