Designing carbon nanotube and nanofiber-polypropylene hybrid cementitious composites with improved pre- and post- crack load carrying and energy absorption capacity

Abstract

This study reports recent developments on carbon nanotube (CNT), nanofiber (CNF), and polypropylene microfiber (PP) hybrid reinforced cementitious composites. Notable characteristics are (i) significantly enhanced load carrying capacity; and (ii) increased energy absorption capability at both elastic and post-first cracking stages. Three point bending tests on notched and unnotched specimens have shown that the addition of 0.3 vol% CNTs and CNFs in PP reinforced mortars increases the modulus of elasticity and first crack strength and toughness by 93%, 64% and 49% respectively. The experimental values perfectly agree with the theoretically determined modulus using a micromechanics-based model. Hybrid mixes showed considerable increase in toughness, exhibited toughness index values I5 of 4 or more, and 4 times higher residual strength. Relative to the PP microfiber reinforced mortar, the developed hybrid material is able to sustain a much higher load and successfully transfer tensile stresses across cracks, without losing its tensile load carrying capacity. Such exceptional mechanical behavior is an important performance factor for serviceability and is interpreted in terms of the mechanism of a synergistic interaction between the nano and micro scale fiber reinforcement.