Cellulose nanofibers to improve the mechanical and durability performance of self-healing Ultra-High Performance Concretes exposed to aggressive waters

The effects of including cellulose nanofibers (CNFs) in Ultra High Performance Concretes (UHPCs) have been studied in this paper in terms of recovery of both durability and mechanical properties because of the stimulated self-healing behavior. To this purpose, flexural tests on 4-point bending on 30 mm thin and 100 mm wide beam specimens have been carried out to evaluate the mechanical recovery due to self-healing, together with Double Edge Wedge Splitting tests that have been performed to identify the tensile stress crack-opening behavior. Moreover, water permeability and chloride diffusion tests have been performed to evaluate the recovery of durability properties on healed specimens subjected to extremely aggressive environments rich in chlorides and sulfates. Microstructural analysis has been also performed to confirm the enhancement on durability performance due to the presence of CNFs. The presence of CNFs has improved self-healing performance of UHPC since for the same crack width value and same healing period (1, 3 or 6 months) the specimens with CNFs reached higher crack sealing rates compared to those without nano-additions. As a matter of fact, the total sealing of the cracks over the 6-month investigated period was only observed on specimens with CNFs.