Improvement of ultra-high-performance concrete matrix with nanocellulose for reduced autogenous shrinkage and enhanced mechanical properties

Despite its numerous benefits and considerable potential, ultra-high-performance concrete (UHPC) faces challenges in wider application due to significant autogenous shrinkage deformation. Typically, efforts to inhibit UHPC autogenous shrinkage may compromise its mechanical properties through the utilization of various internal curing agents, presenting a contradictory situation. To overcome this situation, we explored the utilization of nanocellulose materials, which led to improvements in reducing autogenous shrinkage and enhancing mechanical properties. Experimental findings reveal that incorporating a cellulose nanofiber-2 suspension presents a significant improvement, even at minimal dosages. Specifically, relative to the control group, autogenous shrinkage diminishes by at least 62.2 %, while mechanical properties at 28d are increased by nearly 10 % in NC-3 group. The potential microscopic mechanisms were investigated, revealing that the cellulose nanofiber-2 suspension acts by decelerating the initial hydration rate (before the acceleration period) and subsequently enhancing the nucleation and growth of hydration products (after the acceleration period). In addition, capillary pressure can be effectively decreased by reducing the volume of nanopores and surface tension of the pore solution. Combined with the rigid support and bridging effects after water release, the incorporation of a cellulose nanofiber-2 suspension can significantly inhibit the development of autogenous shrinkage while improving mechanical properties. This novel nano-engineering strategy not only promotes wider industrial applications of UHPC but also holds considerable promise for future advancements.