Hydrophobic modification of ultra-high-performance fiber-reinforced composites with matrices enhanced by aluminum oxide nano-fibers

Abstract

Aluminum oxide nanoparticles can be used in small quantities to create a high-performance and ultra-high-performance cementitious composites. High volumes, up to 20% of supplementary cementitious materials such as silica fume or metakaolin, are often used to achieve the high strength of up to 150 MPa in high performance and ultra-high performance cementitious composites. This research demonstrates that when aluminum oxide (Al2O3) nano-fibers are used in cement-based composites, compressive strength of up to 175 MPa can be achieved at very low dosages of silica fume and metakaolin. This effect is achieved by using low water to cementitious materials ratio, selection of cement, and utilizing the seeding and reinforcing effects of by the nano-fibers. Furthermore, the ultra-high performance cement-based composite (UHPC) can include polyethylene fibers which provide enhanced strain hardening and multi-cracking behavior. The UHPC was tested to evaluate the effects of superhydrophobic modification. Superhydrophobic modification utilizes siloxane-based admixtures to form a well-dispersed air void system whose voids have hydrophobic properties. The experimental results demonstrate that a superhydrophobic modification may reduce the performance of advanced composites with Al2O3 nano-fibers. High-performance cementitious materials are critical for the next generation of infrastructure. This research evaluates the effects of superhydrophobic admixtures in ultra-high-strength fiber-reinforced composites with Al2O3 nano-fibers. The incorporation of small quantities of aluminum oxide nano-fibers in UHPC may prove to be a viable option for compressive strength enhancement; however, incorporating a superhydrophobic air void structure was not effective for enhancement of ductility.