Abstract
This paper aims to study the effect of using modified nano-TiO2 with fly ash (FA) on ultra-high performance concrete's (UHPC) mechanical, transport, and microstructure properties (UHPC). A ball mill was used to disband the nano-TiO2 and distribute it uniformly within the FA powder. In this research, 20% of the cement weight was replaced by FA, and nano-TiO2 was added by 0.4%, 0.8%, 1.2%, 1.6%, and 2% of the FA weight. To investigate the effect of the ball mill period on the UHPC properties, periods of 10, 20, 30, and 40 min were applied to a binder of 20% FA and with 6% nano-TiO2. In addition, a 30-min ball mill period on a binder of 20% FA and 0.4%, 0.8%, 1.2%, 1.6%, and 2% nano-TiO2 was also investigated. Tests of compressive strength after 1, 7, 28, and 91 days of curing in tap water, splitting tensile strength, flexural strength, and modulus of elasticity were performed after 28 days of curing in tap water. Tests of chloride permeability, sorptivity coefficient, water permeability, and microstructure were also performed after 28 days of curing in tap water. The results showed that the addition of higher percentages of nano-TiO2 led to a decrease in workability. The addition of nano-TiO2 improved the mechanical properties. The highest compressive strength of 208.9 MPa was achieved for the mixture of 20% FA with 1.2% nano-TiO2 at the age of 28 days. The 30-min period of application of the ball mill achieved the best performance compared with the other periods. The results of using a ball-mill to remix nano-TiO2 between 1.2% and 2% by weight with FA showed impressive comparative results.