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This research focused on finding the effect of nanosilica (NS) on the properties of self‐compacting concrete (SCC). NS in various proportions of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% was added to SCC with 10% silica fume (SF) or 10% fly ash (FA) by weight of cement to improve the properties of SCC. While the limestone powder (LSP) was used at a fixed supplementation of 15% by cement weight for all mixes. Fifteen SCC mixtures were designed based on the European guidelines for self‐compacting concrete. The properties of fresh SCC were evaluated by several tests of the slump flow, slump T50, V‐funnel, V‐funnel T5min, L‐box J‐ring, and fill box. Meanwhile, several tests evaluated SCC's mechanical properties, including compressive strength, split tensile strength, flexural strength, bond strength, and modulus of elasticity. Moreover, the permeability properties of SCC were evaluated by water permeability and air‐content tests. The effect of applying high temperatures (100–800°C) on the compressive strength of SCC containing NS with cementitious materials (SF, FA, and LSP) was also evaluated. Results showed that adding 3% NS with 10% SF and 15% LSP by weight of cement can be used to achieve the best mechanical properties of SCC. The SFNS3 mixture achieved the highest mechanical properties of 75.1, 11.9, and 41,300 MPa for compressive strength, bond strength, and modulus of elasticity tests. While the results for the slump flow, slump T50cm, and fill box were 680 mm, 6 s, and 93%. [ABSTRACT FROM AUTHOR]

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 re‐mix nano‐TiO2 between 1.2% and 2% by weight with FA showed impressive comparative results. [ABSTRACT FROM AUTHOR]