Influence of free water on dynamic tensile behavior of ultra-high toughness cementitious composites

•Dynamic tensile behavior of dried and saturated UHTCC was evaluated.•Water content of saturated UHTCC reached up to 17%-18% using vacuum saturation method.•Presence of free water in UHTCC decreased tensile strength, but increased the strain rate sensitivity.•The influence of water on DIF was different in UHTCC, SFRC and normal concrete under the similar strain rate. The influence of free water on the dynamic tensile behavior of UHTCC was studied using the dynamic Brazilian test. The result showed that the moisture content of the saturated UHTCC reached up to 17%–18% due to their porous properties, which have an influence on their strain rate, splitting tensile strength and dynamic increase factor (DIF). Under the same impact pressure, the dynamic tensile strain rate of saturated UHTCC decreased by 25%–41% compared with that of dry ones. The softening effect of water on the quasi-static and dynamic tensile strength of UHTCC was observed in the study, and the softening coefficients of UHTCC were influenced by the strain rate. The immersion of free water led to the improved strain rate sensitivity of UHTCC, however, the increase in DIF after water infiltration is less significant in the UHTCC than in the steel fiber reinforced concrete and normal concrete under the similar strain rate. The mechanism underlying such phenomenon was discussed.