ABSTRACTThis research aims to perform a comparison of the mechanical response and the fatigue behaviour of two Ultra-High Performance Concrete (UHPC) mixtures subjected to bending loads: a regular UHPC and a high-thixotropy UHPC. The same materials were used in both mixtures and the only difference was the proportions of water and additive. Rheological tests were performed to validate the thixotropy of mixtures in fresh-state. Additionally, image analysis was applied to get fibre distribution and orientation from beam-cut slices. Thus, the Image pixel complete colour structure (RGB) was analysed to avoid greyscale transformations because of its loss of information. Finally, three-point bending tests were conducted over pre-cracked beams to establish a fatigue equation for the mixtures. Experimental results showed that high-thixotropy UHPC has mechanical properties comparable to regular UHPC.KEYWORDS: UHPCflexural fatiguerheologythixotropy AcknowledgmentsThe research was developed by the Pontificia Universidad Javeriana and Cementos Argos S.A, that contributed with laboratory resources and time of professors and researchers. Also the authors of this work acknowledge and thank the support of the Civil Engineering Laboratory of Pontificia Universidad Javeriana and all technical staff, where the tests were carried out.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was funded by Fondo Nacional de Financiamiento para la Ciencia, la Tecnología y la Innovación Francisco José de Caldas de MinCiencias, Republic of Colombia: Project Code 120380863881 Id: 63881, Rehabilitación de pavimentos con sobrecarpetas de concretos de Ultra Alto desempeño reforzado con fibras de acero UHPFRC. This research was developed by Pontificia Universidad Javeriana, and Argos company which contributed with laboratory resources and time of professors and researchers.