We experimentally investigated the effect of curing conditions on the durability of UHPC under flexuralload.Moreover,the mechanisms of the effect of curing conditions were revealed from the microstructuralpoint of view with environmentalscanning electron microscopy(ESEM)and X-ray computerized tomography(X-ray CT).The experimentalresults show that the flexuralload has negative influence on the durability of UHPC,but UHPC stillexhibits excellent durability under flexuralload.Besides,the curing conditions do show influences on the durability of UHPC.Compared with standard and steam curing,oven curing led to a lower chloride resistance and freeze-thaw performance of UHPC.The microstructure of UHPC paste was detected with ESEM.It is revealed that,compared with standard and steam cured UHPC,the lower reaction degree and internalmicrocracks are the causes for the lower chloride resistance of oven cured UHPC.The defects distribution in UHPC before and after freeze-thaw action was investigated with X-ray CT.The number of defects in oven cured UHPC increases the fastest during the freeze-thaw action due to its more defective microstructure We experimentally investigated the effect of curing conditions on the durability of UHPC under flexurallo. Moreover, the mechanisms of the effect of curing conditions were revealed from the microstructuralpoint of view with environmentalscanning electron microscopy (ESEM) and X-ray computerized tomography (X-ray CT). The experimental results show that the flexurallo has has negative influence on the durability of UHPC, but UHPC stillexhibits excellent durability under flexurallo. Besides, the curing conditions do show influences on the durability of UHPC. Compared with standard and steam curing, to a lower chloride resistance and freeze-thaw performance of UHPC. microstructure of UHPC paste was detected with ESEM. It is revealed that, compared with standard and steam cured UHPC, the lower reaction degree and internal microchips are the causes for the lower chloride resistance of oven cured UHPC.The defects distribution in UHPC before and after freeze-thaw action was investigated with X-ray CT.The number of defects in oven cured UHPC increases the fastest during the freeze-thaw action due to its more defective microstructure