Flexural Performance Of RUHTCC Beam After Sustained Load And Dry-wet Cycles

Some parts of reinforced concrete structures in coastal areas are subject to different types of loads,at the same time,they are often subject to repeated drying and wetting cycles.Concrete is easy to crack and its tensile performance is poor,so it often leads to premature cracking and excessive cracks,which degrade the performance of structural members.Ultra High Toughness Cementitious Composites（UHTCC for short）has better crack inhibition ability,tensile property,durability and self-healing ability than normal concrete.It can be applied to structural members to improve the durability of concrete members.At present,the research of RUHTCC beam is mainly focused load effect and environmental effect separately.Therefore,the flexural behavior of RUHTCC beam under continuous load,dry-wet cycle and combined action of load and dry-wet cycle is studied in this paper.The test variables designed in this paper are loading level（0,30%,60%peak load）,duration of sustained load（0,14,28,56 days）and duration of drying and wetting cycles（0,60,120 days）.The purpose of this study is to investigate the effects of loading level,duration of loading,dry-wet cycles and their coupling on the flexural properties of RUHTCC beams.The main conclusions are as follows:（1）The RUHTCC beam will crack and damage under the action of sustained load and dry-wet cycles,and higher sustained load level and more cycles lead to greater damage.However,the ultimate failure mode and crack morphology of the beam are almost not affected by the loading level and the number of dry-wet cycles.（2）The results show that the stiffness,ductility and bearing capacity of the specimens are reduced by the sustained load.The influence of the sustained load on the stiffness and ductility is more obvious,and the specimens are more prone to crack under the bending load.When the loading level increases from 30%P_max to 60%P_max,the stiffness and bearing capacity decrease with the increase of damage,but the decrease range is small.Under the same loading level,the influence of the duration of loading on the flexural performance of the beam is small.（3）Compared with the specimens without dry-wet cycles,dry-wet cycles significantly reduce the stiffness and bearing capacity of the specimens,and it has a more significant effect on the stiffness.The dry wet cycles make the cracking time of RUHTCC beams advance under bending load.The bending behavior of RUHTCC beams is not affected by the number of dry-wet cycles.（4）Under the combined action of sustained load and dry-wet cycle,the bearing capacity and stiffness of the specimens decreased more obviously,compared with the specimens under sustained load and dry-wet cycle only.However,the failure mode of the specimen has not changed.The combined action of sustained load and dry-wet cycle has the greatest influence on the performance of the specimen at the time of crack re-expansion,and the least influence on the ultimate load and deflection.The duration of sustained load has little effect on the bearing capacity and stiffness of the specimen.（5）When calculating the ultimate bearing capacity of RUHTCC beam,the role of UHTCC in the tensile zone should be considered.The rationality of the model and the reliability of the test data are verified successfully.The degradation formula and damage degradation coefficient of the ultimate bearing capacity of RUHTCC beams under the combined action of sustained load and wetting and drying cycles are given.