Influence Of Parameter Optimization Of Combined Curing On Mechanical Properties And Explosive Spalling Of Ultra-high Performance Concrete Subjected To High Temperature

The influence of curing regime on the mechanical properties and explosive spalling of ultra-high performance concrete with coarse aggregate(UHPC(CA))subjected to high temperature was studied in this thesis.The variables include curing methods,hot water curing temperature and duration,dry air heating temperature and duration and,steel fiber.The optimum combined curing for strength and spalling resistance of UHPC was identified via the first-stage experiment,which was a basic curing for further rsearch.The influence of varing temperature on strength and spalling resistance of UHPC was studied in the following stage.Finally,the influence of combined curing on compressive strength,tensile splitting strength,fracture energy,and spalling behavior of UHPC(CA).The results of mechanical tests show that:(1)the best duration of hot water curing is different with varying temperature.When the temperatures are 60? and 90?,the best duration of hot water curing are 4 d and 3 d,respectively.(2)Compared with the standard curing,the compressive strength and the splitting tensile strength of UHPC greatly increase under the combined curing.For the plain concrete,the fracture energy of concrete under the combined curing is greater than that cured under the standard curing.However,the combined curing has a negative effect on the fracture energy of UHPC with steel fiber.The results of the explosive spalling test show that after explosive spalling test,all the specimens cured under standard curing occur severe explosive spalling.Meanwhile,the combined curing has a significant influence on improving the resistance of UHPC under high temperature,and the improvement can be affected by the temperature and duration of hot water curing and dry air heating.The longer the hot water curing duration is,the severer the explosive spalling behavior of UHPC is.Moreover,raising the temperature of dry air heating is effective to eliminate the spalling occurrence of UHPC under high temperature.The test results of residual mechanical strength of UHPC subjected to 600? show that the UHPC under the combined curing still has high residual compressive strength and tensile splitting strength.Addition of steel fiber has beneficial effect on improve the residual strength of UHPC.Compared to the single type of steel fiber,the hybrid steel fiber has more advantages on the residual strength of UHPC.The research carried out in this thesis indicates that combined curing can greatly improve the mechanical properties and resistance to explosive spalling of UHPC under high temperature.Meanwhile,the temperature and the duration of hot water curing or dry air heating have some impacts on the strength of UHPC.Under the standard curing,the steel fiber incorporated in UHPC can alleviate spalling to some degree.The UHPC under combined curing remains high residual mechanical properties after the explosive spalling test.