Influence Of Curing Regime On Shrinkage,Creep And Basic Mechanical Properties Of Ultra-High Performance Concrete

This thesis mainly studied influence of different curing regimes on shrinkage,creep and basic mechanical properties of ultra-high performance concrete(UHPC).There are two types of UHPC including reactive powder concrete(RPC)and ultra-high performance concrete with coarse aggregate(UHPC-CA).The curing regimes include standard curing,hot water curing,dry air heating and combined curing composed of precuring in hot water and heating in dry air.Through the tests of compressive strength,axial compressive strength and static modulus of elasticity,the influence of different curing regimes on the basic mechanical properties of UHPC is analyzed.According to the actual situation of the project,the shrinkage test of early age shrinkage and drying shrinkage is designed,and the shrinkage performance of UHPC is studied.Based on national standards and test conditions,UHPC creep tests were designed to investigate the effects of different curing regimes on creep properties of UHPC.The mechanical test results reveal that compared with standard curing,heat curing can effectively improve the compressive strength of UHPC,and the optimum curing regime is combined curing.Comparing RPC with UHPC-CA,the addition of coarse aggregate has no adverse effect on the mechanical properties of UHPC.The early age shrinkage test results reveal that the shrinkage rate at early time(0?1 d)is fastest and then has a dramatic decline(during 1-3 d).The shrinkage value at 1 d accounted for more than 70%of the total shrinkage of UHPC in three days.The shrinkage value of UHPC-CA is smaller than that of RPC at the same age,and the shrinkage rate at 3 d of RPC and UHPC-CA reaches 669 ?? and 578 ??,respectively.The drying shrinkage test results reveal that heat curing can obviously reduce drying shrinkage of UHPC,and the effect of combined curing is best in three types of heat curing regimes.In addition,the shrinkage of UHPC-CA under the same curing system is smaller than that of RPC at the same age.The creep test results reveal that the curing regime has great influence on creep,and all heat curing regimes can effectively reduce the creep of UHPC.The inhibitory effect of three heat curing regimes on creep from strong to weak is combined curing,dry air heating and hot water curing.Besides,the addition of coarse aggregate can also reduce the creep of UHPC.The results of this study show that under different curing regimes,combined curing is more conducive to promote cement hydration and pozzolanic activity of mineral admixtures,and to improve the performance of UHPC which includes mechanical properties,shrinkage and creep.And the addition of coarse aggregate has no adverse effects on the mechanical properties,whereas it can improve volumetric stability of UHPC.