Deformation Performance And Regulation Technology Of Ultra High Performance Concrete

Ultra High Performance Concrete(UHPC),as a new type of cement-based composite material characterized with extremely high mechanical properties and durability,has received extensive attention.However,due to the higher dosage of cementitious materials and the extremely low water-binder ratio,UHPC tend to show a large shrinkage and deformation in the early stage,leading to greater cracking hazards,which will affect the structural safety.Therefore,it is of great significance to study the deformation performance and regulation technology of UHPC.In this paper,the initial point as the beginning of the measurement of autogenous shrinkage of UHPC has been used to investigate the influence of water-binder ratio,the maximum size of fine aggregates and also the amount of coarse aggregates and steel fiber on the deformation performance of UHPC.Meanwhile,effects of different dosages of calcium oxide expansive agent and magnesium oxide expansive agent on compensation for shrinkage of UHPC have also been studied,which is hopefully to explore the regulation technology for the Autogenous shrinkage of UHPC.The results can be concluded as follows:(1)Capillary pressure can be used to solve the difficulty in measuring the initial setting time of UHPC,which is also direct and accurate in ascertaining time zero of UHPC.(2)With the decrease of the water-binder ratio from 0.15 to 0.20,the autogenous shrinkage of UHPC at 28 days will first increase and then decrease,which will reach its maximum value at 0.18.However,the changes of the maximum diameter of fine aggregate and the dosage of steel fiber exert less effect on the autogenous shrinkage.While,the replacement of coarse aggregate not only can significantly inhibit the autogenous shrinkage but also can promote the compressive strength.(3)The magnesia expansive agent has a good compensating effect on the autogenous shrinkage of the UHPC.And the higher the activity of MEA as well as the curing temperature,the better compensating effect will present.When the dosage of the 60 sMEA is 6%,the autogenous shrinkage of the UHPC can separately decrease by 25.9% and 39.1% at 20℃ and 38℃.(4)The calcium oxide expansion agent can obviously compensate the autogenous shrinkage of the UHPC.When the dosage of CEA is 3%,the autogenous shrinkage of the UHPC at 28 d present by 72.6%.however,an excessive dose of CEA will cause adverse effects on the compressive strength,furthermore,the changes in curing temperature has little effect on the expansion performance of UHPC.(5)After comprehensively condisering the effect of both MEA and CEA on compensation on the autogenous shrinkage,temperature sensitivity,and also the strength,it can be proposed that the combination of MEA and CEA can properly solve the autogenous shrinkage of UHPC,which can be used as an ideal regulation technology for controlling the autogenous shrinkage of the UHPC...