| With the development of society and the progress of science and technology,people are developing high altitude,ground and marine constantly in forming a high-level,lightweight,and long-span of modern buildings.Human beings broaden their living space continuously.People are developing high altitude,ground and marine constantly in forming a high-level,lightweight,and long-span of modern buildings.All these are realized by improvement of concrete technology and the level production processes.Ultra-high-performance cement-based materials has features like high specific strength,good load capability,resource and energy saving,outstanding durability compared with ordinary concrete,so it could meet the requirements of light weight,high rise,long span and high durability of modern civil engineering.UHPC is the developing directions in concrete technology.However,the low water consumption results in high viscosity of fresh concrete,thus leading to difficulty pumping.There are many pressing issues in the preparation and design of UHPC to be resolved to make it widely applied in engineering structures.Research and development of ultra-high-performance concrete with great rheological behavior has great significance.The paper focuses on systematic study of rheological behavior of cement-based materials with low water-to-binder ratio,the preparation of ultra-high-performance concrete,rheological behavior of low water/binder cement-based material were revealed to provide theoretical basis for the scientific preparation of UHPC.This paper studied the influence of water-binder ratio,binder-sand ratio,superplasticizer and mineral admixtures on the rheological behavior and mechanical properties of low water-binder ratio cement-based materials.Ultra-high-performance cement-based materials mixed with fly ash,microbead and slag can effectively improve the rheological behavior.Due to the huge specific surface area of silica fume,the incorporation of silica fume increased the yield stress and plastic viscosity of the low water/binder cement-based materials and the fluidity became poor.Studying the influence of mineral admixture on the rheological properties and mechanical properties of low water/binder cement-based materials,we can get the best dosage of microbead is 20%-35%,the best dosage of slag is 10%-15%,the best dosage of silica fume is 5%-10%.Microbead was added to ultra-high-performance cement-based materials to improve its fluidity.Microbead have continuous and uniform particle size distribution and dense sphere morphology and the particle size between cement and silica fume particles,it can be optimized the particle size distribution at the micro level,improve the density,thereby increasing the strength and reducing the viscosity.And spherical particles will bring water reduction function and excellent ball lubricating effect,the further reduce the viscosity.Research on the water-binder ratio,consumption of binder,sand ratio and steel fiber content on the working performance and mechanical properties of ultra-high-performance concrete.The results indicate UHPC with slump/spread of 285mm/760mm,T50 of 14.5s,collapse time of 17.1s and V-funnel of 35s,and the compressive strength of 121MPa at 28d had been successfully prepared with W/B of 0.20,binder content of 680kg/m~3(55%C,30%MB,10%SL and 5%SF)and the sand ratio of 40%.Considering comprehensively the influence of steel fiber on the working performance and mechanical properties of ultra-high-performance concrete,it is determined that the appropriate volume content of steel fiber is 1.0%-2.0%,and the prepared ultra-high-performance concrete has better working performance and higher compressive strength.Based on the CFD method,the ultra-high-performance cement-based material is regarded as the Herschel-Bulkley fluid and then finite element model was created for simulation and analysis,and the relationship between the rheological parameters and working performance of the newly-mixed ultra-high-performance concrete is initially established,it can quantitatively reflect the influence of various factors on the rheological properties of fresh concreteThis paper reveals the influence mechanism of various factors on the rheological behavior of ultra-high-performance cement-based materials.In paste with low water-to-binder ratio,the thickness of the water film layer is the fundamental reason that affects the rheological behavior of cement-based materials with low water-binder ratio.The effect of superplasticizer and mineral admixtures on the rheological properties of mortar and paste were studied by the appropriate test methods which were newly-established.The mechanism of water consumption、superplasticizer and mineral admixture the effect on the rheological behavior of low water/binder ratio paste were revealed by calculating the thickness of the water film layer,using an organic carbon analyzer to determine the amount of water reducing agent adsorption,using SEM to characterize the particle morphology of the mineral admixture and quantitatively calculating the particle circularity.The excess paste thickness is the fundamental reason that affects the fluidity of fresh UHPC,and the mechanism of the influence of consumption of cement-based material,aggregate grading and aggregate morphology on the fluidity of ultra-high performance concrete were studied. |
