| The development of new concrete materials with high specific strength is a major need for modern large（giant）buildings because of the difficulty of conventional concrete to meet the requirements of modern super tall and large structures due to its high self-weight and low strength.To this end,this thesis combines the characteristics of UHPC and the properties of lightweight aggregates to carry out the effects of different lightweight aggregates on the mechanical properties of UHPC,and analyze the corresponding mechanisms,which will provide technical support for further development of UHPC with higher specific strength.The following research results were obtained:（1）With the admixture of lightweight aggregates,the apparent density and compressive strength of UHPC with a compressive strength of 120-160 MPa grade showed a decreasing trend.Among them,the apparent density of UHPC was maintained at about 2200 kg/m3 with the strength up to 150 MPa when the volume of hollow glass microsphere was mixed within 50%;the apparent density and compressive strength of UHPC were significantly reduced when the cenosphere were mixed;the apparent density of UHPC was less affected by the mixing of shale ceramic granules,ceramsite sand and cloud concrete stone,and the apparent density of UHPC was about 2000 kg/m3 and the compressive strength was greater than 100MPa,when the volume rate of the above three was 100%.（2）Different lightweight aggregates have different effects on the specific strength of UHPC.Among them,the specific strength of UHPC was significantly reduced when the doping amount of cenosphere was increased,and the specific strength of UHPC was only 42.9×10-3MPa/（kg/m3）when the doping amount was 100%;the addition of ceramsite sand and cloud concrete stone had little effect on the specific strength of UHPC,and the overall specific strength was between 50×10-3MPa/（kg/m3）-70×10-3MPa/（kg/m3）.However,the specific strength of UHPC doped with hollow glass microsphere was reduced first and then increased,and the specific strength can reach 70×10-3 MPa/（kg/m3）or more when it was 100%mixed.（3）Different from the reference group,hollow glass microsphere,cenosphere,ceramsite sand and cloud concrete stone can combine well with cement stone in UHPC respectively,and the microstructure in the transition zone of the interface between the two was dense,and the damage of load action is light aggregate damage first.At the same time,the incorporation of hollow glass microsphere or ceramsite sand in UHPC will make the pore size distribution of microscopic pores refined and the pore volume rate reduced.or ceramic sand mixed with UHPC refined the pore size distribution of microscopic pores and reduced the pore volume rate.（4）There is a close functional relationship between the compressive strength and apparent density of UHPC mixed with lightweight aggregates.A unified mathematical relationship model between compressive strengthσof UHPC and volume rate P of lightweight aggregates was established asσ=σ0e-BP:The B value of 0.7;the B value for mixing with ceramsite sand or cloud concrete stone was taken as 0.7;the B value for mixing with cenosphere was taken as 2.3;the B value for mixing with hollow glass microsphere was taken as 0.6.（5）Among the sevevn types of lightweight aggregates investigated in this thesis,namely rubber,EPS beads,high strength expanded shale,ceramsite sand,cloud concrete stone,cenosphere and hollow glass microsphere,and the UHPC involved,new ultra-high-performance concrete with high specific strength can be prepared by using ceramsite sand and cenosphere.The apparent density of UHPC is 2000 kg/m3,compressive strength is 115.33 MPa,and specific strength is 58.3×10-3MPa/（kg/m3）when 100%of ceramsite sand is blended.With 100%hollow glass microsphere,the apparent density of UHPC is 1725 kg/m3,compressive strength is 125.04 MPa,and specific strength is 72.5×10-3MPa/（kg/m3）. |
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