Preparation And Mechanical Properties Of Ultra-High Performance Concrete With High Elastic Modulus

Ultra-high-performance concrete（UHPC）is widely used in civil engineering,because of its excellent mechanical properties and durability.However,the compressive strength of UHPC is about 200%-300%higher than that of normal concrete,while the elastic modulus of UHPC is only about 50%higher than that of normal concrete at present,which suggests the nonsynchronous increments of UHPC in its elastic modulus and compressive strength.When the structural strength meets the design requirements,it will cause the stiffness of UHPC is insufficient and excessive deformation of the UHPC structure,so that its structure may be damaged.Firstly,the Modified Andreasen and Andersen particle packing model was used to design the initial mix ratio of ultra-high performance concrete with high elastic modulus（HEMUHPC）.Secondly,the effects of three kinds of high-stiffness materials with different contents on the mechanical properties of HEMUHPC were explored,and the reasons for the improvement of the mechanical properties of HEMUHPC were revealed via microscopic experiments.Finally,the 218 data of compressive strength and elastic modulus of UHPC were collected from the literature,and the prediction model for elastic modulus of UHPC was established by the Adaptive Neuro Fuzzy Inference System（ANFIS）.The elastic modulus of HEMUHPC was predicted through the ANFIS model,and thus the reliability of the model was verified.The following main conclusions were drawn from this study.（1）Because of the incorporation of nano-Al₂O₃,the flexural strength,compressive strength and elastic modulus of HEMUHPC increased by5.11%～14.40%,3.35%～19.73%and 6.25%～17.80%,respectively.Nano-Al₂O₃has pozzolanic activity and small particle size,which can fill the internal pores of HEMUHPC,reduce its porosity,improve its microstructure,and then improve the mechanical properties of HEMUHPC.（2）Because of the incorporation of alumina micro-powder,the flexural strength,compressive strength and elastic modulus of HEMUHPC increased by3.54%～11.23%,8.89%～22.83%,6.19%～16.37%,respectively.Alumina micro-powder has pozzolanic activity,small particle size and high stiffness,which can fill the internal pores of HEMUHPC,reduce its porosity and improve its microstructure.In addition,the results of nanoindentation experiments showed that the incorporation of alumina micro-powder can improve the elastic modulus of HEMUHPC matrix,thereby improving its overall elastic modulus.（3）Because of the incorporation of steel chips,the flexural strength,compressive strength and elastic modulus of HEMUHPC increased by1.28%～10.49%,6.38%～15.85%and 9.65%～21.73%,respectively.The particle size of the steel chips used in this paper is slightly smaller than that of quartz sand,thereby reducing the porosity of HEMUHPC,improving its pore structure and improving its mechanical properties.At the same time,the stiffness of steel chips is much higher than that of quartz sand,so the incorporation of steel chips can improve the mechanical properties of HEMUHPC.（4）Because of the incorporation of granite coarse aggregate,the compressive strength and elastic modulus of HEMUHPC increased by 4.45%～16.83%and6.91%～18.76%,respectively.The granite coarse aggregate has high stiffness,and a rigid skeleton with better stiffness can be formed in HEMUHPC,thereby improving the mechanical properties of HEMUHPC.（5）Finally,the prediction model for elastic modulus of UHPC was established via Adaptive Neuro Fuzzy Inference System（ANFIS）.The root mean square error of the training set and the checking set of the model were 2.143 and 3.553,respectively,indicating that the model has high reliability.The error range between the theoretical and experimental results of the elastic modulus of HEMUHPC obtained by this model was between 1.02%and 7.66%,indicating that the model could accurately predict the elastic modulus of HEMUHPC.