Studies On The Preparation,dynamic And Static Performance Of Ultra-high Performance Heavy Concrete

Ultra-high performance concrete(UHPC)is a cement matrix composite with high strength,high toughness and excellent durability.Fine aggregate is the main component of UHPC,which accounts for 35%-50% of the total volume of UHPC.The type,particle size,strength and gradation of fine aggregate have a great impact on the mechanical properties of UHPC.Currently,quartz sand is mostly used as fine aggregate in UHPC.Quartz sand has a low density and is easy to be crushed under high-speed impact,which affects the performance of UHPC in dynamic impact.According to this,this paper use steel sand and magnetite sand instead of quartz sand such as the volume and success preparation has high density,excellent dynamic and static mechanical properties of high performance concrete,and experimental study on the steel sand and magnetite sand content on the mechanical behavior of UHPC dynamic and static performance,and the dosage rate and varieties of steel fiber on the performance of ultra heavy concrete the influence of dynamic and static mechanical properties,The test results show that:(1)Steel sand and magnetite sand replace quartz sand to greatly improve the density and acoustic impedance of UHPC.With the increase of content,the density and acoustic impedance increase.However,the fluidity will be reduced.The greater the content of steel sand and magnetite ore,the worse the fluidity of UHPC will be.Steel fiber has little contribution to the improvement of acoustic impedance due to less content.(2)With the increase of replacement rate of steel sand and magnetite sand,the compressive strength of UHPC tends to increase first and then decrease,and reaches the highest when the replacement rate is 80%;The elastic modulus increases almost linearly with the increase of aggregate substitution rate.There is a small increase in the flexural strength.When the content of steel sand is constant,the compressive strength,flexural strength and elastic modulus of ultra-high performance heavy concrete increase with the increase of the volume content of steel fiber.(3)The Split Hopkinson Pressure Bar(SHPB)test was conducted on the ultra-high performance heavy concrete with three air pressure impact with diameter of 70 mm.The test results showed that the incorporation of steel sand and magnetic sand and the increase of substitution rate could effectively improve the failure form under the dynamic impact of UHPC and enhance the dynamic peak compressive strength.When the replacement rate of steel sand and magnetite ore reaches 80%,the peak strength is the highest.The content and shape of steel fiber affect the failure pattern and stress-strain curve of ultra-high performance heavy concrete.Steel fiber can change the failure form of ultra-high performance heavy concrete from powder to block,and effectively improve the toughness of ultra-high performance heavy concrete.(4)UHPC material has obvious strain rate effect with the instead of steel sand and magnetite asnd,UHPC strain rate sensitivity can be improved,with the increase of dosage of steel shot and magnetite sand,strain rate and the impact peak strength of UHPC relationship curve,the relationship between strain rate and DIF curve trend of first increases and then decreases,and reached the highest when the substitution rate was 80%;The addition of steel fiber and the increase of the content of steel fiber can improve the strain rate sensitivity of ultra-high performance heavy concrete.(5)The main reasons for the strain rate sensitivity of concrete materials are summarized,and the reasons for the increase of the strain rate sensitivity of ultra-high performance heavy concrete are analyzed from three factors.