Experimental Study On Flexural Behavior And Calculation Method Of Ultra High Performance Concrete With Manufactured Sand

Sand as fine aggregate is one of the important components of ultra high performance concrete（UHPC）,natural sand（NS）is unevenly distributed and non renewable in the short term,while manufactured sand（MS）is a potential alternative to natural sand,which can alleviate the ecological pressure and meet the requirements of sustainable development.Due to the multi angular and initial crack defects of manufactured sand,it is easy to destroy the closest packing structure of ultra high performance concrete with manufactured sand（MS-UHPC）,increase the porosity of interface transition zone,make the interface between fiber and matrix become a weak layer,and reduce the material structure properties of MS-UHPC.Up to now,most of the researches have focused on the influence of stone powder on the preparation of MS-UHPC,but less on the structure and properties of MS-UHPC under the influence of the morphology of manufactured sand particles.In this paper,the preparation and optimization design of ms-uhpc were studied;Based on the flexural performance test of model beam,the effects of manufactured sand content and longitudinal reinforcement ratio on the cracking load,crack development and flexural capacity of MS-UHPC beam were studied;The applicability of the current calculation methods for cracking load and flexural capacity of ultra high performance concrete with natural sand（NS-UHPC）beams to MS-UHPC beams is evaluated;The calculation model of cracking moment and ultimate bending moment considering the content of manufactured sand is proposed.The main research contents are as follows:（1）Preparation and optimization of MS-UHPCThrough the physical and mechanical properties test of fine aggregate,the fluidity test of slurry and the mechanical properties test of concrete,the influence of the content of manufactured sand and the characteristics of parent rock on the performance of MS-UHPC was analyzed;The strength conversion formula of MS-UHPC with different content of manufactured sand is proposed,and the matching relationship between reasonable content of manufactured sand and MS-UHPC performance is discussed.It is suggested that the optimal replacement rate of granite sand and basalt sand is 60%and 40% respectively.（2）Experimental study on flexural behavior of MS-UHPC beamsBased on the flexural performance tests of seven MS-UHPC beams,the effects of manufactured sand content on the crack development,deflection,failure mode,cracking load and flexural capacity of MS-UHPC beams were analyzed.The results show that the bending failure of MS-UHPC beams with different content of manufactured sand.Compared with NS-UHPC beams,the cracking load and flexural capacity of MS-UHPC beams decrease by 12.5% and 11.7% respectively under 100%replacement rate of manufactured sand.（3）Evaluation of calculation methods for cracking load and flexural capacityBased on the test results,the applicability of the calculation methods of cracking load and flexural capacity in domestic and foreign codes and scholars’ research to MS-UHPC beams is evaluated.The results show that the stress distribution in tensile zone of MS-UHPC beam is rectangular mode,trapezoidal mode or triangular mode,and the average ratio of the experimental value to the calculated value is 0.82,1.09 and 1.54,respectively.The average ratios of flexural capacity test values to theoretical values calculated by CECS2004,MCS,CECS2020 and ACI are0.74,0.96,1.51 and 1.98,respectively.（4）Bending calculation method of MS-UHPC beam with consideration of manufactured sand contentBased on the fiber bridging theory,and considering the amount of manufactured sand,the calculation method of cracking moment and flexural capacity of MS-UHPC beam is established by the stress balance equation and material constitutive equation.The mean values of the ratios of the test values to the calculated values of the cracking moment and flexural capacity are 1.07 and 1.21,respectively,and the coefficients of variation are 0.1 and 0.07,respectively.It shows that the method can be used to calculate the cracking moment and flexural capacity of MS-UHPC.