Study On Dynamic Properties Of High Strength And High Ductility Cementitious Composites (HSHDCC)

High Strength High Ductility Cementitious Composites（HSHDCC）,as a new type of building material,avoids the low strength of Engineering Cementitious Composites（ECC）,and low ductility of Ultra-High Performance Concrete（UHPC）.Traditional HSHDCC with 2%volume content of polyethylene（PE）fiber has a stable level of compressive strength,more than 60 MPa,and a high tensile strain level,equaling to ECC,but the higher production costs of HSDHCC limits its extensive application.Finding a way to reduce the dosage of fiber and maintaining good mechanical performance,becomes the biggest problem urgently to be solved in the engineering application of HSHDCC.In this paper,a new type of HSHDCC is proposed by introducing a new reinforcing material,calcium carbonate whisker,in order to replace part of the fiber efficiency through the strengthening and toughening effect of calcium carbonate whisker at the microscopic level,so as to reduce the fiber content.The remarkable characteristics of high strength and energy dissipation capacity of HSHDCC,makes the material having a broad application prospects in the area of earthquake resistant structure and seismic strengthening under the environment of dynamic load.At present the domestic and foreign research mainly focuses on HSHDCC materials under quasi-static mechanical properties,and HSHDCC material structural earthquake resistance reinforcement application of the dynamic performance research and study is not enough.To research HSHDCC material mechanical properties under dynamic load,the dynamic properties of HSHDCC materials are preliminarily analyzed from two aspects of experimental research and theoretical derivation in this paper.Based on this,Low cycle repeated tests of columns with different reinforcement materials under different axial compression ratios are carried out,and the influences of reinforcement materials and axial compression ratios on seismic performance of members are analyzed.The specific contents are as follows:（1）Uniaxial tensile tests are carried out on HSHDCC materials at strain rates of10^-5 s^-1～10^-2 s^-1.The effects of fiber content and strain rate on the basic mechanical properties of HSHDCC materials are studied.The result shows that the strength and strain of initial crack and peak strength of each group presents dynamic enhancement.1.5%PE-HSHDCC and 2%PE-HSHDCC ultimate tensile strain and toughness showed a dynamic trend of decrease,while 1.5%PE/0.5%CW-HSHDCC has higher rate sensitivity,and under the high strain rate,the tensile strain and toughness can still be maintained at a high level,and even show a dynamic increase.The maximum tensile peak stress is 9.62MPa,and the ultimate tensile strain can reach 6.4%.The addition of calcium carbonate whiskers enhances the multi-crack cracking ability of HSHDCC to a certain extent.（2）The dynamic tensile constitutive model of HSHDCC is established based on the theory of stable cracking and strain hardening,and the model results show good agreement compared with the experimental results.（3）Uniaxial compression tests are carried out on HSHDCC materials at strain rates of 10^-5s^-1～10^-2s^-1.The results show that the compressive strength of HSHDCC are more than 100MPa,and the peak strain is more than 3000μεat quasi-static strain rates.The sensitivity of 2%PE-HSHDCC and 1.5%PE-HSHDCC is poor at the strain rates of 10^-5s^-1 and 10^-4 s^-1.With the increase of the strain rate,the dynamic enhancement effect of peak stress is obvious,but the peak strain is deteriorated,and the post-peak decline section becomes steepened.With the decrease of fiber content,the post-peak residual strength of the specimen decreases,and the dynamic decrease of peak strain is more significant.After adding calcium carbonate whisker,the toughening effect is obvious.（4）The dynamic compression constitutive model of HSHDCC is established based on the compression damage theory,and the model results show good agreement compared with the experimental results.（5）The seismic performance of reinforced concrete columns reinforced by mortar,steel fiber and new HSHDCC under different axial compression ratios iss studied.The low-cycle repeated tests of 3 RC columns and 9 reinforced members are completed.The test results show that the mortar reinforced columns show high brittleness,and the other reinforced specimens show good ductility.The hysteresis curve of the new HSHDCC reinforced column is fuller and has excellent energy dissipation capacity.The cumulative energy consumption of the new HSHDCC reinforced column is 2 times more than that of the RC column,and with the increase of the axial compression ratio,the new HSHDCC reinforced column can still maintain a good energy dissipation capacity.In addition,based on the truss-arch model,a simplified calculation formula for the shear capacity of HSHDCC strengthened columns is proposed.The theoretical results are in good agreement with the experimental results.