Study On Mechanical Properties Of Hybrid Domestic Fiber Reinforced ECC

Hybrid domestic fiber reinforced Engineered cementitious composite(Hybrid Domestic Fiber Reinforced Engineered Cementitious Composite,HDFR-ECC)is a new type of hybrid domestic fiber reinforced ECC prepared by the hybrid of domestic polyvinyl alcohol fiber(PVA fiber),steel fiber,CaCO3 whiskers and other fibers.The purpose is to make the ECC have high ductility and high strength through the hybrid effect of fibers,so as to improve the engineering applicability of the domestic ECC.Based on the basic principle of localization of raw materials,this paper prepared HDFR-ECC through reasonable mix ratio design,experimental study of its flow properties,static mechanical properties,impact resistance,and analysis of its strengthening and toughening mechanism,so as to play a positive role in the application and promotion of domestic ECC.The main conclusions are as follows:(1)The effects of silica fume content,water-binder ratio and steel fiber substitution rate on the flow performance of HDFR-ECC were studied.The results showed that the fluidity of HDFR-ECC first increased and then decreased with the increase of silica fume content.The fluidity reached the maximum when the silica fume content was 10%,which decreased with the decrease of water-binder ratio and increased with the increase of steel fiber substitution rate.(2)The effects of silica fume content,water-binder ratio and steel fiber substitution rate on static mechanical properties of HDFR-ECC were studied.The results showed that,in terms of uniaxial compressive property,the compressive strength of ECC can be improved with the appropriate dosage of silica fume and the decrease of water-binder ratio.The superior of silica fume content and water-binder ratio were 10%and 0.28,with the increase of steel fiber substitution rate,the 7d compressive strength of ECC decreases and the 28d compressive strength increases.In terms of uniaxial tensile property,the appropriate dosage of silica fume and water-binder ratio can improve the initial cracking and ultimate tensile stress,but reduce the initial cracking and ultimate tensile strain at the same time.The superior of silica fume content and water-binder ratio were 10%and 0.28,the addition of steel fiber has adverse effects on the initial cracking and ultimate tensile properties at 7 days.At the age of 28 days,the initial cracking and ultimate tensile stress were significantly increased,and the strain loss of initial cracking and ultimate tensile stress caused by the growth of curing age was reduced.When the substitution rate of steel fiber was 25%,ECC has better tensile stress and strain.In terms of the bending property of thin plate,appropriate silica fume content and water-binder ratio can improve the initial cracking and ultimate bending stress,but reduce the initial cracking and ultimate bending displacement at the same time.The superior of silica fume content and water-binder ratio were 10%and 0.28,the addition of steel fiber can greatly improve the initial cracking bending displacement and initial cracking and ultimate bending stress at 28 days of age,and the ultimate bending displacement loss caused by the growth of curing age was reduced.When the substitution rate of steel fiber was 25%,ECC has good bending stress and displacement.(3)The impact of steel fiber substitution rate on the impact resistance of HDFR-ECC was studied.The results showed that,the addition of PVA and steel fibers can transforms the original brittle failure of HDFR-ECC into ductile failure.With the increase of steel fiber substitution rate,the number of initial and final cracks,energy consumption after impact cracking and impact ductility index of ECC increase first and then decrease,and reach the maximum value when steel fiber substitution rate was 25%.Compared with the Control,single doped PVA fiber and single doped steel fiber group,the initial cracking times,final cracking times and energy consumption after impact cracking of the hybrid fiber group were significantly increased,while the impact ductile index was slightly increased.(4)The strengthening and toughening mechanism of HDFR-ECC was studied.The results showed that the E3 group of HDFR-ECC fiber bridge stress was 4.89 MPa,and the calculated PSH value of E3 group was 7.13,which met the standard proposed by previous studies that PSH should be greater than 3 when PVA fiber prepared ECC.At the same time,according to the SEM test results shows that steel fiber,PVA fiber and CaCO3 whisker in HDFR-ECC have different characteristics,able to work together in the ECC matrix,can be in multi-scale limit crack propagation,which was conducive to improving the mechanical properties of ECC.