Mechanical Behavior Of Polypropylene Fiber Reinforced Expansive Self-Consolidating Concrete Under Multiaxial Loading

Polypropylene fiber reinforced expansive self-consolidating concrete（PPESCC）is a kind of self-consolidating concrete mixed with polypropylene fiber and expansive agent.It has good cracking resistance,impermeability,and frost resistance,and has a wide application prospect in large area and mass concrete engineering.In the actual structural engineering,this kind of concrete is mostly in the complex stress state,such as biaxial or triaxial stress.The study of failure modes and mechanical properties of PPESCC under multi axial stress also has important engineering and practical significance for the promotion and application of PPESCC.Therefore,this paper mainly studies the biaxial compression,biaxial tension-compression and triaxial compression experiments of normal self-consolidating concrete and expansive self-consolidating concrete with different fiber content under different stress ratios.It analyzes the effects of the different fiber content（0%,0.05%,0.1%by the concrete volume）,the admixture of expansive agent（8%of the mass fraction of cementitious materials）and stress ratio（five stress ratios under biaxial compression,six stress ratios under biaxial tension-compression and eight stress ratios under triaxial compression）on the multiaxial mechanical properties of PPESCC.In this paper,the biaxial test of normal self-consolidating concrete and expansive self-consolidating concrete with different fiber content under different stress ratios are carried out,including 90 specimens under biaxial compression and 108 specimens under biaxial tension-compression.The failure mode of the specimen under biaxial compression mainly depends on the stress ratio,which has nothing to do with the fiber content and the addition of expansion agent.With the increase of the stress ratio,the cube specimen experiences columnar failure,shear failure and lamellar splitting failure respectively.However,the failure mode of the specimens under biaxial tension-compression is tensile failure identically.With the increase of stress ratio,the biaxial compressive strength of different types of concrete first increases and then decreases.The maximum biaxial compressive strength of different types of concrete appears when the stress ratio is 0.5,and the strength enhancement rate can reach 20%-27%.The minimum biaxial compressive strength appears when the stress ratio is 1,which is close to the uniaxial strength of concrete.In this paper,the triaxial compression tests of polypropylene fiber reinforced normal self-consolidating concrete and polypropylene fiber reinforced expansive self-consolidating concrete were carried out,including 81 specimens underσ₁?σ₃=0.05 and 81 specimens underσ₁?σ₃=0.1.The results showed that under the stress ratio designed in this test,the failure modes of normal self-consolidating concrete and expansive self-consolidating concrete with different fiber content are basically the same,which are shear failure.Except EPP0.05/E8-PP0（σ₁?σ₃=0.1）,whenσ₁?σ₃=0.05,0.1,for N-PP0.05/N-PP0,N-PP0.1/N-PP0.05 and EPP0.05/E8-PP0,EPP0.1/EPP0.05,the triaxial compressive strength ratio tends to 1.0,which indicates that the application of triaxial pressure can weaken the effect of polypropylene fiber on compressive strength to a certain extent.Meanwhile,except EPP0.05/PP0（σ₁?σ₃=0.05）,with the application of triaxial pressure,the ratio of triaxial compressive strength of expansive self-compacting concrete to normal self-compacting concrete approaches to 1.0.It shows that the effect of expansive agent on the strength of concrete was weakened by the application of triaxial pressure as well.With the increase of₁?₃,intermediate stress（σ₂?σ₃）at maximum triaxial compressive strength also grows.When₁?₃=0.05,the maximum triaxial compressive strength of concrete appears atσ₂?σ₃=0.25.when₁?₃=0.1,the maximum triaxial compressive strength of concrete appears atσ₂?σ₃=0.5～0.75.The triaxial compressive strength of concrete with different mix proportion increases with the increase of₁?₃.When₁?₃=0.05,the strength of triaxial compression is approximately 2.2 times that of uniaxial compression.When₁?₃=0.1,the strength of triaxial compression is 3.1 times of that of uniaxial compression.Based on Kupfer’s biaxial failure criterion and incremental stress-strain relationship of orthotropic materials,the failure criterion and constitutive model of PPESCC under biaxial compression were established in this paper,which shows high accuracy.Meanwhile,based on Huang-Zhang’s three-parameter failure criterion,the strength failure criterion developed in this paper can be well applied to normal self-consolidating concrete and expansive self-consolidating concrete with different fiber content under triaxial compression.At the same time,the microstructure of polypropylene fiber reinforced expansive self-compacting concrete was observed by scanning electron microscope.The pore characteristics of cement paste,the interface transition zone between coarse aggregate and concrete matrix,and the interface between fiber and matrix were mainly observed and analyzed.It shows that with the incorporation of 0.1%polypropylene fiber,the microstructure of self-compacting concrete was improved,including less pores in the cement matrix and compact interfacial transition zone between coarse aggregate and cement matrix.