Degradation Mechanism Of ECC Under Sulfate Attack:Tensile,Flexural And Bonding Properties With Existing Concrete

Engineered Cementitious Composites（Hereinafter referred to as ECC）has excellent tensile properties,crack control and corrosion resistance.It is used for reinforcement of concrete structure.However,at present,domestic and international studies mainly focus on the degradation of the compressive strength of ECC and the bond performance of ECC/concrete interface under normal conditions.In this paper,the degradation of tensile performance and flexural performance of the ECC under sulfate corrosion and the bond performance of the ECC/concrete interface under normal conditions are studied.The following studies were carried out by using 5%sodium sulfate solution for wet-dry cycles corrosion.（1）In this paper,the degradation of tensile performance and flexural performance of the ECC of different content of fly ash and PVA fiber the corrosion of sulfate wet-dry cycles of 0-120 days are studied by using the thin-plate axial and three-point bending test.It is found that after 120 days of the corrosion test of sulfate wet-dry cycle,the tensile strength of ECC only decreased by 25.6%and the anti-bending strength only decreased by22.1%.The amount of fly ash and PVA fiber in moderation can improve the tensile and bending performance of ECC under the sulfate environment.At the same time,the degradation model of the bending strength of ECC is established.（2）Concrete and ECC are used to reinforce the corroded old concrete specimens,and then the adhesion properties of the interface are studied by the bevel shear test and the splitting tensile test.Then the bond performance of the interface is studied through the slant shear test and splitting tensile test.Discovery destruction occurs mostly from the interface.The slant shear strength and splitting tensile strength of ECC/concrete specimens are greater than the concrete/concrete specimens in the corrosion of the sulfate for 0-120 days.As the number of corrosion days increases,the strength degradation rate of ECC/concrete specimens is slower than that of concrete/concrete specimens.After 120 days of corrosion,the remaining slant shear strength and splitting tensile strength can still be above 70%.（3）Through the test,the degradation of the slant shear strength and the splitting tensile strength of ECC/concrete and concrete/concrete specimens subjected to corrosion are studied.The strength degradation rate of ECC/concrete specimens is lower than that of concrete/concrete specimens.And when the sulfate cycle days are 90 to 120 days,the concrete/concrete specimen is disconnecting directly at the interface.The residual slant shear strength and the splitting tensile strength of the ECC/concrete specimens can remain above 60%.（4）Through micro test of SEM and XRD,the microstructure,corrosion products and mechanism of deterioration of strength of ECC and ECC/concrete specimens subjected to corrosion are studied.The results show that after 120 days of sulfate corrosion,the density of ECC was enhanced by the addition of fly ash and PVA fiber,SO₄^2-is hard to penetrate,and the amount of ettringite is less.ECC and concrete are closely bonded near the interface,forming a compact structure,reducing the formation of ettringite,thus the corrosion resistance of the structure is improved.