Study On Self-healing Properties Of ECC Composite Beams In Marine Environment

The durability of concrete structure directly affects its service life and safety.The main reason for the durability problem is that cracks provide channels for external harmful substances,thus accelerating the deterioration of internal structure.Therefore,timely crack closure is the key to improve durability.Fiber-Reinforced Cement-Based Composite Material(ECC)has the characteristics of high ductility,controllable fineness and multiple cracks.It not only solves the problem of large brittleness and easy cracking of concrete,but also has good crack self-healing potential.It provides a new way to solve the problems of crack maintenance in concrete structure.Therefore,this paper will study the self-healing properties of ECC composite beams with different healing materials.The selected healing materials were dry SAP,SAP pre-absorbed saturated calcium hydroxide solution and crystalline admixture.ECC composite beams are made by replacing 60 mm high concrete in tension zone of concrete beams with ECC.The effects of self-healing behavior of ECC layer on mechanical properties,durability and internal damage recovery of specimens are studied:(1)The pre-loading test was used to damage the precast ECC composite beam,and then it was placed in the seawater environment for healing and maintenance.Then,the loading test was carried out again to study the effect of the self-healing performance of ECC composite beams with different healing materials on the mechanical properties recovery of beams.The results show that the bending stiffness of the specimens is improved obviously after healing and curing,and the deflection of composite beams decreases obviously when the beams are damaged.But the ultimate bearing capacity of composite beams is not improved.In addition,the addition of healing material can improve the recovery effect of bending performance index of composite beam,and the best recovery effect is the crystal admixture.(2)The crack healing effect of ECC composite beams with different mix proportions was observed by microscope.The result shows that all the cracks of the specimens show obvious closing behavior,and the cracks less than 100μm can completely be healed after curing.The results show that the addition of healing materials can improve the healing crack width,especially the specimen with crystal admixture has the highest crack closure rate,and the crack width can be closed is increased to 413μm。(3)The effect of self-healing behavior on durability recovery of ECC composite beam was studied by accelerated corrosion test on the pre-cracked specimens before and after healing and maintenance.The results showed that the occurrence of crack self-healing behavior can prevent the chloride ion transfer in the crack,and have direct protective effect on the steel bar,thus improving the durability of the structure.(4)The changes of internal damage of ECC composite beams before and after healing were studied by ultrasonic pulse test and vibration based damage identification method.The results showed that the ultrasonic sound velocity and basic frequency of all specimens after healing and curing were improved to different extent than before healing,and the healing behavior of cracks had a certain improvement on the recovery of the damage.