Comparative Study on Chloride Ion Permeation Resistance of Polyurea Coated Cement Mortar under the Coupling Effects of Bending Load, Dry-wet Cycle and NaCl Solution Immersion

Abstract

Concrete structures in service are exposed to the combined effect of load and environment. This paper determines the free chloride ion content and the chloride diffusion coefficient in the polyurea coated mortar specimens while exposed to: the co-action of dry-wet cycle and NaCl solution immersion, the co-action of bending load and NaCl solution immersion and the coupling effect of bending load, dry-wet cycle and NaCl solution immersion. Furthermore, the scanning electronic microscopy (SEM) is applied to observe the micro-morphology of the interface between the substrate and the polyurea coating. The results show that, after 90 days of NaCl solution immersion and dry-wet cycles, the chloride ion content of polyurea coated mortar at 6mm depth amounts to 0.0153%, and the chloride diffusion coefficient refers to 1.56×10- 12m2/s. Under 90 days of bending load and NaCl solution immersion, the chloride ion content increases with rising load and when the bending load is 50%, the chloride ion content of polyurea coated mortar at 6mm depth amounts to 0.0163%, the chloride diffusion coefficient refers to 1.92×10-12m2/s, and the polyurea coated mortar features relatively good resistance towards chloride ion permeation. Under the coupling effect of bending load, dry-wet cycle and NaCl solution immersion, compared to the single NaCl solution immersion, the chloride ion content of polyurea coated mortar accumulates to 40.60%, the chloride diffusion coefficient amounts to3.76×10-12m2/s and the resistance towards chloride ion permeation decreases slightly. The SEM morphology results show that, under the coupling effects of above mentioned factors, polyurea coating provides a prominent sealing function, preventing the corrosive media from permeating. The polyurea coating exhibits good resistance to chloride ion permeation under the coupling effects caused by stated factors above.